隧道洞渣加工机制砂制备超高性能混凝土及其力学性能研究

Study on the development and mechanical properties of ultra-high performance concrete based on manufactured sand from tunnel waste

采用隧道洞渣加工机制砂替代传统河砂制备超高性能混凝土(UHPC)。研究不同替代率对其工作性能、干缩、抗折强度、抗压强度和微观性能的影响规律。结果表明:机制砂替代河砂,其工作性能尽管存在一定程度的下降,但依然具备良好的工作性能;机制砂替代掺量为40%时,相应抗压强度和抗折强度均最优;UHPC微观形貌受机制砂影响显著,随着机制砂替代率的增大,UHPC微观孔隙和裂缝逐渐增加。机制砂粗糙的表面和不规则边缘更利于与水泥浆体紧密连接,不规则边缘构造在机制砂颗粒间产生互锁效应,能够进一步增强水泥浆体和骨料的机械咬合力。但是,钢纤维与机制砂界面过渡区微观结构相对疏松,且含有较多微孔洞,使得该处具有较弱的桥接能力,从而导致整体抗折强度的降低。总而言之,洞渣加工机制砂替代传统河砂制备UH-PC是一个行之有效的策略。

Ultra-high performance concrete(UHPC)was prepared by using manufactured sand(MS)which is recycled from tunnel waste to substitute traditional river sand(RS).The influence of different substitution rates on workability,dry shrinkage,flexural/compressive strength and microscopic properties was studied.The results show that although the flowability has decreased to a certain extent,UHPC made by MS still has good working performance.The corresponding compressive/flexural strength are optimal when the MS substitute is 40%.The microscopic morphology of UHPC is significantly affected by MS.With the increase of MS,the micro-voids and cracks of UHPC gradually increase.The rough surface and irregular edges of MS are more conducive to establishing a connection with cement paste.Meanwhile,the irregular edge structure produces an interlocking effect between MS particles,which further enhance the bonding property between cement paste and aggregate.However,the microstructure of the interfacial transition zone between the steel fiber and MS is relatively loosen,and contains many micro-voids,which makes this area a weak bridging ability,resulting in a decrease in the overall flexural strength.In general,it is an effective strategy to replace traditional river sand to prepare UHPC by MS from tunnel waste.