Study On Shrinkage Performance And Early-age Cracking Analysis Of Floor Concrete Mixed With Fiber And Expansive Agent

The shrinkage and early-age(28 days)cracking of concrete are hot issues in current concrete research.In order to find the concrete with characteristics of small shrinkage deformation,good crack resistance and meeting the requirements of compressive strength,to study the early-age shrinkage law of concrete more deeply,and to explore the development law and influencing factors of early-age shrinkage cracking for concrete floor for referencing prediction and prevention of early-age shrinkage cracking,the following studies are carried out.These tests of compressive strength,restrained shrinkage and free shrinkage for concrete with four different mix proportions were implemented and the early-age and long-term(325 days)shrinkage properties of four groups of concrete with different proportioning ratios were analyzed.And the concrete with both fiber and expansive agent(BFE)was obtained,which possessed characteristics of higher compressive strength,smaller shrinkage and better crack resistance.The early-age free shrinkage of concrete specimens mixed with BFE was simulated with the method of simulating humidity field by using temperature field module in ANSYS,and the simulated values of shrinkage strain were compared with the measured values to verify reliability of this simulation.In the process of simulation,the simplified calculation formula of moisture diffusion coefficient,the formula of moisture variation induced from cement and expansive agent hydration,and the formula of expansion deformation resulted from expansive agent hydration were proposed and used to simulate the drying,autogenous and chemical shrinkage,respectively.The three formulas can express the early-age shrinkage of concrete with BFE primely.The numerical analysis shows that the humidity distribution in concrete decreases with the increase of age as a whole,and the moisture near the diffusion surface decreases most dramatically.The smaller the ambient humidity is,the larger the shrinkage deformation of concrete.And the peak of shrinkage strain could be reduced effectively by curing for 7 days.The theoretical research and the parameters of moisture and structure fields of concrete with BFE are applied to the analysis of shrinkage cracking of concrete floor,and the structural analysis model of early-age shrinkage of concrete floor is established.The effects of strength grade,thickness and ambient humidity on early-age moisture variation,shrinkage and cracking of floor concrete with BFE were investigated.The analysis shows that for the floor concrete with BFE,faster growth of early-age stress and easier cracking and can be caused by higher strength grade,smaller thickness and lower ambient humidity.