The traditional interlayer bonding testing methods used for cement-based materials is not suitable for three-dimensional (3D)-printed geopolymers and they have some drawbacks that prevent efficient and accurate testing; accordingly there is an urgent need for a new testing method. In this briefing article, a newly designed fixture method (N-FM) was proposed to test the interlayer bonding strength of a 3D-printed geopolymer made from TJC-1 lunar regolith simulant as a case to show the improvement from the previously used traditional adherence method (T-AM). The results show that these two methods exhibit different failure modes. Interlayer failure, intralayer failure and epoxy resin detaching can be observed from the T-AM, while interlayer failure and diagonal failure can be observed from the N-FM. Compared to 50% by the T-AM, the success rate can be improved up to 90% by the N-FM and the distribution of data is more uniform. The 28-day interlayer bonding strength result from the N-FM was 2.16 MPa, which is considered to be more accurate, and is 30.91% higher than that of the T-AM.

Thallium (Tl) poses a significant pollution risk due to its high volatility during clinker calcination. Thermodynamic calculations and multi-stage monitoring have revealed that, despite sulfur suppression, over 90% of Tl volatilised as thallium chloride at 900°C due to chlorine. Volatilised Tl migrated with gas, condensing in cooler zones, enriching Tl in mill-outlet raw meal. The recycling of Tl-enriched dust from the suspension preheater boiler and bag filter further intensified the Tl enrichment in the kiln-feed raw meal. As this enriched material reached the two-stage cyclone, it re-adsorbed and condensed Tl from the gas and reintroduced Tl back into the high-temperature zone again, forming an internal ‘volatilisation-condensation’ cycle. After calcination, only 0–27.85% of input Tl resided in the clinker, while the bypass system released merely 1.31–6.66%. Crucially, the bag filter efficiently intercepted volatile Tl, preventing detectable Tl emissions from kiln gas. Therefore, despite high volatility, the internal cycle, effective dust capture and dust recycling led to closed-loop circulation and enrichment of most Tl within the system, preventing environmental release. In addition, co-processing Tl-containing solid waste amplified the imbalance between Tl input and output, leading to greater internal circulation and enrichment within the kiln system, without significantly altering clinker Tl content or emissions.

To promote the application of seawater–sea sand concrete (SSC) in marine engineering and investigate the influence of ions in the marine environment on the alkali–silica reaction (ASR) in concrete, the impact of calcium ions on the formation and evolution of ASR products was explored. By incorporating varying amounts of calcium oxide, the characteristics of ASR products (composition and microstructure) in SSC under different calcium/silicon molar ratios (CSRs) were systematically examined, elucidating the influence of the CSR on ASR pathways and product stability. The results showed that, with an increase in the CSR from 0.30 to 0.55, excess Ca2+ ions progressively facilitated the staged transformation of sodium shlykovite into the intermediate phase ASR-P1, followed by further conversion to calcium silicate hydrate gel. Concurrently, the pore solution exhibited significant dilution of Na+ and K+ ions (concentrations reduced to 26.13 mg/l and 7.41 mg/l, respectively), effectively suppressing the formation of deleterious alkali silicate gels. Specimen expansion rates at 14 and 28 days decreased from 0.212% and 0.345% to 0.085% and 0.109% (reductions exceeding 60%), respectively, with 14-day expansion rates remaining below 0.1% at CSR ≥ 0.50. This study proposes a CSR optimisation strategy for ASR mitigation, providing theoretical foundations for the engineering application of SSC in marine environments.

