Abstract The increasing generation of waste electrical and electronic equipment (e-waste) and the environmental impacts of natural aggregate extraction have driven the search for more sustainable concrete materials. This study evaluates whether the partial replacement of coarse aggregate with acrylonitrile butadiene styrene (ABS) plastic waste from e-waste can improve the thermal performance—particularly thermal conductivity—of conventional concrete, while assessing its effects on mechanical behavior and water absorption to identify an optimal incorporation level without significantly compromising strength and durability. Concrete mixtures with 0%, 10%, 12.5%, and 15% ABS were produced and evaluated in terms of workability, compressive and tensile strengths, thermal conductivity, surface temperatures, water absorption, and mesostructural characteristics. Results showed a progressive reduction in mechanical strength with increasing ABS content; however, mixtures with up to 12.5% replacement remained suitable for non-structural applications. Improved thermal performance was observed, with reduced thermal conductivity, especially at the 12.5% replacement level. This ratio is identified as an optimal solution, contributing to the understanding of the thermo-mechanical behavior of concrete incorporating e-waste and supporting the development of more sustainable cementitious materials.

Ultra-High Performance Concretes (UHPC) are cement-based composites with enhanced properties compared to conventional concrete. Their high mechanical strength is achieved through particle packing, resulting in a very dense microstructure. In this context, these materials require improvement to be safely used under elevated temperatures, as they are susceptible to explosive spalling, which primarily occurs due to vapor pressure from internally evaporating water within the element. Given the dense pore structure, this pressure cannot be relieved, causing stresses that exceed the element's strength, leading to explosion. Research indicates that the use of carbon nanotubes (CNT) may have a preventive effect against spalling; however, their mechanisms are not yet well understood. For effective prevention, it is believed that the dispersion of CNT in the cement paste should be quite uniform, necessitating the investigation of different dispersion strategies. Considering this, the present study aims to investigate the performance of UHPC incorporating CNT using different superplasticizers, specifically lignosulfonates (LS) and polycarboxylates (PC), which can be adsorbed by the nanotubes to assist in dispersion. The results indicate that the addition of CNT to UHPC was able to modify the occurrence of spalling starting at 400 °C, with the use of LS allowing the material to be tested up to 600 °C, while the control and the material produced with PC did not resist temperatures beyond 400 °C. This performance could not be attributed to improvements in flexural strength, which were not observed to be significant. The apparent density also did not show substantial changes. Hypothetically, mechanisms can be proposed to explain the improved performance promoted by the presence of CNTs, such as modification of pore size and interconnectivity, which would reduce internal pressure, and a possible reinforcement of the microstructure by bridging effect, allowing it to withstand concentrated stresses that would cause explosion. These mechanisms were not directly revealed in the present study, so it is suggested that they be investigated in future work using complementary characterization techniques, such as pore connectivity analysis, permeability, microstructural mechanical performance, and scanning electron microscopy.

This paper reviews 26 articles on applying machine learning (ML) techniques for predicting carbonation depth in reinforced concrete (RC) structures. The review addresses five key questions concerning (i) commonly used input features, (ii) the most frequent ML methods and their characteristics, (iii) the nature of the datasets used (experimental vs. synthetic), (iv) the extent to which model explainability is incorporated, (v) environmental trends in carbonation modeling, and (vi) how ML approaches can be made more reliable and applicable in practice. The analysis revealed that water-to-binder (w/b) ratio, exposure time, and CO2 concentration are the most widely used predictors, reflecting their direct influence on carbonation mechanisms. The most employed ML models include ANN, RF, SVR, and XGBoost, often selected for their ability to capture nonlinear interactions. Most datasets come from accelerated carbonation tests, though synthetic data—despite limited use—shows strong potential for overcoming experimental constraints. SHapley Additive exPlanation (SHAP) emerged as the leading explainability technique, offering transparent insights into model behavior. Environmentally, integrating recycled aggregates and supplementary cementitious materials is increasingly common, with ML supporting the design of durable and sustainable concretes. Nonetheless, the review highlights key gaps that hinder real—world use, such as scarce natural exposure data, absent standardized metrics, and limited external validation. Progress will rely on richer databases, standardized testing, and integrating interpretable ML into engineering practice.

