Flexural toughness and its evaluation method of ultra-high performance concrete cured at room temperature

This study investigates the effects of water-binder ratio and steel fiber content on the flexural response characteristics of UHPC cured at room temperature by four-point bending tests. These flexural properties include load-deflection curve, flexural strength, initial cracking strength and flexural toughness. Based on the review of existing evaluation methods about flexural toughness, a deflection offset method that can quantitatively determine the initial crack point of UHPC in bending tests is proposed, and the optimized evaluation indicators of UHPC flexural toughness are further established from the perspective of equivalent strength. The proposed method with clear physical meaning and strong applicability can be used to evaluate the flexural toughness of UHPC cured at room temperature during the whole loading process. The results indicate that: (1) The flexural strength and deflection decrease as the water-binder ratio increases from 0.14 to 0.20, in which the decrease of peak deflection is the most significant (56.95%). (2) Although the flexural strength increases linearly with the increase of steel fiber content, the peak deflection increases slowly when the fiber content exceeds 1.0%. (3) The strength and deflection corresponding to the initial cracking point are about 2/3 of the flexural strength and 1/3 of the peak deflection respectively. (4) The flexural toughness decreases with the increasing water-binder ratio, especially when the water-binder ratio exceeds 0.18. (5) The flexural toughness of UHPC increases and the toughening effect of fiber first increases and then decreases with the increase of steel fiber content, and UHPC mixed with 1.5% steel fiber achieves the most remarkable toughening effect. Therefore, the superior flexural toughness and load-bearing capacity of UHPC cured at room temperature are highlighted when the water-binder ratio is less than 0.18 and the steel fiber content exceeds 1.0%.