Category:502 Portland Cement Concrete Base and Pavement
- 1 502.1 Construction Inspection for Sec 502
- 1.1 502.1.2 Material (Sec 502.2)
- 1.2 502.1.3 Equipment (Sec 502.3)
- 1.3 502.1.4 Construction Requirements (Sec 502.4)
- 1.3.1 502.1.4.1 Weather Limitations (Sec 502.4.1)
- 1.3.2 502.1.4.2 Protection Against Rain (Sec 502.4.2)
- 1.3.3 502.1.4.3 Setting Forms (Sec 502.4.3)
- 1.3.4 502.1.4.4 Placing Concrete (Sec 502.4.6)
- 1.3.5 502.1.4.5 Tie Bar Placement (Sec 502.4.7)
- 1.3.6 502.1.4.6 Final Strike-off, Consolidation and Finishing (Sec 502.4.8)
- 1.4 502.1.5 Joints (Sec 502.5)
- 1.5 502.1.6 Curing (Sec 502.6)
- 1.6 502.1.7 Removing Forms (Sec 502.7)
- 1.7 502.1.8 Surface Test (Sec 502.8)
- 1.8 502.1.9 Opening to Traffic (Sec 502.9)
- 1.9 502.1.10 Material Acceptance (Sec 502.10)
- 1.10 502.1.11 Contractor Quality Control (Sec 502.11)
- 1.11 502.1.12 (Sec 502.15)
- 2 502.2 Material Inspection
- 2.1 502.2.1 Scope
- 2.2 502.2.2 Apparatus
- 2.3 502.2.3 Testing
- 2.4 502.2.4 Procedures
- 2.5 502.2.5 Report (Records)
- 2.6 502.2.6 Appendix A
502.1 Construction Inspection for Sec 502
502.1.2 Material (Sec 502.2)
See Material Inspection below.
502.1.3 Equipment (Sec 502.3)
502.1.3.1 Slip-Form Construction (Sec 502.3.2)
Instructions to follow are specifically related to the slip form method.
The track path for slip form pavers is prepared in the same general manner as subgrade for pavement. The track path must be graded, checked, and maintained in a smooth, compacted condition until the pavement is constructed. Any irregularities will be reflected in the finished surface.
When a guide wire (string line) is used, it should be supported and maintained with enough tension to prevent any measurable sag. Immediately ahead of paving, a final check and adjustment should be made to eliminate any irregularities.
When using slip form equipment, uniform distribution of batches is even more important than for formed pavement. Because of physical limitations on the weight of the machine, use of uniformly distributed concrete having proper consistency is extremely critical. Piles of dry concrete will cause the paver to "float" or lift above the true grade. Consolidation of concrete in slip form paving is accomplished by means of vibrators working within the mass of the concrete. Edge slump may be corrected by locating vibrators closer to the edge.
Spreading is normally accomplished by the strike-off blade or auger on the front of the machine. The top surface of the pavement is then shaped and a finish is imparted to the concrete. The inspector should be alert to surface depressions that may occur over dowel assemblies or laps in reinforcement mesh.
The final shape and surface is normally produced by a pan float or plate that is attached to the slip form paver. The specifications require a surface reasonably free of surface voids and tears.
Tongue and groove joints are normally formed in accord with Sec 502.5 of the Standard Specifications. Proper position of keyway and dowels require good construction procedures. Checking of the surface and texturing are basically the same required for formed pavement.
Continuous operation of the slip form paver is necessary for a good riding surface. Each time a slip form paver is required to stop, the machine will tend to settle into the surface of the plastic concrete.
Consolidating and Finishing Equipment (Sec 502.3.2.1) Compacting and finishing by machine is required on all pavement except in specific cases where compacting and finishing by hand methods are authorized by the special provisions or under conditions of the Standard Specifications. Alternate methods, such as using a bridge finish machine, may be used for pavements less than 2000 feet provided all other specifications are met. Equipment for formed pavement will include at least one transverse finishing machine with required vibratory equipment, followed by a transverse float. The work of the transverse finishing machine is the intermediate step in the paving process between placing and spreading of concrete and final mechanical finishing. This machine should consolidate the concrete and leave the surface with a uniform texture to correct elevation and cross section for final finishing.
