Search Results (2,176)

Here, we introduce novel pregelatinized starch-modified silica gels for Portland cement enhancement. The modified SiO₂ gels demonstrate superior mechanical properties compared to pure silica, with optimal starch modification increasing the modulus by 244.8%. Structural characterization reveals that starch alters Si-O bond configurations without covalent bond formation. Applied to Portland cement, the modified gels significantly enhance compressive strength through method-dependent mechanisms. Casting applications show measurable strength improvements, while pressing methods achieve a 42.3% compressive strength increase with superior packing efficiency under confined conditions. The enhancement primarily stems from accelerated C₃S hydration facilitated by the modified silica gels. These findings establish an innovative approach for high-performance cement materials via organic–inorganic composite modification, providing practical formulation guidance across diverse application scenarios. Full article

With the development of novel production routes enabling near-zero emissions from lime manufacturing, the use of lime as a carbon-sequestering component in cementitious materials has attracted increasing attention. To address the intrinsically low early-age strength of lime-enriched binders (LP), this study investigates the modification effect of polyvinyl alcohol (PVA) on LP, with systematic comparisons to ordinary Portland cement (PO) and pure lime systems (LE). The results indicate that, in terms of mechanical performance, the incorporation of PVA significantly enhances the early-age strength of LP, particularly the flexural strength, which increases by 119.3%. In contrast, the strength of PO shows a certain degree of reduction after PVA addition. Regarding carbon uptake performance, the CO₂ sequestration capacity of PO and LE increases by 16.8% and 16.9%, respectively, whereas that of LP slightly decreases by 5.5%. From the hydration perspective, both the heat release rate and cumulative heat of PO and LP are reduced after PVA incorporation. Combined with microstructural analysis, the mechanical enhancement of LP induced by PVA is mainly attributed to the polymer film-forming effect, which compensates for the negative impact caused by the inhibition of hydration. Full article

Rheology plays an important role in the 3D concrete printing technology, because it directly governs the flowability and shape retention of the material, impacting both the printing process and the final quality of the obtained structure. Local raw materials such as Portland cement, washed sand, and tap water were used for the preparation of 3D-printed concrete mixtures. The solid-state polycarboxylate ether with an anti-foaming agent was used as superplasticizer. The Portland cement was partially replaced (by volume) with a natural zeolite additive in amounts ranging from 0% to 9% in 3D-printed concrete mixtures. A rotational rheometer with coaxial cylinders was used in this research for the determination of rheological characteristics of prepared 3D-printed concrete mixtures. The Herschel–Buckley model was used to approximate experimental flow curves and assess rheological parameters such as yield stress, plastic viscosity, and shear-thinning/thickening index. The additional experiments and calculations, such as water bleeding test and evaluation of the carbon footprint of 3D-printed concrete mixtures, were performed in this work. The replacement of Portland cement with natural zeolite additive positively influenced rheological and stability-related properties of 3D-printed concrete mixtures. Natural zeolite additive consistently reduced water bleeding, enhanced yield stress under increasing shear rates, and lowered plastic viscosity, thereby improving flowability and mixture transportation during the 3D printing process. As the shear-thinning/thickening index remained stable (indicating non-thixotropic behavior in most cases), higher amounts of natural zeolite additive introduced slight thixotropy (especially under decreased shear rates). These changes contributed to better shape retention, layer stability, and the ability to print taller and narrower structures without collapse, making natural zeolite additive suitable for use in the optimized processes of 3D concrete printing. A significant decrease in total carbon footprint (from 3% to 19%) was observed in 3D-printed concrete mixtures with an increase in the mentioned amounts of natural zeolite additive, compared to the mixture without this additive. Full article