A consistent approach to reinforced concrete design requires that glass fiber reinforced polymer (GFRP) reinforcing bars be treated in a manner consistent with steel reinforcing bars. International design guides and standards have therefore taken the approach of normalizing the bond characteristics of GFRP bars to those of steel bars by adopting a so-called bond-dependent coefficient, referred to as kb in this work. The present study collects flexure-based bond tests reported in 19 previously reported studies encompassing different GFRP bars surface treatments and diameters embedded in a range of concrete strengths and flexural test geometries. The value of kb was found to be strongly correlated with the GFRP reinforcing bar stress at which kb is determined, while correlations with other factors including concrete strength, cover concrete and GFRP bar diameter were weak. Normalizing kb by the crack width at which was determined is proposed to allow a more consistent treatment of data from different sources. The calculation of the bond coefficient kb was found to be relatively insensitive to the surface treatment of the GFRP bar: whether deformed (ribbed) or sand-coated. The ACI 440- recommended default value, kb = 1.2, was shown to be appropriate for all bar types, although marginally conservative.

Although Glass Fiber -Reinforced Polymer (GFRP) reinforcing bars are becoming commonplace, their mechanical properties - low modulus of elasticity and high tensile strength - result in design of GFRP-reinforced concrete members (GFRP-RC) often being governed by deflection and crack control at the serviceability limit state. Bond performance of GFRP bars impacts the crack control provided and, due to the empirical nature of bond characterization in design, bond of GFRP remains described in relation to that of steel. To describe the bond performance of GFRP bars, a bond -dependent coefficient, kb, is adopted in design guides and standards. The bond and cracking behaviours of GFRP bars embedded in concrete - including the estimation of kb - were investigated through 80 pull-out and 12 prism tension tests. The evaluation of kb using ASTM D7913 pull-out, confirming the bond performance using a smaller number of prism tension tests, is proposed. The results showed that values of kb determined from pull-out test were about 15-20 % greater than those estimated by prism test. Nonetheless, kb values determined from both tests are similar and follow the same trends. These data obtained in this experimental programme supplemented an extant database of 137 comparable pull-out test results covering a range of GFRP bar and concrete parameters. The study concludes that ASTM D7913 pull-out tests are suitable for assessing minimum GFRP reinforcing bar bond criteria although more complex prism tests are likely required to accurately assess kb.

Anais da 2ª Conferência Brasileira de Planejamento Experimental e Análise de Dados: ConBraPA 2022 (978-85-5722-443-8) - Efeitos Da Dispersão De Nanotubos De Carbono Em Geopolímeros A Base De Metacaulim

The inclusion of carbon nanotubes (CNTs) in cementitious composites has been studied due to their electrical, thermal, and mechanical enhancing properties. Considering the hydrophobic characteristics of CNTs, these nanomaterials need to be well dispersed in the aqueous media in which they are inserted to guarantee those gains. Among the methods applied to produce such composites is the dispersion of CNTs on the surface of anhydrous cement particles using non-aqueous suspensions such as acetone, ethanol, or isopropanol. Even though those non-aqueous media have been individually studied by researchers, comparisons of the efficiency of CNTs dispersion was not found in the literature. Therefore, as a novelty, the present article aims to analyze the influence of the addition of the multi-walled CNTs dispersed in the cited three types of non-aqueous suspensions on the cement paste’s electrical and mechanical properties. Pastes containing 0%, 0.5%, and 1.0% of CNTs were prepared on the surface of anhydrous cement particles using a pre-dispersion technique based on simultaneous sonication and mechanical agitation in the three cited media. Tests to determine electric-volumetric resistivity, compressive strength, and splitting tensile strength were performed. It was observed that acetone dispersion decreases the cement paste’s electrical resistivity, even without the addition of CNTs. The cementitious composites with CNTs demonstrated increased mechanical strength (both compressive and tensile) using all three dispersion media. Statistical analysis (analysis of variance—ANOVA—and Tukey’s Test) was performed to evaluate the significance of the results.

