PDF(Pubmed)
Abstract：
The poor early shrinkage and cracking performances of manufactured sand concrete, waste powder concrete, and recycled aggregate concrete are the main difficulties in engineering applications. To solve these problems, early shrinkage and cracking, strength, and impermeability tests were performed on high-volume stone powder manufactured sand concrete mixed with fly ash and slag powder (FS), a shrinkage-reducing agent (SRA), polyvinyl alcohol (PVA) fibers, and a superabsorbent polymer (SAP). Furthermore, the microstructures and pore structures of these concretes were revealed using nuclear magnetic resonance (NMR) and scanning electron microscopy (SEM). The results showed that the mixture of FS, SRA, PVA fibers, and SAP could effectively inhibit the shrinkage strain and cracking area of the concrete. The effect of the SAP on reducing the early shrinkage of the concrete is the greatest, and the shrinkage strain can be reduced by 76.49%. The PVA fibers had the most obvious effect on inhibiting the early cracking of the concrete, and the total cracking area was reduced by 66.91%. Significantly, the incorporation of the FS can improve the particle gradation and the pore structure and improve its compactness. The PVA fibers not only provide good carriers for cement-based materials but also enhance the bonding force between the particles inside the concrete, filling the pores inside the concrete, inhibiting the loss of water, and reducing the generation of internal microcracks. The FS and PVA can reduce the shrinkage and cracking risk and improve the strength and impermeability of the concrete. Although the SRA and SAP can reduce the shrinkage and cracking risks, it will lead to a significant decrease in the later strength and impermeability. The main reason is that the SRA leads to an increase in micropores in the matrix and microcracks near the aggregate, which are not conducive to the development of the strength and penetration resistance of the MS. Similarly, the SAP can promote the rapid formation of ettringite (Aft) at an early age and improve the early shrinkage, early cracking, and early strength of the concrete. However, with an increase in age, the residual pores, after SAP dehydration, will cause the deterioration of the concrete pore structure, resulting in the deterioration of the strength and impermeability.
摘要：
机制砂混凝土的早期收缩和开裂性能较差，废弃粉末混凝土，再生骨料混凝土是工程应用中的主要难点。为了解决这些问题,早期收缩和开裂，力量,并对掺入粉煤灰和矿渣粉（FS）的高体积石粉人造砂混凝土进行了抗渗试验，减缩剂（SRA），聚乙烯醇（PVA）纤维，和超吸收聚合物(SAP)。此外，使用核磁共振（NMR）和扫描电子显微镜（SEM）揭示了这些混凝土的微观结构和孔结构。结果表明,混合FS,SRA,PVA纤维,SAP能有效抑制混凝土的收缩应变和开裂面积。SAP对减少混凝土早期收缩的影响最大，收缩应变可降低76.49%。PVA纤维对混凝土早期开裂的抑制效果最为明显,总开裂面积减少了66.91%。重要的是,掺入FS可以改善颗粒级配和孔结构，并提高其致密性。PVA纤维不仅为水泥基材料提供了良好的载体，而且增强了混凝土内部颗粒之间的结合力，填充混凝土内部的毛孔，抑制水分流失，并减少内部微裂纹的产生。FS和PVA可以降低混凝土的收缩和开裂风险，并提高混凝土的强度和抗渗性。尽管SRA和SAP可以降低收缩和开裂风险，这将导致后期强度和抗渗性的显著降低。主要原因是SRA导致基体中的微孔增加和聚集体附近的微裂纹，这不利于MS的强度和抗穿透性的发展。同样，SAP能促进钙矾石(Aft)的早期快速形成,早期开裂，和混凝土的早期强度。然而,随着年龄的增长，残留的毛孔，SAP脱水后，会导致混凝土孔隙结构的恶化，导致强度和抗渗性的恶化。
