Calcium Oxide Content Research Articles

A novel integrated soft sensing model for online cement clinker quality monitoring based on fuzzy fine-grained classification

The content of free calcium oxide (f-CaO) in cement clinker is an important index for cement quality. For the problems of multiple working conditions and unbalanced distribution of sample labels in cement clinker production, a soft sensing method of cement clinker f-CaO content based on fuzzy fine-grained classification (FF) is proposed. First, a divide-and-conquer strategy is used to divide the samples into high, medium, and low subsets according to cement clinker f-CaO and extract the fine-grained features under diverse types of multiple production conditions. Second, fuzzy classification based on the membership function is used in the FF model to solve the uncertainty of the sample categories. To ensure the rationality of the classification, the fuzzy membership rule is combined with a convolutional neural network to implement the fuzzy classification method. Finally, different feature extraction methods are proposed to be selected according to the data size of various categories of samples. After experimental validation, the evaluation metrics of RMSE decreased by 4.5 % and R2increased by 17.8 % for the direct classification model compared to the single model. The RMSE of the fuzzy classification model over the direct classification model was again reduced by 2.34 % and R2was again improved by 7.24 %, showing the effectiveness of the proposed soft measurement model.

Hybrid XGB model for predicting unconfined compressive strength of solid waste-cement-stabilized cohesive soil

The utilization of cement has been found to have negative environmental impacts. In order to reduce the quantity of cement used and improve the mechanical properties of solid waste-cement-stabilized cohesive soil, the incorporation of solid waste as additives has been investigated. Unconfined compressive strength is a crucial parameter in geotechnical engineering. However, existing empirical formulas have limited accuracy and applicability when it comes to the unconfined compressive strength of solid waste-cement-stabilized cohesive soil. The machine learning model can be used to provide accurate and comprehensive predictions by considering the nonlinear relationships between independent and dependent variables. This study aims to propose a machine learning model tuned by optimization algorithms with high generalization performance in accurately predicting the unconfined compressive strength. Firstly, a database containing 474 specimens was developed. Secondly, eight machine learning models were established, composed five single models and three hybrid models, to train and test the database. Six performance indicators were employed to evaluate the generalization ability of these models. Finally, the optimal model was selected for analysis of the importance of the feature variables using shapley additive explanations, which were compared with those of the existing empirical model. The research findings indicated that, the extreme gradient boosting model tuned with tree-structured parzen estimators exhibited the highest predictive accuracy and generalization ability. The curing age, cement content, plastic limit, and water content were identified as the most critical factors influencing the unconfined compressive strength. Among the chemical components in solid waste, the aluminum oxide content and silicon dioxide content were found to significantly influence the unconfined compressive strength, while the impact of calcium oxide content was relatively minor. Furthermore, the optimal solid waste content was found to be around 10 %. This study made a significant contribution to the effective utilization of waste resources in the context of sustainable construction practices.

Long-Term Performance of Mortars with Combined Incorporation of Ladle Furnace Slag and Metakaolin

Ladle furnace slag (LFS) is used as a supplementary cementitious material (SCM) due to its high calcium oxide (CaO) content. Its binding properties are enhanced in the presence of siliceous materials, such as metakaolin (MK), forming a ternary mixture that can directly replace ordinary Portland cement (OPC). However, despite this blend having already been evaluated in alkali-activated mixtures, knowledge about this mixture in situations of direct replacement of OPC by slag is still lacking. This study evaluates the synergistic effects of combining LFS and MK in cementitious mortars. Due to an insufficient hydration reaction observed in the short term, this study focuses on assessing the long-term performance of these mortars. Both the fresh and hardened states at 28 and 180 days are evaluated, and the resulting microstructural characteristics and constituent phases are also examined. After 180 days of curing, the mortar with MK exhibits superior binding activity compared to the results at 28 days. Although the nominal resistance does not show a clear advantage with the application of MK, a significant reduction in the porosity of the mortar is observed. Microstructural analysis indicates that the addition of MK increases the hydration compounds when mixed with LFS. Importantly, the sample containing MK and LFS showed a 42% reduction in cement consumption, highlighting the potential for resource efficiency. Thus, this study contributes to promoting a circular economy between the steelmaking and civil construction sectors.

