纳米纤维素改性的再生混凝土骨料-基体界面微结构表征

Microstructure characterization of interfacial transition zone between recycled aggregate and cellulose nanofiber modified cement paste

将建筑垃圾中的废弃混凝土破碎后作为骨料形成的再生混凝土,是一种环保、可持续发展的建筑材料。然而,再生骨料表面相较于天然骨料存在更多裂纹和缺陷,因此再生骨料界面过渡区是再生混凝土的薄弱环节。为改性再生骨料界面,提出在基体中掺入纳米纤维素的方法,采用热重分析、扫描电镜和能谱分析等微观测试技术,探究纳米纤维素掺量对再生骨料界面微结构特征的影响规律。结果表明,再生混凝土老界面过渡区结构松散、存在较多孔洞,而掺入适量纳米纤维素后新界面处水泥水化程度、微观结构的致密性以及元素含量分布均匀性都得到改善。适量的纳米纤维素在养护阶段对水分子在水泥颗粒之间均匀分布及充分反应发挥积极作用,且纳米纤维素能与水泥水化产物形成较为致密的网状结构,增强各物相之间的紧密性。

Recycled concrete formed by crushing waste concrete in construction waste as aggregate is an environmentally friendly and sustainable material,which is of great significance for reducing resource consumption and environmental pollution.However,the aggregate surface of recycled concrete has more cracks and defects than that of natural aggregate,resulting in that the interfacial transition zone of recycled aggregate interface is the weak link of recycled concrete.In order to modify the interface between the recycled aggregate and the matrix,a method of incorporating cellulose nanofibers into the matrix was proposed from the perspective of sustainability.The effect of cellulose nanofiber content on the interfacial microstructure around the recycled aggregate was investigated by means of thermogravimetric analysis,scanning electron microscopy and energy spectrum analysis.The results show that the microstructures at the old interfaces of recycled concrete are found to be loose with many holes,and the hydration degree of cement,the density of microstructure and the distribution uniformity of element content at the new interfacial transition zones are improved after adding an appropriate amount of cellulose nanofibers.An appropriate amount of cellulose nanofibers plays a positive role in the uniform distribution and full reaction of water molecules among cement particles in the curing stage,and the cellulose nanofibers can form a relatively dense network structure with the cement hydration products and then enhance the tightness between the micro-phases.