This study aims to explore the feasibility of using circulating fluidized bed fly ash (CFA) as a supplementary cementitious material in both ordinary concrete and recycled aggregate concrete (RAC). Various properties of both concretes, including compressive strength, drying shrinkage, carbonation resistance, surface resistivity, were evaluated. Additionally, the economic and environmental benefits were assessed. Findings indicated that increasing CFA content (mass fraction) progressively increases drying shrinkage rate and carbonation depth in both concretes. At 30% CFA, ordinary concrete showed 10.9% higher 180-day shrinkage and 4.3% greater 28-day carbonation compared to the control, while RAC exhibited 14.7% higher shrinkage and a significant 34.4% increase in carbonation compared to its control. However, at 10% CFA, both concretes showed no significant reduction in compressive strength compared to their respective controls. Up to 20% CFA, a decline of 13.1% and 9.0% was observed in the 28-day compressive strength of ordinary concrete and RAC, respectively. The results indicate that RAC demonstrates better compatibility with CFA compared to ordinary concrete. Additionally, the economic and environmental benefit analysis showed that the lowest cost (8.6 and 7.4 yuan for ordinary concrete and RAC, respectively) and carbon emission (6.2 and 6.7 kg for ordinary concrete and RAC, respectively) for both concretes (normalized per unit of strength) occurred at 10% and 20% CFA, respectively. This study investigated varying CFA dosages to balance performance trade-offs against cost and carbon emissions, establishing the feasibility of CFA utilization in both ordinary concrete and RAC.

The incorporation of circulating fluidized bed (CFB) fly ash into self-leveling cement-based (SLC) paste production presents significant environmental advantages. However, its addition deteriorates the fresh properties of the paste, posing challenges for practical implementation. This research examined the fresh properties of SLC paste blended with CFB fly ash, emphasizing fluidity, rheological characteristics, and bleeding rate. To enhance flowability, polycarboxylate superplasticizer (PCE) was incorporated, with particular emphasis on its interaction with CFB fly ash. The findings reveal that adding CFB fly ash to cement-based paste significantly decreased fluidity while increasing yield stress and plastic viscosity. Incorporating 20 wt.% CFB fly ash reduced paste fluidity by 51.4%, while plastic viscosity and yield stress increased by factors of 2.3 and 73, respectively. While PCE enhanced the fluidity of the blended paste, its water-reducing efficiency diminished, and the bleeding rate of the paste increased with higher CFB fly ash dosage. The water-reducing capability of PCE in the CFB fly ash-blended cement paste with 20 wt.% CFB fly ash decreased by 40.0%, and the bleeding rate of the paste increased from 0.6% to 6.7%. This effect was primarily attributed to the poor compatibility between PCE and CFB fly ash. The decline in PCE efficiency with higher CFB fly ash content, along with its lower adsorption capacity on CFB fly ash compared to cement particles, further confirmed this incompatibility.

Low-calcium circulating fluidized bed fly ash (LCFA) exhibits obvious potential as a supplementary cementitious material (SCM) due to its minimal impact on concrete volume stability. However, its early hydration behavior remains unclear. This study investigates the hydration characteristics of cementitious composites incorporating varying LCFA dosages. Setting time, hydration heat, pore solution ion concentrations (Ca²⁺ and SO₄²⁻), and XRD analysis were employed. Hydration kinetics were described using the Krstulovic–Dabic model, with corresponding kinetic parameters calculated. The results demonstrate that LCFA inhibits the formation of calcium hydroxide (CH) and C-S-H precipitation while delaying sulfate depletion. Consequently, LCFA incorporation significantly extends both initial and final setting times. Hydration kinetics were effectively described by the Krstulovic–Dabic model, identifying three distinct stages of nucleation and crystal growth (NG), interactions at phase boundaries (I), and diffusion (D). Increasing the LCFA dosage reduced the rate constant for the NG process (K_NG′) but increased the rate constants processes of I (K_I′) and D (K_D′). Furthermore, LCFA increased transition points of NG → I (α₁) and I → D (α₂).

Inorganic soil stabilizer represents a promising option to tackle the issues that arise from the land-filling of engineering waste spoil (EWS) due to its economic and environmental benefits. This paper investigates the mechanical and microscopic properties of magnesium oxysulfate soil stabilizer (MOSS) pastes. In addition, the mechanical properties of a novel type of engineering waste spoil-based specimens (EWSS), fabricated using MOSS to solidify high-content EWS, were systematically investigated. The results show that a larger mean particle size and BJH adsorption average pore diameter of LBM were found to accelerate the heat flow rate of the hydration reaction. Specifically, the peak heat flow and total hydration heat attained 30.25 mW/g and 283.9 J/g, respectively, under the condition of an MgO-to-MgSO₄ molar ratio of 9: 1 with LBM2 as the raw material. Furthermore, when the weight ratio of EWS rose from 5% to 80%, the compressive and flexural strengths of EWSS pastes at the 28-day curing age were reduced by 47.0% and 53.3% relative to the reference MOSS pastes.