![]() ![]() Allowable variations in cement content and compaction requirements are major contributors to differences between design and actual strength. When making the decision, consider that, because of production variables, a significant difference can exist between the strength indicated by a cylinder and the actual strength of the finished product. Based on test results, decide whether the percentage of cement specified in the special provisions will produce the design strength in the finished product.However, a test should always be made at 5 percent for aggregate qualification. For suppliers whose past performance has been reliably verified, consider using such information in lieu of testing.For aggregates of borderline quality, consider making additional initial strength tests at varying gradations within specifications, using 5 percent cement. Request strength tests at 5 percent cement and other percentages above and below 5 percent, usually in 0.5 percent increments, to determine the correct cement content. Advise the contractor that any significant material change, including variations in gradation, requires new tests for quality characteristics. The fine aggregate usually has the most variable effect on strength. Compressive strengths of CTB can vary significantly because of variations in aggregate gradation and the type of cement used. For initial testing, obtain representative samples from the contractor’s source of CTB aggregate and test for the required quality characteristics.If mutually agreed with the contractor, hold a preconstruction meeting with the contractor and the district materials unit before construction to discuss the quality control plan and contractor’s method for performing each element of work affecting material quality, including acceptance testing priorities, shipping of samples, lines of communication for test results, timeframes for reporting quality control and acceptance test results, and any contractual testing dispute resolution processes.Obtain the contractor’s quality control plan, which details the methods the contractor will use to assure quality of work and conformance with the requirements of Standard Specifications.Include the following steps in the preliminary review and inspections: The special provisions will specify the percentage of cement to be added to the CTB. The bid item list and plans will specify the class and mix method. However, plant-mixed is most common.Īlthough the spread method may be specified in the special provisions, CTB may be spread by one of three allowable methods: Type 1, Type 2, or Type 3. CTB specified as either Class A or Class B is generally used with asphalt pavements and can be either plant-mixed or road-mixed. Section 27, “Cement Treated Bases,” of the Standard Specifications provides requirements for placing CTB-a mix of aggregate, portland cement, and water. This section provides guidelines for inspecting cement treated base (CTB). Section 27 Cement Treated Bases 4-2701 General 4-2703C Depositing and Spreading Cement Treated Base.4-2703B Plant-Mixed Cement Treated Base. ![]()
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