Sodium silicate is a commonly used activator in geopolymer that is produced commercially. In this study, rice husk ash (RHA) from agricultural waste was used to synthesize sodium silicate as an activator for geopolymer cement. This white ash was applied for producing sodium silicate with different molarities (8, 10, and 12) and then used to synthesize fly ash-based geopolymer cement. Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), and Fourier Transform Infrared Spectroscopy (FTIR) were applied to investigate the micro-characteristics of the geopolymerization products. Bulk density, water absorption, compressive strength, flexural strength, and fracture toughness were carried out to measure and evaluate the geopolymers with sodium silicate. The combination of 10 M NaOH with sodium silicate increased the compressive strength by 16.21% and the flexural strength and fracture toughness by 81.6%. However, sodium silicate combined with 12 M NaOH decreased compressive strengths by 13.23% and flexural strength and fracture toughness by 61.94%. The lowest water absorption value of 12.3% was obtained in a geopolymer paste using sodium silicate combined with 10 M NaOH, and the largest was 13.3% for sodium silicate combined with 8 M NaOH. The microstructure analysis showed the hydrated calcium alumina silicate gel (C–A–S–H) and the SEM image also revealed a compact geopolymer matrix. Thus, it can be concluded that sodium silicate from rice husk ash can be utilized as an activator or reactive material to produce geopolymer cement with a good geopolymer network.

Abstract The building industry is one of the greatest environmental impact causers in the planet. Cement is the second most used material in the world and the consumption of concrete ranges between 20 to 30 Gt yearly. This demand for the materials ten ds to increase for the next 100 years. The increase of concrete strength to reduce the material consumption is one of the options proposed in literature to reduce the environmental impacts in building industry. However, few studies have been carried about the actual advantages of this strategy in building production. In this paper, a 15-storey reinforced concrete building was designed with three different concrete grades for its columns: 30 MPa, 40 MPa and 50 MPa. The results for the volume of concrete and the amount of reinforcing steel to produce the columns were used to perform a cradle-to-gate life cycle assessment (LCA) to determine the alternative with less environmental impacts in the production stage. Results indicate an advantage to adopt higher strength concretes in columns to reduce environmental impacts and the consumption of materials. Direct effects of higher strength in concretes made possible to reduce the consumption of concrete by 15%. There was also a significant reduction caused by indirect effects of higher strengths in concrete, with the reducing of steel consumption up to 22%. With the combination of the direct and indirect effects of higher compressive strengths, it was possible to reduce the environmental impacts of reinforced concrete in all categories studied in the LCA.

The development of nanotechnology has made it possible to design new materials and improve existing ones. Regarding new supplementary admixtures for cement-based materials, nanosilica is more advantageous than any other nanomaterial. This is due to its high pozzolanic reactivity, besides its filling and seeding effects, which are a consequence of the higher and more reactive specific surface area of the nanosilica and its amorphous structure. Nonetheless, when used improperly or in an inadequate dosage, such a nanomaterial may negatively affect the cement admixture, compromising both fresh and hardened properties. Hence, it is fundamental to understand the nanosilica’s behavior inside the cementitious medium. This review paper is based on recent literature about the incorporation of nanosilica in cementitious materials. The analyses showed that, once incorporated in the cement matrix, nanosilica tends to agglomerate. The behavior of such agglomerates influences both the pozzolanic filling and seeding effects. Therefore, a suitable dispersion of the nanoparticles must be achieved. In this sense, third-generation superplasticizers are used, usually up to 3% of cement mass. The mechanical properties of cement-based materials with nanosilica depend on the amount of nanomaterial and on its specific surface area. There is not an agreement on the optimum dosage of nanosilica, however, percentages up to 5% in cement mass seem to provide a better performance, when compared to greater ones. It is not worthy to use nanosilicas with excessive specific surface area values, because they tend to form large agglomerates, reducing fluidity and compressive strength. Particles with surface areas up to 300 m2/g usually present good performance. Nanosilica improves the early age strength and contributes to the pore refinement of cement-based materials. The combination of nanosilica with other nanomaterials or industrial by-products can improve the mixture’s performance. Nonetheless, the use of silica nanoparticles with agricultural wastes negatively affects the mechanical properties at early ages.

