Key Engineering Materials Vol. 634

Abstract: The present study reports the industrial production of fired-clay masonry bricks containing 2.5% phosphatization sludge, the result of a research project carried out in three stages: laboratory, pilot production, and industrial production. After validation of the results of the first and second stages, the local environment authorities issued a permit to produce these bricks on industrial scale and to commercialize them. One of the requirements was the monitoring of the dimensional, mechanical and environmental performance of these bricks at 6-month intervals. This study presents the results of the monitoring of these characteristics in a 5-year period. After each sampling, bricks containing phosphate sludge were measured and submitted to compressive strength, as well to environmental analyses following the official Brazilian standards. The analyses of results of measurements and compressive strength show that the bricks manufactured with 2.5% phosphate sludge were approved for use in the construction industry. Additionally, the fired-clay bricks were classified as a non-inert material. This is not be considered an obstacle to commercializing these bricks, since conventional fired-clay bricks belong to the same class, and present higher levels of solubilized iron and aluminum, above the value defined in the national standard. The results obtained in the environmental, dimensional and mechanical analyses of fired-clay masonry bricks with phosphatization sludge demonstrate that they meet the requirements for production and commercialization.

Abstract: The incorporation of fly ash (FA) in cementitious matrices have been frequently used in order to make the matrix more resistant to the action of chlorides. On the other hand, it is known that Ca (OH)₂ existing in the matrix is partially consumed by the pozzolanic reactions, which facilitates the advancement of carbonation. Given that the combined action between carbonation and chloride penetration is a fact little known, we speculate about the behaviour of the matrix in this context. This study investigates the influence of the presence of chlorides on the carbonation in mortars with FA. Samples with 0% and 40% replacement of cement CEM I 42.5 R for FA were molded with water/binder 0.56 and 0.52 respectively. After 90 days of curing the specimens were subjected to cycles of immersion/drying for 56 days. Half of the samples was subjected to the following cycle: two days in a solution containing NaCl (concentration equal to 3.5 %); 12 days in the carbonation chamber (4% of CO₂). The other half was: two days in water; 12 days in the carbonation chamber. Then, the development of carbonation was evaluated. The results indicate that the presence of chlorides influences the carbonation. The specimens submitted to the exclusive action of CO₂ showed a greater depth of carbonation compared to that presented by the specimens subjected to combined action. This may be related to changes in properties of the matrix which may lead to further refinement of the pores and related to the presence of the salt that can lead to partial filling of the pores and the increase in moisture content .

Abstract: The objective of the present study was to assess the properties of plastering mortar that uses cellulose pulp waste as absorbent material. Waste was characterized by thermogravimetric analysis (TGA), Fourier Transform Infrared Spectroscopy (FTIR), scanning electron microscope (SEM), X-ray diffraction (XRD, and absorption of aqueous solutions with pH variations. The incorporation of 0.5%, 1% and 1.5% of waste in a plastering mortar prepared with Portland cement, lime and sand (1:1:6) was proved viable. Mortars were analyzed and compared with a control mortar. The properties of fresh mortars analyzed were: consistency index, squeeze-flow, incorporated air, water retention and density. The properties of hardened mortars analyzed were (after 28 days): tensile resistance on flexural stress, compression strength, density, absorption by capillarity and capillarity coefficient, total water absorption, void index, specific weight and linear retraction. The addition of waste resulted in improved mechanical properties, compared to the control mortar. An increase of 4% was observed in tensile resistance on flexural stress, and of 7% in compression strength for the mortar prepared with 1.5% cellulose pulp.

