Abstract:
The ban on asbestos-cement roofing sheets in many countries due to the associated health hazards of asbestos fibre resulted in the search for alternative fibres. Environmental concerns about CO2 emissions in cement manufacturing have also necessitated research on cement admixtures and CO2 utilisation. However, limited information exists on the properties and curing of natural fibre-reinforced cement composite tiles cured in CO2 in Nigeria. This study was conducted to investigate the behaviour of coconut husk fibre-reinforced composite tiles produced with selected cement admixtures cured in two CO2 media.
Coconut husk was shredded,chopped and screened into random fibre lengths of 0.5–1.9mm. Chicken Egg Shell Ash (CESA) and Rice Husk Ash (RHA), produced by incineration in accordance with standardprocedures, and Calcium Carbide Waste (CCW) were used as partial replacements for cement. Thermal-Degradation-Temperatures (TDT) of coconut husk fibre, CESA, RHA and CCW were determined using standard procedure. For flat (30x20x0.6cm3) and corrugated (40x30x0.6cm3) tile production, cement was partially replaced with 10%RHA, 10%CESA, 5%CCW, 15%RHA+15%CESA, 15%CCW+15%CESA and7.5%RHA+7.5%CCW+15%CESA,respectively based on preliminary tests. Coconut fibre content (4% w/w), water/cement ratio (0.4) and cement/sand ratio (1:2) were constant.Five replicate samples were used. Curing was done inwet and dry CO2 chambers. Density, Moisture Content (MC), Water Absorption (WA), Moduli of Elasticity and Rupture (MOE, MOR) and Thermal Conductivity (TC) of the samples were determined using standard methods. Composite microstructure was examined under Scanning Election Microscope (SEM). Flat and corrugated tiles installed on roof frames for natural weathering test in Ibadan were continuously monitored for 720 days spanning dry and wet seasons. Post-installation densities were determined. Data were analysed using descriptive and inferential statistics, and ANOVA at α0.05.
The TDTs of coconut husk fibre, CESA and CCW were150, 400 and 450oC, respectively, while RHA exhibited no thermal degradation. Tile density ranged between 1.8g/cm3 (10% RHA) and 2.0g/cm3(15%RHA+15%CESA). Moisture content (6.8–11.0%) correlated positively with the density (R2=0.95-0.99).The WA values (7.5-8.8%) were relatively low. The MOE (1.5-2.8 GPa) and MOR (1.42-5.01MPa) of samples cured in wet CO2 were significantly lower compared to samples cured in dry CO2 (MOE: 12.9-29.5 GPa; MOR: 7.6-12.9 MPa). The 15%CCW+15%CESA composites cured in dry CO2 had the highest MOE and MOR. Density correlated positively with MOE (R2=0.85-0.98). Cement admixture and curing methods had significant effects on WA, MOE and MOR. Thermal conductivity ranged from 1.1 to 1.5 W/mK. The images revealed denser pores in fibre-matrix composites cured in wet CO2 than those cured in dry CO2, an indication of a stronger fibre-matrix interaction largely responsible for the superior performance of the 15%CCW+15%CESA cured in dry CO2. Weathering resulted in reduction in density largely attributable to leaching which was more pronounced in corrugatedthan flattiles.
A mixture of cement, egg shell ash and calcium carbide waste reinforced with coconut husk-fibre, cured in dry CO2exhibited a strong fibre-matrix interaction and performed best as a roofing tile. Flat tiles exhibited better weathering resistance than corrugated tiles.