Graphene oxide has been pointed as a reinforcing material of cement composites. Besides being a material with good dispersion in water, it has a high modulus of elasticity, high tensile strength, high specific surface and high thermal and electrical conductivity. In order to deepen the knowledge about the use of graphene oxide in cement composites, this paper presents a wide bibliographic review on the effects of graphene oxide addition on Portland cement composites. The methodology used for the selection of academic articles was ProKnow-C, (Knowledge Development Process - Constructivist), a literary revision tool that allows the disclosure of the current stage of academic knowledge related to the study topic. By means of this method it was possible to select, from a crude sample of 1354 articles, the 47 most relevant articles that showed the changes in mechanical properties, rheological behavior and microstructure of cement composites with addition of graphene oxide, as well as dispersion techniques used. Thus, the main conclusions, current research gaps and study opportunities were summarized, constituting a reference base to guide future work involving graphene oxide.

RESUMO O óxido de grafeno tem sido apontado como um material de reforço para compósitos de cimento. Além de ser um material com boa dispersão em água, ele apresenta elevado módulo de elasticidade, elevada resistência à tração, elevada superfície específica e alta condutividade térmica e elétrica. Visando aprofundar o conhecimento acerca do uso do óxido de grafeno em compósitos de cimento, o presente trabalho apresenta uma ampla revisão bibliográfica sobre os efeitos da adição do óxido de grafeno em compósitos de cimento Portland. A metodologia empregada para a seleção dos artigos acadêmicos foi o ProKnow-C, (Knowledge Development Process – Constructivist), ferramenta de revisão literária que permite a evidenciação do estágio atual do conhecimento acadêmico relacionado ao tema de estudo. Por meio desta metodologia de busca e seleção de artigos, foi possível selecionar, a partir de uma amostra bruta de 1354 artigos, os 47 artigos mais relevantes que apresentam as alterações nas propriedades mecânicas, no comportamento reológico e na microestrutura de compósitos de cimento com adição de óxido de grafeno, bem como técnicas de dispersão utilizadas. Dessa forma, as principais conclusões, as lacunas atuais de pesquisa e as oportunidades de estudo foram sumarizadas, constituindo uma base de referência para orientar trabalhos futuros envolvendo o uso de óxido de grafeno para a preparação de compósitos de cimento.

Cement composites prepared with nanoparticles have been widely studied in order to achieve superior performance structures. The incorporation of carbon nanotubes (CNTs) is an excellent alternative due to their mechanical, electrical, and thermal properties. However, effective dispersion is essential to ensure strength gains. In the present work, cement pastes were prepared incorporating CNTs in proportions up to 0.10% by weight of cement, dispersed on the surface of anhydrous cement particles in isopropanol suspension and using ultrasonic agitation. Digital image correlation was employed to obtain basic mechanical parameters of three-point bending tests. The results indicated a 34% gain in compressive strength and 12% in flexural tensile strength gains, respectively, as well as a 70% gain in fracture energy and 14% in fracture toughness in the presence of 0.05% CNTs were recorded. These results suggest that CNTs act as crack propagation controllers. Moreover, CNT presence contributes to pore volume reduction, increases the density of cement pastes, and suggests that CNTs additionally act as nucleation sites of the cement hydration products. Scanning electron microscopy images indicate effective dispersion as a result of the methodology adopted, plus strong bonding between CNTs and the cement hydration product. Therefore, CNTs can be used to obtain more resistant and durable cement-based composites.

