Zhang Mingming, Gao Shan, Liu Tong, Guo Shuyu, Zhang Shuotian
School of Civil Engineering, Xijing University, Xi'an 710123, China.
School of Civil Engineering, Xi'an University of Architecture and Technology, Xi'an 710055, China.
Materials (Basel). 2024 May 20;17(10):2465. doi: 10.3390/ma17102465.
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.
机制砂混凝土、废粉混凝土和再生骨料混凝土早期收缩和开裂性能较差，是工程应用中的主要难题。为解决这些问题，对掺加粉煤灰和矿渣粉（FS）、减缩剂（SRA）、聚乙烯醇（PVA）纤维和高吸水性聚合物（SAP）的大掺量石粉机制砂混凝土进行了早期收缩与开裂、强度及抗渗性试验。此外，利用核磁共振（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，FS、SRA、PVA纤维和SAP的复合能有效抑制混凝土的收缩应变和开裂面积。SAP对降低混凝土早期收缩的效果最为显著，收缩应变可降低76.49%。PVA纤维对抑制混凝土早期开裂的效果最为明显，总开裂面积减少66.91%。值得注意的是，掺入FS可改善颗粒级配和孔结构，提高其密实性。PVA纤维不仅为水泥基材料提供良好的载体，还增强混凝土内部颗粒间的粘结力，填充混凝土内部孔隙，抑制水分流失，减少内部微裂纹的产生。FS和PVA可降低收缩和开裂风险，提高混凝土的强度和抗渗性。虽然SRA和SAP可降低收缩和开裂风险，但会导致后期强度和抗渗性显著下降。主要原因是SRA导致基体中微孔增加以及骨料附近微裂纹产生，不利于机制砂强度和抗渗性的发展。同样，SAP可促进早期钙矾石（Aft）的快速形成，改善混凝土的早期收缩、早期开裂和早期强度。然而，随着龄期增长，SAP脱水后的残余孔隙会导致混凝土孔结构劣化，从而使强度和抗渗性变差。
