- 1 501.1 Construction Inspection for Sec 501
- 1.1 501.1.1 Material (Sec 501.2)
- 1.2 501.1.2 Mix Design (Sec 501.3)
- 1.3 501.1.3 Sampling (Sec 501.4)
- 1.3.1 501.1.3.1 Pumping Concrete
- 1.3.2 501.1.3.2 Sampling from Stationary Mixers Except Paving Mixers
- 1.3.3 501.1.3.3 Sampling Central or Truck Mixed Concrete
- 1.3.4 501.1.3.4 Protection of sample
- 1.3.5 501.1.3.5 Compressive Strength
- 1.4 501.1.4 Consistency (Sec 501.5)
- 1.5 501.1.5 Measurement of Material (Sec 501.6)
- 1.6 501.1.6 Central and Truck Mixed Concrete (Sec 501.8)
- 1.7 501.1.7 Volumetric Batched and Continuous Mixed Concrete (Sec 501.9)
- 1.8 501.1.8 Air-Entrained Concrete (Sec 501.10)
- 1.9 501.1.9 2AA Sheet For Concrete Pavement
- 2 501.2 Materials Inspection for Sec 501
- 2.1 501.2.1 Scope
- 2.2 501.2.2 Mix Design Procedures
- 2.3 501.2.3 Mix Design Information
- 2.4 501.2.4 District Procedures
- 2.4.1 501.2.4.1 Portland Cement
- 2.4.2 501.2.4.2 Supplemental Cementitous Materials
- 2.4.3 501.2.4.3 Admixtures
- 2.4.4 501.2.4.4 Water
- 2.4.5 501.2.4.5 Air Content
- 2.4.6 501.2.4.6 Aggregate Properties
- 2.4.7 501.2.4.7 Batch Weights
- 2.4.8 501.2.4.8 Percent Fine Aggregate
- 2.4.9 501.2.4.9 Dry Yield
- 2.4.10 501.2.4.10 Cement Factor
- 2.4.11 501.2.4.11 Water Factor
- 2.4.12 501.2.4.12 Water/Cement Ratio
- 2.4.13 501.2.4.13 Mix Proportions
- 2.4.14 501.2.4.14 Percent Air in Mortar
- 2.4.15 501.2.4.15 Percent Supplemental Cementitous Material
- 2.4.16 501.2.4.16 Gradations
- 2.5 501.2.5 Laboratory Mix Verification
- 2.6 501.2.6 Precast Concrete
- 2.7 501.2.7 Class A-1 Concrete
- 2.8 501.2.8 Testing Equipment
- 2.9 501.2.9 Aluminum Powder
501.1 Construction Inspection for Sec 501
|Water Reducer, PCCP|
|Full Report 2001|
|Aggregate, Gradation Optimization|
|Pavement, Precast Prestressed Concrete|
|See also: Research Publications|
501.1.1 Material (Sec 501.2)
Sec 501.2 of the Standard Specifications include specific requirements of material to be used. Plant inspectors are responsible to the resident engineer for verifying acceptability of all materials before they are incorporated into the work.
The proportioning plant inspector is responsible for inspecting control of materials and batching operations. The inspector's duties will start at the time materials are being stockpiled and will continue until final records for the project are complete. The inspector must be provided information about source and type of aggregates intended for use, and mix proportions. The inspector must be familiar with inspection procedures for determining moisture content, scale weights, and inspection of batching equipment, the performance of tests, and reports. The inspector should become familiar with the contents of manufacturer's brochures on the proposed batching equipment to understand its operation. The contractor will normally have this information.
The proportioning plant inspector must be certain that all materials have been properly inspected and approved before permitting their use. Cement is normally accompanied by appropriate certification as described in Section 1019 of the Standard Specifications. Aggregate suppliers will be designated in AWP.
501.1.2 Mix Design (Sec 501.3)
The contractor shall design and submit all concrete mixes to district Materials for review and approval. The mix shall be designed by absolute volume methods or an optimized mix design. Optimized refers to a well graded combined aggregate gradation resulting in lower water demand, improved workability, and improved finishing characteristics. If contractor elects to use an optimized mix, the mix design shall be submitted with the target gradation and allowable gradation range. Representative samples may need to be sent to Construction and Materials for laboratory testing.
Optimized mix designs may have a reduction in cement of 0.5 sack per cubic yard from the table shown in Sec 501.3.6 of the Standard Specifications. If cement is reduced, the mixture may be subject to review and approval by the engineer.
501.1.3 Sampling (Sec 501.4)
Sampling of fresh concrete by these instructions will meet the requirements of Section 501.4 of the Standard Specifications. Each sample should be large enough to permit completion of all necessary tests. Methods described should be tempered with judgment to assure that samples are as nearly as possible representative of the true nature and condition of the concrete sampled. For safety reasons, sampling should always be coordinated through contractor personnel.
501.1.3.1 Pumping Concrete
There has been discussion about the proper place to sample concrete when it is being pumped. The following guidelines will assure uniformity of contract enforcement statewide.
Ordinarily the most representative sample will be taken at the point of final discharge. For safety reasons, however, it is not always practical to do so. When concrete is being pumped our procedure has been to take samples at the truck chute. Usually there is no significant difference unless a new or reconditioned pump is being used, the concrete is being pumped a long distance or if there are high vertical drops in the line.
The first load should be checked at both points. The difference between the truck and the pump should be checked regularly, especially if there are significant changes in drop or distance, and certainly if a different pump is used.
Consider the change in air content when determining specification compliance. If you find that the air drops by 0.3%, subtract that from the reading at the truck. If you are on the low side at the truck the air should be adjusted accordingly. The correction factor from loss through pumping would also apply to the slump. The reported slump and air content should be what is at the point of placement.
The concrete truck boom shall be configured to minimize the free fall of concrete of the point of discharge. This is to minimize segregation, and loss of air and slump.
501.1.3.2 Sampling from Stationary Mixers Except Paving Mixers
The sample is to be obtained by passing a receptacle completely through the discharge stream of the mixer at about the middle of the batch, or by diverting the stream completely so that it discharges into a container. Do not restrict flow from the mixer in a way that can cause concrete to segregate. This method should be used for both tilting and non-tilting mixers.
501.1.3.3 Sampling Central or Truck Mixed Concrete
The entire sample for slump and air tests and for molding compressive strength specimens may be taken at one time, after approximately one cubic yard of concrete has been discharged. The sample shall be taken from at least 5 different parts of the pile. Acceptability of concrete for slump and air content and, when applicable, for strength requirements, will be determined by tests on these samples.
501.1.3.4 Protection of sample
After the sample has been obtained, it must be protected from direct sunlight and wind until it is used, which must not be more than 15 minutes after sampling. When the sample has been moved to the place where the test is to be made or specimens are to be molded it should be mixed with a shovel if necessary to assure uniformity of the mixed sample.
501.1.3.5 Compressive Strength
Compressive tests are performed both in the field and in the laboratory on cylindrical specimens of concrete, 6 in. diameter and 12 in. tall (6x12) or 4 in. diameter and 8 in. tall (4x8). The Standard Specifications require use of compressive specimens for job control of concrete production.
All concrete for air and slump tests as well as preparation of the specimens should be secured from a single batch of concrete. Air and slump tests should always be made on samples of concrete used for preparation of compressive specimens.
Cylinder forms shall be filled with fresh concrete in accordance with the instructions provided by AASHTO T 23 (ASTM C 31). Care should be taken when placing the caps on the molds to avoid damage to the surface of the concrete. The lids should be kept on tight to prevent moisture loss.
Curing of compressive specimens will depend on whether they are for standard cure or field cure.
Standard Cure is used for the following purposes:
- 1) Specified strength for 28-day testing
- 2) Check of mixture proportions or design strength
- 3) Quality control (i.e. monitoring mix variability)
- 4) Maturity meter curve.
Standard curing involves two phases of curing: initial and final.
Each set of compressive test specimens for standard cure consists of two 6x12 cylinders or three 4x8 cylinders.
Standard Cure specimens shall be cured in accordance with AASHTO T23 (ASTM C31) for initial and final curing.
Standard Cure – Initial
If specimens cannot be molded at the place where they will receive initial curing, immediately after finishing move the specimens to an initial curing place for storage. Recommended method for initial curing is keeping the specimen in the plastic mold covered with a plastic lid or place in a damp sand pit for a maximum of 48 hours in a temperature range from 60° F to 80° F and an environment preventing moisture loss.
Standard Cure - Final
Upon completion of initial curing and within 30 minutes of removing the molds, cure specimens with free water maintained on their surfaces at all times at a temperature of 70° F to 77° F using water storage tanks or moisture room per AASHTO M201 (ASTM C511).
- Storage Tanks
- When water tanks are used for final curing the temperature shall be maintained at 70° F to 77° F. Method of recording temperature is required.
- Transportation of Specimens
- Specimens may be transported to the Central Laboratory for final curing. To transport, after the initial cure period, the specimen shall be removed from the mold and placed in a plastic bag to maintain free moisture during shipping. Specimens should not be transported to begin final cure until at least 8 hours after final set. During transporting, use suitable material to prevent damage from jarring and use suitable insulation material during cold weather.
- Show shipper's name and address on the outside of the box. The box comes with the address of Central Laboratory printed on the side and a preprinted form that provides basic information about the cylinders. If the box does not have the form preprinted, contact the Central Laboratory for copies of the self stick form. AASHTOWare Project Sample ID number should be written on the side of cylinders or cylinder molds.
