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The main objective of this study was to evaluate the use of construction and demolition waste (CDW) from the Passo Fundo region of Rio Grande do Sul (RS), Brazil, in the development of aerated foamed concrete. This waste had not yet been characterized or even reused. CDW was processed (sieved only), characterized, and used as an aggregate, completely substituting natural sand. The influence of CDW granulometry and the amount of foam upon compressive strength, wet and dry bulk density, water absorption, and the air voids of concrete blocks were determined. Results showed that CDW has regular characteristics for the development of aerated foamed concrete. Compressive strength and density decreased as the amount of foam increased, while water absorption and air voids also increased. Also, CDW that was classified as coarse showed higher compressive strength. On average, CDW medium-sized particles had a higher air void content, while water absorption showed little variation with respect to granulometry. CDW residue from the region of study can be used as aggregate for the development of aerated foamed concrete. However, it must characterized before being used to guarantee the quality of the final product.

The main aim of this work was to evaluate the influence and optimize the factors of the TIG-MIG/MAG hybrid welding process on the geometry of the weld bead. An experimental design using the Taguchi methodology (robust design method) was used to conduct the experiments. The experiments were carried out according to an orthogonal matrix with 27 experiments, with three replicates each, totaling 81 test specimens. The factors (MIG/MAG shielding gas type, MIG/MAG voltage, MIG/MAG wire feed, gas flow rate of TIG, electric current intensity of TIG and welding speed) were varied with three levels each. Penetration, heat-affected zone (HAZ), bead width and bead height were the response variables analyzed. The results showed that the penetration was significantly influenced by the MIG/MAG wire feed, MIG/MAG shielding gas type, MIG/MAG voltage and welding speed. The HAZ has been influenced by MIG/MAG voltage, MIG/MAG shielding gas type, welding speed and electric current intensity of TIG. All factors had effects on the width, except the MIG/MAG wire feed. The bead height was significantly influenced by the MIG/MAG wire feed and by the electric current intensity of TIG. Optimizing the process was performed, so that for each output variable, the values of the factors that should be used were indicated, and the optimization was confirmed by welding test specimens.

Defects in the crystalline structure of quartz facilitate the connection with the alkali hydroxides, since under a high alkalinity condition (e.g., in concrete), the Si-O bonds of quartz are easily broken. This study set out to investigate the influence of the deformation structures of quartz on its susceptibility to the alkali–silica reaction. A granite, a protomylonite, and a mylonite were selected for this study. Using optical microscopy, the quartz grains contained in these rocks were quantified and their texture characterized. The quartz samples extracted from the rocks were analyzed by magnetic nuclear resonance, to evaluate their potential for dissolving silica as well as changes in their atomic scale before and after the reaction with alkali hydroxides. These analyses were compared with the results of the accelerated mortar bar test. The study showed that the quartz with intense undulatory extinction and deformation bands denotes the most favorable condition to the development of the alkali–silica reaction. However, on an atomic scale, the slightly deformed grains were highly prone to react. Thus, in a high alkalinity condition, over a long period of time, any quartz tends to develop the alkali–silica reaction, regardless of the deformation degree of the grain.

The construction industry is recognized for its high consumption of natural resources, resulting in significant environmental impacts. Given this reality, it is essential to seek new methods and solutions that minimize the impact of this activity on the environment. An innovative approach consists of using pigments derived from acid mine drainage (AMD) as a sustainable alternative in the production of mortar for decorative façade cladding. In this context, the main objective of this paper was to evaluate the physical/mechanical properties of decorative mortars developed by partially replacing natural sand with pigment from acid mine drainage. Initially, the pigment (yellow) was produced, characterized, and compared with a commercial pigment. Sequentially, decorative mortars were developed with different pigment concentrations (0%, 2%, 4%, and 6%). The mortars were subjected to compressive strength, flexural tensile strength, shrinkage, loss of mass, and colorimetry tests. The results showed that compressive strength, flexural tensile strength, weight loss, and dimensional variation were significantly affected by the partial addition of pigment to replace natural aggregate. In other words, there was a decrease in strength and an increase in mass loss and expansion of the mortars. However, the main factor influencing these variables was the greater amount of water added in the higher substitution cases. The addition of water was necessary to keep the consistency constant. A possible solution to maintain the same amount of water and avoid negative effects on the mortar properties would be to use additives in the mortar formulation in future work. Therefore, this research contributes to the search for more sustainable solutions in civil construction, exploring the use of pigments from AMD as a viable alternative to reduce the environmental impacts associated with this industry.

The use of solid waste for the development of new building materials has been an alternative to reduce environmental impacts through the preservation of natural resources. In this context, this paper evaluates the possibility of using agate gemstone waste, called rolled powder, which basically consists of silica (SiO2), in the manufacture of aerated foamed concrete blocks completely replacing the natural sand. Preformed foam was used as the air entrained by mechanical stirring with a mixture of natural foaming agents derived from coconut. To produce test specimens, the water/cement ratio and foam concentrations were varied, with three and four levels, respectively. The specimens were left for 28 days at room temperature to be cured, and then underwent analysis to determine their compressive strength, density, and the distribution of air-voids. The experiments demonstrated that the best water/cement ratio was 1.28 for 18% (of total solid mass) addition of foam, which generated a sample with a density of 430 kg/m3, and a compressive strength of 1.07 MPa. The result for compressive strength is 11% smaller than the requirements of the Brazilian standard (NBR 13438) for autoclaved aerated concrete blocks, but the results are promising.

