高性能再生骨料混凝土的性能与微结构

通过制备系列配合比的普通再生骨料混凝土(recycled aggregate concrete,RAC)和高性能再生骨料混凝土(high performance recycled aggregate concrete,HPRAC),研究再生骨料取代量对混凝土性能和微结构的影响.结果表明:RAC的力学性能和耐久性随着再生骨料取代量的增加而有所降低,但HPRAC仍具有良好的力学性能,并且抗渗性较高,具有抵抗300次冻融循环的耐久性.HPRAC水泥石基体较为密实,界面过渡区被致密的水化产物填充,孔隙变小,氢氧化钙和钙矾石含量均较少.     

冻融循环下受硫酸镁侵蚀混凝土内腐蚀产物热分析研究

进行了冻融条件下硫酸镁侵蚀混凝土腐蚀试验.采用热分析技术,对侵蚀混凝土内腐蚀产物进行了辨别和定量分析.结果表明:冻融循环与硫酸镁侵蚀共同作用下,混凝土腐蚀产物主要是钙矾石和石膏;混凝土中钙矾石和石膏的含量表层比第二层多,在同一深度处,腐蚀产物的含量随着冻融循环次数的增加而增多,但达到一定的冻融循环次数,表层中钙矾石含量有所降低,且第二层中钙矾石含量大于第一层.     

硫酸盐侵蚀下混凝土内腐蚀反应-扩散过程的实验研究

通过开展硫酸盐腐蚀试验,研究了硫酸盐侵蚀环境下混凝土中内部硫酸盐浓度随时间和空间的变化规律,探讨了混凝土内部各组分浓度的变化与硫酸根离子浓度之间的关系.结果表明:随着侵蚀时间的增加,反应扩散不断进行,混凝土内部硫酸根离子浓度不断增加,越靠近侵蚀表面浓度越高;水泥水化产物中二水石膏、氢氧化钙和腐蚀产物的浓度变化与硫酸盐浓度变化之间存在一定的联系,随着二水石膏和氢氧化钙含量的减少,钙矾石含量前期增长较快,后期渐渐趋于稳定,硫酸盐浓度变化速率不断减小,直至混凝土内外环境中硫酸盐浓度差达到平稳状态.     

抗硫酸盐侵蚀防腐剂对混凝土性能影响

在相同配合比条件下,选用三种不同性能的水泥配制混凝土,研究不同种类胶凝材料对混凝土的工作性能、力学性能以及抗侵蚀性能的影响.通过SEM扫描电镜观察混凝土3d、7d、28 d的浆体—骨料界面过渡区的微观结构以及水化产物形貌.试验结果表明:掺入10％ SSP防腐剂后,混凝土的工作性能、力学性能均优于基准和抗硫酸盐水泥混凝土.水泥水化后期,浆体—骨料界面过渡区很难区分,水化产物增多.SSP防腐剂可以促进水泥的水化程度,生成较多的钙矾石和C-S-H凝胶,使结构更致密,提高混凝土的抗侵蚀性能.     

硫酸盐侵蚀下钙矾石的形成和膨胀机理研究现状

钙矾石是水泥混凝土硫酸盐侵蚀过程中的重要产物之一,钙矾石的形成可能会引起混凝土膨胀、开裂,本文在讨论水泥混凝土中钙矾石的形成和形貌的基础上,从钙矾石的形成环境-反应机理-形貌-膨胀机理出发综述了不同反应机制下形成的钙矾石对应的膨胀性能及钙矾石型硫酸盐侵蚀的膨胀机理,最后对钙矾石型硫酸盐侵蚀现状进行了总结.     

硫酸盐侵蚀作用下混凝土损伤层与微观研究

混凝土损伤层性能劣化规律对研究硫酸盐侵蚀作用下混凝土耐久性具有重要意义.采用超声波平测法,研究了硫酸盐与干湿交替作用下不同水胶比混凝土的损伤层厚度变化规律,从损伤层角度分析了混凝土的损伤劣化特点与性能退化规律,并采用X衍射方法对混凝土中的主要侵蚀产物进行分析.研究结果表明:随着水胶比增大,混凝土中钙矾石和石膏不断增多,氢氧化钙含量逐步减小,宏观表现为混凝土损伤层中超声波速逐渐减小,损伤层厚度增大.当混凝土损伤层越厚、声速越低时,表明其密实度降低,损伤劣化程度增大.通过测量混凝土损伤层厚度,可以有效判断硫酸盐侵蚀作用下混凝土损伤劣化情况.     

