Search Results (21)

This research paper provides new insights into the impact of accelerated mineralization of alkaline waste materials on the physical and mechanical behavior of low-carbon cement-based mortars. Standardized eco-cement mortars were prepared by replacing Portland cement with 7% and 20% proportions of three alkaline waste materials (white ladle furnace slag, biomass ash, and fine concrete waste fraction) that had been previously carbonated in a static reactor at predefined humidity and CO₂ concentration. The mortars’ physical (total/capillary water absorption, electrical resistivity) and mechanical properties (compressive strength up to 90 d of curing) were analyzed, and their microstructures were examined using mercury intrusion porosimetry and computed tomography. The results reveal that carbonated waste materials generate a greater heat of hydration and have a lower total and capillary water absorption capacity, while the electrical resistivity and compressive strength tests generally indicate that they behave similarly to mortars not containing carbonated minerals. Mercury intrusion porosimetry (microporosity) indicates an increase in total porosity, with no clear refinement versus non-carbonated materials, while computed tomography (macroporosity) reveals a refinement of the pore structure with a significant reduction in the number of larger pores (>0.09 mm³) and intermediate pores (0.001–0.09 mm³) when carbonated residues are incorporated that varies depending on waste material. The construction and demolition waste (CCDW-C) introduced the best physical and mechanical behavior. These studies confirm the possibility of recycling carbonated waste materials as low-carbon supplementary cementitious materials (SCMs). Full article

The feasibility of producing high-quality zinc phosphate cement based on a frit-sintered mixture of ZnO, SiO₂, MgO, and Bi₂O₃ oxides, with the addition of phosphorous slag and an aqueous solution of orthophosphoric acid as the mixing liquid, was demonstrated. The raw materials used for zinc phosphate cement preparation were investigated using various physicochemical analysis methods. It was found that the phosphorous slag contains silicon oxide (37.6%), aluminum oxide (4.49%), calcium oxide (42.4%), magnesium oxide (2.19%), as well as fluorine (1.94%) and calcium fluoride (4.91%). The slag predominantly consists of an amorphous glassy phase with minor inclusions of crystalline components. During the sintering process, the addition of 1.5–3.0 wt.% phosphorous slag to the frit promotes the formation of low-melting eutectics due to the presence of fluorides, resulting in a 100 °C reduction in the sintering temperature. An optimal zinc phosphate cement powder composition was developed, comprising: ZnO—83.0%, MgO—9.0%, SiO₂—3.5%, Bi₂O₃—3.0%, and phosphorous slag—1.5%. The resulting sintered product exhibited a whiteness of 97.8%, which exceeds that of the reference sample by 2.6%. Upon mixing the powder with the mixing liquid, zinc ions are released first, initiating a chemical reaction that leads to the formation of zinc, magnesium, and aluminum phosphates. The compressive strength of the resulting composite cements ranged from 101.8 to 111.9 MPa, fully complying with the requirements for cement grade as specified in GOST 31578-2012. Full article

The Spanish cement sector must adapt its production model to a green economy model. This study focuses on the use of new secondary main constituents (SMCs) suitable for a cement plant that specializes in sulfate-resistant (SR) cement production, defining a framework of technical conditions for their usage and their economic and environmental feasibility. Low-calcium-carbonate-content albero, steel slags, and iron silicate were the tested SMCs; however, they are not currently permitted in cement manufacture. CEM I 42.5 R-SR 3 (type I-SR) was mixed with 5%, 20%, and 30% of these new SMCs. XRF, XRD, leaching and other chemical tests, setting, and hardening tests were performed with no significant issues. Albero is the best option, on the whole, because of the following characteristics: availability, >100 Mt; proximity, 3 km; and acceptable compressive strength level. However, black slag cement with 30% SMC after 28 days shows the best performance, with a compressive strength of 41.3 MPa compared to 35.3 MPa for albero cement and 56.5 MPa for the type I-SR reference. Albero and steel slag at 30% content are the best option according to the cost savings of 32% (−31.5 EUR/t and −31.6 EUR/t, respectively) compared to the type I-SR reference. Regarding the carbon footprint, albero and steel slag at 30% content have the least impact, showing a 31% reduction (−254.8 kg CO₂/t and −255.2 kg CO₂/t, respectively) compared to the type I-SR reference. The studied SMCs meet the analytical conditions and—with the corresponding regulatory changes—offer potential cost savings for SR cement production, exhibiting a competitive advantage. Full article