Abstract: The objective of this study is to evaluate the use of polyurethane (PU) coated textile wastes processed with ethylene-vinyl acetate (EVA) as lightweight aggregates in fly ash-based and alkali-activated metakaolin mortars, targeting the development of non-structural elements for civil construction. The PU/EVA waste was processed in three different proportions: 30/70, 50/50 and 70/30. Reference mortars were prepared using a 1:2 (fly ash + metakaolin: conventional construction sand) ratio, by mass. The PU/EVA-waste-containing mortars were prepared via partial replacement of natural sand with the waste in percentages of 10%, 20%, 30% and 40%, relative to the volume of the sand. The activators used in all mortars were NaOH and Na₂SiO₃. The mortars were cured at 80 °C for 21 hours and subsequently removed from the molds and maintained at room temperature until testing was conducted for compressive strength (at ages of 7, 28 and 91 days), leaching (7 days) and solubilization (7 days). Based on the results for compressive strength, the optimum PU/EVA content was 50% for a sand-to-waste replacement percentage of 40%. At an age of 28 days these mortars reached strengths greater than 2.5 MPa which, from a mechanical standpoint, allows for the production of non-structural elements for civil construction like sealing blocks, side walls or finish mortars. From an environmental perspective, no hazardous substances were detected in the leaching and solubilized extracts in any of the PU/EVA waste containing mortars.

Abstract: Environmental harm caused by construction and demolition waste (CDW) can be minimized by using it as a raw material in other products used in civil construction. In Brazil, there are several studies on the use of CDW as an aggregate in asphalt paving mixtures. However, this application is limited by the excess of fine aggregates present in these waste materials. Therefore, a technical feasibility study was done to evaluate the use of soil, cement and CDW mixtures for road pavement base and sub-base applications by determining the Unconfined Compressive Strength of cylindrical specimens molded with mixtures of soil, cement and CDW, with cement in proportions of 2%, 4% and 6% by dry weight of the mixture of soil and CDW with variations of: 100% soil and 0% CDW; 75% soil and 25% CDW; and 50% soil and 50% CDW. Soils were sourced from the cities of Maringá and Mandaguaçu in the state of Parana with the following granulometric characteristics, respectively: high clay content and high fine sand distribution. The construction debris, derived from the grinding of ceramic bricks and mortar, was composed of the fraction that passed through a #10 sieve (2.0mm). The soils, the debris and their mixtures were classified by determining their physical properties, compaction properties and unconfined compressive strength. Results showed that the addition of CDW to soil and cement mixtures improves compaction characteristics and increases compressive strength.

Abstract: The rice in the south of Brazil is one of the main economy activities, which produce a large volume of waste coming from the beneficiation industries. The main goal of this research is evaluate the feasibility of use of rice husk ash, burning on fluidized flow (FF) and sliding grid (SG) for mortars. The characterization methods of rice husk ash (RHA) included loss on ignition, particle size distribution by laser, x-ray diffraction, x-ray fluorescence spectrometer, pozzolanic activity index and specific mass. Mortar specimens were molded with the proportion of 1:3 in mass and water/binder ratio of 0.51. The Portland cement was replaced by RHA with the proportion of 10%, 15% and 20%. Compressive strength, water absorption, air voids content, hydration-releasing heat curves, mercury intrusion porosimetry and scanning electron microscope were performed for all mortars. The mechanical performance of mortar with RHA replacement, shows to be satisfactory and feasible alternative for the final waste disposal.

Abstract: In order to overcome the hydrographic network, the landforms, and the most different types of barriers, many timber bridges were constructed around the world, especially in secondary roads where the raw materials (wood) can be found in the vicinity, what reduces the construction costs.The deck can be made of reinforced concrete with the purpose of increasing the durability, strength and stiffness of these structures, and using rubber particles can not only decrease the costs and impact on the environment, but can also confer some advantages on the structure, such as a better impact absorption, and a lower cracking due to the abrasion wear, water absorption or self-weight.The analysis of the bending behavior of these superstructures was performed through the study of ten mixed T section composite beams, with wooden web (mimicking the stringers) and a reinforced concrete top flange (mimicking the deck) with varying rubber waste percentage. Steel bars set to “X”, glued with epoxy resin on the wood, allowed the connection between wood and concrete, reducing manufacturing costs with high shear strength resistance. The constituent materials were characterized mechanically and the composite beams were equipped with a dial indicator and strain gauges, and then broken in flexure tests. At the same time, the rubber particles percentage was correlated with the following parameters: stress, strain, elasticity modulus, loads and displacements, what enabled us to find which rubber addition percentage was most adequate in order for this kind of structure to be in accordance with the project requirements for the resistance.

