accelerate the hardening of mixtures of Portland cement and water include 

 some of the soluble chlorides, carbonates, silicates, fluosilicates, and 

 hydroxides (Steinour, 1960), and also some organic compounds such as 

 triethanolamine (Newman, et al . , 1943). Calcium aluminate cements and 

 finely ground hydrated Portland cement have also been advocated. 



Some of the soluble chlorides, particularly calcium chloride (Highway 

 Research Board, 1952) and to a much lesser extent triethanolamine, have 

 general applicability as admixtures in concrete. Some of the other materials 

 are suitable only for use in the preparation of quick-set cements. 



By far the best known and most widely used accelerator is calcium 

 chloride. Many other materials have been found to accelerate the strength 

 gain of concrete but, in general, they are seldom used, and only limited 

 information concerning their effect on the properties of concrete is 

 available. Most of the information given on accelerators applies mainly to 

 the use of calcium chloride. The effects of accelerators on some of the 

 properties of concrete are as follows: 



(a) The setting time, initial and final, is reduced. The amount 

 of reduction varies with the amount of accelerator used, the 

 temperature of the concrete, and the ambient temperature. Excessive 

 amounts of the accelerator may cause rapid setting. 



(b) Less air-entraining admixture is required to produce the 

 required air content. However, in some cases larger bubble sizes 

 and higher spacing factors are obtained. 



(c) Earlier heat release is obtained but there is no 

 appreciable effect on the total heat of hydration. 



(d) Compressive strength is increased substantially at early 

 ages. The ultimate strength may be reduced slightly. The increase 

 in flexural strength is usually less than that of the compressive 

 strength. 



(e) It is generally considered that the volume change is 

 increased for both moist curing and drying conditions. There 



is a question of the degree of the effect caused by the accelerators 

 as opposed to other factors influencing volume change. 



(f) The resistance to freezing and thawing and to scaling 

 caused by the use of deicing salts is increased at early ages, but 

 may be decreased at later ages. 



(g) The resistance to sulfate attack is decreased. 



(h) The expansion produced by alkali-aggregate reaction is 

 greater. This can easily be controlled by the use of low alkali 

 cement or pozzolans. 



(i) Corrosion of metals may occur, especially in the use of 

 calcium chloride when steam curing is employed. The use of calcium 

 chloride in recommended amounts does not cause progressive corrosion 



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