This study evaluated the potential of incorporating TiO₂ nanoparticles (NT) into cementitious composites to provide self-cleaning and self-sanitising properties, as well as the partial replacement of natural aggregates with recycled glass (RGA), ceramic brick (RBA), granulated blast furnace slag (GBA), and textolite waste (RTA) from electronic equipment on these properties. Based on the research results, the addition of NT to cementitious composites led to a significant reduction in contact angle, which means an increase in surface hydrophilicity. At the same time, Rhodamine B stain fading was highlighted, with the degree of whiteness recovery of NT composites exceeding that of the control by up to 11% for natural aggregate compositions, 10.6% for RGA compositions, 19.9% for RBA compositions, 15% for GBA compositions, and 13% for RTA compositions. In a mould-contaminated environment, it was shown that the introduction of NT allowed the material to develop a biocidal surface capacity which is also influenced by the nature of the aggregates used. Furthermore, the study revealed that, under controlled conditions, certain recycled waste aggregates, such as textolite, promoted mould growth, while others, such as brick and slag, inhibited it, highlighting not just the effect of the addition of NT, but also the significant influence of the aggregate type on the microbial resistance of cementitious composites. These improvements in the performance of cementitious composites are particularly advantageous when applied to prefabricated elements intended for the finishing and decorative surfaces of institutional (schools, administrative buildings, religious structures, etc.) or residential buildings. Full article

There is a lack of scientific understanding of adding an oyster shell powder (OSP) to geopolymer concrete. The purpose of this study is: (1) to evaluate the high-temperature resistance of the alkali-activated slag ceramic powder (CP) mixture added with OSP at different temperatures, (2) to address the lack of application of environmentally friendly building materials, and (3) to reduce solid waste of OSP pollution and protect the environment. OSP replaces granulated blast furnace slag (GBFS) and CP at 10% and 20% (based on binder), respectively. The mixture was heated to 400.0, 600.0, and 800.0 °C after curing for 180 days. The results of the experiment are summarized as follows: (1) The thermogravimetric (TG) results indicated that the OSP20 samples produced more CASH gels than the control OSP0. (2) As the temperature increased, the compressive strength and ultrasonic pulse velocity (UPV) both decreased. (3) Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) results reveal that the mixture undergoes a phase transition at 800.0 °C, and compared with the control OSP0, OSP20 undergoes a different phase transition. (4) The size change and appearance image results indicate that the mixture with added OSP inhibits shrinkage, and calcium carbonate decomposes to produce off-white CaO. To sum up, adding OSP can effectively reduce the damage of high temperatures (800.0 °C) on the properties of alkali-activated binders. Full article

The research focuses on pozzolanic additives, which are compatible with traditional lime mortars, and enable the modification of the rheological, physical and mechanical properties of tested composites. It was noted that lime mortars with fluidised bed fly ash require sand without impurities to avoid possible ettringite crystallisation. The work presents siliceous fly ash and fluidised bed combustion fly ash to modify the frost resistance and mechanical properties of traditional lime mortars with and without the addition of cement. The results show better effects using fluidised bed ash. Traditional Portland cement CEM I 42.5R was used to activate ash and increase the results. The possibility of a significant improvement of properties is indicated with a hybrid addition to the lime binder of 15–30% ash (siliceous or fluidised bed ash) and 15–30% cement. Changing the class and type of cement provides an additional opportunity to alter the properties of the composites. For architectural reasons relating to colour, the suitability of lighter fluidised bed ash instead of darker siliceous ash and of white Portland cement instead of the traditional grey cement can be used. The proposed mortars can be the basis for future modifications with admixtures and additives, e.g., metakaolin, polymers, fibres, slag, glass powder and impregnating agents. Full article

The online preparation of fibers using molten modified blast furnace slag can not only achieve the high-value-added utilization of the slag but can also make use of the sensible heat of the slag. In this paper, blast furnace slag was modified using iron tailings, and was then used to prepare slag fiber online; the effects of the acidity coefficient on the properties of the molten modified blast furnace slag and modified blast furnace slag fiber were investigated. With an increase in the acidity coefficient from 1.2 to 1.6, the temperature range of the slag melt, with viscosity in the 1–3 Pa·s range, increased from 101.2 °C to 119.9 °C. The melting temperature increased from 1326.2 °C to 1388.7 °C, and the suitable fiber-forming temperature range increased from 70.7 °C to 82.9 °C. With the increasing acidity coefficient, the crystallization temperature of the molten modified slag decreased markedly. When the acidity coefficient was greater than 1.4, the slag system was still in a disordered glassy phase at 1100 °C. The hardening speed gradually reduced with the increasing acidity coefficient when the modified slag was cooled at the critical cooling rate, resulting in a gradual increase in fiber formability. The fibers prepared from the modified slag at different acidity coefficients had smooth surfaces, and were arranged in a crossed manner at the macroscopic level. Their color was white, and small quantities of slag balls were doped inside the fibers. With an increase in the acidity coefficient from 1.2 to 1.6, the average fiber diameter increased from 4.2 μm to 8.2 μm, and their slag ball content increased from 0.73% to 4.49%. Overall, the acidity coefficient of modified blast furnace slag should be less than 1.5 in actual production. Full article