Study of mechanical properties of building ceramics with the addition of non-traditional raw materials

The current economic situation and increased attention to environmental protection encourage manufacturers of building materials, in particular ceramic bricks, to look for alternative types of raw materials that make it possible to reduce its cost with good quality of finished products. Mining waste is especially promising, among which peridotites stand out, which have huge reserves and are practically not used. The purpose of the work is to obtain building ceramics with the addition of peridotite and study its mechanical properties.The chemical and mineralogical compositions of raw materials have been determined. Silicon and aluminum oxides account for 78.5% in clay and 61% in peridotites.The latter are characterized by a high content of calcium, magnesium and iron oxides (34.65%). Clay is composed of clay minerals, as well as quartz and feldspar. Tremolite, enstatite and olivine are present in peridotites. The dependence of the mechanical strength of ceramic samples on their firing temperature, the content of the additive and the degree of its grinding has been established. The optimal amount of peridotite is 10%, at which the compressive strength has the maximum value over the entire grinding range of the additive. With an increase in the firing temperature to 1050оC, a slow increase in the strength of the samples occurs. At 1100оC, there is a sharp jump in strength parameters, which increase by 3.6–4.7 times, depending on the granulometric composition of the additive.The main properties of the obtained ceramics were determined. It has been established that peridotites are a promising additive for the production of ordinary bricks with a compressive strength of up to 60 MPa and an average density of up to 2400 kg/m3.

Identifying Key Environmental Drivers of Reach‐Scale Salmonid eDNA Recovery With Random Forest

ABSTRACTEnvironmental DNA (eDNA) sampling from rivers has emerged as a promising new method for monitoring freshwater organisms of management concern. However, eDNA sampling cannot yet offer reliable estimates of a target species' abundance/biomass or confident determinations of a species' absence from a river segment. To unlock these abilities—and thereby greatly improve eDNA as a tool for management decision‐making—the influence of local environmental factors on eDNA fate must be better understood. At nine river sites across the central California coast, we added a known quantity of novel eDNA (Brook Trout, Salvelinus fontinalis) and collected eDNA at sequential downstream distances for qPCR analysis. We then used random forest modeling to identify the most important environmental factors to reach‐scale (≤ 200 m) sampling outcomes and characterize salmonid eDNA fate. Our final model identified six factors important to sampling outcomes, including five environmental factors (discharge, local catchment calcium oxide content, average depth of the sampling cross‐section, presence of pools, and impervious cover of the watershed) and one factor regarding our experimental design (the number of qPCR technical replicates). Our results highlight the notable effects of cross‐sectional area, turbulence, and catchment geology on eDNA fate, and we suggest the discharge and presence of pools as useful proxies for evaluating a site's favorability for eDNA recovery.

SYNTHESIS OF PRECIPITATED CALCIUM CARBONATE IN THE FORM OF CALCITE CRYSTALS AS A VALORIZATION OF LIME CARBIDE SLAG WASTE

The presence of high level of calcium oxide (CaO) has been detected in lime carbide (LC) slag waste generated form the acetylene gas industry. There is untapped potential for the valorization of LC-slag waste, where the calcium oxide content can be converted into Precipitated Calcium Carbonate (PCC/CaCO3) which is valuable and can contribute to carbon dioxide sequestration. Calcium carbonate has unique advantages as a carrier, but some critical problems need to be addressed, such as low productivity, disordered structure, and weak adsorption ability. In this study, the desired type of crystal is calcite which has the most stable characteristics from the other types of crystals. Micro-bubble reactor is used as a method of dispersing CO2 in converting CaO to PCC/CaCO3. This method has the advantage of being able to maintain CO2 gas bubbles longer in solution so that the reaction time that occurs can also be optimize. The LC-Slag valorization process was carried out by varying the LC-slag concentration between 3-7% w/w and the reaction time between 15 - 35 minutes. The dispersion of CO2 gas is fixed at a flow rate of 2.5 L/m. From the yield, it can be seen that the longer the reaction time, the yield of PCC/CaCO3 produced is also greater. At 35 minute reaction time and concentration LC-Slag Waste varied 3, 5, and 7% w/w, the produced yields were 89.44, 95.00, and 93.76%, respectively. This is evidenced by the results of SEM and XRD analysis. In the future, this treatment method is expected to provide more insight and guidance for the valorization of LC-slag waste and CO2 mineralization in the acetylene gas industry.

