Effects Of Curing On Early Shrinkage And Cracking Of Foamed Concrete

In recent years, foamed concrete has been obtained more and more application. Shrinkage and cracking are important factors to the durability of foamed concrete. The prompt solution of the problems exposed during the application of foamed concrete is demanded. A lot of research has been done on this topic, but most of them are based on the common concrete. Therefore, it’s quite necessary to research on the effects of curing on early shrinkage and cracking of foamed concreteIn order to know well about the deformation capability of the foamed concrete, we have a systematic study on the volume change and cracking of foamed concrete under different environment. This paper includes the following research contents:the early shrinkage deformation of foamed concrete from casting to 3 days were measured by non-contact method of displacement sensor, analyzed the deformation characteristics of foamed concrete during 3 days; using apparatus based on the principle of differential transformer to measure drying shrinkage within 28 days; using ring test evaluate the shrinkage cracking potential of foamed concrete under different environmental conditions directly. The test data was analyzed by the method of multiple factor variance analysis.The experimental results demonstrate that the early age deformation curve of foamed concrete based on the temperature of 25 ℃ is characterized by plastic shrinking at initial several hours after casting and then swelling with a gradually rate, which can be divided into three parts. Early shrinkage curve under high temperature conditions can be divided into three parts, and showed an early expansion characteristic initially. The end point of swelling corresponding to the transformation point of plastic state to solid state and this point can be defined as the starting time of effective deformation of foamed concrete. The effective deformation of foamed concrete starting time is ahead of schedule with the rising temperature. When the temperature rises from 25℃to 65℃,and the water cement ratio is 0.5, the starting time of effective deformation of foamed concrete decreases from5.5 to 12.5h.Improving the environment temperature has a great effect on dry shrinkage. When the temperature rises from 25℃to 65℃, ages of 28 days’drying shrinkage of foamed concrete ranges from 1588×10-6～1850×10-6.When the temperature fixed, the foamed concrete’s deformation with RH15% is more obvious than the RH75%. As the water-cement ratio and temperature rises, the effect of humidity on foamed concrete’s deformation is weakened.High temperature increases the cracking risk of ring test, decrease of water cement ratio is advantageous to the resistance to cracking of foamed concrete.