Search Results (132)

This study presents a cost-effective, carbon-negative construction material for affordable housing, developed entirely from locally available agricultural wastes: rice husk ash, wood ash, and rice straw—materials often problematic to dispose of in many African regions. Rice husk ash provides high amorphous silica, acting as a strong pozzolanic agent. Wood ash contributes calcium oxide and alkalis to serve as a reactive binder, while rice straw functions as a lightweight organic filler, enhancing thermal insulation and indoor climate comfort. These materials undergo natural pozzolanic reactions with water, eliminating the need for Portland cement—a major global source of anthropogenic CO₂ emissions (~900 kg CO₂/ton cement). This process is inherently carbon-negative, not only avoiding emissions from cement production but also capturing atmospheric CO₂ during lime carbonation in the hardening phase. Field trials in Kenya confirmed the composite’s sufficient structural strength for low-cost housing, with added benefits including termite resistance and suitability for unskilled laborers. In a collaboration between the University of Tartu and Kenyatta University, a semi-automatic mixing and casting system was developed, enabling fast, low-labor construction of full-scale houses. This innovation aligns with Kenya’s Big Four development agenda and supports sustainable rural development, post-disaster reconstruction, and climate mitigation through scalable, eco-friendly building solutions. Full article

This study investigates the effects of incorporating recycled concrete powder (RCP) as a supplementary cementitious material in Portland cement composites at replacement levels of 5–30% by weight. A comprehensive characterization using isothermal calorimetry, electrical conductivity measurements, thermogravimetric analysis, FT-IR spectroscopy, and scanning electron microscopy revealed that RCP modified the hydration behavior and microstructural development. The results showed a linear 16.5% reduction in the total heat of hydration (from 145.38 to 121.44 J/g) at 30% RCP content, accompanied by a 26.5% decrease in peak electrical conductivity (19.16 to 14.08 mS/cm) and delayed reaction kinetics. Thermal analysis demonstrated an increased stability of hydration products, with portlandite decomposition temperatures rising by up to 10.8 °C. Microstructural observations confirmed the formation of denser but more amorphous C–S–H phases alongside increased interfacial porosity at higher RCP contents. The study provides quantitative evidence of RCP’s dual functionality as both an inert filler and a nucleation agent, identifying an optimal 20–25% replacement range that balances performance and sustainability. These findings advance the understanding of construction waste utilization in cementitious materials and provide practical solutions for developing more sustainable building composites while addressing circular economy objectives in the construction sector. Full article

This study systematically investigates the utilization of marble industry waste—waste marble powder (WMP) as partial cement replacement and waste marble aggregates (WMA) as partial fine aggregate replacement—in self-compacting concrete (SCC). A detailed experimental program evaluated the effects of various replacement levels (5%, 10%, and 20% for WMP; 20%, 30%, and 40% for WMA) on compressive strength and durability, particularly resistance to aggressive sulfuric acid environments. Results indicated that a 5% WMP replacement increased compressive strength by 4.9%, attributed primarily to the filler effect, whereas higher levels (10–20%) led to strength reductions due to limited pozzolanic activity and cement dilution. In contrast, WMA replacement consistently enhanced strength (maximum increase of 11.5% at 30% substitution) due to improved particle packing and aggregate-paste interface densification. Durability tests revealed significantly reduced compressive strength losses and mass loss in marble-containing mixtures compared to control samples, with optimal acid resistance observed at 20% WMP and 40% WMA replacements. A comprehensive life cycle assessment demonstrated notable reductions in environmental impacts, including up to 20% decreases in Global Warming Potential (GWP) at 20% WMP replacement. A desirability-based eco-cost-mechanical optimization—simultaneously integrating mechanical strength, environmental indicators, and production cost—identified the 10% WMP substitution mix as the most sustainable option, achieving optimal balance among key performance criteria. These findings underscore the significant potential for marble waste reuse in SCC, promoting environmental sustainability, resource efficiency, and improved concrete durability in chemically aggressive environments. Full article

Cement production is a major contributor to CO₂ emissions, while construction and demolition waste (CDW) presents growing environmental challenges. The new European standard UNE-EN 197-6 permits the use of recycled concrete fines as partial clinker replacements, providing a regulatory framework for integrating CDW into cementitious systems. This study investigates two CDW-derived fillers, FHH (recycled concrete filler) and FHC (recycled ceramic–concrete mixed filler), as partial substitutes for ordinary Portland cement (OPC). The materials were characterized using XRD, XRF, FTIR, and particle size analysis. Cement pastes and mortars with 10%, 20%, and 30% volume replacements were evaluated for hydration behavior, mechanical performance, and durability. At lower replacement levels, FHC promoted ettringite formation and microstructural refinement, while FHH favored carbonate hydrate development; both fillers also exhibited durability comparable to the control. At higher levels, they maintained satisfactory compressive strength. This study offers critical insights into the integration of CDW-derived fillers into cementitious systems, revealing their potential to significantly reduce clinker consumption while maintaining high mechanical and durability standards. Full article

