Study On The Volume Deformation And Cracking Of Concrete Exposed To Temperature And Humidity Of China’s Western Region

Shrinkage and cracking are important factors to the durability of concrete. A lot ofresearch has been done on this topic in recent years, but most of them are conducted bythe standard methods at a fixed ambient conditions. In fact, concrete applied in realproject is affected by many factors under complicated conditions. In order to know wellabout the deformation capability of the concrete under western environment and providethe basic data describing the improvement of the durability of concrete in engineeringapplication, we have a systematic study on the volume change and cracking ofhigh-performance concrete and ordinary concrete under western environment.This paper includes the following research contents: the study of the early agecompressive strength and splitting tensile strength of concrete, the autogenousshrinkage deformation of concrete from casting to14days were measured bynon-contact method of displacement sensor, analysted the deformation characteristicsof concrete during1day, using apparatus based on the principle of differentialtransformer to measure total drying shrinkage within28days, using ring test evaluatethe shrinkage cracking potential of concrete under different environmental conditionsdirectly.Firstly,The early age autogenous deformation curve of concrete based on the roomtemperature of20℃is characterized by plastic shrinking at initial several hours aftercasting and then swelling with a gradually rate, which can be divided into four parts.Autogenous shrinkage curve under high temperature conditions can be divided intothree parts, and showed an early expansion characteristic initially.The end point ofswelling corresponding to the transformation point of plastic state to solid state and thispoint can be defined as the starting time of effective deformation of concrete, themaxmim effective deformation can be difined as peak deformation of early age.Secondly, the experiment result showed that the effective deformation of concretestarting time is ahead of schedule with the reduction of water cement ratio and the risingtemperature.When the temperature rises from20℃to65℃,and the water cement ratiois0.3, the starting time of effective deformation of concrete decreases from6.67to3.16h.After the concrete has been poured for to14hours, the concrete’s deformation indifferent groups reaches the peak value. When the temperature ranges from20℃to65℃,0.3water–cement ratio concrete’s peak deformation in early age ranges from131×10^-6to1095×10^-6.Although, improving the environment temperature has a great effect on autogenousshrinkage, but has little effect on dry shrinkage shrinkage. As the temperature ranges from20℃to65℃,ages of14day and0.3water-cement ratio concrete’s autogenousshrinkage ranges from303×10^-6to1054×10^-6. Ages of28days’ drying shrinkage ofconcrete ranges from312×10^-6611×10^-6.When the temperature is35℃,the concrete’sdeformation with RH15%is more obvious than the RH60%. As the water-cement ratioand temperature rises, the effect of humidity on concrete’s deformation is weakened.High temperature increases the cracking risk of ring test, increase of water cement ratiois advantageous to the resistance to cracking of concrete and groups of highperformance concrete incorporated of mineral admixtures delayed the early cracking ofconcrete in the measurement.