Ash blended cement composites: Eco-friendly and sustainable option for utilization of corncob ash

Abstract

Corncob, byproduct of maize crop, is one of the biomass from agricultural waste that is being used as energy source since it has significant energy content. After being burnt, the ash is disposed to landfill sites or ash ponds, locking the useful land. Moreover, corncob ash (CCA) is rich in silica and can be used as pozzolan but this characteristic is linked with temperature and grinding conditions. Hence, we aimed at evaluating the most favorable conditions of incineration and grinding to determine the pozzolanic activity of CCA. At first, the open burnt ash was sieved through #50 and #12 sieves (ashes retained on #12, #50 and pan were denoted as R12, R50 and R00 respectively) to find incineration requirement. It was found that R00 ash having smaller particle size could directly be used as pozzolan whereas R12 and R50 ashes having larger particle sizes needed further incineration. Thereafter, the research was divided into four phases to find optimum incineration (temperature and time) and grinding conditions. In Phase I, R12 ash was incinerated at 400 °C, 500 °C, 600 °C, 700 °C and 800 °C for 2 h to find the optimum incineration temperature. Best results for Chapelle activity (438 mg/g), CaO reduction in Frattini (82.8%) and Pozzolanic activity index (PAI) (97.3%) obtained at 500 °C signified it as optimum incineration temperature. In Phase II, R50 ash was incinerated at optimum temperature i.e. 500 °C for different time intervals (15, 30, 60 and 120 min) to find optimum incineration time and possibly reduce energy requirement. Test results showed that incineration time of 30 min was optimum and hence in comparison to larger particle size (R12 sample), ash having smaller particle size (R50 sample) require less time to achieve required pozzolanic activity. In Phase III, all three sieved ashes (R12, R00 and R50) incinerated at optimum conditions were mixed (to make use of entire corncob ash) and it was found to possess adequate PAI (80.3%). Based on above three phases, it can be concluded that R00 ash as obtained from sieving, R12 ash incinerated at 500 °C for 2 h and R50 ash incinerated at 500 °C for 30 min, provided good results mutually as well as independently. Finally, in Phase IV, the optimum grinding time was determined by grinding ash for 30, 60, 120 and 240 min. Test results showed that the surface area increased with the increase in grinding duration. However, keeping in mind that grinding is energy intensive process, 60 min of grinding showing specific surface area of 4220 cm2/gm, Chapelle activity of 511.05 mg/g and 28 days PAI of 77.6%, was selected as optimum. Thus, corncob ash after optimum conditions of incineration and grinding can successfully be used in cement based composites. Moreover, it would address sustainability issues of ash disposal and natural resources depletion by reducing the amount of cement production.