Search Results (741)

Mineral expansive from FDG—flue-gas desulfurization—blended with calcium aluminate cement CAC was analyzed as mitigation shrinkage of alkali-activated residual mortars AAM. The AAM mortars were composed of red mud (RM) and bottom ash (BA), as precursors of a metakaolin MK-based system. MK replacement (0, 50, 70%) in alkaline solution (10M) and ratio 1:2 (binder/sand) was studied. Engineering properties were performed, and included mechanical strength, setting times, and dry shrinkage (HR 60%), as well as the microstructure formed at 7 d and 28 days. A total of 10% CAC-FGD dosage was the most efficient, reducing drying shrinkage by 23% and autogenous shrinkage by up to 30%. The findings showed that this addition also improved mechanical strength by approximately 16% at 28 days. Under the addition of CAC-FGD, the results suggest the presence of aluminosilicate gels of the (Na,C)-(A)-S-H type and the formation of ettringite, which are possibly responsible for ensuring good performance and a controlled expansion that, in turn, compensates for the shrinkage of the activated mortars. Full article

This study presents a novel approach to the development of self-compacting concrete (SCC) by partially replacing both cement and fine aggregate (sand) with waste marble sludge (WMS), a byproduct of the marble industry. The research aims to evaluate the feasibility of incorporating this industrial waste into SCC to enhance sustainability without compromising performance. To assess the fresh and hardened properties of the proposed mixtures, a comprehensive experimental program was conducted. Tests included slump flow, T₅₀, and V-funnel for evaluating workability, as well as measurements of specific gravity, compressive strength, flexural strength, Brazilian tensile strength, and water absorption at 28 days of curing. The results demonstrated that the mix containing 5% cement replacement and 20% sand replacement with marble sludge exhibited the highest mechanical performance, achieving a compressive strength of 48.2 MPa, tensile strength of 3.9 MPa, and flexural strength of 4.4 MPa. Furthermore, increasing the percentage of cement replacement led to enhanced flowability, as evidenced by an increase in slump flow diameter and a reduction in V-funnel flow time, indicating improved workability. Overall, the findings suggest that controlled incorporation of WMS can produce SCC with desirable mechanical and rheological properties, offering a promising pathway for sustainable concrete production. In addition to the technical performance, a carbon footprint analysis was conducted to examine the environmental benefits of marble sludge utilization. The mixture with 10% cement and 20% sand replacement exhibited the lowest carbon footprint, while the 7.5% replacement level provided the best balance between strength and sustainability. Full article

Natural sand extraction for concrete manufacturing is a global issue for ecological balance and environmental concerns. This study introduced three mixes with three newly developed sand types to replace natural sand in concrete manufacturing. Additionally, three more mixes were made by incorporating optimized 10% silica fume. The durability of the prepared mixes was evaluated at high temperatures of (150–750 °C) at the interval of 150 °C and against immersion in a 5% sulfuric acid solution for 28, 56, 91, and 182 days, respectively. The study’s results reported the stability of the samples up to 300 °C, and then the fall of the samples started at 450 °C. Severe damage in the samples was formed at about 600 °C, and finally, a total collapse was seen at 750 °C. From (150 to 750 °C), the mix TYPE-3SSFC with a sustainable sand combination (50% recycled sand + 45% desert sand + 5% crumb rubber) and 10% silica fume showed better resistance than the other mixes. The compressive strength in the mix TYPE-3SSFC was 20.6%, 16.3%, 14.7%, 21.3%, 26.5%, and 43.2% higher than the mix TYPE-3SC with 10% silica fume. The mix TYPE-3SSFC with optimized 10% silica fume content showed better resistance against 5% sulfuric acid solution than those without silica fume. By morphological analysis, the mix TYPE-3SSFC showed that the interface improved due to the dense interconnectivity of the concrete mix between the crumb rubber paste and silica fume content. A dense calcite crystal was also seen in the mixture, which confirmed the study’s results. The mix with TYPE 2-Sand (100% recycled sand) revealed inferior results, low stability, and high damage. Thus, 100% recycled sand is not recommended for structural concrete. Full article

