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.     

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。     

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.     

严苛侵蚀作用对优化导电混凝土性能的影响

干湿交替和硫酸盐腐蚀引起的损伤严重影响导电混凝土服役时的长期稳定性。本研究以碳纤维、石墨作为导电相材料,掺入粉煤灰和硅灰制备导电混凝土,在干湿交替和硫酸盐腐蚀耦合作用下,讨论粉煤灰、硅灰掺量对导电混凝土力学性能与电学性能的影响。综合导电混凝土的力学性能与电学性能衰变定义了服役性能劣化指标。结果表明：掺入粉煤灰和硅灰后提升了导电混凝土在干湿交替和硫酸盐腐蚀下的耐久性和导电稳定性;当粉煤灰和硅灰的总掺量一定时,提高粉煤灰占比能够有效降低干湿交替和硫酸盐腐蚀造成的强度损失,并提高导电混凝土的导电稳定性。     

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。     

干湿循环-硫酸盐侵蚀下矿物掺和料对混凝土耐久性的影响

研究了干湿循环-硫酸盐侵蚀耦合作用下,纯水泥混凝土、粉煤灰掺量10%和20%的粉煤灰混凝土及矿粉掺量15%和30%的矿粉混凝土的质量损失率、抗压强度和氯离子扩散系数的演变规律.采用X射线衍射、扫描电子显微镜、能谱分析研究了侵蚀后试件的微观形貌与物质元素组成.结果表明干湿循环-硫酸盐侵蚀耦合作用下混凝土性能发展分为2个阶段:即侵蚀初期性能的提高段与随后性能的劣化段:矿物掺和料的掺入不能改善混凝土的抗干湿循环-硫酸盐侵蚀性能.     

在不同溶液中混凝土对氯离子的固化程度

研究了不同粉煤灰、矿粉、硅灰掺量的混凝土在单一氯盐、复合溶液以及青海盐湖卤水溶液中的氯离子结合规律.结果表明:混凝土在氯盐溶液中结合氯离子的产物为Fricdel's盐,其在NaCl腐蚀溶液中的氯离子结合能力最大,复合溶液和青海盐湖卤水溶液中由于硫酸根离子的存在降低了混凝土的氧离子结合能力,且随腐蚀溶液中的硫酸盐浓度增加而降低.普通混凝土在青海盐湖溶液中腐蚀,其氯离子结合能力在0.15左右:粉煤灰、矿渣和硅灰混凝土的氯离子结合能力分别为0.13～0.24,0.25～0.40和0.20～0.34.混凝土中掺加20%粉煤灰,或35%矿渣以及8%硅灰对氯离子具有最大的结合效果.此外,还使用热分析和X射线衍射技术研究了上述规律产生的微观机理.     

全浸泡作用下混凝土抗硫酸盐侵蚀性能试验研究

研究了不同水胶比混凝土试件在(20 ±2)℃全浸泡作用下的抗硫酸盐侵蚀性能.试验制作了0.32与0.36两种水胶比的普通硅酸盐水泥、中抗硫水泥以及矿粉-硅灰复掺的混凝土试件,试件标养28 d后,测定了各试件在(20 ±2)℃的3%Na2SO4溶液中全浸泡侵蚀的抗压侵蚀系数、相对动弹性模量,并且测定了侵蚀240 d后混凝土的含气量和连通孔隙率,对混凝土在(20 ±2)℃下的抗硫酸盐侵蚀性能进行了评价.结果表明:在(20 ±2)℃全浸泡作用下,(1)混凝土抗硫酸盐侵蚀性能E>A>B,中抗硫水泥主要通过限制C3A的含量,进而改善混凝土抗硫酸盐侵蚀性能,不一定在任何环境下都适用;(2)0.36水胶比混凝土抗硫酸盐侵蚀性能低于0.32水胶比混凝土,抗硫酸盐侵蚀性能随着水胶比的降低而提高;(3)低水胶比混凝土复掺矿粉-硅灰后抗硫酸盐侵蚀性能得到显著的提高;(4)混凝土抗压侵蚀系数和相对动弹性模量高度相关,侵蚀240 d后,不同配比混凝土的含气量与连通孔隙率趋势极为接近,相关系数为0.93,因此可以合理选择试验评价指标,减少原材料浪费和试验工作量.     