Normally, a roll of concrete should be carried ahead of the front screed. These rolls of concrete should be continuous across the width being placed. If there is a deficiency at any point in the width of pavement, a low spot will develop at that point. Also, if the head of concrete in front of the screeds varies continually, the surge will vary accordingly and a wavy or rough surface will be left. The work of distribution and finishing must be coordinated to give uniform and acceptable results.
Concrete must be thoroughly vibrated along forms or sides and along expansion and key type longitudinal joints by means of mechanical vibrators. Attachments to the finishing machine and/or spreader may be used to vibrate concrete along forms and longitudinal joints if satisfactory results are obtained. The general area between forms requires vibration by use of machine operated tube type vibrators or pan type vibrators. Vibrating tubes must extend into concrete the distance necessary to provide adequate consolidation. They should be operated only when covered by a complete roll of concrete. Approved pan type vibrators may be used in lieu of tube type. It is essential that the vibrating pan does not come in contact with the top of forms and that it has adjustment for setting the bottom of the vibrating pan near the proposed elevation of the finished pavement surface. Frequency of various vibrators in use should be checked and recorded in the slab inspector's diary. After the transverse machine finishing operations are completed, Standard Specifications require the surface to be smoothed and consolidate by any approved mechanical transverse float which will satisfactorily finish the pavement.
Forms and Keyways (Sec 502.3.2.2) Before forms are set, they should be individually inspected to determine if they meet the requirements of Standard Specification Sec 502.3.2.2. Pin keys should be straight and free moving in the pockets and capable of holding forms tight against pins. Joint locks should not be bent or worn and should be capable of holding ends of the form in true alignment. Twisted, bent or otherwise defective forms should be rejected and their use forbidden until they are repaired, reinspected, and found to be in acceptable condition. Rejected forms should be marked in a manner which prevents their accidental use.
Elevation of the subgrade for forms should be established by the contractor from offset stakes which have been set by the engineer for that purpose. Many contractors now use an electronically guided subgrade cutting device. This machine travels on its own tracks prior to form setting and produces a true subgrade and form line. After the grade for the forms has been cut, the area under the forms should be compacted to the same density as the undisturbed portion of the pavement subgrade.
Forms should be set true to established alignment and grade. Building of pedestals of earth or base material or any other shimming to bring the forms to required grade should not be permitted when the forms serve as tracks for paving equipment, in addition to serving as forms for concrete.
Pins of sufficient strength and length to securely hold forms in place during placing and finishing concrete should be driven in all pin holes and wedges and form locks should be driven tight.
Inspection of forms for curved form lines is basically the same as for straight form lines. Keyways for multiple lane form paving must be held in proper position against the face of the roadway forms. Tie bars or hook dowels must be correctly spaced and securely fastened. Tie bars are normally bent back under the keyway so that forms may be placed. Care should be taken in restraightening these bars to prevent breaking the bars.
Keyways for slip form construction are formed by various methods. It is critical that any tie bars required receive sufficient vibration to assure a satisfactory bond.
502.1.3.2 Vibrators (Sec 502.3.3)
Vibrators should meet the requirements of Sec 502.3.3 of the Standard Specifications. The inspector should check and record the frequency and the type of vibrators being used before beginning work. The frequencies should be rechecked at random occasionally thereafter. The contractor is required by the Standard Specifications to have available at all times a tachometer for use in checking vibrator frequencies.