This study investigates the use of preliminary thermochemical activation in a NaHCO₃ solution under elevated pressure and temperature to modify the chemically stable and hard-to-process phase composition of various mineral raw materials and improve the recovery of valuable components. The method was tested on various types of mineral raw materials, including slag from the reductive smelting of red mud from alumina production prior to acid leaching, ash before chemical beneficiation, gibbsite–kaolinite bauxite prior to gravity separation, and nephelines, for which the sintering process was replaced with chemical beneficiation. The slag from the reductive smelting of red mud was also tested before acid leaching. The activation of slag enhanced tricalcium silicate formation lead to leaching recoveries of ~96% for rare earth elements, ~92% for TiO₂, ~98% for CaO and Al₂O₃, and 50% for Fe₂O₃, compared to much lower values without activation. With ash, activation eliminated the sillimanite and hedenbergite phases, increased mullite and free silica, and formed calcite, resulting in a 15–20% higher silica recovery. With gibbsite–kaolinite bauxite, activation altered kaolinite, siderite, quartz, and hematite contents; eliminated calcium silicate; and improved the silicon modulus of the sand fraction by 35.9% during gravity beneficiation. For nepheline ore, activation promoted the formation of albite and hydrosodalite, eliminated corundum and andradite, and increased silica recovery from 33.58% to 59.6%. These results demonstrate that thermochemical activation effectively transforms mineral structures and significantly improves the efficiency of subsequent beneficiation processes. Full article

To advance the adoption of manufactured sand, this study investigated concrete mix designs wherein manufactured sand partially substituted natural river sand and fully replaced fine aggregates. The influences of the water–binder ratio and fly ash content were also examined. Experimental findings indicate that at replacement rates of 50% and 70%, the workability and mechanical properties of mixed sand concrete experienced a decline. The mechanical performance of concrete improved as the water–binder ratio decreased. Additionally, the strength properties of manufactured sand concrete initially increased with higher fly ash content but slightly decreased when fly ash content reached 30%. Nevertheless, all strength metrics still satisfied the design specifications. Thus, the overall performance of high-performance concrete incorporating manufactured sand remains favorable, demonstrating its viability as a full replacement for river sand in concrete production. Full article

High-performance geopolymer concrete (HPGC) is an eco-friendly type of concrete that is traditionally made of slag, silica fume (SF), and quartz sand. Recycling industrial waste in HPGC presents an eco-friendly approach for maximizing sustainability in the construction sector. This study evaluates the impact of incorporating recycled fine aggregates like crumb rubber (CR), glass waste (GW), and ceramic waste (CW) as partial replacements for quartz sand in HPGC at 10%, 20%, and 40% by volume. GW and CW were also used in binder size as full replacements for SF. The novelty of this research lies in its comprehensive evaluation of waste-integrated HPGC under diverse conditions, including mechanical performance, durability (water absorption, sulfate/chloride/acid resistance), thermal stability (up to 600 °C), and microstructure analysis, while addressing critical gaps in eco-friendly construction materials. The results indicate that CW significantly enhanced compressive strength, increasing by 24–29% at 10% and 40% replacement levels, whereas CR reduced strength by 69.2–83.5%. GW effectively decreases water absorption by 66–72% compared to CW and CR. Both CW and GW improved chemical resistance, reducing compressive strength loss by 15–33% under sulfate and acid attacks. CW exhibited superior residual strength at 600 °C, reaching 96.4 MPa, compared to 54.5 MPa for GW. However, fully replacing SF with GW or CW as a binder resulted in performance deterioration, making it unsuitable. This study demonstrates that incorporating recycled waste materials in HPGC enhances its mechanical and durability properties, making it a viable option for sustainable construction. The findings support the integration of CW and GW as eco-friendly alternatives in HPGC applications. Full article

Currently, many foundries successfully reuse sand multiple times within their production cycle. However, when the sand can no longer be reused, it is disposed of, resulting in environmental damage and high disposal costs for the company. The present research aims to explore the potential reuse of foundry sands as fine aggregate in concrete. Since this by-product is classified as non-hazardous waste, it can offer interesting opportunities for the recycling of a material that is currently one of the most widely used in the construction industry. This paper studies the potential reuse of green sand (GS) and chemically bonded sand (CBS) as a partial replacement for natural sand (NS) in concrete. Concrete specimens made with 10%, 20%, and 30% of foundry sand were tested, and a comparative analysis was carried out with the standard mixture in terms of chemical–physical properties, workability, and mechanical properties. The results showed a reduction in the performance of concrete specimens prepared with foundry sands. The lowest reductions in the strength, which were always below 10%, were observed for a 10% inclusion rate of both GS and CBS, with slightly better performance for CBS. Performance reductions tend to increase with higher replacement rates. However, these performance reductions turn out to be acceptable for concrete used in non-structural applications. Full article

