【作者】 李长成；

【导师】 姚燕；

【作者基本信息】 中国建筑材料科学研究总院 ， 材料学， 2011， 博士

【摘要】 碳硫硅钙石型硫酸盐侵蚀（Thaumasite form of sulfate attack，TSA）直接破坏水泥石中的C-S-H凝胶，将其转化为无胶凝性烂泥状物质，导致水泥基材料性能劣化，严重影响混凝土工程耐久性。尽管早在1965年就有人提出TSA问题，但它真正为人们所重视只是近10多年的事情，许多问题需进一步研究。碳硫硅钙石的化学组成、晶体结构与钙矾石十分相似，常规测试分析易混淆，且大多数只能实现定性或半定量分析。TSA影响因素还存在学术争议和研究盲点，如粉煤灰是否能抑制TSA破坏。多因素耦合作用下水泥基材料发生TSA破坏的可能性、性能退化规律及破坏机理研究极少。此外，尚未建立有效的水泥基材料TSA破坏预防措施。这些问题严重制约了混凝土结构工程的服役寿命，造成巨大的破坏和浪费。针对上述问题，结合我国新疆地区腐蚀环境特点，本文研究了内掺法加速碳硫硅钙石形成的可行性和碳硫硅钙石的量化表征；研究了温度、粉煤灰及氯离子等因素对TSA的影响规律和作用机理；研制了适用于多因素耦合试验中对混凝土试件准确加载的设备；通过大量系统试验获得了多因素耦合作用下水泥基材料性能劣化规律和破坏机理；在上述成果基础上，开发了预防水泥基材料TSA破坏的TSA抑制剂。主要研究结论如下：1.内掺10%硫酸镁显著加速水泥基材料中碳硫硅钙石形成，6个月后，样品中有23.73%碳硫硅钙石形成，具有典型的TSA破坏特征。基于样品外观、IR及XRD/Rietveld精修等手段，建立了一种碳硫硅钙石的快速定量鉴别方法，有助于提高水泥基材料TSA研究的精确性、快捷性。2.借助碳硫硅钙石的快速定量鉴别方法，阐明了温度、粉煤灰及氯离子对水泥基材料TSA影响规律。⑴（5±2）℃下，掺石灰石粉水泥基材料发生TSA，腐蚀产物以碳硫硅钙石、石膏为主，性能劣化严重。（20±1）℃下，掺石灰石粉水泥基材料发生钙矾石/石膏型硫酸盐侵蚀，腐蚀产物以钙矾石、石膏为主，性能劣化较轻。⑵粉煤灰对水泥基材料TSA的影响与其组成、掺量及细度等因素有关。粉煤灰活性指数对碳硫硅钙石形成影响最大，可作为筛选粉煤灰预防TSA破坏的指标。活性指数大于80%的粉煤灰掺量达到50%时可显著改善水泥基材料抗TSA性能。⑶氯离子降低碳硫硅钙石形成速度，进而减缓TSA破坏进程，并且复合溶液中氯离子浓度越高，减缓效果越显著。依据宏观性能、腐蚀产物物相演变过程，提出氯离子对水泥基材料TSA影响的三个阶段：抑制期、衰退期及失效期。3.开发了一种自定位可拆卸式混凝土耐久性试验应力加载装置，适用于多因素耦合试验研究中对混凝土试件准确施加弯拉应力。该装置由可拆卸的应力加载夹具、自定位夹具和应力测控夹具组成，便于定期校正、保持应力恒定，克服了传统装置加载不准确、应力松弛问题。4.揭示了低温硫酸盐侵蚀、干湿循环、弯拉应力耦合作用下水泥基材料性能劣化规律和破坏机理。⑴“低温硫酸盐侵蚀+干湿循环”双因素作用下，干湿循环减缓内掺10%硫酸镁样品TSA破坏程度，但引起的盐类结晶侵蚀导致内掺10%盐湖卤水样品发生剥蚀性破坏，性能劣化程度较低温硫酸盐侵蚀单因素损伤加重。⑵“低温硫酸盐侵蚀+弯拉应力”双重因素作用下，样品发生突然断裂破坏，主裂缝在弯拉应力作用下形成、扩展并发生失稳，断裂时水泥基材料未发生TSA破坏。⑶“低温硫酸盐侵蚀+干湿循环+弯拉应力”三因素作用下，“干湿循环+弯拉应力”累计叠加损伤加速水泥基材料断裂破坏，断裂时水泥基材料均未发生TSA破坏。5.提出了水泥基材料中预防TSA破坏发生的理论，抑制剂的作用机理有两个方面，即物理固化、化学固化。依据TSA化学侵蚀过程及Ba²⁺多级长效缓释，化学固化分为三个阶段，即BaSO₄形成期、硫酸盐侵蚀过渡期及碳硫硅钙石、钙矾石分解期。采用“叠加包裹”技术开发了KM型、K型TSA抑制剂，具有Ba²⁺多级长效缓释特性，显著提高水泥基材料抗TSA性能，抑制效果KM型优于K型。此外，TSA抑制剂对新拌混凝土工作性、硬化混凝土强度性能及耐久性具有一定的改善作用。更多还原

