Search Results (51)

This study investigates the potential for sustainable concrete production using industrial by-products: used foundry sand (UFS) and coal bottom ash (CBA). These materials were partially substituted for natural aggregates to reduce environmental impact and promote circular economy practices. UFS was used as a replacement for fine aggregate, while both fine and coarse CBA were tested as substitutes for sand and gravel, respectively. The materials were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS) to evaluate their mineralogical and microstructural properties. Six concrete mixtures were prepared with varying replacement levels (up to 70% total aggregate substitution) at a constant water-to-cement ratio of 0.50. Compressive strength tests were conducted at 28 days, supported by microstructural observations. Results showed that high levels of UFS and CBA led to reduced strength, mainly due to weak interfacial bonding and porous ash particles. However, moderate replacement levels (e.g., 20% fine CBA) maintained high strength with good structural integrity. The study concludes that both UFS and CBA can be used effectively in concrete when carefully dosed. The findings support the use of industrial waste in construction, provided that material properties are well understood and replacement levels are optimized. Full article

From a geotechnical engineering viewpoint, recycling and reuse of crushed glass and tire rubber can significantly help reduce the demand for natural resources (i.e., sand and gravel aggregates). Following an earlier study by the authors aimed at characterizing gravel–rubber mixtures (GRM), this paper focuses on the geotechnical assessment of gravel–glass–rubber mixtures (GGRM) made of recycled crushed green glass bottles and recycled granulated tire rubber. Specifically, the compaction, one-dimensional compressibility, and shear strength characteristics of GGRM prepared at 40% and 55% rubber content by volume (R_B) with varying glass content by volume (G_L) are investigated. It is found that compacted GGRM possesses high strength (i.e., friction angle ≥ 30°) and adequate compressibility, making it a suitable general and structural fill material for use in eco-friendly geotechnical applications. Full article

Concrete demolition waste represents a critical bottleneck in achieving a circular economy for the construction sector. This study develops a system-dynamics model that couples material flows with economic and logistical feedback to quantify how cost structures affect concrete recycling in the Sydney (Australia) metropolitan area. The model is calibrated with (i) official New South Wales 2020–2021 construction-and-demolition waste statistics, (ii) concrete consumption data scaled from state infrastructure reports, and (iii) parameters elicited from structured interviews with recycling contractors and plant operators. Scenario analysis systematically varies recycling-plant fees, landfill levies, and transport costs to trace their nonlinear impacts on three core performance metrics: recycling rate, cumulative landfill mass, and virgin gravel extraction. Results reveal distinct cost tipping points: a 10% rise in landfill-logistics costs or a 25% drop in recycling logistics costs shifts more than 95% of concrete waste into the recycling stream, cutting landfill volumes by up to 47% and reducing virgin aggregate demand by 5%. Conversely, easing landfill costs by 25% reverses these gains, driving landfill dependency above 99% and increasing gravel extraction by 39%. These findings demonstrate that carefully calibrated economic levers can override logistical inefficiencies and accelerate circular construction outcomes. The system-dynamics framework offers policymakers and industry stakeholders a decision-support tool for setting landfill levies, recycling subsidies, and infrastructure investments that jointly minimize waste and conserve natural resources. Full article

This report presents the results of cracking tests on concrete beams. The test specimens were created in ten different series. Each series comprised two beams, six cylinders, and twelve cubic samples intended for the determination of strength properties. These samples varied in terms of the type of concrete mixture (fiber-reinforced fine aggregate concrete and plain concrete), the applied steel fibers (50/0.8 mm and 30/0.55 mm), the longitudinal reinforcement ratio in beams (0.6%, 0.9%, 1.3%, and 1.8%), and the inclusion (or exclusion) of compressed reinforcement and vertical stirrups. The fine aggregate concrete was made from waste sand, which is a byproduct of the hydroclassification process of gravel. The use of this sand in fiber concrete will help reduce the exploitation of natural resources and lower carbon dioxide emissions. Based on four-point beam bending tests, the study experimentally determined cracking moments, crack spacing, and crack width. Additionally, these results were compared with calculations proposed by L. Vandewalle and Domski, as well as with the methods outlined in Eurocode 2. The analyses conducted show that the best agreement between the research results and the calculations was obtained for Domski’s proposal. It follows that the average percentage error was 38.4%, indicating the safe use of this method. Full article