Investigation on utilization and microstructure of fine iron tailing slag in road subbase construction

The iron tailing slag is solid waste produced during the iron ore refining process and is considered a potential hydraulic material that can be used in road construction. This study focused on fine iron tailing from a location in Hebei, China, to prepare road subbase specimen with a high proportion of fine iron tailing. The research investigated the effects of raw material ratios and additives on the 7-day unconfined compressive strength and elastic modulus of the specimens, as well as their mechanisms of action. A series of single-factor experiments were conducted using a controlled variable approach, including the mass ratio of slag to fly ash (SFR), cement content, and calcium oxide content. It was found that under the conditions of an SFR of 6:1, a calcium oxide content of 4 %, a cement content of 5 %, and a water-resistant base stabilizer additive of 0.02 %, the eco-friendly road subbase specimen achieved a 7-day unconfined compressive strength of 1.97 MPa and an elastic modulus of 286 MPa, demonstrating good mechanical properties. Additionally, a linear relationship was observed between the cement content and the 7-day unconfined compressive strength of the specimen: Rc = 0.253w + 0.793. Using characterization techniques such as X-ray Fluorescence Spectroscopy (XRF), X-Ray diffraction (XRD), Scanning Electron Microscope & Energy Dispersive Spectroscopy (SEM-EDS), and Fourier Transform Infrared Spectroscopy (FTIR), a dense structure was observed in the slag-based road subbase specimen, composed of needle-rod hydrated calcium silicate (C-S-H) gel, hydrated calcium aluminate (C-A-H), hydrated calcium silicoaluminate (C-A-S-H), flake-like hydrated magnesium silicate (M-S-H) gel, and a system containing a large amount of Forsterite. Finally, the study examined the impact mechanisms of five additives—Na2CO3, Na2O·2SiO2, triethanolamine (C6H15NO3), CaSO4, and a water-resistant base stabilizer—on the compressive strength and elastic modulus of the slag road base specimen. It was concluded that the water-resistant base stabilizer significantly improved strength and reduced water absorption. The road subbase specimen can be used by simply mixing at room temperature and pressure, offering broad prospects for industrial application. This technology provides a paradigm for the comprehensive utilization of fine iron tailing and the preparation of new road subbase materials.

Low-Cost and Eco-Friendly Calcium Oxide Prepared via Thermal Decompositions of Calcium Carbonate and Calcium Acetate Precursors Derived from Waste Oyster Shells.

Waste oyster shells were utilized to produce calcium carbonate (CaCO3) by grinding. This CaCO3 was then reacted with acetic acid to yield calcium acetate monohydrate (Ca(CH3COO)2·H2O). Both CaCO3 and Ca(CH3COO)2·H2O were used as precursors for synthesizing calcium oxide (CaO) through thermal decomposition at 900 °C and 750 °C, respectively. The yields of CaO from both precursors, determined through calcination experiments and thermogravimetric analysis (TGA), exceeded 100% due to the high purity of the raw agents and the formation of calcium hydroxide (Ca(OH)2). X-ray fluorescence (XRF) analysis revealed a CaO content of 87.8% for CaO-CC and 91.5% for CaO-CA, indicating the purity and contamination levels. X-ray diffraction (XRD) patterns confirmed the presence of CaO and minor peaks of Ca(OH)2, attributed to moisture adsorption. Fourier-transform infrared (FTIR) spectroscopy identified the vibrational characteristics of the Ca-O bond. Scanning electron microscopy (SEM) showed similar morphologies for both CaO-CC and CaO-CA, with CaO-CA displaying a significant amount of rod-like crystals. Based on these results, calcium acetate monohydrate (CA) is recommended as the superior precursor for synthesizing high-purity CaO, offering advantages for various applications.