外部硫酸盐侵蚀作用后混凝土的侵蚀特征研究

通过逐层分析的方法对硫酸盐侵蚀后混凝土的侵蚀产物进行了定性研究。研究表明,在5%Na2SO4溶液干湿循环作用后,混凝土的损伤程度由表及里逐渐降低;石膏广泛存在于混凝土表层,表层下方存在大量石膏和极少量钙矾石,内部区域石膏和钙矾石共存。石膏是硫酸钠侵蚀最主要的产物,是导致混凝土表层粉化和胶凝特性完全丧失的主要原因。     

废轮胎橡胶混凝土界面过渡区特征试验研究

采用SEM、EDS等测试技术,研究了1~3 mm废轮胎橡胶颗粒混凝土中橡胶与水泥石界面过渡区(ITZ)的微观形貌,水化产物分布以及ITZ宽度。结果表明:橡胶混凝土中橡胶与水泥石的界面粘结较普通混凝土中粗骨料与水泥石更为薄弱,ITZ的结构较为松散,孔隙率也较大;界面区水化产物中C-S-H凝胶含量小于普通混凝土,氢氧化钙晶体(CH)和钙矾石晶体(AFt)的含量则大于普通混凝土;1~3 mm橡胶颗粒混凝土ITZ宽度约为50 μm,而普通混凝土仅有40 μm,比普通混凝土更加不稳定。     

基于微观分析研究钙矾石在硫酸镁溶液中的稳定性

当水泥混凝土材料进行服役时往往会受到MgSO4的侵蚀,在该过程中常伴随着各种物理与化学变化.通过研究浸泡MgSO4溶液中达到两年的水泥砂浆试块中钙钒石等物质变化,并通过合成钙钒石研究这一趋势的变化规律.结果 表明,在水泥砂浆试块中存在由钙矾石向石膏转化的趋势.通过合成钙矾石的热重-差热分析研究该过程中的变化,实验结果表明在碱性环境下的钙矾石在硫酸镁的存在下会分解成石膏等产物.通过对差示扫描量热仪数据进行微分处理研究其中Mg(OH)2的变化,并发现在碱性环境下随着外界硫酸镁溶液的增加Mg(OH)2的含量也逐渐增加.     

一种新形态钙矾石—管状钙矾石

用扫描电镜、Ｘ射线能谱仪观测和分析了硫铝酸盐水泥系列的水化产物钙矾石的一种特殊显微形貌－管状钙矾石。在水泥净浆试体中、界面上、不同石膏掺量的水泥浆试体、砂浆试体、水化的熟料颗粒中均可观测到管状钙矾石。它的形成可能与非平衡状态生产的熟料中Ｃ４Ａ３Ｓ矿相的某种晶体结构有关。     

Sulfate attack on alkali-activated slag concrete

This paper presents an investigation into durability of alkali-activated slag (AAS) concrete in sulfate environment. Two tests were used to determine resistance of AAS concrete to sulfate attack. These tests involved immersion in 5% magnesium sulfate and 5% sodium sulfate solutions. The main parameters studied were evolution of compressive strength, products of degradation, and microstructural changes. After 12 months of exposure to the sodium sulfate solution, the strength decrease was up to 17% for AAS concrete and up to 25% for ordinary Portland cement (OPC) concrete. After the same period of exposure to the magnesium sulfate solution, the compressive strength decrease was more substantial, up to 37% for OPC and 23% for AAS. The main products of degradation were ettringite and gypsum in the case of Portland cement and gypsum in AAS. OPC samples had significant expansion, cracking, and loss of concrete, while AAS samples were not expanded but cracked in the test. During experiments with the sodium sulfate solution, some increase in strength of AAS concrete was recorded, likely due to continuing hydration.     

