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The study of alkali-activated materials as a replacement for portland cement has been growing in recent years due to the sustainable nature of these materials. Nevertheless, ternary alkali-activated pastes using waste glass as a precursor have been insufficiently studied concerning their rheological, mechanical, and microstructural properties. In addition, there is a lack of research studying alkali-activated mixtures using basic oxygen furnace (BOF) slag and glass waste as precursors. Therefore, this paper aims to study the effect of glass powder (GP) content as a precursor, the effect of the activator ratio in alkali-activated ternary pastes of BOF slag, metakaolin (MK), and GP, and the influence of the Na2SiO3/NaOH ratio on its mixtures. The activator solutions of NaOH and Na2SiO3/NaOH were used in the production of the pastes. The liquid/solid ratio was kept fixed at 0.6 and the molarity of the NaOH solution was fixed at 12 M, seeking to analyze the impact of the Na2SiO3/NaOH ratio, with adopted values of 0.75, 1.5, and 2.5. We also aimed to study the impact of the glass content in the mixture for the values of 10%, 20%, and 25%, replacing the BOF slag. The workability by the minislump test, rheology, compressive strength for 1 and 28 days, and microstructural parameters were analyzed. ANOVA was performed to determine the significance of variables in the workability and compressive strength parameters. Pastes with the highest activator ratio (Na2SiO3/NaOH=2.5) produced better compressive strength (34.74 to 36.11 MPa) and lower minislump spreads (90 to 98 mm) compared with the mixtures with Na2SiO3/NaOH=1.5 and 0.75, besides indicating a denser microstructure, linked to higher production of aluminosilicate gels. Higher GP contents generated pastes with lower mechanical performance (16.7 MPa for Na2SiO3/NaOH=0.75) and microstructural qualities, albeit with better workability (124-mm minislump spread). [ABSTRACT FROM AUTHOR]

This paper presents the influence of ceramic waste powder (CWP) inclusion on the physico-mechanical properties and microstructure analysis of alkali-activated pastes prior and after exposure to elevated temperatures. Such geopolymer specimens were designed upon replacing ground granulated blast-furnace slag (GGBFS) with CWP at ratios of 0%, 5%, 10%, 15% and 20%, by mass. The water absorption and compressive strength (wet and dry) of non-exposed samples were determined at curing ages of 1, 7, 14 and 28 days. After that, the specimens were exposed to high temperatures of 200, 400, 600 and 1000 °C with a heating rate of 5 °C/min. The characteristics of tested samples such as visual inspection, residual compressive strength and microstructure were evaluated. Techniques as Fourier Transform Infrared spectroscopy (FTIR), Thermogravimetric Analysis (TGA/DTG) and Scanning Electron Microscopy (SEM) were used for studying molecular and microstructure of geopolymer composite. Results indicated that the inclusion of CWP with slag in composite structure based geopolymer enhanced the physico-mechanical properties and microstructure of mixtures before and after thermal exposure. The specimens made of 15% CWP displayed superior thermal stability in terms of remaining compressive strength and microstructure than the reference ones. [ABSTRACT FROM AUTHOR]

In the current investigation, pozzocrete fly ash (PFA) was employed to assess its effects on physical, mechanical and radiation shielding properties of alkali-activated geopolymer mixtures prepared using calcined concrete waste-based dolomite aggregate (DCW). Two series of geopolymer samples comprising 6% and 10% sodium hydroxide as alkaline activator were designed. Concrete waste was partially substituted by PFA at levels of 0%, 10%, 15%, 20% and 30%, by weight. Bulk density, compressive strength, attenuation coefficients (μ & μ m) as well gamma transmission factors (half-value layer, HVL; tenth-value layer, TVL and mean free path, MFP) of studied samples were determined at different hydration times. The gamma attenuation coefficients of the blend were experimentally conducted with NaI (Tl) scintillation detector utilizing radiation sources namely Cs-137 with photon energy of 0.662 MeV and Co-60 with photon energies of 1.173 and 1.333 MeV. The inclusion of 15% PFA in DCW-geopolymer system alkali-activated with 10% NH has resulted in the enhancement of both physical and mechanical properties. In a similar fashion, this geopolymer composite demonstrated superior performance in terms of attenuation of gamma rays through a 5 cm thickness shield over the corresponding mixtures. [Display omitted] • Assessing the impact of PFA on physico-mechanical properties of DCW paste-based geopolymer. • Assessing the performance of DCW-PFA composite geopolymer against gamma-radiation. • Exploring new and low-cost geopolymer for gamma-ray attenuation via 5 cm thickness shield. • Mixture with 15% PFA exhibited superior resistance against gamma radiation at different photon energies. [ABSTRACT FROM AUTHOR]

The engineering properties of alkali activated materials (AAMs) mainly depend on the constituent materials and their mixture proportions. Despite many studies on the characterization of AAMs, guidelines for mixture design of AAMs and their applications in engineering practice are not available. Extensive experimental studies are still necessary for the investigation of the role of different constituents on the properties of AAMs. This paper focuses on the development of alkali-activated fly ash (FA) and ground granulated blast furnace slag (GBFS) paste mixtures in order to determine their suitability for making concretes. In particular, the influence of the GBFS/FA ratio and liquid-to-binder (l/b) ratio on the slump, setting, strength, and autogenous shrinkage of the alkali activated pastes is studied.It is shown that fresh properties largely depend on the type of precursor (GBFS or FA). The slump and setting time of GBFS-rich pastes was significantly reduced. These pastes also have higher compressive strength than FA-rich pastes. The study identifies important practical challenges for application of the studied mixtures, such as the behavior of their flexural strength and high amplitudes of autogenous shrinkage of GBFS-rich mixtures. Finally, the optimum GBFS/FA ratio for their future use in concretes is recommended. [ABSTRACT FROM AUTHOR]