Investigation of metakaolin-based geopolymers mortar production and application in construction

Ordinary Portland cement is the main used material in the current construction industries. In cement production, high energy is spent and gas emissions are released due to the high temperature required for the process. To produce a ton of cement needs 3 Gigajoules of energy and releases a ton of CO2 which is one of the greenhouse gases that cause the global warming. Global cement industry contributes with around 5% of all man-made CO2 emissions. In order to reduce the emissions of the construction sector, there is a need to develop alternative binder materials. Geopolymer is an inorganic, eco-material. The binders in geopolymer are materials rich in silica (Si) and aluminum (Al) like fly ash or metakaolin, and these materials need to be activated by alkali solution. Although geopolymer is cementless, it shows similar features to Portland cement. In this thesis, the mechanical and thermal properties of metakaolin-based geopolymer mortars are examined. The mortars were made by partially replacing metakaolin with colemanite with different percentages (10%, 20%, and 30%), and then a comparison was made between non-fibrous mixes and basalt fiber reinforced ones, where two different lengths of basalt fiber were used. The alkali solution is made by a combination of sodium hydroxide and sodium silicate for metakaolin activation. Alkaline solution to metakaolin ratio was 1:1, and the concentration of sodium hydroxide was 10M. The geopolymer samples were placed at room temperature for 24h after casting and then they were cured for 72h in an electrical oven at 60oC temperature. The compressive and flexural strengths of geopolymer mortar were tested at ages 7 and 28 days. As the results showed, replacing metakaolin with colemanite up to 10% by weight give positive results. On the other hand, using colemanite more the 10% wt. adversely affect the mechanical strengths, although using colemanite 20% wt. yielded acceptable results in terms of compressive strength. Using basalt fiber in the mixes had a high improvement in terms of flexural strength unless the content of colemanite did not exceed 10% wt.