Abstract: The objective of this study is to evaluate the effect of the relationship of waste polyurethane (PU) and Ethylene-Vinyl Acetate (EVA), as a replacement for conventional construction sand, on the physical properties of water absorption, bulk density and open porosity of fly ash-based and alkali-activated metakaolin mortars. By means of processing involving extrusion and milling, PU/EVA-based aggregates were prepared in three proportions: 30/70, 50/50 and 70/30. The reference alkali-activated mortars were prepared using a 1:2 (fly ash + metakaolin : conventional construction sand) ratio, by weight. The waste-containing mortars were prepared via partial replacement of construction sand with the PU/EVA waste in percentages of 10%, 20%, 30% and 40%, relative to the volume of sand. The activators used in all mortars were NaOH and Na₂SiO₃. The mortars were cured at 80°C for 21 hours. Based on the procedures of ASTM C 642, the water absorption, open porosity and bulk density of the alkali-activated mortars were determined at the ages of 7, 28 and 91 days. The open porosity and water absorption values ​​increased as the amount of sand replaced with PU/EVA waste increased. The absorption values ​​were found to be in the range from 8.0% to 17.00%. The values ​​obtained for open porosity varied from 20.00% to 29.00%. With regard to bulk density, the behavior was reversed: increasing the amount of sand replaced by waste, decreased the bulk density value. The values ​​ranged between 2.10 and 2.48 kg/dm³. Therefore, based on these results, mortars containing up to 40% PU/EVA have potential for use in the manufacture of non-load-bearing elements for civil construction.

Abstract: The cement industry is responsible for a large part of the global environmental problems: is the largest consumer of natural resources; the most responsible for the emission of greenhouse gases, including about 1.8 Gt of CO₂; and requires huge amounts of energy, corresponding to between 12 and 15% of industrial energy use. The cement is also not used in the most appropriate manner, since 40% of the consumption of concrete is due to the renovation and repair of buildings, making concrete structures inefficient because its durability is relatively low. However, in the future, concrete can and should evolve in order to improve its eco-efficiency, with a smaller amount of cement in its composition, replacing it with high quantities of mineral additions, particularly fly ash. Nevertheless, current technology may not allow this type of concrete to be very efficient, because its long-term durability may be compromised. In fact, with increasing dosage of pozzolanic mineral additions, alkali paste components are consumed in the reaction leaving it vulnerable to concrete carbonation which may compromise the passivation layer needed for steel rebar protection against corrosion. This article explores a promising approach to mitigate this problem, which consists in the careful addition of hydrated lime in the concrete composition, highlighting the synergy of its components, significantly enhancing its carbonation resistance. It is proposed, therefore, to manufacture a concrete with high volume of fly ash, low cement content and high service life period: an efficient and sustainable concrete. In this context, an experimental campaign was developed with the aim of characterization of pastes behavior with high fly ash content, in particular with respect to its durability. The results will be presented and properly analyzed.

Abstract: In this paper it was investigated how the use of recycled fine aggregate influences the stress-strain behavior of mortar mixtures with different strengths. The mix design composition of the studied mortars, expressed by mass, were 1:2:0.45, 1:4:0.68 and 1:6:1.05 (cement: sand: water/cement ratio). The substitution percentages by mass of the natural aggregate by recycled aggregate were 15, 25 and 50%. The recycled aggregate had a grain size distribution comparable to that of natural sand and was obtained by grinding the waste produced by the partial demolition of UFRJ’s University Hospital. The mortars were evaluated under uniaxial compressive strength test after 28 days of curing. The results indicated that for the two higher strength classes the substitution rates affects its mechanical response by decreasing the strength. Besides, for the lower strength class the recycled aggregate could promote an increase of strength in the case of 25% of replacement.