Geopolymer is an attractive construction binder owing to its ability to improve the properties of the concrete and preserves the environment from the high CO2 emission. Geopolymer technology will convert the potential hazardous industrial waste such as fly ash into valuable construction materials. However, there is a need of studying the properties of iron-based geopolymer in order to enhance the fundamental and knowledge of the geopolymer research also development in this study area. Fly ash which contains a significant amount of iron oxide (Fe2O3) was used as a precursor and tested at different curing duration (1, 3, 7, 14 and 28 days). Crystallization of iron oxide (Fe2O3) contained in the fly ash under geopolymerization process will be able to turn waste fly ash into a strong concrete materials, simultaneously creating a waste-to-wealth economy. Furthermore, the formation of fayalite detected from the microstructure characterization is mainly contribute to the strength development of the fly ash after 28 days curing.
This investigative study aims to study the mechanical and morphological properties of fly ash (FA)-based geopolymer paste as a repair material when applied on ordinary Portland cement (OPC) overlay concrete. The first part of this study investigates the optimal mix design of FA-based geopolymer paste with various NaOH concentrations of 8, 10, 12, and 14 M, which were used later as a repair material. The second part studies the bonding strength using a slant shear test between the geopolymer repair material and OPC substrate concrete. The results showed that a shorter setting time corresponds to the higher NaOH molarity, within the range of 53 and 30 min at 8 and 14 M, respectively. The compressive strength of FA-based geopolymer paste was found to reach 92.5 MPa at 60 days. Also, from the slant shear test results, prism specimens with 125 mm length and 50 mm wide have a large bond strength of 11 MPa at 12 M. The scanning electron microscopy/energy-dispersive X-ray (SEM/EDX) analysis showed that the OPC substrate has a significant effect on slant shear bond strength, where the presence of free cations of Ca2+ on the OPC substrate surface contributed to the formation of calcium alumina-silicate hydrate gel (C-A-S-H) by building various cross-links of Ca-O-Si.
In recent years, research and development of geopolymers has gained significant interest in the fields of repairs and restoration. This paper investigates the application of a geopolymer as a repair material by implementation of high-calcium fly ash (FA) as a main precursor, activated by a sodium hydroxide and sodium silicate solution. Three methods of concrete substrate surface preparation were cast and patched: as-cast against ordinary Portland cement concrete (OPCC), with drilled holes, wire-brushed, and left as-cast against the OPCC grade 30. This study indicated that FA-based geopolymer repair materials (GRMs) possessed very high bonding strength at early stages and that the behavior was not affected significantly by high surface treatment roughness. In addition, the investigations using scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX) spectroscopy have revealed that the geopolymer repair material became chemically bonded to the OPC concrete substrate, due to the formation of a C–A–S–H gel. Fundamentally, the geopolymer network is composed of tetrahedral anions (SiO4)4− and (AlO4)5− sharing the oxygen, which requires positive ions such as Na+, K+, Li+, Ca2+, Na+, Ba2+, NH4+, and H3O+. The availability of calcium hydroxide (Ca(OH)2) at the surface of the OPCC substrate, which was rich in calcium ions (Ca2+), reacted with the geopolymer; this compensated the electron vacancies of the framework cavities at the bonding zone between the GRM and the OPCC substrate.
Geopolymerization consists of several chemical reactions that has been reported widely as an exothermic reaction. Previous studies on heat released during geopolymerization used metakaolin and fly ash of F class as a precursor for geopolymer. Meanwhile, in this study, fly ash of C class is used and a preliminary study has been conducted on determining the exothermic reaction of the geopolymerization with various ratios of solid-to-liquid ranging from 1.5 to 2.5. The amount of heat released was determined by using Differential Scanning Calorimeter. It was proven that different solid-to-liquid ratio affected the amount of heat released during geopolymerization as the highest amount of the heat released were recorded at the optimum solid-to-liquid ratio of 2.0.
Dolomite is a carbonate mineral in nature. Dolomite (CaMg(CO3)2) is an anhydrous carbonate mineral composed of calcium, magnesium, and carbonate. The word dolomite is also used to describe the sedimentary carbonate rock, which is composed predominantly of the mineral dolomite (also known as dolostone). Dolomite had been one of the frequent used materials in most of researches due to its accessibility to acquire and the properties. The composition of Ca and Mg became one of the main attractions for the usage of this natural mineral. One of the main properties needed to be studied when using any materials is morphology of the martial. Morphology analysis can give much valuable information about the surface topography and composition of the sample. Other than that, detailed three-dimensional and topographical imaging can also be obtained. This can helps the researches to finds the core value or the novelty in their study. Thus, reviews for the morphology analysis of dolomite were done to investigate how the structures of dolomite develop for certain study and usage. Besides that, dolomite as an addition into certain materials were reviewed and compared to observe the interactions and changes happened.
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