Utilization of cow bone waste and calcium oxide for the solidification and stabilization of MSWI fly ash: Towards sustainable practices

The quest for sustainable waste management practices has catalysed the development of innovative approaches to transform waste into resourceful products. This study explores the effectiveness of cow bone waste and calcium oxide (CaO) as agents in the stabilization/solidification (S/S) process of Municipal Solid Waste Incineration (MSWI) fly ash derived from two distinct cities employing both grate-type and circulating fluidized bed incinerators in China. Employing a robust experimental framework, the research evaluated the stabilization efficacy for heavy metals, monitored the progression of pH, and quantified the compressive strength of the treated MSWI fly ash. Moreover, it conducted risk assessment and economic analyses. Incorporating CBW and CaO into the MSWI fly ash from grate-type incinerators significantly enhanced the Pb stabilization efficiency, achieving up to 99.7 % when adding 31 % CBW and 7 % CaO. This treatment resulted in the leaching of other heavy metals, which were also below the standard landfill limits. In the circulating fluidized bed incinerator fly ash, the leaching concentrations of heavy metals in the treated samples were reduced by up to 98.6 % for Cd and 64.4 % for Ni.Additionally, an increase in CaO content was found to substantially improve the compressive strength of the solidified samples across all tested curing periods (7, 14, and 28 days). The optimal compressive strength result, observed at 28 days, reached 1.2 MPa, compared to the raw fly ash, which exhibited only 0.77 MPa when adding just 9 % CaO. This highlights CaO's critical role in enhancing the mechanical integrity of the treated MSWI fly ash. The study concludes that strategically calibrated ratios of cow bone waste and CaO attenuate the environmental hazard presented by MSWI fly ash and bolster its mechanical attributes, thereby repurposing the waste into a viable material for construction.

Physico-chemical characterization of cupola slag: Enhancing its utility in construction

Cupola slag is a waste material of the steel and iron industries. Its composition is determined by the cupola furnace and other elements used in steel and iron manufacturing. This paper investigates the characterization behavior of various cupola slag materials. As a result, x-ray fluorescence (XRF), x-ray diffraction (XRD), thermogravimetry differential thermal analysis, and scanning electron microscopy (SEM) methods were used to characterize three cupola slag samples from distinct origins. In addition, various physical properties were used to compare different cupola slags. The specific gravity values of CS-1 (cupola slag-1 sample), CS-2 (cupola slag-2 sample), and CS-3 (cupola slag-3 sample) are 1.36, 2.5, and 2.917, respectively. The density and water absorption for CS-1, CS-2, and CS-3 are 1414.86, 1477.71, and 1796 kg/m3, and 0.37%, 0.32%, and 0.26%, respectively. Cupola slag also includes a larger percentage of lime, according to XRF data, which contributes to its improved binding characteristics. A higher calcium oxide content in CS-3 could facilitate the pozzolanic process. The presence of angular particles that aid in material binding is seen in the SEM image. Compounds with a nanostructure are then flawlessly blended into the mixture and grouped with calcium alumina silicates formed by cement hydration. The XRD pattern of cupola slag exhibits high peaks, indicating that the material is crystalline in character and can be utilized as sand. It also shows the presence of other chemical compounds, such as silica, which ranges from 30% to 45%. CS-1 and CS-2 have comparable XRD patterns. However, CS-3 has a somewhat different pattern because of the greater CaO content. Weight loss begins at higher temperatures, which shows that the material is stable at higher temperatures, according to a thermo-gravimetric study. The differential thermal analysis curve of CS-3 indicates that the material remains stable up to a temperature of 600 °C. The physical characteristics of all cupola slag samples show that cupola slag may be utilized to make sustainable building materials because of its lower specific gravity, density, and water absorption.

