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• Quantifying the properties of multiple ITZs in RAC subjected to aggressive ion environment. • Investigating the effects of old and new concrete strength on the properties of multiple ITZs in RAC. • Establishing the relationship between the micro-hardness of multiple ITZs and exposure days. Recycled aggregate concrete (RAC) is inevitably subjected to various aggressive environments; however, the damage behavior of multiple interfacial transition zones (ITZs) in RAC under such environments has received little consideration in previous studies. Therefore, this paper was developed to quantify the influence of sulfate and chloride attack on the properties of multiple ITZs in RAC. A modeled RAC sample that contained multiple ITZs was first prepared, and the micro-hardness and micro-structure of multiple ITZs undergoing sulfate and chloride attack were determined. The results showed that the ITZ OA-NM between old aggregate and new mortar was the weak point of RAC when the new concrete strength was lower than the old concrete strength; however, the ITZ OA-OM between old aggregate and old mortar was the weakness of RAC when the new concrete strength was higher than the old concrete strength. A binomial relationship between ITZs properties and sulfate attack duration was observed, and the micro-hardness of multiple ITZs decreased linearly with increasing chloride attack duration. The degradation model for the micro-hardness of multiple ITZs was similar to that for the compressive strength of RAC subjected to an aggressive ion environment. The properties of ITZ OA-NM were more sensitive to aggressive ion attack compared with that of other ITZs. Increasing the strength of new concrete is an effective method of improving the properties of multiple ITZs in RAC. [ABSTRACT FROM AUTHOR]

Improving the adaptability of polycarboxylate superplasticizers (PCE) in high-clay content mortar is of great significance in enhancing the workability and mechanical properties of mortar containing clay. In this study, the potassium-based alkaline electrolyzed water (AEW) was used as mixing water for cement mortar. The excellent properties of AEW enabled PCE to be more compatible in cement mortar containing montmorillonite (MT) or kaolin (GL), improving the performance of mortar containing clay. The results showed that compared with ordinary tap water (OTW), the adsorption rate of clay minerals on PCE decreased in the AEW environment, and the clay interlayer spacing of MT was also reduced. AEW can inhibit the intercalation and adsorption of PCE molecular side chains by clay minerals to some extent. However, due to its unique crystal structure, the adsorption of MT on PCE was still significantly higher than that of GL. At the same time, increasing the content of clay mineral led to a decrease in mortar performance. Compared with the GL series, the MT series had a more significant negative impact on mortar fluidity and strengths. AEW also can promote hydration reactions, release more hydration heat, and produce more hydration products to encapsulate clay particles, thereby improving the workability and mechanical properties of cement paste containing clay. Furthermore, the high-activity AEW is rich in positively charged metal ions that can interact with clay minerals preferentially over cement particles, which enables the clay interlayer structure to be quickly saturated by AEW water molecules, effectively hindering the adsorption of PCE by clay minerals. However, in both the OTW and AEW environments, the intercalation effect of GL on PCE molecular side chains was not significant. Therefore, AEW has great potential in improving the adaptability of PCE in muddy cement pastes, which can help to enhance the workability and mechanical properties of muddy cement composites. This study provides theoretical references for preparing high-performance anti-clay concrete. • The excellent properties of AEW enabled PCE to be more compatible in cement-based materials containing montmorillonite (MT) or kaolin (GL). • AEW can mitigate the adsorption of MT to the PCE molecular side chains, while the interlayer of GL is both basically not intercalated with PCE molecular side chains. • For different clay minerals series of mortar, AEW mortar both exhibits significantly higher fluidity and strengths than ordinary tap water (OTW) mortar. [ABSTRACT FROM AUTHOR]

Synthesis of high belite sulfoaluminate cement at low sintering temperatures (1225–1300 °C) using petroleum coke desulfurization residue (PCDR), fly ash (FA), carbide slag (CS), and bauxite (BX) was investigated. The thermal behavior, mechanical properties, heat of hydration, and hydration products of the developed binder were systematically studied. The results showed that the target C 4 A 3 S, β-C 2 S, and C 4 AF phases were successfully produced at 1225–1300 °C, and the industrial solid wastes can use up to 80%. The optimal sintering condition to obtain satisfactory clinker strength was 1300 °C, 45 min, and 10 °C/min, and the corresponding 1-d and 28-d strengths were 27.7 and 51.4 MPa. The early hydration products were mainly composed of AFt, AH 3 , unhydrated C 4 A 3 S, C 2 S, CaSO 4 , and trace CH. The network structure formed by AFt interweaving was filled with AH 3 colloid, which was conducive to the improvement of cement strength. Furthermore, the cumulative heat release of the developed cement (191 J/g) in 3-d was lower than that of the sulphoaluminate cement (SAC) (198 J/g), effectively alleviating the rapid setting as compared to SAC and broadening its application range. [ABSTRACT FROM AUTHOR]

[Display omitted] • The utilization of industrial solid waste and construction waste developed AARAC with controllable performance. • A strength-based mix design method was proposed for AARAC using a linear fitting formula. • The reference mix proportion of AAC suitable for different strength grades was optimized. • The performance differences between AARAC and AANAC were systematically assessed. Recycled concrete aggregates (RCA) are produced from demolished buildings and old rigid pavements, which are deemed as solid waste, comprising primarily old aggregate and cement mortar. In this study, the use of RCA was introduced in alkali-activated concrete (AAC) to investigate the feasibility of designing the mix proportion of alkali-activated recycled aggregate concrete (AARAC) using a linear fitting formula. A total of 32 mixes, with the amount of cementitious materials varying from 350 kg/m3 to 500 kg/m3 and the sol ratio from 0.43 to 0.55, were prepared for the regression analysis of the relationships between multiple parameters. The tests for water consumption, compressive strength and durability were included. The experimental results indicate that concrete prepared using high-quality RCA exhibited lower water consumption and higher compressive strength. When the natural aggregate (NA) was replaced by the RCA, the compressive strength reached its highest value of 54.0 MPa. Moreover, as the strength grade increased, the chloride penetration resistance, anti-carbonization performance, and freezing resistance of AARAC gradually increased, while the shrinkage decreased. In conclusion, this study provides a new method for the mix design of AARAC, which contributes to the advancement of solid waste management in the construction industry. [ABSTRACT FROM AUTHOR]