低温(10℃)-干湿循环下水泥砂浆抗硫酸盐侵蚀试验研究

在低温(10 ℃)-干湿循环双重环境下,对不同水灰比不同胶凝材料方案的水泥砂浆试件的抗硫酸盐侵蚀性能进行了试验研究,其中水灰比采用0.5和0.36,胶凝材料分别为普通硅酸盐水泥、中抗硫酸盐硅酸盐水泥和在普通硅酸盐水泥中分别掺入15%矿粉+1%硅灰和15%矿粉+3%硅灰.结果表明:在低温(10 ℃)-干湿循环双重条件下,既存在化学侵蚀又存在物理侵蚀,但是以物理侵蚀为主;通过降低水灰比或者使用抗硫酸盐硅酸盐水泥能显著提高砂浆抗硫酸盐侵蚀性能;在不同的水灰比下,复掺矿粉和硅灰会得到不同的效果,在低水灰比时能提高抗硫酸盐侵蚀的性能,在高水灰比时反而会降低抗硫酸盐侵蚀的性能.     

碳酸盐和硫酸盐作用下混凝土宏-细观损伤机理

通过对混凝土试件的碳酸盐与硫酸盐盐类侵蚀试验,观察混凝土宏-细观结构破坏特征,总结相对动弹性模量与质量损失变化规律,进而分析混凝土内部结构破坏机理.结果 表明,碳酸盐侵蚀作用下混凝土剥蚀比硫酸盐严重,而且混凝土内部侵蚀产物不同,硫酸钠溶液侵蚀混凝土主要以生成晶体石膏和晶体钙矾石为主,碳酸钠溶液侵蚀混凝土则会在混凝土内部生成大苏打.盐溶液浸泡侵蚀作用下的混凝土质量损失率和相对动弹性模量变化规律都会经历先增大后减小的过程.水灰比对质量损失率的影响大于盐溶液类型,盐溶液对相对动弹性模量的影响大于水灰比.根据实测损伤变化规律,建立了盐类侵蚀条件下混凝土的相对动弹性模量-侵蚀时间方程.     

Thaumasite formation in a tunnel of Bapanxia Dam in Western China

A site investigation and sampling was carried out on a sulfate-attacked concrete structure in Bapanxia Hydraulic Power Plant in Western China. The concrete had been exposed to ground water containing substantial concentrations of salts (SO₄²⁻, CO₃²⁻ and Cl⁻) for about 6 years and was analyzed with X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), laser-Raman spectroscopy and Fourier transform infrared (FTIR) spectroscopy. It is shown that a white mushy mixture consisting of thaumasite, ettringite, gypsum and calcite is present in the residual concrete. This paper reports the first instance of the thaumasite form of sulfate attack of concrete in China.     

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.     

The role of pH in thaumasite sulfate attack

The thaumasite form of sulfate attack (TSA) has been recognised in recent years as a distinct mechanism by which degradation of buried concrete can occur in the presence of an external source of sulfate ions. There is, however, disagreement about the role of pH. It has been proposed that attack by sulfuric acid, produced by oxidation of pyrite, is sometimes the primary cause of deterioration. Others believe that the acid is rapidly neutralised giving a higher concentration of sulfate ions in the ground, hence increasing the extent of attack. The aim of the laboratory study reported here was to understand the role of sulfuric acid in TSA by examining concrete cubes, made from three types of cement and two types of aggregate, immersed at low temperature in two solutions, one alkaline corresponding to BRE Design Sulfate Class DS-3 and the other acidic. It is concluded that the presence of acid does not promote the formation of thaumasite. Although degradation of the concrete was observed in acid conditions, the mechanism was not TSA as observed in alkaline conditions.     