This paper presents a microstructural, mineralogical, and mechanical study of low-carbon autoclaved concrete (AC), achieved by partially or fully replacing ordinary Portland cement (OPC) with ground-granulated blast furnace slag (BFS) and substituting lime with calcium carbide slag (CCS). Fourteen mixes were produced and evaluated in the green state and after autoclaving. Quantitative X-ray diffraction (XRD) using the Rietveld method, density, compressive strength, and life cycle assessment (LCA) were conducted. Results show that mixes containing BFS achieve green strengths equal to or higher than the OPC reference, ensuring integrity during autoclaving. Using BFS with an adequate calcium supply promotes the formation of pre-autoclave portlandite, which in turn favors tobermorite development and yields post-autoclave strengths comparable to the OPC reference. Partial lime replacement with CCS (50%) maintains mineralogy and strength, whereas excessive CCS may reduce available portlandite and lower strength. Life-cycle assessment indicates that raw material supply dominates emissions and that removing OPC cuts total CO₂ by 44% without compromising mechanical performance. These findings demonstrate the feasibility of OPC-lean/OPC-free, lime-optimized autoclaved concretes with substantially lower embodied impacts. Full article

Glass wool waste constitutes a rapidly increasing fraction of construction and demolition residues, yet it remains one of the most challenging insulation materials to recycle. Its non-combustible nature, extremely low bulk density, and high fibre elasticity preclude energy recovery and severely limit conventional mechanical recycling routes, resulting in long-term landfilling and loss of mineral resources. Converting glass wool waste into a fine mineral powder represents a potentially viable pathway for its integration into low-carbon construction materials, provided that industrial scalability, particle-size control, and chemical compatibility with cementitious binders are ensured. This study investigates the industrial-scale milling of end-of-life glass wool waste in a ventilated horizontal ball mill. It compares two grinding routes: a corundum-free route (BK) and an abrasive-assisted route (ZK) employing α-Al₂O₃ corundum to intensify fibre fragmentation. Particle size distribution was quantified by laser diffraction using cumulative and differential analyses, as well as characteristic diameters. The results confirm that abrasive-assisted milling significantly enhances fragmentation efficiency and reduces the coarse fibre fraction. However, the study demonstrates that this gain in fineness is inherently coupled with the incorporation of α-Al₂O₃ into the milled powder, introducing a chemically foreign crystalline phase that cannot be removed by post-processing. From a cement-oriented perspective, this contamination represents a critical limitation, as α-Al₂O₃ may interfere with hydration reactions, aluminate–sulfate equilibria, and microstructural development in Portland and calcium sulfoaluminate binders. In contrast, the corundum-free milling route yields a slightly coarser, chemically unmodified powder, offering improved process robustness, lower operational complexity, and greater compatibility with circular economy objectives. The study establishes that, for the circular reuse of fibrous insulation waste in cementitious systems, particle fineness alone is insufficient as an optimization criterion. Instead, the combined consideration of fineness, chemical purity, and binder compatibility governs the realistic and sustainable reuse potential of recycled glass wool powders. Full article

Artificial reefs are an important tool for marine ecological restoration and fishery resource proliferation, and are widely used around the world. Among them, Japan, the United States, China, South Korea, Australia, and the Mediterranean coastal countries have particularly invested in scientific research and practice in this field, and the reefs’ material selection, structural performance, and ecological benefits have attracted much attention. The purpose of this paper is to summarize the preparation methods, characterization methods (such as microstructure analysis and mechanical tests) and mechanical properties (such as compressive strength and durability) of new concrete materials (steel slag-blast furnace slag concrete, oyster shell concrete, sulfoaluminate cement concrete, recycled brick concrete, silica fume concrete, and banana peel filler concrete) that artificial reefs and ceramic artificial reefs developed in recent years, and to explore the resource utilization potential of different waste materials. At the same time, the biostatistical methods (such as species abundance and community diversity) of wood, shipwreck, steel, rock, waste tire, and ordinary concrete artificial reefs and their effects on the marine environment were compared and analyzed. In addition, the potential impact of artificial reef deployment on local fishermen’s income was also assessed. It is found that the use of steel slag, blast furnace slag, sulfoaluminate cement, and silica fume instead of traditional Portland cement can better improve the mechanical properties of concrete artificial reefs (compressive strength can be increased by up to 20%) and reduce the surface pH to neutral, which is more conducive to the adhesion and growth of marine organisms. The compressive strength of oyster shell concrete and banana peel filler concrete artificial reef is not as good as that of traditional Portland cement concrete artificial reef, but it still avoids the waste of a large amount of solid waste resources, provides necessary nutritional support for aquatic organisms, and also improves its chemical erosion resistance. The deployment of artificial reefs of timber, wrecks, steel, rock, waste tires, and ordinary concrete has significantly increased the species richness and biomass in the adjacent waters and effectively promoted the development of fisheries. Cases show that artificial reefs can significantly increase fishermen’s income (such as an increase of about EUR 13 in the value of a unit effort in a certain area), but the long-term benefits depend on effective supervision and community co-management mechanisms. This paper provides a scientific basis for the research and development of artificial reef materials and the optimization of ecological benefits, and promotes the sustainable development of marine ecological restoration technology and fishery economy. Full article