The main objective of this study was to evaluate the use of additives in producing foamed concrete blocks, which were made by totally replacing natural sand with civil construction waste (CCW). The concrete blocks were developed in accordance with an experimental design that used the complete factorial statistical method, for which three factors with different levels were considered: cement type (CP-V, CP II-Z, and CP II-F); use of additive (without additive, plasticizer, air entrainment, and superplasticizer) and foam amount (5.7%, 7.7%, and 9.5% of the total mass). The influence of each factor and the interactions between them were assessed on the following response variables: compressive strength, dry and saturated density, air voids, water absorption, and thermal conductivity. The results show that all factors had a significant influence on the variable response. For example, the use of the superplasticizer additive resulted in higher compressive strength, lower density, lower air void, and lower thermal conductivity. Finally, the use of additives had little influence on the response variables in relation to the other factors.

Foam stabilization plays a critical role in the production of foamed mortar, a material widely applied in civil construction due to its thermal insulation and lightweight structural benefits. This study investigates the use of magnetite derived from acid mine drainage (AMD) as a sustainable foam-stabilizing agent. Magnetite’s magnetic properties enhance foam stability by improving air bubble distribution within the mortar. A total of 30 different mixtures were produced, varying the sand-to-cement ratio, type of cement and magnetite content. The compressive strength and tensile flexural strength of the foamed mortars ranged from 0.62 ± 0.04 MPa to 7.33 ± 0.30 MPa and from 0.44 ± 0.12 MPa to 2.82 ± 0.16 MPa, respectively; porosity ranged from 31.8% ± 1.86 to 75.6% ± 2.2; dry and wet bulk density ranged from 423 ± 23 kg.m−3 to 1576 ± 96 kg.m−3 and from 615 ± 9 kg.m−3 to 1828 ± 122 kg.m−3, respectively; water absorption ranged from 8.9% ± 0.9 to 45.8% ± 10.6; and thermal conductivity ranged from 0.54 ± 0.03 W·m−1·K−1 to 0.17 ± 0.03 W·m−1·K−1. Results demonstrated that increasing magnetite content led to greater foam stability and porosity but decreased mechanical strength and density. The sand-to-cement ratio significantly affected all measured properties, while the type of cement had minimal influence. These findings suggest that AMD-derived magnetite is a promising additive for optimizing the performance of lightweight, sustainable foamed mortars.

The waste generated from the process of steel shot blasting must be safely disposed of due to its classification, non-hazardous and non-inert, and, consequently, is sent to landfills. One of the possibilities for reusing this waste is in the cement materials industry. In this context, the aim of this study was to evaluate the addition of waste from steel shot blasting, thereby replacing natural sand, for the manufacture of cementitious material with properties that shield against ionizing radiation. Three forms of steel shot (commercial steel shot—AG1, intermediate steel shot waste—AG2, and steel shot dust—AG3) were used to replace natural sand in different proportions (0%, 10%, 20%, 30%, and 40% by volume). Compressive strength results were found with values above the minimum compressive strength (20 MPa) requirement of structural concrete. The results indicated that AG1, AG2, and AG3 can be used to attenuate X-ray radiation. Regarding the reference samples (mortar developed without natural sand replacement), an increase in X-ray shielding of 76.7%, 72.5%, and 59.3% was found for samples with AG1, AG2, and AG3, respectively. Therefore, the waste generated in the steel shot blasting process had the potential to be used in mortar developed to attenuate X-ray radiation.

Coal is an abundant resource which can be used to produce low-cost energy; however, its usage causes great environmental damage. Before mineral coal can be used, it must be processed to remove coal tailings. These tailings contain pyrite and accumulate in large dumps, presenting significant environmental liabilities, such as acid mine drainage. Another industry that generates environmental liabilities is the chrome-plating industry, mainly because it produces hexavalent chromium (Cr6+) waste. The main aim of this work was to evaluate Cr6+ as a reduction agent in trivalent chromium (Cr3+) conversion in the leaching of coal-mine waste containing pyrite. Cr3+ is about 100 times less toxic than Cr6+ and can be easily removed from industrial effluents by alkaline precipitation. There are several sources of effluents containing Cr6+—a compound which is known worldwide to be toxic, carcinogenic, and mutagenic. A leaching and treatment device was developed and tested for waste treatment. The results indicated that the developed treatment system reduced 100% of Cr6+ to Cr3+ through pyrite leaching in a Cr6+ wastewater sample from the electroplating industry. In addition, the chromium sludge resulting from the treatment process, after calcination, was tested in a ceramic glaze as a pigment and, when compared with an industrial pigment, showed similar mineralogical characteristics.

The main aim of this study is to determine the best process parameters for the robotized Gas Metal Arc Welding (GMAW) of LNE 700 advanced high-strength steel. This article evaluates some quality criteria such as the microhardness, the heat-affected zone (HAZ) and the convexity in the welded joints. The assays are performed using an experimental design, based on the Taguchi method. The analysis of the results identified some factors of greatest influence and how best to combine them to determine an optimum condition for welding LNE 700 high strength steel. Moreover, the influence of welding parameters on quality criteria is determined.