低温硫酸盐侵蚀环境中水泥石腐蚀产物

研究了水胶比为0.45,掺35%石灰石粉水泥基材料标准养护28d后在(5±2)℃浸泡于SO2-4质量分数为3.38%的钠盐、镁盐、铝盐3种硫酸盐侵蚀溶液中15周时的破坏状况和强度损失率.采用Fourier红外光谱、X射线衍射、扫描电子显微镜、能谱以及Raman光谱确定水泥石腐蚀物相和组成.结果表明:镁盐溶液中试件抗压强度损失率最大,其次是钠盐溶液中试件,铝盐溶液中试件抗压强度损失率最小;钠盐溶液和铝盐溶液中水泥石主要腐蚀产物是钙矾石和石膏;镁盐溶液中水泥石主要腐蚀产物是钙矾石、石膏、碳硫硅酸钙和少量水镁石.     

特性环境对水泥砂浆硫酸盐侵蚀类型的影响

研究了硫酸盐种类(Na2SO4,MgSO4)及温度(5 ℃,20 ℃)等影响因素对水泥砂浆硫酸盐侵蚀类型的影响,以明确碳硫硅酸钙型硫酸盐侵蚀的特性环境条件.试验结果表明:掺加石灰石粉的水泥砂浆试件置于5% MgSO4溶液、5 ℃及20 ℃温度环境下浸泡450 d后,均能生成碳硫硅酸钙.而一般水泥砂浆试件置于5% Na2SO4溶液、5 ℃及20 ℃温度环境浸泡侵蚀后,未生成碳硫硅酸钙.证明水泥混凝土在＞15 ℃的硫酸盐侵蚀环境下亦可生成碳硫硅酸钙,而Mg2 的存在对碳硫硅酸钙的形成过程具有加速催化作用.     

煅烧制度对硫硅酸钙结构及水化性能的影响EI北大核心CSCD

硫硅酸钙水化活性的发挥对新型贝利特-硫铝酸钙-硫硅酸钙水泥力学性能的发展至关重要,为了探寻硫硅酸钙水化活性提升的适宜煅烧制度,采用分析纯试剂于不同煅烧制度下合成硫硅酸钙单矿物。利用扫描电子显微镜、X射线衍射结合Rietveld精修、^(29)Si固体核磁、综合热分析和等温量热仪等,研究了煅烧制度对硫硅酸钙微观结构、晶体结构、水化活性及力学性能的影响。结果表明:一次煅烧制得的硫硅酸钙晶粒形态不规则,尺寸普遍较大(约10μm),而二次煅烧可减小硫硅酸钙晶粒尺寸(约5μm),其形态规则,多数呈现为卵粒状。鼓风急冷可降低硫硅酸钙结晶度,提高其早期水化活性,促进其早期力学性能快速发展。一次煅烧、鼓风急冷制得的硫硅酸钙晶体结构发育程度最低,早期水化活性和发展强度最高。随炉冷却制得的硫硅酸钙结晶度较高,早期水化活性低,但中后期力学性能可快速发展。     

内掺硫酸镁加速水泥基材料TSA破坏

为满足实验室研究水泥基材料的碳硫硅钙石型硫酸盐侵蚀(thaumasite form of sulfate attack,TSA)破坏的需要,研究了一种快速生成碳硫硅钙石的途径。将内掺10%硫酸镁的水泥-石灰石粉净浆样品浸泡在(5±2)℃水中,进行硫酸盐侵蚀加速试验,观察侵蚀后样品外观,并用X射线衍射、红外光谱分析腐蚀产物。结果表明:浸泡6个月后,样品失去强度,变为一种白色、柔软且无黏结力的烂泥状物质,腐蚀产物以碳硫硅钙石、石膏为主,并含有少量钙矾石,具有典型的TSA破坏特征。与硫酸盐溶液外部侵蚀相比,内掺法显著加速水泥基材料TSA破坏。X射线衍射结合红外光谱分析可以有效鉴定碳硫硅钙石存在。     

矿渣对水泥石抗碳硫硅钙石型硫酸盐腐蚀性能的影响

采用抗压强度试验、X射线衍射(XRD)试验、傅里叶红外光谱(FTIR)试验和电子扫描显微镜(SEM)试验研究了不同矿渣掺量的水泥石在5℃,5wt％MgSO4溶液环境下抗压强度、腐蚀产物组成及微观结构特性.结果表明:硫酸盐作为矿渣活性的激发剂,在腐蚀早期能够提高水泥石强度,体系中掺入矿渣能有效改善水泥石抗碳硫硅钙石型硫酸盐腐蚀(TSA)作用.未掺矿渣的普通硅酸盐水泥在5℃,5wt％MgSO4溶液环境中腐蚀产物为白色泥状碳硫硅钙石,其腐蚀类型为典型的碳硫硅钙石型硫酸盐腐蚀;当体系中掺入矿渣后,水泥石硫酸盐腐蚀类型逐渐由TSA型向石膏型转变.矿渣掺量为30％时,体系中既发现了TSA作用产物也发现了石膏型腐蚀产物,当矿渣掺量大于40％时,体系硫酸盐腐蚀类型以石膏型为主.     

