Experiment on control measures of shrinkage and cracking of high strength manufactured sand concrete containing a large amount of high absorbency stone powder

Abstract

The early-age shrinkage, crack resistance and mechanical properties of high strength manufactured sand concrete containing a large amount of high absorbency stone powder were conducted in order to solve the early-age shrinkage and cracking problem of concrete by adding expansion agent, shrinkage reducing agent, polyvinyl alcohol (PVA) fiber, super absorbent polymer (SAP). The mechanism of inhibiting shrinkage and cracking of high strength manufactured sand concrete containing a large amount of high absorbency stone powder was revealed by testing pore structure and microstructure morphology using low-field nuclear magnetic spectroscopy and scanning electron microscope. The test results show that the addition of expansion agent, shrinkage reducing agent, PVA fiber and pre-absorbent SAP can all effectively inhibit the early-age shrinkage and cracking of concrete. Compared with the benchmark group concrete, incorporating pre-absorbent SAP is the best measure to reduce the early-age shrinkage of concrete and the shrinkage strain will be reduced by 93%. The most obvious inhibitory effect on the cracking of concrete is incorporating PVA fiber and the total cracking area can be reduced by 68.26%. The mechanical properties of the concrete are improved because of pre-absorbent SAP and PVA fiber. However, the mechanical properties of concrete have a certain decrease because of incorporating expansion agent and shrinkage reducing agent. SEM images show that SAP can release the pre-absorbed water into the concrete and promote the cement hydration reaction, while the incorporation of PVA fiber improves the internal pore structure of the concrete and has a good filling and bridging effect. The low-field nuclear magnetic resonance experiments show that the mechanism of inhibiting shrinkage and cracking is to improve the pore structure of concrete and enhance the compactness of the interface, thereby reducing early shrinkage and improving crack resistance.