In order to reduce the amount of natural aggregates and cementitious material in 3D printed concrete, this study used recycled fine aggregate (RFA) to partially replace natural fine aggregate and clay brick powder (CBP) to replace cement. The fluidity and compressive strength test of cast-in-situ concretes with RFA only (0, 25%, 50%, 75% and 100% replacement ratio), with CBP only (0, 5%, 10%, 15%, 20% and 30% replacement ratio) and with both of them were firstly carried out to obtain the optimal replacement ratio of RFA and CBP. Then, it investigated the effect of the addition of 50%RFA and 10%CBP and the corresponding mix proportion adjustment methods (adding extra water and increasing water reducer dosage) on the fresh and harden properties of 3D printed concrete. The test results indicate that the decreasing amplitude of the compressive strength of cast-in-situ concrete is within 10% when the replacement ratio of RFA is less than 50%. With the increase of CBP replacement ratio from 0 to 30%, the compressive strength of cast-in-situ concrete increases first, then decreases and then slightly increases. The specimen with CBP content of 10% exhibits the highest compressive strength. Compared to the concrete with 50%RFA only, the concrete with 50%RFA and 10%CBP has higher strength, while the fluidity is almost kept unchanged. For 3D printed concrete, the addition of 50% recycled fine aggregate and 10% brick powder and additional water can keep the initial expansion of 3D printed concrete unchanged and improve the buildability of concrete, but it can decrease the slump, opening time, compressive and split tensile strength and increase intensity anisotropy. However, increasing water reducer dosage in the mixture can not only significantly improve the fluidity, opening time and compressive strength of 3D printed concrete, but also reduce the intensity anisotropy.

Municipal solid waste incineration bottom ash (IBA) shows large heterogeneity because of different garbage composition, incineration process and storage conditions. The effective cooperation for one batch of recycled concrete (mortar) may be ineffective for another batch, resulting in large dispersion of recycled concrete (mortar) performance, which limits its application. In order to explore the heterogeneity of IBA from different sources and the strength variability of recycled mortar, this study collected a total of 14 batches of IBA samples from different incinerators and different monthly sources and tested for their physical and chemical properties. And it investigated the workability, compressive strength, and splitting tensile strength of IBA recycled mortar. Statistical analysis was conducted to assess the level of strength variability in IBA recycled mortar. The test results showed that the crushing index, porosity, sulfide, and chloride content of IBA did not meet the specifications for recycled fine aggregates, and there is significant heterogeneity in IBA from different origins. When the recycled cement mortar below M20 strength grade is prepared with a substitution rate of 50% IBA which is from a single incineration plant of different months, the strength is not significantly reduced compared with that of natural aggregate mortar, and the strength variability is similar to that of ordinary recycled aggregate concrete and the standard deviation is also lower than the recommended value of the specification. However, when used to prepare the recycled cement mortar above M20, the reduction in compressive strength was significant (reduced by 23%～32%). Due to higher compressive strength variability of IBA recycled mortars from two different incineration plants, it was not recommended to use IBA recycled mortars from different incineration plants together.

Textile reinforced mortar (TRM) strengthening is a method of using mortar as an inorganic adhesive to stick textile onto the surface of components to form a strengthening layer. It has advantages such as light weight, high strength, minimal change in cross-sectional dimensions, good high-temperature resistance, and excellent durability, and thus has gained widespread attention in recent years. TRM typically uses polymer-modified cement mortar as the adhesive, but the production of cement has high energy consumption and carbon emissions. To achieve the “dual carbon” goals, this paper proposed to replace cement with geopolymer, which has much lower production energy consumption and carbon emissions while offering mechanical properties similar to cement, thus forming a textile reinforced mesh-enhanced geopolymer mortar (TRGM) strengthening method. This paper employed carbon textile reinforced geopolymer mortar to strengthen two-way reinforced concrete slabs. The flexural performance tests and finite element analysis were conducted on the unstrengthened and strengthened slabs with different aspect ratios and different numbers of TRGM layers. The strengthening effect of TRGM, the contribution of bidirectional fibers to bearing capacity, and the force transmission mechanism of the strengthened slabs were investigated. The results show that TRGM strengthening can effectively improve the post-cracking stiffness and flexural carrying capacity of two-way slabs and inhibit crack propagation, especially the widthwise cracks. The strengthening effect of TRGM increases with the increase in the aspect ratio of the two-way slabs. The bearing capacity of the strengthened slab with one layer of TRGM was greatly influenced by the overlap of the textile and strengthening construction quality, which made the strengthening efficiency of one layer of TRGM lower than that of two layers. The overlap of the fiber mesh may affect the strength of the fibers, and the design should ensure that the fibers have sufficient overlap length. After the widthwise reinforcement yielding, the ratio of bending moment borne in the widthwise direction to the lengthwise direction gradually decreased, since the contribution of the longitudinal reinforcement and fibers to the bearing capacity gradually increased. As the mid-span deflection increases, the proportion of tensile force borne by the fibers shows a wave-like trend, first decreasing, then increasing, and subsequently decreasing again.