This study aimed to evaluate mortar performance by substituting part of standard sand with recycled fine aggregates sourced from concrete waste, aiming to assess mechanical properties and durability. Moreover, this study examined the use of crystallizing agents to understand their impact on mortar properties. Four mortar series were prepared with sand substitution percentages ranging from 25% to 100% while adhering to the diverse fraction proportions within the standardized sand particle size distribution. Mechanical results indicate that incorporating recycled concrete sand significantly enhances mechanical properties with respect to standard sand. The study showed the technical feasibility of producing mortars with up to 100% recycled fine concrete aggregate with enhanced compressive strength, albeit requiring higher superplasticizer dosages. The addition of crystallizing agents provided an increase in flexural strength in specific conditions, while they did not provide a significant improvement to compressive strength. Full article

This research investigates the feasibility of producing eco-friendly self-compacting concrete (SCC) by partially replacing both fine and coarse natural aggregates with waste marble sludge (WMS), a byproduct of the marble industry. The objective is to evaluate whether this substitution enhances or compromises the concrete’s performance while contributing to sustainability. A comprehensive experimental program was conducted to assess fresh and hardened properties of SCC with varying WMS content. Fresh-state tests—including slump flow, T₅₀ time, and V-funnel flow time—were used to evaluate workability, flowability, and viscosity. Hardened properties were measured through compressive, flexural, and Brazilian tensile strengths, along with water absorption after 28 days of curing. The mix with 10% replacement of both sand and coarse aggregate showed the most balanced performance, achieving a slump flow of 690 mm and a V-funnel time of 6 s, alongside enhanced mechanical properties—compressive strength 48.6 MPa, tensile strength 3.9 MPa, and flexural strength 4.5 MPa—and reduced water absorption (4.9%). A complementary cost model quantified direct material cost per cubic meter and a performance-normalized efficiency metric (compressive strength per cost). The cost decreased monotonically from 99.1 $/m³ for the base mix to $90.7 $/m³ at 20% + 20% WMS (−8.4% overall), while the strength-per-cost peaked at the 10% + 10% mix (0.51 MPa/USD; +12% vs. base). Results demonstrate that WMS can simultaneously improve rheology and mechanical performance and reduce material cost, offering a practical pathway for resource conservation and circular economy concrete production. Full article

Natural radionuclides (⁴⁰K, ²¹⁰Pb, ²²⁶Ra, ²³²Th, and ²³⁸U) were evaluated for the first time on volcanic ash soils of the Argentine Patagonian Andes. The study was carried out along a topoedaphoclimatic gradient, encompassing soils from Xeric Mollisols to Udic Andisols, and different land uses. Median mass-specific activities of the lithogenic radionuclides ⁴⁰K, ²¹⁰Pb, ²²⁶Ra, ²³²Th, and ²³⁸U were 375, 8, 17, 19, and 29 (Bq kg⁻¹), respectively, all falling within global natural background levels, yet distinct spatial and vertical patterns emerged. Radionuclide activities increased with sand content and decreased with organic matter, highlighting the role of the parent material and texture. In dry-site Mollisols, ⁴⁰K and ²¹⁰Pb increased with depth, while in humid-site Udands, activities declined with depth, suggesting leaching and surface accumulation by allophane–organic matter complexes. The 238U/226Ra activity ratio showed disequilibrium, indicating young, developing soil profiles. In Xerolls, where native forest was replaced by afforestation and rangeland use, erosion-driven degradation was evident. The distribution of radionuclides along the slopes was closely linked to the topographic position and slope gradient. These results underscore the sensitivity of radionuclide patterns to parent material, soil-forming processes and land use and provide a valuable reference for environmental monitoring in volcanic landscapes. Full article

Aeolian sand is the primary geological material for construction in desert regions, and its stabilization with industrial solid wastes-based geopolymer (ISWG) provides an eco-friendly treatment replacing cement. This study comparatively investigated the enhancement effects of chemical activators and expansive agents on compressive strength of aeolian sand stabilized by ISWG (ASIG). Three chemical activators—NaOH, Ca(OH)₂, and CaCl₂—along with two expansive agents—desulfurized gypsum and bentonite—were considered. Through X-ray diffraction, thermogravimetric analysis, scanning electron microscopy, mercury intrusion porosimetry and pH values tests, the enhancement mechanisms of the additives on ASIG were elucidated. Results demonstrate that the expansive agent exhibits significantly superior strengthening effects on ASIG compared to the widely applied chemical activators. Chemical activators promoted ISWs dissolution and hydration product synthesis, thereby densifying the hydration product matrix but concurrently enlarged interparticle pores. Desulfurized gypsum incorporation induced morphological changes in ettringite, and excessive desulfurized gypsum generated substantial ettringite that disrupted gel matrix. In contrast, bentonite demonstrated superior pore-filling efficacy while densifying gel matrix through a compaction effect. These findings highlight bentonite superior compatibility with the unique microstructure of aeolian sand compared to conventional alkaline activators or expansive agents, and better effectiveness in enhancing the strength of ASIG. Full article