- Necessary boxes, cardboard liners, polyethylene bags, wire ties and rolls of strapping tape are stock items available by requisition.
Field cure is used for the following purposes:
- 1) Opening to traffic strength or staged construction
- 2) Comparison with test results of standard cure to in place methods, such as maturity method verification
- 3) Adequacy of curing and protection of concrete in the structure, such as cold weather placement
- 4) Form removal.
Field curing shall be in accordance with AASHTO T23 (ASTM C 31). Store cylinders in or on the structure as near as practical to the represented concrete. Protect all surfaces of the cylinders from the elements and ensure a temperature and moisture environment similar to the formed work. To meet these conditions specimens made for the purpose of determining when a structure is capable of being put in service shall be removed from the molds at the time of removal of form work.
Compressive test specimens for field cures may consist of one or more sets for either 6x12 cylinders or 4x8 cylinders.
Specimens prepared to determine when forms may be removed will be cured as described above except for bridge decks or heated concrete.
- - Specimens representing bridge decks are to be cured in plastic molds on the deck under wet mats until the cylinders are to be broken or wet curing is discontinued. If cylinders remain after wet curing has ended, they shall remain in plastic molds under field conditions until they are to be broken.
- - Specimens representing heated concrete are to be left in the enclosure subject to the same protection as concrete they represent until they are to be broken. Cylinders should be in plastic molds and covered with wet burlap for 48 hours. Cylinders left after the heating period has ended shall remain in plastic molds under field conditions until they are to be broken.
Curing of bridge decks shall be in accordance with Standard Specification 704, wet curing shall be maintained for 7 days and until the concrete has reached a minimum of 3000 psi.
501.1.3.5.2 QC/QA Testing Requirements
A set of QA standard cure specimens shall be prepared and tested to verify the 28-day compressive strength of each mix design during initial production and for every 500 cubic yards thereafter or once for every project with less than 500 cubic yards. Any change in mix design shall also require standard cure verification. Verification of mix design by standard cure specimens may represent multiple concurrent projects using the same mix design. The MoDOT inspector should also prepare QA field cure specimens, for every 500 cubic yards or once for every project with less than 500 cubic yards, to verify the contractor field cure strength results.
QC field cure specimens shall be prepared for each structural pour and for every 100 cubic yards where it is necessary to control construction processes such as falsework or form removal, discontinuance of heating or wet curing, opening to traffic, and acceptance. The contractor may stop testing QC field cure specimens, representing a construction process, once the minimum strength requirement has been met. The contractor may cast as many specimens as desired to verify minimum strength. The contractor is not required to arbitrarily test at the completion of 28 days, if minimum strength has been met at an earlier time for a particular construction process.
A set of QA standard cure specimens shall be prepared and tested to verify the 28-day compressive strength of each mix design during initial production for any size paving project.
Both QC and QA field core specimens shall be used for acceptance of any paving project greater than 7500 sq. yd., except as noted for phased construction, below. Since these cores are used in QLA and PWL calculations to determine payment, they must be tested at 28 days. Cylinder specimens may be made at any time for informational purposes.
For paving projects with small quantities (< 7500 sq. yd.), or with larger quantities of phased construction exempted from QLA and PWL calculations, either a set of QC standard cure cylinder specimens or QC field core specimens shall be tested for compressive strength for every 2000 sq. yd. Testing of QC cores/cylinders may discontinue once opening strength and/or design strength has been achieved.
Section 608 Items
A set of QA standard cure specimens shall be prepared and tested to verify the 28-day compressive strength of each mix design during initial production for any size project with sidewalk, median, paved approaches, etc. Either a set of QA standard cure cylinder specimens or QA field core specimens shall be tested for compressive strength for every 500 cubic yards, or once for every project with less than 500 cubic yards to verify the contractor field cure strength results.
Either a set of QC standard cure cylinder specimens or QC field core specimens shall be tested for compressive strength for every 100 cu yd. Testing of QC cores/cylinders may discontinue once opening strength and/or design strength has been achieved.
A calibrated testing machine must be used by a certified technician. The AWP MA Sample Record, General must be completed documenting the testing. Testing is to be done in the hydraulically operated compressive testing machine. If there is doubt as to the 28-day strength of the cylinder, relative to the working capability of the available testing machine, send the cylinders to the Central Laboratory. All specimens are to be loaded to failure.
All cylinders are to be tested using a neoprene cap in a steel extrusion controller placed on each end of the cylinder. The neoprene caps have 6 1/8 in. diameters and are 1/2 in. thick. The caps are made from neoprene and no substitution of material or cap is to be made. A 50 durometer neoprene cap is used for concrete with a cement factor of less than 7.5 sacks per yard. Otherwise, a 60 durometer neoprene cap is used. The caps should be replaced if worn or after a maximum of 100 cylinder breaks.
The steel extrusion controller’s outside bearing surface is to be maintained free of gouges, dents or protrusions greater than 0.03125 in. or 0.0625 sq. in. surface area. The inside bearing surface is to be maintained to within 0.002 in. of plane.
Care should be taken when molding the specimen since irregularities can result in poor test results. Specimens should be tested using neoprene pads per ASTM C1231 or capped in accordance to AASHTO T231.
Projections on the ends of test specimens should not be higher than 0.20 inches, and corrected as necessary before testing.
Neither end of the concrete cylinder is to depart from perpendicularity to the axis of more than 0.5 degrees or 0.12” in 12”(0.08” in 8”). Neither end of the cylinder is to be marked by scratching in the date, cylinder number, etc. Cylinders not meeting these conditions shall not be tested unless the irregularity is first corrected.
Neither end of the cylinder is to be marked by scratching in the date, cylinder number, etc. Cylinders not meeting these conditions shall not be tested unless the irregularity is first corrected.
Neither end of the cylinder is to be marked by scratching in the date, cylinder number, etc. Cylinders not meeting these conditions shall not be tested unless the irregularity is first corrected.
A sufficient amount of ordinary corn starch is used to completely fill any void between the edge of the neoprene pad and the steel extrusion controller and to lubricate the face of the neoprene pad that contacts the concrete cylinder. In lieu of corn starch, Pledge spray wax has been used with good results.
The same surface of the neoprene cap is to bear on the concrete cylinder for all tests performed with that cap.
Place a steel extrusion controller containing a neoprene cap on the top and bottom surface of the concrete surface. As the upper bearing block is lowered, carefully align the cylinder's axis with the center of thrust of the upper block. The upper block should be carefully seated to obtain uniform bearing. No loose particles are allowed between the concrete cylinder and the neoprene caps or between the bearing surfaces of the extrusion controllers and the bearing surfaces of the test machine.
Concrete cylinders tested with neoprene caps rupture more intensely than comparable cylinders tested with sulfur-mortar caps. The test machine is to be equipped with a protective cage to protect the operator from flying fragments.
Once the cylinder is carefully seated, load shall be carefully and uniformly applied. The last half of the anticipated maximum load must be applied at a constant rate which falls within the range of 35 ± 7 (that is, 28 to 42) psi per second or between 352 and 528 pounds force per second for 4 in. diameter cylinders and between 792 and 1187 pounds force per second for 6 in. diameter cylinders on the gauge dial. The first half of load may be applied at a faster rate. Load is to be increased until the specimen fails. Needle travel or digital load readout will usually slow, or even stop, just before visible failure. The maximum distance of ram movement is 2 inches.
On digital readout machines, total load is captured automatically. On dial readout machines, although the red needle is supposed to indicate total load, it should be watched carefully to be sure it does not spring back at failure of the specimen. As soon as the specimen fails, the pressure should be released allowing the upper block to return to the unloaded position.
All test data shall be recorded in AASHTOWare Project. Results of the tests are to be reported to the nearest 10 psi.
501.1.4 Consistency (Sec 501.5)
Consistency (slump) of concrete should be determined each time an air-entrainment test is made. Other tests for consistency of concrete should be made as necessary to maintain proper control of the concrete. Placement of concrete should not be permitted until tests for both air entrainment and consistency have been made and results show that specification requirements have been met. When routine tests indicate a deviation from specifications for consistency, placementshould be suspended until adjustments have been made and additional tests completed which show concrete to be within specifications limits. Consistency tests are to be made according to the following instructions which will comply with the specification requirements pertaining to AASHTO designation T-119.
A considerable number of tests have been completed comparing results of testing air entrained concrete samples at the truck discharge point and the pump discharge point. The tests, with few exceptions, indicated that there are only minor variations in the results of the tests, with the tests from the pump discharge location usually slightly lower in air content and slump. If slump goes up drastically there probably would have to be a foreign liquid entering the system from somewhere. A high slump above the 6 to 7 in. range normally indicates a risk of segregation. Timing in taking slump tests is important. The designated location for quality control sampling to determine air content and slump is the point of truck discharge. When any of the following conditions occur, it may be necessary to obtain a check sample at the point of pump discharge to assure that there is no significant variation in test results:
- 1. When a new or reconditioned concrete pump is placed into operation.
- 2. When there are any indications that a substantial change in air content or slump has occurred between the two points of discharge.
The mold for use in the performance of the slump test is available on requisition. It will be made of galvanized steel, not thinner than #16 gauge, and will have the shape of a frustum of a right circular cone with approximate inside diameters at the top of 4 in. and at the bottom of 8 in. Height will be approximately 12 in. The mold is satisfactory if the above dimensions are within 1/16 in. The mold will have foot pieces, and handles for moving mold at end of the test. A mold which clamps to a nonabsorbent base plate is acceptable.