不同硫酸盐环境下铝酸三钙的劣化过程及机制

主要研究了硫酸钠和硫酸镁溶液对铝酸三钙（C₃A）单矿浆体损伤的影响,使用外观、膨胀率、质量变化研究了浆体宏观性能的劣化,并进一步采用半定量X射线衍射分析（XRD）和扫描电子显微镜（SEM）分析了浆体的侵蚀产物含量和微结构,最后采用光学显微镜原位研究了C₃A-CaSO₄体系下钙矾石的形成特征。研究结果表明：外部的硫酸根能够扩散进入水泥基材料与含铝相的水化产物发生反应形成钙矾石,针棒状钙矾石在有限的空间中不断形成,会导致试件膨胀并引起质量的增加。在硫酸钠溶液中浸泡120 h后浆体中钙矾石质量分数上升到20.12%,而硫酸镁溶液中浆体的钙矾石质量分数仅为6.87%。与硫酸钠溶液不同,镁离子的存在会与孔溶液中的氢氧根发生反应形成氢氧化镁附着在表层,抑制了外部硫酸根的侵入,同时该环境下氢氧根的消耗引起的较低pH有利于石膏的生长。     

On the relevance of volume increase for the length changes of mortar bars in sulfate solutions

The ingress of sulfate ions into cementitious materials leads to the formation of ettringite, gypsum and other phases. The increase in solid volume through the formation of these phases is often assumed to be the only reason for expansion. In this paper we systematically compare the volume increase predicted by thermodynamic modeling to macroscopic expansion for mortars made with CEM I in different sulfate solutions and for mortars made with a range of blended cements in sodium sulfate solution. It is shown that the length changes cannot be explained by simple volume increase alone.A more plausible explanation of expansion lies in the theory of crystallization pressure, in which crystals forming from a supersaturated solution may exert pressure on their surroundings. It is observed that expansion occurs in systems where thermodynamic modeling predicts the co-existence of ettringite with gypsum. In such a case, if monosulfate and gypsum are both present locally, the solution can be highly supersaturated with respect to ettringite, whose formation in confined conditions (such as within C–S–H) can then exert expansive forces.     

Effects of gypsum formation on the performance of cement mortars during external sulfate attack

Sodium sulfate attack was studied on C₃S mortars, along with ASTM Type I Portland cement (PC) mortars, in an attempt to independently evaluate the effect of gypsum formation on the performance. The quantity of gypsum and ettringite, as measured by differential scanning calorimetry (DSC), increased with the time of immersion in the sulfate solution. An increase in length of the mortar specimens was also registered along with the increase in the quantity of gypsum. This result suggests that the formation of gypsum could be expansive. Indeed, considerable expansion, although delayed compared to PC mortars, was observed in the C₃S mortars. Thus, it can be concluded that the expansion of the PC mortars occurred due to the combined effect of gypsum and ettringite formation, while the expansion of C₃S mortars occurred as a result of gypsum formation.Thaumasite formation as small inclusions was also detected in both the C₃S and the PC mortars, especially in regions of high gypsum deposition. The formation of thaumasite, despite the absence of carbonate bearing minerals and low temperatures, could be because of the carbonation of the surface zones of the mortars. However, it would be speculative to attribute any expansion to the formation of thaumasite, since it was detected only in minute amounts in the microstructural investigation.     

石膏矿渣水泥混凝土抗硫酸钠侵蚀性能研究

石膏矿渣水泥具有低水化热、良好抗化学侵蚀性能等优点,是一种低碳绿色胶凝材料。为了明确原材料对石膏矿渣水泥混凝土抗硫酸盐侵蚀性能的影响,对比研究了不同化学组成及活性矿粉制备的石膏矿渣水泥混凝土的强度发展及抗硫酸钠侵蚀性能。结果表明:提高矿粉中Al₂O₃含量可以有效提高石膏矿渣水泥混凝土早期3 d强度;石膏矿渣水泥混凝土在硫酸钠环境下表现出强度软化型劣化;提高水泥用量、降低水灰比可以有效提高低活性矿粉制备的石膏矿渣水泥混凝土的抗硫酸钠侵蚀性能,但不利于高活性矿粉制备的石膏矿渣水泥混凝土的抗硫酸钠侵蚀性能。研究为低活性矿粉制备石膏矿渣水泥混凝土及其寿命预测提供试验数据支撑。     

Micro-Analysis of ＂Sulfate Salt Weathering Distress on Concrete＂：Ⅱ.Concrete

运用环境扫描电镜、能谱仪和X射线衍射等微观分析手段研究了稳定环境中,半浸泡混凝土试件在硫酸钠和硫酸镁溶液中的劣化破坏特征,以及混凝土碳化对＂混凝土硫酸盐结晶破坏＂的影响。结果表明：粗骨料界面过渡区生成的大量钙矾石和石膏等晶体是引起混凝土试件劣化的原因;在碳化混凝土内发现了硫酸钠结晶破坏现象。     

