Preparation of ettringite with different aspect ratios and its effect on the mechanical properties of mortar
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摘要: 为探究不同尺寸钙矾石对胶砂早强性能的影响，本文使用不同分散剂制得不同尺寸的钙矾石(AFt-0、AFt-1和AFt-2)，通过红外光谱(IR)、X射线衍射(XRD)及电镜形貌(SEM)对制备的系列AFt进行表征，通过胶砂抗压强度、胶砂微观形貌、水泥水化热、水泥凝结时间等分析手段比较不同尺寸钙矾石对胶砂的力学性能、微观结构及水化作用的影响。结果表明：加入分散剂能控制钙矾石尺寸大小，同时提高钙矾石在溶液中的悬浮稳定性。不同尺寸钙矾石掺入胶砂后均能提高其早期抗压强度，而随着钙矾石尺寸减小，早期抗压强度提升幅度更大，其中掺入AFt-2的胶砂8 h抗压强度较同龄期空白样提高了225%，接近空白样1 d的抗压强度。从胶砂微观结构中也可以看出，掺入钙矾石尺寸越小，胶砂中钙矾石的早期形成量越多，这利于胶砂形成早期骨架体系。通过水化热分析也发现，随着钙矾石尺寸减小，水泥水化速度加快，水泥凝结时间缩短。Abstract: To investigate the influence of different sizes of ettringite on the early strength performance of foundry sand, various sizes of ettringite (AFt-0, AFt-1, and AFt-2) were first prepared using different dispersants. The prepared series of AFt were characterized by infrared spectroscopy (IR), X-ray diffraction (XRD), and scanning electron microscopy (SEM). Comparative analyses were conducted on the mechanical properties, microscopic morphology, hydration heat of cement, and setting time of foundry sand using different analytical methods to assess the effects of various sizes of ettringite on the foundry sand. The results show that adding dispersants could control the size of ettringite and improve its suspension stability in solution. The addition of ettringite of different sizes could enhance the early compressive strength of foundry sand, with a greater increase observed as the size of ettringite decreases. Specifically, incorporating AFt-2 into the foundry sand increases the compressive strength by 225% compared to the blank sample at the same age, approaching the compressive strength of the blank sample at 1 day. Microscopic structural analysis of the foundry sand also reveals that with decreasing ettringite size, the early formation of ettringite in the foundry sand increases, which facilitates the formation of an early skeleton system in the foundry sand. Hydration heat analysis further indicates that as the size of ettringite decreases, the rate of cement hydration accelerates, leading to a shorter cement setting time.
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Key words:
- dispersants /
- ettringite /
- silane coupling agent /
- compressive strength /
- mortar
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图 7 不同尺寸钙矾石对胶砂抗压强度的影响
Figure 7. Influence of different sizes of ettringite on compressive strength of foundry sand
图 8 不同尺寸钙矾石对胶砂微观形貌的影响
Figure 8. Influence of different sizes of ettringite on microscopic morphology of foundry sand
图 9 不同尺寸钙矾石对水泥水化放热曲线的影响
Figure 9. Influence of different sizes of ettringite on heat release curve of foundry sand
图 10 不同尺寸钙矾石对水泥凝结时间的影响
Figure 10. Influence of different sizes of ettringite on cement setting time
图 11 水泥溶液体系中AFt-2的作用模型
Figure 11. Model of the role of AFt-2 in cementitious solution system
表 1 水泥的主要化学组成
Table 1. Main chemical composition of cement
Cement SiO2 CaO MgO Fe2O3 Al2O3 SO3 Na2O K2O Reference/wt% 20.06 63.32 2.46 3.02 5.28 2.69 0.06 0.76 
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表 2 分散剂组成及GPC数据
Table 2. Composition and GPC data of dispersants
Dispersant n(AA):n(KH-570):n(TPEG2400) Mn Mw PDI PCE-1 4:0:1 25400 42700 1.68 PCE-2 4:1:1 35000 69000 1.97 Notes: GPC is gel permeation chromatography; AA is acrylic acid; KH-570 is γ-methacryloxypropyl trimethoxy silane; TPEG2400 is isobutene polyoxyethylene ether with a molecular weight of 2400; Mn is the number average molecular weight; Mw is the weight average molecular weight; PDI is the polymer dispersity index; PCE-1 and PCE-2 are dispersants prepared.
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表 3 钙矾石合成原料
Table 3. Raw materials for the synthesis of ettringite
Sample Composition of synthetic materials AFt-0 Ca(NO3)2·4 H2O Al2(SO4)3·18 H2O - AFt-1 Ca(NO3)2·4 H2O Al2(SO4)3·18 H2O PCE-1 AFt-2 Ca(NO3)2·4 H2O Al2(SO4)3·18 H2O PCE-2
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