The tamping rod which is used to consolidate the material in the cone shall be a round, straight, steel rod 5/8 inch in diameter, with one end rounded to a hemispherical tip. Length should be approximately 2 feet.
A sample of concrete from which consistency tests are to be made must be representative of the entire batch. Samples should be obtained in accordance with the method of sampling fresh concrete, Section 501.4 of the Standard Specifications.
The mold, which must be clean, should be dampened and placed on a flat, moist, nonabsorbent rigid surface. Hold the mold firmly in place during filling, by standing on the foot pieces.
From the sample of concrete, fill the mold in three layers, each layer being approximately 1/3 the volume of the mold. One-third of the volume fills it to a depth of about 2-5/8 in., 2/3 of the volume fills it to a depth of about 6-l/8 in.
Rod each layer with 25 strokes of the tamping rod. Distribute strokes uniformly over entire cross section of the layer. For the bottom layer this will necessitate inclining the rod slightly and making approximately one-half of the strokes near the perimeter and then progressing with vertical strokes spiraling toward the center. Rod the bottom layer throughout its depth. The other two layers are to be rodded throughout their depth so that strokes just penetrate into the underlying layer approximately 1 inch.
In filling and rodding the top layer, heap concrete above the mold before rodding is started. If, during the rodding operation, concrete subsides below top of the mold, add additional concrete to keep an excess of concrete above top of the mold. After rodding has been completed, strike off the surface of concrete by means of a screeding and rolling motion of the tamping rod.
Immediately remove the mold from the concrete by carefully raising it in a vertical direction. This should be done in approximately 5 seconds by a steady upward lift, with no sideways or twisting motion being imparted to the concrete. The entire operation from start of filling through removal of mold should be carried out without interruption. It should be completed within an elapsed time of approximately 2 1/2 minutes.
Immediately measure slump determining the difference between height of the mold and height over the displaced original center of the top surface of the specimen. Slump is measured to the nearest 1/4 inch of subsidence below top of the mold.
A record of each slump test performed should be recorded in AWP.
501.1.5 Measurement of Material (Sec 501.6)
501.1.5.1 Mass Determination (Sec 501.6.1)
The plant inspector must assure that all equipment is of an approved design and that all installations meet requirements of the specifications. There must be no attachments to scales or weighing hoppers which might hamper free movement of any part of the weighing mechanism, or cause inaccurate weighing during actual operation of the equipment.
501.1.5.2 Mixing Water (Sec 501.6.2)
Control of the amount of water added to the batch at the concrete mixer is a highly important part of the proportioning process. This is true whether water is being added through a paving mixer or is being added to central or truck mixed concrete at the plant. The inspector should be acquainted with the mechanical operation and construction of the water system. All joints should be water tight and all valves should close tightly. Leakage of water into the mixer before or after the measuring tank has been discharged should not be permitted.
501.1.5.3 Scale Calibration (Sec 501.6.3)
Scales may be calibrated in the following manner: Balance the scales accurately with no load. Use standard test weights for the test load. Test weights are suspended from the weighing hopper in such a manner that the test load is uniformly distributed. Load the scale, using combinations of weights totaling approximately 1000 pounds with test weights as required by Sec 501 of the Standard Specifications, so that the added weights will produce a load that is a multiple of an increment on the scale indicator. Load the scales to approximately 75% of the working load. Then use combinations of weights, totaling not more than 150 pounds, for the remainder of the test. Record scale readings for each increment of test weight. When the maximum number of standard weights has been placed on the scale equal to an increment on the scale indicator and weight recorded, remove weights and draw a quantity of aggregate equal to the test load from the bins in the weighing hopper. Apply standard weights again, and repeat this procedure until each scale has been calibrated to a load approximately 5% greater than the maximum working load.
Calibration of scales on concrete proportioning plants other than PCC pavement plants vary as follows:
- Scale should be loaded in approximately 1000 pound increments (depending on number of standard 50 pound test weights required) so that the added weights will produce a load that is a multiple of an increment on the scale indicator. Load the scale to within approximately 250 pounds of each working load, and then by not more than 150 pound increments to approximately 250 pounds beyond each working load. Included in this range would be working loads for each batch size commonly used for each aggregate, when more than one aggregate is weighed on the same scale, such as dial scales.
PCC pavement plants should be calibrated before actual proportioning starts from any new plant set up. Scale verification by the contractor or producer shall occur six months after the last plant calibration.
Calibration for other than PCC pavement plants should be at the start of the construction season. Plants located in urban areas may require more frequent calibration. Verification is required to determine if any wear and tear on the weighing equipment has occurred during the previous six months.
Check sensitivity of the scale during the calibration test by applying a small weight and observing movement of the indicator. For aggregate scales, this weight should be 5 pounds and for cement scales, 2 pounds or less. In any case, the sensitivity weight should not be greater than 0.1% of the nominal capacity of the scale. Movement on the indicator should be sufficient to indicate that the scale is out of balance.
Check the balance of each scale assembly with all weigh beams in the system free and the weight indicator counterweights moved to zero.
The inspector should check scales for balance and sensitivity of each scale assembly at random at least twice each day. These checks should be noted in the diary.
Verification of weighing equipment will consist of balancing the scales and then loading the scale to approximately 250 pounds below the scale setting, then adding approximately 500 pounds of standard test weight in not more than 150 pound increments to bring the scale to approximately 250 pounds over the scale setting.
These weight intervals for calibration, verification, balance and sensitivity are considered to be the maximum. If difficulty is encountered with the batching operation or if any of the aforementioned checks indicate excessive deviations, the plant should be recalibrated to ensure compliance.
Sec 502.4.5 of the Standard Specifications sets out certain conditions under which automatic batching equipment must be furnished. In addition to calibration procedures, automatic equipment must be checked for compliance with requirements of Sec 502.4.5 of the Standard Specifications. It is particularly important to ascertain that the discharge mechanism will not operate when ingredients have not been weighed within specified tolerances.
This check can be made by adding or removing a weight slightly greater than the permissible tolerance to see if the discharge mechanism locks and appropriate warning is given, such as a light buzzer.
In the case of a breakdown in equipment which requires a shift to manual operation, the time of breakdown should be noted in the inspector's diary. The contractor should be promptly advised of the limitation for manual batching.
Water Measuring Devices. Control of the amount of water added to the batch at the concrete mixer is a highly important part of the proportioning process. This is true whether water is being added through a paving mixer or is being added to central or truck mixed concrete at the plant. The inspector should be acquainted with the mechanical operation and construction of the water system. All joints should be water tight and all valves should close tightly. Leakage of water into the mixer before or after the measuring tank has been discharged should not be permitted.
Inspection and calibration of the water system should be performed with utmost care and thoroughness. The water measuring device must be calibrated to determine accuracy of measurements. The most common type of measuring device consists of a tank which may be emptied to various levels by adjusting the height of a movable discharge pipe inside the tank. These devices should be calibrated by weighing the amount of water discharged at various settings on the gauge dial. On some installations water may be weighed, in which case, it will be necessary to calibrate the weighing device by using standard weights. Operation of the water system during calibration should be similar to operating conditions. The full range of water measurements required during mixing operations should be covered during calibration. Several checks should be made at various settings to determine if the device will consistently measure the correct quantity within the permissible tolerances allowed by Sec 501.6 of the Standard Specifications. The water meter will be verified at the same frequency as the weighing equipment. At least one setting shall be verified within the working range.
Admixture Dispensers. All measuring devices for dispensing of admixtures should also be carefully checked. The admixture dispensers shall be calibrated by a commercial scale company, the admixture company or the concrete plant company. Admixture dispensers are usually checked by causing the dispenser to discharge into a graduate where the quantity may be accurately measured. Repeated measurements should establish that the dispenser will operate within tolerances permitted by the Standard Specifications. Results of all calibrations, verifications, and sensitivity checks should be made a part of the permanent records. Whenever the admixture dispenser is in question, the inspector has the authority to verify the dispenser.
501.1.6 Central and Truck Mixed Concrete (Sec 501.8)
501.1.6.1 Equipment (Sec 501.8.1)
Central Mix Concrete is to be transported to point of delivery according to Sec 501.8 of the Standard Specifications.
501.1.6.2 Central Mixing (Sec 501.8.2)
Mixing time for a central mixing plant may be adjusted as set out in ASTM C-94 or by the Standard Specifications serving as the controlling test. The procedure is outlined below, or at the contractor's option the test may exactly follow ASTM C-94.
Test for Uniformity of Concrete
General. This test is used as the basis for determining whether mixing time may be reduced for central mixed concrete as provided by Sec 501.8.2. The variation within a batch as permitted and listed in the following table shall be represented by the difference, for each property listed, between the highest and lowest values obtained from the different portions of the same batch. The comparison is to be made between two individual samples taken after discharge of approximately 15% and 85% of the same batch within an elapsed time of not more than 15 minutes. Tests are performed by the contractor in the presence of project personnel.
|Requirements for Uniformity of Concrete|
|Item||Test||Requirement, expressed as maximum permissible difference in results of tests of samples taken from two locations in the concrete batch|
|1.||Weight per cubic foot calculated to an air-free basis||1.0 lb.|
|2.||Air content, percent by volume percent of concrete||1.0|
|4.||Coarse aggregate content, portion by weight of each sample retained on No. 4 sieve||6.0%|
|5.||Unit weight of air-free mortar based on average for all comparative samples tested||1.6%|
|6.||Average compressive strength at 7 days for each sample, based on average strength of all comparative test specimens||7.5%|
A general guide to the frequency for uniform tests is for a test to be conducted for initial production of each construction season. If a plant was producing a uniform product at the end of the previous season, the contractor may proceed with normal operations while the tests are being performed. Uniformity tests should be repeated any time appearance for the mix indicates some change or after charging procedures have been altered from those used during the previous test and production. Uniformity test results indicating compliance are to be in the project file prior to production. The test results for that test conducted at the beginning of the construction season are to be sent to the district office and forwarded to the Division of Construction and Materials. This record will be made available, upon request, when the plant is subsequently relocated within the same construction season. Results should show contractor, project, location, type materials, type plant, batching sequence, batch size and results of the various test requirements.