Recycling wastewater from washing concrete trucks in concrete production addresses both economic and sustainability needs. In the present article, wastewater from washing concrete trucks was added to cement pastes made with two different types of cement for comparison. OPC type CEM I 42.5 was compared to pozzolanic cement type CEM IV/B (P-W) 32.5 in terms of hydration behavior and compressive strength development. The hydration of ordinary Portland cement (CEM I 42.5) was accelerated, while the hydration of pozzolanic cement (CEM IV 32.5) showed a relatively lower total normalized heat. Cement pastes were produced from both cement types, and compressive strength, thermal analysis, and setting time tests were performed for their characterization. The early-age kinetics and compressive strength development of CEM I 42.5 pastes indicate that hydration with wastewater leads to a slight increase in compressive strength. Test concrete prepared with pozzolanic cement (CEM IV 32.5) exhibited increased capillary voids, which contributed to less favorable mechanical and durability performance. Compared to the reference concrete, compressive strength was reduced by 7% at 28 days. Wastewater utilization increased the initial absorption rate by approximately 20%, but the calculated chloride content at the exposed concrete surface decreased after the addition of wastewater compared to the control mix. The carbonation depth of concrete with wastewater increased by 1–2 mm, with an uneven penetration zone, but the compressive strength after carbonation increased. Overall, the type of cement used appears to significantly influence the performance of concrete prepared with wastewater. For wastewater collected from sedimentation tanks, replacing fresh water at a 100% rate and using it with pozzolanic cement to produce concrete, it seems that the mechanical properties and durability are only slightly affected. Full article

This study presents the development and optimisation of a standardised rheological test method based on rotational rheometry for the characterisation of cementitious mixtures designed for 3D printing. Tests were performed using a Discovery HR-20 rotational rheometer (TA Instruments, New Castle, DE, USA) equipped with a concentric-cylinder cup-and-paddle geometry. A high-early-strength Portland cement (ASTM C1157 Type HE) with a constant water-to-cement ratio (w/c) of 0.35 was employed. The methodological framework comprised five sequential stages: (i) assessment of the pre-conditioning effect; (ii) standardisation of the static shear test; (iii) optimisation of pre-conditioning parameters; (iv) standardisation of the dynamic shear test; and (v) evaluation of the influence of sample volume. Optimal conditions were determined as follows: for pre-conditioning, a shear rate of 50 s⁻¹, holding time (H_t) of 30 s, and rest period of 180 s; for the static shear test, a shear rate range of 0.05–0.10 s⁻¹ with a H_t of 60 s; for the dynamic shear test, a 30 s ramp up/down, maximum shear rate of 100 s⁻¹, and H_t of 90 s. An optimal sample volume ranging between 150 and 175 mL was established. The proposed method represents a robust and reproducible experimental protocol for evaluating, comparing, and optimising the rheological behaviour of cementitious mixtures using rotational rheometry, providing a reliable tool for the formulation of mixtures tailored to additive manufacturing or 3D printing processes. Full article

The accelerated carbonation of fresh concrete and recycled aggregates is one of the safest methods of CO₂ sequestration as it mineralizes CO₂, preventing its escape into the atmosphere. CO₂ injection during batching of concrete improves its strength and may partially replace Portland cement, as with supplementary cementitious materials (SCMs). The curing of concrete by incorporation of CO₂ also accelerates early strength development, which may enable early stripping of formwork/moulds for precast and in situ construction. The carbonation process may also be used for the beneficiation of recycled aggregates sourced from demolition waste. The CO₂ mineralization technique may also be used for producing low-carbon, carbon-neutral, or carbon-negative concrete constituents via the carbonation of mineral feedstock, including industrial wastes like steel slag, mine tailings, or raw quarried minerals. This research paper analyses various available technologies for CO₂ storage in concrete, CO₂ curing and mixing of concrete, and CO₂ injection for improving the properties of recycled aggregates. Carbon dioxide can be incorporated into concrete both through reaction with hydrating cement and through incorporation in recycled aggregates, giving a product of similar properties to concrete made from virgin materials. In this contribution we explore the various methodologies available to incorporate CO₂ in both hydrating cement and recycled aggregates and develop a protocol for best practice. We find that the loss of concrete strength due to the incorporation of recycled aggregates can be mitigated by CO₂ curing of the aggregates and the hydrating concrete, giving no negative strength consequences and sequestering around 30 kg of CO₂ per cubic metre of concrete. Full article

