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Even to date, the excessive mining of natural river sand is an unattempted issue. It is a global problem that impacts the river's ecosystem and the environment. This study has attempted to develop a new technique to modify vacant desert sand to replace 100% natural river sand. A technique is introduced in this study to modify desert sand by adding manufactured and recycled sand separately. Four new concrete mixes were prepared with developed modified sand. Additional four mixes were obtained when 12.5% ordinary Portland cement was replaced with silica fume. A detailed compressive strength was evaluated on 8 prepared mixes at curing ages of 3, 7, 28, 56, 91, and 360 days. The physical properties, such as density, absorption, and porosity, were evaluated at 28 days. The sulphuric acid attack was also studied to evaluate durability at 28, 56, 91, and 120 days. The developed concrete mixes with 12.5% silica fume at all curing phases revealed higher compressive strength than those without. The developed sustainable modified sand with 12.5% silica fume filled the pores and absorbed less water than the samples without silica fume. The modified sand with 12.5% silica fume revealed better density, water absorption, and voids and showed better resistance against 5% sulphuric acid solution than those without silica fume. It is concluded that all newly developed mixes showed satisfactory results. Moreover, the mix of (50% desert sand + 50% recycled sand) and 12.5% silica fume is the best sustainable mix for replacing 100% river sand and 12.5% cement from the concrete industry. Highlights A novel methodology has been developed to utilize 50% desert sand in the concrete industry. This study recommends the amendment in ACI-211.1-91 using fine desert sand in concrete. The modified sand concrete that was developed passed the strength and durability criteria. The mix (50%RS + 50%DS2 + 12.5%SF) is the best sustainable concrete for this study.

This study investigates the use of recycled concrete aggregates as a replacement for natural sand in printable mortars, comparing the properties of both fresh and hardened states. Two types of mortars were considered, natural mortar and recycled mortar, with further variations based on mixing methods under ordinary atmospheric pressure and vacuum pressure. The experimental approach included air content, mini-slump, printability, and various hardened state tests such as compressive strength and porosity measurements using both water absorption and mercury intrusion porosimetry (MIP). The results showed that mortars made with recycled sand exhibited higher fluidity, as evidenced by an increase in slump of approximately 50 to 70 mm across 30 min, compared to those made with natural sand. This difference was attributed to the pre-saturation of recycled sand, which, as a hypothesis, may increase with the amount of free water available while mixing under vacuum. Additionally, mortars containing recycled sand exhibited higher water-accessible porosity (approximately +7% compared to natural mortars) and lower compressive strength, with a reduction of about 5 to 10% for printed and cast samples, with the decrease being more pronounced in printed specimens. However, vacuum mixing was found to significantly reduce entrapped air content, by about 53% in natural mortars and 62% in recycled ones, and to enhance the workability of both types. The pore size distribution indicated that recycled mortars had a more complex pore network, with pores in the ranges of [0.01–0.1] mm and [0.1–1] mm, contributing to increased porosity and reduced mechanical strength. Overall, this study demonstrates the potential of using recycled sand in mortar formulations, with proper control of pre-saturation and mixing conditions to optimize performance in both fresh and hardened states.

To advance the use of industrial solid waste and recycled concrete, this study explores the impact of fly ash and slag powder on the mechanical properties, freeze–thaw resistance, and carbonation resistance of manufactured sand recycled aggregate concrete (MRAC). Different FSMRAC (Fly Ash and Slag Powder MRAC) mixtures were prepared by varying the amounts of fly ash and slag powder. The results show that fly ash and slag powder enhance the splitting tensile strength of MRAC more than its compressive strength. when the contents of fly ash and slag powder are 0% and 30%, respectively, the FSMRAC attains maximum compressive strength of 48.6 MPa and splitting tensile strength of 3.8 MPa, representing increases of 2.96% and 5.6% in compressive and splitting tensile strengths, respectively, compared to MRAC. A total addition of 30% fly ash and slag powder effectively reduces the loss of mechanical properties under freeze–thaw conditions. When the fly ash-to-slag powder ratio (F:S) exceeds 1.5, it improves carbonation resistance and compressive strength; when the ratio is below 1.5, it enhances splitting tensile strength resistance to freeze–thaw cycles. Slag powder promotes hydration and improves mechanical properties, while fly ash densifies the concrete matrix and lowers the carbonation rate. Response Surface Methodology (RSM) analysis indicates that both materials improve MRAC’s properties. Higher fly ash content benefits compressive strength and carbonation resistance, while higher slag powder content improves splitting tensile strength.