It is necessary to establish uniformity at each batch size furnished, however, a practical way of doing this is to perform the tests on the smallest and largest batch size the contractor proposes to furnish. The largest batch tested is never to exceed the manufacturer's rated mixing capacity. The smallest size batch tested must be of a size that a will allow uniform addition of all components, especially air-entraining agent and water, uising the same sequence and discharge times as larger batches. It will be the inspector's responsibility to determine whether all of the mix components can be uniformly and continuously batched at that batch size, with that plant.
Test Procedure. The procedure for uniformity testing is found in MoDOT TM-82.
Multiple Drums. For plants having more than one mixer drum, the prescibed tests may be performed on only one drum if the drums are made by the same manufacturer, are of the same size and are in comparable condition as to wear of blades, etc.
Application of Results. Mix time may be reduced as permitted by the contract provisions if 5 of the 6 items tested for uniformity are within the limits shown above; however, the minimum mixing time shall be 60 seconds.
501.1.6.3 Truck Mixing (Sec 501.8.3)
When truck mixed concrete is used, the following additional items should be checked by the Q.A. inspector.
- a. Mixes must be of an approved type and must be in a condition to produce uniform and well mixed concrete.
- b. Rating plates must provide all information required by Sec 501.8.5 of the Standard Specifications.
- c. Water measuring devices should be calibrated for accuracy within limits set by Sec 501.6.2 of the Standard Specifications.
- d. Drums should be checked for excessively worn blades and for hardened concrete.
- e. Drum or blade speed should be checked to determine that it is within limits of the manufacturer's recommendation.
- f. Mixing time is controlled by a specified number of revolutions at a specified speed.
501.1.7 Volumetric Batched and Continuous Mixed Concrete (Sec 501.9)
Upon written request by the contractor, the engineer may approve the use of concrete proportioned by volume. If concrete is proportioned by volume, all requirements of the Standard Specifications shall apply. The resident engineer and inspector should thoroughly familiarize themselves with the specification requirements of volumetric batched and continuous mixed concrete.
501.1.7.1 Calibration (Sec 501.9.3)
The following is to establish a procedure for calibrating units used for volumetric proportioning of low slump concrete, latex modified concrete and other concrete pours, except bridge decks, when approved by the Engineer.
- a. Stop watch reading to 0.1 second.
- b. Scales, minimum capacity of 200 lbs. and accurate to within 0.5% of the test load.
- c. A suitable container for test sample. (The bottom 1/4 of a 55 gallon barrel is satisfactory).
- d. 250 and 1000 milliliter graduated cylinders.
Before calibrating the unit, the inspector should become familiar with the general operation, controls, storage compartments, etc. of the volumetric proportioning unit. Proportioning tolerances and proportioning devices such as counter, flow meter, and calibrated gate openings shall be in accordance with Job Special Provision "Portland Cement Concrete Volumetric Batching and Continuous Mixing". The cement discharge rate for any unit is constant when operated in a given gear. For those units equipped with a range of gears on the cement feeder, the operator should be consulted as to what gear the unit will be operated in during the pour. Calibration shall be in that gear in which the concrete mix is to be produced. Mechanically driven units are equipped with tachometers and these units must be calibrated and operated under load at the RPM reading specified by the manufacturer within a tolerance of 50 RPM. On the all hydraulic proportioning units, it is only necessary to advance the throttle until it is against the preset stop. It is important to remember that calibration data obtained for one unit cannot be used on any other unit.
Calibration of all proportioning devices shall be on a weight basis with the exception of the admixture flow meters which may be calibrated on either a weight or a volume basis.
The first step in calibrating a volumetric proportioning unit is to determine the exact cement meter count and the corresponding time in seconds, to 0.1 second, for the discharge of one sack or 94 lbs. of cement. Both aggregate bins should be empty and the main conveyor belt should be clean. Check to ensure that all bin vibrators and the cement bin aeration system are functioning properly. Set throttle to hold the specified RPM reading on mechanical drive units or advance throttle to the preset stop on hydraulic drive units. Discharge enough cement to ensure that the main conveyor belt is fully primed and then reset the cement meter so it reads zero. Discharge approximately 100 pounds of cement into a clean, tared container. Carefully time the run by starting and stopping the stop watch at exactly the same time that the main clutch is engaged and disengaged. Record the actual weight of cement discharged, the cement meter count and the time to the nearest 0.1 second. A minimum of six test runs shall be made. Divide the total meter counts for the six test runs by the total weight of cement discharged and multiply this factor by 94 (the weight of one sack of cement) to determine the meter count to discharge one sack of cement. Likewise, divide the total number of seconds for the six test runs by the total weight of cement discharged and multiply this factor by 94 to determine the time, to the nearest 0.1 second, to discharge one sack of cement.
Calibration procedures and calculations for both fine and coarse aggregate are the same. Because the gates on the fine and coarse aggregate bins of a volumetric proportioning unit do not completely close, only one of these materials can be charged into the mixer at any one time during calibration. Assuming that fine aggregate bin is to be calibrated first, fill it at least two-thirds full with sand and make sure the coarse aggregate bin is empty. Check to ensure that all bin vibrators are functioning properly and that the Cement Meter-Feeder clutch is disengaged to prevent cement discharge while calibrating the aggregate bins. The operator should set the sand gate control at the approximate setting for the weight desired based on previous experience. Set the throttle as noted above. Discharge and waste enough fine aggregate to ensure that the main conveyor belt is fully primed. Discharge approximately 150 to 200 pounds of fine aggregate into a clean, tared container. Carefully time the run by starting and stopping the stop watch exactly when the main clutch is engaged and disengaged. Record the weight of fine aggregate and the actual time to the nearest 0.1 second. Using these two figures and the time determined above, set up a direct proportion to calculate the amount of fine aggregate delivered in the exact length of time it takes to deliver 94 pounds of cement. If the actual quantity delivered is not within the allowable tolerance of the quantity required, adjust the gate control as needed and repeat the above procedure. Several trial runs may be necessary to obtain the correct gate setting. Once this gate setting has been established, at least three runs should be made to verify that it is correct. Empty the fine aggregate bin, charge the coarse aggregate bin and follow the same procedure as above to determine the coarse aggregate gate setting. If several mixes will be used from the same proportioning unit, coarse and fine aggregate bin curves may be plotted using three or more gate settings. The curves should cover the full range of aggregate flow rates anticipated and should be verified within the appropriate tolerances.
When admixtures are used the dispensers on the volumetric proportioning unit shall be calibrated. Calibration may be on either a weight or a volume basis. Dilution of admixtures is usually necessary in order that accurately measurable quantities can be dispensed through the flow meters. Set the throttle as noted above. Set the flow meter at a given point and discharge a sufficient amount of solution into a clean container to obtain an accurate measurement or weight. Carefully time the run to the nearest 0.1 second. Record the quantity of solution delivered and the time. Using these two figures and the time determined above, set up a direct proportion to calculate the amount of solution delivered in the exact length of time it takes to deliver 94 pounds of cement. Repeat the above procedure at least two more times at the same setting and average the results. In the same manner, determine the flow rate at two more points and plot a curve of meter setting vs. flow rate. Verify the curve at a point near where it is anticipated the flow meter will be set during mix production.
The rate of flow through the water flow meter should be determined and a calibration curve plotted as follows: Set the throttle as above. Set the flow meter at a given point and discharge a sufficient quantity of water into a clean, tared container to obtain an accurate weight. Carefully time the run to the nearest 0.1 second. Record the quantity of water delivered and the time. Using these two figures and the time determined above, set up a direct proportion to calculate the amount of water delivered in the exact length of time it takes to deliver 94 pounds of cement. Repeat the above procedure at least two more times at the same setting and average the results. In the same manner determine the flow rate at two more points and plot a curve of meter setting vs. flow rate. Verify the curve at a point near where it is anticipated the flow meter will be set during mix production. When determining the meter setting for actual mix production, the amount of water in the admixture solutions as well as moisture in the aggregates must be taken into consideration and subtracted from the design gallons of water per sack of cement.
501.1.7.2 Verification (Sec 501.9.4)
Proportioning devices shall be verified by running the one-quarter cubic yard test in accordance with the Job Special provisions. Adjust the mix conveyor so that it is at an angle of about 20 degrees. Set the throttle as noted in Calibration. With all controls set for the designated mix, discharge enough mixed material to ensure that the entire length of the mix conveyor contains properly proportioned concrete and then stop the mixing action. Immediately reset the cement meter to zero and swing end of the mix conveyor over the one-quarter cubic yard container (36 in. x 36 in. x 9 in.). Activate the mixer and discharge mixed material into the container until the cement meter count shown that the quantity of cement for one-quarter cubic yard of concrete has been dispensed. Screed the concrete level. Mixes with very low slumps may require vibration. A tolerance of +1/8 inch from the top of the container will be permitted.