Aggregates such as sand and gravel are the most mined resources on Earth and are the largest component in concrete. They are essential for construction but are becoming increasingly scarce. At the same time, large amounts of biomass ashes are produced in wood-fired power plants, offering potential as a partial substitute for decreasing sand resources. Due to the combustion technology of circulating fluidized bed boilers, their bottom ash offers high potential as a viable alternative to natural sand. This review examines previous research to assess the feasibility of replacing sand in concrete with bottom ash. Specific cementitious products are identified, where the substitution could realistically be performed in the concrete industry. Benefits and issues with partial substitution of bottom ash from wood combustion are discussed, and gaps in the research regarding sand replacements with bottom ash, notably the durability of the resulting concrete, are shown. Bottom ash has positive properties relevant for use in mortar and concrete, both regarding physical and chemical properties. Although limited research exists in the field, several researchers have demonstrated promising results when substituting sand for bottom ash in mortars. For lower substitution levels, little effect on the fresh and hardened properties is found. Full article

Coal gangue (CG) is one of the most frequent solid wastes in the world, and it poses a severe hazard to both human society and natural ecosystems. In light of the progressive increase in environmental awareness and the unavoidable trend of the requirements of a sustainable development plan, how to efficiently use these vast quantities of CG has become an important subject in China. Concrete aggregate, which can not only solve environmental pollution but also compensate for the scarcity of natural gravel and sand resources, is the most cost-effective and eco-friendly way to utilize CG resources in accordance with the strategic requirements of green and sustainable development. However, how to deal with the preparation of high-quality gangue aggregate needs to be targeted research; blindly using gangue for concrete may bring some safety hazards. This requires that based on the source, distribution, storage, chemical composition, mineral composition of the gangue and the problems in the utilization process, efforts are made to open up the key routes of gangue concrete utilization, and to provide theoretical guidance for the high-value and environmentally friendly utilization of the CG. This paper summarizes the CG aggregate characteristics and its impact on concrete performance, discusses the technical means to improve the performance of CG aggregate concrete, and analyzes if the current CG aggregate in the concrete application of the problem still exists, with a view to gradually realize the CG of low-energy consumption bulk utilization. The popularization and application of CG aggregate will accelerate the solution of the environmental pollution problem it brings, and can to a certain extent alleviate the current situation in that the supply of natural sand and gravel resources is insufficient to meet the demand; the sustainable development of today’s research on CG aggregate for concrete has important environmental and economic significance. Full article

Natural aggregates are widely used in the construction sector. Their production and generation entail environmental impacts, which must be identified and reduced as far as possible in order for the construction sector to achieve sustainability. The objective of this research is the environmental characterization, through the Life Cycle Assessment methodology, of the production of 1 ton of natural coarse aggregate produced in a common gravel pit in Spain, with a cradle-to-gate scope. The activity data are collected from inventory databases from national companies. Their results reveal emissions of 4.30 kg CO₂ eq, the consumption of 106.08 MJ of fossil fuels and the use of 12.52 m³ of natural water per ton of natural coarse aggregate. Subsequently, innovative concepts are explored to mitigate the previously defined environmental impacts through the creation of vine cultivation. The most relevant results indicate that 1 hectare of vine cultivation generates a net balance of emissions of −3.785 tCO₂, acting as a carbon sink, which means producing a total of 879.6 t of natural coarse aggregates produced in gravel pits free of CO₂ emissions. By applying this cultivation to the construction sector, the aim is to make companies in the sector aware that by adopting this measure, at least in the global warming impact category, environmental impacts can be mitigated and thus contribute to achieving greater sustainability in the sector. Full article

Adding domestic waste into cement mortar or replacing fine aggregate can effectively reduce the use of natural sand and gravel and reduce carbon emissions, thereby preventing waste from polluting the Earth’s environment. This study explored a sustainable method for recycling television plastic shell waste (TPSW) by using it as a partial replacement for sand in cement mortar production. By evaluating water–cement ratios (0.4, 0.5, 0.6), ages (3, 7, 28, 56, 91 days), and TPSW levels (0%, 5%, 10%, 15%), this research assessed key properties, such as the slump, compressive strength, and durability. The results show that the TPSW absorbed less water than natural sand, increased the number of pores and slightly reduced the strength. However, a 5% substitution led to a minimal performance loss after 91 days, while it improved the sulfate resistance and resistivity. Overall, incorporating 5% TPSW reduces the environmental impact and carbon emissions, offering a sustainable solution for cement production. Full article

Adverse climatic conditions, particularly excessive water and frost, necessitate the design of thick protective sub-ballast layers when dealing with frost-susceptible subgrade surfaces, especially when using standard natural materials (crushed aggregate or gravel–sand). Given the current preference for conserving natural construction materials and promoting sustainable development in the dimensioning of sub-ballast layers, it is advisable to incorporate various thermal insulation, composite, or suitable recycled materials in their design. Therefore, the paper analyses the impact of incorporating different thermal insulation materials (including extruded polystyrene, Liapor, Liapor concrete, and composite foam concrete) into sub-ballast layers. As part of the experimental research, these modified sub-ballast layers were constructed on a real scale in the outdoor environment of the University of Žilina (UNIZA) campus. They were subsequently compared in terms of their thermal resistance to climatic loads. The research results demonstrate that extruded polystyrene provides the optimal thermal insulation effect in modified sub-ballast layers, which was subsequently used in the numerical modelling of railway track structure freezing under different climatic loads. Full article