矿粉对水泥基材料抗碳硫硅钙石侵蚀破坏的定量分析

研究了矿粉对水泥基材料抗碳硫硅钙石侵蚀性的影响,将制得试件在温度5℃、质量浓度10%MgSO4溶液中养护,对不同龄期试件进行力学性能测试,并对侵蚀产物进行X射线衍射、拉曼光谱定性分析及Rietveld方法定量分析。结果表明：未掺矿粉试件受侵蚀后腐蚀产物中碳硫硅钙石占12.68%,而掺20%和40%矿粉试件中碳硫硅钙石分别只占2.79%和2.19%。矿粉的掺入可以使水泥基材料的抗碳硫硅钙石侵蚀破坏性能提高,但不能完全抑制碳硫硅钙石侵蚀破坏的发生。     

氯离子对碳硫硅钙石形成的影响

研究了氯离子对碳硫硅钙石形成的影响,将水泥-石灰石粉净浆样品浸泡在(5±2)℃不同质量分数的NaCl/Na2SO4复合溶液中,观察侵蚀后样品的外观,并对腐蚀产物进行x射线衍射、红外光谱分析.结果表明:纯Na2SO4溶液中的样品发生碳硫硅钙石型硫酸盐侵蚀,腐蚀产物以碳硫硅钙石及石膏为主,随着时间的延长而日益严重,由表及里...     

硫/有序介孔碳复合材料的制备及其电化学性能

用模板法合成有序介孔碳材料(ordered mesoporous carbon,OMC),以该材料作为硫的载体,用低温熔融的方法制备了硫/有序介孔碳(S/OMC)复合材料.通过透射电子显微镜、比表面分析和X射线粉末衍射仪对材料进行表征.结果表明:OMC孔道有序,比表面积高达1 600m2/g,硫在OMC内分散性良好.对...     

硫硅酸钙对粉煤灰水泥体系性能的影响

硫硅酸钙是硫铝酸盐水泥熟料煅烧过程中形成的一种过渡性矿物,该矿物在Al(OH)4-存在条件下活性可得以有效激发,本文研究了硫硅酸钙对粉煤灰硅酸盐水泥体系凝结时间、强度的影响规律,并对水泥体系7d水化产物进行了XRD分析.结果表明,当硫硅酸钙掺量为5％时,水泥初凝、终凝时间稍微延长,当硫硅酸钙的掺量大于5％时,粉煤灰水泥体系的初凝、终凝时间显著低于未掺粉煤灰的水泥体系;硫硅酸钙5％掺量下可显著提高粉煤灰水泥体系的早期、后期强度,当硫硅酸钙掺量为15％时,水泥强度有所降低;从水化产物的微观分析来看,硫硅酸钙适宜的掺加促进了水泥矿物的水化以及水化产物钙矾石的形成,并且在粉煤灰掺入后,水化产物的形成量增加更加明显.     

温度对碳硫硅钙石形成的影响

研究了环境温度对碳硫硅钙石形成的影响。将浸泡于不同温度的质量分数为10％的MgSO4溶液中的含石灰石粉水泥石试样进行X射线衍射分析、扫描电子显微分析、能谱分析和激光Raman光谱分析。结果表明：掺石灰石粉的水泥石在0～10℃的温度范围内,可形成碳硫硅钙石的硫酸盐侵蚀破坏。环境温度越低,碳硫硅钙石形成得越早。     

碳硫硅钙石形成机制的定量分析

设计了两种人工合成碳硫硅钙石的实验方法以研究水泥基材料中碳硫硅钙石的侵蚀机理。用X射线衍射、Raman光谱对水泥基材料不同龄期的反应产物进行定性分析,并采用Rietveld方法进行定量表征。结果表明：碳硫硅钙石在不能生成钙矾石的环境下仍可形成,说明其可以直接反应生成;在有钙矾石生成的环境下,碳硫硅钙石也可生成,表明碳硫硅钙石形成机理存在Woodfordite转变机理。钙钒石的存在提高了碳硫硅钙石的产率。相比较而言,Woodfordite转变机理比直接生成机理更容易发生,且两种机理可以同时并存。     

SO42-/C3A对单矿C3S水泥浆体中碳硫硅钙石形成的影响

碳硫硅钙石型硫酸盐侵蚀是一种以碳硫硅钙石为生成产物的硫酸盐侵蚀,碳硫硅钙石的形成过程与水泥基材料中铝源及外界环境中硫酸盐密切相关。以铝酸三钙(C₃A)为铝源,Na₂SO₄溶液为侵蚀介质,采用单矿硅酸三钙(C₃S)制备水泥浆体,通过XRD、FTIR、SEM/EDS等测试技术表征不同SO^2-₄与C₃A摩尔比(S/Al比)对单矿C₃S水泥浆体中碳硫硅钙石形成的影响,旨在揭示碳硫硅钙石形成机理并探讨抑制其形成的方法。结果表明:当S/Al比为3时,侵蚀14个月后在侵蚀产物中依然没有检测到碳硫硅钙石;当S/Al比为6和9时,侵蚀3个月即可检测到碳硫硅钙石,这表明外部硫酸根离子浓度越高越有利于碳硫硅钙石的形成。     