501.1.8 Air-Entrained Concrete (Sec 501.10)
Test methods outlined in the following paragraphs were derived from AASHTO T-152 to provide a basis for determining air content of freshly mixed concrete. Principles involved are based on the fact that air is the only compressible component in freshly mixed concrete. Operation of testing equipment is to be in accordance with the manufacturer's instructions.
The pressure method of determining air entrainment is to be used for concrete intended for both structures and pavement, with the exception of lightweight concrete. Porosity of lightweight aggregates introduces errors into results which make other procedures necessary.
Air test are to be made at the beginning of each pour on structures and for each 100 cubic yards thereafter.
Equipment used to determine the air content of concrete shall meet the requirements of AASHTO T-152. All types of apparatus used for determining air content by the pressure method have several features in common:
- (a) A measuring bowl which is sufficiently rigid to make a pressure tight container of accurate volume and which is suitable to hold a representative sample of the concrete to be tested.
- (b) A cover which is designed to be attached to the measuring bowl in a way which produces a rigid, pressure-tight assembly.
- (c) Means of applying a known pressure to the system, and for observing its effect on the volume of the sample.
- (d) Appropriate tools for placing and consolidating the sample and using the apparatus. A tampering rod 5/8 inch in diameter with a hemispherical tip is furnished for compacting concrete. This rod should be approximately 2 feet in length. A mallet with a rubber or rawhide head weighing approximately 1/2 lb. is furnished for tapping the measuring bowl during the testing process. Other accessories such as a trowel, strike-off bar, funnel, and water measure are part of the set.
The following procedures for calibration of the apparatus, determination of air content of concrete, and calculations of results will be given in general terms since minor changes are necessary for different types of apparatus. However, the intent will serve as a guide to exact procedures to be used if equipment furnished is slightly different.
Aggregate correction factors shall be made available by the district to the Central Laboratory when coarse aggregate samples are submitted for AASHTO T161 testing.
Protex Meter. Calibration of pressure-type apparatus is affected by changes in barometric pressure such as those caused by changes of temperature and humidity, and by rough handling. Steps (a) through (e) normally need be made only at time of initial calibration, and occasionally there after to check the stability of volume for the calibration cylinder and measuring bowl. Step (f) must be made as frequently as necessary to ensure that proper gauge pressure is being used in tests for air content of concrete.
- (a) Calibration of the calibration cylinder. Accurately determine weight of water, w, in grams required to fill the calibration cylinder, using a scale sensitive to 0.5 gram.
- (b) Calibration of measuring bowl. Determine weight of water, W, (in pounds) required to fill the measuring bowl. Use a scale sensitive to 0.1 percent of the weight of the bowl filled with water. Slide a glass plate carefully over the flange of the bowl in a way to ensure that the bowl is completely filled with water. A thin film of cup grease smeared on the flange of the bowl will make a water tight joint between the glass plate and top of the bowl.
- (c) Determination of Constant, R. The constant, R, represents the volume of the calibration cylinder expressed as a percentage of the volume of the measuring bowl. Calculate R by the following equation:
- If scales of adequate capacity are available and the inspector so desires, W may be determined in grams. If that is done the equation reduces to:
- (d) Determination of expansion factor, D. Determine the expansion factor, D, for any given apparatus assembly by filling the apparatus with water only. Make certain that all entrapped air has been removed and the water level is exactly on the zero mark. Apply an air pressure approximately equal to the operating pressure, P, determined by the calibration test described in (f). The amount the water column lowers will be the equivalent expansion factor, D, for that particular apparatus and pressure. For this portion of the calibration, it will be satisfactory to use an approximate value for P. This is determined by making a preliminary calibration test as described in (f), except that an approximate value for calibration factor, K, will be used. For this test, K, will be approximate, because the factor, D, as yet unknown, is assumed to be zero. See (e).
- (e) Determination of calibration factor, K. The calibration factor, K, is the amount the water column must be depressed during the calibration procedure to obtain the gauge pressure required, so that graduations on the glass tube correspond directly to the percentage of air introduced into the measuring bowl by the calibration cylinder when the bowl is level full of water. Calculate K as follows:
- (f) Calibration test to determine operating pressure, P, on pressure gauge. If the rim of the calibration cylinder contains no recesses or projections, fit it with three or more spacers equally spaced around the circumference. Invert cylinder and place it at the center of the dry bottom of the measuring bowl. The spacers provide opening for flow of water into the calibration cylinder when pressure is applied. Secure the inverted cylinder against displacement and carefully lower the conical cover into place and clamp. After cover is clamped in place, carefully adjust the apparatus assembly to a true vertical position. Add water at air temperature by means of the tube and funnel until water rises above the zero mark in the standpipe. Close vent and pump air into the apparatus to the approximate operating pressure. Incline the assembly about 30 degrees from vertical, and using bottom of the bowl as a pivot, describe several complete circles with the upper end of the standpipe. Simultaneously, tap over and sides of the bowl lightly to remove any entrapped air which might be adhering to inner surfaces of the apparatus. Return the apparatus to a vertical position, gradually release pressure to avoid loss of air (from the calibration cylinder), and open vent. Bring water level exactly to the zero mark by bleeding water through the petcock in the top of the conical cover. When the zero mark has been reached, close vent and then apply pressure until the water level has dropped an amount equivalent to about 0.1 to 0.2 percent of air more than the value of the calibration factor, K, determined as described in (e). To relieve local restraints lightly tap sides of the bowl. When the water level is exactly at the value of calibration factor, K, read the pressure, P, indicated by the gauge and record to the nearest 0.1 psi. Gradually release pressure and open vent to determine whether the water level returns to the zero mark when sides of the bowl are tapped lightly. Failure to do so indicates loss of air from the calibration cylinder or loss of water due to a leak in the assembly. If the water level fails to return to within 0.05% air of the zero mark and no leakage beyond a few drops of water is found, some air probably was lost from the calibration cylinder. In this case, repeat the entire calibration procedure, step by step. If leakage is more than a few drops of water, tighten the leaking joint before repeating the calibration procedure. Check the indicated pressure reading promptly by bringing the water level exactly to the zero mark, closing vent, and applying the pressure, P, just determined. Tap gauge lightly with a finger. When gauge indicates the exact pressure, P, water column should read the value of the calibration factor K, used in the first pressure application. The reading should be within about 0.5 percent of air.
Soiltest Meter The easiest method of calibrating the Soiltest Air Meter is by using the calibration block.
Note: Use the 5% block only for checking in-between annual calibrations. The 5% block must be calibrated alongside the yearly calibration of the air-pot to note any offsets.
- a. Fill the material container with water.
- b. Place the 5 percent calibration block in the material container.
- c. Place and clamp lid onto the container, run air test as you normally would for concrete.
- d. If the gauge hand indicates 5 percent air (± any calibrated offset), the equipment is properly calibrated.
- e. If the gauge hand indicates air content other than 5 percent, adjust the initial starting point (the yellow needle) and run through the test again. This may be done a few times until the gauge is properly calibrated.
Determination of Aggregate Correction Factor. Determine the aggregate correction factor on a combined sample of fine and coarse aggregate by the methods outlined in the following paragraphs:
Calculate weights of fine and coarse aggregate present in the volume, S, of the sample of fresh concrete whose air content is to be determined as follows:
- Fs = weight of fine aggregate in concrete sample under test, in lbs.
- S = volume of concrete sample (Same as volume of measuring bowl of apparatus), in cubic feet.
- B = volume of concrete produced per batch, in cubic feet.
- Fb = total weight of fine aggregate in batch, in lbs.
- Cs = weight of coarse aggregate in concrete sample under test, in lbs., and
- Cb = total weight of coarse aggregate in batch, in lbs.
Mix representative samples of fine aggregate of weight, Fs, and coarse aggregate of weight, C, and place in the measuring bowl which has been previously filled 1/3 full of water. Add mixed aggregate a little at a time until all of the aggregate is inundated. Add each scoopful in a manner that will entrap as little air as possible. Promptly remove accumulations of foam. Tap sides of the bowl and lightly rod the upper inch of the aggregate about 10 times. Stir after each addition of mixed aggregate to eliminate entrapped air.
When all of the aggregate has been placed in the bowl and inundated for at least 5 minutes, strike off all foam and excess water, and thoroughly clean flanges of both the bowl and conical cover so that when the cover is clamped in place, a pressure tight seal will be obtained. Complete test as described below. The aggregate correction factor, G, is equal to h1-h2, as determined in the tests on the aggregate. The factor will normally remain fairly constant for any given aggregates but since different aggregates will have different factors, a new factor must be determined for each source.
501.1.8.2 Procedure for Determining Air Content of Concrete
With the Protex Meter, place a representative sample of concrete in the measuring bowl in three equal layers. Consolidate each layer by rodding, and by tapping the bowl. When concrete is placed, consolidate each layer of concrete with 25 strokes of the tamping rod, evenly distributed over the cross section. Follow the rodding of each layer by tapping sides of the bowl with the mallet, until cavities left by rodding are leveled out and no large bubbles of air appear on the surface of the rodded layer. When rodding the first layer, rod should not strike bottom of the bowl. In rodding the second and final layers, use only enough force to cause the rod to penetrate the surface of the previous layer. Slightly overfill the bowl with the third layer. After rodding, remove excess concrete by sliding the strike off bar across the top flange with a sawing motion, until the bowl is just level full.