The recovery of Mn and Al from two industrial waste of ferromanganese and aluminum production processes was investigated via implementing a high temperature smelting—aluminothermic reduction process. The experiments were carried out with or without CaO flux addition, and two dross qualities. It was observed that the prepared mixtures of the materials yield homogeneous metal and slag products in terms of chemical composition and the distribution of phases. However, the separation of produced metal phase from the slag at elevated temperatures occurs when a higher amount of CaO is added. Viscosity calculations and equilibrium study indicated that the better metal and slag separation is obtained when the produced slag has lower viscosity and lower liquidus. It was found that the process yields Al-Mn-Si alloys, and it is accompanied with complete recovery of Mn, Si and Fe and the unreacted Al in the process. Moreover, the quality of metal product was less dependent on the slightly different dross quality, and the concentration of minor Ca in metal is slightly increased with significant increase of CaO in the slag phase. Full article

Concrete is the most widely used building material, but it is also a recognized pollutant, causing significant issues for sustainability in terms of resource depletion, energy use, and greenhouse gas emissions. As a result, efforts should be concentrated on reducing concrete’s environmental consequences in order to increase its long-term viability. In order to design environmentally friendly concrete mixtures, this research intended to create a prediction model for the compressive strength of those mixtures. The concrete mixtures that were used in this study to build our proposed prediction model are concrete mixtures that contain both recycled aggregate concrete (RAC) and ground granulated blast-furnace slag (GGBFS). A white-box machine learning model known as multivariate polynomial regression (MPR) was developed to predict the compressive strength of eco-friendly concrete. The model was compared with the other two machine learning models, where one is also a white-box machine learning model, namely linear regression (LR), and the other is the black-box machine learning model, which is a support vector machine (SVM). The newly suggested model shows robust estimation capabilities and outperforms the other two models in terms of R² (coefficient of determination) and RMSE (root mean absolute error) measurements. Full article

Heavy mineral sands are the source of various commodities such as white titanium dioxide pigment and titanium metal. The three case studies in this paper show the value of X-ray diffraction (XRD) and statistical methods such as data clustering for process optimization and quality control during heavy mineral processing. The potential of XRD as an automatable, reliable tool, useful in the characterization of heavy mineral concentrates, product streams and titania slag is demonstrated. The recent development of ultra-high-speed X-ray detectors and automated quantification allows for ‘on the fly’ quantitative X-ray diffraction analysis and truly interactive process control, especially in the sector of heavy mineral concentration and processing. Apart from the information about the composition of a raw ore, heavy mineral concentrate and the various product streams or titania slag, this paper provides useful information by the quantitative determination of the crystalline phases and the amorphous content. The analysis of the phases can help to optimize the concentration of ores and reduction of ilmenite concentrate. Traditionally, quality control of heavy mineral concentrates and titania slag relies mainly on elemental, chemical, gravimetrical, and magnetic analysis. Since the efficiency of concentration of minerals in the different product streams and reduction depends on the content of the different minerals, and for the latter on the titanium and iron phases such as ilmenite FeTiO₃, rutile TiO₂, anatase TiO_2, or the various titanium oxides with different oxidation stages, fast and direct analysis of the phases is required. Full article

Recycled aluminum salt slag (RASS) is an industrial by-product generated from the melting of white dross and aluminum scraps during the secondary smelter process. Insufficient knowledge in the aspects of engineering characteristics, and the environmental risks associated with RASS, is the primary barrier to the utilization of RASS as a substitute material for natural quarry materials in the field of geotechnical construction. In this research, comprehensive geotechnical and environmental engineering tests were conducted to evaluate the feasibility of utilizing RASS as a sustainable geomaterial. This was undertaken by comparing the laboratory testing results for RASS with a well-known recycled material, namely recycled concrete aggregate (RCA), and the relevant specifications set forth by the local road authority. The geotechnical engineering assessment included particle size distribution, flakiness index, organic content, pH, particle density, water absorption, modified Proctor compaction, aggregate impact value, Los Angeles (LA) abrasion, hydraulic conductivity, and California bearing ratio (CBR). The CBR results of the RASS samples satisfied the minimum CBR value (>80%) for usage as pavement subbase material in road construction. In addition, the repeated load triaxial (RLT) tests were carried out on the RASS samples to assess the response of the RASS under cyclic loading conditions. Furthermore, a range of chemical tests, consisting of leaching and polycyclic aromatic hydrocarbon tests, were also performed on the RASS to address the environmental concerns. Comparing the chemical test results with the environmental protection authorities’ guidelines provided satisfactory evidence that RASS will not pose any environmental and health issues throughout its service life as a geotechnical construction material. Full article