The demolition of old structures in concrete generates materials which can be recycled in the form of aggregates for new concrete, thus preserving natural resources. These recycled concrete aggregates are composed of natural elements bounded with hardened hydrated cement paste. The fine fraction (sands and fillers) is however more difficult to reuse than aggregates because it contains a high proportion of cement paste which absorbs a lot of water. The recycling of these products in the cement process is an interesting alternative way. In this paper, the possibility to use recycled concrete and fine material from de-dusting process of crushing platform for demolition concrete as alternative raw material for cement production was investigated. After a full chemical characterization of the recycled concrete sands and fines (XRF, XRD, DTA-TGA…), several cement raw-mixes were prepared by substituting partially or fully clay or marl. The generated clinkers have been characterized by different analytical techniques (TGA/DTA, XRF, XRD, SEM…). If the chemical composition of the raw is well balanced, the substitution of one of the cement raw meal components by recycled concrete sands does not affect the clinker. However, the free lime content may vary, including the initial quartz content of the recycled concrete sands used.

Carbonation has long been considered harmful to the durability of steel reinforced concrete structures especially with the increasing CO2 and temperature globally. In coastal construction, the chloride ions even make it worse. By replacing the steel with chloride-insensitive reinforcement such as fiber reinforced polymer (FRP), sea sand is a potential alternative to river sand, even carbonation could be utilized due to the acid resistance of FRP. In this paper, seawater sea-sand recycled aggregate concrete (SSRAC) was prepared, which had different hydration and carbonation from ordinary concrete (OC). The test results showed that the carbonation depth at 28 days of SSRAC increased up to 179.13% of OC. A modified carbonation model based on pore evolution was established. On the other hand, the increasement of carbonatable material in SSRAC was up to 14.32%. Combined with this characteristic, the carbon emission and absorption assessment were carried out. It is found that the CO2 absorption of SSRAC can be up to 325% of OC in 10 years’ service, and the total carbon emission including carbon sequestration over the whole life of SSRAC with a salinity of 4% is 45.73% of OC. This research verifies that it is expected to achieve more CO2 sequestration rapidly in SSRAC, which could probably help design low-carbon concrete structures.

In response to the issues of microcrack susceptibility, high brittleness, and unstable mechanical properties of desert sand recycled aggregate concrete (DSRAC), this study experimentally investigated the mechanical performance of DSRAC reinforced with hybrid steel–FERRO fibers. By testing macroscopic properties (compressive, splitting tensile, and flexural strengths) under different desert sand replacement ratios and fiber dosages, combined with microscopic analysis, the fiber-matrix interfacial behavior and toughening mechanism were clarified. The results showed that (1) DSRAC achieved optimal compressive strength when desert sand replaced 30% natural sand, with an obvious early strength enhancement; (2) both steel fibers and FERRO fibers independently improved DSRAC’s mechanical properties, while their hybrid combination (especially F0.15-S0.5 group) exhibited a superior synergistic strengthening effect, significantly outperforming single-fiber groups; (3) the established constitutive model accurately described the stress–strain response of hybrid fiber-reinforced DSRAC; (4) microscopic observations confirmed fibers inhibited crack propagation via bridging and stress dispersion, with hybrid fibers exerting multi-scale synergistic effects. This study provided theoretical–technical support for resource utilization of desert sand and recycled aggregates, and offered practical references for localized infrastructure materials (e.g., rural road subgrades and small-span culverts) in desert-rich regions and high-value reuse of construction waste in prefabricated components, advancing eco-friendly concrete in sustainable construction.

Typical effects of coarse and fine aggregates on the long-term properties of sea sand recycled aggregate concrete (SSRAC) are analyzed by a series of axial compression tests. Two different types of fine (coarse) aggregates are considered: sea sand and river sand (natural and recycled coarse aggregates). Variations in SSRAC properties at different ages are investigated. A novel test system is developed via axial compression experiments and the digital image correlation method to obtain the deformation field and crack development of concrete. Supportive results show that the compressive strength of SSRAC increase with decreasing recycled coarse aggregate replacement percentage and increasing sea sand chloride ion content. The elastic modulus of SSRAC increases with age. However, the Poisson’s ratio reduces after 2 years. Typical axial stress-strain curves of SSRAC vary with age. Generally, the effect of coarse aggregates on the axial deformation of SSRAC is clear; however, the deformation differences between coarse aggregate and cement mortar reduce by adopting sea sand. The aggregate type changes the crack characteristics and propagation of SSRAC. Finally, an analytical expression is suggested to construct the long-term stress-strain curve of SSRAC.

