Geopolymers are polymeric materials that have attracted attention in the construction industry owing to low production cost and environmental friendly. They can be used as construction materials to replace the conventional Portland cement reference to their mechanical strength and durability. The use of industrial wastes such as fly ash as sources of geopolymer synthesis is on the rise. Interstitial water in the geopolymer structures evaporates during high temperature application, which in turn causes cracking. Fortunately, this can be avoided by making the polymer matrix homogenous and pore free, and above all, it helps improve thermal stability and mechanical strength.
Researchers led by Dr. Pavadee Aungkavattana from National Science and Technology Development Agency in Thailand proposed a new method improve thermal shock resistance and enhance compressive strength of geopolymers using basalt fibers as the reinforcing agent. The effect of TiO2 on thermal shock resistance and compressive strength of fly ash-based geopolymer was investigated. Their work is now published in peer-reviewed journal, Construction and Building Materials.
The authors chose a 5 M alkali activator owing to good workability of the mixing paste. The activator was prepared by mixing sodium silicate and sodium hydroxide solution. The study reported that the use of high CaO content fly ash would result to faster initial setting time. The cubic geopolymer composites were prepared for thermal shock resistance and compressive strength measurements. Thermal shock resistance of the geopolymer composite was determined by measuring the retained compressive strength after the cubes have been through heating and cooling. In each cycle the cubes were placed in a furnace at 8000 C with a 10 min soaking period. Thereafter, they were rapidly taken out to room temperature for 10 min.
C-S-H phase is the main hydration product in cement production. The formation of the C-S-H phase and alumino-silicate framework in the experiment indicates that geopolymerization and hydration reactions occur simultaneously. The samples showed amorphous with some crystalline phases, C-S-H phase and the intensity of anatase increased with increasing TiO2 wt%. An increase in the C-S-H phase suggests that TiO2 accelerated the hydration reaction in geopolymers. Compressive strength of the geopolymer composites was evaluated after aged 28 days. It was observed that the 28-day aged compressive strength before the thermal cycle slightly increased with TiO2 addition. The 5 wt% TiO2 added samples recorded a 7.8% compressive strength higher than TiO2 free ones.
Thermal shock resistance behavior of the geopolymers was investigated. A sharp decline for all samples was recorded after thermal cycles. The strength of samples added with 5 wt% TiO2 gradually decreased from 29.2 to 25.7 MPa. In TiO2 free samples, a sharp decrease in strength from 25.3-18.0 MPa was recorded.
This study found that TiO2 promoted the hydration reactions in the geopolymer structures, which improved the compressive strength and enhanced thermal shock resistance at 8000 C. The compressive strength in composites with 5 wt% TiO2 after the 15 thermal cycles was 44% higher than TiO2 free samples. From this study, it can be concluded that TiO2 played an important role in improving the thermal shock resistance and compressive strength in fly ash-based geopolymer composites.
Patthamaporn Timakul, Weerada Rattanaprasit, Pavadee Aungkavattana. Enhancement of compressive strength and thermal shock resistance of fly ash-based geopolymer composites. Construction and Building Materials, Volume 121, 2016, Pages 653–658.
National Metal and Materials Technology Center (MTEC), National Science and Technology Development Agency (NSTDA), 114 Thailand Science Park, Pahonyothin Rd., Klong Luang, Pathumthani 12120, Thailand.Go To Construction and Building Materials