Technical Questions

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




Question: Substantial structural damage

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: Resistance to cycles of freezing and thawing

Question: Requirements for durable concrete

Question: The effect of air content on concrete strength

Question: The importance of concrete cover

Question: Unsoundness in portland cement

Question: Requirements for storing and handling aggregate

Question: Specialty admixtures

Question: Precautions against sulfate attack

Question: Improving the abrasion resistance of concrete

Question: What is the effect of freezing on concrete?

Question: Can the strength gain of concrete that has ceased due to drying out at early ages be restored by moist curing?

Question: Embedded metals other than reinforcing steel

Question: Definition of concrete, hydraulic cement, mortar, and grout

Question: Evaluating the properties of hardened concrete

Question: Aging of concrete

Question: Consistency, plastic consistency, and workability

Question: The effect of entrained air on the workability of concrete

Question: Definition of setting time

Question: The difference between setting and hardening

Question: Measurement of setting time

Question: Factors affecting time of setting

Question: False and flash set

Question: Strength of concrete

Question: Factors governing the strength of concrete

Question: Air content common limits

Question: Factors affecting permeability

Question: The relationship between porosity and permeability of concrete

Question: Other important properties of concrete

Question: What is reinforced concrete?

Question: The importance of reinforcement in concrete

Question: Reinforced concrete vs. prestressed concrete

Question: Epoxy-coated reinforcement

Question: Definition of low-density concrete

Question: Definition of portland cement

Question: Standard specifications for cements

Question: The earliest use of portland cement

Question: Materials used to produce portland cement

Question: The making of portland cement

Question: The purpose of calcium sulfate (gypsum)

Question: Factors affecting cement properties

Question: Effects of cement fineness on cement properties

Question: The cause of false set

Question: Definition of “hot cement”

Question: Notable changes in modern portland cement properties

Question: Characteristics of cement that affect compressive strength

Question: Why is Type IV cement rarely produced and Type V cement rarely used?

Question: What is slag cement or ground granulated blast-furnace slag (GGBFS)

Question: Benefits of using slag cement

Question: What is a pozzolan?

Question: What does a pozzolan do in the concrete?

Question: Using and handling pozzolans

Question: Importance of using pozzolans in hydraulic and environmental structures

Question: Are pozzolans all alike?

Question: The effect of pozzolans on water demand

Question: The effect of pozzolans on shrinkage

Question: The effect of pozzolans on freezing and thawing resistance

Question: What is a natural pozzolan?

Question: What is fly ash?

Question: Do all fly ashes behave in a similar way?

Question: What is silica fume?

Question: What is aggregate?

Question: Why is combined aggregate grading used?

Question: Aggregate classification by density

Question: Advantages of low-density aggregate

Question: What are high-density aggregates?

Question: Important requirements of a concrete aggregate

Question: The effect of aggregate on concrete durability

Question: How can durable aggregates be ensured?

Question: Characteristics of aggregate affecting concrete strength

Question: The effect of surface texture and cleanness on concrete strength

Question: The effect of aggregate shape on concrete strength

Question: The effect of aggregate grading on concrete strength

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

Question: The effect of aggregate strength on concrete strength

Question: The effect of aggregate characteristics on concrete shrinkage and permeability

Question: What is an admixture?

Question: What is an air-entraining admixture?

Question: What are water-reducing admixtures?

Question: What are set-controlling admixtures?

Question: Do different admixtures of a given type always perform the same?

Question: Do some water-reducing admixtures induce bleeding?

Question: Are retarding admixtures reliable as to the time of setting?

Question: The effect of water-reducing admixtures on drying shrinkage

Question: What fibers are used in concrete?

Question: Why is the workability of concrete important?

Question: How is workability measured and specified?

Question: Definition of controlled low-strength material (CLSM)

Question: What is shotcrete and when is it used?

Question: What is involved in the process of mixture proportioning?

Question: The ultimate objective in proportioning concrete

Question: How do the requirements of placing affect the selection of proportions of aggregates and cementitious material?

Question: How does the relative amount of each ingredient used in concrete influence the properties of concrete?

Question: Are the proportions of ingredients inter-related to produce concrete of a given workability?

Question: The basic approach used in the ACI mixture proportioning method

Question: How is the selection of mixture proportions affected by the materials to be used and the placing requirements?

Question: The most important single factor affecting compressive strength

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

Question: What correction should be made for absorbed water and surface water carried by the aggregates?

Question: What consideration should be given to water that may be lost from concrete between the time it leaves the mixer and its final consolidation in the form?

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

Question: The effect of water-cementitious ratio on permeability and shrinkage

Question: What water-cementitious material ratio should be used for a particular job when strength requirements are to govern?

Question: Is personal protection needed when handling concrete?

Question: How should the aggregates and other ingredients be measured to obtain uniformity in proportions?

Question: How can the adequacy of mixing be determined?

Question: What factors affect the mixing time?

Question: How can segregation of the concrete between the mixer and its final point of placement be prevented?

Question: Why is a plastic consistency usually desirable for placing concrete?

Question: If the cementitious material paste is not sufficient in amount to float all of the aggregate particles, what is the result?

Question: If the paste is ample in amount, but is too thin and watery to float the aggregate particles, what is the result?

Question: Can you have too much paste or mortar?

Question: Can the importance of proper consistency for placing be overemphasized?

Question: What are the essential requirements of consistency?

Question: What range in slump is recommended for various types of construction?

Question: How is concrete placed?

Question: What is yield?

Question: Why is consolidation needed?

Question: How is concrete consolidated?

Question: How should the concrete be consolidated to obtain a complete filling of the forms and around the reinforcement?

Question: Does over-vibration cause segregation and loss of air content?

Question: What is the importance of consolidation on strength?

Question: What is the purpose of finishing and texturing concrete surfaces?

Question: When can the finishing procedure be started?

Question: What is curing?

Question: What is meant by properly cured concrete?

Question: Is there any measure of the completeness or adequacy of curing?

Question: How much water goes into combination with the cement during the hardening of concrete?

Question: What methods are commonly used to ensure sufficient moisture for curing concrete?

Question: How does the temperature influence curing?

Question: What methods are used for protecting concrete against low temperatures?

Question: Can the heat liberated by the hydrating cement be relied on to give protection during cold weather?

Question: When heated enclosures are used to protect freshly placed concrete, what precautions are necessary?

Question: When water and aggregate are heated, are any limitations necessary?

Question: Are any temperature limitations necessary in curing concrete in hot weather?

Question: When is steam curing used?

Question: How can the effectiveness of curing be measured?

Question: What is the importance of curing on strength?

Question: Will concrete continue to increase in strength if there is no moisture present?

Question: Does additional curing improve the properties of concrete in other ways than in strength?

Question: Can tests be conducted by anyone?

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

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

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

Question: How is the slump test made?

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

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

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

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

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

Question: Is density a good indicator of air content?

Question: How is the temperature of concrete measured?

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

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

Question: Popouts or popoffs?

Question: What is calcium-aluminate cement?

Question: What is architectural concrete?

Question: What is autogenous shrinkage?

Question: Difference between a contraction joint, isolation joint, expansion joint, construction joint, and a cold joint

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

Question: What is mass concrete?

Question: Protecting concrete from cycles of freezing and thawing

Question: What steps are taken in the repair of concrete structures?

Question: Do we always need to repair cracked concrete?

Question: What is D-cracking?


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