Thoroughly clean flanges of the bowl and conical cover so that when the cover is clamped in place, a pressure-tight seal will be obtained. Assemble the apparatus and add water over the concrete by means of the tube. Water should be added until it rises to about the half way mark in the standpipe. Incline the apparatus assembly about 30 degrees from vertical, using bottom of the bowl as a pivot. Describe several complete circles with the upper end of the column, simultaneously tapping the conical cover lightly to remove any entrapped air bubbles above the concrete sample. Return the apparatus assembly to its vertical position. Fill the water column lightly above the zero mark, while lightly tapping sides of the bowl. Foam on the surface of the water column may be removed with a syringe or with spray of alcohol to provide a clear meniscus. Bring the water level to the zero mark of the graduated tube before closing vent at top of the water column.
Apply slightly more than the desired test pressure, P (about 0.2 psi more), to the concrete by means of the hand pump. To relieve local restraints, tap sides of the measure. When the pressure gauge indicates exact test pressure, P (as determined in accordance with instructions for the calibration test), read the water level, h1, and record to the nearest division or half division (0.10 or 0.05% air content) on the graduated bore tube or gauge glass of the standpipe. For extremely harsh mixes, it may be necessary to tap the bowl vigorously until further tapping produces no change in indicated air content. Gradually release air pressure to vent at the top of the water column, and tap sides of the bowl lightly for about 1 minute. Record the water level, h2, to the nearest division or half division. The apparent air content, A1, is equal to h1-h2.
Repeat the steps described in Section 501.16.4.3.3.2 without adding water to reestablish the water level at the zero mark. The two consecutive determinations of apparent air content should check within 0.2% of the air. Use the average to get the value, A1, to be used in calculating the air content, A, in accordance with Section 501.16.4.4.
CALCULATION. Calculate the air content of the concrete as follows:
- A = A1 – G
- A = Air content percentage, by volume of concrete.
- A1 = Apparent air content percentage, by volume of concrete.
- G = Aggregate correction factor percentage, by volume.
Concrete placement shall be halted if results of tests for entrained air indicate non-compliance with specification requirements.
Data for tests for air entrainment should be entered directly in a bound field book by the inspector. The aggregate correction factor should be determined at start of the work for each mix and complete data and calculations entered in the field book. Each test for determination of operating pressure, P, must also be entered.
In the record of test for air entrainment the aggregate correction factor and operating pressure used should be identified with the test from which they were determined. This can be done by reference to book and page number on which the test is recorded.
501.1.9 2AA Sheet For Concrete Pavement
The 2AA Sheet is a summary and graphic record of the design, typical section, materials, and methods used in the construction of the base, surfacing, and shoulders of a portland cement concrete paving project. It will include data on the throughway at all interchanges and underpasses. It is not necessary to prepare a 2AA Sheet for pavement in traffic interchanges or underpasses constructed in isolated sections 750 feet or less in length or isolated areas within the primary travelway of 1000 S.Y or less. The blank 2AA Sheet can be located on Micro Station Directory. t:\standard\wsmod\design\seed_i\i_2aa-2d.dgn
Information provided on this sheet is valuable for future investigations and often is not available from any other source. Information on the paving work is to be recorded by daily entries made by the plant inspector on a 2AA Sheet, kept as a work sheet in the laboratory during the paving. This requires close liaison between the plant inspector and the field inspection force. If the slab inspector notes any changes in construction details or other data of the type required on the 2AA Sheet, the slab inspector should immediately notify the plant inspector of the change and the station where it occurred. The plant inspector should promptly plot it on the 2AA work sheet. Inspectors on base and shoulder construction should provide data in a like manner so that a complete, accurate record can be kept up-to-date.
The resident engineer is responsible for assuring proper cooperation of personnel to carry out the task of meeting this responsibility.
The District Construction and Materials Engineer will be responsible for the accuracy of entries regarding materials, proportions, design and certain other information. Upon completion of each 2AA Sheet it should be promptly submitted to the District Construction and Materials Engineer for approval. When the District Construction and Materials Engineer has approved the 2AA Sheet, it will be sent promptly to the Division of Construction and Materials.
While working on the 2AA Sheet in the field, care should be taken to ensure accuracy and sufficient legibility to permit preparation of the finished sheet by the Division of Construction and Materials for a permanent record. The resident engineer is relieved of the work of drafting the finished 2AA Sheet but is responsible for seeing that the work sheet is properly prepared. Use of an H pencil will often eliminate the need for further work before printing.
The sheet is to be prepared by entering to scale the stationing of the project, including all exceptions and equations, on the proper line near the top of the chart. A scale of 1 in. equals 1000 ft. is recommended for projects over 13,500 ft. in length. For shorter projects or more detailed work a larger scale may be used to advantage.
Appropriate data should be entered opposite the proper heading listed on the left. A short vertical line should be used to indicate a change. Horizontal lines should be drawn to show clearly the limits of a particular material, design or method. Stationing of changes should be plotted and recorded on the graphs. To identify a specific design the number of the standard drawing, along with the latest revision date on it, is to be shown. When alternate types of a design are shown on the same standard drawing or special sheet, it is essential to note the type designation of the alternate actually used, as well as the drawing number. If a standard drawing has been modified for a specific project, it becomes a special sheet in the plans and is identified by its special sheet number.
The name or designation of an item should be shown. If space is insufficient it may be necessary to use footnotes and legends, especially in case of special procedures or unusual conditions. If the entry opposite any heading should be "None", show this on the left outside the graph.
501.1.9.3 Required Information
Although the information required is generally self-explanatory, a brief comment will be made on some items:
- Contractor. This is the prime contractor.
- Paved by. The name of the organization which did the actual paving.
- Equipment. List all major machinery and tools that may affect the quality of the base, surfacing, and shoulders. Do not list such items as cranes, bulldozers, storage tanks, concrete saws, and the like.
- Type of Construction. Give a brief description of the class of work. If grading and/or bridges are included in the contract, indicate this fact.
- Total Length. Show the length of the project to the nearest 0.0001 mile.
- Exceptions. Show all exceptions listed on the 2A Sheet. Also show the location and lengths of the portions of the project where concrete pavement was not built.
- Equations. Show all equations listed on the 2A Sheet.
- Location of Project. Briefly describe the project location by reference to landmarks such as towns, rivers, route intersections, etc.
- Date of Construction. These dates should cover the actual period of paving operations.
- Daily Temperature. The minimum and maximum daily temperatures should be shown for the period representing each day's run.
- Typical Section.
- Graded Earth. The roadbed widths and the standard drawing numbers should be shown when grading and paving are parts of the same contract. So state, if grading was done under a previous contract.
- Pavement. Give the pavement dimensions. Draw a sketch in the lower right portion of the 2AA Sheet showing the typical section of the base, pavement and shoulders.
- Coarse Aggregate. Show the source, including the location of the plant and name of producer. If there is not enough space on the graph, use a key at the bottom of the sheet.
- Fine Aggregate. Show the information in the same way used for the coarse aggregate.
- Cement. Show the brand of cement used, the name of the manufacturer and the location of the plant. Note whether sack or bulk cement was used.
- Admixture. Show the type and proportions of any admixture used. Note if none was used.
- Proportions. Show the mix proportions, such as 1:1.62:3.30.
- Mixing Water. Show the daily average of gallons of water per sack of cement. If unusual conditions cause wide variation show the range.
- Air Entrained Concrete. Show the daily average air content of the mix and the name of the air-entraining agent used.
- Distributed Reinforcement. This term refers to wire fabric and bar mat. Show the design number, type, and length of sheets. If the pavement is non-reinforced so note.
- Expansion. These are usually used only at bridge ends and at intersections so the type of joint and general location will suffice. If expansion joints are used at other locations, the type, spacing and design standard number should be shown.
- Contraction. Show the standard number of type of joint and load transfer units.
- Longitudinal. Show standard numbers and type. If the longitudinal joint is located other than at centerline, it should be noted.
- Construction. Show standard number and type.
- Surface Texture. List type of texture provided.
- 1. List station limits of any texture loss due to rain, etc.
- 2. If surface is retextured show limits of retextured area and method used.*
- 3. If more than one method of surface texturing is used note this fact under remarks and list limits for each method.
- Item 3. does not apply to areas of bump removal but only to areas where retexturing is performed as a result of loss of original texture due to rain, etc.
- Curing Method. Show the method of curing, the rate of application and the brand name of the material used if applicable.
- Drainage Structures. Show only the types used. It is not necessary to show the several sizes and locations of culverts. However, the type, length, and location for each underdrain should be shown.
- Guard Rail. Show only the Standard Drawing Number.
- Special Materials. Show if any special materials were used, special procedures followed, or unusual conditions encountered. Give station limits. Use footnotes if space is insufficient.
- Subgrade. These entries refer to the soil on which the base or subbase is laid. Any variations should be located on the graphic record.
- Method of Compacting Embankments. Indicate the thickness of lifts, type of compacting equipment, any special processing required, etc. Note location of any variations.
- Treatment. Indicate the degree of moisture and density control, the station limits of any undergrading and backfilling performed or select subgrade material used. Show the limits of any chemical or bituminous subgrade modification.
- Condition. Describe condition of subgrade or soil condition at time of placing base by such terms as: firm, soft, muddy, dry, rutted, etc. Note location of any change in subgrade condition.
- Soil Type. Show the soil type and range in Group Index number from the soil survey.
