Search Results (155)

This research focuses on improving the characteristics of recycled concrete and utilizing solid waste resources through the combination of industrial waste pre-impregnation and the carbonation process. A novel pre-impregnation–carbonation aggregate method is proposed to increase the content of carbonatable components in the surface-bonded mortar of recycled coarse aggregate by pre-impregnating it with carbide slag slurry (CSS). This approach enhances the subsequent carbonation effect and thus the properties of recycled aggregates. The experimental results showed that the method significantly improved the water absorption, crushing value, and apparent density of the recycled aggregate. Additionally, it enhanced the compressive strength, split tensile strength, and flexural strength of the recycled concrete produced using the aggregate improved by this method. Microanalysis revealed that CO₂ reacts with calcium hydroxide and hydrated calcium silicate (C-S-H) to produce calcite-type calcium carbonate and amorphous silica gel. These reaction products fill microcracks and pores on the aggregate and densify the aggregate–paste interfacial transition zone (ITZ), thereby improving the properties of recycled concrete. This study presents a practical approach for the high-value utilization of construction waste and the production of low-carbon building materials by enhancing the quality of recycled concrete. Additionally, carbon sequestration demonstrates broad promise for engineering applications. Full article

Rare earth elements (REEs) have garnered significant global attention due to their essential role in advanced technologies. Sri Lanka is endowed with various REE-bearing minerals, including the apatite-rich deposit in the Eppawala area, commonly known as Eppawala rock phosphate (ERP). However, direct extraction of REEs from ERP is technically challenging and economically unfeasible. This study introduces a novel, integrated approach for recovering REEs from ERP as a by-product of nitrophosphate fertilizer production. The process involves nitric acid-based acidolysis of apatite, optimized at 10 M nitric acid for 2 h at 70 °C with a pulp density of 2.4 mL/g. During cooling crystallization, 42 wt% of calcium was removed as Ca(NO₃)₂.4H₂O while REEs remained in the solution. REEs were then selectively precipitated as REE phosphates via pH-controlled addition of ammonium hydroxide, minimizing the co-precipitation with calcium. Further separation was achieved through selective dissolution in a sulfuric–phosphoric acid mixture, followed by precipitation as sodium rare earth double sulfates. The process achieved over 90% total REE recovery with extraction efficiencies in the order of Pr > Nd > Ce > Gd > Sm > Y > Dy. Samples were characterized for their phase composition, elemental content, and morphology. The fertilizer results confirmed the successful production of a nutrient-rich nitrophosphate (NP) with 18.2% nitrogen and 13.9% phosphorus (as P₂O₅) with a low moisture content (0.6%) and minimal free acid (0.1%), indicating strong agronomic value and storage stability. This study represents one of the pioneering efforts to valorize Sri Lanka’s apatite through a novel, dual-purpose, and circular approach, recovering REEs while simultaneously producing high-quality fertilizer. Full article

In order to address a challenging issue in the recycling of construction debris, the impact of carbonization treatment on the characteristics of recycled aggregates (RCAs) was experimentally examined in this work. Both direct carbonization and carbonization following calcium hydroxide pretreatment were used in the study to assess the impact of carbonization on the physical characteristics of recycled aggregates. According to the findings, carbonization raised the recycled aggregates’ apparent density while drastically lowering their porosity and water absorption (by as much as 20–30%). Although the recycled aggregate’s crushing index marginally increased with age, its overall physical qualities remained excellent. Pretreatment with calcium hydroxide can improve the physical characteristics of recycled aggregates, further optimize their pore structure, and efficiently encourage the carbonation process. Furthermore, recycled aggregate’s crushing index can be considerably decreased and its quality much enhanced by the ultrasonic cavitation treatment. According to the study, the carbonation-treated recycled aggregate’s microstructure was denser in the interfacial transition zone and had a stronger link with the cement paste, improving the recycled aggregate concrete’s overall performance. XRD, infrared spectral analysis, and SEM scanning were used to determine the increased calcium carbonate content in the recycled aggregate following carbonation treatment as well as its microstructure improvement process. The findings offer fresh concepts for achieving resource efficiency and environmental preservation through the use of recycled aggregates in concrete, as well as theoretical backing for their use. Full article

