含水率及加载速率对纤维增韧喷射混凝土弯曲韧性的影响

Influences of moisture content and loading rate on flexural toughness of fiber reinforced shotcrete

试验中观察到含水率及加载速率对钢纤维、粗合成纤维增韧喷射混凝土弯曲韧性测试中的脆断概率影响显著,为此,研究了这2个试验条件对弯曲韧性测试的影响.试件在(20±2)℃、(60±5)%相对湿度条件下分别干燥0,16,24及72 h,获得不同程度的干湿状态;然后按照ASTM C1609及CECS 13的三分点加载,以0.05 mm/min加载速率测试弯曲韧性.对于干燥时间分别为24和72 h的试件,以0.05,0.10及0.20 mm/min加载速率分别测试其弯曲韧性.结果表明,随着含水率降低,第一峰值弯曲强度明显降低;未经干燥的水饱和试件弯韧试验中均发生脆断,但经干燥非饱和试件的特定挠度下残余弯曲强度、弯曲韧性T100,2.0随含水率降低而呈现降低趋势.纤维增韧喷射混凝土第一峰值强度、残余弯曲强度、弯曲韧性随加载速率提高而增大;配合比相同时,相对含水率较高,上述抗弯性能随加载速率提高而增大的趋势更为明显;其原因可以解释为受孔隙中自由水Stefan效应引发黏聚力作用.

Influences of moisture content and loading rate on flexural toughness were experimentally studied for fiber reinforced shotcrete （FRSC） with steel fiber or macro synthetic polypropylene fiber. According to the four- point bending test method specified in ASTM C1609 and Chinese standard CECS 13, the flexural toughness of specimens after drying for 0 h, 16 h, 24 h and 72 h under conditions of （20±2）℃ and （60±5）% relative humidity was tested at a loading rate of 0.05 mm/min. For the specimens dried for 24 h or 72 h, the flexural toughness was tested at loading rates of 0.05 mm/min, 0.10 mm/min, and 0.20 ram/rain respectively. With the moisture content decreasing, the first-peak flexural strength decreased visibly. Brittle fracture happened to all the saturated FRSC specimens without drying during the bending tests. However, for the non-saturated specimens after drying for different periods, the residual flexural strength at prescribed deflections and flexural toughness T10o,2.0 exhibited decreasing tendency with the decrease in the moisture content of the specimens. The first-peak flexural strength, residual flexural strength at prescribed deflections and the flexural toughness T100,2.0 of FRSC increased with the increase of loading rate. Given the same mix proportions, FRSC with higher relative water content presented more obvious increase of the mentioned flexural properties with loading rate increasing. This may be explained by the cohesive force caused by the Stefan effect.