XRD和FTIR的掺硅酸钠富水材料强度演化机制

Strength Evolution Mechanism of Water-Rich Material Blending with Sodium Silicate by XRD and FTIR

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14d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3d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14d后,XRD结果显示,在d=11.75,6.24出现C2ASH8的衍射峰,而直至28d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3643cm^-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28d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 CAH 10 and C 2AH 8 with hexagonal structures changed to be C 3AH 6 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 C 2ASH 8 at d=11.75 and 6.24.And the diffraction intensity of C 3AH 6 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 C 3AH 6 and appeared at 3 643 cm^-1 in FT-IR.This indicates that the addition of sodium silicate can inhibit the formation of C 3AH 6 by promoting transformation of CAH 10 and C 2AH 8 to C 2ASH 8.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 C 2ASH 8 had an obvious increase,besides,C 3AH 6 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.