采用等量砂浆法的再生混凝土基本力学性能预测方法

Prediction of mechanical properties of recycled concrete prepared with equivalent mortar volume method

传统的再生混凝土配制方法将残余砂浆当作天然粗骨料,但残余砂浆的基本性能较天然粗骨料差,这使得所配制的再生混凝土较普通混凝土性能差;近年来,学者通过调整再生粗骨料和天然砂浆的体积掺量,使所配再生混凝土中砂浆的总体积与普通混凝土中的砂浆体积相同(该配制方法称为等量砂浆法,简称EMV).目前针对该配制方法得到的EMV混凝土力学性能的研究较少.首先对影响EMV混凝土力学性能的因素进行评述,并基于课题组及文献试验数据验证典型规范预测计算式的适用性,对不适用的计算式进行修正.研究结果表明,粗骨料取代率及残余砂浆含量是影响EMV混凝土力学性能的主要参数,EMV混凝土的抗压强度和弹性模量随取代率增大呈现降低的趋势;基体混凝土强度和矿物添加剂含量对EMV混凝土力学性能也有一定影响;EC2规范可有效预测EMV混凝土的各项力学性能,ACI 318规范低估了EMV混凝土的早期抗压强度和干燥收缩变形,采用修正的ACI 318规范模型,可以有效预测EMV混凝土的基本力学性能。

The residual mortar is treated as coarse aggregate for concrete production when using traditional mixing methods,and lower mechanical properties are accordingly obtained in the resulting concrete due to the residual mortar with inferior properties.Recently,the total volume of(natural and residual)mortar in recycled concrete was kept constant with that of natural mortar in natural concrete,thereafter this new mixing method was referred to as equivalent mortar volume(EMV)mixing method.To date limited research effort has been devoted to this research area.In this context,the influential factors on the mechanical properties of EMV concrete were evaluated,and the current prediction equations in typical specifications have been benchmarked against available test results from literature,and further modified.The obtained results showed that the replacement ratio and residual mortar content are the primary factors influencing the mechanical properties of EMV concrete,and with increasing replacement ratio of recycled aggregate,EMV concrete exhibited lower compressive strength and elastic modulus,the properties of parent concrete and concrete admixtures also affected the properties of EMV concrete.EC2 well predicted the properties of EMV concrete,while ACI 318 underestimated the compressive strength and elastic modulus of EMV concrete.The modified ACI 318 formula could well predict the mechanical properties of EMV concrete.