Category:1033 Precast Drainage Units

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MGS Information
Current General Services Specifications (MGS) By Subject

This article establishes procedures for inspecting, acceptance and reporting of precast reinforced concrete manhole and drop inlet sections and appurtenances such as grade rings, tops and special sections. Refer to Sec 1033 for MoDOT’s specifications.

For Laboratory testing and sample reporting procedures, refer to EPG 1033.4 Laboratory Testing Guidelines for Sec 1033.

Acceptance of precast drainage units may be on the basis of an approved, industry recognized QC program, inspection by MoDOT, or a combination of the two methods, at the discretion of the district. Approval of QC programs is the responsibility of Central Office. Currently the QC programs of the American Concrete Pipe Association (ACPA) and National Precast Concrete Association (NPCA) are approved. Prior to allowing production under a QC program, the district must confirm that the producer's certification is current and that it covers the material being produced. The district must initially, and on a recurring basis, confirm that the producer routinely and diligently follows the requirements of the QC program, and that material produced for MoDOT is specification compliant. This confirmation will be in the form of a quality assurance visit, including a review of all applicable paperwork, a review of the producer’s QC process, and an active inspection of current production (a SiteManager plant inspection record is required - 1033XXQCP). When a producer is allowed by the district to produce under a QC program, the producer must agree to notify the district in advance of their intended production schedule. Acceptance of precast drainage units with MoDOT inspection is to be based on the inspection of materials being incorporated into the sections, the amount and placement of reinforcement, and inspection of the finished section.

If Class B or B-1 concrete is used, compressive tests and absorption test specimens will not be required. If a commercial concrete is used, both compressive tests and absorption tests will be needed.


1033.1 Apparatus

(a) Rule with suitable graduations to accurately measure the material to be inspected.

(b) OK - MoDOTstamp.

(c) Weather-resistant marking materials.

(d) Applicable AASHTO specifications.

1033.2 Procedure

1033.2.1 Product Types

Drop Inlets and Manholes. All concrete units produced under Sec 1033 should be covered by producer quality management as outlined in Sec 1001 and EPG 1001.2 Producer Quality Management.

If needed, compressive tests may be made on either standard rodded concrete cylinders or cylinders compacted and cured in a similar manner to the sections under consideration for acceptance, or, at the option of the manufacturer, on cores drilled from the wall of the sections in accordance with AASHTO M 199. Cylinders or cores are to be tested in accordance with AASHTO M 199.

Hardware and Grates. All miscellaneous components needed to complete the drop inlet and manhole facilities such as grates and steps should be inspected as necessary for conformance with the plans and specifications.

If needed, absorption tests shall be made on a core cut from the full wall thickness.

1033.2.2 Materials

1033.2.2.1 Concrete

When Class B or B-1 concrete is used; materials, proportioning, mixing, slump and transportation of portland cement concrete shall be in accordance with Sec 501.

No matter what type of concrete is used the minimum proportion of cement needed will be in accordance with AASHTO M 199. Air entrainment will not be required.

Occasional individual cylinders or cores may fall below the design strength for some unknown reason. The allowances for deficient strengths are described under AASHTO M 199. Compressive tests are to be performed at the fabricating plant unless questionable results are being obtained, in which case the cylinders or cores may be submitted to MoDOT’s Central Laboratory.

1033.2.2.2 Reinforcing Steel

All reinforcing steel used for precast drainage units shall be in accordance with the PAL process.

1033.2.3 Quality Control

When operating under a producer quality management plan, the plant should have a competent QC process. Any non-conforming product should be handled as described in Sec 1001 and EPG 1001.2 Producer Quality Management.

The sections are to be inspected by the producer for amount and placement of reinforcing steel. The amount and placement of reinforcing steel in rectangular drop inlets is to be as shown in the plans and shop drawings. Reinforcing steel for all other sections is to be as specified in Sec 1033.

Common deviations that can be repaired or corrected by QC as deviant work may include but not limited to the following:

  • Honey combing
  • Poor surface texture
  • Minor spall repair not penetrating to the rebar
  • Missing block outs that requiring coring but not cutting rebar
  • Missing lifting loops.

The finished sections are to be examined for conformance to dimensions, workmanship, and marking. Permissible variations in dimensions and rejection criteria for workmanship are specified in Sec 1033. Prior to shipment a MoDOT ID number shall be obtained from the district to satisfy the shipping hold point. Each acceptable section shall be marked by indenting into the concrete or painting on with waterproof paint the following:

(a) Date of manufacture.
(b) Name or trademark of the manufacturer.
(c) Industry quality program indicator (stamp). Sections rejected by the manufacturer may be marked or handled in accordance with the producer quality management program but the rejection must be clearly indicated.
(d) If the section is found to be unacceptable during an audit, the Sample ID number, provided by the district, must be obliterated.

Hold points for precast drainage units should include a shipping hold point and a hold point for any repaired non-conforming units.

1033.2.4 MoDOT Quality Assurance and Audit

District construction and materials staff should perform MoDOT Quality Assurance testing on a quarterly basis and audits at least once a year for plants that are producing product routinely for MoDOT. An audit may also be initiated to address specific concerns. MoDOT Quality Assurance testing is recommended at the below frequency.

Tested Property1Test Method MoDOT Quality Assurance
Air T152 Quarterly
Slump T119 Quarterly
Coarse Aggregate Deleterious TM 71 Quarterly
Coarse Aggregate Absorption T85 Quarterly
Compressive strength T22 Quarterly
Absorption (per mix) T280 Once a year
1 All samples shall be taken at the precast plant

Individual sections that are inspected during the MoDOT audit may be marked with "OK-MoDOT" by the inspector. Rejected sections are to be marked with a single vertical mark, near the manufacturers marking and shall be made with weather resistant marking material.

An inspector should visually check PAL materials and verify paperwork when possible as part of the audit.

During an audit or when performing MoDOT Quality Assurance testing, inspection of the concrete mixture components should be performed as necessary. Sampling, testing, and reporting of the components should follow the appropriate specifications and practices.

1033.2.5 Handling Storage, Shipping

Drop inlets and manholes should be treated with care during handling. Often the shapes are large or otherwise difficult to handle without damaging. Addition of temporary reinforcing is allowed to aid in handling and is common among pieces with large blockouts. 1033.3 Special Designs and Shop Drawings. Procedures for submitting special or modified designs are described in Sec 1033.4.2. Additional information related to special designs may be found in EPG 106.16 Special Designs. Special and modified design units may require additional inspection including QC, QA or MoDOT auditing.

1033.3 Reporting

Units inspected and accepted by a quality management program must be reported to the district prior to shipment. Shipment information will be recorded in SiteManager by the district. The district will provide the producer with the Sample ID number(s) for the product. A single Sample ID may represent multiple sections, and that information should be indicated in the Sample Record.

Finished sections shall be reported through SiteManager. The following information is to be included on the appropriate template, in addition to that normally required for a sample record:

(a) Quantity, size and length, that is: 8 each, 2 ft. x 3 ft. to 6.0 ft. long (8 each, 600 mm x 900 mm to 1800 mm long).
(b) Date of production.
(c) Description (as to type of inlet, etc.).
(d) ID No. or reference number, if needed.

Specific test templates exist in SiteManager for Manholes, Drop Inlets and Type S Headwalls. These templates may be used in place of the free form test and do not require all the above information. The above information may be entered, but is considered optional since lumping of similar sections is allowed.

During an MoDOT audit, all components and materials reviewed should be covered by individual sample records separate from the shipping sample records.

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