CHARACTERISTICS OF REACTIVE POWDER CONCRETE PRODUCED WITH LOCALLY SOURCED UNREFINED METAKAOLIN AND GEAR INNER WIRE

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Department of Environmental Design

ABSTRACT
With the soaring need to use innovative and sustainable materials in the construction industry, a new concrete known as Reactive Powder Concrete (RPC) is currently a material of significant interest globally. The concrete has cement, silica fume, fine sand, quartz sand and fibre as its ingredients. However, silica fume and fibre are relatively expensive in Nigeria due to their non-availability. This research evaluated the properties of RPC produced with unrefined Metakaolin (MK) as substitute to silica fume and Gear Inner Wire (GIW) as fibre. Reactive powder concrete specimens produced with up to 30% MK by weight of cement, and a constant GIW content of 0.25% by weight of concrete were subjected to compressive strength (50mmx50mmx50mm), tensile strength (100mmx50mm) and flexural strength (50mmx50mmx160mm) tests (at 27oC) at 7, 14, 28, 90 and 180 days of curing. Residual compressive strength, ultrasonic pulse velocities of the RPC samples after heating to temperature of 200 oC, 400 oC, 600 oC and 800oC for 2 hours were also assessed. In addition, X-ray diffraction, Fourier transform infrared spectroscopy and scanning electron microscopy analysis were undertaken to examine the microstructure of the specimens. Similarly, RPC produced with 20% silica fume as control was tested. Mathematical models were developed using DataFit software. Results showed that unrefined MK of up to 20% by weight of cement can be used to produce RPC with 72.5 N/mm2 compressive strength and 0.25% GIW by weight of concrete can be used to produce RPC with tensile strength and flexural strength of 7.1 N/mm2 and 22.3 N/mm2 respectively. Reactive powder concrete with 20% MK performed better than other samples (10% MK & 30% MK) in terms of residual strength, absorption and ultrasonic pulse velocity (UPV) when exposed to elevated temperatures. It was found that at higher temperature of 800oC, all RPC specimens experienced drastic reduction in strength but 20% MK and 30% MK showed relatively better strength retention capacity as substantiated by the XRD results compared to the 20% SF and 10% MK specimens. It was recommended that unrefined metakaolin and gear inner wires can be used in the production of RPC. Models developed can be used to predict the compressive strength, flexural strength and water absorption capacity of RPC produced with unrefined MK and GIW.