Using response surface analysis for the optimization of mechanical strength and microstructure of geopolymers with different SiO2/Al2O3 and SiO2/Na2O ratios

Mechanical Property and Microstructure of Fly Ash-Based Geopolymer Activated by Sodium Silicate

Effect of synthesis conditions on mechanical properties and microstructure of coal gasification slag-based geopolymer

Geopolymers have been considered a sustainable alternative to ordinary Portland cement (CEM I) for its lower embodied carbon and ability to make use of industrial by-products. Additionally, its excellent engineering properties of high strength, low permeability, good chemical resistance, and excellent fire resistance also strike a chord in the minds of researchers. The goal of this study is to clarify the effect of calcium sources on the mechanical properties and microstructures of the geopolymers. CEM I was chosen as the sole calcium source, while metakaolin was used as the source material. Five distinct geopolymers were prepared, having various ratio of CEM I: 0%, 5%, 10%, 20%, and 30%. The alkali-activator was a mixture of 12 M sodium hydroxide (NaOH) and sodium silicate (Na2SiO3), utilizing compressive strength and flexural strength to evaluate the changes of the geopolymers' mechanical properties. SEM, XRD, and FTIR were used to examine microscopic features, evaluate internal morphology, and analyze changes in components of the geopolymers containing different amounts of CEM I. The experimental results indicated that the optimal incorporation of CEM I was 5%. Under this dosage, the compressive strength and flexural strength of the geopolymers can reach 71.1 MPa and 6.75 MPa, respectively. With the incorporation of CEM I, the heat released by cement hydration can accelerate the geopolymerization reaction between silica-alumina materials and alkaline solutions. Additionally, the coexistence of N-A-S-H gel from components of an aluminosilicate mix and C-S-H gel from the CEM I promoted a more densified microstructure of the geopolymers and improved the geopolymer's strength. However, as the amount of CEM I in the mixture increased, the geopolymer matrix was unable to provide enough water for the CEM I to hydrate, which prevented excessive CEM I from forming hydration products, weakening the workability of the matrix and eventually hindering the development of geopolymer strength.

Effects of GBFS content and curing methods on the working performance and microstructure of ternary geopolymers based on high-content steel slag

Understanding the relationship between geopolymer composition, microstructure and mechanical properties

Esta pesquisa tem por objetivo apresentar o cenário atual da Construção Civil de alguns Estados brasileiros, demonstrando os locais que estabeleceram a parada do setor e os que continuaram a atuação normalmente, sendo feito uma comparação levando em consideração a densidade demográfica dos Estados e a maior e menor quantidade de óbitos até a data atual e também demonstrar as medidas adotas nos canteiros de obras para evitar a propagação da doença. O método de pesquisa foi realizado com base em dados coletados nas Secretarias Estaduais de Saúde e Sindicatos da Indústria da Construção (Sinduscon) dos Estados, de jornais e revistas de 8 Estados brasileiros sendo 4 que possuem menor quantidade de óbitos e 4 que possuem maiores quantidades de óbitos registrados. Foi gerando um valor, chamado índice “I” (Óbitos / Densidade Demográfica), desta forma foi possível entender o impacto que a indústria da Construção Civil pode trazer para a propagação da COVID-19, já que o setor Construção Civil movimenta os outros setores, como lojas de materiais de construção, distribuidoras, restaurantes, transportes públicos, entre outros. Verificou-se quais Estados o setor da Construção Civil está cumprindo com a paralisação do setor e comparar dados dos Estados que estão com os maiores índices desta doença, verificando se há alguma correlação para o aumento de casos confirmados. Os Estados que possuem maiores quantidade de óbitos foram SP > RJ > CE > PE, porém seus índices foram diferentes, relacionando-os com o controle ou descontrole da prevenção do vírus na construção civil e em outros setores, onde se comparados com índice “I” a sequência é SP > CE > PE > RJ, sendo I = 13,57 para São Paulo já Estados que possuem menores quantidades de óbitos foram TO < MS < MT < AC e seus comparativos por índice “I” continuam na mesma sequência, tendo o Tocantins com o menor índice entre todos os Estados, I = 0,53. Foram adotadas algumas medidas essenciais para evitar a propagação do coronavírus como o uso de termômetros na entrada do trabalho, marcação no piso para manter as pessoas distanciadas, distanciamento entre as mesas e retirada dos assentos intermediários, higienização de canteiros, distribuição de cartazes informativos pela obra, redefinição de turnos, entre outras medidas são bastante importantes pra o bem estar e saúde dos operários.