Preparation of calcium aluminate and spinel by hydrolysis and calcination from secondary aluminum dross

AbstractThe direct extraction of alumina from secondary aluminum dross (SAD), which is a dangerous solid waste, is difficult. Moreover, this process easily produces a large amount of solid waste residue, which is not easily utilized. In this paper, a new green process was developed to prepare calcium aluminate and Mg‐Al spinel from SAD by hydrolysis–calcification roasting. The effects of calcium oxide (CaO) content, sintering temperature, and holding time on the properties of calcium aluminate were investigated by single‐factor experiments. The phase transformation mechanism of calcium aluminate was studied by thermodynamic analysis, X‐ray diffraction analysis, X‐ray fluorescence spectroscopy, and scanning electron microscopy. Under the optimal conditions (Ca/Al molar ratio of 0.8, sintering temperature of 1300°C, and holding time of 2 h), the main calcium aluminate phases are CaAl2O4 and Ca2Al2SiO7, the soluble alumina content of the calcium aluminate sample is 49.71 wt.%, and the main phases of the acid‐insoluble residue are Mg‐Al spinel and a very small amount of CaTiO3. The Ca/Al ratio is the key factor affecting the calcium aluminate phase—with increasing Ca/Al ratio, the calcium aluminate phase is transformed from CaAl4O7 to CaAl2O4 and eventually to Ca12Al14O33, and the Si‐containing phase changes from Ca2Al2SiO7 to CaSiO4.

Carbonation of one-part alkali-activated materials incorporated by MgO: Phase characteristics and micromechanical properties

The role of magnesium oxide (MgO) in the carbonation of cementitious materials, particularly alkali-activated materials (AAM), which is a promising low-carbon alternative to ordinary Portland cement (OPC), has garnered significant attention. However, there remains a lack of clear understanding regarding its underlying mechanisms and interrelation with calcium oxide (CaO) content. This study aims to understand the influence of MgO on carbonation mechanisms, carbonation products, and (C, N)–A–S–H gel micromechanical properties in AAM. Four different binder formulations were examined by varying contents of slag, class F fly ash, and light-burned MgO. A powder-type sodium metasilicate was used as an alkaline activator. CO2 curing was conducted in a CO2 incubator with 1 % concentration and under atmospheric pressure for up to 56 days using pulverized paste binders. The carbonation mechanism, polymorphs of carbonation products, and the micromechanical properties of the (C, N)–A–S–H gel matrix were characterized by conducting laboratory tests including pH measurement, XRD, TGA, DSC, nitrogen adsorption, and nanoindentation at various carbonation stages. A noticeable pattern of pH initially dropping and then rising was observed. Integrated XRD-TGA demonstrated the evolution, polymorphism, and amount of calcium carbonate phases. Higher MgO content in AAM binders favored the formation of aragonite and hydrotalcite. Extensive nanoindentation results and their statistical analysis revealed binder-specific trends in the pozzolanic matrix stiffness before and after carbonation. The findings of this study can be used in developing AAM binders as building materials and to provide a deeper understating of the carbonation reactions in AAM binders.

Experimental investigation of radiation shielding competence of B2O3-Na2O-Al2O3-BaO-CaO glass system

