Shrinkage property is a significant indicator of the durability of concrete, and the shrinkage of green recycled concrete is particularly problematic. In this paper, construction waste was crushed and screened to generate simple-crushed recycled coarse aggregate (SCRCA). The SCRCA was then subjected to particle shaping to create primary particle-shaped recycled coarse aggregate (PPRCA). On this basis, the PPRCA was particle-shaped again to obtain the secondary particle-shaped recycled coarse aggregate (SPRCA). Under conditions where the dosage of cementitious material is 300 kg/m³ and the sand rate is 38%, a new high-belite sulphoaluminate cement (HBSAC) with low carbon emission and superior efficiency was used as the basic cementitious material. Taking the quality of recycled coarse aggregate (SCRCA, PPRCA, and SPRCA) and the replacement ratio (25%, 50%, 75%, and 100%) as the influencing factors to prepare the green recycled concrete, the workability and shrinkage property of the prepared concrete were analyzed. The results show that the water consumption of green recycled concrete decreases as the quality of the recycled coarse aggregate (RCA) increases and the replacement ratio decreases, provided that the green recycled concrete achieves the same workability. With the improvement of RCA quality and the decrease of replacement ratio, the shrinkage of recycled concrete decreases. The shrinkage performance of green recycled concrete configured with the SPRCA completely replacing the natural coarse aggregate (NCA) is basically the same as that of the natural aggregate concrete (NAC).

To enhance forestry solid waste reuse, reduce building energy consumption, and increase building capacity, producing lightweight concrete with new materials has garnered recent attention. This study used waste wood and expanded perlite (EP) to design lightweight thermal insulation recycled concrete (LTIRC) with varying volume admixtures. Compared to mineral aggregate, wood aggregate (WA) and EP exhibit significant differences in water absorption, particle morphology, density, and crushing index. This study aimed to prepare LTIRC using two lightweight aggregates (WA & EP) and evaluate their dry density, mechanical properties, thermal properties, chloride ion permeability, and frost resistance. The results showed WA and EP introduction effectively reduced concrete bulk weight and met the dry density standard for lightweight concrete. In terms of thermal insulation performance, both WA and EP are characterized by porous, low–density, and low thermal conductivity. Consequently, LTIRC thermal conductivity was reduced by up to 76.5% versus conventional concrete, effectively increasing resistance to heat flow through concrete and providing potential for building energy savings. Additionally, WA and EP addition caused LTIRC to experience mechanical and durability property deterioration. However, some LTIRC achieved over 80% of the strength of natural aggregate concrete. Moreover, WA addition inhibited internal crack generation in LTIRC and slowed concrete damage from increased WA and EP dosage. The maximum mass loss of LTIPC was 2.72% after 100 freeze–thaw cycles. LTIPC precast panels are suitable for preparing low-carbon insulated building wall panels.

Although the energy structure has been gradually enriched in recent years, China, as the world’s largest producer and consumer of coal, still accounts for more than 50% of resources. Therefore, in this paper, the high carbon fly ash raw ash (HCFARA) was mechanically activated, and the flotation was treated to obtain decarburized fly ash (DFA) with a loss on ignition of 1.18%, water demand ratio of 101% and strength activity coefficient of 74.5%. With the exception of for water demand ratio, the rest meet the national requirements for the use of Class I fly ash. The foam concrete was prepared by partially replacing cement with decarburized fly ash in different proportions and at different water-to-cement ratios (0.3, 0.4 and 0.5) in order to study its dry density, porosity, compressive strength and thermal conductivity. The results show that the porosity of foam concrete grows with the increase in water-to-cement ratio and fly ash replacement rate. In addition, the dry density and thermal conductivity of the prepared foam concrete can meet the requirements of A05 grade foam concrete (Density less than 500 kg/m³, thermal conductivity less than 0.12 W/(m·k)). The compressive strength can meet the requirements of C0.3 grade foam concrete (Minimum use standard).

Solutions are needed to solve the problem of a large amount of construction solid waste and a shortage of natural aggregate (coarse and fine aggregates). In this paper, simple-crushed coarse aggregate (SCRCA) and simple-crushed fine aggregate (SCRFA) were obtained by simple-crushing of construction solid waste. On this basis, SCRCA and SCRFA were treated with particle-shaping to obtain particle-shaping coarse aggregate (PSRCA) and particle-shaping fine aggregate (PSRFA), and the recycled powder (RP) produced in the process of particle-shaping was collected. Under the condition of a 1:4 cement-sand ratio, RP was used to replace cement with four substitution rates of 0, 10%, 20%, and 30%, and dry-mixed masonry mortar was prepared with 100% SCRFA, PSRFA, and river sand (RS). The basic and mechanical properties and microstructure of hydration products of dry-mixed mortar were analyzed, and the maximum substitution rate of RP was determined. Under the condition that the amount of cementitious material is 400 kg/m³ and the RP is at the maximum replacement rate, three different aggregate combinations to prepare concrete are the 100% use of SCRCA and SCRFA, PSRCA and PSRFA, and RS and natural aggregate (NCA); the workability, mechanical properties, and aggregate interface transition zone of the prepared concrete were analyzed. The results show that when the replacement rate of RP is less than 20%, it has little effect on the properties of products. The performance of PSRCA and PSRFA after treatment is better than that of SCRCA and SCRFA. Under different RP substitution rates, the performance of dry-mixed mortar prepared with PSRFA is very close to that prepared with RS. The performance of recycled concrete prepared with PSRCA and PSRFA is also very close to that of products prepared with NCA and RS. The failure morphology of PSRCA and RSRFA concrete is also similar to that of NCA and RS concrete.

In this paper, the properties of sulphoaluminate based recycled concrete, with high workability and low and medium strength, prepared by recycled powder (RP), recycled coarse aggregate (RCA), and high belite sulphoaluminate cement (HBSAC), were systematically studied. Under the condition of a water binder ratio of 0.45, sulphoaluminate based recycled concrete, with different mix proportions, was prepared by replacing sulphoaluminate cement with RP and natural coarse aggregate (NCA) with RCA. The workability, mechanical properties, durability, and hydration products of the prepared concrete were analyzed. The results showed that when RP and RCA were used together, the workability of recycled concrete could fully meet the pumping demand in actual construction. When the mass replacement rate of RP was less than 30% and that of RCA was less than 20%, the strength of recycled concrete could completely reach the design strength grade, while those that did not reach the design strength grade could reach the next grade. The durability performance was also good.

Controlling structural deformation is essential for the structural stability of 3D-printed cement composites. In this paper, carbonated recycled aggregate (CRA) was incorporated into 3D-printed magnesium phosphate cement composites (MPCCs) to control rheology and improve buildability. Experimental results show that CRA increased the static yield stress from 2210.96 to 6238.18 Pa and the storage modulus. When the incorporation of CRA was more than 15%, the phase angle was less than 45°, indicating predominantly solid-like behavior. Additionally, due to the higher porosity, the compressive strength and flexural strength of 3D-printed MPCCs decrease with the increasing CRA content; however, the decline tendency becomes significantly more pronounced when CRA content exceeds 10%. Structural deformation decreased from 14.39% to 6.91%, attributed to the rough surface of CRA, which promotes more uniform stress transfer during stacking. This study demonstrates a simple upcycling route that improves the printing stability and sustainability of 3D-printed magnesium phosphate cement composites (MPCCs).