The article reviews the literature on the potential utilization of decommissioned wind turbine blade waste (WTBW) in construction materials, including geopolymers, which are rarely discussed. The review indicates that only the mechanical processing of WTBW creates prerequisites for its possible use as fillers in construction materials; however, adjustments to the composition of binding materials are necessary. Wind turbine blades (WTBs) are usually made from strong and durable composite materials, thus posing serious recycling and environmental challenges. Thermal process methods are promising approaches for recovering glass fibers from thermosets of WTBW through pyrolysis or converting WTBW into fibers via plasma processing. Preliminary durability studies of such recovered and recycled glass fibers have demonstrated their potential application in geopolymers or cement-based materials. Implementing these technologies would expand the waste management system, completing recycling and reuse solutions. To successfully adopt more environmentally friendly solutions, further development of geopolymer production processes and sustainable fiber recovery is recommended. Full article

Geopolymers are a sustainable alternative to Portland cement, with the potential to significantly reduce the carbon footprint of conventional cement production. This study investigates the valorization of industrial waste iron powder (IP) as a fine filler in geopolymers synthesized from volcanic tuff (VTF). Composites were prepared with IP substitutions of 5%, 10%, and 20% by weight, using sodium hydroxide and sodium silicate as alkaline activators. Microstructural and phase analyses were conducted using scanning electron microscope coupled with energy dispersive X-ray spectroscopy (SEM-EDS), X-ray fluorescence (XRF), X-ray diffraction (XRD), and differential scanning calorimetry (DSC), while rheological properties, compressive strength, and flexural strength were assessed. The impact of curing temperatures (25 °C and 80 °C) on mechanical performance was evaluated. Results revealed that air content increased to 3.5% with 20% IP substitution, accompanied by a slight rise in flow time (0.8–2 s). Compressive and flexural strengths at 25 °C decreased by up to 22.48% and 28.39%, respectively. Elevated curing at 80 °C further reduced compressive and flexural strengths by an average of 45.30% and 64.68%, highlighting the adverse effects of higher temperatures. Although these formulations are not suitable for load-bearing applications, the findings suggest potential for non-structural uses, such as pavement base layers, aligning with sustainable construction principles by repurposing industrial waste and reducing reliance on energy-intensive cement production. Full article

This study explores the stabilization and utilization of hazardous waste (HW) derived from iron oxide powders containing arsenic, a byproduct of a water purification process. Cement paste samples were prepared with varying waste content (0.0%, 2.5%, 10% and 20% by weight) through mechanical mixing of all the components. Utilizing this waste offers two key environmental benefits: first, it addresses the issue of large-scale waste production globally by providing a method for its stabilization; second, it reduces cement consumption in concrete by serving as an admixture and filler, thereby lowering the cement industry’s significant CO₂ emissions. After 28 days, compressive strength and density tests were conducted, and the microstructure was examined using scanning electron microscopy and X-ray diffraction. The results demonstrated compressive strengths exceeding 20 MPa, with the presence of calcite, portlandite, and ettringite phases in the samples. Additionally, Weibull statistics were conducted over a wide number of samples per composition in order to account for the variability of the compression properties, which can be important for deciding the applications. The results showed that the prepared formulations can be used in structural applications such as walls, infrastructure, sidewalks, and soil stabilization. Full article

Seashells have been explored as a partial replacement for cement in cementitious matrices to promote sustainable waste management and decrease the carbon footprint associated with cement production. As research in this area expands, it is essential to synthesize current findings and practices to guide future studies on the feasibility of using seashells as a filler. This study analyzed existing research on using seashells as a partial cement replacement in cementitious composites through a systematic literature review conducted across six scientific databases, yielding 44 studies for data analysis and synthesis. Key findings identified the shell processing methods, established typical ranges for shell powder’s physical–chemical properties and dosage, and quantified the impact on mechanical properties in binary mixtures. The reported effects on mechanical properties varied among studies, potentially due to differences in processing techniques and the origins of the shells. Most improvements in composite properties were observed with 5% to 15% cement replacement in binary mixtures. Overall, incorporating shell powder reduces the carbon emissions of the produced composites. Further detailed investigations into shell processing variables and dosages are recommended to better understand how these factors influence the properties of the composites produced. Full article