High-belite calcium sulfoaluminate cement (HBCSA) is a low carbon dioxide binder but suffers from slow early strength development due to its low hydration rate. Adding calcium oxide (CaO) can increase the hydration rate, but the synthesis of HBCSA clinker containing a designed amount of calcium oxide remains unexplored. In this study, a method was developed to produce calcium oxide–C2S–C4A3S¯ (CBCSA) clinkers for autoclaved aerated concrete (AAC). Experiments were performed to systematically examine the effects of the calcination temperature, retention time and minor oxides on the mineral composition of the clinkers, along with the influence of the mineral composition on the slurry properties and the physical–mechanical performance of the AAC. The results indicated that the optimal calcination temperature was 1230–1290°C and the optimal retention time was 30–60 min. The CBCSA clinker prepared with 26.5% calcium oxide, 8.8% C4A3S¯ and 44.7% C2S produced an AAC slurry with well-matched foaming and thickening rates, shortening the pre-curing time. The resulting AAC blocks achieved a bulk density of 724 kg/m3 and a compressive strength of 7.00 MPa, demonstrating that the CBCSA preserved environmental benefits while enhancing the production efficiency of AAC.

To advance sustainable construction, in this study, red mud-based geopolymer recycled aggregate concrete (GRAC) was synthesised using industrial waste (red mud) and construction waste (recycled coarse aggregate (RCA)). Orthogonal experiments optimised the geopolymer mortar mix design, identifying sodium silicate concentration (30%), ground granulated blast furnace slag (GGBS) content (40%), lime (5%) and gypsum (0%) as the optimal proportion. Sodium silicate concentration was the most critical factor influencing compressive strength, followed by GGBS content, while lime and gypsum exhibited minimal effects. The optimised mortar achieved a 28 days compressive strength of 61.48 MPa – which is 36.90% higher than ordinary Portland cement (OPC) mortar. GRAC specimens with 0–100% RCA replacement were subsequently prepared. Compressive strength decreased with increasing RCA content, peaking at 50% replacement (45.96 MPa at 28 days, 2.64% above OPC concrete). Microstructural analysis by way of scanning electron microscopy/X-ray diffraction analysis revealed: depolymerisation of red mud and GGBS minerals released active Ca, Si and Al components; geopolymerisation formed a hybrid zeolite-like framework and calcium aluminosilicate hydrate (C–A–S–H) gel; the geopolymer matrix filled RCA surface microcracks, enhancing interfacial bonding. GRAC’s superior strength stems from synergistic RCA–geopolymer interactions, reducing cement consumption and natural resource extraction. This work demonstrates high-value recycling of dual waste streams for sustainable infrastructure development.

Low-carbon-dioxide belite–ye’elimite–Q phase clinker (BYQ clinker) was designed and prepared, and its performance was explored in this work to realise the utilisation of gold mining and alumina industrial solid waste and the reduction of carbon dioxide emission. This new system of BYQ clinker was designed based on the investigation involved in the Q phase formation and Q–C4A3$ coexistence. In detail, the effects of temperature and magnesium oxide (MgO) composition on the calcining of the Q phase, the coexistence mechanism of Q phase and C4A3$, as well as the effects of sodium oxide (Na2O) on Q phase and C4A3$ were discussed. The results showed that the Q phase was calcined at 1350°C when the content of magnesium oxide was 3.37–5.37%. The ratio of Q phase/C4A3$ was greater than 1:1 in order to realise the coexistence of Q phase and C4A3$. Also, C4A3$ and Q phase can accommodate some amount of sodium oxide. These findings provide the foundation for the successful preparation of BYQ clinker using 35% gold mining and alumina industrial solid waste, with red mud accounting for 4%. The BYQ clinker was sintered at 1350°C and demonstrated excellent hydration activity, high early strength and a remarkable capability for immobilising heavy metal ions present in industrial solid waste raw materials.

The use of co-calcined rice husk (RH) and red mud (RM) in cement mortar was investigated in this study. The effects of these additives on mechanical properties, electromagnetic shielding performance and environmental benefits were systematically analysed. The addition of calcined RH and RM notably improved the compressive strength of the cement mortar and exhibited strong electromagnetic wave absorption capabilities, particularly in the mid-frequency range. Under optimal conditions (5% dosage with RH and RM co-calcined at 800°C), the compressive strength increased by 3.03% at 7 days and by 8.33% at 28 days as compared with the control mortar. The material exhibited six absorption bandwidths spanning from low to high frequency, with the strongest absorption peak at 10.73 GHz, a reflection loss of −37.8 dB and an absorption bandwidth of 0.71 GHz (<−10 dB). Based on the principles of sustainable design, RH and RM, as agricultural and industrial wastes, were repurposed to develop a cement-based composite material that balances structural strength and electromagnetic absorption.