Seed-sown wildflower meadows are becoming increasingly important in our cities. One of the best methods is to design low-maintenance green spaces with an ecological approach. They can be used either to create perennial beds or to enrich and replace larger areas of regularly mown grass. Seeded surfaces are closer to a functioning ecosystem. The seed mixtures available in Hungary include seeds of native and non-native species, but due to a lack of time or resources, they have not been tested and have been in the field almost immediately. With our research, launched in autumn 2023, we tried to fill this gap and established seed-sown perennial beds in Budapest (Hungary), in ten plots in different media, using a seed mix of native species (96 taxa). Our experiment is an attempt to answer the question of what makes a seed-sown herbaceous plantation successful in the long term in an urban environment. Which species will emerge first, in which medium and which will persist in the long term? What will be the cover, diversity of the plots, the phenology of each species at different times of the year and to what extent does this depend on the medium and the frequency of irrigation? Which taxa will appear in each growing medium, and will there be taxa that can only develop in certain media? The study reports on the first experiences of the long-term study, according to which there were dynamically developing stands, but we observed a basically negative correlation between rapidly developing media and diversity. The most diverse species set was provided by the andesite aggregate medium, followed by green roof substrate, then demolition rubble with sand and sand. Full article

Rapid urbanization and industrialization have increased atmospheric pollution, particularly via sulfur oxides (SO_x) that form sulfuric acid and accelerate the degradation of cementitious materials. While Portland-cement systems have been widely studied, less is known about the acid resistance of geopolymer mortars. This study investigates the durability and microstructural evolution of metakaolin–red mud geopolymer mortars incorporating limestone, marble, and basalt powders as partial sand replacements (5, 10, and 15 wt %). Specimens were immersed in 3% H₂SO₄ for 30, 60, and 90 days, with performance evaluated via compressive and flexural strength, weight loss, and ultrasonic pulse velocity (UPV), alongside scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). After 90 days, the optimal basalt-filled mix (15 wt %) retained 84% of its initial compressive strength (46.8 MPa), compared with 61% for the control; mass loss decreased from 6.4% (control) to 3.2%, and UPV degradation was reduced by 35%. Microstructural analyses indicate denser gel phases and reduced microcracking in basalt- and marble-filled mixes. These results demonstrate that industrial by-product fillers can significantly improve sulfuric-acid resistance while supporting more sustainable binder technology. Full article

In this research work, five different types of post-consumer plastics were mechanically ground into fine aggregate, and each type was used to prepare 2 in. (50 mm) mortar cubes by partial volumetric replacement of the sand. The purpose is to evaluate the effect of the plastic type and its shape on the density and the compressive strength of concrete. The plastic products used in this study are usually not collected by curbside recycling facilities and are discarded in landfills or incinerated. The different types of plastics investigated were Polyethylene terephthalate (PET), High-Density Polyethylene (HDPE), Polypropylene (PP), Polystyrene (PS), and Acrylonitrile Butadiene Styrene (ABS). A total of 180 cubes with 5%, 10%, and 15% replacement were prepared and tested for their densities at the age of 28 days and their compressive strengths at the ages of 7 and 28 days. This work concluded by proposing general equations to predict the reduction in the density and compressive strength of the mortar with the increment in the plastic replacement. Full article

Desert sand (DS) serves as a sustainable alternative to river sand in concrete production, delivering environmental and economic benefits. Furthermore, the durability of concrete structures in cold regions is severely affected by freeze–thaw (F-T) cycles. Therefore, this study employed a central pull-out test to examine the bond performance between desert sand concrete (DSC) and steel bars subjected to F-T cycles, considering the effects of the number of F-T cycles, DS replacement ratios (i.e., the replacement ratio of river sand by DS), and the type of reinforcement. The F-T cycle numbers tested were 0, 25, 50, and 75 cycles. The DS replacement ratios were varied at 0%, 20%, 40%, 60%, 80%, and 100%. The plain and threaded steel bars (PSBs and TSBs) were selected for the experiment. The results indicate a decrease in bond strength for both PSB and TSB specimens with increasing F-T cycle numbers. Regarding the DS replacement ratios, bond strength initially decreased, with an increasing replacement rate, then increased, and eventually reduced again. Notably, significantly improved bonding was observed for steel reinforcement in DSC containing 40% or 60% DS compared to plain concrete. Additionally, the bond strengths of PSB specimens were lower than those of TSB specimens under identical conditions. A calculation formula for the bond–slip characteristic was derived using statistical regression, which considered multiple factors. Eventually, a bond–slip constitutive model was developed for the interface between DSC and reinforced steel, showing a high degree of consistency with the experimental data. Full article