硫酸盐侵蚀下石膏形成引起的水泥净浆破坏

通过掺加石灰石粉,对长期浸泡在5%(质量分数)Na2SO4溶液中的水泥净浆试件所产生的有害化合物进行了研究.结果表明:在Na2SO4溶液侵蚀下,水泥净浆试件因产生石膏膨胀开裂、表面软化而形成从表到里的破坏,石膏膨胀是其主要劣化方式;水泥净浆破坏机理是石膏膨胀和胶凝物质分解;保持浸泡溶液的pH值,会抑制水泥净浆试件中钙矾石的生成.因此,在水泥混凝土中加入石灰石粉可以检验其抗硫酸盐侵蚀性能.     

混凝土硫酸盐侵蚀破坏机理与预防措施

根据腐蚀产物将水泥混凝土硫酸盐侵蚀分为钙矾石型和碳硫硅酸钙型两大类,分析了不同类型硫酸盐侵蚀的发生条件、化学反应机理和混凝土外观破坏特征,并从原材料选择、配合比设计等方面提出不同类型硫酸盐侵蚀破坏的预防措施,从而为实际混凝土工程硫酸盐侵蚀破坏原因分析和耐久性设计提供参考。     

碳硫硅钙石的结构特征及其对水泥基材料造成的破坏

概述了碳硫硅钙石的晶体结构特征,存在于水泥基材料中的碳硫硅钙石的形成机理和破坏特点,对建筑工程中碳硫硅钙石型硫酸盐侵蚀的破坏阶段进行了详细的描述,最后提出了防护碳硫硅钙石侵蚀发生的措施。     

地聚物抗硫酸盐侵蚀性能的试验研究

对地聚物和普通硅酸盐水泥的抗硫酸盐侵蚀性能进行了试验研究,通过研究地聚物的抗硫酸盐侵蚀机理,采用干湿循环法,对侵蚀后的产物进行了X射线衍射分析,结果表明:在5%的硫酸钠溶液中,地聚物砂浆主要是由于硫酸钠浸入试块孔隙中盐结晶体积膨胀而破坏。     

盐渍土中硫酸盐对混凝土造成侵蚀的机理综述

输电线路基础处于盐渍土的服役环境中时,硫酸盐侵蚀对混凝土的破坏是威胁输电线路基础耐久性的一个重要原因。作为一项复杂的物理化学作用,硫酸盐侵蚀机理受胶凝材料、水灰比、侵蚀介质等多种因素影响。本文从物理作用和化学作用两个角度分别阐述了硫酸盐侵蚀对混凝土耐久性破坏的机理,并论述了不同矿物掺合料对混凝土抗硫酸盐侵蚀性的影响。     

水泥基灌浆料加固梁试验研究与开裂模型分析北大核心CSCD

相较于传统的现浇梁,用水泥基灌浆料增大截面法加固的梁的破坏机理和开裂模型发生了变化。经典的钢筋混凝土结构理论已不能完全适用于加固梁的性能分析。为了研究加固梁的破坏机理和开裂模型,对3根水泥基灌浆料加固的钢筋混凝土梁进行试验研究。通过研究发现,用水泥基灌浆料加固后梁的开裂承载力相较于加固前提高5~7倍,由此提出了水泥基灌浆料加固梁基于桁架模型的开裂破坏模型理论,很好地解释了水泥基灌浆料加固梁开裂破坏的作用机理。     

水泥基材料抗TSA侵蚀性能影响因素研究

研究了不同配合比掺石灰石粉水泥砂浆在不同硫酸盐溶液中浸泡1年期间的外观、强度和矿物成分变化。结果表明,水灰比越低,砂浆抗TSA侵蚀性能越好;不同品种水泥的抗TSA侵蚀能力由高到低依次为:硫铝酸盐水泥>抗硫酸盐水泥>普硅水泥;掺硅灰和矿渣细粉均能明显改善混凝土抗TSA侵蚀性能,且矿渣粉掺量越大效果越明显。镁盐对碳硫硅酸钙晶体(thaumasite)的生成和TSA侵蚀破坏具有一定促进作用;水泥基材料TSA侵蚀破坏也可能发生于15℃以上环境中,环境温度对水泥基材料整体抗硫酸盐侵蚀性能的影响规律与材料组分有关。     

水泥基灌浆料加固梁试验研究与开裂模型分析

相较于传统的现浇梁,用水泥基灌浆料增大截面法加固的梁的破坏机理和开裂模型发生了变化。经典的钢筋混凝土结构理论已不能完全适用于加固梁的性能分析。为了研究加固梁的破坏机理和开裂模型,对3根水泥基灌浆料加固的钢筋混凝土梁进行试验研究。通过研究发现,用水泥基灌浆料加固后梁的开裂承载力相较于加固前提高5~7倍,由此提出了水泥基灌浆料加固梁基于桁架模型的开裂破坏模型理论,很好地解释了水泥基灌浆料加固梁开裂破坏的作用机理。     

混凝土抗硫酸盐侵蚀性能的测试与评价方法综述

对当前国内外关于水泥混凝土抗硫酸盐侵蚀的各种测试评价方法进行了评述.从侵蚀环境、评价方法、侵蚀机理等角度分析了这些方法的合理性及不足之处,并提出了有待解决的问题.     

