纳米改性对再生混凝土双K断裂参数的影响

再生骨料与天然骨料相比,表观密度低,吸水率大,压碎指标大,导致再生混凝土的性能较差。本文采用纳米SiO_2溶液对再生混凝土进行改性处理,通过三点弯曲梁法对再生骨料取代率不同(0,50%,70%,100%)的试件、取代率50%和100%下不同纳米SiO_2掺量的试件共12组60根试件进行断裂实验,用双K断裂参数评价再生混凝土的断裂性能,研究再生骨料取代率和纳米SiO_2掺量对再生混凝土断裂性能的影响。结果表明,再生混凝土的起裂韧度和失稳韧度整体随着再生骨料取代率的增加而降低;适量纳米SiO_2的掺入能提高再生混凝土的断裂韧度,再生骨料取代率50%和100%、纳米SiO_2掺量1.0%时再生混凝土的起裂韧度和失稳韧度提升程度最大,分别达到0.6929 MPa·m~(1/2)、1.3073 MPa·m~(1/2)和0.5552 MPa·m~(1/2)、1.2410 MPa·m~(1/2)。

Effect of nano-modification on double-K fracture parameters of recycled concrete

Compared with natural aggregate,recycled aggregate has lower apparent density,higher water absorption and larger crushing index.Therefore,there are some defects in the performance of recycled aggregate concrete (RAC).In this paper,nano-SiO₂ solution was used to strengthen RAC.Three-point bending beam method was adopted to conduct fracture experiment of specimens with varying recycled aggregate replacement rates (0,50%,70%,100%) and specimens with varying replacement rates (50% and 100%) and varying SiO₂ addition,12 groups of 60 specimens in all.Double-K fracture parameters were used to assess the fracture property of recycled concrete and to investigate the effect of recycled aggregate replacement rates and addition of SiO₂ on the fracture property of recycled concrete.The results show that the initial cracking toughness and the unstable fracture toughness of RAC decreased with the increase of RAC rate.Appropriate amount of nano-SiO₂ can improve the fracture toughness of RAC,when the replacement rates of recycled aggregate were 50% and 100% respectively,and the content of nano-SiO₂ was 1.0%,the enhancement for initial cracking toughness and unstable fracture toughness of recycled concrete was the highest,reaching 0.6929 MPa·m^1/2 and 1.3073 MPa·m^1/2 respectively for recycled concrete with 50% recycled aggregate and 0.5552MPa·m^1/2 and 1.2410MPa·m^1/2 respectively for recycled concrete with 100% recycled aggregate.