Silica gel made of natural waste materials of sugarcane bagasse has initiated a new trend in pozzolanic area. The employment of eco-friendly approach by using low concentration acids and natural drying via solar heat-based equipment in the pre-treatment process were projected to minimize the energy consumption in producing silica ash. Conversion of ultrafine silica ash from sugarcane bagasse into silica gel was conducted by-using a modified hydrothermal method. NaOH and HCI solution were employed in the dissolution and gelification of soluble silica. Analysis on the effect of silica gel in cementitious system was evaluated by including it in mortar specimen as a pozzolan to replace certain portions of Portland cement. Inclusion of additional siliceous gel showed enhancement in the cement hydration process, which resulted in early hardening and the consolidated formation of cement matrix to further contribute in the strength development. Measurement of pozzolanic reactivity of silica gel via Chapelle method verified the active consumption of Ca(OH)2 by the soluble silica, which illustrates the possible formation of secondary calcium silicate hydrate (C-S-H) from the pozzolanic reaction. Densi- fication of pore structure via large voids was observed via porosity test at age of 7 and 28 days. Based on the experimental result of this study, silica gel has presented an encouraging prospect to be used as a cement replacement material. Its rapid reaction during the early age would be beneficial in providing early strength properties to the cement-based product.
eco-friendly, pozzolanic materials, sugarcane bagasse, silica.
 United Nations Environment Programme. Focal Areas, Waste Agricultural Biomass, 2015.
 Rocha, G.J.M., Nascimento, V.M., da Silva, V.F.N., Corso, D.L.S. & Gonçalves, A.R., Contributing to the environmental sustainability of the second generation ethanol pro- duction: delignification of sugarcane bagasse with sodium hydroxide recycling. Indus- trial Crops and Products, 59, pp. 63–68, 2014. http://dx.doi.org/10.1016/j.indcrop.2014.05.002
 Rukzon, S. & Chindaprasirt, P., Utilization of bagasse ash in high-strength concrete. Materials & Design, 34, pp. 45–50, 2012. http://dx.doi.org/10.1016/j.matdes.2011.07.045
 Singh, K.J. & All Jawald, S.M., Utilization of sugarcane bagasse ash (SCBA) as pozzolanic material in concrete. A Review. IJBSTR, 1, pp. 42–44, 2013.
 Turgut, P., Manufacturing of building bricks without Portland cement. Journal of Cleaner Production, 37, pp. 361–367, 2012. http://dx.doi.org/10.1016/j.jclepro.2012.07.047
 Kanraj, D., Baharudeen, A., Dev, V.G. & Santhanam, M., Performance evaluation of sugarcane bagasse ash blended cement in concrete. Cement and Concrete Composites, 59, pp. 77–88, 2015. http://dx.doi.org/10.1016/j.cemconcomp.2015.03.004
 Shafig, N., Hussein, A.A.E., Nuruddin, M.F. & Memon, F.A., Compressive strength and microstructure of sugarcane bagasse ash in concrete. Journal of Applied Sciences, Engineering and Technology, 7(12), pp. 2569–2577, 2014.
 Toledo Filho, R.D., Cordeiro, G.C., Tavarse, L.M. & Fairbairn, E.M., Ultrafine grinding of sugarcane bagasse ash for application as pozzolanic admixture in concrete. Cement and Concrete Research, 39(2), pp. 110–115, 2009. http://dx.doi.org/10.1016/j.cemconres.2008.11.005
 Sales, A. & Lima, S.A., Use of Brazilian sugarcane bagasse ash in concrete as sand replacement. Waste Management, 30(6), pp. 1114–1122, 2010. http://dx.doi.org/10.1016/j.wasman.2010.01.026
 Riding, K.A. & Ataie, F.F., Impact of pretreatments and enzymatic hydrolysis on agri- cultural residue ash suitability for concrete. Construction and Building Materials, 58, pp. 25–30, 2014. http://dx.doi.org/10.1016/j.conbuildmat.2014.01.099
 Wyman, C.E. & Jacobsen, S.E., Cellulose and hemicellulose hydrolysis models for application to current and novel pretreatment processes. Applied Biochemical Biotech- nology, 84, pp. 81–96, 2000.
 Johar, N., Ahmad, I. & Dufresne, A., Extraction, preparation and characterization of cellulose fibres and nanocrystals from rice husk. Industrial Crops and Products, 37(1), pp. 93–99, 2012. http://dx.doi.org/10.1016/j.indcrop.2011.12.016
 Setyawan, H., Muljani, S., Wibawa, G. & Altway, A., A facile method for the produc- tion of high-surface-area mesoporous silica gels from geothermal sludge. Advanced Powder Technology, 25(5), pp. 1593–1599, 2014. http://dx.doi.org/10.1016/j.apt.2014.05.012
 Embong, R., Shafiq, N., Kusbiantoro, A. & Nuruddin, M.F., Effectiveness of low concentration acid and solar drying as pre-treatment features for producing pozzolanic sugarcane bagasse ash. Journal of Cleaner Production, 112, pp. 953–962, 2016. http://dx.doi.org/10.1016/j.jclepro.2015.09.066
 Hwang, C.L., The Use of Rice Husk Ash in Concrete. Waste Materials Used in Concrete Manufacturing, ed. S. Chandra, Noyes Publication: USA, p. 198, 1997.
 Govindarajan, D. & Jayalakshmi, G., XRD, FTIR and Microstructure studies of cal- cined sugarcane bagasse ash. Advances in Applied Science Research, 2(3), pp. 544–549, 2011.
 Lima, S.P.B.D., Vasconcelos, R.P.D., Paiva, O.A., Cordeiro, G.C., Chaves, M.R.D.M., Toledo Filho, R.D. & Fairbairn, E.D.M.R., Production of silica gel from residual rice husk ash. Journal of Quimica Nova, 34(1), pp. 71–75, 2011. http://dx.doi.org/10.1590/S0100-40422011000100014