In this study, the effect of SiO2/Al2O3 (S/A), Na2O/Al2O3 (N/A) and H2O/Na2O (H/N) molar ratios on bending and compressive strength of geopolymer were investigated. The geopolymerization mechanism was also analyzed from microstructure difference by FTIR. The experimental results showed that compressive strength and bending strength of geopolymer has an opposite reaction under different critical molar ratios. The increase of S/A molar ratio and the decrease of N/A and H/N molar ratios have resulted in an increase of the compressive strength. However, it caused a noticeable decrease in bending strength. The microstructure of geopolymer indicated that the degree of polymerization and cohesion of geopolymer have systematical depending on these critical molar ratios, making the mechanical properties of geopolymer susceptible to different types of loads. This paper reveals the relationship between the microstructure of geopolymer and different mechanical properties and helps to selectively prepare corresponding geopolymer for different loading patterns.

Strength development and microstructure of sustainable geopolymers made from alkali-activated ground granulated blast-furnace slag, calcium carbide residue, and red mud

29Si and 27Al NMR study of the structural transformation of calcined kaolin residue-based geopolymer using low alkali activator content for sustainable construction materials

Thermal stability and microstructure of metakaolin-based geopolymer blended with rice husk ash

This paper experimentally studied the effects of different molybdenum tailings (MoT) content, standard curing and 60 °C water curing conditions on the compressive strength of fly ash-based geopolymers at different ages. X-ray diffraction (XRD), scanning electron microscopy/energy dispersive spectrometer (SEM/EDS) and Fourier-transform infrared spectroscopy (FTIR) were applied to investigate the effect of the content of MoT and different curing conditions on the reaction products, microstructure and chemical composition of fly ash-based geopolymers. The results show that MoT content and curing conditions have synergistic effects on the compressive strength of fly ash-based geopolymers. For standard curing, the increase in MoT content is detrimental to the development of compressive strength, and an obvious weak interfacial transition zone between MoT and the gel product is observed in specimen containing 40 wt% MoT; meanwhile, under water curing conditions, the compressive strength of geopolymers first increases and then decreases with the increase in MoT, and the 28-day compressive strength can reach 90.3 MPa when the content of MoT is 10 wt%. The SEM results show that the curing conditions have a great influence on the microstructure of the geopolymer matrix, and the microstructure of the specimens under the water curing conditions is smoother and denser, with fewer pores. EDS analyses show that the gel product constituting the geopolymer matrix is N(C)-A-S-H gel; MoT can participate in the reaction, and the mass ratio of Ca/(Si + Al) of N(C)-A-S-H gel increases with the increase in MoT, resulting in a decrease in compressive strength. In addition, the results of the FTIR confirm that water curing can increase the degree of crosslinks in the gel phase.

Despite the significant representativeness of the civil construction sector in the economy, construction and demolition waste (CDW) management is still a challenge in most Brazilian municipalities. In this context, the main objective of this work is to evaluate the potential application of reverse logistics (RL) principles in CDW management in the civil construction sector in the Brazilian city of Curitiba and to propose a conceptual model to help in the CDW management. In the first stage of the research, civil construction sector professionals pondered relevant criteria to make up the RL system by application of the Delphi method questionnaire and by analytic hierarchy process (AHP). In the second stage, a conceptual model was developed, highlighting the potential of applying RL precepts among agents in the civil construction sector production chain in Curitiba. The model proposed assists in understanding the flow of materials in the RL system and each service provider's responsibilities in carrying out construction related activities, including CDW management, in addition to compliance with legislation and minimisation of environmental impacts.