This study explores the impact of thermal cycling and rubber particle content on the static and dynamic compressive properties of rubber–polyethylene fiber-reinforced engineered cementitious composites (RPECC). Through static and dynamic compression tests, supplemented by scanning electron microscopy and energy-dispersive X-ray spectroscopy, the mechanical behavior and microstructural evolution of RPECC under thermal cycling were analyzed. Results indicate that increasing rubber content from 10% to 30% enhances toughness and strain capacity but reduces the static compressive strength of ECC by up to 17.9% at 30%. Thermal cycling reduced strength: static and dynamic compressive strengths decreased by 18.0% and 41.2%, respectively, after 270 cycles. Dynamic tests demonstrated that RPECC is sensitive to strain rate. For example, C-20 specimens exhibited increases in dynamic strength of 6.9% and 9.9% as strain rate rose from 60.2 s⁻¹ to 77.4 s⁻¹ and 110.8 s⁻¹, respectively, and the dynamic increase factor correlated linearly with strain rate. By contrast, excessive rubber content (30%) diminishes dynamic strengthening, indicating that 20% rubber is optimal for enhancing strain rate sensitivity. Thermal cycling facilitates the formation of hydration products, such as calcium hydroxide, and creates interfacial defects, further deteriorating mechanical performance. These findings provide a reliable foundation for optimizing RPECC mix design and ductility in environments subject to temperature fluctuations and dynamic loading. Full article

Treating poultry manure with calcium compounds is the primary technique for inactivating toxic pathogens such as bacteria, fungi, or viruses and decreasing the risk of biological contaminant release into the environment. On the other hand, the preferable method for reducing its volume is incineration with the aim of obtaining highly concentrated fertilizer. This paper presents the optimization of the biological deactivation of fresh poultry manure using calcium hydroxide via central composite design and response surface methodology. The results revealed that the optimum parameters required to decrease the number of E. coli bacteria to below the acceptable level (1000 CFU/g) were 5.0 wt% Ca(OH)₂ at 22 °C and an exposure time of 209 h. A regression analysis showed a good fit of the approximated parameters to the experimental data (R² = 98%, R_adj.² = 97%). Additionally, laboratory tests involving ash samples obtained from the incineration of poultry manure with the addition of 5 wt% calcium hydroxide (T = 500 °C, t = 5 h) intended as a fertilizer for degraded soils were performed. The analysis revealed that the content of pure manure ash in the sample incinerated with Ca(OH)₂ was approximately 47.5%. An X-ray diffraction analysis of the ash sample revealed that the main crystalline component was calcite (67.5 wt% CaCO₃), the phases containing phosphorus were apatite (3 wt%) and hydroxyapatite (3 wt%), whereas the source of the bioavailable form of phosphorus was the amorphous phase (15.5 wt%). An analysis of the ash extracts in a 2% citric acid solution revealed that the phosphorus concentration (287 mg/L) was two times lower than that of potassium (661 mg/L). The best results of phytotoxicity tests with Sinapis alba were obtained for soils containing no more than 1.0 wt% ash with calcium hydroxide. Full article

Milk of lime (MOL), a suspension of calcium oxide and calcium hydroxide, is vital in the purification of sugar beet and cane juices. This study evaluates the application of Fourier Transform Near-Infrared (FT-NIR) spectroscopy combined with chemometric models—Partial Least Squares (PLS) and Principal Component Regression (PCR)—for rapid, non-destructive assessment of key MOL parameters: density, total lime content, calcium oxide availability, and sucrose content. Ninety samples were analyzed using both wet chemistry and FT-NIR. The predictive performance was assessed using the coefficient of determination (R²). High predictive accuracy was observed for density (PLS: R² = 0.8274; PCR: R² = 0.8795) and calcium oxide availability (PLS: R² = 0.9035; PCR: R² = 0.9115). Total lime content showed moderate accuracy (PLS: R² = 0.7748; PCR: R² = 0.7983), while sucrose content exhibited low predictive power (PLS: R² = 0.2312; PCR: R² = 0.3747). The weak performance was noted for %CaO (PLS: R² = 0.4893; PCR: R² = 0.2409), likely due to spectral overlap and matrix complexity. Despite these challenges, FT-NIR remains a viable, reagent-free method for monitoring MOL, with the potential to enhance process control in the sugar industry. Future work should focus on refining calibration strategies and addressing spectral interferences to improve predictive accuracy for complex matrices. Full article

To study the chloride transport properties of urban rail transit structures under the action of stray currents, electrochemical tests were employed as part of this paper to investigate the impact of stray currents on cementitious materials and pore structure and further analyze the chloride distribution of specimens in different conditions. Results show that a stray current accelerates calcium ion precipitation in chloride solutions, reducing calcium hydroxide content compared to unelectrified specimens. This dissolution alters the concrete pore structure, increasing porosity by 26.3%, 31.2%, and 36.1% for specimens electrified at 50 mA, 100 mA, and 150 mA, respectively, after 28 days. The effect coefficient k_p of stray currents on the porosity of concrete is given with the test results. Electrified specimens have a higher chloride content compared to unelectrified specimens, with free chloride increasing more than bound chloride as current and time increase. The chloride ion binding capacity of concrete electrified at 150 mA is only 60% that of unelectrified, indicating the significant weakening effect of stray currents on it. Full article

