掺石灰石粉混凝土抗硫酸盐侵蚀性能及改善机理

为提高掺石灰石粉混凝土在硫酸盐环境下的耐久性能,研究掺石灰石粉混凝土抗硫酸盐侵蚀性能以及粉煤灰/矿粉改善机理,通过混凝土硫酸盐干湿循环实验,得到试件外观及抗压强度变化,采用傅里叶红外光谱、XRD、SEM/EDS分析探究侵蚀产物物相组成.研究结果表明,硫酸钠结晶作用和生成的侵蚀产物石膏导致试件膨胀开裂,强度性能下降.石灰石粉的掺入增加了侵蚀产物中石膏的含量,从而引起混凝土试件抗侵蚀性能的下降,单掺25％和50％(质量分数)石灰石粉试件抗压强度耐蚀系数分别下降了23.1％和33.9％.粉煤灰/矿粉与石灰石粉互掺时表现出互补的协同效应,改善了掺石灰石粉混凝土抗硫酸盐干湿循环侵蚀的性能.矿粉的效果优于粉煤灰,胶凝材料采用66％水泥-17％石灰石粉-17％(质量分数)矿粉组成的混凝土表现出最优的抗侵蚀性能.     

内掺白云石水泥基材料抗硫酸盐侵蚀性能

为考察白云石对水泥基材料抗硫酸盐侵蚀性能的影响，本文采用10%、20%、30%(质量分数，下同)白云石掺入水泥净浆与水泥砂浆试件中，在低温条件下浸泡于5%硫酸镁和5%硫酸钠溶液中，并进行硫酸盐侵蚀试验。定期观察试件的宏观形貌变化，并定量分析其侵蚀产物。测定水泥砂浆试件抗折强度与抗压强度并进行宏观分析，以此得出不同种类硫酸盐对试件生成碳硫硅钙石的影响。采用热力学模拟探究白云石对水泥胶凝体系产物的影响。结果表明：当白云石掺量为10%～20%时，能抑制水泥基材料中碳硫硅钙石的生成，水泥基材料的抗硫酸盐侵蚀性能有较大提高，水泥砂浆试件抗折强度有明显改善，这与热力学模拟结果基本一致。     

石膏对碳硫硅钙石型硫酸盐破坏的影响

通过将内掺不同种类和不同质量分数二水石膏的水泥-石灰石粉净浆和胶砂试件在(5±1)℃的低温条件下长期浸泡,并定期观测试件外观形貌与抗压强度变化,同时对净浆试件取样进行X射线衍射和Fourier红外光谱分析,研究了石膏掺量对水泥基材料碳硫硅钙石(TSA)型硫酸盐破坏的影响及破坏机理。结果表明:当净浆试件中石膏掺量≥10%时发生了TSA型硫酸盐破坏,而石膏掺量为7.0%和3.5%的净浆试件均未发生破坏;水泥基材料中的石膏是否会引起TSA型硫酸盐破坏与水泥基材料中所用水泥的铝酸三钙含量有关。     

硫酸盐侵蚀作用下水泥砂浆损伤试验研究

在硫酸盐侵蚀环境下,混凝土内部硫酸盐腐蚀产物的生成是造成混凝土体积膨胀破坏和耐久性劣化的主要原因。通过测定不同硫酸盐侵蚀龄期(30 d,60 d,90 d,120 d,150 d,180 d),不同水灰比(0.4,0.5,0.6)下普通硅酸盐水泥和高抗硫酸盐水泥砂浆的抗折强度,研究硫酸盐侵蚀对砂浆抗折强度的影响。试验结果表明,通过5%硫酸钠溶液长期浸泡试验,水泥砂浆试件抗折强度随着侵蚀龄期的增加呈先增大后下降的变化趋势;对于普通硅酸盐水泥试件来说,水灰比越大,抗折强度开始出现下降的龄期越早;高抗硫酸盐水泥砂浆试件出现强度下降的龄期较普通硅酸盐水泥砂浆晚,且0.4水灰比高抗硫酸盐水泥砂浆试件至侵蚀后期,其抗折强度均未出现明显下降,说明高抗硫酸盐水泥较普通硅酸盐水泥具有较好的抗硫酸盐侵蚀性能。     