502.1.3.3 Concrete Saw (Sec 502.3.4)
Sawed contraction joints are used almost exclusively on Missouri projects. Joints may constructed with either a wet or dry cut saw. Joints should be sawed in a progressive manner and as soon as possible without excessive raveling of concrete. Slight raveling is not objectionable and is actually a good indication that sawing is being done at the proper time. Pavement placed in the morning should generally be sawed the same day, possibly 6 to 8 hours after placing. Sawing should be continued until all joints are cut. Spot checks of depth and width of sawed joints should be made at periodic intervals during the sawing operation to document compliance with specifications. Information obtained should be recorded and made part of the permanent project record. Whenever a crack occurs ahead of a saw cut, sawing at that joint should be immediately stopped and the saw should be moved ahead several joints. There, cut a joint, or even several joints, then return and cut intervening joints. Whenever cracks occur, sawing is not being done soon enough. Sawing operations should be immediately modified so that such cracking does not recur. Standard Specifications do not require it, but it is desirable that the sawed joints be flushed or blown out immediately after sawing to prevent sawdust from setting in the joint.
502.1.3.4 Equipment for Sealing Joints (Sec 502.3.5)
All joints should be sealed as specified as soon as concrete is sufficiently dry to permit a bond between the sealing compound and concrete. Sealing should be completed before the pavement is opened to traffic, including construction traffic. Material and equipment for sealing joints should be carefully checked by the inspector for conformance with requirements of the specifications. The principal point to watch in heating of joint material is to assure that adequate circulation of material is provided and temperatures are not excessive so that material will not be overheated either in its entirety or in spots. Sealing material must be installed in a way that will fill the joint opening completely and uniformly. Sealing material should be approximately one-half inch below the pavement surface after it has settled into its final position. The height to which the joint is filled will vary according to the temperature, and resultant expansion, of the pavement. When pavement is cool and has contracted, the joint seal should be left below the pavement surface a sufficient amount so as to avoid its extrusion above the pavement surface as the joint closes with expansion. Overfilling joints is as undesirable as underfilling them.
502.1.3.5 Field Laboratory (Sec 502.3.7)
The field laboratory, when provided in accordance with the specifications, should be equipped with the following:
- Set of Scales sensitive to 0.1 gram, for moisture determinations.
- Gas stove, for drying samples.
- Small pans, for drying and weighing samples.
- Friction top cans, for protecting samples prior to weighing.
- Thermometer, for taking temperature of materials during heating season.
- Maximum-minimum thermometer, for recording of air temperatures.
- Shovel, hand scoop, quartering cloths.
In addition to the above equipment, it is desirable to have a set of sieves for the purpose of checking aggregate stockpiles when segregation or degradation is suspected and, if the plant is to produce light weight concrete, equipment for the determination of entrained air by AASHTO T 152 and weight per cubic foot by AASHTO T 121.
502.1.4 Construction Requirements (Sec 502.4)
502.1.4.1 Weather Limitations (Sec 502.4.1)
Concrete placed during cold weather must be produced, delivered and finished in compliance with Sec 502.4 and 703.3.10 of the Standard Specifications and in a manner to provide for a minimum loss of heat. The plant inspector has an additional responsibility in this case to determine temperatures of aggregates and mix and to assure that methods being used for the heating of materials will not produce detrimental effects by overheating part of the mixture. The inspector must also take care to see that no frozen material is introduced into the mix.
All concrete shall be effectively protected from freezing (Sec 502.4.1) until a minimum compressive strength of 3500 pounds per square inch (psi) has been attained.
The purpose of the specification is to ensure that the concrete does not freeze until it achieves a compressive strength of 3500psi. MoDOT does not want to tell the contractor how to protect the concrete from freezing. When the weather forecast predicts air temperatures below 32 deg F, it will be the contractor’s responsibility to decide how to protect the concrete from freezing. In some instances, the contractor may elect not to protect the concrete from freezing. Regardless of the contractor’s decision, the contractor is required to provide a way of monitoring the concrete, which demonstrates that the concrete has not frozen.
A maturity meter or other internal temperature measuring devices are excellent tools for monitoring the temperature of the concrete. If it is determined that concrete has frozen, the material will be deemed unacceptable. If the contractor uses a sensor to monitor internal temperature, it shall be located within a half inch of the top of the slab.