Alkali-activated slag-like powder (AASP) materials are a novel type of binder prepared by activating slag-like powder (SP) with alkaline activators, providing a sustainable alternative to traditional cement for construction in remote mountainous regions, as well as on islands and reefs far from the inland, reducing transportation costs, shortening construction timelines, and minimizing energy consumption. SP is locally produced from siliceous and calcareous materials through calcining, water quenching, and grinding, exhibiting reactivity similar to that of ground granulated blast-furnace slag. In this study, siliceous sand and ground calcium carbonate powder were utilized to produce SP, with sodium carbonate (Na₂CO₃), sodium hydroxide (NaOH), and their mixture serving as activators. The results indicated that the Ca/Si ratio in SP, along with the dosage of Na₂CO₃ (D_sc) and Na₂O content (N_c) in the activator, significantly affected the compressive strength of AASP materials at both early and late stages. The 28-day compressive strength reached up to 78.95 MPa, comparable to that of alkali-activated slag (AAS) materials. The optimum mix ratio for Na₂CO₃-NaOH based AASP materials was also determined to be 80% D_sc and 8% N_c (C8N2-8). Microscopic analyses were employed to investigate the changes in the macroscopic properties of AASP materials driven by hydration products, chemical group composition, and microstructure. Full article

To address the high carbon emissions and resource dependency associated with conventional ordinary Portland cement (OPC) production, this study systematically investigated the preparation processes, hydration mechanisms, and chemical properties of high-belite calcium sulfoaluminate (HBCSA) and calcium sulfoaluminate (CSA) cements based from industrial solid wastes. The results demonstrate that substituting natural raw materials (e.g., limestone and gypsum) with industrial solid wastes—including fly ash, phosphogypsum, steel slag, and red mud—not only reduces raw material costs but also mitigates land occupation and pollution caused by waste accumulation. Under optimized calcination regimes, clinkers containing key mineral phases (C₄A₃S⁻ and C₂S) were successfully synthesized. Hydration products, such as ettringite (AFt), aluminum hydroxide (AH₃), and C-S-H gel, were identified, where AFt crystals form a three-dimensional framework through disordered growth, whereas AH₃ and C-S-H fill the matrix to create a dense interfacial transition zone (ITZ), thereby increasing the mechanical strength. The incorporation of steel slag and granulated blast furnace slag was found to increase the setting time, with low reactivity contributing to reduced strength development in the hardened paste. In contrast, Solid-waste gypsum did not significantly differ from natural gypsum in stabilizing ettringite (AFt). Furthermore, this study clarified key roles of components in HBCSA/CSA systems; Fe₂O₃ serves as a flux but substitutes some Al₂O₃, reducing C₄A₃S⁻ content. CaSO₄ retards hydration while stabilizing strength via sustained AFt formation. CaCO₃ provides nucleation sites and CaO but risks AFt expansion, degrading strength. These insights enable optimized clinker designs balancing reactivity, stability, and strength. Full article

Considering the urgent need for sustainable construction materials, this study investigates the mechanical and microstructural responses of novel hybrid geopolymer concrete blends incorporating Fly Ash (FA), Ground Granulated Blast Furnace Slag (GGBS), Cement (C) and Precipitated Silica (PS) as partial replacements for traditional cementitious materials. The motive lies in reducing CO₂ emissions associated with Ordinary Portland Cement (OPC). The main aim of the study was to optimise the proportions of industrial wastes for enhanced performance and sustainability. The geopolymer mixes were activated using a 10 M sodium hydroxide (NaOH)—Sodium Silicate (Na₂SiO₃) solution and cast into cubes (100 mm), cylinders (100 mm × 200 mm) and prism specimens for compressive, split tensile and flexural strength testing, respectively. Six combinations of mixes were studied: FA/C (50:50), GGBS/C (50:50), FA/C/PS (50:40:10), FA/GGBS/PS (50:40:10), GGBS/C (50:50) and GGBS/FA/PS (50:40:10). The results indicated that the blend with 50% FA, 40% GGBS and 10% PS exhibited higher strength. Mixes with GGBS and PS presented a l0 lower slump due to rapid setting and higher water demand, while GGBS-FA-cement mixes indicated better workability. GGBS/C exhibited a 24.6% rise in compressive strength for 7 days, whereas FA/C presented a 31.3% rise at 90 days. GGBS/FA mix indicated a 35.5% strength drop from 28 days to 90 days. SEM and EDS analyses showed that FA-rich mixes had porous microstructures, while GGBS-based mixes formed denser matrices with increased calcium content. Full article

