The corrosion behavior of Mg, AZ31 and AZ91 has been evaluated in 3.5% NaCl solution using weight loss, electrochemical polarization and impedance measurements. Corrosion rate derived from the weight losses demonstrated the occurrence of steeply fast corrosion reaction on AZ91 alloy after three hours of immersion, indicating the start of galvanic corrosion. An increase of corrosion rate with immersion time was also observed for AZ31 but with lesser extent than AZ91 alloy. Whereas Mg metals showed a decrease of corrosion rate with immersion time, suggesting the formation of a protective layer on their surfaces. In contrast, the corrosion current density (I corr ) derived from the Tafel plots, exhibited their corrosion resistances in order of Mg > AZ91 > AZ31. Electrochemical charge transfer resistance (R ct ) and double layer capacitance measured by electrochemical impedance spectroscopy (EIS), are well in accordance with the measured I corr. EIS measurements with time and microstructural examination of the corroded and uncorroded samples are helpful in elucidation of results measured by electrochemical polarization.

In this study, the effect of nano-silica (NS) and silica fume (SF) on workability, setting time, compressive strength and microstructural properties of fly ash-ground granulated blast furnace slag (FA-GGBFS) based geopolymer concrete (GPC) is investigated. Five mixtures of each containing 0.5%, 1.0%, 1.5%, 2.0% and 2.5% NS and SF are prepared for this investigation. The optimum GPC mixture with NS resulted in compressive strength of 63 MPa and the SF modified GPC achieved a compressive strength of 59.59 MPa after 28 days of outdoor temperature curing (Avg. temp. 31.4 ). The hardened concrete samples are analyzed through X-ray diffraction (XRD), X-ray fluorescence (XRF), field emission scanning electron microscope (FESEM), Fourier transform infrared spectroscopy (FTIR), and petrographic examination, for the better understanding of geopolymer mineralogy, mechanism and microstructure. Results indicate that both NS and SF facilitated a higher degree of geopolymerization, leading to the densification of the geopolymer matrix which led to the improvement of the properties of FA-GGBFS based GPC.

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In the last few decades, the demand for cement production increased and caused a massive ecological issue by emitting 8% of the global CO2, as the making of 1 ton of ordinary Portland cement (OPC) emits almost a single ton of CO2. Significant air pollution and damage to human health are associated with the construction and cement industries. Consequently, environmentalists and governments have ordered to strongly control emission rates by using other ecofriendly supplemental cementing materials. Rice husk is a cultivated by-product material, obtained from the rice plant in enormous quantities. With no beneficial use, it is an organic waste material that causes dumping issues. Rice husk has a high silica content that makes it appropriate for use in OPC; burning it generates a high pozzolanic reactive rice husk ash (RHA) for renewable cement-based recyclable material. Using cost-effective and commonly obtainable RHA as mineral fillers in concrete brings plentiful advantages to the technical characteristics of concrete and to ensure a clean environment. With RHA, concrete composites that are robust, highly resistant to aggressive environments, sustainable and economically feasible can be produced. However, the production of sustainable and greener concrete composites also has become a key concern in the construction industries internationally. This article reviews the source, clean production, pozzolanic activity and chemical composition of RHA. This literature review also provides critical reviews on the properties, hardening conditions and behaviors of RHA-based concrete composites, in addition to summarizing the research recent findings, to ultimately produce complete insights into the possible applications of RHA as raw building materials for producing greener concrete composites—all towards industrializing ecofriendly buildings.

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