The following are suggested guidelines that can be used to protect PCC Pavement after placement when temperatures may drop below freezing for relatively short periods of time:
- 27 degrees F to 32 degrees F - 1 layer of burlap
- 24 degrees F to 27 degrees F - 2 layers of burlap
- Below 24 degrees F - Straw or equal
Regardless of precautions taken the contractor shall assume all risks, and all frozen concrete shall be replaced at the contractor's expense.
502.1.4.2 Protection Against Rain (Sec 502.4.2)
Edges and surfaces of pavement should be protected against any damage until it is accepted by the Department. Any damaged pavement must be repaired or replaced by the contractor at the contractor's expense before acceptance.
502.1.4.3 Setting Forms (Sec 502.4.3)
See Forms and Keyways.
Condition of Subgrade (Sec 502.4.4) Pavement subgrade should be brought to true shape in accordance with [Sec 502.4.4] of the Standard Specifications. After subgrade has been cut to the proper elevation, it should be recompacted. Prior to placing concrete, the subgrade should be checked for conformance to the plan typical section. The inspector must observe and record in a field book station limits which have been checked. Before placing concrete, subgrade should be thoroughly moistened to avoid absorption of water from the concrete.
502.1.4.4 Placing Concrete (Sec 502.4.6)
The contractor is responsible for construction of structurally sound pavement with desired riding qualities. Necessary checks and tests on this phase of the operation must be performed to determine that it meets contract requirements. To do this, the inspector must have a thorough knowledge of plans and specifications, recognize good construction practices, have a working knowledge of equipment used, be able to issue clearcut decisions to the contractor's representative, and be fully aware of all required tests and reports and their significance. Contractor will be allowed to place concrete directly on the subgrade or prepared base, provided there is no damage or distortion to the underlying material.
502.1.4.5 Tie Bar Placement (Sec 502.4.7)
Tie bars installed across the center line should be parallel to the surface and at right angles to center line. Unless an approved mechanical device operating immediately behind the spreader, or behind the strike-off on slip form paving, is used for the installation, they must be installed before placing the concrete and must be held securely in position.
502.1.4.6 Final Strike-off, Consolidation and Finishing (Sec 502.4.8)
Added Finishing Water (Sec 502.4.8.2) The addition of water to facilitate finishing should be discouraged. If it is necessary to add water, it must be in the form of a fog spray. When conditions require the addition of moisture by use of a fog spray, the inspector should refer to Sec 502.4.8.2 of the Standard Specifications for a guide as to further action to be taken.
Surface Texture (Sec 502.4.8.3) A uniform roughened finish shall be applied to the surface to obtain desired friction characteristics. The final surface texture shall be tested in accordance with ASTM E 965 (The Hockey Puck Test).
(Sec 502.4.8.3.4) ASTM E 965 will be waived if tining or diamond grinding is used as the final surface texture. Tining, either transverse or longitudinal, shall be applied when most of the water sheen has disappeared but before concrete becomes nonplastic.
502.1.5 Joints (Sec 502.5)
When dowel supporting assemblies are required for transverse joints, they must be laid out and marked so that the exact center line of the assembly can be reestablished. It is critical that dowels be aligned as nearly as possible to be parallel to the pavement conterline and to the pavement surface. Excessive lubrication is to be avoided. Generally, the assemblies are held in correct position by the use of metal stakes or pins that are left in the pavement. Small wires used for holding dowel supporting assemblies together during fabrication and shipment should be cut after installation. Dowels should be coated as provided by Standard Drawing 502.10 and Section 1057.3 of the Standard Specifications. Dowel Bar Inserters (DBI) may be used upon approval by the engineer.
502.1.5.1 Expansion Joints (Sec 502.5.1)
Expansion joints should be placed as shown on the plans and as required by Section 502.5.1 of the Standard Specifications.
