初始损伤对喷射混凝土抗硫酸盐侵蚀性能的影响

Effect of Initial Damage on Sulfate Attack Resistance of Shotcrete

为揭示有初始损伤的喷射混凝土在硫酸侵蚀作用下的性能劣化规律,根据超声波波速变化定义初始损伤度,利用压力试验机对混凝土试件进行初始损伤预制,使初始损伤出现5个不同梯度:0.10、0.15、0.20、0.25、0.30。通过干湿循环硫酸盐侵蚀试验,以外观形貌、质量变化率、相对动弹模量作为评价指标,并借助微观形貌分析和化学组成分析,系统研究了初始损伤度对喷射混凝土抗硫酸盐侵蚀性能的影响,探讨了影响机理,建立了初始损伤喷射混凝土在硫酸盐侵蚀作用下的损伤演化模型。结果表明,在整个侵蚀过程中,随着侵蚀时间的延长,喷射混凝土试件质量和相对动弹模量均呈先增大后减小的变化趋势。初始损伤度为0.10时混凝土受硫酸盐侵蚀过程影响较小,基本可以忽略。初始损伤度超过0.10后,试件在硫酸盐侵蚀作用下的劣化速度加快。经历180个干湿循环侵蚀后,初始损伤度为0.15、0.20、0.25、0.30组试件的质量较基准组分别下降了2.9%、3.4%、4.0%和4.7%,相对动弹模量分别降至0.42、0.34、0.28、0.16。预制初始损伤所产生的砂浆微裂缝和骨料位移为硫酸盐的侵入提供了有利条件,损伤度为0.10的试件表面有少量剥蚀,内部微裂纹较基准组略多,但腐蚀劣化并不严重。损伤度为0.30的试件表皮几乎全部脱落,内部出现了大量贯穿裂缝,裂缝较宽且深,反应产物中石膏和钙矾石晶体衍射峰强度最高,侵蚀损伤最为严重。根据相对动弹模量变化定义侵蚀损伤因子,所建立的损伤模型曲线与试验结果吻合较好,拟合相关系数均在0.94以上,可以较好地反映不同初始损伤喷射混凝土的损伤劣化规律。

In order to reveal the performance degradation law of shotcrete with initial damage under sulfate attack,the initial damage degree was defined according to the change of ultrasonic wave velocity.The initial damage of concrete specimens was prefabricated by pressure testing machine,and the initial damage presented five different gradients:0.10,0.15,0.20,0.25 and 0.30.The dry-wet cycle sulfate attack test was carried out on shotcrete,and the appearance,mass change rate and relative dynamic elastic modulus were used as evaluation indexes.The effect of initial damage on the sulfate attack resistance of shotcrete was systematically studied by means of micro-morphology analysis and chemical composition analysis.The mechanism of damage effect was discussed and the damage evolution model of initial damaged shotcrete under sulfate attack was established.The results show that with the extension of erosion time,the mass and relative dynamic elastic modulus of shotcrete specimens increase first and then decrease in the whole erosion process.When the initial damage degree is 0.10,the sulfate attack process has little effect on concrete,which can be basically ignored.After the initial damage exceeds 0.10,the deterioration speed of specimens under sulfate attack is accelerated.After 180 dry-wet cycles,compared with reference group,the mass of specimens with initial damage of 0.15,0.20,0.25,and 0.30 decreases by 2.9%,3.4%,4.0%,and 4.7%,respectively.The relative dynamic elastic modulus drops to 0.42,0.34,0.28,and 0.16,respectively.The mortar microcracks and aggregate displacement caused by the initial damage of prefabrication provide favorable conditions for the intrusion of sulfate.There is a small amount of erosion on the surface of the specimens with a damage degree of 0.10.And the internal microcracks of specimens are slightly more than reference group,but the erosion deterioration is not serious.The epidermis of specimens with a damage degree of 0.30 almost fall off.There are a large number of through cracks in the interior,which are wide and deep.Among the reaction products,the diffraction peak intensity of gypsum and ettringite crystal is the highest,and the erosion damage is the most serious.The erosion damage factor is defined in terms of relative dynamic elastic modulus changes.The established damage model curves are in good agreement with the test results,and the fitting correlation coefficients are all above 0.94.The model can better reflect the damage deterioration law of shotcrete with different initial damage.