Evaluation of green cement paste from geopolymer using coal fly ash, coal bottom ash and rice husk ash as alumino-silicate resource

• Main Author: Sumabat, Ana Karmela
• Format: text
• Language: English
• Published: Animo Repository 2016
• Subjects: Cement; Portland cement; Chemical Engineering
• Online Access: https://animorepository.dlsu.edu.ph/etd_masteral/5129
• Institution: De La Salle University

The increasing consumption of construction materials brought about by industrial and economic development has led to higher Ordinary Portland Cement (OPC) demand. The environmental consequence of this increase in demand has resulted in the emission of high volumes of greenhouse gases (GHG). Geopolymer synthesis is one mitigating action for decreasing global GHG emissions from OPC production as it is reported to have lower carbon footprint while utilizing industrial waste as raw materials. This study evaluates the potential of ternary blend geopolymer derived from coal fly ash (CFA), coal bottom ash (CBA) and rice husk ash (RHA) as a green alternative binder for concrete. Binder components, CFA, CBA and RHA were investigated as potential components for alkaline-activated geopolymer. The alkaline activator considered in this study is a mix of sodium hydroxide (NaOH) and water glass (WG) solution. The particle size, mass ratio of sodium silicate to sodium hydroxide solution (WG:NaOH), liquid:solid ratio and interaction between WG:NaOH, and liquid to solid ratio are process conditions identified as significant using Definitive Screening Design (DSD). Process conditions were fixed based on the results of DSD (WG:NaOH=0.3 liquid:solid ratio=0.6 particle size < 150um ) and used as process parameters for the statistical mix design. Response surface methodology, used for mix design optimization resulted in the optimized compressive strength of 13.19 MPa, volumetric weight of 1975 kg/m3 and water absorption of 1715 g/m3. Validation run for the geopolymer cement paste resulted in 12.45±0.53 MPa at 28 days curing. There is a difference of 12.19% between the regression model-generated value at an optimal mix formulation of 50% CBA and 50% CFA. Meanwhile, actual volumetric weight of the cement paste is 1231± 98.1 kg/m3 with an error of 37.68% and actual water absorption is 1898.0 ± 5.6 g/m3 having an error of 10.67%. The embodied energy was computed for the blended CFA and CBA geopolymer binder and concrete. Emergy analysis of the geopolymer concrete resulted in an emergy value of 6.87x1012 SeJ/kg or 1.21 x107 SeJ/m3 geopolymer concrete which is relatively higher than that of OPC concrete (1.89 x109 SeJ/kg). Calculated values for greenhouse gas (GHG) amounted to 89.15 kg CO2 eq/m3 geopolymer which is lower than literature value for OPC concrete of 320 CO2 eq/m3 .The geopolymer concrete cost is 92% lower than OPC concrete at 11.84 USD/m3 or 0.0067 USD/ kg.