- Granular Base. This refers to the course, generally 4 inches thick, immediately below the pavement.
- Type, Dimensions and Type Aggregate Used. Show the type of aggregate base, any apparent variations in thickness, density, moisture or stability, and the type of aggregate (gravel or crushed stone).
- Condition. Describe the condition and characteristics of the base with terms such as firm, yielding, spongy, open, loose, rutting, ravelling, etc. Include special notes based on observation during construction such as: Whether the base remained stable or deteriorated in some manner under construction traffic and if it was necessary to add a leveling course of fine material to facilitate final shaping of the surface.
- Shoulders. Take information for this item from special sheets in the plans for the specific project. The typical section sketch is used to show details.
- Type. Enter the proper term such as earth, aggregate surfaced, stabilized, or the appropriate letter from the typical section in the design plans. If the shoulder type is a special design, indicate this by descriptive terms. If necessary, use footnotes or references to plan sheets, special provisions, etc.
- Treatment. Shoulder stabilization may involve application of various materials or treatments. Indicate the kind of treatment by such descriptive terms as: untreated, soil cement, bituminous stabilized, calcium chloride stabilized, cement stabilized, sandasphalt mat, asphaltic concrete, seal coat, color coat, and 2 in. by 2 ft. A.C. edge strip.
- Date Open to Traffic. Show date the pavement was first subjected to vehicular traffic, including contractor's equipment.
- Defects Observed in Completed Pavement. Note any outstanding defects and the date when they were first discovered.
- Signature. The signature required is that of the plant inspector who prepares the 2AA Sheet and enters the date. Before the summary is submitted to the District Construction and Materials Engineer, it is to be checked and approved by the Resident Engineer. The checking procedure should be carefully followed to assure an accurate and complete summary.
501.1.9.4 Large Projects
On large projects, it is often necessary to use more than one sheet. In this case, it is not necessary to repeat the information under equipment, material, and special procedures keys or the pavement cross section on the second or succeeding sheets unless a different pavement design is used on part of the work.
501.2 Materials Inspection for Sec 501
|Water Reducer, PCCP|
|Full Report 2001|
|See also: Research Publications|
To establish uniform procedures for evaluating and approving Portland cement concrete mix designs. Calibration of the plant and performance of uniformity tests of concrete are to be performed in accordance with plant inspection guidance.
501.2.2 Mix Design Procedures
Portland cement concrete mix designs will be reviewed by district Materials for specification compliance. The district will approve concrete mix designs complying with the specifications and meeting the guidelines outlined in this guidance. After reviewing the concrete mix, the district will prepare a letter advising the contractor whether the concrete mix has been approved or rejected. A copy of the approved concrete mix shall be sent to the Materials Field Office (See example format).
501.2.3 Mix Design Information
Concrete mix designs shall contain, but are not limited to, the following information:
- (a) Source, type and specific gravity of Portland cement
- (b) Source, type and specific gravity of supplementary cementitious materials (if used)
- (c) Source, name, type and amount of admixtures.
- (d) Source, type (formation, etc.), ledge number if applicable, and gradation of the aggregate.
- (e) Specific gravity and absorption of each aggregate fraction in accordance with AASHTO T-85 for coarse aggregate and AASHTO T-84 for fine aggregate, including all raw data.
- (f) Unit weight of each aggregate fraction in accordance with AASHTO T-19, including the raw data.
- (g) The percentage of each aggregate component used for optimized concrete mixes.
- (h) The design air content and slump.
- (i) Batch weights of coarse, intermediate and fine aggregates.
- (j) Batch weights of Portland cement and supplemental cementitous materials.
- (k) Batch weight of water.
To aid the contractor in submitting concrete mix designs to the district for approval, there is a concrete mix design submittal form which may be used by the contractor. This form contains all of the required information needed for the mix design to be evaluated. This form can be accessed by MoDOT personnel in SharePoint at Concrete Mix Design Submittal Form.
501.2.4 District Procedures
When a Portland cement concrete mix has been received by the district, the district will check the calculations thoroughly and ensure that the materials listed and sieve analysis shown are correct and that the proposed proportions comply with Specifications. It may be necessary for the district to advise the contractor to make adjustments to their mix design in order to comply with the Specifications.
501.2.4.1 Portland Cement
- The specific gravity of Portland cement shall range from 3.10 to 3.20. If the material does not fall within this range, contact the Central Laboratory. The Chemical Laboratory will review their records and determine if the specific gravity shown on the mix design is acceptable. For blended cements, contact the Central Laboratory to determine if the specific gravity is appropriate.
- When a Type A water reducer is used in pavement concrete for paving purposes, the minimum cement content can be reduced by 0.25 sacks per yard.
- When a concrete mix is optimized, the minimum cement content may be reduced by 0.5 sack per yard.
- In no case should the cement content be more than 0.5 sacks per yard below the cement contents specified in Sec 501.3.2.
501.2.4.2 Supplemental Cementitous Materials
Supplemental cementitous materials shall be from approved sources in accordance with Ground Granulated Blast Furnace Slag and Fly Ash for Concrete. When supplemental cementitous materials are used, ensure that the total percent of replacement does not exceed the limits specified in Sec 501.14.
The specific gravity of supplemental cementitous materials shall be within the following ranges:
|Fly Ash (Type C)||2.55 - 2.75|
|GGBFS (Grade 100 and 110)||2.85 - 2.95|
For Type F fly ash, contact the Central Laboratory to determine if the specific gravity is appropriate.
If the material does not fall within the above range, contact the Central Laboratory. The Chemical Laboratory will review their records and determine if the specific gravity shown on the mix design is acceptable.
Concrete admixtures shall be in accordance with guidance on concrete admixtures.
When a high range water reducer is being used a letter from the admixture company shall be furnished stating that the admixture is compatible with the other admixtures (i.e. air entrainment, retarder, accelerator, etc. by brand name) being used in the mixture.
Ensure the amount of water being used in the concrete mix does not exceed the maximum water content specified in Sec 501.5. In no case shall the water/cement ratio be below 0.30.
501.2.4.5 Air Content
The concrete mix shall be designed at an air content (total mix) greater than the minimum air content of 5.0 percent specified in Sec 501.10.2. Mixes designed below 5.0 percent shall not be approved.
501.2.4.6 Aggregate Properties
|Aggregate, Gradation Optimization|
|See also: Research Publications|
Physical characteristics of the aggregate shown on the mix design shall be compared with the values contained in the document entitled "Physical Characteristics of Principal Portland Cement Concrete Aggregates in Missouri". For new sources, compare the data with test results obtained on samples submitted for dry rodded unit weight, specific gravity and absorption as received as required in General Requirements for Material. Favorable comparison will be obtained when the aggregate properties shown on the mix design comply with the following criteria:
|Aggregate Fraction||Bulk Sp. Gr.||Absorption (%)||Unit Weight (lbs/ft3)|
When aggregate properties do not compare favorably, 2 bags of material will need to be submitted to the Central Laboratory for each aggregate fraction not comparing favorably. The dry rodded unit weight, specific gravity, and absorption as received will be determined. Test results will be compared with the aggregate properties shown on the concrete mix design. If the aggregate properties still do not compare favorably, the mix design will not be approved until a consensus is reached between the contractor and the Department on what the aggregate properties should be.
501.2.4.7 Batch Weights
Batch weights will be confirmed by determining the absolute volume of each component being used in the mix design. The absolute volume of each component plus the volume of air should add up to 27.00 +/- 0.04 cubic feet per cubic yard. Mixes exceeding this limit will need to be adjusted by the contractor and resubmitted for approval.
Determining Absolute Volumes.
- Mix design submitted:
|Batch Weight (pounds)|
- Material properties submitted:
|Unit Weight (lbs/ft3)||Specific Gravity||Absorption (%)|
- Calculate absolute volumes:
- Coarse Aggregate = (1855) / (2.63 x 62.4) = 11.30 cu. ft. per cubic yard
- Fine Aggregate = (1230) / (2.62 x 62.4) = 7.52 cu. ft. per cubic yard
- Cement = (479) / (3.14 x 62.4) = 2.44 cu. ft. per cubic yard
- Fly Ash = (85) / (2.68 x 62.4) = 0.51 cu. ft. per cubic yard
- Water = (225) / (1.00 x 62.4) = 3.61 cu. ft. per cubic yard
- Air Content = (6.0 / 100) x (27.0) = 1.62 cu. ft. per cubic yard
- Total = 27.00 cu. ft. per cubic yard
- Round absolute volumes to 0.01.
501.2.4.8 Percent Fine Aggregate
The percent fine aggregate by absolute volume should range from 35 to 46 percent. Concrete mixes that exceed these limits will need to be evaluated by the Materials Field Office.
The following procedure is used to determine the percent fine aggregate being used in the concrete mix.
- Percent fine aggregate = (7.52 x 100)/(7.52 + 11.30)
- Percent fine aggregate = 39.96%, rounds to 40%
501.2.4.9 Dry Yield
The following procedure is used to determine the dry yield for the concrete mix.
- Dry yield = (11.30 + 7.52 + 2.44 + 0.51)
- Dry yield = 21.77 cu. ft. per cubic yard
501.2.4.10 Cement Factor
The following procedure is used to determine the cement factor.
- Cement Factor = (479 + 85)/94
- Cement Factor = 6.00 sacks of cement per cubic yard
501.2.4.11 Water Factor
The following procedure is used to determine the water factor.
