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|Title:||Expansive cements and their use|
|Authors:||Hoff, G. C. (George C.)|
|Publisher:||Concrete Laboratory (U.S.)|
Engineer Research and Development Center (U.S.)
|Series/Report no.:||CTIAC report ; no. 8.|
Abstract: The primary purpose of expansive cement concrete is to minimize cracking in ccncrete pavements and structures caused by drying shrinkage. Various types of expansive cements and their properties are reviewed. The expansive mechanism and factors affecting it are also reviewed. The physical properties of expansive concrete along with practical considerations such as mixing, placing, finishing, and curing are discussed. Structural design criteria for these concretes are reviewed. Applications are suggested. Expansive cement types K, M, and S are available in shrinkage-compensating and self-stressing grade G. The amount of expansive potential a cement has determines its grading and is controlled by the ingredients end formulation of the cement. The effective utilization of this potential is controlled by the cement supplier or user or both. Cement content, aggregate type, mixing times, curing, temperature, and restraint can affect expansions. Expansive cement is effective only when the hardened paste made with the cement is sufficiently restrained from expanding; so that compressive stresses are developed in the material. Seven-day restrained prim expansion for concrete made with shrinkage-compensating cement are usually within the limits of 0.03%, to 0.10%. This corresponds to compressive prestress developments in the concrete in the range of 25 to 100 psi (0.17 to 0. 69, megapascals). The proportioning and properties of concrete made with shrinkages-compensation (expansive cement are generally similar to those of corresponding portland cement concrete made with. type I and type II cements. Additional batching water may be required with types K and S cement to achieve the necessary workability. Increases in water-cement ratio of 0.05 to 0.10 over that of comparably designed portland cement concrete are common The additional water does not affect the strength. Most air entraining water reducing, and water-reducing-retarding admixtures can be used with expansive cements, but their capability be checked. No special placing equipment and techniques are needed for expansive cement concrete. Water curing is an absolute necessity. Finishing may require greater manpower for shorter periods of time than for normal concrete finishing operations. The most reliable and controllable restraint for expansive cement concrete is provided by conventional reinforcing steel. In most instances, nonload-bearing members and slabs on grade should contain a minimum of 0.15% reinforcement. Using expansive cement concretes, slab placement areas can be increased approximately 10 times over those presently obtained with conventional concrete, thus eliminating many construction joints. Maximum contraction joint spacings of up to 150 ft (45.7 meters) are possible. Shrinkage-compensating concretes have been used in most situations where portland cement concretes have been used (i.e. in parking facilities, tilt-up construction, pavements, water and waste-water works, swimming pools, sports arenas, tennis courts, architectural applications, and precast operations).
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