Featured Application: The use of construction and demolition waste (CDW) in the development of building materials has been done constantly. The CDW from Passo Fundo region of Rio Grande do Sul/Brazil can be used in development of foamed concrete fully replacing the natural sand. Abstract: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.

Abstract: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.

Abstract: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 (SiO 2 ), 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/m 3 , 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.

Acid mine drainage (AMD) in the coal mining industry is recognized as one of the major sources of environmental damage. The active treatment of AMD involves adding alkaline reagents to wastewater so as to raise pH and to precipitate dissolved metals in the form of oxides/hydroxides. Studies have shown that yellow pigment (goethite) can be produced from the iron present in AMD. However, the presence of other metals can prevent the formation of pigment. Therefore, this paper seeks to evaluate several processes for purifying iron sludge so as to obtain raw material that can be recovered from AMD and thereby obtain a good quality of yellow pigment. The experiments were carried out by causing precipitation with strong and weak bases and removing other metals from the sludge by washing and filtering the sludge or by centrifugation. The results show that the color, type and morphology of the compounds changed, depending on the number of contaminants, and that these factors are strongly dependent on the type of reagent and less dependent on the separation process and the repetition of washes.

The physical and mechanical properties of foamed geopolymers were determined. The geopolymers were made with two different metakaolins (from Metacaulim do Brasil -MB, and Pantano Grande/RS -MPG) as precursors, with NaOH and Na 2 SiO 3 as activators, and with the addition of foam, which was produced with the foaming agent diethanolamide of coconut fatty acid with a minimum of 80% concentration. Also, two times (2.5 and 4 h) were used for the calcination of MPG at 750 °C. The results showed that all factors (precursors type, alkali content, silica modulus, and foam content) had a significant influence on the response variables, which presented the following variations: compressive strength of 0.36 to 3.23 MPa; thermal conductivity from 0.22 to 0.42 W/(m.K); saturated bulk density from 1176 to 1364 kg/m 3 ; dry bulk density of 619 to 864 kg/m 3 ; air void from 46.4% to 62.5%; and water absorption from 55.7% to 95.4%. It was also concluded that the precursor type was the factor that had the most influence on the properties of foamed geopolymers, with MPG calcined for 4 h being the best, as greater compressive strength and low thermal conductivity were obtained.

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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.

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.