Effect Of Set-retarders And Early-age Curing On Compressive Strength Of Concrete

Now, China is carrying out fundamental construction in large scale. As one of most important structure materials, control of the quality of concrete is of much significance for the development of social and economical for our country.Abnormal setting of concrete and improper control of curing condition is two important factors affecting the quality of concrete. In this paper, the effects of common set-retarders and early-age curing on properties of concrete are studied so as to control the quality of concrete.The effects of five common set-retarders on setting time of cement paste and concrete and strength of concrete are studied. To cement paste, amount of set-retarders added in cement has a critical value. To concrete, the setting time of concrete extends with amount of set-retarders increase. The effects of various set-retarders on strength of concrete are different. 28-day strength of concrete decrease in different degree with amount of Ca-lignosulphonate, Ca-solassate and sucrose increase. However, 28-day strength of concrete increase with amount of tartaric acid and Na1P2O7 increase. It is benefit for control the quality of concrete.The effects of gypsum on fluidity of cement mortar and setting time of cement paste are not significant when it used as retarder of cement. Whereas, when 0.3% Ca-lignosulphonate or Ca-solassate added in cement used anhydrite gypsum as retarder, loss of fluidity of cement mortar is rapid, quick setting is occurred. Unsuitability of admixture to cement comes out.Various curing condition and different amount of water evaporated in early-age curing would lead to different strength of concrete. In the environment of T50 ± 2~C and RH=30 ± 3% the effects of faces and time for losing water on strcngth of concrete are studied. Result show that the more the loss of water at early-age, the lower strength of concrete acquired. For the concrete which losing water is little at early-age, strengthen curing, the strength of concrete will be compensated.Experiment results showed that the effects of temperature, humidity, wind- II -speed, sunshine and mixture of concrete are significant. At plastic state, rate of water loss in concrete is quickened; measures should be taken to prevent it in practical construction.