ACI 363.2R-98 Guide to Quality Control and Testing of High-Strength Concrete.
2.1—Introduction Quality control and testing of high-strength concrete are more critical than is the case for normal-strength concrete, because seemingly minor deviations from specified require- ments can result in major deficiencies in quality or test re- sults. For example, it is well documented (Carino et al. 1994) that compressive-strength test results are more sensitive to testing conditions as the strength of the concrete increases. The quality of high-strength concrete is controlled by the quality and uniformity of the ingredients, and by the mix- ing, placing, and curing conditions. A high level of quality control is essential for those involved in the production, testing, transportation, placing, and curing of the concrete. Careful consideration of placing restrictions, workability, difficulties during transportation, field curing require- ments, and the inspection and testing process is required. Thorough planning and teamwork by the inspector, con- tractor, Architect/Engineer, producer, and owner are essen- tial for the successful use of high-strength concrete. This chapter reviews critical activities prior to the start of construction. A preconstruction meeting is essential to clari- fy the roles of the members of the construction team and re- view the planned quality control and testing program. Special attention is required during the trial-batch phase to assure that selected mixtures will perform as required under field conditions. Planning for inspection and testing of high- strength concrete involves giving attention to personnel re- quirements, equipment needs, test methods, and the prepara- tion and handling of test specimens.
2.2—Preconstruction meeting Small variations in mixture proportions and deviations from standard testing practices can have greater adverse ef- fects on the actual or measured strength of high-strength concrete than with normal-strength concrete. Therefore, project participants should meet before construction to clar- ify contract requirements, discuss planned placing condi- tions and procedures, and review the planned inspection and testing programs of the various parties. The effects on the concrete of time, temperature, placing, consolidation, and curing should be reviewed. Acceptance criteria for standard- cured test specimens, in-place tests, and core test results should be established. The capabilities and qualifications of the contractor’s work force, the inspection staff, and the test- ing and batching facilities also should be reviewed.
Trial batches—The complexity of the prequalification pro- cess depends on local experience. Where the specified strength has been widely produced for previous projects, a review of available test data may adequately measure performance. When a strength higher than previously supplied is specified, or where there is limited experience in the supply of that strength concrete, a more detailed prequalification procedure should be carried out. This should generally include the pro- duction of a trial batch of the proposed mixture proportions. The trial concrete should be cast into monoliths representative of typical structural sizes on the project. Fresh concrete should be tested for slump, air content, and temperature. Hardened concrete should be tested to determine compressive strength and modulus of elasticity based on standard-cured cylinders and on cores drilled from the monolith. Strengths of cores and standard-cured cylinders tested at the same age should be cor- related. In massive elements, core strength may vary with dis- tance from the surface due to different temperature histories. Therefore, relationships should be established for a specific core depth. If cores need to be removed during construction, the correlation allows interpretation of core strength results. The monolith also should be instrumented to determine the maximum internal temperature and the temperature gradients developed throughout the cross section.ACI 363.2R pdf download.