硅酸盐水泥和铝酸盐水泥是广泛应用的无机注浆材料, 混合使用这两种材料可制备凝结时间短及强度高的胶凝材料。 然而, 在富水条件下(水灰比大于1), 添加适量二水石膏所制备的硅酸盐-铝酸盐水泥基材料水化后期发生强度衰减。 为了改善硅酸盐-铝酸盐水泥基富水材料的强度性能, 将一定量的硅酸钠掺入硅酸盐水泥-铝酸盐水泥-二水石膏三元体系中。 采用RMT-150力学试验系统测试含不同硅酸钠掺入量的硅酸盐-铝酸盐水泥基富水材料的强度, 分析其强度演化特性及掺入硅酸钠对其强度的影响; 采用扫描电镜(SEM), X射线衍射(XRD)及傅里叶变换红外光谱(FTIR)对不同硅酸钠掺量的富水材料微观结构进行表征, 分析其微观形貌、 物相的变化规律, 进而揭示该富水材料的强度演化机制。 强度试验结果显示, 不掺硅酸钠的富水材料早期强度低, 并且后期强度发生衰减; 而硅酸钠的掺入有助于提高硅酸盐-铝酸盐水泥基富水材料的早期强度, 并且在一定程度上减少材料固化后的后期强度衰减量, 当硅酸钠掺入量高于3%以上时, 可以有效控制该富水材料后期强度的衰减。 SEM, XRD及FTIR研究结果表明: 不掺硅酸钠的硅酸盐-铝酸盐水泥基富水材料水化14 d时, 检测到所属六方晶系的物相CAH10 及C2AH8转变为具有立方晶系结构的C3AH6, 这种晶型转变是导致该富水材料强度衰减的原因。 相比不掺硅酸钠的富水材料, 当硅酸钠掺入1%时, 富水材料水化3 d生成更多的水化硅酸钙(C-S-H)凝胶, 这有利于提高富水材料的早期强度; 水化14 d后, XRD结果显示, 在d=11.75, 6.24 出现C2ASH8的衍射峰, 而直至28 d才检测到C3AH6(d=5.16, 3.18 )衍射峰, 并且C3AH6衍射强度较不掺硅酸钠的材料低, FTIR谱3 643 cm-1处出现的振动带证实了这一发现。 这说明掺入1%硅酸钠促使六方晶系(CAH10 及C2AH8)转变为C2ASH8, 进而抑制了CAH10及C2AH8向C3AH6的转变。 但是, 添加1%的硅酸钠却不足以完全抑制富水材料水化后期的晶型转变, 因此富水材料水化后期仍会发生强度衰减。 当硅酸钠掺入量升至4%时, 硅酸盐-铝酸盐水泥基富水材料中的C2ASH8生成量显著增大, 并且水化28 d后未检测到C3AH6, 表明富水材料内的晶型转变完全得以抑制, 材料水化后期强度衰减得到有效控制。

Portland cement (PC) and calcium aluminate cement (CAC) are sorts of inorganic materials applied widely. Gel materials, with short setting time and high strengths, can be prepared by blending PC and CAC. Under rich-water conditions (water-cement ratio>1), the PC-CAC-based rich-water materials can be obtained by adding appropriate amount of gypsum into Portland cement-calcium aluminate cement binary system. However, the long-term strength of the rich-water materials tended to decrease. To improve the strength properties of the PC-CAC-based rich-water materials, certain amount of sodium silicate was blended into the PC-CAC-gypsum ternary system. Herein, RMT-150 mechanical experimental system was applied to test the strengths of the PC-CAC-based water-rich materials with different additions of sodium silicate, thus the strength evolution properties and the impact of sodium silicate on the strength can be illuminated. Then, scanning electron microscopy (SEM), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR) were adopted to characterize the micro-structures of the corresponding materials, aiming to analyze the development of micro-morphologies and hydrated phases, further to illuminate the strength evolution mechanism of the PC-CAC-based rich-water materials. Strength test results show that the early strength of the rich-water material was low, and its long-term strength would be reduced; however, by adding the sodium silicate, the early strength of the PC-CAC-based rich-water materials can be improved, and the long-term strength retrogression can be reduced partly. When the addition of the sodium silicate was more than 3%, the long-term strength retrogression of the rich-water material could be controlled effectively. The results of SEM, XRD and FT-IR indicate that without addition of sodium silicate and hydrated for 14 days, the CAH10 and C2AH8 with hexagonal structures changed to be C3AH6 with cubic structures, and this crystal transformation caused the long-term strength attenuation of the PC-CAC based water-rich material. When the sodium silicate addition was 1%, on the 3th day for hydration, more calcium silicate hydrate (C-S-H) gel formed compared with the rich-water material without sodium silicate, which brought benefits to the increase of the early strength of the PC-CAC-based rich-water material. After 14 days of hydration, XRD presented the diffraction peaks of C2ASH8 at d=11.75 and 6.24 . And the diffraction intensity of C3AH6 was detected on the 28th day, and was lower than that in the material without sodium silicate, which was confirmed by the vibration bond caused by C3AH6 and appeared at 3 643 cm-1 in FT-IR. This indicates that the addition of sodium silicate can inhibit the formation of C3AH6 by promoting transformation of CAH10 and C2AH8 to C2ASH8. However, the crystal conversion could not be inhibited completely by the sodium silicate addition of 1%, thus the long-term strength still decreased. When the sodium silicate addition rose to 4%, the formation of C2ASH8 had an obvious increase, besides, C3AH6 could not be detected on the 28th day, which indicates that the crystal transformation has been inhibited completely. Therefore, the long-term strength retrogression of the rich-water material was controlled effectively.