Effects of carbonation on mechanical properties of CAC-GGBFS blended strain hardening cementitious composites

Abstract

Calcium aluminate cement (CAC)—based strain hardening cementitious composites (SHCC) has been developed and used for the rehabilitation of sewerage pipelines. In addition to well-known microbiologically induced corrosion, CO 2 concentration in the sewerage environment is high, which may cause significant carbonation of pipelines. Thus, this paper aims to investigate the effects of carbonation on the mechanical performance of CAC-based SHCC. Two types of CAC-based SHCC with different strength grades and a referenced OPC-based SHCC were prepared. The accelerated carbonation test was conducted in a carbonation chamber with a 5% CO 2 concentration. The compressive and tensile behaviour of SHCC was tested first, and microstructure analysis, e.g., X-ray diffraction and scanning electron microscopy, was then performed. The results showed that CAC-based SHCC specimens exhibited robust strain-hardening performance as well as large deformation capacity in tension due to the fiber-bridging effect. Also, the compressive and tensile strength was significantly improved as well as achieving a higher tensile strain capacity after carbonation when compared with OPC-based SHCC. Microstructure analysis revealed that the metastable phases in carbonated CAC-based SHCC were converted into stable phases and calcium carbonate polymorphs, densifying the binder matrix. The obtained results of this paper may provide new insight into utilizing carbonation to avoid the unstable conversion of hydrates in calcium aluminate cement. 基于铝酸盐水泥（CAC）的应变硬化水泥基复合材料（SHCC）已成功应用于污水管道的修复。除了微生物引起的腐蚀外，污水环境中的高浓度CO 2 也会导致管道严重碳化。因此，本文旨在研究碳化对基于CAC的 SHCC力学性能的影响。制备了两种不同强度等级的基于CAC的SHCC试样和一种基于普通硅酸盐水泥（OPC）的SHCC试样作为参照。加速碳化试验在CO 2 浓度为5%的碳化室中进行。首先进行SHCC的抗压和抗拉强度测试，然后利用X射线衍射和扫描电子显微镜等进行微观结构分析。结果表明，由于纤维桥接效应，基于CAC的SHCC试样表现出稳健的应变硬化性能及较大的拉伸变形能力。此外，与基于OPC的SHCC相比，CAC的SHCC抗压和抗拉强度显著提高，并且在碳化后得到更高的拉伸应变能力。微观结构分析表明，碳化后的基于CAC的SHCC试样中的亚稳相转变为稳定相和碳酸钙多晶型，使胶凝基体更致密。本文的研究为利用碳化避免CAC水化产物的不稳定转变提供了新的见解。