Concrete production contributes approximately 4–8% of global cardon dioxide emissions, largely due to Portland cement. Incorporating municipal solid waste (MSW) into concrete offers a pathway to reduce cement demand while supporting circular economy objectives. This study evaluates the mechanical performance, environmental impacts, and optimization potential of concrete incorporating three MSW-derived materials: cardboard kraft fibers (KFs), recycled high-density polyethylene (HDPE), and textile fibers. A maximum 10% cement replacement strategy was adopted. Compressive strength was assessed at 7, 14, and 28 days, and a cradle-to-gate life cycle assessment (LCA) was conducted using OpenLCA to quantify global warming potential (GWP100) and other midpoint impacts. A surrogate-based optimization implemented using Non-dominated Sorting Genetic Algorithm II (NSGA-II) was applied to minimize cost and GWP while enforcing compressive strength as a feasibility constraint. The results show that fiber-based wastes significantly reduce embodied carbon, with KF achieving the largest GWP reduction (19%) and textile waste achieving moderate reductions (10%) relative to the control. HDPE-modified concrete exhibited near-control mechanical performance but increased GWP and fossil depletion due to polymer processing burdens. The optimization results revealed well-defined Pareto trade-offs for KF and textile concretes, identifying clear compromise solutions between cost and emissions, while HDPE was consistently dominated. Overall, textile waste emerged as the most balanced option, offering favorable environmental gains with minimal cost and acceptable mechanical performance. The integrated LCA optimization framework demonstrates a robust approach for evaluating MSW-derived concrete and supports evidence-based decision-making toward low-carbon, circular construction materials. Full article

To address the high-carbon emissions associated with the large use of Portland cement (PC) in traditional engineered cementitious composites (ECCs) and the resource constraints on supplementary cementitious materials (SCMs), this study proposes a strategy combining limestone calcined clay cement (LC³) as a PC replacement with the incorporation of hybrid synthetic fibers to develop low-carbon, environmentally friendly ECCs. The fundamental properties of the LC³-ECC were tested, and a sustainability analysis was conducted. The experimental results show that an increase in water-to-binder ratio (W/B) or superplasticizer (SP) dosage significantly enhanced fluidity while reducing the yield stress and plastic viscosity. An LC³-ECC with a W/B of 0.25, 0.45% SP and 2% polyethylene fibers exhibited the best tensile performance, achieving an ultimate tensile strain of 8.40%. In contrast, an increase in polypropylene fiber led to a degradation in crack-resistant properties. In terms of sustainability, replacing the PC with LC³ significantly reduced carbon emissions by 19.1–20.8%, while the cost of the limestone calcined clay cement–polypropylene fiber (LC³-PP) was approximately 50% of that of the limestone calcined clay cement–polyvinyl alcohol fiber (LC³-PVA). Furthermore, an integrated evaluation framework encompassing rheological, mechanical and environmental factors was established using performance radar charts. The dataset on the performance results and the developed assessment framework provide a foundation for optimizing the mixture proportioning of LC³-ECC in practical engineering applications. Full article

The construction sector faces the dual challenge of reducing energy consumption and mitigating the environmental burden of construction and demolition waste (CDW). Geopolymers offer a low-carbon alternative to Portland cement, yet their performance depends strongly on precursor composition. This study presents an extensive investigation of precursor chemistry, mechanical performance and phase composition, focusing on the partial substitution of ground granulated blast furnace slag (GGBFS) with mechanically activated CDW powder (15% and 30% by weight) alongside fly ash (FA). The oxide composition, amorphous content and particle size distribution were analyzed, using XRF, XRD and laser diffraction to evaluate the reactivity. Mortar samples were subsequently synthesized and tested for compressive and flexural strength, ultrasonic pulse velocity, density and porosity. The results demonstrate that while mechanically activated CDW incorporation decreases early strength compared with GGBFS-rich systems, compressive strengths above 45 MPa were attained at 28 days, with continuous improvement to >69 MPa for aged composites. The relationship between precursor chemistry, precursor sizes and mechanical performance highlights the feasibility of CDW valorization in geopolymer binders, contributing to energy efficiency, circular economy strategies and sustainable construction materials. Full article

