粗骨料UHPC的基本力学性能及弯曲韧性评价方法

Basic mechanical behavior and flexural toughness evaluation method of coarse aggregate UHPC

为探究粗骨料UHPC的基本力学性能及自由收缩性能,进行基本力学性能试验及自由收缩试验,并与钢纤维混凝土、UHPC的性能进行对比。评议现有纤维混凝土弯曲韧性评价方法的优点和不足;提出可量化确定UHPC梁弯拉初裂点的偏移法;分别从能量和等效弯拉强度两个角度优化UHPC弯曲韧性的评价方法,并对3种混凝土的弯曲韧性进行评估。研究结果表明:相比于UHPC,粗骨料UHPC的弹性模量提高了10%,立方体抗压强度降低了15%,抗弯拉强度降低了6%;粗骨料UHPC的抗弯拉强度为钢纤维混凝土的1.8倍。0~91d龄期范围内,粗骨料UHPC的自由收缩量与钢纤维混凝土基本相同;3d和91d龄期的粗骨料UHPC的自由收缩量相比UHPC分别降低了63%和55%;通过添加粗骨料可降低UHPC早期收缩开裂的风险。提出的UHPC弯曲韧性评价新方法,克服了现有评价方法的不足,适用性强,可评价UHPC梁受荷全过程的弯曲韧性。粗骨料UHPC和UHPC的弯曲韧性明显优于钢纤维混凝土;相比UHPC,粗骨料UHPC的峰前弯曲韧性指数与峰前弯曲韧性比最大降幅分别为28%和22%;峰后弯曲韧性指数与峰后弯曲韧性比降幅均在11%以内。

In order to investigate the basic mechanical behavior and free-shrinkage behavior of coarse aggregate UHPC(CA-UHPC),the tests on basic mechanical behavior and free-shrinkage of CA-UHPC were designed and conducted,and the behaviors of CA-UHPC were compared with those of UHPC and steel fiber reinforced concrete(SFRC).The advantages and disadvantages of flexural toughness evaluation methods currently used for fiber reinforced concrete were discussed.The offset method to quantitatively capture the first-crack point of UHPC beam under bending and tension actions was proposed.Furthermore,a new method of evaluating flexural toughness of CA-UHPC from the perspectives of energy and equivalent flexural-tensile strength was optimized,and the flexural toughness of CA-UHPC,UHPC and SFRC were evaluated based on the proposed evaluation method.The results show that the elastic modulus of CA-UHPC is 10%higher than that of UHPC,while cubic compressive strength and flexural strength are 15%and 6%lower respectively.The flexural-tensile strength of CA-UHPC is 1.8 times that of SFRC.The free shrinkage of CA-UHPC during 91 days is almost the same as that of SFRC,while the shrinkages of CA-UHPC at the age of 3 days and 91 days are 63%and 55%lower than that of UHPC.Accordingly,adding coarse aggregates to UHPC may reduce the risk of early-age cracking of UHPC.The proposed evaluation method can effectively evaluate the flexural toughness of the UHPC beam during its whole loading process.In addition,the flexural toughness of UHPC and CA-UHPC is significantly better than that of SFRC.The maximum decreasing amplitudes of pre-peak flexural toughness index and flexural toughness ratio ofCA-UHPC are 28%and 22%lower than that of UHPC,while the decreasing amplitudes of the post-peak flexural toughness index and flexural toughness ratio are within 11%.