Search Results (6)

The innovation inherent to employing expanded polystyrene (EPS) beads lies in its transformative impact on traditional concrete practices. Through the incorporation of EPS beads in concrete mixtures, a novel approach emerges that significantly alters the material’s characteristics, and opens up new avenues for construction and design. Studying the shear behavior of RC beams made with EPS beads is essential for advancing knowledge, improving design practices, ensuring structural integrity, and promoting the effective and responsible use of innovative materials in construction. This research experimentally investigated the effect of using EPS beads and pozzolana aggregate (PA) on the shear behavior of the RC beams. A total of 27 simply supported rectangular beams were cast, using three novel distinct mix designs, and were subjected to two-point load testing until failure. These three mixes were categorized as follows: a control mix, a mix with only EPS, and a mix with EPS, along with an additive. The ultimate failure load was experimentally recorded for all specimens, and the influence of the temperature (300 °C and 600 °C) on the RC beams made with EPS was examined. The findings revealed a reduction in the concrete compressive strength and density in the beams containing EPS and EPS with superplasticizers of (21.7%, 24.9%) and (11.3%, 16.2%), respectively. Additionally, EPS played a significant role in diminishing the ultimate shear capacity of the beams, compared to the control beams, by about 19.4%. However, the addition of a superplasticizer along with the EPS helped to maintain the beam capacity, to some extent. Conversely, the beams exposed to a temperature of 300 °C exhibited an almost similar capacity to that of the control beams without heating. Nevertheless, at 600 °C, the beams displayed a noticeable decrease in the ultimate load capacity, compared to the unheated control beams. Full article

Lately, several machine learning (ML) techniques are emerging as alternative and efficient ways to predict how component properties influence the properties of the final mixture. In the area of civil engineering, recent research already uses ML techniques with conventional concrete dosages. The importance of discussing its use in the Brazilian context is inserted in an international context in which this methodology is already being applied, and it is necessary to verify the applicability of these techniques with national databases or what is created from national input data. In this research, one of these techniques, an artificial neural network (ANN), is used to determine the compressive strength of conventional Brazilian concrete at 7 and 28 days by using a database built through publications in congresses and academic works and comparing it with the reference database of Yeh. The data were organized into nine variables in which the data samples for training and test sets vary in five different cases. The eight possible input variables were: consumption of cement, blast furnace slag, pozzolana, water, additive, fine aggregate, coarse aggregate, and age. The response variable was the compressive strength of the concrete. Using international data as a training set and Brazilian data as a test set, or vice versa, did not show satisfactory results in isolation. The results showed a variation in the five scenarios; however, when using the Brazilian and the reference data sets together as test and training sets, higher R² values were obtained, showing that in the union of the two databases, a good predictive model is obtained. Full article

This article presents the physical and mechanical properties of geopolymer concrete with lightweight artificial aggregate. A research experiment where the influence of fly ash–slag mix (FA-S), as part of a pozzolanic additive, on the properties of geopolymers was carried out and the most favorable molar concentration of sodium hydroxide solution was determined. The values of three variables of the examined properties of the geopolymer lightweight concrete (GLC) were adopted: X₁—the content of the pozzolanic additives with fly ash + flay ash–slag (FA + FA-S) mix: 200, 400 and 600 kg/m³; X₂—the total amount of FA-S in the pozzolanic additives: 0, 50 and 100%; X₃—the molarity of the activator NaOH: (8, 10 and 12 M). In order to increase the adhesion of the lightweight artificial aggregate to the geopolymer matrix, the impregnation of the NaOH solution was used. Based on the obtained results for the GLC’s compressive strength after 28 days, water absorption, dry and saturated density and thermal conductivity index, it was found that the most favorable parameters were obtained with 400 kg/m³ of pozzolanic additives (with 50% FA-S and 50% FA) and 10 NaOH molarity. Changes in the activator’s concentration from 8 to 10 M improved the compressive strength by 54% (for a pozzolana content of 200 kg/m³) and by 26% (for a pozzolana content of 600 kg/m³). The increase in the content of pozzolanic additives from 200 to 400 kg/m³ resulted in a decrease in water absorption from 23% to 18%. The highest conductivity coefficient, equal to 0.463 W/m·K, was determined, where the largest amount of pozzolanic additives and the least lightweight aggregate were added. The structural tests used scanning electron microscopy analysis, and the beneficial effect of impregnating the artificial aggregate with NaOH solution was proved. It resulted in a compact interfacial transition zone (ITZ) between the lightweight aggregate and the geopolymer matrix because of the chemical composition (e.g., silica amount), the silica content and the alkali presoaking process. Full article

In this study, bentonite (a naturally occurring pozzolana) was incorporated as a partial replacement (up to 20%) for high-calcium fly ash (HCFA)-based geopolymeric natural aggregate concrete (GNAC) and geopolymeric recycled aggregate concrete (GRAC). The mechanical (compressive strength and splitting tensile strength), durability (chloride migration coefficient, water absorption, and acid attack resistance), and rheological properties (slump test, fresh density, and workability) were investigated. The results revealed that incorporation of bentonite (10 wt % with ordinary Portland cement) showed appreciable improvement in the strength and durability of both the GNAC and GRAC, though its effect is more significant for GRAC than the GNAC. Full article

Recycling of construction and demolition waste is a central point of discussion throughout the world. The application of recycled concrete as partial replacement of mineral aggregates in concrete mixes is one of the alternatives in the reduction of pollution and savings in carbon emissions. The combined influence of the recycled crushed concrete, lime, and natural pozzolana on the mechanical and sustainable properties of concrete materials is firstly proposed in this study. In this research, unconventional construction materials are employed to produce concrete: the recycled crushed concrete is used as coarse aggregate, while lime and natural pozzolana are used as a partial replacement for cement. Substitutions of 10%, 20%, 50% of gravel are made with recycled aggregates, and 2%, 5%, 10% of cement with lime and natural pozzolan. Tests on the fresh and hardened properties, destructive (compressive strength) and non-destructive tests (sclerometer rebound and ultrasound) of mixtures are carried out. It is shown that the use of recycled materials can provide an increase in compressive strength of up to 34% with respect to conventional concrete. Life cycle cost and sustainability assessments indicate that concrete materials incorporating recycled aggregate possess good economic and environmental impacts. Full article

An end-of-Life Tyre (ELT) is a type of waste that can generate negative social and environmental impacts due to its disposal. Considering that rubber can improve concrete properties and the massive use of concrete as construction material, the addition of ELT rubber in concrete mixes is attractive. However, concrete mechanical properties are negatively affected due to the rubber-cementitious matrix interaction. Although rubber treatments have been developed to minimise the negative effects, the geo-dependency of the mix makes necessary to find cost-effective and practical solutions that will allow a real use of the ELT waste. Therefore, the objective of the present study is to characterise the properties of cement mortars with the addition of ELT rubber under three surface treatments: hydration, oxidation-sulphonation, and hydrogen peroxide. The results show that hydration is the most favourable treatment from a technical, practical, and economical point of view. In fact, with this treatment, it is possible to add up to 5% ELT rubber, with respect to the aggregate weight, and still exceed the design strength without adding more cement or additives as other investigations. The use of Portland Pozzolana Cement, with local fly ash waste, contributes as well to the promissory results obtained. Full article