In this paper, a new method of basic oxygen furnace (BOF) slag component modification with a regulator was studied. The main mineral was designed as C₄AF, C₂S and C₃S in modified BOF slag, and the batching method, mineral compositions, hydration rate, activation index and capability of resisting sulfate corrode also were studied. XRD, BEI and EDS were used to characterize the mineral formation, and SEM was used to study the morphology of hydration products. The results show that most inert phase in BOF slag can be converted into active minerals of C₄AF and C₂S through reasonable batching calculation and the amount of regulating agent. The formation of C₄AF and C₂S in modified BOF slag is better, and a small amount of MgO is embedded in the white intermediate phase, but C₃S is not detected. With the increase in the CaO/SiO₂ ratio in raw materials, the CaO/SiO₂ ratio of calcium silicate minerals in modified BOF slag increases, the contents of f-CaO are less than 1.0%, and the activity index improves. Compared with the BOF slag, the activity index and exothermic rate of modified BOF slag improved obviously, and the activity index of 90 days is close to 100%. With the increase in modified BOF slag B cement, the flexural strength decrease; however, the capability of resisting sulfate corrode is improved due to the constant formation of a short rod-like shape ettringite in Na₂SO₄ solution and the improvement of the structure densification of the hydration products. Full article

Soda residue (SR), an industrial solid waste, pollutes the environment due to its high alkalinity and chloride ion content. SR can be used as an alkali activator of ground granulated blast furnace slag (GGBFS). This study investigated the effects of four types of SR-activated GGBFS cementitious materials (pastes) with different mass ratios of SR to GGBFS (8:92, 16:84, 24:76, 34:68) on the physical properties, mechanical strength, and chloride binding capacity. The hydration mechanism of the pastes was also studied. Results showed that with the increasing addition of SR, the density of the pastes decreased, and more white aggregates of SR appeared causing the increase of water absorption and porosity of the pastes. The pastes with 16% SR addition had the maximum compressive strength (34.1 MPa, 28 d), so the optimum proportion of SR addition in the pastes was 16%. With the increases of SR addition, the amount of chloride element in the initial pastes increases. When the proportion of SR addition is 8%, the mass percentage of free chloride ion in the pastes at 28 d is 0.13%. The main hydration products of the pastes were C–S–H gels, ettringite, and Friedel’s salt, and the amount of ettringite varied with the amount of SR addition and curing time. Full article

A substantial amount of attention has been paid to viscosity due to its substantial effect on the fluid dynamics of molten blast furnace slag and slag metal reaction kinetics during the pyrometallurgy process. To clarify the influence mechanism of unburned pulverized coal (UPC) on blast furnace (BF) slag viscosity, the effects of different contents of UPC on the BF slag viscosity, free-running temperature and viscous flow activation energy were investigated. The slag viscosity was measured by the rotating cylinder method, and the microstructure of the cooled slag was observed by SEM. As a result, the main reason for a change in the slag viscosity, free-running temperature and viscous flow activation energy was that the UPC entering the slag formed a large number of white particles that predominantly comprised deposited carbon and a high melting point solid solution. In addition, the disintegration or polymerization of the Si_x${\mathrm{O}}_y^{z-}$ structure was also a contributing factor. When the content of the UPC was 0.6%, the free-running temperature and viscous flow activation energy of slag were 1623 K and 120.969 kJ/mol, respectively, which are lower than those of the slag without UPC. However, the free-running temperature and viscous flow activation energy increased to 1668 K and 286.625 kJ/mol, respectively, when the content of UPC increased to 4%, which are higher than those of slag without UPC. Full article

Blast furnace ferronickel slag (BFFS) is generated in the production of ferronickel alloys and is used as cement replacement in concrete or mortar. The effectivity in reducing cement consumption and improving performance are limited. By referring to the paste replacement method, this work used BFFS to replace an equal volume of the white Portland cement paste to obtain greater performance enhancement. BFFS was used with five levels of replacement (0%, 5%, 10%, 15%, 20%) and four water-to-cement ratios (0.40, 0.45, 0.50, 0.55) were designed. Fluidity, mechanical strength, hydration products, and pore structure of every mixture were measured. The results showed that the workability of the mortars decreased due to the reduced volume of water, but the 28-day compressive strength of the mortars increased, and the cement content of the mortars was also reduced by 33 wt %. The X-ray diffraction (XRD) patterns revealed that there existed a carboaluminate phase, and the presence of the ettringite was stabilized, indicating that the accumulating amount of the hydration products of the mortar increased. Furthermore, the BFFS could consume the portlandite and free water to form a higher amount of chemically bound water due to its pozzolanic activity. A high degree of hydration and a large volume of the hydration products refined the porosity of the hardened mortars, which explained the enhancement of the strength of the mortars. Compared to the cement replacement method, the paste replacement method was more effective in preparing eco-friendly mortar or concrete by recycling BFFS for reducing the cement content of the mortar while improving its strength. Full article