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.     

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...     

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。     

Sulfate attack of concrete building foundations induced by sewage waters

A case history of a severe degradation of concrete foundation plinths and piers of an about-35-year-old building located in Northern Italy is described. Significant amounts of gypsum, near ettringite and/or thaumasite were detected by X-ray diffraction analyses performed on ground concrete samples. Large gypsum crystals were mainly located at the interface between the cement paste and aggregates, as observed by scanning electron microscopy coupled to energy-dispersive spectroscopy microanalysis. The degradation effects increased with decreasing the distance of concrete structures from an absorbing well located in the courtyard of the building. The well was recognized as the sulfate source due to the microorganism metabolism of sulfur compounds present in the sewage. Consequences of this attack were a very poor bond strength between cement paste and aggregates and a severe cracking of the concrete cover of the steel reinforcement.     

Evaporation — a key mechanism for the thaumasite form of sulfate attack

Understanding the mechanisms leading to chemical attack on concrete is crucial in order to prevent damage of concrete structures. To date, most studies on sulfate attack and thaumasite formation are based on empirical approaches, as the identification of associated reaction mechanisms and paths is known to be highly complex. In this study, sulfate damaged concrete from Austrian tunnels was investigated by mineralogical, chemical and isotope methods to identify the reactions which caused intense concrete alteration. Major, minor and trace elemental contents as well as isotope ratios of local ground water (GW), drainage water (DW) and interstitial solutions (IS), extracted from damaged concrete material, were analyzed.Locally occurring GW contained 3 to 545 mg L^− 1 of SO₄ and is thus regarded as slightly aggressive to concrete in accordance to standard specifications (e.g. DIN EN 206-1). The concrete linings and drainage systems of the studied tunnels, however, have partly suffered from intensive sulfate attack. Heavily damaged concrete consisted mainly of thaumasite, secondary calcite, gypsum, and relicts of aggregates. Surprisingly, the concentrations of dissolved ions were extremely enriched in the IS with up to 30,000 and 12,000 mg L^− 1 of SO₄ and Cl, respectively. Analyses of aqueous ions with a highly conservative behavior, e.g. K, Rb and Li, as well as ²H/H and ¹⁸O/¹⁶O isotope ratios of H₂O of the IS showed an intensive accumulation of ions and discrimination of the light isotopes vs. the GW. These isotope signals of the IS clearly revealed evaporation at distinct relative humidities. From ion accumulation and isotope fractionation individual total and current evaporation degrees were estimated. Our combined elemental and isotopic approach verified wetting–drying cycles within a highly dynamic concrete-solution-atmosphere system. Based on these boundary conditions, key factors controlling thaumasite formation are discussed regarding the development of more sulfate-resistant concrete and concrete structures.     

含碳硫硅酸钙腐蚀产物的微观结构与生成机理

通过X射线衍射分析、扫描电镜、X射线光电子能谱分析、Fourier变换红外光谱分析及激光Raman光谱分析等现代测试技术,分析英国某桥墩基部腐蚀产物的微观结构,证实所取样品中含有大量的碳硫硅酸钙晶体,已发生了明显的碳硫硅酸钙型硫酸盐侵蚀.探讨了碳硫硅酸钙的腐蚀机理.     

The effects of the thaumasite form of sulfate attack on skin friction at the concrete/clay interface

The paper presents the effects of thaumasite sulfate attack (TSA) on skin friction at the concrete/clay interface. Using clay-restrained conditions thaumasite formed attached to the concrete culminating in thaumasite layers of up to 24 mm depending on interface pH and applied pressure. Thaumasite at the interface did not decrease the shear strength including skin friction and cohesion. Therefore it was concluded that TSA occurring at piles or foundation bases does not affect the stability of the superstructure regarding loss of friction and settlements.