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 ...

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...

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 cementi...

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

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...

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 l...

Question: The effect of changes in proportions of the fine and coarse aggregate or the quantity of cementi...

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 require...

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 par...

Question: If the paste is ample in amount, but is too thin and watery to float the aggregate particles, wh...

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...

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 con...

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, an...

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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