With the scarcity of river sand resources, sea sand is also increasingly being used to prepare cementitious materials. Considering the threat of chloride salts still present in desalinated sea sand, this study investigates the effect of Na+, Mg2+, Ca2+ (contained on the surface of simulated desalinated sea sand) and metakaolin (MK) additions on the chloride binding properties of simulated desalinated sea sand mortar. The chloride binding capacity of the mortar and the hydration products of the mortar were analysed by chloride content measurement, X-ray diffraction, differential thermogravimetry, Fourier transform infrared spectroscopy and energy dispersive spectroscopy. The results show that Ca2+ and Mg2+ have a greater positive effect on improving the chloride binding capacity of mortar than Na+. This is because Ca2+ promotes the positive potential of the C–S–H gel in the mortar and Mg2+ facilitates the generation of a solid solution of Friedel’s salts and AFm in the mortar. The addition of MK in mortar improves the physical binding ability of the mortar to chloride ions. This improvement is primarily attributed to the increased production of C–S–H gel and C–A–S–H gel resulting from the addition of MK. This study is expected to provide theoretical support to facilitate the application of desalinated sea sand.

Superplasticizers (SPs) are indispensable in modern concrete technology. A novel, cost-effective method for synthesizing a high-performance SP using coal-based humic acid (CHA) derived from lignite is presented. Through oxidative depolymerization of lignite to prepare CHA, followed by sulfomethylation and condensation reactions, a CHA-based SP (called SP(CHA)) was successfully developed. Structural characterization confirmed the successful synthesis of CHA and its transformation into SP(CHA). Notably, the CHA demonstrated superior sulfomethylation reactivity compared with a commercially available sodium humate (NaA). Performance evaluations showed that the synthesized SP(CHA) outperformed both a commercial sulfonated naphthalene–formaldehyde condensate and SP(NaA) in terms of water-reduction efficiency, slump retention, and enhanced long-term compressive strength. Specifically, SP(CHA) achieved a water-reducing rate of 16.4% and a 28-day compressive strength improvement of 23.2%, exceeding the benchmarks for high-efficiency water reducers. By harnessing abundant and low-cost lignite resources, the approach holds substantial promise for advancing sustainable construction practices.

The frost resistance of recycled aggregate concrete (RAC) is a crucial performance indicator in its engineering application. Considering the complexity of factors that affect the frost resistance of RAC, in this study five neural network algorithms were employed, back-propagation neural network, radial basis function network, convolutional neural network, support vector machine and random forest regressor, along with two optimisations methods, particle swarm optimisation-back-propagation (PSO-BPNN) and genetic algorithm-back-propagation to predict the frost resistance of RAC. A database was compiled from 616 mixes in the peer-reviewed literature, and eight variables affecting the freeze–thaw resistance of RAC were taken as inputs. The compressive strength, mass loss rate and relative dynamic elastic modulus after freeze–thaw cycles were taken as outputs. The results showed that the main factors affecting the freezing resistance of RAC were the number of freeze–thaw cycles, the replacement rate of recycled aggregates, crushing index and water–cement ratio. Among the seven algorithms, the PSO-BPNN model had the best comprehensive prediction performance, with R2 of predicted compressive strength reaching 0.9714. It provides a reference value for further research on RAC frost resistance.

Although numerous durability investigations on self-consolidating concrete (SCC) have urged partial replacement of cement with pozzolans, contradictory results exist regarding the salt scaling resistance of pozzolanic concrete. Hence, this study was carried out on the salt scaling resistance of binary, ternary and quaternary pozzolanic SCC utilising trass, pumice and silica fume pozzolans in nine mixtures along with two air-entrained ones. The binary, SF10, the majority of ternaries, SF10T10, SF10T20 and SF10P10, and the air-entrained, SF10A3% and SF10T20P20A3% mixtures showed acceptable resistance against salt scaling with scaling lower than 0.8 kg/m2, as opposed to the quaternary mixes. The effect of pozzolans on the salt scaling resistance of concrete is highly dependent on the silicon dioxide (SiO2) + aluminium oxide (Al2O3) + iron (III) oxide (Fe2O3) content of the pozzolan. Also, microstructural analysis through scanning electron microscopy reflected the presence of ettringite and Friedel’s salt from the scaled surface. Furthermore, except for compressive strength, the ternary and quaternary mixes, SF10T10P10, SF10T20P10, SF10T10P20 and SF10T20P20, performed generally better than the binary one in the rapid chloride penetration test, but they had similar pulse velocity, depth of penetration, water absorption and electrical resistivity.

