真空去水压制成型对机制砂混凝土性能的影响

为顺应当今建筑工业化和固废资源化趋势,工程界提出了采用真空去水压制成型新工艺,以实现机制砂混凝土的高效预制生产。本文研究了真空去水压制成型时间对不同初始水灰比(W/C)机制砂混凝土性能的影响,结果表明：与天然砂混凝土相比,真空去水压制能更显著提升机制砂混凝土的强度,主要是由于在高密实成型条件下,机制砂充分发挥了嵌锁效应,经真空负压-0.07 MPa及压制15 MPa处理100 s后,机制砂混凝土初始W/C从0.58降低至0.32,抗压强度提升了44.6%,延长处理时间性能提升效果减弱,尤其是对W/C较小的混凝土;压汞测孔(MIP)发现真空去水压制后混凝土硬化体孔隙率大幅降低,尤其是大于50 nm的有害孔,与压制前相比,其比例下降均超过70%,孔径分布得到了改善,且水化程度均提高至0.6以上;扫描电子显微镜(SEM)和X射线衍射(XRD)表明,经真空去水压制处理后,混凝土内硬化浆体变得更密实,定向排列的针状钙矾石及片状Ca(OH)₂含量减少,而界面过渡区(ITZ)黏结性能提高。采用真空去水压制成型机制砂混凝土,符合现代预制混凝土构件生产的绿色、节能、环保发展要求。

Influence on Performances of Machine-Made Sand Concrete Fabricated by Vacuum Water-Removal and Compression Technique

In order to adapt to the current trend of building industrialization and solid waste recycling, a new technology of vacuum water-removal and compression was proposed in the engineering field to achieve a highly efficient pre-fabrication of machine-made sand concrete. In this study, the effect of the time of vacuum water-removal and compression treatment on the performances of machine-made sand concrete with varied initial water-to-cement ratio (W/C) was investigated. Results show that vacuum water-removal and compression can significantly improve the strength of machine-made sand concrete as compared to natural sand concrete, primarily due to the locking effect of the machine-made sand under the condition of high compaction by the treatment. The initial W/C of machine-made sand concrete decreases from 0.58 to 0.32 and the compressive strength increases by 44.6% after being treated with -0.07 MPa vacuum pressure and 15 MPa compression for 100 s. However, the improvement of performances weakens with prolonged treatment time, especially for concrete with lower W/C. Mercury intrusion porosimetry (MIP) results reveal that the porosity of concrete decreases significantly after vacuum water-removal and compression treatment. In particular, the proportion of capillary pores with pore size larger than 50 nm decreases by more than 70%. Thus, the pore size distribution is improved. The hydration degree also increases to more than 0.6. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) show that the hardened paste in concrete is densified, the amounts of aligned needle-shaped ettringite and plate-shaped Ca(OH)₂ are reduced, and the bonding property of interfacial transition zone (ITZ) is improved by vacuum water-removal and compression. The machine-made sand concrete fabricated by vacuum water-removal and compression is in line with the developing trend of green, energy saving and environmental protection for the production of modern pre-cast concrete members.