粉煤灰与矿渣、硅灰复掺混凝土干湿循环下抗硫酸盐侵蚀性能研究

为探索粉煤灰与矿渣、硅灰复掺混凝土干湿循环作用下的抗硫酸盐侵蚀性能,在室内开展了三组掺合料混凝土在3种不同浓度硫酸根溶液侵蚀以及4种硫酸盐溶液侵蚀下的干湿循环和抗压试验。结果表明:掺合料种类对混凝土抗硫酸盐侵蚀能力的影响较大,掺入硅灰能明显提升混凝土抗硫酸盐侵蚀能力,复掺15%粉煤灰+30%矿渣+5%硅灰试验组的抗硫酸盐侵蚀能力最强;硫酸根离子浓度越高,生成的钙矾石和石膏量越多,混凝土的抗侵蚀能力越弱;MgSO_4对混凝土的侵蚀能力强于Na_2SO_4,掺入NaCl能减弱硫酸盐的侵蚀能力,混凝土对四种硫酸盐的抗侵蚀能力大小依次为:5% Na_2SO_4+3.5%NaCl>5% Na_2SO_4>5%MgSO_4+3.5%NaCl>5%MgSO_4。     

石灰石粉对水泥基材料抗硫酸盐侵蚀性的影响及其机理

用天然石灰石粉等质量取代水泥20%和30%,将制备的水泥净浆和砂浆试件常温浸泡在0.35 mol/L Na2SO4溶液中,测量试件的线长度和抗折强度随浸泡时间的变化.结果表明:石灰石粉对水泥基材料的抗硫酸盐性有严重的影响,它们使水泥基材料在硫酸盐环境中的强度急剧下降并导致水泥基材料产生较大体积膨胀,引起开裂.掺石灰石粉的水泥基材料主要因形成大量较大尺寸的石膏晶体而膨胀开裂.石膏的形成导致硫酸盐侵蚀水泥基材料产生膨胀开裂.因此,在硫酸盐侵蚀环境下,不宜采用含石灰石粉的复合水泥或将石灰石粉作为矿物掺合料制备的混凝土.     

Differentiating seawater and groundwater sulfate attack in Portland cement mortars

The study reported in this article deals with understanding the physical, chemical and microstructural differences in sulfate attack from seawater and groundwater. Portland cement mortars were completely immersed in solutions of seawater and groundwater. Physical properties such as length, mass, and compressive strength were monitored periodically. Thermal analysis was used to study the relative amounts of phases such as ettringite, gypsum, and calcium hydroxide, and microstructural studies were conducted by scanning electron microscopy. Portland cement mortars performed better in seawater solution compared to groundwater solution. The difference in performance could be attributed to the reduction in the quantity of the expansive attack products (gypsum and ettringite). The high Cl concentration of seawater could have played an important role by binding the C₃A to form chloroaluminate compounds, such as Friedel's salt (detected in the microstructural studies), and also by lowering the expansive potential of ettringite. Furthermore, the thicker layer of brucite forming on the specimens in seawater could have afforded better protection against ingress of the solution than in groundwater.     

Influence of bicarbonate ions on the deterioration of mortar bars in sulfate solutions

This work investigates the influence of bicarbonate ions on the deterioration of cementitious material exposed to sulfate ions. Mortars based on a CEM I and on a CEM III/B cement were investigated. Experimental investigations were compared to thermodynamic modeling and phase characterization to understand the differences in deterioration.The presence of bicarbonate ions significantly reduced the expansion of the CEM I mortars. Thermodynamic modeling showed that at high concentrations of bicarbonate ettringite and gypsum become unstable. Microstructural characterization combined with information from thermodynamic modeling suggests that conditions of high supersaturation with respect to ettringite are unlikely in the samples exposed in solutions containing bicarbonate. Consequently, expansive forces are not generated by the crystallization pressure of ettringite.There was little expansion of the CEM III/B sample even in the sodium sulfate solution. In the bicarbonate solution this mortar showed a highly leached zone at the surface in which calcite was observed.