硫酸盐侵蚀作用下水泥砂浆膨胀率试验研究

在硫酸盐侵蚀环境下,混凝土内部硫酸盐腐蚀产物的生成是造成混凝土体积膨胀破坏和耐久性劣化的主要原因。通过测定不同硫酸盐侵蚀龄期,不同水灰比下普通硅酸盐水泥和高抗硫酸盐水泥砂浆的膨胀率,旨在研究硫酸盐侵蚀对砂浆膨胀率的影响。试验结果表明,在5%的硫酸钠溶液中长期浸泡的不同试件,其膨胀率均呈现初期增长较快,随后经过一个平稳增长的阶段。在浸泡120 d后,普通硅酸盐砂浆试件0.5和0.6水灰比会由于硫酸盐侵蚀造成的内部损伤,膨胀率出现骤增,而抗硫酸盐水泥由于其较好的抗硫酸盐侵蚀性使其膨胀率仍保持缓慢增长;普通硅酸盐水泥试件在硫酸钠溶液中浸泡150 d后,0.4、0.5和0.6水灰比试件膨胀率分别达到0.162%、0.383%和0.491%,分别为抗硫酸盐水泥砂浆试件膨胀率的1.0倍、2.3倍和2.8倍。说明硫酸盐侵蚀加速了砂浆的体积膨胀速率,同时高抗硫酸盐水泥较普通硅酸盐水泥具有较好的抗硫酸盐侵蚀性能。     

低温对水泥砂浆硫酸盐侵蚀速率的影响试验研究

对于低温环境下普通硅酸盐、抗硫酸盐水泥砂浆试件的硫酸盐侵蚀情况进行了试验研究,建立了两阶段侵蚀破坏模型来反应温度对硫酸盐侵蚀速率的影响.通过将不同水泥品种不同水灰比试件浸泡在5℃、10℃、20℃环境下3％硫酸钠溶液中,以抗折强度为评价指标分析不同温度下硫酸盐侵蚀速率.结果表明:普通硅酸盐水泥、抗硫酸盐水泥砂浆试件随着温度的降低,受到的硫酸盐侵蚀逐渐加剧.抗折强度降低速率随着温度的降低而加快,同时降低水灰比可以提高水泥砂浆抗硫酸盐侵蚀能力.     

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。     

PNIPAM温敏凝胶对水泥材料抗硫酸盐侵蚀性能的影响

利用自制聚N-异丙基丙烯酰胺(PNIPAM)温敏凝胶制备水泥材料,并开展硫酸盐溶液侵蚀试验,测量试件质量与强度变化;同时采用SEM、MIP和水化热测试等手段,研究PNIPAM凝胶对水泥材料抗硫酸盐侵蚀性能的影响机理。结果表明,PNIPAM凝胶相变会释水,促进水泥材料的水化,改善内部孔结构,提高水泥材料力学性能;质量分数为1.0%的PNIPAM凝胶可降低水泥材料受硫酸盐侵蚀的质量损失和强度损失;PNIIPAM凝胶具有相变特性,可以抵消部分膨胀型侵蚀产物对水泥材料内部造成的破坏,提高水泥材料的抗硫酸盐侵蚀性能。     

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.     

