Experimental Study On The Shrinkage And Early-age Crack Resistance Performance Of Internal-Curing Concrete

High performance concrete are widely used because of the advantages of high strength, high performance and high durability, but its concrete shrinkage cracking problem caused by the characteristic of low water-cement ratio is gradually highlighted, which causes a serious threat to the safety and durability of engineering structures. The concrete internal curing technique provides a new way for solving concrete shrinkage and cracking problem. Considering the curing agent content, particle size, water diversion mode and types, this article analyzes the influence rule of curing agent to the early age mechanical property, shrinkage and crack resistance property of concrete, through test research based on the non-contact method and slab method, and compares them with the basic concrete. A shrinkage prediction model applied to internal curing concrete is established, which will provide guidance for internal curing materials in the practical engineering application.(1)SAP has similar effects on seven days compressive strength and seven days flexural strength of concrete. The 10 times water absorption way produces adverse effect on the strength of concrete, with the increase of SAP content, the intensity level to reduce is more obvious; the 10 times water absorption and buckle the water way and the 0 times water absorption way have the enhanced effect on the strength of concrete.(2)Shrinkage test results show that the concrete has shown an obvious expansion phenomenon in the hours after starting testing, the incorporation of SAP or LWA may improve the early age expansion and prolong the expansion time. When the effective water-cement ratio is constant, with the pre-soaked SAP content increasing, the reduction rate of shrinkage of concrete presents a law of first increases and then decreases, the reasonable dosage is 0.2%; the water diversion way of largest reduction rate is the 10 times water absorption way; for purpose to improve the effect of concrete shrinkage deformation, the 100 mesh particle size of SAP has an obvious effect than the 60 mesh; Considering the seven days strength test results and the shrinkage test results, SAP is more suitable than LWA to be used for concrete internal curing. In internal curing concrete, the curing effect is more reflected in the early age concrete curing.(3)According to the results of internal curing concrete shrinkage test up to 180 days, the establishment of two shrinkage prediction model proposes calculation formula for the internal curing concrete, the calculated values agree well with the measured level.(4)The crack test results show that the addition of SAP and LWA can significantly improve the early age crack resistance property of concrete. For SAP concrete mixed with 100 mesh and 0 times water absorption way, with the increase of dosage of SAP, initial cracking time delays and cracking area decreases gradually; the 10 times water absorption and buckle the water way has the best anti-cracking effect in the three kinds of water absorption ways. Adding SAP to concrete has more obvious reduce effect on the concrete cracking area than adding LWA at the same time after the initial crack.