Previous research on cement aging mainly focuses on construction cement, exploring the mechanisms through which aging conditions affect cement properties. However, the impact of aging on oil well cement remains understudied. Aging of cement under high-humidity conditions leads to significant alterations in its properties, indicating that the cement formulation needs to be adjusted to reduce the negative effects during cementing operations. The effect of aging on particle size, mineral composition, and early hydration behavior of oil well cement after 0, 7, 14, and 28 d at 90% relative humidity (±3%RH) and 25 °C (±2 °C) was investigated. The results showed that, during the aging process, the uptake of H₂O and CO₂ from the surrounding atmosphere by cement leads to slight hydration. This process was associated with a reduction in the specific surface area and surface energy. The contents of hydration products ettringite (AFt) and calcium hydroxide (CH) increased, whereas the amounts of C₃S and C₃A decreased. Consequently, the early hydration rate of cement decreased along with a reduction in the cumulative heat release. As the aging time increased, the compressive strength and thickening time of the cement pastes decreased, and the rheological properties deteriorated. Under the experimental temperature and humidity conditions, the permissible aging time without significant deterioration should not exceed 7 d, with a maximum permissible aging time of 14 d. Full article

Oat (Avena sativa L.) is one of the most important self-fertilizing field plants belonging to the Poaceae family. It has no significant requirements regarding growing conditions but has a very good reaction to fertilization. The current research evaluated the significance of the effects of individual applications of mineral (NPK) and organo-mineral (OMF) fertilizers, as well as their individual combination with slaked lime (calcium hydroxide, Ca(OH)₂), on the yield, morphological traits [mean number of leaves per plant—MNLP, minimum leaf length (cm) per plant—MinLL, maximum leaf length (cm) per plant—MaxLL, number of ears per plant—NEP], and physiological parameters (nitrogen balance index—NBI, content of chlorophyll—Chl, flavonoids—Flv, anthocyanins—Ant) of organic and pelleted (graded) oat plants, comparing the treatments and in relation to the control. The experiment was performed in semi-controlled glasshouse conditions, in pots, from the fourth week of March to the fourth week of June 2024, using Vertisol soil. This soil is characterized as light clay with an acid reaction. Physiological parameters were measured using a Dualex leaf clip sensor. The results obtained showed that physiological parameters in both oat types significantly differed (p < 0.05) between the treatments applied and in relation to the control, whereas the morphological traits did not significantly differ (p > 0.05) between the treatments. Statistically significant differences (p < 0.05) in the yield of both oat types were most pronounced in the OMF + Slaked Lime treatment (organic: 4.49 g pot⁻¹; pelleted: 4.61 g pot⁻¹) in relation to the control (organic: 2.48 g pot⁻¹; pelleted: 2.63 g pot⁻¹). The pelleted oats showed slightly better results for the effects of different treatments across all tested parameters compared to organic oats. In conclusion, the best results were obtained with the use of OMF + Slaked Lime, which could be proposed as the optimal fertilization treatment for pelleted and organic oat cultivation based on this research. Full article

Transportation infrastructure such as concrete pavements, parapets, barriers, and bridge decks in cold regions are usually exposed to a heavy amount of deicing chemicals during the winter for ice and snow control. Various deicer salts can physically and chemically react with concrete and result in damage and deterioration. Currently, Idaho uses four different types of deicers during the winter: salt brine, mag bud converse, freeze guard plus, and mag chloride. The most often utilized substance is salt brine, which is created by dissolving rock salt at a concentration of 23.3%. Eight concrete mixtures for paving and structural purposes were made and put through a battery of durability tests. Following batching, measurements were made of the unit weight, entrained air, slump, and super air meter (SAM) fresh characteristics. Rapid freeze–thaw (F-T) cycle experiments, deicing scaling tests, and surface electrical resistivity testing were used to test and assess all mixes. Tests with mag bud converse, freeze guard plus mag chloride, and acid-soluble chloride were conducted following an extended period of soaking in salt brine. Two different structural mixtures were suggested as a result of the severe scaling observed in the structural mixtures lacking supplemental cementitious materials (SCMs) and the moderate scaling observed in the other combinations. The correlated values of the SAM number with the spacing factor have been shown that mixture with no SCMs has a spacing factor of 0.24, which is higher than the recommended value of 0.2 and concentrations of acid soluble chloride over the threshold limit were discernible. In addition, the highest weight of calcium hydroxide using the TGA test was observed. For all examined mixes, the residual elastic moduli after 300 cycles varied between 76.0 and 83.3 percent of the initial moduli. Mixture M5 displayed the lowest percentage of initial E (76.0 percent), while mixtures M1 and M2 showed the highest percentage of residual E (83.3 and 80.0 percent, respectively) among the evaluated combinations. There were no significant variations in the percentage of maintained stiffness between the combinations. As a result, it was difficult to identify distinct patterns about how the air content or SAM number affected the mixture’s durability. Class C coal fly ash and silica fume were present in the suggested mixtures, which were assessed using the same testing matrix as the original mixtures. Because of their exceptional durability against large concentrations of chemical deicers, the main findings suggest altering the concrete compositions to incorporate SCMs in a ternary form. Full article

