Study On The Shrinkage-cracking Reducing Methods Of Concrete Exposed To Temperature And Humidity Of China’s Western Region

With the use of high performance concrete, the problem of shrinkage cracking ofconcrete becomes more and more outstanding which is a great challenge for thedurability of concrete structures. Although the related research has a lot of achievements,there are few of them considering the influence of environmental conditions onshrinkage cracking reducing methods. In this paper, the main research includes twoaspects: i) analysis of the effect of different shrinkage cracking reducing methods on thecracking resistance of concrete under different environmental conditions; ii) study onthe optimal methods to reduce shrinkage cracks in China’s western region throughcomparing various shrinkage cracking reducing measures.In this paper, the compressive strength and splitting tensile strength were measuredto study the effect of shrinkage cracking reducing methods on the mechanicalperformance. In addition, autogeneous shrinkage, drying shrinkage as well as circleconstrains contraction in different conditions were investigated which include normaltemperature environment, high temperature with low humidity environment and largetemperature difference between day and night. Moreover, the pore structure of concreteby mercury intrusion method under different conditions was compared to analyzemechanisms and shrinkage reducing results of various shrinkage cracking reducingmeasures.The results show that the effect of shrinkage cracking reducing methods on thestrength of concrete seems insignificant. The addition of polypropylene fiber can reducethe plastic shrinkage of concrete, but increase the porosity of concrete andmacro-porous quantity as well as drying shrinkage of concrete. Generally the influenceof polypropylene fiber on the shrinkage deformation and cracking resistance of concreteis not obvious. The shrinkage-reducing agent can significantly improve the crackingresistance of concrete which is reflected by decrease of the autogenous shrinkage anddrying shrinkage with the compactness of concrete structure. The expansive agent canevidently decrease the shrinkage cracking of concrete, while it contributes to the porestructure slightly. The main function of curing agent is not reducing shrinkagedeformation, but improving the anti-cracking performance of concrete. And it showsgood composite effect on the cracking resistance with shrinkage-reducing agent orexpansive agent.With the increase of environmental temperature and the decrease of humidity, thehydration speed and reaction process of concrete accelerated and the moisture loss rateincreased. The pore structure of concrete changes from micro-pore to macro-pore withlarger porosity. The early shrinkage deformation of concrete is enlarged due to high temperature and low humidity, therefore the risk of concrete cracking is increased.