502.1.6 Curing (Sec 502.6)
Any of the approved methods of curing outlined in Sec 502.6 of the Standard Specifications will give satisfactory results if correctly applied. Regardless of the method used, curing material should be applied uniformly and at specified rate as soon as it can be placed without marring the surface. This normally is about the time the water sheen disappears from the concrete surface. During windy, hot, dry weather, it is important that the finishing be completed rapidly and curing material placed before the surface dries out to the extent that shrinkage cracks develop. If curing is unavoidably delayed, the surface must be covered with wet burlap or a fog spray must be applied to the surface. Amount of curing agent being used should be checked at regular intervals during the day to determine if the required amount is applied. This information should also be recorded in a field book and made part of the project records. The inspector should be familiar with Sec 502.6 in order that this important phase of the paving operation may be carried out in conformance with the intent of the Standard Specifications.
502.1.7 Removing Forms (Sec 502.7)
Good judgment is necessary in determining proper time for removal of side forms. Weather conditions and temperature will control to a considerable extent the time that must elapse between placing of concrete and removal of forms. In all cases the concrete should be sufficiently hard that spalling will not occur along the pavement edge when forms are pulled, and surface will not be marred by devices used to pull form pins. Care must also be used in loosening pin keys and form locks to avoid excessive force on sides of the pavement. Immediately after removal of forms, any honeycomb noted should be patched, and an approved curing agent should be applied to sides of the pavement. Sides may be backfilled with earth in lieu of applying a curing agent.
502.1.8 Surface Test (Sec 502.8)
Surface of the pavement should be thoroughly tested by profilographing or straightedging as required by the specifications, as soon as practicable following placing of the pavement. If straightedging is required, each lane of pavement should receive one pass of the straightedge with paths being located near the center of the lane. The procedures for testing with the profilograph are set forth in the Test Method MoDOT TM 59. The results obtained from these profilographs shall be submitted on the Profilograph Pavement Smoothness form with distribution as indicated on the form. A summary of the profilograph smoothness results for all projects completed within the year is also required and should be submitted by February 1st of the following year.
502.1.8.1 Profilographing (Sec 502.8.2)
502.1.8.2 Calibration (Sec 502.8.4)
All machines are calibrated annually at the airport runway located at Linn State. There are usually 2 dates set up in the Spring to accomplish this task. Machines can also be calibrated by appointment by contacting the Division of Construction and Materials.
Comparison (Sec 502.8.4.3) If the results do not compare and there is a suspicion that there is something wrong with one of the profilograph machines, contact the Division of Construction and Materials to get the machine or machines recalibrated.
Settings (Sec 502.8.4.5) A Certificate of Calibration will be issued for each machine that is calibrated. Attached to this certificate is the settings that shall be used when profilographing a MoDOT project. Changes to these settings will void the calibration.
Profilogram Quality Acceptance (Sec 502.8.5.3) Typically the project office should profilograph 10 % of a project.
Profilograph Path (Sec 502.8.5.10) The path of the profilograph shall be near the center of each traffic lane. For example, a 24 ft. wide pavement would have 2 traces located 6 ft. on each side of the center line.
Segment Definition (Sec 502.8.5.11) A segment is typically 0.1 mile. If the last segment in a section is greater than 250 ft. it shall be considered a separate segment. If the last segment is 250 ft. or less, it shall be added to the previous segment.
502.1.9 Opening to Traffic (Sec 502.9)
The compressive strength may be determined by compressive cylinders or the maturity method.
502.1.10 Material Acceptance (Sec 502.10)
The material acceptance will be evaluated on a lot by lot basis on the compressive strength and thickness. For a favorable comparison, Quality Control (QC) and Quality Acceptance (QA) test results should be within two standard deviations.
502.1.10.1 Coring (Sec 502.10.3)
The contractor should take care when extracting cores. The following are some hints to accomplish this:
- Utilize sharp drill bit
- Ensure drill is perpendicular to surface
- Ensure drill is held steady
- Drill until base is reached
- Use plenty of water
Cores should be handled with care. Do not throw or drop cores. Secure cores while in transit to avoid tumbling. If any core has been damaged, contractor shall contact engineer and a new random sample core shall be obtained.
(Sec 502.10.3.1) Thickness Measurement Hints:
- Remove underlying material with chisel
- Place specimen upside down in device
- Check calibration of device
- Take 9 readings
- 1 reading at center
- 8 readings along circumference
- Read to the nearest 0.1 in.