This research work aims to compare the strength and fracture mechanics properties of plain concretes, obtained from different coarse aggregates. During the study, mechanical parameters including compressive strength (f_cm) and splitting tensile strength (f_ctm), as well as fracture parameters involving critical stress intensity factor $\left(K_{\mathrm{I}\mathrm{c}}^{\mathrm{S}}\right)$ and critical crack tip opening displacement (CTOD_c) were evaluated. The effect of the aggregates used on the brittleness of the concretes was also analyzed. For better understanding of the crack initiation and propagation in concretes with different coarse aggregates, a macroscopic failure surfaces examination of the tested beams is also presented. Crushed aggregates covered were basalt (BA), granite (GT), and limestone (LM), and natural peeble gravel aggregate (GL) were used in the concrete mixtures. Fracture toughness tests were performed on an MTS 810 testing machine. Due to the high strength of the rock material, the rough surface of the aggregate grains, and good bonding in the ITZ area between the aggregate and the paste, the concretes with crushed aggregates exhibited high fracture toughness. Both of the analyzed fracture mechanics parameters, i.e., ${ K}_{\mathrm{I}\mathrm{c}}^{\mathrm{S}}$ and CTOD_c, increased significantly in the case of concretes which were manufactured with crushed aggregates. They amounted, in comparison to concrete based on gravel aggregate, to levels ranging from 20% for concrete with limestone aggregate to over 30% for concrete with a granite aggregate, and to as much as over 70% for concrete with basalt aggregate. On the other hand, the concrete with gravel aggregate showed the lowest fracture toughness because of the smooth surface of the aggregate grains and poor bonding between the aggregate and the cement paste. However, the fracture process in each series of concrete was quasi-plastic in the case of gravel concrete, semi-brittle in the case of limestone concrete, and clearly brittle in the case of the concretes based on granite and basalt aggregates. The results obtained help to explain how the coarse aggregate type affects the strength parameters and fracture toughness at bending. Full article

In recent years, with the development of the construction industry and the wide application of concrete materials, the demand for natural resources such as sand and gravel in China has continued to grow. The Xinjiang region is rich in natural desert sand resources due to its large desert area, which are inexpensive and easy to obtain, providing new possibilities for the production of concrete materials. The use of natural desert sand as concrete aggregate not only reduces the cost of construction but also contributes to the protection of the environment and the rational development and utilization of natural resources. However, poor particle gradation in natural desert sand leads to poor concrete properties. In this study, the Dinger–Funk equation was used to optimize the aggregate gradation of natural desert sand from Toksun, Xinjiang, and concrete specimens were prepared for mechanical properties and sulfate erosion resistance tests. The test results show that the four groups of aggregates optimized by the Dinger–Funk equation are better than the single gradation and natural gradation in terms of apparent density, bulk density, void ratio, mechanical properties, and durability of concrete. Where the distribution modulus n = 0.3 was the best, the compressive strength, splitting strength, and flexural strength were increased by 13.14%, 15.71%, and 11.08%, respectively, as compared to the natural gradation. After 90 sulfate erosion and dry–wet cycles, the mass change rate and relative dynamic elastic modulus of concrete specimens first increased and then decreased, and at the distribution modulus n = 0.3, the aggregate particles of 0.3–0.6 mm, 0.6–1.18 mm, and 1.18–2.36 mm accounted for 26.98%, 32.33%, and 40.69%, respectively, and the smallest of the mass change rates of durability was the best. Full article

The increasing demand for concrete reduces natural resources, such as sand and gravel, and also leads to a sharp increase in the amount of waste concrete produced. Due to the fact that the physical and mechanical properties of waste concrete made of recycled aggregates (RAs) differ greatly, it is difficult to use directly as a raw material for reinforced concrete (RC) components, which greatly restricts the popularization and application of RAs in actual projects. Utilizing the alkali aggregate properties of RAs to capture CO₂ from industrial waste gases is an innovative way of enhancing their properties and promoting their application in real projects. However, the extent of the influence of original concrete strength (OCS) and coarse aggregate size (CAS) on the accelerated carbonation modification of RA is not clear, and a quantitative description is still required. For this purpose, accelerated carbonation tests on recycled coarse aggregate (RCA) samples under completely dry condition were carried out, and the variation laws for the physical property indicators of RCA samples before and after accelerated carbonation versus the OCS and CAS were revealed. Moreover, the influence degrees of the two factors, OCS and CAS, on the property enhancement of RCAs after accelerated carbonation were clarified, and the results of OCS and CAS corresponding to the best accelerated carbonation effects of RCAs were determined. By analyzing the micromorphology of RCA before and after accelerated carbonation, the reasons for property enhancement of RCAs with various OCSs and CASs under the best carbonation modifications were clarified. The findings will contribute to the development of basic theoretical research on accelerated carbonation modification of RA and have important scientific value. Full article