Aiming to extend the scope of utilizing glass in radiation shielding, this work investigates the radiation interaction response of a borate-based glass system. Four borate-glass samples of different substituting concentrations of calcium oxide (70-x\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$70-x$$\\end{document})B2O3:10\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$10$$\\end{document} Na2O :5\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$:5$$\\end{document} Al2O3:15\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$:15$$\\end{document} BaO:x\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$x$$\\end{document} CaO were prepared. To assess the shielding performance of the prepared glass samples, a high-purity germanium detector and different radioactive sources (different energies) were used. Via the narrow beam method, the linear attenuation coefficients (LACs) were experimentally measured. So, the transmission factor (TF), the half-value layer (HVL), the tenth value layer (TVL), the mean free path (MFP), and the radiation protection efficiency (RPE) were calculated for all prepared samples. It was observed that the increase of the concentration of calcium oxide in the proposed borate-based glass samples leads to improve their performance in shielding against radiation. At low energy, the RPE of the samples is almost 100%. However, it was observed that as energy of the radiation source increases, the shielding performance of the samples will decrease. High energy dependence was found when calculating TF, HVL, TVL, and MFP. They were increased with the increase of the energy of the incident photons. At 0.662 MeV, the TF values are equal to 79.26, 79.00, 79.72, and 78.43% for BNABC-1, BNABC-2, BNABC-3, and BNABC-4 in the same oder, respectively. The application of the proposed composition of borate-based glass as a transparent shield against low-energy ionizing radiation was highlighted.

Res-BiLSTMs model based on multi-task attention for real-time measurement of the free calcium oxide content

Abstract The content of free calcium oxide (f-CaO) is the primary economic index to evaluate the quality of cement. A residual bidirectional long short-term memory network model (Res-BiLSTMs) based on a multi-task attention mechanism was proposed for the characteristics of cement clinker production, used for online monitoring f-CaO content. The model utilizes the Bi-LSTM as the foundational component and combines the residual network to construct the Res-BiLSTMs coding structure, which aims to summarize the multi-level characteristic information of the input sequence. Additionally, a multi-task attention mechanism is introduced, combining the attention mechanism with semi-supervision to extract control coupling and data coupling among devices and variables. The results demonstrate that the addition of the multi-task attention mechanism led to a reduction in model errors by 0.0175 and 0.022, respectively, and an improvement in the degree of fit by 14.61%. The effectiveness of the multi-task attention mechanism for quality monitoring is confirmed. Compared to traditional LSTM, this model exhibited a reduction in errors by 0.0469 and 0.019, respectively, an increase in the correlation coefficient by 45.37%, and outperformed all other models in the comparison. The model’s measurement performance under limited labeled samples is also validated.

Heterogeneous Calcium Oxide Catalytic Filaments for Three-Dimensional Printing: Preparation, Characterization, and Use in Methyl Ester Production.

This study aimed to investigate heterogeneous catalytic filaments of calcium oxide (CaO) for fused deposition modeling three-dimensional (3D) printers. The CaO catalysts were blended with acrylonitrile butadiene styrene (ABS) plastic to form catalytic filaments. A single-screw filament extruder was used to prepare the filaments, following which their mechanical properties, thermal properties, morphology, catalytic characteristics in biodiesel production, and reusability were evaluated. In accordance with the results, a maximum CaO catalyst content of 15 wt % was recommended to be blended in the ABS pellet. The hardness and compressive strength of these catalytic filaments were shown to be improved. Subsequently, the catalytic filaments with the highest CaO content (15 wt %) were used to produce methyl ester from pretreated sludge palm oil through the transesterification process. To determine the recommended conditions for achieving the highest purity of methyl ester in biodiesel, the process parameters were optimized. A methyl ester purity of 96.58 wt % and a biodiesel yield of 79.7 wt % could be achieved under the recommended conditions of a 9.0:1 methanol to oil molar ratio, 75.0 wt % catalytic filament loading, and 4.0 h reaction time. Furthermore, the reusability of the 15 wt % CaO catalytic filaments was evaluated in a batch process with multiple transesterification cycles. The results indicated that the purity of methyl ester dropped to 95.0 wt % only after the fourth cycle. The method used in this study for preparing and characterizing CaO catalytic filaments can potentially serve as a novel approach for constructing biodiesel reactors using 3D printing technology.