Plastic film, also known as low-density polyethylene (LDPE), poses serious environmental challenges due to mass production, short life cycle, and poor waste management. The main aim of this paper was to examine the suitability of using agricultural waste film as a binder in construction composites instead of the traditional cement slurry. Molten at temperatures of around 120–150 °C wastes was mixed with fine sand and gravel aggregate as filler. Twelve samples consisting of different mixtures were produced—F20, F25, F30, F35, F40, F45, F50, F60, F70, F80, F90, and F100—where a given number indicates the weight ratio of film waste to aggregate used. The composites were subjected to various tests, including volumetric density, compressive strength, and flexural strength. The volumetric density ($\rho$) of the composites decreased with increasing amounts of waste. Composites containing 100% recyclate (F100) depicted density, $\rho$ = 0.74 g/cm³, was 50.7% lower than for a composite that contained 20% recyclate (F20). The highest soakability was recorded in F20 (2.19%). Subsequently, the absorbency tested in composites decreased with increasing recyclate content. Compression strength (σ_comp) was highest for F40 (σ_comp = 39.46 MPa). In contrast, F20 had the lowest recorded compressive strength value (σ_comp = 11.13 MPa) and was 71.8% lower than F40. F70 had the highest recorded flexural strength value (σ_flex = 27.77 MPa). The other composites showed lower strength for higher amounts of recyclate and the amount of sand. SEM imaging proved that the contact zone between the aggregate grains and the bonding phase of the recycled film was consistent, with no anomalies, cracks, or voids. The results prove that LDPE film waste is suitable for use as a binder in building composites. However, appropriately selecting proportions of the recyclate, sand, and gravel aggregate is crucial to obtain a composite with technical parameters similar to those of cementitious composites. Full article

The marble industry in Afghanistan generates significant waste due to a lack of skilled labor and advanced machinery, which is often discarded in landfills. Previous studies suggest that marble waste can be utilized in construction, particularly in cement-based structures. This research investigates using marble waste in concrete as a replacement for cement and sand to address environmental concerns and promote sustainability. A comparative study replaced marble waste with a calcareous filler from Omya SAS. The marble waste, collected from a mining site in Nangarhar, Afghanistan, consisted of 29% particles smaller than 63 μm and 71% sand particles. The waste marble (WM) was added to concrete as a replacement for cement and sand at 3.5%, 4%, and 4.5% by volume. Limestone filler (LF) replaced only cement in the concrete mix. The reference concrete mix aimed for a C25/30 strength. The results showed slight improvements in concrete workability with increasing waste marble content. The optimal WM dosage was 4%, which led to a 9% reduction in compressive strength and a 7% drop in splitting tensile strength. However, this dosage reduced concrete density, improving transfer properties and resulting in cheaper, lighter concrete. The 4% WM dosage corresponds to 7.5% cement and 12% sand replacement. Full article

Global coal consumption is continuously increasing. It is still the primary fuel used in power plants. Despite policies in the European Union aimed at reducing coal consumption, there are countries in the world where coal use continues to rise (China and India are the largest consumers of coal). Coal combustion produces waste, 70% of which is fly ash. It consists mainly of SiO₂ and Al₂O₃. Fly ash also includes Fe₂O₃, TiO₂, MgO, K₂O, and CaO. This article describes various methods of using fly ash. Fly ash can be used in the cement industry, as a filler in materials, in zeolite synthesis, in cenosphere separation, in agriculture, in water purification, in road construction as an asphalt filler, and in mine backfilling. An interesting method of using fly ash as a filler in the production of rigid polyurethane foam was also described. The article concerns potential uses in accordance with the principles of a Circular Economy. The environmental, energy, and material aspects are discussed. Full article