The liquid accelerator plays a vital role in shotcrete construction. Now, liquid accelerators exhibit several serious issues, including slow setting times, low late-stage strength and high preparation costs. Despite the availability of various types of liquid accelerators on the market, addressing these issues remains challenging. In this study, a low-alkali liquid accelerator (SLA) is prepared using the water bath heating method. This accelerator promotes the setting and hardening of cement and improves late-stage strength through the synergistic effect of low dosages of sodium fluorosilicate (SF) and sodium silicate (SS), while also reducing the preparation costs. At a dosage of 7% SLA, the cement paste achieves a final setting time of 3 min 30 s. The 1 day compressive strength of the mortar reaches 9.5 MPa, and the 28 day compressive strength is 7% higher than the control sample. It is found that the synergistic effect of SS and SF generates silicon dioxide gels and C–S–H gels while creating an alkaline environment that promotes the dissolution of the coating layer of hydration products and silicate mineral phases. Thus, SLA prepared through the synergistic action of SS and SF effectively overcomes the shortcomings of liquid accelerators.

Evaluating the durability of concrete materials through experimental research is a lengthy, costly and inefficient process. Traditional empirical formulae offer limited accuracy in predicting durability and fail to guide concrete proportioning based on performance. Consequently, it is crucial to develop new, efficient tools for material quality control and performance prediction. This can be achieved by elucidating the process involved in machine learning (ML) models, delineating the fundamental operating principles and benefits of prevalent algorithms, and critically reviewing ML-based durability index prediction algorithms and their practical applications and future directions. In this study, CiteSpace software was used to assess the current state of ML research in the prediction of concrete durability. A comprehensive analysis of the number of publications, research focal points and emerging trends was conducted. This not only furnishes references for future research but also aims to facilitate more effective utilisation of ML technology, thereby fostering the development of innovative construction materials and advancing the goal of environmental sustainability.

The influence of foam content and activator content on the properties of alkali-activated slag foamed concrete (AASFC) was studied. It was found that, when the foam content was increased from 3% to 12%, the effective foam ratio (EFR) and the water absorption of the AASFC increased, while the compressive strength and dry density decreased. For the same foam content, when the activator content was increased from 4% to 6%, the EFR and water absorption decreased, while the dry density increased. The AASFC showed good performance with an activator content of 5%. When the foam content was increased, the amount of large pores and interconnected pores increased. However, the foam content had little effect on the average pore size and pore roundness. For the same foam content, when the activator content was increased from 4% to 6%, the porosity and amount of interconnected pores decreased. With an increase in foam content from 9% to 12%, the porosity increased significantly and the thermal conductivity was significantly decreased. A property prediction model was established that may provide the foundation for AASFC mix design.

Buildings in coastal areas have suffered from seawater immersion and tidal erosion for a long time, and the resistance of building structures to sulfate erosion has always been a concern. To solve this problem, an attempt is made in this paper to develop a new low-carbon-dioxide green geopolymer cementitious material that is resistant to sulfate attack. The effect of this geopolymer material on sulfate erosion resistance is investigated in terms of alkali admixture, alkali modulus, water–binder ratio and fly ash admixture. In this paper, the geopolymer materials were tested for sulfate erosion resistance by dry–wet cycle sulfate erosion mechanism. It was shown that the contribution to improving the resistance of geopolymer materials to magnesium sulfate (MgSO4) attack can be ranked as follows: water–binder ratio > fly ash content > alkali content > alkali modulus. Increasing the alkali admixture, water–binder ratio and fly ash admixture and decreasing the alkali modulus will promote the generation of gypsum in the specimen; Mg2+ in magnesium sulfate solution makes the volcanic ash reaction products decalcify, and the free Ca2+ and [SO4]2− combine to generate gypsum, causing gypsum-type erosion damage in the specimen.

Ultra-high-performance concrete (UHPC) is renowned for its exceptional strength, durability, and structural integrity, offering sustainable solutions for construction. However, concerns persist regarding its long-term performance under various environments due to unhydrated cementitious particles. In this study, the effect of steel fiber content on the long-term stability of UHPC in tap water, outdoor, and seawater environments over 720 days was investigated. In these three environments, adding 1–3% steel fiber increased the compressive strength of the UHPC by 4.5–11.5%, 9.5–18.5%, and 0.4–3.5%, respectively. The steel fibers also effectively reduced length changes, decreasing the rate by 26.3%, 57.0%, and 26.3%, respectively. Microstructural analysis confirmed the formation of calcite and brucite under seawater curing, indicating chemical interactions between seawater components and cement-based materials. After 720 days in seawater, the surface fibers exhibited corrosion, but the internal fibers were intact. The results of this work provide insights into UHPC’s long-term stability in diverse environments, which is critical for the durability and safety of infrastructure.