Use of Polylactic Acid Added with Calcium Oxide and 3-Iodo-2-Propynly Butyl Carbamate as an Antifungal Agent and Bio-degradable Soil Remediator

This work studied the use of polylactic acid added with calcium oxide (CaO) and 3-Iodo-2-propynly butyl carbamate (IPBC) for agricultural applications. CaO content of 30 pph was fixed, while IPBC contents were varied at 0, 2.5, 5.0, 7.5 and 10.0 ppm in the polymer matrix. All ingredients were mixed by the extrusion process for receiving the PLA, PLA/CaO, and PLA/CaO/IPBC granules. The pH value, antifungal activities of Phytophthora parasitica, tomato growth, and disposal degradation were also investigated. The experimental results indicated that the acidic condition of the PLA granules increased with increasing IPBC contents but was compromised by CaO. An IPBC was an effective antifungal agent. It was also promoted and activated by CaO. Growth of P. parasitica can be inhibited by CaO synergized IPBC for the PLA/CaO granules with four different IPBC contents and the PLA/CaO granules with the four different IPBC contents were an effective antifungal agent. A PLA/CaO granule with an IPBC content of 2.5 ppm can be developed to compete with an unused condition. A PLA/CaO granule with an IPBC content of 10 ppm was recommended for agricultural applications. A PLA/CaO/IPBC 10 acted as an effective antifungal agent and compostable for soil bioremediatory before planting. Over the 45-day experimental period, the maximum percentage of weight loss of a PLA/CaO granule with an IPBC content of 10 ppm was influenced by moisture and initial PLA loading. A PLA/CaO granule with an IPBC content of 10 ppm (47.2%) had a faster degradation rate than a PLA/CaO granule (45.3%) and a neat PLA granule (15.0%).

Clinker-free CaO-activated silica fume as a cementitious binder for pavement application

Ordinary Portland cement (OPC) production requires heating limestone up to 1450 °C and produces 0.5–0.9 kg of carbon dioxide for every 1 kg produced. Moreover, the massive volume of cement manufactured around the world every year adds to the urgent need to look for sustainable alternatives. This work proposes a novel calcium oxide (CaO)-activated high-volume silica fume mixture as a cementitious binder for pavement application that can address the sustainability concern with cement (because producing CaO requires a much lower calcination temperature than OPC, and that CaO is also used in low-volume in the binder). The combination of low-volume CaO and high-volume silica fume, particularly as a pavement binder has not been studied in the literature before. The compressive and flexural strength results showed that even by using a small fraction of CaO in the binder, it is possible to obtain acceptable strengths that satisfy ASTM pavement design guidelines, while OPC is unable to provide similar strengths at such low dosage. The mix having CaO content as 30 % of the silica fume content (CSF-30) shows the highest compressive strength (28d: 18.4 MPa) and flexural strength (28d: 4 MPa). In contrast, the maximum OPC-silica fume compressive and flexural strengths observed are 13.9 MPa and 2.9 MPa respectively at 28d From the microstructural results, it was seen that CaO–silica fume develops strength due to formation of calcite and calcium silicate hydrate. Almost all CaO–silica fume mixes exhibited lower porosity compared to their OPC-silica fume counterparts; CSF-30, the mix having the best mechanical performance showed the lowest porosity at 28d (2.8 %). A comparative sustainability analysis followed by a 5D analysis considering all the parameters studied in this work revealed that CSF-30 is the best binder alternative (overall score: 5.24). The results of this work will be useful for pavement users, designers, researchers, engineers, and relevant government officials, in having a sustainable clinker-free alternative pavement binder to OPC, particularly for low-volume roads, that satisfies the pavement design guidelines.

Engineering Properties and Microstructure of Soils Stabilized by Red-Mud-Based Cementitious Material.