The formulation of binary, ternary, and quaternary supplementary cementitious materials (SCMs) on an optimized silica fume amount using fly ash, ultrafine (MQ), and limestone powders (LS) is the most sustainable approach to recycling these types of solid wastes for durable concrete. The optimum replacement level of 10% silica fume was blended with different replacement levels of 5, 8, 10, and 15% MQ to formulate different ternary mixes to evaluate the filling effect of MQ. Different ternary mixes containing 10% silica fume and 5, 10, and 15% LS were also produced to examine the effectiveness of both ternary mixtures with either MQ or LS. The quaternary mixtures with 10% silica fume optimized with 20% fly ash and 10% MQ or 10% LS were evaluated for compressive strength, chloride permeability, and porosity. The MQ showed the best filling effect compared to LS. The hot curing conditions significantly enhanced the performance of ternary and quaternary mixtures. Two effects of fillers were observed: the diluting effect brought on by replacement levels and the enhanced filling effect. At early curing, the strength loss resulting from the high replacement level was around 39%; however, this drop could be minimized to approximately 7% under hot curing conditions. It has been demonstrated that the binary, ternary, and quaternary systems offer the best solution to the environmental and durability issues caused by cement. The economic analysis highlights that optimized HPC mixtures with SCMs and fillers, particularly the quaternary mix, achieve superior cost-efficiency and mechanical performance, demonstrating their potential for sustainable and high-performance engineering applications. Full article

As the world’s largest producer of construction waste, China’s recycling and related policies are of the biggest concern to the world. However, the effective disposal and reuse of this waste has become an important issue since currently China still has a very low recycling ratio compared to developed countries, and most of the waste concrete was only simply broken and used as low-grade recycled aggregates for subgrade cushion, cement stabilized crushed stone, and filler wall. In this paper, a concrete cycle model focusing on how to effectively recycle and utilize waste concrete is put forward to prepare high quality recycled concrete, especially through a series of technical means, such as effective separation, carbon sequestration, and reactivation. Producing high quality recycled concrete can not only replace traditional concrete but also effectively reduce the consumption and waste of raw materials. What’s more, the calculation results show a potential of significantly carbon sink; for every ton of recycled cement produced, the CO₂ emission could be reduced by 0.35–0.77 tons compared to ordinary Portland cement, corresponding to a reduction of 47%–94%; and for every ton of recycled concrete produced, the CO₂ emission could be reduced by 0.186 tons compared to normal concrete. A yearly CO₂ sequestration of 1.4–3.08 gigatonnes could happen if the ordinary Portland cement could be replaced by the recycled cement around the world. Taking the currently accumulated construction and demolition (C&D) wastes globally, the production of recycled cement, recycled aggregates, and recycled concrete could induce a significant carbon sink in the world. Full article

The valorisation of sludges from aggregate production into construction materials is required for full circularity in mining waste management. This study explores valorisation pathways, relevant regulatory frameworks, and End-of-Waste (EoW) criteria for specific settings in Spain and Norway. The explored valorisation routes involved the production of filler, supplementary cementitious materials (SCMs), and lightweight aggregates (LWAs) for the production of cement-based products, and precursors for 3D printed construction material. The sludge from Norway revealed a non-polluted stream and a stream contaminated with organic phases and clays. Sludge-based filler proved suitable in concrete production with contents of up to 40% of total binder, providing adequate consistency and cohesion. However, clays in the sludge increased the demand for water and superplasticizer. Clay contents were still insufficient for the applications as SCMs, as the calcined sludge demonstrated limited reactivity. The application to produce LWAs was promising, but further microstructure optimization is still required. The clay content was also relevant for the sludge from the site in Spain, as it provided 3D printing mixes with good plasticity. The dosage optimization still required the addition of enzymes, limestone, and natural fibres to improve cohesion, workability, and resistance to the cracking of the 3D printing mix. Full article

Cement-based composites (CBCs) are essential in the construction sector due to their cost-effectiveness, availability, and versatility, but they struggle with low tensile strength and poor heat resistance. Recent advancements have highlighted the potential of nanomaterials, particularly graphene oxide (GO), in enhancing the mechanical, thermal, and electrical properties of CBCs. This study aims to provide a comprehensive review of the incorporation of GO into cementitious composites, examining its impact on microstructure, mechanical properties, rheology, and durability; thus, a bibliometric review and scientometric analysis were conducted to thoroughly evaluate the existing literature. A total of 263 studies were selected for thorough study. It can be concluded that GO content acts as a pore filler, decreasing porosity by 23% and average pore size by 22%, while boosting compressive strength by up to 15% at a 0.05% concentration. It also enhances workability, stability, and resistance to chloride ingress, sulfate attack, alkali–silica reaction, and carbonation. Incorporating GO reduces cement consumption and carbon footprint, leading to more durable structures and supporting sustainable construction by efficiently utilizing waste materials. The optimal GO concentration for these benefits ranges from 0.03% to 0.1% by weight of cement, as higher concentrations may cause agglomeration. GO-modified cementitious materials are well suited for high-performance and durable applications, particularly in environments with chemical and mechanical stresses. Full article