Technical Questions

ACI Committees, Membership, and Staff have answered common questions on a variety of concrete related topics.




Question: Size of test cylinder

Question: Curing Cylinders for Acceptance Testing

Question: Why are many non-destructive tests used as “estimators” of concrete strength?

Question: Alternative methods for measuring crack width

Question: Improving the abrasion resistance of concrete

Question: Maximum temperature limits for hot-weather concreting

Question: Estimating in-place concrete strength

Question: Low-strength cylinder test results

Question: How should samples of freshly mixed concrete be taken in the field to provide information on concrete in the structure?

Question: The effect of maximum size of aggregate on concrete strength

Question: Resistance to cycles of freezing and thawing

Question: What test conditions affect the results of compressive strength tests of concrete?

Question: The effect of air content on concrete strength

Question: The effect of changes in proportions of the fine and coarse aggregate or the quantity of cementitious material on the strength

Question: How is the air content of freshly mixed concrete determined?

Question: Strength of concrete

Question: Mixture design and strength submittals

Question: Air tests for nonair-entrained concrete

Question: How are properties of concrete in the structure measured?

Question: What are rebound, penetration resistance, pullout, and break-off tests?

Question: How is the shrinkage of concrete determined?

Question: ACI code for evaluating existing buildings prior to repair

Question: Definition of portland cement

Question: How is the temperature of concrete measured?

Question: Using cube tests in lieu of cylinder tests

Question: Factors governing the strength of concrete

Question: How can durable aggregates be ensured?

Question: Why is the workability of concrete important?

Question: How is workability measured and specified?

Question: How is the required strength selected, measured, and obtained?

Question: Consistency, plastic consistency, and workability

Question: Measurement of setting time

Question: What test is available to evaluate the behavior of no-slump concrete as it is vibrated?

Question: Is the cutting of cores or other shaped specimens directly from a completed structure ever used for determining the strength of the concrete?

Question: Using core strength to calculate compressive strength of an existing structure

Question: Important requirements of a concrete aggregate

Question: How can it be determined that an admixture will serve its intended purpose?

Question: What methods of capping are recommended for compression specimens?

Question: Definition of setting time

Question: Are there any tests that may be made directly on the structure to determine if the concrete has developed adequate strength without risk of overloading or causing damage to the structure?

Question: Is the slump test of value as a measure of consistency or workability?

Question: How is the abrasion resistance of concrete determined?

Question: Rebound hammer and in-place strength testing

Question: Standards for 7-day and 28-day strength test results

Question: How is the permeability of concrete determined?

Question: What procedure should be followed for standard curing of specimens for strength tests?

Question: The cause of false set

Question: When is the slump test useful in detecting changes in the concrete?

Question: What tests are necessary or desirable in making a series of trial mixtures to arrive at a suitable mixture for a particular job?

Question: Why is the slump test not an absolute measure of consistency or workability?

Question: Is density a good indicator of air content?

Question: Precautions against sulfate attack

Question: How is the air content of hardened concrete determined?

Question: Protecting against excessive expansion due to alkali-aggregate reaction (AAR)

Question: The most important single factor affecting compressive strength

Question: If time is not available for preliminary tests, how can the desired strengths be ensured?

Question: How can the surface or free water carried by the aggregates be determined?

Question: What are the ultrasonic pulse velocity and the pulse echo tests?

Question: How is strength estimated by the maturity method?

Question: Can trial mixtures be made with full-size batches at the start of a job?

Question: When does the slump test provide a useful indication of workability?

Question: Is storing the specimens on the structure always a satisfactory procedure for estimating in-place strength?

Question: Curing Test Specimen at High Temperatures

Question: How is the resistance to alkali-aggregate reaction (AAR) determined?

Question: False and flash set

Question: The difference between setting and hardening

Question: How is the water-cementitious material ratio (w/cm) expressed?

Question: How is the slump test made?

Question: Does the method of molding test specimens affect the test results?

Question: Are load tests on completed structures ever employed?

Question: Is pulse velocity related to strength?

Question: Unsoundness in portland cement

Question: Are there data relating w/cm to flexural strength that are as reliable as those for compressive strength?

Question: Can tests be conducted by anyone?

Question: Why is a spherically seated bearing block required in testing cylinders?

Question: What other uses are there for the pulse velocity?

Question: How is the resistance to sulfate determined?

Question: Addition of lime in curing tanks

Question: What irregularities are to be avoided in the test specimen?

Question: Does a wet specimen test higher than a dry one?

Question: How is the resistance to freezing and thawing determined?


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