Red mud (RM) is an industrial waste generated in the process of aluminum refinement. The recycling and reusing of RM have become urgent problems to be solved. To explore the feasibility of using RM in geotechnical engineering, this study combined magnesium oxide (MgO) (or calcium oxide (CaO)) with RM as an RM-based binder, which was then used to stabilize the soil. The physical, mechanical, and micro-structural properties of the stabilized soil were investigated. As the content of MgO or CaO in the mixture increased, the unconfined compressive strength (UCS) of the RM-based cementitious materials first increased and then decreased. For the soils stabilized with RM-MgO or RM-CaO, the UCS increased and then decreased, reaching a maximum at RM:MgO = 5:5 or RM:CaO = 8:2. The addition of sodium hydroxide (NaOH) promoted the hydration reaction. The UCS enhancement ranged from 8.09% to 66.67% for the RM-MgO stabilized soils and 204.6% to 346.6% for the RM-CaO stabilized soils. The optimum ratio of the RM-MgO stabilized soil (with NaOH) was 2:8, while that of the RM-CaO stabilized soil (with NaOH) was 4:6. Freeze-thaw cycles reduced the UCS of the stabilized soil, but the resistance of the stabilized soil to freeze-thaw erosion was significantly improved by the addition of RM-MgO or RM-CaO, and the soil stabilized with RM-MgO had better freeze-thaw resistance than that with RM-CaO. The hydrated magnesium silicate generated by the RM-MgO stabilized soil and the hydrated calcium silicate generated by the RM-CaO stabilized soil helped to improve the UCS of the stabilized soil. The freeze-thaw cycles did not weaken the formation of hydration products in the stabilized soil but could result in physical damage to the stabilized soils. The decrease in the UCS of the stabilized soil was mainly due to physical damage.

Experimental Study on Calcination of Portland Cement Clinker Using Different Contents of Stainless Steel Slag.

In order to increase the utilization rate of stainless steel slag, reduce storage needs, and mitigate environmental impacts, this study replaces a portion of limestone with varying amounts of stainless steel slag in the calcination of Portland cement clinker. The study primarily examines the influence of stainless steel slag on the phase composition, microstructure, compressive strength, and free calcium oxide (ƒ-CaO) content of Portland cement clinker. The results show the following: (1) Using stainless steel slag to calcine Portland cement clinker can lower the calcination temperature, reducing industrial production costs and energy consumption. (2) With an increase in the amount of stainless steel slag, the dicalcium silicate (C2S) and tricalcium silicate (C3S) phases in Portland cement clinker initially increase and then decrease; the C3S crystals gradually transform into continuous hexagonal plate-shaped distributions, while the tricalcium aluminate (C3A) and tetracalcium aluminoferrite (C4AF) crystal structures become denser. When the stainless steel slag content is 15%, the dicalcium silicate and tricalcium silicate phases are at their peak; the C3S crystals are continuously distributed with a relatively dense structure, and C3A and C4AF crystals melt and sinter together, becoming distributed around C3S. (3) As stainless steel slag content increases, the compressive strength of Portland cement clinker at 3 days, 7 days, and 28 days increases and then decreases, while ƒ-CaO content decreases and then increases. When the stainless steel slag content is 15%, the compressive strength at 28 days is at its highest, 64.4 MPa, with the lowest ƒ-CaO content, 0.78%. The test results provide a basis for the utilization of stainless steel slag in the calcination of Portland cement clinker.

Study on the effect and mechanism of microwave excitation on the activity of recycled powder of waste concrete

By crushing the prepared cement paste, the recycled powder (RP) was prepared by grinding. The study systematically investigated the effects of microwave power and activation time on the activity of RP. The results showed that the maximum enhancement in the activity of RP occurs when the microwave power is set to 490 W and the activation time is 10 minutes, with the activity increased by 14 %, 15 %, and 22 % at 3, 7, and 28 days, respectively. After microwave activation of RP, the decomposition of C-(A)-S-H and ettringite in the RP provides calcium, silicon, and aluminum phases, and the evaporation of bound water promotes the secondary hydration of RP. After microwave activation, the content of calcium oxide (CaO) in the RP increases, while the contents of silicon dioxide (SiO2) and alumina oxide (Al2O3) decrease; Adding activated RP to prepare mortar generates more hydration products to fill the pores, making the structure more compact. Compared with the control group, the porosity of the MRP-5 group decreased by 2.38 %.