There is a constant drive to improve the properties of recycled concrete owing to its inferior strength and fracture toughness compared to normal concrete and recent progress in graphene oxide (GO) nanomaterials impelling nanosized reinforcements to recycled concrete. Here, GO-modified natural sand (NS)- or recycled sand (RS)-based mortars (GONMs or GORMs) with six GO fractions (w_GOs) were fabricated to explore their 28 d mechanical strengths (f²⁸_t, f²⁸_c), fracture toughness (K_IC, δ_c), and microhardness (H_v), as well as their crystal phases (using X-ray powder diffraction) and microstructures (using scanning electronic microscopy). Results reveal, greater enhancements in mechanical strengths (4.50% and 10.61% in f²⁸_t, 4.76% and 13.87% in f²⁸_c), fracture toughness (16.49% and 38.17% in K_IC, 160.14% and 286.59% in δ_c), and microhardness (21.02% and 52.70% in H_v) of GORM with just 0.025 wt‰ and 0.05 wt‰ GO, respectively, with respect to the control are achieved when comparing with those of GONM with the same w_GO. More zigzag surfaces, more irregular weak interface slips, and the relatively lower strengths of RS bring the superiority of the template and reshaping effects of GO into full play in GORM rather than in GONM. These outcomes benefit a wide range of applications of recycled concrete products.

The use of construction and demolition waste (CDW) to prepare recycled admixtures is of great significance for the complete resource reutilization of CDW. In this paper, different kinds of CDW were prepared into recycled powder (RP) with a specific particle size (0–45 µm or 0–75 µm). The fineness, water requirement ratio (WRR), fluidity, loss on ignition (LOI), strength activity index (SAI) and compatibility of cement and superplasticizer (CCS) were examined. The above test results were analyzed by advanced analysis tools, such as laser particle size analysis, XRD, XRF, DSC-TGA, SEM, and BET. The properties of different types of RPs varied greatly, which was closely related to the microstructure, particle morphology and chemical composition of the RP. The experimental results showed that all kinds of RPs after grinding had a high fineness and good particle size distribution, and the mineral composition was dominated by SiO₂ with the content exceeding 50%. The WRR of various RPs was between 105% and 112%, and the SAI was between 68% and 78%, but the LOI varied greatly. Different types of RPs had a negative impact on the CCS, but the compatibility of cement and naphthalene-based superplasticizer was less affected. The content of recycled brick powder (RBP) in a hybrid recycled powder (HRP) was an important factor. When the content of RBP in HRP exceeded 50%, the HRP could meet the basic performance requirements of fly ash.

In this study, a variety of industrial solid wastes, including petroleum coke desulfurization slag, fly ash and carbide slag with natural resource bauxite, were used as raw materials to prepare high belite suphoaluminate cement, which contains a certain CaSO₄ content without adding natural gypsum to the clinker. The sintering temperature, mineral composition, and the physical and mechanical properties of the cement clinkers were investigated. The techniques adopted included a comprehensive thermal analysis (DSC-TG), X-ray diffraction (XRD), X-ray fluorescence (XRF) and scanning electron microscopy (SEM). The results revealed that it is completely feasible to prepare high belite sulphoaluminate cement with the various industrial solid wastes mentioned above and the utilization rate of the solid wastes is up to 80%. The sintering temperature ranges from 1225 °C to 1350 °C, and the optimal sintering temperature is approximately 1300 °C. The clinkers prepared at 1300 °C set and harden quickly and have a slightly higher water requirement of normal consistency. The mechanical strength is greatly affected by the CaSO₄ and 3CaO·3Al₂O₃·CaSO₄ contents and the most reasonable CaSO₄ content is 15%.

This research focused on the modification effects on recycled concrete (RC) prepared with nano-SiO₂ and CO₂ cured recycled coarse aggregates (RCA) subjected to an aggressive ions environment. For this purpose, RCA was first simply crushed and modified by nano-SiO₂ and CO_2, respectively, and the compressive strength, ions permeability as well as the macro properties and features of the interface transition zone (ITZ) of RC were investigated after soaking in 3.5% NaCl solution and 5% Na₂SO₄ solution for 30 days, respectively. The results show that nano-SiO₂ modified RC displays higher compressive strength and ions penetration resistance than that treated by carbonation. Besides, we find that ions attack has a significant influence on the microcracks width and micro-hardness of the ITZ between old aggregate and old mortar. The surface topography, elemental distribution and micro-hardness demonstrate that nano-SiO₂ curing can significantly decrease the microcracks width as well as Cl⁻ and SO₄²⁻ penetration in ITZ, thus increasing the micro-hardness, compared with CO₂ treatment.