Research On The Early Shrinkage Cracking Performance Of Concrete Under Constraint Conditions

With the application of concrete expands gradually, the durability of concretecaused by shrinkage cracking has been exposed. The problem of concrete shrinkage andcracking has been researched in recent years in the world, but most are still in the phaseof non-restraint and qualitative research. Therefore, it is very important to observe theshrinkage and cracking of concrete in restraint condition.Firstly, splitting tensile strength,1day to15day cubic compressive strength andelastic modulus of concrete and so on are measured, the law of the basic mechanicalproperties of concrete along with age is completed.Secondly, based on the capillary theory, using the sample of concrete in slabrestraint condition, combining the viscoelastic model of concrete at early age, thecalculation of the concrete shrinkage is complete.By fiber Bragg grating sensor, the values of the concrete shrinkage and crackingwith different slump and surface wind speed in slab restraint condition at early age aremeasured. We research the differences of shrinkage cracking stress and actual splittingtension stress, then find out that the shrinkage stress in the condition of concretecracking is only75%of the splitting tension stress at the same age. The cumulation ofinner stress causes the concrete shrinkage cracking in restraint condition. Comparing theacutal value of shrinkage by fiber Bragg grating sensor to the theoretical value, we findout that the theoretical value is more bigger than the value measured, but they arealmost the same after3days.At last, by measuring the strain of the steel and concrete ring using fiber Bragggrating sensor, the shrinkage law of concrete ring and the cracking stress at early agesare researched. Combining with the mechanical properties of concrete at early ages, wefind that the shrinkage cracking stress of the concrete ring is40%lower than thesplitting tension strength at the same age. Comparing the concrete shrinkage cracking inthree types of restraint condition, we conclude that the resstraint degree is higher, thecracking age is earlier and the smaller the cracking stress,but the higher the crackinglevel.