Alkali-activated foam pastes (AAFPs) have significantly different hydration and carbonation mechanisms compared with ordinary Portland cement (OPC) pastes. An accurate determination of the carbonation depth of AAFP is crucial for evaluating their carbon dioxide storage potential. The main objective of this study was to determine whether detection methods for carbonation depth developed for OPC are applicable to AAFP. An AAFP was prepared using fly ash, ground granulated blast-furnace slag, sodium hydroxide solution, waterglass solution and hydrogen peroxide as the main raw materials. The applicability of the phenolphthalein–alcohol solution method (PASM) and the layer-by-layer grinding pH method (LGPM) for measuring the carbonation depth of AAFP was analysed using rapid carbonation tests, thermogravimetric analysis, X-ray diffraction, scanning electron microscopy and other characterisations of AAFP samples. The results showed that the carbonation depth and carbonation rate coefficient of the AAFP measured using the LGPM were, respectively, 1.42–1.65 and 1.64 times higher than those measured using the PASM. The LGPM was able to determine the carbonation depth of the AAFP more accurately, enabling the precise identification of the AAFP into three carbonation zones: a fully carbonated zone (pH ≈ 9.50–9.88), a partially carbonated zone (pH ≈ 9.88–12.12) and an uncarbonated zone (pH ≈ 12.12–12.62). For a more accurate evaluation of the carbonation process and carbon dioxide sequestration capacity of AAFP, it is thus recommended to use the LGPM to determine the carbonation depth.

The aim of this work was to optimise mortar properties through the combined use of local byproducts, specifically silica fume (SF) and crushed limestone sand (CLS). The optimisation process involved examining the effects of SF and CLS, both separately and in combination, on the mortar’s rheology, mechanical strength and porosity. Three levels of SF replacement (5%, 10% and 15% by cement weight) and three levels of CLS replacement (16.67%, 33.34% and 50% by sand weight) were examined. The workability of fresh mortars was measured using an LCPC workability meter, and the superplasticiser (SP) demand was also quantified. The hardened-state tests included the mass at 28 days, compressive and flexural strengths at 7 and 28 days of curing, and porosity at 28 days. The optimal mix, containing 10% SF and 50% CLS, demonstrated excellent performance: compared with the control mix, the 28-day compressive strength was increased by 70% to 45.9 MPa and the porosity was reduced by 61% to 1.8%. This was achieved while maintaining good workability (15 s flow time) with only 1.2% SP. In addition to optimising the mortar formulation and improving its performance, this study significantly contributes to the understanding of how local byproducts (SF and CLS) can be effectively used in cementitious materials.

Current standards for evaluating the three-dimensional (3D) printability of concrete rely heavily on observational methods, lacking well-defined criteria. In this work, quantitative printability criteria were established by investigating the impact of carbon fibre (CF) volume fraction (0–0.60%) on the rheology, early-age strength and hydration kinetics of 3D printable high-strength engineered cementitious composites, validated through practical printing tests. Key results demonstrate that increasing the CF content to 0.45% significantly enhanced the rheological properties, increasing the static yield stress by 20.89%, the dynamic yield stress by 41.19% and plastic viscosity by 44.35%. Furthermore, the early-age mechanical strength exhibited a substantial five-fold increase with CF content up to 0.60%, achieving a peak strength of 176.03 kPa. This improvement in strength and rheology correlated with accelerated hydration as the CF fraction was increased from 0 to 0.60%, evidenced by a reduction in the termination point of the accelerated reaction phase from 28.4 h to 19.8 h. Practical printing verification confirmed that optimal printability, defined as the ability to exceed 25 layers, occurred within specific rheological and strength thresholds (static yield stress of 800–980 Pa, dynamic yield stress of 200–320 Pa and early-age strength of 30–120 kPa). These findings establish validated quantitative criteria for assessing the 3D printability of concrete.