碳硫硅钙石对混凝土的破坏作用

阐述了碳硫硅钙石（thaumasite)的形成机理、形成条件及破坏机理。指出在低温环境下,当混凝土中存在C－S－H凝胶、碳酸盐、硫酸盐及充足的水时,混凝土中可形成碳硫硅钙石,使混凝土遭受破坏,并对此提出了预防措施。     

利用Wiener过程探究镁水泥混凝土中涂层钢筋在盐类环境下的腐蚀寿命

采用氯盐溶液和硫酸盐溶液浸泡镁水泥钢筋混凝土构件,使构件中的涂层钢筋加速锈蚀,并利用电化学工作站进行电化学试验;以腐蚀电流密度作为钢筋耐久性退化指标,建立一元Wiener过程预测模型进行钢筋腐蚀寿命预测.结果 表明:在氯盐溶液环境下,镁水泥混凝土构件中的钢筋受腐蚀问题较之硫酸盐溶液环境更为突出,且涂层在2种盐溶液环境中均对钢筋起到了较好的防护效果;在氯盐溶液环境中,涂层钢筋在1500 d附近进入中等腐蚀阶段,在硫酸盐溶液环境中,涂层钢筋在22000 d进入中等腐蚀阶段.     

Significance of compaction time delay on compaction and strength characteristics of sulfate resistant cement-treated expansive soil

The addition of cement for stabilization of expansive soils is one of the most commonly used methods. As with every calcium-based stabilizer, the time delay between the physical mixing of the stabilizer and compaction plays an important role in achieving the desired results after stabilization. However, a clear insight on the determination of optimum time delay for achieving the maximum desired compaction properties of cement-stabilized soils is yet to be established. Furthermore, the recent studies highlighted the use of sulfate to mitigate the negative effect of compaction time delay. The only drawback with the use of sulfate along with calcium-based stabilizers is the formation of ettringite, which deteriorates the stabilized soil matrix. In view of this, the present study is aimed at using the sulfate resistant cement (SRC) as a stabilizer along with the controlled addition of sulfate solutions to mitigate the negative effect of compaction time delay in stabilizing the expansive soil. To bring out the above effects, three periods of time delays (0 h, 6 h and 24 h) and three sulfate concentrations of 5000 parts per million (ppm), 10,000 ppm and 20,000 ppm were adopted. The experimental results showed that the delay in compaction resulted in the formation of clogs and reduction of strength of SRC-stabilized expansive soil. Upon sulfate addition to SRC-stabilized expansive soil, the formation clogs was not curtailed and resulted in the formation of ettringite clusters. These formations were captured with the help of scanning electron microscope (SEM) images and validated with electron dispersive X-ray spectroscopy (EDAX) analysis. Further, an attempt is also made to explain the mechanism of density and strength reduction with the aid of physico-chemical properties and mercury intrusion porosimetry (MIP) studies.     

水泥基材料在腐蚀环境中生成碳硫硅钙石的机理研究

为探索石灰石粉混凝土在低温硫酸盐环境下生成碳硫硅钙石的机理,将石灰石粉混凝土及采用硫铝酸盐水泥制备的水泥基胶凝材料分别浸泡于质量分数为10%的硫酸镁溶液和碳酸钠溶液中,进行抗压强度测试,并通过扫描电镜(SEM)、X射线衍射(XRD)及红外光谱等微观试验手段,研究并分析了碳硫硅钙石的形成原因.结果表明:低温硫酸镁溶液中的石灰石粉混凝土抗压强度随浸泡时间的延长呈现先增长后减小的趋势,表面出现膨胀剥落现象,生成大量的二水石膏,发生膨胀腐蚀;碳酸钠溶液中的硫铝酸盐水泥基胶凝材料发生了泥化现象,其抗压强度随浸泡时间延长逐渐降低,内部水化产物钙矾石随浸泡时间延长逐渐减少,发生异相结晶转换生成碳硫硅钙石.混凝土中掺加石灰石粉并不是造成碳硫硅钙石型硫酸盐腐蚀(TSA)的主要因素,水泥基胶凝材料硬化体中的钙矾石长期处于含CO2-3环境中才会生成大量烂泥状的碳硫硅钙石,造成胶凝材料破坏.     

