【作者】 刘鹏；

【导师】 杨长辉；

【作者基本信息】 重庆大学 ， 材料科学与工程， 2022， 硕士

【摘要】 我国盐渍土、盐湖分布广泛,海岸线绵长,在该类环境中的混凝土易受到硫酸盐化学腐蚀和物理结晶破坏。碱矿渣混凝土具有优良的抗硫酸盐化学腐蚀性能,具有较好的应用前景,然而其具有较强的吸水性,其孔溶液离子浓度大,具有较大的硫酸盐结晶破坏风险。因此明确碱矿渣混凝土的综合抗硫酸盐侵蚀性能对碱矿渣水泥及混凝土的研究和应用具有理论意义和实用价值。本文研究了半浸泡条件下碱矿渣砂浆的抗硫酸盐侵蚀性能,讨论了硫酸盐浓度、砂浆水胶比和碱当量等参数对碱矿渣砂浆的表观结晶、力学性能和质量变化的影响;测试了碱矿渣砂浆内部碱度及SO₄^2-、Na⁺、Ca²⁺和Mg²⁺的浓度变化;通过XRD、FTIR、热分析、SEM-EDS和BSE等技术研究了碱矿渣砂浆的微观结构及水化产物的稳定性;结合试验结果与相关理论,分析了半浸泡条件下碱矿渣砂浆硫酸盐侵蚀破坏机理。研究揭示的主要规律如下:碱矿渣砂浆的吸水速率和吸水量都能够达到普通硅酸盐水泥砂浆的1.5～2倍,碱矿渣砂浆吸水速率随砂浆水胶比增大而增大。碱矿渣砂浆在硫酸钠溶液中的毛细吸收速率会出现一定程度的降低,但吸收量基本保持不变。半浸泡条件下碱矿渣砂浆在90-120d内开始出现明显的表面结晶,侵蚀龄期小于120d时,碱矿渣砂浆抗压强度持续增长,大于120d后持续降低,在360d时的抗压强度相对于120d时下降了16.4%。碱矿渣砂浆的硫酸钠结晶破坏程度随水胶比和碱当量的增大而增大,普通硅酸盐水泥砂浆结晶程度弱于碱矿渣砂浆。半浸泡条件下碱矿渣砂浆蒸发区域的SO₄^2-浓度快速增长,砂浆各区域的SO₄^2-浓度与其表面盐结晶特征相对应。水胶比和硫酸钠溶液浓度的增大会促进碱矿渣砂浆各区域的SO₄^2-浓度增长。碱矿渣砂浆内部存在大量Na⁺,导致其更易达到硫酸钠过饱和,半浸泡条件下碱矿渣砂浆内部的碱会持续溢出,内部碱度降低。碱矿渣砂浆浸泡区域和蒸发区域内部均分布有大量微裂纹,且微裂纹占比接近,半浸泡条件下碱矿渣砂浆硫酸盐侵蚀主要发生在砂浆表面。碱矿渣砂浆水化产物具有较好的稳定性,未发生其它明显化学反应,砂浆的破坏主要由硫酸钠结晶导致。碱矿渣砂浆的高吸水性和内部高离子浓度导致其具有更大的硫酸盐结晶破坏风险。半浸泡条件下碱矿渣砂浆的硫酸盐侵蚀破坏过程主要分为三个阶段:（1）砂浆浸泡区域通过毛细作用吸收硫酸钠溶液进入砂浆内部,砂浆蒸发区域水分不断蒸发,硫酸钠在砂浆表面不断聚集,浓度不断增大;（2）随着浓度的进一步增大达到硫酸钠的超饱和状态,硫酸钠晶体开始生长,砂浆表面开始出现结晶;（3）碱矿渣砂浆表面结晶程度达到破坏基体的相关要求,砂浆表层开始脱落,强度出现降低。更多还原

【Abstract】 Saline soils and saline lakes are widely distributed in China and the coastline is quite long.Concrete in this kind of environment is susceptible to chemical corrosion of sulfate and physical crystallization damage.Alkali-activated slag（AAS）concrete has excellent resistance to chemical sulfate corrosion and has a good application prospect.However,it has a strong water absorption,and its pore solution has a large ion concentration,which has a great risk of sulfate crystallization destruction.Therefore,it is of theoretical significance and practical value to clarify the comprehensive sulfate resistance of AAS concrete for the research and application of AAS cement and concrete.In this paper,the sulfate attack resistance of AAS mortar in partial immersion environment was studied,and the effects of sulfate concentration,water-binder ratio and alkali equivalent on surface crystallization,mechanical properties and quality of AAS mortar were discussed.The changes of alkalinity and concentration of SO₄^2-,Na⁺,Ca²⁺and Mg²⁺in AAS mortar were measured.The microstructure of AAS and the stability of hydration products were studied by XRD,FTIR,thermal analysis,SEM-EDS and BSE.Combined with the experimental results and related theories,the sulfate erosion mechanism of AAS mortar in partial immersion environment was analyzed.The main rules revealed by the study are as follows:The water absorption rate and amount of AAS mortar can reach 1.5～2 times of ordinary Portland cement（OPC）mortar,and the water absorption rate of AAS increases with the increase of water-binder ratio of mortar.The water absorption rate of AAS mortar in sodium sulfate solution decreased to a certain extent,but the water absorption quantity basically remained unchanged.The surface crystallization of AAS mortar began to appear within 90-、120 days,and its compressive strength continued to increase in the first 120 days,and continued to decrease after 120 days in partial immersion environment.The compressive strength at 360 days decreased by 16.4%compared with that at 120 days.The damage degree of sodium sulfate crystallization of AAS mortar increased with the increase of water-binder ratio and alkali equivalent,and the crystallization degree of OPC mortar is weaker than that of AAS mortarThe concentration of SO₄^2-in evaporation area AAS mortar increased rapidly in partial immersion environment,and the concentration of SO₄^2-in each area of mortar corresponds to its surface salt crystallization characteristics.The increase of water-binder ratio and sodium sulfate solution concentration can promote the increase of SO₄^2-concentration in each area of AAS mortar.There was a large amount of Na⁺in AAS mortar,which made it easier to reach sodium sulfate supersaturation,and the alkali in AAS mortar will continue to overflow in partial immersion environment.There are a large number of micro-cracks in the soaking and evaporation areas of AAS mortar,where the proportion of micro-cracks is close to each other.sulfate erosion mainly occurred on the surface of AAS mortar.The hydration products of AAS mortar had a good stability,and no other obvious chemical reaction occurred.The damage of mortar was mainly caused by sodium sulfate crystallization.The water absorption and high ionic concentration of AAS mortar led to a greater risk of sulfate crystallization destruction.The process of sulfate erosion and destruction of AAS mortar in partial immersion environment can be divided into three stages:（1）The soaking area of mortar absorbed sodium sulfate solution into the mortar interior through capillary action,and the water in the evaporation area of mortar began to evaporate continuously,and the sodium sulfate accumulates on the mortar surface with increasing concentration;（2）With the further increase of concentration to reach the supersaturated state of sodium sulfate,sodium sulfate crystals began to grow,and the surface of mortar began to crystallize;（3）The surface crystallization degree of AAS mortar reached the relevant requirements of matrix destruction,and the surface of mortar began to fall off,and the strength decreased.更多还原