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The depletion of natural coarse aggregates (NCAs) and rising environmental concerns have accelerated the demand for sustainable alternatives in concrete production. This study presents the development of cold-bonded alkali-activated artificial aggregates (AAAs) using fly ash (FA) and ground granulated blast furnace slag (GGBFS) as binders. AAAs were produced through disc pelletization, ambient curing, and surface treatment with an alkaline solution to improve aggregate quality. The produced AAAs exhibited a specific gravity of 1.83–2.02, bulk density of 1201–1241  kg m −3 , water absorption of 1.54%–1.03%, impact values of 21.65%–15.62%, and crushing values of 24%–20.06%. Concrete mixes were prepared by replacing NCAs with AAAs at 30%, 60%, and 100% replacement levels in M30-grade concrete. The compressive strength of the mixes ranged from 41.88 MPa (30% AAAs) to 38.21 MPa (100% AAAs), remaining within acceptable structural limits. Despite a slight reduction in density and mechanical strength with increasing AAAs content, all mixes showed satisfactory workability and ultrasonic pulse velocity. Scanning electron microscopy confirmed enhanced microstructural densification with higher GGBFS content. Environmental and cost assessments indicated that while AAAs involve higher production costs, they reduce CO 2 emissions significantly, supporting sustainable construction goals. A 60% replacement level offered an optimal trade-off between strength, environmental impact, and cost. The findings confirm that AAAs are a viable, eco-friendly substitute for NCAs in structural concrete applications.

The excessive use of natural aggregates raises mining activity. Further, it leads to environmental damage, which can be reduced using artificial aggregates produced from waste powdered materials. This study discussed the production process of alkali-activated artificial coarse aggregates and how their use affects the behavior of concrete. The different concrete mixtures were designed by replacing natural aggregates with artificial ones at different percentages. Various tests were conducted to determine concrete’s fresh, hardened, permeability, and microstructural characteristics. The result showed that concrete incorporated with artificial aggregates can achieve higher workability and lower density than natural aggregate concrete. The mechanical strengths were slightly decreased as the percentage addition of artificial aggregates in a mix increased. However, adding up to 50% showed comparable results to natural aggregate concrete. The water permeability and chloride ion penetration were within the standard limits for all the mixes. The scanning electron micrographs showed a solid and compact ITZ between the phases. XRD pattern revealed that the addition of artificial aggregates had not changed the mineralogical composition of the concrete; the formation of hydrated products helps concrete obtain strength. The study concluded that artificial aggregates could effectively replace natural coarse aggregate in producing structural concrete with many advantages.

The study investigates the use of artificial aggregates (AAs), specifically manufactured from ground granulated blast furnace slag (GGBFS) and ordinary Portland cement (OPC), to mitigate environmental harm caused by illegal quarrying due to the scarcity of natural aggregates (NAs). A cold-bonded pelletization technique was employed to produce five types of AAs with varying proportions of GGBFS & OPC as 82.5:17.5, 85:15, 87.5:12.5, 90:10, 95:5. The AAs with maximum OPC content exhibited a density of 1298 kg m −3 , water absorption of 4.8%, and crushing and impact values of 28.6% and 26.3%, respectively. The impact of these AAs on concrete properties was assessed, revealing that AAs facilitated the production of workable concrete with low-density ranges between 1700–2337 kg m −3 . Despite a decrease in concrete strength with higher AAs content, structural requirements were met, demonstrating AAs’ potential to effectively substitute natural coarse aggregates (NCAs). The concrete microstructure confirmed the formation of a strong interfacial transition zone (ITZ) and strength-developing cement-hydrated products. This research underscores the scientific contribution of AAs to address aggregate scarcity sustainably and recommends its application in structural elements by experimental validation.

Infrastructure development and urbanization have created a demand for the prime construction material—\"Concrete.\" The manufacture of concrete has pressurized the aggregate supply chain for over-exploitation of natural resources leading to eco-detrimental impacts besides environmental regulations. The auxiliary sectors of the construction industry are creating a vast quantum of by-products and waste, causing environmental degradation, which concerns governing bodies. Developing aggregates artificially using these by-products and waste materials would be an eco-friendly and economical solution. This article provides an overview of the ingredients, production methods, and factors influencing the characteristics of such sustainable building materials, which can substitute conventional aggregates in the near future.

This study aimed to investigate the recycling opportunities for industrial byproducts and their contribution to innovative concrete manufacturing processes. The attention was mainly focused on municipal solid waste incineration fly ash (MSWI-FA) and its employment, after a washing pre-treatment, as the main component in artificially manufactured aggregates containing cement and ground granulated blast furnace slag (GGBFS) in different percentages. The produced aggregates were used to produce lightweight concrete (LWC) containing both artificial aggregates only and artificial aggregates mixed with a relatively small percentage of recycled polyethylene terephthalate (PET) in the sand form. Thereby, the possibility of producing concrete with good mechanical properties and enhanced thermal properties was investigated through effective PET reuse with beneficial impacts on the thermal insulation of structures. Based on the obtained results, the samples containing artificial aggregates had lower compressive strength (up to 30%) but better thermal performance (up to 25%) with respect to the reference sample made from natural aggregates. Moreover, substituting 10% of recycled aggregates with PET led to a greater reduction in resistance while improving the thermal conductivity. This type of concrete could improve the economic and environmental aspects by incorporating industrial wastes—mainly fly ash—thereby lowering the use of cement, which would lead to a reduction in CO2 emissions.

