风沙冲蚀与碳化耦合作用下风积沙粉体混凝土耐久性能

该研究以风积沙粉体为水泥替代材料的风积沙粉体混凝土为研究对象,设计风沙冲蚀-碳化、碳化-风沙冲蚀2种工况,探讨其在风沙冲蚀、碳化环境下的劣化机理及耐久性能。结果表明,风沙冲蚀时,90o冲蚀角作用时以撞击作用为主,产生冲蚀坑洞,45°冲蚀角作用时以削切作用为主,产生冲蚀沟壑,且风沙冲蚀破坏混凝土表面水泥石结构,可使碳化深度增加3倍以上;碳化作用时,普通混凝土碳化时是由于氢氧化钙和水化硅酸钙发生脱钙反应,风积沙粉体混凝土则是由于氢氧化钙、水化硅酸钙和钙矾石发生脱钙反应,且由于碳化产物自身的膨胀作用使混凝土变的疏松,使风沙冲蚀后质量损失增加1.6倍以上;风积沙粉体混凝土内部孔径在20 nm以下的无害孔的比例多于普通混凝土21.37个百分点,200 nm以上多害孔少于普通混凝土13.93个百分点,其劣化显著性低于普通混凝土;相对于单一工况,风沙冲蚀、碳化耦合作用下劣化显著性更高,且风沙冲蚀-碳化耦合作用劣化显著性低于碳化-风沙冲蚀耦合作用,风沙冲蚀-碳化耦合作用后的10~15 mm范围内出现碳化区域、碳化产物发生变化(生成硫酸钙)及非碳化区域的混合区,且风沙冲蚀-碳化耦合作用后风积沙粉体混凝土孔隙度下降0.47%,20 nm以下的无害孔的比例高出普通混凝土25.15%。

Durability of aeolian sand powder concrete under mechanism of aeolian sand blowing erosion and carbonization

Aeolian sand (different from mechanical sand), which is widely distributed in Inner Mongolia, China, is generated from wind erosion and very easy to obtained. In this paper, we studied aeolian sand powder as the cement substitute material and tested its durability under wind sand erosion. During wind sand event, concrete can be destroyed by the sand from the air, which is also called the sand erosion of deflation. Aeolian sand blowing erosion -carbonation and carbonation-aeolian sand blowing erosion were designed as two working conditions in this study. The aeolian sand blowing erosion tester, carbonization tester, universal testing machine, ultra-deep three-dimensional microscope, nuclear magnetic resonance technology, X-ray phase analysis, field emission scanning electron microscopy, etc. were selected in the laboratory to determine the deterioration mechanism and durability in aeolian sand blowing erosion of deflation and carbonization environment. The results showed that when aeolian sand erosion occurred, especially in the very beginning, the impact angle of 90° erosion angle dominated the impact, resulting in erosion pits which could be seen by human eyes. The effect of 45° erosion angle was mainly on the cutting action of erosion action, producing erosion gullies. And aeolian sand blowing erosion destroyed the cement stone structure on the surface of the concrete, exposing the coarse aggregates that were wrapped inside, increasing the carbonation depth by up to 3 times. The carbonization mechanism of ordinary concrete and aeolian sand powder concrete in carbonization was different, which was reported before. When ordinary concrete was carbonized, decalcification reaction occurred due to calcium hydroxide and calcium silicate hydration. Aeolian sand powder concrete was decalcified due to calcium hydroxide, calcium silicate hydrate, and ettringite. However, due to the swelling effect of the carbonized product itself, the concrete became loose, and the quality loss after aeolian sand erosion was increased by more than 1.6 times. The ratio of non-hazardous pores with an inner pore diameter below 20 nm in aeolian sand powder concrete was more than 21.37 percent point of that of ordinary concrete, and the harmful pores above 200 nm were less than 13.93 percent point of ordinary concrete, and the deterioration was less obvious than ordinary concrete, which could be the essential evidence that the durability the aeolian sand powder concrete was higher than that of ordinary concrete. Compared with a single working condition, the degradation under aeolian sand erosion and carbonation coupling was significantly higher, and the deterioration of aeolian sand blowing erosion -carbonization coupling was significantly lower than that of carbonization- aeolian sand blowing erosion. Along the direction of carbonization, in the range of 10-15 mm after the aeolian sand erosion and carbonation coupling effect, the carbonized zone, the non-carbonized zone, and the mixed zone where the carbonized product changes occurred (formation of calcium sulfate). With the results, researchers could attain several laws about the aeolian sand powder concrete, which could be the basic theory for the development. Our research also provides more choice and basis for the construction of water conservancy projects, and the social and economic benefits are remarkable.