钢纤维对超高性能混凝土干燥收缩的影响

研究了在(20±2)℃、相对湿度为(50±5)%的环境中钢纤维体积掺量为0%、1%、2%和3%的超高性能混凝土(UHPC)的干燥收缩。结果表明:UHPC在前7d的干燥收缩发展速率较快,7d后发展速率逐渐减缓;但当钢纤维掺量超过2%后,钢纤维对干燥收缩的改善作用明显降低,相比钢纤维掺量为2%的UHPC,3%掺量UHPC的干燥收缩仅仅降低了1.5%。钢纤维高弹模及它与基体的界面粘结有效降低了混凝土的干燥收缩,但钢纤维掺量过多可导致多孔薄弱的界面区增加,从而使其对混凝土的收缩抑制作用减小。粉煤灰对超高性能混凝土干燥收缩的抑制作用大于矿粉。提出的新的数学拟合指数公式相比于文献中常用的ACI和王铁梦公式与实测结果吻合度更好。

Effects of Steel Fiber on Drying Shrinkage of Ultra High Performance Concrete

This paper reports the study of the influence of steel fibers on drying shrinkage of ultra-high performance concrete (UHPC) at fiber volume content of 0％,1％,2％ and 3％,temperature of (20-2) ℃ and relative humidity of (50±5) ％.The re sults showed that during the first 7 days,the drying shrinkage rate of UHPC was very fast,while after 7 days it gradually decreased.The interfacial bonding of steel fiber and the physical properties of steel fiber can effectively reduce the drying shrinkage.However,when the steel fiber exceeds an optimal volume,the effect of steel fiber on drying shrinkage can decrease.Compared with the steel fiber content at 2％,the drying shrinkage of the UHPC with 3％ steel fiber was decreased by only 1.5％.The reason is that the increase in the steel fiber leads to an increase in the interface layer,the interface transition zone is usually more porous than the matrix,which easily leads to shrinkage,and consequently reducing the beneficial effect of steel fiber on drying shrinkage control.It was also found that the inhibition of fly ash on the drying shrinkage of UHPC was higher than slag.The experiment also tested the classic dry shrinkage models:the ACI model and the Wang Tiemeng model.Based on the two models and the experimental fitting,a new mathematical model (a combined index model) has been proposed.The results showed that the combined index model fitted better than the two models mentioned above.