大掺量高吸附性石粉高强机制砂混凝土收缩开裂抑制试验

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

针对大掺量高吸附性石粉高强机制砂混凝土早期易发生收缩开裂的问题,开展了掺加膨胀剂、减缩剂、聚乙烯醇(PVA)纤维、高吸水树脂(SAP)混凝土的早期收缩、抗裂和力学试验,并利用核磁共振仪和扫描电子显微镜对混凝土孔结构和微观形貌进行了测试,揭示抑制收缩开裂的机制。试验结果表明:掺入膨胀剂、减缩剂、PVA纤维、预吸水SAP均能有效抑制混凝土早期收缩和开裂,其中掺预吸水SAP降低早期收缩的效果最好,收缩应变可降低93%,PVA纤维抑制早期开裂的作用最明显,总开裂面积可降低68.26%,同时,掺入两者会使混凝土力学性能提高,而掺入膨胀剂和减缩剂会使混凝土力学性能降低。SEM图像表明,SAP能将预吸收的水分释放到混凝土中,促进水泥水化反应,而PVA纤维的掺入改善了混凝土内部孔隙结构,有良好的填充作用和桥接作用。核磁共振试验表明,抑制收缩开裂的机制是通过改善混凝土孔隙结构,增强界面密实度,从而减小早期收缩,进而提高抗裂性能。

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.