PRODUCTION AND CHARACTERIZATION OF GEOPOLYMER AS CEMENT FROM BAMBOO ASH AND METAKAOLIN

• Main Author: PURBASARI - NIM: 33014001 , APRILINA
• Format: Dissertations
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/25710
• Institution: Institut Teknologi Bandung

<p align="justify"><br /> Portland cement production process at temperature of about 1400 °C requires high energy and produces CO2 emissions of about 5-7% of global CO2 emissions. Alternative Portland cement substitute with lower energy consumption and CO2 emissions is geopolymer. Geopolymer production process utilizes the reaction of materials containing alumino-silicate oxide (e.g. waste of combustion product) with an alkaline solution at low temperature (below 100 °C). Studies on the application of geopolymer as Portland cement substitute have shown high mechanical strength, resistance to high/low temperature and acidic/alkaline environment, as well as the reduction of CO2 emissions by up to 90%. Besides the production of geopolymer from solid waste has the potential to reduce the environmental burden with lower production cost by 10-30%. <br /> <br /> Raw materials of geopolymer are alumino-silicate materials, either natural minerals or solid wastes. Natural minerals which has been widely studied for the production of geopolymer are kaolin (Al2O3.2SiO2.2H2O) and calcined kaolin or metakaolin (Si2O5,Al2O2). Solid wastes containing alumino-silicate oxide such as fly ash, slag, and biomass ash also can be used as geopolymer raw materials. Ash from bamboo combustion, as well as other biomass ash, has the potential to be used as geopolymer raw material. Bamboo can be used as energy source because bamboo has calorific value equivalent to wood, grows easily on various types of soil with age of 3-5 years, and is difficult to decompose naturally. High content of alkali compounds in bamboo ash will increase the risk of sintering and slag formation in the combustion process so that additives such as kaolin can be added to increase the melting point of biomass ash. <br /> <br /> The use of bamboo ash as geopolymer raw material has never been done up to now so that will be interesting to be learned. The bamboo ash can be mixed with metakaolin because kaolin as metakaolin source is widely available in Indonesia. Bamboo and kaolin can be mixed and calcined together so that bamboo turns into bamboo ash and kaolin turns into metakaolin in a co-combustion process. The cocombustion product is then reacted with an alkaline activator to form geopolymer. Operating condition of combustion process and operating condition of geopolymerization process need to be studied to obtain geopolymer having good mechanical strength and resistance to extreme environments. Utilization of bamboo and kaolin as geopolymer raw material is expected to contribute to the effort to obtain environmentally friendly cement. <br /> <br /> The general purpose of this research is to produce geopolymer as Portland cement substitute which is environmentally friendly by utilizing natural mineral resources as well as the reuse of biomass waste material available in Indonesia, namely kaolin and bamboo ash. The research was conducted in four stages, comprising preparation of raw materials, production of geopolymer and optimization of geopolymerization, characterization of geopolymer in extreme environment, microstructure and mechanism study of geopolymerization. <br /> <br /> In the first phase of research, the results showed that bamboo could be used as energy source. Co-combustion of bamboo and kaolin as additives could reduce the risk of sintering or slag formation and product of co-combustion could be used as geopolymer raw material. Optimization result of geopolymerization in the second phase of research showed that the use of mixture of KOH 10 N and NaSilicate solution (mass ratio of 1:2) and curing time of 8 hours could produce geopolymer having compressive strength at 28 days of 35.6 MPa (higher than the minimum compressive strength of mortar based on ASTM C270, which is 17.2 MPa). Geopolymer from co-combustion residuals of bamboo and kaolin showed relatively good resistance to acid environment and high temperature based on the third phase of research result. The resistance test in 5 % H2SO4 solution up to 80 oC for 6 weeks to geopolymer mortar showed a slight change in visual appearance with decreasing of mass and decreasing of compressive strength lower than Portland cement mortar, i.e. 4.9 % and 23.3 %. Thermal characterization by thermogravimetric analysis of geopolymer showed that geopolymer would experience dehydration, densification by viscous sintering, and further densification if exposed to high temperature up to 1000 oC with a mass loss of 19.5 %. The results of FTIR, XRD and SEM analysis in the fourth stage of research showed that both geopolymers from co-combustion product of bamboo and kaolin as well as geopolymer from mixture of bamboo ash and metakaolin that calcined separately had relatively similar microstructures with the same geopolymerization mechanism although there were differences in the microstructure of raw materials. The proposed theoretical geopolymerization mechanism through stages: dissolution of aluminates and silicates from aluminosilicate materials by hydroxide ions, gel formation and reorganization, polymerization and hardening.<p align="justify"><br />