Study On The Mechanism Of Early Age Crack Generating Of Ready-Mixed Concrete And Crack Controlling

Nowadays,concrete gradually has become one of the necessary basic materials to the human beings.The concrete used by the construction project is usually supplied by the ready-mixed concrete factory.Owing to the larger liquidity,the cementitious material and the sand-aggregate ratio are large,ready-mixed concrete has large shrinkage and emerges early age cracking easily.Ready-mixed concrete technology has been developing differently in different areas of China.In northwest,the early age cracking of ready-mixed concrete is very serious.The character of climate in Lanzhou are analyzed and some approach are discussed to the goal of how to control the early age cracking due to design of mixture proportions,material selection,mix round and construction technics optimization according to the developmental actuality of ready-mixed concrete technology in Lanzhou.This paper studies the early age shrinkage and cracking of ready-mixed concrete and it is discussed from three aspects including formation mechanics,experimental investigation and theoretical research.The following problems are mainly discussed in this dissertation.(1)First,make an analysis and a summary of the early age shrinkage and cracking in ready-mixed concrete.With the reference to literature both at home and abroad,study the basic forms of early age cracking and reasons why cracking emerge.(2)The paper proceed early age shrinkage experiments on the ready-mixed concrete(including only polypropylene fiber in the ready-mixed concrete,only expansive admixture in the ready-mixed concrete,both polypropylene fiber and expansive admixture in the ready-mixed concrete).(3)Through the slab test,we research the influence of early age cracking of ready-mixed concrete from the water binder radio varieties,mineral admixture and early age curing.(4)Adopting the method of orthogonal experimental design in the early age cracking of ready-mixed concrete,study was carried out on effect of early age cracking of ready-mixed concrete on water binder radio varieties,sand-aggregate ratio,mineral admixture and polypropylene fiber.The experiment results indicate that the control methods on early age cracking of ready-mixed concrete are effective,it provides convenience for the similar problem and their application may be extended.