Cement production is one of the most important industries on the planet, and humans have relied on is use dating back to the dawn of civilization. Cement manufacturing has increased at an exponential rate, reaching 3 billion metric tons in 2015, representing a 6.3% annual growth rate and accounting for around 5–8% of global carbon dioxide (CO₂) emissions. Geopolymer materials, which are inorganic polymers made from a wide range of aluminosilicate powders, such as metakaolin, fly ash, and blast furnace or steel slags, have also been elicited for use due to concerns about the high energy consumption and CO₂ emissions connected with cement and concrete manufacturing. This study focused on the mechanical and durability properties of metakaolin in concrete production. X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive spectroscopy (EDS) analyses were used to confirm the characteristics of kaolin and metakaolin. The results showed that 15 wt.% metakaolin can be used to partially replace cement, and that metakaolin, when synthesized with alkaline activators, can also be utilized as a geopolymer to totally replace cement in concrete production. For predicting the compressive strength of different concrete mixtures, few practical models have been presented. This research has shed light on the possibility of utilizing ecologically friendly materials in the building, construction, and transportation sectors to decrease carbon dioxide emissions.

Carbon fibers (CFs) are made mostly from a non-environmentally friendly polyacrylonitrile (PAN) and little from rayon. PAN-based CFs, require huge amount of energy for its production aside its contributions to the global CO₂ emission. Therefore, there is recourse to a more environmentally friendly sources of CFs biomass. Recently lignin has been recognized as a potential renewable raw material for carbon fibers to replace PAN-based. The magnitude and quality of CO₂ emission of lignin-based CFs are dependent on the processing route. On this premise; this review examines the various lignin-based CFs processing route adopted by researcher in the recent past to establish the most viable route with minimum carbon footprint emission. Outcome of the review shows that the major advantages of aromatic polymer (AP) generated precursor over PAN is the presence of higher quantity of guaiacyl units and oxygen content which makes the stabilization phase efficient and faster requiring less energy. Though there are several methods and options for the various stages of conversion of lignocellulosic biomass into CFs as highlighted in the study, establishing an optimum processing route will be a trade-off amongst various issues of concern; carcinogenic risk, carbon footprint emission, CFs Yield and mechanical strength of the CFs. Inferences from the study shows that the L-CF significantly produced reduced climatic impact in terms of CO₂ emission.

Microstructural characterisation, physical and chemical properties of rice husk ash as viable Pozzolan in building material: a case study of some Nigerian grown rice varieties

The incorporation of pozzolanic materials in concrete construction is progressively increasing. This is due to technological advancement and climate change problems associated with carbon emissions resulting from the large-scale manufacturing of cement and its usage for concrete production. In this study, metakaolin obtained was used to partially substitute cement in metakaolin-concrete. Calcination temperatures of kaolin were varied from 500°C to 800°C at an interval of 100°C for 60 minutes. The metakaolin obtained was used to partially replace cement at 0, 5, 10, 15, 20 and 25 % by weight using a mix ratio of 1:2:4 and 0.4 water-cement ratio. Compressive strength test was carried out at curing ages of 7, 28 and 90 days, while the flexural strength test was performed at curing ages of 28 and 90 days. For both compressive and flexural strengths, 15 % by weight replacement with metakaolin gave the best strength values at all temperatures. An Increase in temperature led to a significant increase in the strength of metakaolin-concrete. ANOVA showed all factors significantly affected the flexural strength (P < 0.1), whilst the calcination temperature was significant (P < 0.1) to the compressive strength. This study showed that metakaolin is a supplementary cementitious material (SCM) and is a potential alternative to cement and can be used in the construction industry. Also, the calcination temperature of kaolin has a significant effect on the properties of the resulting metakaolin-concrete produced from it.

The use of cement contributes to global CO2 emission and this leads to the depletion of ozone layer,causing global warming. The quest to reduce or eliminate this problem has resulted in the discovery of metakaolin-based geopolymer as an alternative to the use of cement in construction work. In this study, metakaolin obtainedas a result of kaolin calcination from some deposits in Nigeria; Ogun (Imeko), Edo (Okpela), Ondo (Ifon)and Ekiti (Isan-Ekiti) were characterized and used to determine the compressive and flexural strength of metakaolin-based geopolymer concrete (Mk-GPC). Cubes of 150 × 150 × 150 mm were used for the compressive strengthtest and reinforced concrete beams of size 150 × 250 × 2160 mm were produced to test for flexural strength. A water-absorption test was also carried out on Mk-GPC and the effect of ball-milling was assessed on the strengthproperties. The results from the various tests showed that 800°C for 1 hour of calcination of kaolin gives bestcombination of performance properties due to the presence of amorphous silica in metakaolin. Mk-GPC gavehigher compressive strength and at an early age than ordinary Portland cement (OPC) concrete. The water absorptioncapacities of Mk-GPC were higher than the control samples. In the flexural strength test, the reinforcedbeams failed in flexural-shear mode and the shear capacities at 28-, 56- and 90-day curing age of the beams werebetween 0.656 and 0.938 MPa for Mk-GPC beams and between 0.563 and 0.844 MPa for the control beams. Themoment capacities for the beams were between 19.25 and 33.25 (×10³ kgm²/s²) for Mk-GPC beams and were between22.75 and 28.0 (×10³ kgm²/s²) for the control beams. The study has revealed that metakaolin-based geopolymercan serve as an alternative to cement for sustainable construction in the Nigerian construction industry.