XRD, EDX and IR analysis of solid solutions between thaumasite and ettringite

Solid solutions between thaumasite and ettringite were prepared by methods analogous to those well established for the preparation of thaumasite and ettringite. The extent of immiscibility in this system is investigated by varying the Al:Si and SO₄²⁻:CO₃²⁻ ratios in reactant mixtures. The solids produced were analysed by quantitative X-ray diffraction, with Rietveld refinement also providing accurate unit cell dimensions, energy-dispersive X-ray analysis and infrared spectroscopy. The compositional and unit cell variations in the solid solution are discussed. A wide variety of solid solution compositions were produced with both the thaumasite and ettringite structures, but all preparations were considerably diluted by secondary amorphous products.     

混凝土在SO42-和CO32-共同存在下的腐蚀破坏

对西部水工混凝土受地下盐水侵蚀现状进行了现场调查和取样。用X射线衍射、扫描电子显微镜、X射线能量色散谱仪和激光Raman光谱等方法研究了实际运行6a龄期混凝土的腐蚀产物。结果发现：在SO4^2-和CO3^2-长期作用下混凝土的腐蚀产物是由硅灰石膏、钙矾石、石膏和方解石组成的一种白色稀泥状混合物,经对该混合物分析证实处于低温、高湿、硫酸盐、碳酸盐条件下,混凝土发生了硅灰石膏型硫酸盐侵蚀破坏。     

Microstructural study of sulfate attack on ordinary and limestone Portland cements at ambient temperature

This paper presents an investigation on the mechanism of sulfate attack on Portland cements (PCs) containing limestone filler. It is based on the analysis of microstructure and composition of mortar specimens (ASTM C 1012) stored for 2 years in sodium sulfate solution (0.352 M). Microstructure was studied using quantitative X-ray diffraction (XRD) on samples taken from the surface to the core of the specimens. The profile of compounds formed by sulfate attack was determined millimeter by millimeter at 1 and 2 years. Results show that sulfate attack in mortars containing limestone filler is characterized by an inward movement of the reaction front leading first to the formation of ettringite, later to gypsum deposition, and finally to thaumasite formation when the decalcification of mortar leads to the breakdown of C-S-H.     

A thermodynamic and experimental study of the conditions of thaumasite formation

The formation of thaumasite was investigated with the progressive equilibrium approach (PEA). This approach experimentally simulates the conditions of various levels of sulfate addition in hardened cement pastes. The influence of limestone, time, C₃A content, temperature and leaching on thaumasite formation was investigated. The results show that thaumasite formation is favoured at lower temperatures (8 °C) independently of the type of cement clinker (high or low C₃A content) used. Thaumasite was found to form only in systems where limestone was present and where sufficient sulfate had been added. Thaumasite precipitated only in systems where the Al present has already been consumed to form ettringite and the molar SO₃/Al₂O₃ ratio exceeded 3. In leached samples (reduction of portlandite and alkalis) slightly less thaumasite was formed whereas gypsum and ettringite are favoured under these conditions. The PEA, used to investigate the chemical aspects of sulfate attack was found to be a good tool for simulating external sulfate attack. Generally, thaumasite was detected were it was modelled to be stable in significant amounts. However, in this study equilibrium conditions were not reached after 9 months.     

The thaumasite form of sulfate attack in concrete of Yongan Dam

According to microanalytical investigations, it is shown that the concrete of Yongan Dam is deteriorated due to the thaumasite form of sulfate attack (TSA). Analysis results of scanning electron microscopy (SEM), Energy Disperse X-ray (EDX) and X-ray Diffraction (XRD) are supported by the analysis of the concrete composition and the geographical conditions of the dam.     

Thaumasite-ettringite solid solutions in degraded mortars

The thaumasite form of sulfate attack (TSA) has been observed in mortar prisms made from Portland-limestone cements after laboratory storage in 1.8% magnesium sulfate solution at 5 °C for 5 years. The prisms all showed evident signs of degradation, which increased with increasing limestone content. X-ray powder diffraction indicated that a solid solution was formed in all the prisms, which was based on the crystal structure of thaumasite, but extended towards the chemical composition of ettringite. The prism made from the cement with the highest level (35%) of limestone replacement gave the greatest amount of the thaumasite solid solution and had a composition close to the thaumasite end member, whereas those cements with lower (15%, 5% and 0%) levels of replacement gave reduced amounts of the solid solution and had greater lattice parameters. The solid solutions that have been observed are compared with those reported by Barnett et al. for synthetic thaumasite samples grown from sucrose solution.