Compressive Strength Testing Hints:
- Calibrate testing machine every 18 months (recommended every 12 months)
- Make sure core is centered
- Make sure core is perpendicular
- Use correct loading rate (20 – 50 psi/sec.)
- Apply load till failure
- Cap cores in accordance with AASHTO T-231
- Placing 14-inches of PCCP
- Is Lot 2, sublot D, an outlier?
Lot 2 Test Results A 5550 B 5500 C 5250 D 4290
Determine the average for the compressive strengths in question.
Second, determine the standard deviation for the compressive strengths in question.
Third, determine the T-statistic for the compressive strength in question.
Fourth, review Table 1 in ASTM E 178 to determine if value in question is an outlier.
- n = 4
- Significance Level = 5%
- T-statistic = 1.462
- Value to the right so NOT an outlier
If sample is identified as an outlier, a new core shall be taken at the same offset within approximately 2 feet of the original sample core. It shall be retested accordingly. A spreadsheet is available to determine outliers and is located at V:\Materials Forms.
502.1.11 Contractor Quality Control (Sec 502.11)
Gradation and Deleterious Material (Sec 502.11.2.1.1)
- Aggregate Sampling Hints:
- Bin Discharge
- Ensure sampling device cuts entire stream of material
- Do not over fill the sample device
- Ensure sampling device is cleaned out
- Plant operating at usual production rates
- Obtain 3 or more equal increments
- Use AASHTO T-2
- Sample template fits the belt
- Sweep all the fines from the belt
- Obtain 3 or more increments
- Ensure that the contractor is aware that a belt sample is being obtained
- Ensure that template is pushed all the all the way to the belt
- AASHTO T-2
- After Sampling Aggregate
- Ensure that the proper sample size was obtained
- Field Inspection Guide, Field Section 1001.3.1.5
- Remix material during splitting process
- MoDOT Test Method T-66
- Use AASHTO T-248 splitting procedure
- Aggregate Testing Hints
- Ensure sieves not damaged
- Ensure nesting sieve is used
- Do not over load the sieves
- Ensure sieves are cleaned
- Ensure proper test sample size used
- Field Inspection Guide, Field Section 1001.5.1.2
- Make sure balance is calibrated and level
- Deleterious Testing Hints
- Ensure proper testing size
- For Coarse Aggregate
- Field Inspection Guide, Field Section 1001.5.5.3
- For Fine Aggregate Field Inspection Guide, Field Section 1001.5.7.2
- Ensure balance is calibrated and level
- Do not soak in water
- Ensure proper lighting
Moisture Content (Sec 502.11.2.1.2)
- Moisture Content Testing Hints
- Ensure balance is calibrated and level
- Use correct sample size
- Prevent loss of material when stirring
- Do not over heat sample
- Use glass plate to check for moisture
- Use air-tight container to prevent moisture loss prior to testing
Slump (Sec 502.11.2.2)
- Slump Testing Hints
- Perform test within 2 1/2 minutes
- Fill mold in 3 equal volumes
- Do not use rebar as tamper rod
- Perform on level ground
- Pre-wet equipment before testing
- Lift mold straight up
- Rod concrete properly
Entrained Air Content (Sec 502.11.2.3)
- Air Content Testing Hints
- Rod concrete properly
- Fill mold in 3 equal layers
- Perform on level ground
- Do not use rebar as tamping rod
- Use aggregate correction factor
- Tap sides of bowl after each layer
- Pre-wet equipment before testing
- Use calibrated equipment
502.1.12 (Sec 502.15)
502.1.12.1 Pay Factors (Sec 502.15.7)
- Placing 14-inches of PCCP
- What is the total pay factor for Lot No. 1?
Lot 1 Test Results Sublot Compressive Strength lb/in.2 Thickness in. A 4020 14.3 B 4850 13.7 C 6310 14.6 D 4940 14.1
First, determine the average for each pay factor item.
Second, determine the standard deviation for each pay factor item.
- 1)Standard Deviation of Compressive Strength.