Coarse aggregate is considered the most vital aspect, providing quantity and strength to the concrete. The aggregates are obtained mainly from natural resources by quarrying rocks or riverbeds. Each year, construction industries use large amounts of natural aggregates, resulting in the depletion of raw materials. Different methods, such as sintering, cold bombing, autoclaving, and geopolymerization, can prepare artificial coarse aggregates. Geopolymerization is a chemical reaction between an alkali solution and source materials containing alumina and silicate. The main objective of this study is to develop artificial aggregates with M sand dust and fly ash by geo polymerization. The ratio of Fly ash to M Sand Dust adopted is 40:60 by weight. Different molarities of sodium hydroxide was used for making the artificial aggregates with a solution-to-binder (S/B) ratio of 3.5 and a sodium silicate-to-sodium hydroxide ratio of 2.5. The mechanical properties of the developed lightweight aggregate are determined as per the specification requirement in IS 9142 (1979) for artificial lightweight aggregates for concrete masonry units. By comparison, these geopolymer aggregates are sustainable, and aggregates with 12 molarity NaOH showed better properties than other molarity NaOH aggregates based on its mechanical properties.

This paper investigates the influence of different amounts of recycled coarse aggregates obtained from a demolished RCC culvert 15 years old on the properties of recycled aggregate concrete (RAC). A new term called “coarse aggregate replacement ratio (CRR)” is introduced and is defined as the ratio of weight of recycled coarse aggregate to the total weight of coarse aggregate in a concrete mix. To analyze the behaviour of concrete in both the fresh and hardened state, a coarse aggregate replacement ratio of 0, 0.25, 0.50 and 1.0 are adopted in the concrete mixes. The properties namely compressive and indirect tensile strengths, modulus of elasticity, water absorption, volume of voids, density of hardened concrete and depth of chloride penetration are studied. From the experimental results it is observed that the concrete cured in air after 7 days of wet curing shows better strength than concrete cured completely under water for 28 days for all coarse aggregate replacement ratios. The volume of voids and water absorption of recycled aggregate concrete are 2.61 and 1.82% higher than those of normal concrete due to the high absorption capacity of old mortar adhered to recycled aggregates. The relationships among compressive strength, tensile strengths and modulus of elasticity are developed and verified with the models reported in the literature for both normal and recycled aggregate concrete. In addition, the non-destructive testing parameters such as rebound number and UPV (Ultrasonic pulse velocity) are reported. The study demonstrates the potential use of field recycled coarse aggregates (RCA) in concrete.

The preparation of high-strength phosphogypsum aggregates (HPA) was explored in this study by the compaction–fragmentation–grinding–hydration process from mixture of PG GGBS OPC dry powders. The dry powder blocks were first produced by compaction using the programed pressure and then was crushed into small pieces with angular shapes. The small pieces were grinded and then sprayed with saturated lime water. Hydration occurs in water-sprayed pieces, and the high-strength phosphogypsum aggregates (HPA) was produced after 28 days curing. The apparent density and cylinder compression strength of the HPA in drying state were up to 2010 kg/m3 and 23.58 MPa, respectively. These results indicated that the rehydration process after compaction can make the prepared HPA obtain high density and strength, solving the shortcoming of the high-doped phosphogypsum products with low strength. Investigating phosphorus and fluoride pollutants in HPA showed that they met the requirements of water with Class I. Finally, the microscopic analysis of XRD and SEM identified that the phase type of the HPA were CaSO4 and ettringite. The changes in the internal pores of the HPA in the curing process were explored by mercury intrusion porosimetry and the results further verified the HPA is well compacted.

This research aims to examine the mechanical behavior of lightweight concrete produced by replacing natural coarse aggregates with expanded polystyrene (EPS) beads. The difference particle sized of EPS beads with diameter of 2.0 and 5.0 mm was used to replaced natural coarse aggregate (crushed limestone) at the rates of 35, 50 and 65% by volume. The compressive strength of concrete was evaluated at 7, 14 and 28 days. Additionally, the mechanical properties in term of splitting tensile strength and elastic modulus of concrete were also measured at 28 days. The results demonstrated that the compressive strength of the concrete reduced with increasing EPS bead replacement. However, specimens with smaller EPS beads exhibited slightly higher compressive strength compared to those with larger beads. Using 35% EPS beads with size of 2.0 mm as artificial aggregate to replace coarse aggregate resulted in compressive strengths of 28.3, 31.2, and 34.5 MPa at 7, 14, and 28 days, respectively. All the concrete can be classified as lightweight concrete for structures due to its compressive strength being higher than 17 MPa. Splitting tensile strength and elastic modulus of concrete depended on concrete strength similar to conventional concrete using natural coarse aggregate.

The use of mineral waste for the production of lightweight artificial aggregate is an important element of activities for sustainable development in construction and the implementation of the objectives of the circular economy. The article presents the physical, mechanical, and ecological properties of an innovative artificial aggregate produced from bottom sediments, concrete dust, and municipal solid waste incineration fly ash. The obtained research results confirm that the developed material achieves technological properties comparable to artificial aggregates available on the market, both commercial and those derived from recycling. However, the increased leachability of chlorides and sulphates remains a significant challenge, which may limit the scope of its applications. Despite this, the material shows the potential for use, among others, in the production of lightweight concrete. The analyses carried out have shown that the thermal hardening processes (200–400 °C) and autoclaving do not guarantee full immobilization of harmful substances contained in the raw materials for the production of this type of aggregate.