乳化沥青对超高性能混凝土工程特性及增韧效果的影响

Effect of emulsified asphalt on engineering properties and toughening effect of ultra-high performance concrete

开裂是目前超高性能混凝土(UHPC)的主要破坏形式,增加弯曲韧性是解决UHPC开裂破坏的主要技术途径.为探究乳化沥青在水泥基材中的增韧效果,研究了不同类型及掺量的乳化沥青对UHPC工作性能、力学强度和弯曲韧性的影响.结果表明阴离子乳化沥青和阳离子乳化沥青均会小幅度降低UHPC的工作性能与力学强度,但能有效提升UHPC的弯曲韧性.相较于阳离子乳化沥青,阴离子乳化沥青UHPC的工作性能与力学强度优于阳离子乳化沥青UHPC,增韧效果更显著;综合考虑力学性能及工作性能,推荐使用阴离子乳化沥青,且优选掺量为3%.通过扫描电子显微镜观察掺入乳化沥青后的UHPC微观结构,发现乳化沥青可有效优化混凝土内部结构、填充微裂缝;乳化沥青的黏弹特性能够有效抑制微裂缝的形成与发展.

At present,cracking is the main form of damage to ultra-high performance concrete(UHPC),and increasing flexural toughness is the primary technical approach to addressing this issue.Currently,fiber,polymer,or nanomaterial modification is commonly used to improve UHPC toughness.Emulsified asphalt has also demonstrated the potential to toughen and resist cracking.To investigate the toughening effect of emulsified asphalt in cementitious materials,this study employed a method in which emulsified asphalt and water are added simultaneously during wet mixing to prepare UHPC specimens.The effects of different types and dosages of emulsified asphalt on the workability,mechanical strength,and flexural toughness of UHPC were investigated through extensibility tests,flexural toughness tests,compressive strength tests,flexural strength tests,and tensile strength tests.The results showed that the workability of UHPC mixes with two types of emulsified asphalt gradually decreased as the emulsified asphalt dosage increased.When the dosage of either type of emulsified asphalt exceeded 3%,the extension did not meet the specification requirements.Furthermore,as the dosage of the two types of emulsified asphalt increased,the mechanical strength of the UHPC slightly decreased.Compared with the same dosage of cationic emulsified asphalt,anionic emulsified asphalt had a smaller impact on the mechanical strength of UHPC because anionic emulsified asphalt and cement hydration products both carried the same charge,causing them to repel each other.This mutual repulsion reduced the influence of emulsified asphalt on the cement hydration reaction process,which was conducive to the generation of cement hydration products.Consequently,the negative impact on the formation of UHPC strength was lessened,and the uniformity of the steel fiber distribution within the UHPC was ensured.In terms of flexural toughness,both types of emulsified asphalt enhanced the flexural toughness of the UHPC,with anionic emulsified asphalt providing better results than cationic emulsified asphalt.Compared with cationic emulsified asphalt,anionic emulsified asphalt resulted in better workability and mechanical strength in the UHPC,and its toughening effect was more significant.Considering both mechanical properties and overall performance,the use of anionic emulsified asphalt in UHPC is recommended,with an optimal dosage of 3%.The microstructure of UHPC specimens without emulsified asphalt and those mixed with 3%anionic emulsified asphalt was observed using a scanning electron microscope.The observations revealed that emulsified asphalt could fill the original microcracks in UHPC,improve the internal structure of the matrix,increase the effective contact area between steel fibers and the matrix to a certain extent,and enhance the toughening effect of steel fibers.Additionally,the viscoelastic properties of emulsified asphalt increased the energy required for crack propagation,effectively reducing the generation and development of microcracks and serving as a buffer for the destabilization damage of hydration products.