钢筋砼结构受硫酸盐腐蚀及其处理方法的几点探讨

为研究硫酸盐腐蚀下结构耐久性及其修复,本文主要针对钢筋混凝土结构,分析硫酸盐腐蚀的机理,论述了受蚀前提高钢筋混凝土结构耐久性的措施,探讨了修复和加固受蚀后钢筋混凝土结构的方法,并以一化工厂为例,在其受蚀后,采用添加一定比例外加剂的普通硅酸盐水泥进行修复,结果表明新老混凝土结合良好,工作状态正常。通过分析其腐蚀机理得到的修补措施行之有效。     

石灰石粉混凝土及其硫酸盐侵蚀特性综述

石灰石粉是一种新型的混凝土掺合料,推动绿色混凝土的发展.主要介绍了石灰石粉在混凝土中的应用情况和国内外研究现状,对石灰石粉混凝土的性能做了简要的概述;同时,介绍了掺入石灰石粉对水泥石的TSA破坏机理,并提出了相应的改善措施,在保证混凝土性能不变的情况下,充分有效利用石灰石粉;最后,对其应用前景及研究方向做了简要分析.     

Chemical sulfate attack performance of partially exposed cement and cement + fly ash paste

When concrete elements are partially exposed to sulfate rich environment, the upper part of concrete in contact with air will be deteriorated more severely than the underground part. Fly ash additions seem to accelerate the collapse of concrete in such an environment. Although concrete technologists attribute concrete damage mainly to salt crystallization or physical sulfate attack, the influence of chemical sulfate attack cannot be neglected and should also be studied.The objective of this paper is twofold. First, pore solution expression test was conducted to squeeze pore solution of different parts of cement paste partially exposed to Na₂SO₄ solution. The sulfate concentration and pH value of pore solution were measured. Results showed that the sulfate concentration of the pore solution in the upper part of paste in contact with air was much higher than in the lower submerged part. Fly ash additions could draw more sulfates into the paste in a shorter time, forming a higher concentration sulfate pore solution than in normal concrete.The second test was designed to simulate the effect of severe exposure condition on reactive products of cement paste. Pure cement and cement + fly ash (25% dosage) pastes were immersed in 5%, 15% and 30% at 30 °C and 15% at 40 °C Na₂SO₄ solutions. Thermogravimetric analysis was used to analyze the reaction products of the paste. The results indicate that more ettringite and gypsum were formed in cement + fly ash paste than pure cement paste.     

岩石结构特征对白云质灰岩碱活性的影响

运用LSCM和SEM等对河北唐山白云质灰岩TSA1和TSA2的岩石结构进行分析,并采用RILEM AAR-2、CECS:48、RILEM AAR-5和NRAA 02检测集料的碱活性。结果表明,TSA1和TSA2都不具有碱硅酸活性,TSA1具有碱碳酸盐反应活性,TSA2可能具有潜在碱碳酸盐反应活性;TSA1中白云石-方解石间隙尺寸小于TSA2,其他结构特征无明显差异。白云石-方解石间隙尺寸是影响白云质灰岩碱碳酸盐反应活性的重要因素之一,尺寸越小,ACR膨胀值越大。     

基于技术特性的工程咨询企业技术战略联盟决策规则研究

技术战略联盟已成为工程咨询企业应对市场和技术双重竞争压力的有效手段,其联盟模式选择受到诸多因素的影响。从企业技术管理特性出发,分析了企业技术特性的内容和指标,研究技术战略联盟模式选择的决策规则,为工程咨询企业的联盟模式选择做出有益指导。研究结果表明:企业和盟友的技术分工方式、技术合作层次和技术获取形式共同决定技术战略联盟模式的选择,有明确合作项目的企业联盟选择项目型联盟模式或产学研联盟模式,无明确合作项目的企业联盟则根据技术合作层次从项目型、产学研、股权型和松散型联盟模式中选择.     

Fundamental properties of powder,paste and mortar of surface modified cement and process of the surface modification

The cement particles which were modified to a round-shape were prepared by a dry impact blending method in which the surface of the cement particles were modified by strong impact. The properties of the powder, paste and mortar of surface modified cement (namely spherical cement), which was prepared in most suitable treatment time (20 min), were examined. As a result, it was found that the cement was more fluid than normal portland cement, and that the water/cement ratio was decreased by 10 wt.%. In addition, the process for formation of the surface modified cement was presumed to be embedding of fine cement particles under 3 μm onto other larger core particle surfaces. Furthermore, though a decrease in the crystallinity of the cement and the dehydration of the gypsum in the cement took place due to the surface modification of the cement particles, the amount of change was slight. The hardened mortar of surface modified cement was approximately 45% stronger than that of normal portland cement.