弯曲应力作用下喷射混凝土抗碳化性能研究

Influence of Shotcrete Carbonation Resistance Under Bending Stress

为研究隧道喷射混凝土衬砌的碳化规律,采用快速碳化试验方法,研究了不同弯曲应力作用下喷射混凝土及钢纤维喷射混凝土抗碳化性能,在考虑弯曲应力、钢纤维掺量、喷射混凝土施工方式的基础上对普通混凝土碳化深度预测模型进行修正。同时,采用冷场发射扫描电镜对碳化后喷射混凝土微观结构进行分析。结果表明:喷射混凝土碳化深度服从Fick第一定律,扩散系数随应力水平的增加而增加;喷射混凝土碳化深度明显小于普通混凝土,而钢纤维的加入进一步提高了喷射混凝土抗碳化性能。通过对碳化后喷射混凝碳化后力学性能及微观结构进行分析,得出喷射混凝土抗压强度、劈裂抗拉强度及抗折强度随着碳化深度的增大而增大,且喷射混凝土中原始微气孔及裂缝中钙矾石、氢氧化钙等晶体为Ca CO3晶体的成核和生长提供有利条件,碳化产物持续生成并阻塞毛细孔,使其密实度增加,力学性能增大。

The durability experiments of shotcrete with and without steel fiber under bending stress in accelerated carbonation corrosive environments were carried out to investigate the carbonation regularity of tunnel lining.Meanwhile,the concrete carbonization predictive model was modified for considering bending stress,steel fiber addition and construction mode.Furthermore,the microstructure of shotcrete after accelerating carbonation was analyzed by using cold field emission scanning electron microscope(FESEM).The results showed that the carbonation depth obeyed Fick first law and diffusion coefficient raised with the increase of bending stress.The carbonation depth of shotcrete was much less than that of ordinary concrete.Simultaneously,the carbonation resistance of steel fiber reinforced shotcrete(SFRS) was much better than that of shotcrete.For analyzing the mechanical properties and microstructure of shotcrete after carbonation,the cubic compressive strength,splitting tensile strength and flexural strength were tested,and the mechanical performance of specimen increased with carbonation depth.The channels for carbon dioxide taking into shotcrete were provided by the original micro pores and creaks.Moreover,the favorable conditions for calcite crystal nucleation and growing were also supplied by ettringite and portlandite which consists in defeats.With the carbonation reaction development,the carbonation products were continuously consumed and blocked the micro-pores.