- Water factor = 225/(6.00 x 8.3333)
- Water factor = 4.50 gallons per sack of cement
501.2.4.12 Water/Cement Ratio
The following procedure is used to determine the water/cement ratio.
- Water/Cement Ratio = 225/(479 + 85)
- Water/Cement Ratio = 0.3989, rounds to 0.40
501.2.4.13 Mix Proportions
Mix proportions of aggregates are equal to the absolute volume of that aggregate in a one-sack batch divided by the absolute volume of one cubic foot (dry rodded) of that aggregate. The mix proportions are rounded to the nearest 0.05. The following procedures are used to determine the concrete mix proportions.
Absolute volume of one cubic foot of fine aggregate = 111/(2.62 x 62.4)
Absolute volume of one cubic foot of fine aggregate = 0.678949, rounds to 0.6789
- Fine aggregate proportion = (7.52/6.0)/0.6789
- Fine aggregate proportion = 1.8461, rounds to 1.85
- Absolute volume of one cubic foot of coarse aggregate = 98/(2.63 x 62.4)
- Absolute volume of one cubic foot of coarse aggregate = 0.597153, rounds to 0.5972
Coarse aggregate proportion =(11.30/6.0)/0.5972
Coarse aggregate proportion = 3.1536, rounds to 3.15
The mix proportions of cement, fine aggregate, and coarse aggregate are:
- 1 : 1.85 : 3.15
501.2.4.14 Percent Air in Mortar
Air entrainment is generally considered effective for freeze-thaw resistance when the volume of air in the mortar fraction of the concrete (material passing the No. 4 sieve) is 8.0 percent or greater. The following procedure is to be used to determine the percent air in mortar.
- Percent air in mortar = (1.62 x 100)/(27.00 – 11.30)
- Percent air in mortar = 10.318%, rounds to 10.3%
- The amount of material in the coarse aggregate passing the No. 4 sieve is considered to be negligible for the purpose of this design check.
Concrete mixes below 8.0 percent will need to be evaluated by the Materials Field Office.
501.2.4.15 Percent Supplemental Cementitous Material
The following procedure is used to determine the percent of cement replaced with a supplemental cementitous material.
- Percent suppl. cementitous materials = (85 x 100)/(479 + 85)
- Percent suppl. cementitous materials = 15.07%, rounds to 15%
For non-optimized concrete mixes, each aggregate fraction shall comply with the requirements contained in Sec 1005.2 for the coarse aggregate and Sec 1005.3 for the fine aggregate. For optimized concrete mixes, the contractor shall submit with the mix design the target gradation and allowable tolerance for each aggregate fraction being used in the mix. The combined aggregate gradation of the optimized concrete mix will be reviewed to determine if the gradation is well-graded and suitable for use in an optimized concrete mix. Individual aggregate fractions used in an optimized concrete mix shall comply with the requirements contained in Sec 501.3.
501.4.16.1 Calculate the Coarseness Factor1 and Workability Factor1 of the optimized concrete mix. These values will be plotted on the Coarseness Factor Chart1 to determine if the combined aggregate gradation is optimized.
501.4.16.1.1 The following procedure is used to calculate the Coarseness Factor.
501.4.16.1.2 The following procedure is used to calculate the Workability Factor.
501.4.16.1.2.1 The Coarseness Factor Chart is based upon 6.0 sacks (564 pounds) of cement per cubic yard. When the total amount of cementitous materials exceeds 6.0 sack of cement, the Workability Factor needs to be adjusted plus 2.5 percent per sack of cement equivalent. When the total amount of cementitous materials is below 6.0 sack of cement, the Workability Factor needs to be adjusted minus 2.5 percent per sack of cement equivalent.
501.4.16.2 Optimized concrete mixes which do not meet these limits will be sent to the Materials Field Office for mix verification.
501.4.16.3 The procedures for reviewing the combined aggregate gradation of an optimized concrete mix are shown in an example.
501.2.5 Laboratory Mix Verification
If during the review process the district identifies a concrete mix that needs further evaluation, the concrete mix may be sent to the Materials Field Office for further evaluation and possibly mix verification, if deemed necessary. A copy of the mix design and the contractor’s request letter shall be submitted to the Materials Field Office accompanied by a letter of transmittal outlining the reasons the mix needs further evaluation. When possible, the concrete mix and correspondence should be transmitted electronically. The Materials Field Office e-mail address is MFO.
501.2.5.1 Trial Batch
If requested, the district will need to obtain and submit material to the Central Laboratory for trial batch purposes. The following amount of material will be need for conducting trial batches:
|Type of Material||Minimum Amount of Material|
|Supplemental Cementitous Materialsa||1 quart|
|Coarse Aggregateb||600 pounds|
|Fine Aggregate||350 pounds|
- aFor each type being used
- bIf the coarse aggregate is furnished in more than one fraction, use the proportions hown on the mix design to determine the amount of each coarse aggregate fraction to submit. A minimum of 150 pounds should be submitted.
Aggregates are to be obtained and submitted to the Central Laboratory in accordance with General Requirements for Material.
A letter of transmittal will accompany the approved concrete mix to the District Operations Engineer with distribution as follows:
|Copy of Letter||Copy of Letter of Transmittal and Approved Mix|
|Field Office File||1|
The letter of transmittal and the approved concrete mix will be sent by electronic mail to the individuals listed above.
A copy of the approved concrete mix accompanied by a letter of transmittal from the District Operations Engineer is to be forwarded to the contractor.
501.2.6 Precast Concrete
|Pavement, Precast Prestressed Concrete|
|See also: Research Publications|
The use of approved high range water reducers and non-chloride accelerators will be permitted for use in precast concrete having a minimum cement content of 564 pounds and no other specific air or slump mix requirements, if approved by the District Operations Engineer except for concrete pipe. Requests for additives to concrete pipe should be directly to the State Construction and Materials Engineer.
501.2.6.1 The producer shall furnish a mix design to the District Operations Engineer, for approval, which shall indicate the batch weights, including the amount of admixture(s) to be used.
501.2.6.2 The admixture(s) are to be within the manufacturer’s recommended dosage levels.
501.2.6.3 The accelerators shall be of the non-chloride type.
501.2.6.4 The supplier of the high range water reducer shall furnish for the District Operation Engineer’s file, a certification stating the admixture being furnished is considered to be compatible with the other admixtures (i.e. air entrainment, retarded, accelerator, etc. by brand name) being used in the mixture. Any changes in sources of admixture will require a re-submittal of the certification.
501.2.6.5 A copy of the approval of the mix design using the above admixtures shall be submitted to the State Construction and Materials Engineer.
501.2.7 Class A-1 Concrete
Class A-1 Concrete was created for prestress work. It provides a smaller aggregate, which is necessary to accommodate the often-minimal clearance between forms and reinforcement, or within the reinforcement cage. It also provides additional cement to accommodate the water demand associated with the smaller rock, and to obtain faster strength gain. Class A-1 Concrete for work other than prestress may be modified as follows:
501.2.7.1 Gradation D stone may be substituted for Gradation E stone, when the piece being cast does not have clearance problems that might cause Gradation D stone to bridge and cause voids or low density areas within the piece. When the district and the precaster are in agreement on the desirability of the Gradation D substitution, Construction and Materials shall be contacted with the proposal.
501.2.7.2 Construction and Materials will review the proposal and will approve or disapprove the substitution of Gradation D stone for Gradation E stone in the designated application.
501.2.7.3 Following approval by Construction and Materials, a no-cost change order will be issued on the associated contract to record the intent to use a non-specified substitution of material.
501.2.8 Testing Equipment
All Quality Control (QC) testing shall be performed on QC test equipment. Quality Assurance (QA) testing shall be performed on QA test equipment. QC tests shall not be performed using QA testing equipment and QA tests shall not be performed using QC testing equipment. QA samples may be submitted to the Central Laboratory for testing if the district does not have the necessary testing equipment.
501.2.9 Aluminum Powder
For closure pours, unpolished aluminum powder may be added to offset shrinkage that will occur as concrete hardens. The aluminum powder reacts with the cement to generate hydrogen gas. The formation of hydrogen gas causes the concrete to expand, which offsets the shrinkage.
501.2.9.1 The manufacturer shall specify the dosage rate for the unpolished aluminum powder. Typical dosage rate ranges from 2.5 to 5.5 grams per 100 pounds of Portland cement. Concrete involving supplementary cementitious materials (i.e. fly ash, GGBFS, silica fume), only the Portland cement portion should be treated at the recommended dosage rate, unless otherwise stated by the manufacturer.
501.2.9.2 Determining Unpolished Aluminum Powder Batch Weight.
Mix Design Submitted:
|Portland Cement||400 lbs/yd3|
|Fly Ash||100 lbs/yd3|
|Unpolished Aluminum Powder||3 grams per 100 lbs of cement|
Unpolished Aluminum Powder Batch Weight = (400/100) x 3
Unpolished Aluminum Powder Batch Weight = 12 gm/yd3
Prior to concrete placement, the contractor shall prepare trial batches. Trial batches are performed to ensure the concrete complies with the specifications before using the concrete mix.
To prevent hydrogen gas from being trapped in the top portion of compressive strength cylinders, plastic lids should not be placed immediately after filling molds. Plastic lids should be placed 1 hour after filling the mold. Wet burlap shall be placed over the top of the mold until the plastic lids are placed.
501.2.9.3 Unpolished aluminum powder is to be accepted on the basis of the container label or manufacturer’s certification.