Performance degradation and damage model of concrete incorporating rice husk ash under sulfate attack
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摘要: 为证实稻壳灰(RHA)对混凝土硫酸盐侵蚀性能的改善作用,优选出掺RHA混凝土配比,并与普通混凝土(NC)对比,研究质量分数5wt%的Na2SO4溶液侵蚀270天内,表观现象、抗压、抗拉强度、有效孔隙率、动弹性模量等性能指标劣化规律,利用SEM观察硫酸盐侵蚀前后试件微观结构变化。结果表明:随侵蚀时间增加,混凝土试件逐渐局部剥落、体积膨胀;抗压、抗拉强度先提高后急剧下降,有效孔隙率先降低后提高,相对动弹性模量先提高后下降;微观分析表明混凝土水化产物与侵蚀介质反应生成钙矾石和石膏,填充内部孔隙,而随侵蚀进行膨胀性钙矾石与石膏超过内部抗拉强度产生裂隙,引起结构膨胀破坏、力学性能劣化。而RHA掺入混凝土生成水化硅酸钙凝胶,提高材料强度和耐腐蚀性,各阶段掺RHA混凝土劣化程度均优于NC。最终建立损伤本构模型,并与实测值对比,准确性较高。Abstract: To prove the improvement of rice husk ash (RHA) on sulfate erosion performance of concrete, the ratio of RHA concrete was optimized and compared with normal concrete (NC). The performance degradation progresses of concrete specimens within 270 days under solution attack with 5wt%Na2SO4 were studied, which included changes of apparent phenomenon, compressive strength, tensile strength, effective porosity and dynamic elasticity modulus. The micro-structure changes of concrete specimens under sulfate attack were observed by SEM. The results show that the concrete specimens gradually appear local spalling and expansion with the increase of corrosion time. The compressive and tensile strength increase and then decrease sharply, the effective porosity decreases and then increases, and the relative dynamic elasticity modulus increases and then decreases. Microscopic analysis shows that the ettringite and gypsum are formed from the hydration products of concrete react with the corrosive medium, which fill pores of concrete. Whereas, with the increase of corrosion time, the expansion of the ettringite and gypsum exceeds the internal tensile strength, resulting structural expansion failure and deterioration of mechanical properties. However, RHA mixing with concrete can produce calcium silicate hydrate, which improves the strength and sulfate resistance of concrete. In each stage, the deterioration degree of RHA concrete is better than that of NC. Finally, the damage constitutive models are established, and have higher accuracy compared with the measured value.
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表 1 RHA的化学成分占比
Table 1. Chemical composition of RHA
Composition SiO2 K2O CaO Fe2O3 MgO Ignition loss Content/wt% 85.6 2.51 2.44 0.56 0.51 8.38 表 2 混凝土配合比
Table 2. Concrete mixture ratio
(kg·m−3) Concrete number Cement material Gravel Sand Water Water reducer Cement RHA NC 368 0 1202 633 210 2.1 3%RHA/NC 357 11 1202 633 219 2.1 6%RHA/NC 346 22 1202 633 228 2.2 9%RHA/NC 335 33 1202 633 237 2.3 12%RHA/NC 324 44 1202 633 246 2.4 15%RHA/NC 313 55 1202 633 255 2.5 Notes: NC—Normal concrete; x%RHA/NC—Rich husk ash concrete with rich husk ash (mass ratio to cementitious material) of x%, respectively. 表 3 混凝土力学性能测试结果
Table 3. Concrete mechanical properties test results
Concrete number Slump/mm Compressive strength/MPa Splitting tensile strength/MPa 7 days 28 days 7 days 28 days NC 168 26.2 32.4 2.7 3.5 3%RHA/NC 170 27.0 34.2 2.9 3.9 6%RHA/NC 165 28.2 36.8 3.0 4.2 9%RHA/NC 175 26.7 42.3 2.8 4.6 12%RHA/NC 180 24.7 40.7 2.4 4.1 15%RHA/NC 178 20.8 35.3 1.8 3.3 表 4 不同侵蚀时间下混凝土的固有属性m和F值
Table 4. Concrete inherent attribute m and F values under different erosion time
Erosion
time/daysNC 9%RHA/NC m F/10−3 m F/10−3 0 0.35 1.17 0.39 1.68 30 0.35 1.20 0.40 1.77 60 0.36 1.27 0.42 1.97 90 0.38 1.50 0.42 2.04 120 0.37 1.47 0.43 2.10 150 0.35 1.22 0.42 2.02 180 0.34 1.00 0.40 1.80 210 0.32 0.81 0.38 1.58 240 0.30 0.67 0.37 1.43 270 0.30 0.62 0.35 1.23 -
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