- 2)Standard Deviation of Thickness.
Third, determine the lower quality index, QL for each pay factor item.
- L-Compressive Strength
- Remember there is no upper limit
Fourth, determine the lower percent within limit, for each pay factor item.
- Select from Table III in Sec 502.
- Remember that in all cases.
Fifth, determine the total percent within limit, for each pay factor item.
Sixth, determine the pay factor, , for each pay factor item.
- Both above 70 so use the following equation:
Seventh, determine the total pay factor, , for the Lot.
502.2 Material Inspection
To establish procedures for submitting concrete cores to the Central Laboratory, establish procedures for reviewing and approving concrete quality control plans, reporting pavement thickness and compressive strength, and preparing a summary sheet for Portland cement concrete pavement and base.
The following material is needed for shipping cores:
- (a) Plastic bag (minimum 12” x 21”)
- (b) Felt-tip marker
- (c) Strapping Tape
- (d) Cardboard Box (concrete cylinder box 14” x 14” x 7”)
Pavement thickness and compressive strength are to be determined from cores extracted from the pavement. The same core will be used to determine the pavement thickness and the compressive strength. Pavement thickness is determined by measuring the core in accordance with AASHTO T 148. After determining the pavement thickness, the core is sawed to a length/diameter (l/d) ratio of 2.0 and capped in accordance with AASHTO T 231. After 28 days, the compressive strength of the core will be tested in accordance with AASHTO T 22. Quality Assurance cores may be tested either by the Quality Assurance Inspector, using district equipment, or by the Central Laboratory. Quality Assurance cores will not to be tested using Quality Control testing equipment. Quality Control cores shall not be tested using Quality Assurance testing equipment.
502.2.4.1 Sampling Cores
Cores shall not be taken until the concrete has attained a compressive strength of 3,000 psi. The location of Quality Control and Quality Assurance cores shall be determined using random sampling procedures in accordance with ASTM D 3665. The engineer will be responsible for determining the sample locations. In no case should the contractor be permitted to determine random sample locations of Quality Control cores. All cores shall be sampled in accordance with AASHTO T 24. Quality Assurance cores will be extracted by the contractor and provided to the Quality Assurance Inspector for evaluation. The district will need to establish procedures for maintaining the chain of custody of extracted cores.
502.2.4.2 Handling Cores
After the core is removed from the hole, wipe off the surface water and allow the remaining surface moisture to evaporate. When the surface appears to be dried, write the following information on the side of the core:
- (a) Job No.
- (b) Route
- (c) County
- (d) Lot
- (e) Sublot
502.2.4.2.1 Place the core into a separate plastic bag and seal the bag to prevent moisture lose. This should be performed within one hour after the core is drilled.
502.2.4.2.2 If a Quality Control or Quality Assurance core is dropped, exposed to freezing temperatures, or otherwise mishandled in some fashion the Resident Engineer should be contacted immediately. A replacement core should be taken at a new random sample location as soon as possible if it is believed the core no longer represents the in-place concrete. Studies have shown the compressive strength can be reduced when a specimen is dropped.
502.2.4.2.3 Cores should be kept in an environment that has a temperature range of 60 to 80 ° F. Cores should be protected from direct sunlight.
502.2.4.3 Shipping Cores
The plastic bag, containing the core, should be packed carefully into the cylinder box to prevent the cores from being damaged during shipment. A cylinder box will hold two 6-inch diameter cores or three 4-inch diameter cores. Do not over pack the cylinder box to avoid potentially damaging the cores or damaging the plastic bags. Packing material should be used to stabilize the cores to prevent them from moving around during shipping. Cores over 14 inches may require the use of a large cardboard box to prevent them from being damaged during shipping. The following information should placed on the side of the cylinder box:
- (a) Sample Identification Number
- (b) Date of Pour
- (c) Lot
- (d) Sublot
- (e) Special Instruction
502.2.4.3.1 Cores need be shipped to the Central Laboratory as soon as possible after drilling. According to AASHTO T 24, specimens need to be sawed no later than two days after extracting the cores from the pavement. The district will need to work closely with the contractor on when Quality Assurance cores will be taken. This will aid the district in arranging for the shipment of the cores. Cores will need to arrive at the Central Laboratory in a timely manner so the cores can be sawed within the allotted time.
