【作者】 王琴；

【导师】 杨鼎宜；

【作者基本信息】 扬州大学 ， 结构工程， 2008， 硕士

【摘要】 混凝土的耐久性研究具有广泛而深远的意义,从材料角度研究混凝土耐久性主要针对混凝土耐腐蚀、抗冻、碳化及耐钢筋锈蚀等问题,实际环境中混凝土腐蚀常常不是单一的状态,环境中其他的因素对腐蚀有或多或少的影响,研究时要考虑多因素损伤的混凝土性能分析。海工建筑及水工混凝土结构中均会发生混凝土干湿循环破坏,海平面附近的混凝土最易破坏,硫酸盐侵蚀是混凝土化学侵蚀中最广泛普通的形式,结合两种侵蚀对混凝土劣化研究有重要的理论和工程实践意义。本文主要研究硫酸盐侵蚀和干湿循环损伤共同作用下对混凝土的宏观损伤规律,将三种不同水灰比的混凝土试件（W/C=0.4、0.55、0.7）分组放在四种不同的浸泡环境中,清水以及Na₂SO₄%=3.0%、5.0%和8.0%的硫酸盐溶液,采用单因素硫酸盐侵蚀和干湿循环与盐侵蚀双因素试验对比宏观力学性能劣化,并建立基于动弹性模量Ed的累积损伤演化模型。混凝土性能的劣化是微观结构形态演化在宏观上的反映,所以本文结合相应微观试验来分析干湿循环和盐侵蚀的损伤机理以及不同水灰比试件在不同硫酸钠浓度溶液中盐侵蚀和干湿循环腐蚀双因素的交互叠加效应。微观试验主要针对硫酸盐主要侵蚀产物钙矾石晶体的生长,利用XRD中K值法定量分析不同工况下试件中钙矾石生长量变化规律,并利用ESEM对其微观孔隙结构变化进行观察,分析固相侵蚀结晶物的生长形态、膨胀特性等。本文的宏观与微观试验研究得出了一些初步结论,硫酸钠溶液常温浸泡440天的侵蚀试验结果表明硫酸盐侵蚀过程是长期缓慢的过程,Ed演化规律一般是前期密实增强—平缓—缓慢下降,混凝土试件处在负损伤阶段。在干湿循环与盐侵蚀共同作用过程中干湿循环损伤和盐侵蚀有一定的超叠加效应,浓度越高超叠加效应越明显,在叠加效应中硫酸盐侵蚀对混凝土的劣化起主要作用。对应的不同水灰比损伤量D的损伤演化模型也可以反映出干湿循环和盐浸泡损伤过程的差别,三种水灰比混凝土的损伤演化规律类似,均可以用二次多项式来拟合,公式D = A+BT+CT²,损伤变化基本上是缓慢至加速增长,一般浓度越高损伤变化速度越快,水灰比对损伤变化的影响不大。微观试验结果表明双因素作用环境中E的含量比浸泡中的要多一些,水灰比较小的可达到1.6%².0%,水灰比大的可达到3.0%左右,基本上是大幅增长—相对平缓的趋势,水灰比较大的试件,这种前后变化差异更明显。通过ESEM等微观测试手段发现,干湿循环与硫酸钠侵蚀作用下混凝土的破坏主要是盐析晶和侵蚀产物的体积膨胀造成裂缝的扩展,水灰比越大,内部界面处裂隙开展越迅速。硫酸盐化学侵蚀产物主要是钙矾石晶体,通过ESEM对微观侵蚀晶体生长形态进行观察分析,有微晶态和簇状辐射的针状等不同形态,水灰比较大试件中,针状钙矾石带密集成簇生长在孔缝中,干湿循环中局部浓度较高处有石膏侵蚀物存在,也有明显的硫酸盐物理侵蚀,在内部及表面析出Na₂SO₄等结晶物。两种损伤机理受到材料结构、空间环境和介质浓度等多种因素的影响,需要进一步综合研究。更多还原

【Abstract】 The durability of concrete involves resistance to corrosion, frost, carbonation, stress corrosion and so on in material subject have much extended and far-reaching meaning to be studied. However, in practice, several deterioration mechanisms exist in erosion environment, other factors have more or less infection to cauterization. Therefore, it is necessary to study the properties of the concrete subjected to more deterioration mechanisms. In seaside architecture and water conservancy, the degradation of concrete construction usually is the result of dry and wet cycles, and the concrete of sea level nearby is breached much easy. The sulfate attack is a extensive erosion of physical and chemical attack, combined with dry and wet cycles attack to be studied to avail significative reference on deterioration theory and practice of concrete construction.The macro-mechanical damage performance of concrete subjected to drying–wetting cycles and sodium sulfate attack in solution were investigated in this paper. Three water-cement ratio（0.4,0.55,0.7） of concrete specimens were placed in four different sulfate erosion solutions, 0%, 3%, 5% and 8% sodium sulfate concentration respectively. Compare and contrast single sulfate immersed test with sulfate attack& drying-wetting cycles double factors test, and the evolution damage model of the relative dynamic modulus of elasticity （Ed） of concrete is proposed based on continuum damage mechanics.For the degradation of concrete is a reflection of the micro damage mechanics, the micro-experiments include two contents, the one is the analysis of quantitative evolution of Ettringite vs. erosion time measured with the method of K value approximate calculation in XRD （X-Radial Diffraction）, the second is observing the formation and growth law of Ettringite, sodium sulfate crystal etc. corrosive crystals and the evolution of concrete micro-structure in sulfate&D/W erosion in situation by ESEM （Environment Scan Electron Microscope）.There are several conclusions in macro and micro aspects of sulfate&D/W erosion tests. The results of single sulfate immersed 440d test indicate the sulfate erosion is a chronically process and the evolution of Ed submit to early enhancing consistency, keeping and descending further, corresponding with the negative damage mechanics of concrete in test phase. There are certain interaction effect between the action of drying–wetting cycles and sulfate attack., especially in the high concentration solution. The degradation of concrete priority to sulfate attack.The distinctions of damage performance of concrete in sulfate&drying-wetting cycles tests are revealed by the different evolution damage models. The damage evolution equation of three differenr W/C concrete is fit in same curve, the expression is D = A+BT+CT², the change of damage slowly , and then the trend of accelerated increase later, the higher concentration the faster change, the W/C has small effect on damage.In the micro-experiments, the quantity of Ettringite in sulfate&frost tests is more than sulfate immersion, and improve obviously early till keeping later. The content range is 1.6% ².0% in small W/C ratio concrete and 3.0% in bigger. The effect of sulfate concentration and the interfacial crack extend rapidity along with the ratio increasing in ESEM. The primary corrosive crystal is ettringite to sodium sulfate attack, it have several different growth modality in different interspaces, the gelatinous crystals and fascicular crystals are also observed in small ratio micro- structure specimens, and that, a large volume of the minuteness needle crystals exist in broad voids or cracks in big W/C ratio specimens, and gypsum crystals also exist in high sulfate ion local. Furthermore, the physical erosion of Na₂SO₄ crystal inside or exterior of concrete also is distinct in sulfate&drying-wetting cycles circumstance. The significant influence of material configuration, void circumstance, and erosion medium etc. to the two damage mechanisms is complicated and need to be investigated farther.更多还原