This study investigates the use of fly ash to mitigate the long-term performance degradation of Portland cement-based sealing materials in high-salinity environments, such as those found in gas storage reservoirs. We systematically evaluated the evolution of material properties under different temperatures and curing periods. Our integrated methodology combining mechanical tests, microstructural analysis, and chloride migration assessment, reveals a multi-faceted mechanism by which fly ash enhances chloride resistance. The key findings demonstrate that reactive Al₂O₃ in fly ash promotes the formation of Friedel’s salt, increasing chemical chloride binding and reducing the chloride ingress rate in the Portland cement–Fly ash system (PFS) to only 26.6% of that in the Portland Cement system (PCS). Concurrently, the pozzolanic reaction consumes portlandite (Ca(OH)₂), forming stable C-A-S-H gel and refining the pore structure by filling interconnected channels. This nanoscale pore refinement decreased permeability by nearly an order of magnitude. After 90 days of curing in 90 °C saline solution, PFS achieved a compressive strength of 28.2 MPa and maintained an exceptionally low internal chloride content of 0.08 wt.%, demonstrating superior long-term durability. This work clarifies the synergistic mechanisms of fly ash modification and temperature effects, providing a theoretical basis for optimizing sealing materials for deep geological reservoirs and experimental support for the application of fly ash in high-temperature, high-salinity engineering environments. Full article

Mine waste remains a persistent challenge for the minerals industry, posing significant environmental concerns if not properly managed. The 1996 Marcopper Mining Disaster in Marinduque, Philippines, left a legacy of mine tailings that continue to threaten local ecosystems and communities. This study investigates the valorization and stabilization of Marcopper river sediments laden with mine tailings using a combined geopolymerization and cement hydration approach. Hybrid mortar samples were prepared with 7.5%, 15%, 22.5%, and 30% mine tailings by weight, utilizing potassium hydroxide (KOH) as an alkaline activator at concentrations of 1 M and 3 M, combined with Ordinary Portland Cement (OPC). The mechanical properties of the hybrid geopolymer cement mortars were assessed via unconfined compression tests, and their crystalline structure, phase composition, surface morphology, and chemical bonding were also analyzed. Static leaching tests were performed to evaluate heavy metal mobility in the geopolymer matrix. The compression tests yielded strength values ranging from 24.22 MPa to 53.99 MPa, meeting ASTM C150 strength requirements. In addition, leaching tests confirmed the effective encapsulation and immobilization of heavy metals, demonstrating the potential of this method for mitigating the environmental risks associated with mine tailings. Full article

This study investigated the effects of incorporating rice husk ash (RHA) as a partial replacement for cement on the properties of concrete. To determine the optimal replacement level, RHA was used to replace cement in varying proportions, ranging from 0% to 25% in 5% increments. The mix with 0% RHA served as the control. The properties evaluated included setting time, density, and compressive strength. The results revealed that blending RHA with cement increased the initial setting time. This was attributed to the lower calcium oxide (CaO₂) content of RHA, which slows early-age hydration reactions. Conversely, the final setting time was reduced due to the pozzolanic activity of RHA, which enhances later-stage reactions. Additionally, the inclusion of RHA resulted in a decrease in concrete density, owing to its lower specific gravity and bulk density compared to Portland cement. Despite this, RHA-modified specimens exhibited higher compressive strengths than the control specimens. This strength enhancement was linked to the formation of additional calcium–silicate–hydrate (C-S-H) gel due to the pozzolanic reaction between amorphous silica in RHA and calcium hydroxide (CaOH) from hydration reaction. The gel fills concrete voids at the microstructural level, producing a denser and more compact concrete matrix. Based on the balance between strength and durability, the optimal RHA replacement level was identified as 10%. Full article