Early Concrete Volume Changes and Their Control
M. A. Swayze
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The types of volume changes occurring in concrete, in order of their incidence in a freshly mixed batch. are caused by water absorption, sedimentation, cement hydration, thermal change, and wetting or drying of the concrete. Cement hydration causes relatively large amounts of water to be absorbed by concrete in the first 24 hr. Where curing water is not supplied during the period when concrete is heating up from cement hy-dration; tests with Carlson strain meters have shown the possibility of offsetting thermal expansion by the autogenous shrinkage. At the time when the concrete reaches maximum temperature, the delayed curing leaves it in an unsaturated condition. If water is supplied to concrete during the cooling period, the induced volume change from absorption decreases shrinkaae from heat loss. This treatment will materially decrease the large thermal shrinkages which produce cracking in concrete whose final structure is established at high temperatures. It is applicable to highway slabs and structural members of similar size, but will be less effective in large masses. An appendix presents some of the significance of the paper for the highway engineer. It deals with the harmful effects on highway surfaces of too liberal application of curing water through curing mats at early ages.