【Abstract】 Thaumasite form of sulfate attack （TSA） directly destroys the main binding phasecalcium-silicate-hydrate （C-S-H） in hardened cement. Cement matrixes are convertedinto mush from the surface inwards. The properities of cement-based materials andconcrete structure durability are strongly influenced by TSA. Although the first caseof TSA was reported in1965, TSA has only received considerable attention in recentyears. There are still many problems remained unsolved by now.Thaumasite is very difficult to distinguish from ettringite due to the close similarityin crystal structure and morphology. Meanwhile, there exist some disputes aboutinfluence factors of TSA, such as whether fly ash can inhibit TSA. The investigationon the possibility of TSA, degradation and deterioration mechanism of cement-basedmaterials under combined actions are also rare. And above all, effective preventivemeasures of TSA have not yet been established. These problems not only influencethe service life of concrete structure seriously but also make great economic loss.A serial of experimental programs were designed to solve the above problems.Accelerating thaumasite formation by internal doping method and quantitativecharacterization of thaumasite were explored. The researches on mechanism andeffects of temperature, fly ash and chloride ions on TSA had also been carried out. Anappropriate setup was designed to exert controllable flexural stress to concretespecimens. The properities and deterioration mechanism of concrete under combinedactions were investigated deeply. TSA inhibitors were developed to prevent TSA inthis paper as well. Main conclusions of this paper are as follows:Thaumasite formation was successfully accelerated by internal doping10%ofmagnesium sulfate in cement-limestone powder pastes at （5±2）℃. Thaumasitecontent was up to23.73%after6-month immersion in water with a typicalcharacteristic of TSA damage. A rapid quantitative identification method ofthaumasite including visual inspection, IR spectrum and XRD/Rietveld refinementwas also established which would improve the accuracy and rapidness of TSA’sresearch.The influences of temperature, fly ash and chloride ions on TSA in cement-basedmaterials were illustrated.⑴Cement-based materials with limestone powder tookplace TSA and the corrosion products were mainly thaumasite and gypsum at （5±2）℃.But the corrosion products were mainly ettringite and gypsum at （20±1）℃.⑵Effects of fly ash on TSA were closely related to the composition, content andfineness of fly ash. The activity index of fly ash had a maximum gray relevancedegree with quantity of thuamasite formation which could be used as an index forfiltering fly ash to prevent TSA. Fly ash with an activity index>80%could improvethe resistance to TSA in cement-based materials when the replacement reached50%.⑶Chloride ions could slow down the process of TSA by reducing the rate ofthaumasite formation. With the increment of chloride ions concentration in NaCl/Na2SO₄solution, the influence grew gradually. The processes of chloride ions’effects on TSA were divided into three stages: inhibition stage, recession stage andfailure stage.A self-localization detachable stress loading device was invented to exertcontrollable flexural stress to concrete specimens in combined action tests as well.This device consisted of stress loading fixture, self-localization fixture and stressmonitoring fixture which easy to apply regular calibration and maintain constantflexural stress. The new device overcomed inaccurate stress loading and stressrelaxation problems of common setup.The degradation and deterioration mechanism of cement-based materials undercombined actions of low-temperature sulfate attack, wetting-drying cycle and flexuralstress were obtained.⑴When samples subjected to the combined action of lowtemperature sulfate attack and wetting-drying cycles, the latter greatly weakened thedamage degree of samples with magnesium sulfate by slowing down TSA. Butcrystallization pressure caused by salt crystallization corrosion due to wetting-dryingcycles had destructive effects on samples with salt lake brine.⑵A sudden breakwas the main-type destroys of cement-based materials under the action of both lowtemperature sulfate attack and flexural stress. The latter promoted a major crackforming and propagating rapidly throughout the specimens. And there was nothaumasite in corrosion products.⑶When samples subjected to the combined actionof three-factors, the deterioration was greatly accelerated due to cumulative damagescaused by “wetting-drying cycles+flexural stress”. Moreover, corrosion productswere free from of thaumasite.The mechanism for preventing TSA damage in cement-based materials includingphysical solidification and chemical solidification was also presented in this paper. Inview of TSA chemical process and slow release of Ba²⁺of TSA inhibitors, the processof chemical solidification was divided into three stages: barium sulfate formationstage,sulfate attack transitional stage and thaumasite/ettringite decomposition stage. KMtype and K type TSA inhibitors prepared by “multi-coating technique” had along-term multilevel slow release of Ba²⁺. The resistance to TSA of cement-basedmaterials could be significantly improved by these TSA inhibitors. Furthermore, TSAinhibitors had certain improving effects on workability of fresh concrete, strength anddurability of hardened concrete.更多还原