The extraction of materials, such as sand and gravel, required for the manufacture of concrete results in the overexploitation of natural resources and a large release of CO₂ emissions into the environment. Therefore, the search for alternatives to partially replace these aggregates has become an important issue to solve. Nonetheless, the demand for producing sustainable yet high-strength and durable concrete using alternative materials has led concrete technologists to develop high-performance concrete. These novel concretes possess superior engineering properties, such as high durability and ductility, low maintenance costs, high mechanical strength, and prolonged service life. Currently, there is significant interest in the development of concrete–polymer compounds, primarily to improve the mechanical properties of the material. In this context, the present study explores the partial replacement of fine aggregate with recycled Polyethylene terephthalate (R-PET) in different proportions to produce green structural concrete, with the aim of studying its impact on the mechanical and electrochemical properties. The mechanical properties evaluated were the compressive and flexural strengths, while the electrochemical properties were evaluated through the open circuit potential and polarization curves. The results indicated that specimens containing different R-PET percentages as a replacement for fine aggregate showed higher increases in compressive and flexural strengths. It was also found that the presence of R-PET decreased the corrosion rate of the reinforcing steel when seawater was used as the electrolyte. Full article

Concrete prepared using Gobi sand and gravel instead of ordinary sand and gravel is referred to as Gobi concrete. In order to explore the effect of fibers on the frost resistance of Gobi concrete, as well as to enhance the service life of Gobi aggregate concrete in Northwest China, experiments were conducted with fiber types (polypropylene fibers, basalt fibers, polypropylene–basalt fibers) and fiber volume fractions (0%, 0.1%, 0.2%, 0.3%) as variable parameters. This study investigated the surface morphology, mass loss rate, and relative dynamic elastic modulus of fiber-reinforced Gobi concrete after different freeze–thaw cycles (0, 25, 50, 75, 100). Corresponding frost damage deterioration models were proposed. The results indicate that fibers have a favorable effect on the anti-peeling performance, mass loss rate, and dynamic elastic modulus of Gobi aggregate concrete. The improvement levels of different fiber types are in the following order: 0.1% basalt-polypropylene fibers, 0.2% polypropylene fibers, and 0.3% basalt fibers. Compared to Gobi concrete exposed to natural environmental conditions, the freeze–thaw cycle numbers increased by 343, 79, and 69 times, respectively. A quadratic polynomial damage model for fiber-reinforced Gobi concrete, using relative dynamic elastic modulus as the damage variable, was established and demonstrated good predictive performance. Full article

Geopolymer concrete (GPC) represents an innovative green and low-carbon construction material, offering a viable alternative to ordinary Portland cement concrete (OPC) in building applications. However, existing studies tend to overlook the recyclability aspect of GPC for future use. Various structural applications necessitate the use of concrete with distinct strength characteristics. The recyclability of the parent concrete is influenced by these varying strengths. This study examined the recycling potential of GPC across a spectrum of strength grades (40, 60, 80, and 100 MPa, marked as C40, C60, C80, and C100) when subjected to freeze–thaw conditions. Recycling 5–16 mm recycled geopolymer coarse aggregate (RGAs) from GPC prepared from 5 to 16 mm natural coarse aggregates (NAs). The cementitious material comprised 60% metakaolin and 40% slag, with natural gravel serving as the NAs, and the alkali activator consisting of sodium hydroxide solution and sodium silicate solution. The strength of the GPC was modulated by altering the Na/Al ratio. After 350 freeze–thaw cycles, the GPC specimens underwent crushing, washing, and sieving to produce RGAs. Subsequently, their physical properties (apparent density, water absorption, crushing index, and attached mortar content and microstructure (microhardness, SEM, and XRD) were thoroughly examined. The findings indicated that GPC with strength grades of C100, C80, and C60 were capable of enduring 350 freeze–thaw cycles, in contrast to C40, which did not withstand these conditions. RGAs derived from GPC of strength grades C100 and C80 complied with the criteria for Class II recycled aggregates, whereas RGAs produced from GPC of strength grade C60 aligned with the Class III level. A higher-strength grade in the parent concrete correlated with enhanced performance characteristics in the resulting recycled aggregates. Full article