Research On Early Age Cracking Of Ready-mixed Concrete Projects And Its Control Technology

Cracking is always a hot issue in the field of concrete structure research. With the widely use of the ready-mixed concrete, the production process and the construction craft have been improved greatly. But it leads to the constriction of the ready-mixed concrete .The ready-mixed concrete cracking can be caused by loading or deformation. The latter one is commonly considered as the main factor. The phenomenon of early ready-mixed concrete cracking is especially serious and need to be solved urgently.Basis on the research at home and abroad, this paper makes a summary of the micro and macroscopic cracks in ready-mixed concrete, studies the basic forms of cracks and the reasons why cracks emerge. Four main reasons have been put forward including the materials used, the construction factors, the environment for use and external force of structure. Research on the influence of early-age shrinkage deformation for ready-mixed concrete, the dying shrinkage, plastic shrinkage, and temperature shrinkage will affect the concrete cracking higher. The varieties and contents of raw materials, such as cement, sand, fly ash and additives, are discussed. The possibility of the prevention of the concrete cracking is to use proper raw materials.Early mechanical properties of concrete can have the vital significance to its early cracking resistance. The developing rules with the tensile strength and the elastic tensile modulus of early age ready-mixed concrete are presented in this paper. In the view of micro mechanics, the mechanism of ready-mixed concrete cracking is expatiated, the effect of double admixing technology and slump on cracking properties in ready-mixed concrete is analyzed. If the ready-mixed concrete is mixed with different content of fly ash, slump can be used as a control indicator on evaluation of ready-mixed concrete cracking performance.This paper uses a improved ring shrinkage method aimed at early-age shrinkage of ready-mixed concrete. The apparatus, procedure, principle and applicability for this test method are discussed especially. The test method can be used to discuss the age and tendency of shrinkage cracking. It also provides the datum of stress which can evaluate the cracking properties of ready-mixed concrete.Because the temperature has the very tremendous influence to early-age shrinkage of ready-mixed concrete, each kind of factors which influenced on early-age concrete temperature is analyzed. The thermal properties of the raw materials are theoretically analyzed and the necessary control measures of materials temperature are calculated. The general way is reducing the use of cement, using low-heated cement, adding admixture, cutting down the pouring temperature in construction, controlling the temperature of raw materials, reducing the restriction from both the out and inner space.