纳米偏高岭土及细骨料对UHPC力学性能的影响

Effect of Nano-metakaolin and Fine Aggregate on the Mechanical Behavior of Ultra High Performance Concrete

采用优良的矿物掺和料和绿色细骨料取代部分水泥和石英砂的方式制备生态型超高性能混凝土(UHPC),可优化其性能并降低材料制备过程中的碳排放。目前尚缺乏对生态型UHPC材料的拉伸应变强化性能的研究。通过轴拉试验、抗压强度及工作性能测试,研究纳米偏高岭土掺量(0%、3%及6%)及细骨料类型(石英砂、河砂及机制砂)对UHPC力学性能的影响规律,并结合微观结构分析阐明纳米偏高岭土及机制砂对UHPC拉伸应变强化性能的影响机理。研究表明:纳米偏高岭土可提高钢纤维-UHPC基体界面的粘结性能,提升UHPC拉伸应变强化能力及钢纤维有效锚固恢复效率。机制砂可提高UHPC的开裂强度,使其拉伸应变强化能力提升受限;钢纤维拔出阶段机制砂不能提供有效的摩擦阻力,拔出的钢纤维表面沟槽不明显且粘连较少的基体碎渣,加快了UHPC的应变软化速率。

Using good mineral admixtures and green fine aggregates to partially replace cements and quartz sands to prepare ecological ultra high performance concrete(UHPC)can optimize its properties and reduce the carbon emission during material preparation.There is a lack of research about the tensile strain hardening behavior of ecological UHPC.The influence of nano-metakaolin contents(0%,3%and 6%)and fine aggregate types(quartz sand,river sand and manufactured sand)on the mechanical properties of UHPC was studied via uniaxial tensile tests,compressive strength tests and workability measurements.Finally,the tensile strain hardening mechanism of UHPC incorporated with nano-metakaolin and manufactured sand was clarified based on microstructural analysis.The results show that nano-metakaolin can improve the bond behavior of steel fiber-UHPC matrix interface,and increase the strain hardening capacity of UHPC and raise the recovery efficiency of steel fiber effective anchorage.The promotion space of the strain hardening capacity of UHPC incorporated with manufactured sands is relatively low due to that manufactured sands can improve the high cracking strength of UHPC.The drawing resistance provided by manufactured sands for steel fibers is insufficient during steel fiber pulling out,and the scratch grooves are unobvious and the crushed debris of UHPC matrix is slight on the surface of the pulled-out steel fibers.This makes the tensile strain softening rate of UHPC accelerated.