A novel composite cementitious material was constructed by synergistically utilizing multiple industrial solid wastes, including electrolytic manganese residue (EMR), red mud (RM), and ground granulated blast furnace slag (GGBS), with calcium hydroxide [Ca(OH)₂] as an alkaline activator. In addition, the mechanical properties of the composite cementitious materials were systematically analyzed under different raw material ratios, alkali activator dosages, and water-binder ratios. To further investigate the hydration products and mechanisms of the composite cementitious material, characterization methods, for instance, XRD, FT-IR, SEM-EDS, and TG-DTG, were employed to characterize the materials. To ensure that the composite cementitious material does not cause additional environmental pressure, it was analyzed for toxic leaching. The relevant experimental results indicate that the optimal ratio of the EMR–RM–GGBS–Ca(OH)₂ components of the composite cementitious material is EMR content of 20%, RM content of 15%, GGBS content of 52%, calcium hydroxide as alkali activator content of 13%, and water-binder ratio of 0.5. Under the optimal ratio, the composite cementitious material at 28 days exhibited a compressive strength of 27.9 MPa, as well as a flexural strength of 7.5 MPa. The hydration products in the as-synthesized composite cementitious material system primarily encompassed ettringite (AFt) and hydrated calcium silicate (C-S-H), and their tight bonding in the middle and later curing stages was the main source of engineering mechanical strength. The heavy metal concentrations in the 28-day leaching solution of the EMR–RM–GGBS–Ca(OH)₂ composite cementitious material fall within the limits prescribed by the drinking water hygiene standard (GB5749-2022), indicating that this composite material exhibits satisfactory safety performance. To sum up, it is elucidated that the novel process involved in this research provide useful references for the pollution-free treatment and resource utilization of solid wastes such as red mud and electrolytic manganese residue in the future. Full article

This study evaluates the influence of multiwall carbon nanotubes (MWCNTs), reduced graphene oxide (rGO), and magnesium oxide (MgO) on the thermal conductivity of alkali-activated engineered composites (AAECs). Thirty-two ambient-cured AAECs consisting of two types of powdered-form reagents/activators (type 1—calcium hydroxide: sodium meta silicate = 1:2.5; type 2—calcium hydroxide: sodium sulfate 2.5:1), two dosages of MgO (0 and 0.5%) of MgO, three percentages (0, 0.3%, and 0.6%) of MWCNTs/rGO, and binary (45% ground granulated blast furnace slag ‘GGBFS’ and 55% Class C fly ash ‘FA-C’) and ternary combinations (40% GGBFS, 25% FA-C and 35% class F fly ash ‘FA-F’) of industrial-waste-based source materials, silica sand, and polyvinyl alcohol (PVA) fiber were developed using the ‘one-part dry mix’ technique. Problems associated with the dispersion and agglomeration of nanomaterials during production were avoided through the use of defined ultra-sonication with a high-shear mixing protocol. The impact of the combination of source materials, activators, and MgO/MWCNT/rGO dosages and their combinations on the thermal properties of AAECs is evaluated and discussed based on temperature–time history and thermal conductivity/diffusivity properties along with micro-structural characteristics. It was found that the change in temperature of the AAECs decreased during testing with the addition of MWCNTs/rGO/MgO. The thermal conductivity and diffusivity of AAECs increased with the increase in MWCNT/rGO/MgO contents due to the formation of additional crystalline reaction products, improved matrix connectivity, and high conductivity of nanomaterials. MWCNT AAECs showed the highest thermal conductivity of 0.91–1.26 W/mK with 49% enhancement compared to control AAECs followed by rGO AAECs. The study confirmed the viability of producing MgO/MWCNT/rGO-incorporated AAECs with enhanced thermal properties. Full article