For complete utilization of construction and demolition (C&D) waste, an investigation of all size fractions of C&D waste generated during the recycling process should be conducted. In this work, the effects of three recycled concrete materials with different sizes (recycled coarse aggregate (RCA) with a size of 4.75–25 mm, recycled fine aggregate (RFA) of 0.15–4.75 mm, and recycled powder (RP) smaller than 0.15 mm) produced from concrete waste on the fresh and hardened mechanical properties of concrete were evaluated. The replacement ratios of natural coarse and fine aggregates by RCA and RFA were 30, 60, and 100%, and those of ordinary Portland cement for RP were 10, 20, and 30%. The results showed that the concrete properties deteriorated with increasing replacement ratio regardless of the type of recycled materials. The properties were reduced in the order of the use of RFA, RCA, and the simultaneous use of RCA and RFA. In addition, concrete with 30% RP showed lower mechanical strength than concrete with 100% RCA and 100% RFA. However, all concretes could be applicable for structural purposes under different environmental exposure conditions. In particular, concretes with 10% RP and 20% RP showed better cost-benefits compared to natural aggregate concrete with 100% ordinary Portland cement. These promising findings provide valuable initiatives for the effective and complete recycling of C&D waste.

Sand has been considered to be something of an immeasurable quantity. There are many indications that this view is no longer valid and that the limiting of natural aggregates usage is doubly justified. Firstly, the extraction of natural aggregates is expensive and has a huge impact on the environment. The main issues in sand and gravel mining are the large areas that are affected, ground water level changes, illegal mining, unsuitability of desert and marine sand, and costs of transport. Secondly, metallurgical waste can be used as a substitute for natural aggregates. This is doubly beneficial—the waste is recycled and the use of natural aggregates is reduced. Waste is stored in landfills that take up large areas and there is also the possibility of ground and groundwater pollution by hazardous compounds. The research presented in this article focuses on the technological conditions of using metallurgical waste in its original form and as a component of recycled concrete aggregate (RCA). The use of metallurgical sludge waste or crushed or round RCA to produce concrete deteriorates the consistency and does not significantly affect the air content and density of the concrete mix. RCA lowers the density of hardened concrete. Metallurgical sludge waste or RCA usage adversely affect the absorbability and permeability of concrete. Concrete containing metallurgical sludge waste is of higher compressive strength after 7 and 28 days, with up to 60% of waste as a sand replacement. RCA concrete achieved higher compressive strength also.

River sand supplies are decreasing due to overexploitation and illicit sand mining. One ton of Portland cement production (the main binder in concrete) emits about one ton of carbon dioxide into the atmosphere. Thus, this study replaced conventional cement and river sand (R sand) with recycled waste materials (fly ash and manufactured sand (M sand)). The concrete mix proportions were designed using M40 grade, and the Ordinary Portland cement (OPC) and R sand were replaced with 0–85 wt% of fly ash and 0-100 wt% of M sand. The concrete samples were tested for compressive strength after 3–90 days of curing. Furthermore, machine learning (ML) techniques were engaged to predict the compressive strength of the concrete samples using Extreme Gradient Boosting (XGBoost), Long Short-Term Memory (LSTM), Support Vector Machine (SVM), and Gaussian Process Regression (GPR). Besides, the concrete samples containing fly ash, M sand, and R sand were characterized for microstructures and elemental compositions using SEM-EDS. The results revealed improved concrete compressive strength by incorporating fly ash and M sand. After 28 days of curing, OPC and R sand were partially replaced with 25 and 50 wt% of fly ash and M sand attained the designed strength of M 40 grade concrete. XGBoost model yielded the most accurate performance metrics for forecasting the compressive strength in training and testing phases with R 2 values equal to 0.9999 and 0.9964, respectively, compared to LSTM, SVM, and GPR. Thus, the XGBoost approach can be a viable technique for forecasting the strength of concrete incorporating fly ash and M sand. SEM-EDS analyses revealed compact formations with high calcium and silicon counts. Thus, the XGBoost approach can be a viable technique for forecasting the strength of concrete incorporating fly ash and M sand.