502.2.4.3.2 Be advised that cores are to be kept in the plastic bags for at least five days after last being exposed to moisture before compressive strength testing. The purpose of the 5-day waiting period is to reduce the moisture gradient introduced when the core was drilled or wetted during sawing.
502.2.4.4 Filling Core Holes
The contractor is responsible for filling core holes after extracting the cores. The contractor shall use an approved non-shrinkage grout to fill the holes. The contractor is to fill the holes within 1 day of sampling the cores.
502.2.4.4.1 Before placing the mixture, all free water shall be removed from the bottom of the core hole. A sponge may be used for this purpose. If the hole is difficult to dry, cement may be sprinkled in the bottom. The hole shall be filled in two layers with each layer thoroughly rodded. The top layer shall be troweled to a slightly high, smooth surface.
502.2.4.4.2 Additives may be used to accelerate setting time where traffic may damage patches. Approval for additives is to be obtained from the State Construction and Materials Engineer.
502.2.4.5 Concrete Quality Control Plan
The contractor shall develop a concrete quality control plan. The concrete quality control plan shall be submitted to District Materials for review and approval. During the review process, District Materials should work closely with the Resident Engineer.
502.4.5.1 The concrete quality control plan shall include the following information:
- (a) The contractors representative in charge of QC and the project level representative if
different from the contractor representative. Contact information should be recorded for these individual.
- (b) Identify the number of sublots each lot will utilize and describe how lots and sublots will be designated.
- (c) State the method for determining when concrete cores can be extracted
- (d) State the method for demonstrating the concrete has been protected from freezing.
- (e) State the location where control charts will be posted.
- (f) For optimized concrete mix, state the target gradation and allowable gradation ranges for
each fraction being used.
- (g) A proposed independent third party name, contact, address and phone number for dispute resolution. The format concrete quality control plans should follow is shown in Appendix A.
502.2.4.5.2 During the review process, District Materials should consult with the Resident Engineer to ensure the engineer agrees with the proposed method of demonstrating that concrete has been protected from freezing and where control charts are to be posted.
502.2.4.5.3 Concrete mix designs shall not be approved until the concrete quality control plan has approved. The concrete quality control plan shall be approved prior to placing any concrete on the project.
502.2.4.5.4 A copy of the approved concrete quality control plan shall be sent to the Construction and Materials Field Office.
502.2.4.6 2AA Summary Sheet for Concrete Paving
The Resident Engineer is responsible for assuring that the 2AA work sheet is properly prepared in accordance with Sec 501.19 of the Construction Manual. Upon completion of the 2AA sheet, it will be submitted to the Operations Engineer who will be responsible for the accuracy of entries regarding materials proportions, design and other information with which the Resident Engineer is familiar. After approval, the 2AA sheet shall be submitted to the State Construction and Materials Engineer, for processing. Prints will be made for distribution and insertion in the final plans.
502.2.5 Report (Records)
Test results shall be reported through SiteManager in accordance with Automation Section AS-3510. Template No. SAA551AA shall be used for reporting pavement thickness and compressive strength.
502.2.6 Appendix A
|QC contact person||Phone Number|
|On-site QC contact Person(s)||Phone Number(s)|
This section shall identify the number of sub-lots being utilized in a lot; 4, 5 or 6. It shall also describe how lots and sub-lots are to be designated.
Compressive Strength Determination
State the test method that will be used to determine when concrete cores can be extracted from the pavement; Maturity Method or Cylinders.
Cold Weather Concrete
State the method being used to demonstrate the concrete has been protected from freezing.
State the location where control charts will be posted.
Aggregate Gradations (optimized mixes only)
State the target gradation and allowable gradation range for each fraction being used in the concrete mix.
Third Party Resolution
This section shall list the independent third party name, address, contact name and phone number.