Development of Alkali Activated Cement (Geopolymer Cement) using Meta Kaolin and Volcanic ash from Uganda as base materials.

Abstract

Addition of Supplementary Cementitious Materials (SCM’s) in quantities larger than 5% increases the water demand of cements. EN 197 limits the amount of cement clinker that can be replaced with SCM’s to 35% for CEM II and 55% for CEM IV Portland Pozzolana Cements. According to the ACI mix design procedure, in order to maintain the required strength of a mix, the water to cement ratio has to be kept as low as possible. This leads to addition of more cement that counteracts the effect of the reduced clinker percentages in terms of reducing carbon dioxide emissions and the embedded energy of Portland cement. Geopolymer Cement (GPC) is a new cement technology that eliminates the use of Calcium Carbonate (limestone) in the cement production process while still providing strengths of up to 70 MPa. Calcium Carbonate is the main carbon dioxide producing component in the manufacture of OPC. Its elimination reduces carbon dioxide emissions by over 80% and the energy requirement of the cement production process. Production of GPC involves use of finely ground pozzolanic aluminosilicate materials such as fly ash and blast furnace slag, kaolinitic clays, volcanic tuffs and ashes and agricultural waste products like rice husk ash to react with alkaline solutions to form a binder that has cementitious properties. This study explored the use of volcanic ash and kaolin sourced from Uganda in Tororo and Kabale districts respectively as precursors in the production on geopolymer cement. The raw samples were mechanically activated by grinding And Kaolin clay was further activated thermally in a furnace at a temperature of 7500C for two hours. Grinding was done using a pulverizer to form fine cementitious material that was sieved through a 150µm ASTM standard sieve. The sieved material was mixed with a mixture of Sodium silicate solution and sodium hydroxide solution and standard sand to form geopolymer cubes that were tested for compressive strength according to ASTM C109. Additionally, the fresh mortar was tested for setting time (ASTM C191-04) and flow properties. A high compressive strength was obtained when the samples were heat cured initially, the highest being 22 MPa for metakaolin samples and 5.2MPa for Volcanic ash samples, the strength increased with the duration of initial heat curing. From the characterization tests done, the samples fit the requirements of class N natural pozzolans according to ASTM C618. The LOI values were below 10%. The process of calcination increased the percentage concentration of Aluminum, Silicon and Iron Oxides to 91% from 65% in raw uncalcined kaolin. This process modified the physical and chemical properties of the kaolin into highly reactive pozzolana. This is evidenced by the high values of compressive strength of the metakaolin geopolymer samples. For the same mix ratio, volcanic ash geopolymer mortar had better flow properties (76%) compared to metakaolin samples (73%). Volcanic ash samples had a longer setting time compared to Metakaolin samples. Initial heat curing reduced the setting times of both samples with the mortar cubes gaining strength as early as 12 hours.