The mortar behavior depends on the rheological characteristics, and the interaction and proportion between its components, which can affect mechanical and durability properties, and also can generate pathologies. This work intends to study the mixed mortar’s mechanical and durability properties, according to effects of variation of constituent elements (cement, hydraulic lime and sand) through the simplex network method. Water consumption, entrained air, compressive strength, flexural tensile strength, pull off strength, elasticity modulus, water absorption index, porosity, density and cracks were evaluated. The results showed that the excessive cement content enhances some mechanical properties, however it reduces the durability because of cracks and detaching. The hydraulic lime and the aggregate in excess tend to reduce the pull off strength and the durability because of the powder behavior of the mortar. This study evidences that it is necessary to define the adequate components proportion focusing in pull of strength and durability indicators.

Ultra High Performance Concretes (UHPC) are known for exceptional mechanical and durability properties due to optimized particle packing and a denser microstructure. However, the very tight packing of particles resulting in a dense microstructure can be a cause of problems in UHPCs when exposed to higher temperatures. The low porosity delays the movement of water vapour inside de concrete and a layer of condensed water is created, preventing water to escape the microstructure and increasing internal pressure, that may result in explosive spalling. In this research, carbon nanotubes (CNTs) were introduced in UHPCs to assess their influence on the properties after exposition to high temperatures. Specimens were subjected to slow and fast heating rates and occurrence of spalling was investigated. Mechanical tests, such as compressive strength (before heating and after heating) and splitting tensile strength were conducted to investigate the impact of CNTs on the mechanical properties. Gas permeability tests were performed to investigate alterations in porosity due to the presence of CNTs. Results show that the presence of CNTs can reduce the occurrence of spalling at additions of 0.05% and 0.10% by weight of cement. CNTs can also increase the residual strength at temperatures up to 300 degrees C at a slow heating rate. At the same time, the 28-day compressive and splitting tensile strengths remained unaltered and oxygen permeability coefficients were reduced when CNTs were added to the matrix. (C) 2020 Elsevier Ltd. All rights reserved.

This paper explores the caracteristics, limitations and challenges of bacteria based self-healing concrete.A systematic review was carried out by selecting publications of the last ten years on the area.Under proper conditions, bacteria induce the precipitation of calcium carbonate, which is deposited inside the concrete pores, decreasing its porosity and increasing its compressive strength.Bacteria type and its nutrientes, directly affect the precipitated products.Ureolytic bacteria, of the genus Bacillus, are the most investigated type, due to their high resistance to alcaline media.Self-healing effect is higher at early ages concretes, dropping progressively over time.In order to avoid this, bacteria are encapsulated or immobilized by protective materials, which increases theirs life cycle inside concrete's alcaline medium.

O modal rodoviário é o principal sistema logístico do Brasil, sendo responsável pelo transporte de 60% de todas as cargas no território e 57% das rodovias brasileiras apresentam algum tipo de manifestação patológica, isso ocorre devido a projetos de design ruins, aumento imprevisto de cargas rodoviárias e falta de manutenção preventiva.Estudos recentes mostraram o potencial da adição de óxido de grafeno (GO) em revestimentos asfálticos

Carbon nanotubes (CNTs) can be incorporated into cement-based materials in order to nucleate hydration products, enhance mechanical behavior, control micro crack formation and reduce deformation. Given that, the present paper investigates the mechanical behavior of a cement paste system reinforced with 0.05% and 0.10% of CNTs dispersed in a non-aqueous media of isopropanol on the surface of cement particles. Even though compromising the consistency and affecting the setting time, if well dispersed and properly bonded to the cement hydration products, the CNTs can act as nucleation site of cement hydration products and improve the mechanical properties of a cement paste system. Three-point bending tests in notched specimens and direct tensile tests were carried out using the manufactured material. The presence of CNTs on the cement paste resulted in a 90% of gain in fracture energy, 46% of flexural strength, and 47% tensile strength with addition of up to 0.10% of CNTs. Through SEM observation it is possible to affirm that the dispersion process was effective and CNTs acted as nucleation sites of cement hydration products, allowing its use as a reinforcement material.