To maximize the utilization of red mud in geopolymers, a red mud–metakaolin (RM-MK) geopolymer and red mud–fly ash (RM-FA) geopolymer were prepared, respectively. The effects of red mud content on the compressive strength and microstructure of the geopolymers were investigated under three different curing conditions. The results showed that the strength of the geopolymer decreased linearly with an increase in the red mud content, whether curing at room temperature or 80 °C. Surprisingly, curing in an autoclave, the appropriate amount of red mud had a favorable impact on the mechanical properties of the geopolymers. When the amount of red mud was 50%, the strength of the RM-MK geopolymer reached its highest compressive strength, 36.3 MPa, and the strength of the RM-FA geopolymer reached its highest at 31.7 MPa. Compared with curing at low temperature, curing the red mud-based geopolymers under a higher temperature and higher pressure can maximize the use of red mud. XRD analysis indicated that zeolite minerals formed. The SEM results showed that the geopolymers cured in an autoclave had a dense structure.

The civil construction sector is under pressure to make construction processes more sustainable, that is, aligned with economic, social, and environmental sustainability. Thus, the research question considers: How do Industry 4.0 Technologies help civil construction face challenges and identify new opportunities to become sustainable? The general objective of this work is to offer a current overview of publications that associate the civil construction sector; Industry 4.0 Technologies and sustainability, and identify the challenges and opportunities of the Industry 4.0 Technologies set to contribute to sustainability achievement. The research method was a bibliographic review combined with bibliometric analysis in SCOPUS databases. The results show that civil construction faces the challenge of reducing the consumption of natural resources, ensuring safe work, and optimizing processes, especially handwork. However, the insertion of Industry 4.0 Technologies into civil construction has allowed sensors, robots, modelling and simulation systems, artificial intelligence, and drones to have their productivity, efficiency, safety, strategic and environmental management enhanced. Furthermore, Industry 4.0 Technologies can contribute to civil construction through innovative, sustainable, and technological solutions focused on the flow of work, which can provide growth through the balance of costs/benefits in the management of projects and works. Thus, it is expected that this article will contribute to discussions around the possibility of construction becoming sustainable with the support of Industry 4.0 Technologies.

Carbonates are primary minerals of the carbonatites and kamafugites sourced from Toro-Ankole geological region of the East African Rift system. Consequently, these materials are silica undersaturated. They are currently utilized as mineral additions in production of Portland pozzolana cements in Uganda. No published work exists to show how their unique composition might affect their pozzolanic performance and other concrete properties. This study investigated the effect of the carbonate minerals in the natural pozzolans and calcination on setting time, standard consistency, workability, soundness, early heat of hydration and strength development of blended cements. Two (2) samples, a carbonatite and a kamafugite sourced from deposits located in the Toro-Ankole geological region of the East African rift system were calcined in a furnace at 825 °C for one hour. The samples were then subjected to XRD analysis for mineralogical composition characterisation and to establish the effect of calcination at 825 °C on mineralogy. Setting time, standard consistency, workability, soundness and strength development were studied following standard procedures for testing blended Portland cements. Calcination led to a gain in compressive strength for both test pozzolans, the kamafugites showing a higher gain in strength than the carbonatite. The higher gain in pozzolanic performance for the kamafugites is likely due to kaolinite, a secondary mineral in the test pozzolan whose pozzolanic reactivity is activated by thermal destabilization. Calcination also led to pacification of the early age properties of cements blended with test carbonatites and kamafugites. The study reveals the carbonate minerals in the test pozzolans as a considered factor in accelerating early hydration of Portland cement. Hydration progression of Portland cement controls the important properties of fresh concrete (workability, setting and paste microstructure), which in turn directly impacts on the strength and durability properties of hardened concrete. Cements blended with carbonate bearing natural pozzolans therefore present interesting perspectives on how paste microstructure composition and durability performance properties might be impacted.