5℃环境下水泥砂浆抗硫酸盐侵蚀性能试验研究

研究了不同水泥品种、矿物掺合料对水泥基材料在5℃下抗硫酸盐侵蚀的性能的影响,分别采用普通硅酸盐水泥、中抗硫水泥以及加入矿粉与硅灰的水泥砂浆试件,测试各试样在(5±1)℃的3%Na2 SO4溶液浸泡后的强度变化情况,综合考虑砂浆强度与抗蚀系数对砂浆抗硫酸盐侵蚀性能进行评价,并运用SEM、EDS、XRD分析方法对腐蚀机理进行了分析.结果表明:在5℃环境下,砂浆试样的强度普遍低于常温环境下,砂浆抗硫酸盐侵蚀能力15%矿粉+3%硅灰>中抗硫水泥>15%矿粉+1%硅灰>普通硅酸盐水泥;加入矿物掺合料明显改善了水泥砂浆抗硫酸盐侵蚀性能,并且硅灰的含量越高效果越明显;低温下腐蚀产物不仅有石膏,还有碳硫硅钙石的生成.     

Potential use of natural perlite powder as a pozzolanic mineral admixture in Portland cement

This paper investigates the effect of incorporating natural perlite powder (NPP) as a cement replacement on cementitious materials properties. For this purpose, cement pastes and mortars were prepared by replacing 5, 10, 15, and 20% of NPP by mass of the Portland cement. Physicomechanical performances of pastes and mortars based NPP were inspected using normal consistency, setting times, heat of hydration, and compressive strength testing. Resistance against sodium sulfate attack and sulfuric acid attack were also assessed to investigate the durability characteristics of different mortar mixes. Experimental results show that cement pastes and mortars incorporating up to 20% of NPP demonstrate satisfactory physical and mechanical properties with very comparable results to cementitious materials without NPP. In addition, improved sulfate and acid attacks resistance with increased NPP content were demonstrated. The X-ray diffraction analyses confirm that NPP can be considered as a good pozzolanic material that can be used satisfactorily as a mineral admixture in cement production.     

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.     

Hydration and durability of sulphate-resisting and slag cement blends in Caron's Lake water

The problem of aggressive attack of sulphate and chloride ions has been of considerable scientific and technological interest because this attack is one of the factors responsible for damage to concrete. The corrosive action of chlorides is due to the formation of chloroaluminate hydrates, which causes softening of concrete. Sulphate ions can enter into chemical reactions with certain constituents of concrete, producing sulphoaluminate hydrates and gypsum, which cause the expansion of concrete. The aim of the present work is to study the hydration and the durability of mixed cement (sulphate-resisting and slag cement blends) pastes and mortars in Caron's Lake water. Different mixes of sulphate-resisting cement (SRC) with various proportions of slag cement were prepared and immersed in tap water for 3, 7, 28 and 90 days. The durability of the cement mortars was followed by curing the samples in tap water for 28 days (zero time) then immersed in Caron's Lake water for 1, 3, 6, 9 and 12 months. The hydration behavior was measured by the determination of the compressive strength, free lime, evaporable and nonevaporable water, total chloride and total sulphate contents at each curing time. The increase of substitution of SRC with blast-furnace slag cement (BFSC) up to 30% increases slightly the total pore volume. The free lime contents decrease sharply in the first months of immersion then slightly up to 1 year. The blended cement pastes made of SRC with BFSC up to 30 mass% have lower values of total chloride and total sulphate, while the mortars containing only SRC have lower values of compressive strength than those of all blended cement mortars at all curing ages of immersion under Caron's Lake water. Useful conclusions and recommendations concerning the use of 70 mass% of SRC with 30 mass% slag cement produces a highly durable mixed cement.     

石膏掺量对高阿利特水泥防腐抗渗性能的影响研究

研究了石膏掺量对高阿利特水泥抗海水侵蚀和抗渗性能的影响,并与普通水泥进行了比较。利用XRD、SEM—EDS等测试方法对水泥水化产物的物相组成和形貌进行分析、观察;用压汞法对水泥硬化浆体的孔结构进行了分析。结果表明,石膏掺量对高阿利特水泥硬化浆体的致密性有较大影响,进而影响水泥砂浆的抗海水侵蚀性能,石膏的适宜掺量为5％,在此掺量下高阿利特水泥的抗蚀系数达1．01,而普通水泥的抗蚀系数仅为0．87,高阿利特水泥的有害孔较少,总孔隙率较低,抗渗性能得到较大改善。     

Effect of large amounts of natural pozzolan addition on properties of blended cements

In this study, the effects of 35, 45, and 55 wt.% natural pozzolan addition on the properties of blended cement pastes and mortars were investigated. Blended cements with 450 m²/kg Blaine fineness were produced from a Turkish volcanic tuff in a laboratory mill by intergrinding portland cement clinker, natural pozzolan, and gypsum. The cements were tested for particle size distribution, setting time, heat of hydration, compressive strength, alkali-silica activity, and sulfate resistance. Cement pastes were tested by TGA for Ca(OH)₂ content and by XRD for the crystalline hydration products. The compressive strength of the mortars made with blended cements containing large amounts of natural pozzolan was lower than that of the portland cement at all tested ages up to 91 days. Blended cements containing large amounts of pozzolan exhibited much less expansion with respect to portland cement in accelerated alkali-silica test and in a 36-week sulfate immersion test.     

石灰石粉对砂浆早期强度的影响

石灰石粉作为辅助胶凝材料以其经济环保而备受重视。为了说明石灰石粉掺量对砂浆28d力学性能影响,通过石灰石粉替代水泥比分别为0,10％,20％,30％,40％,50％,60％,并应用灰色理论建立GM（1,1）模型,来定量分析石灰石粉掺量对砂浆抗压强度的影响。     

Properties of alite cements

For carrying out a comprehensive investigation on physical and mechanical properties of alite mortars and concretes, large quantities of monoclinic alite were produced at the University of California at Berkeley. Laboratory-size specimens were employed to determine strength, drying shrinkage, and sulfate resisting characteristics of mortars and concretes made with alite cements. Small amounts of gypsum (3%) addition accelerated the setting and hardening of the alite cements, however, large amounts (6%) resulted in strength deterioration. Drying shrinkage of alite concretes was significantly lower than portland cement concretes of the same fineness. Long term sulfate immersion of concrete specimens made with an alite cement caused serious spalling and strength loss.     

The influence of potassium-sodium ratio in cement on concrete expansion due to alkali-aggregate reaction

In concrete containing potentially reactive aggregates, deleterious alkali-aggregate-reaction (AAR) can be prevented by the use of suitable mineral admixtures or by limiting cement content and alkalis (Na₂O-equivalent) of the cement. However, the Na₂O-equivalent of cement may not always accurately define the potential of cement to cause AAR. In this study, the potential reactivity of concrete produced with cements having similar Na₂O-equivalents but different K/Na-ratios has been measured and the composition of gel has been analyzed. Additionally, pastes and mortars have been produced to study the development of pore solution composition.The expansion of the concrete mixtures shows significant differences depending on the cement used. The different K/Na-ratio present in the cements is reflected in the pore solution of pastes and mortars and in the gel present in aggregates of the concrete mixtures. As the hydroxide concentration in the pore solutions of pastes and mortars produced with the different cements is nearly identical, the difference in K/Na-ratio has to be the reason for the observed differences in concrete expansion.     

掺煅烧石膏水泥早期水化过程的研究

利用DTA，XRD，IR测定水泥水化浆体的化学结合水和Ca(OH)2的生成量，研究了煅烧石膏，二水石膏对硅酸盐水泥早期水化过程的影响。结果表明：在水化龄期相同时，掺煅烧石膏水泥浆体中水化产物同掺二水石膏相比，Ca(OH)2生成量大；在1d前无钙钒石（AFt)生成，结合水量在1d前，前者高于后者，而1d后则相反。指出了煅烧石膏加快水泥水化产物形成的机理在于：由于它的溶解度较低，在水泥水化初期（1d前），存在于水泥中的铝酸盐相不能形成AFt，从而减缓了AFt对水泥水化的延缓作用，加速了整个熟料矿物相的水化。