Development and performance evaluation of wollastonite–fly ash geopolymer bricks with embedded IoT sensors for strength monitoring

Due to the growing need for green or intelligent building materials, the development of new sustainable materials to replace traditional fired clay bricks has gained traction. In this research, the manufacture of geopolymer bricks from the mixture of fly ash and wollastonite, along with an IoT-based strength evaluation system, has been considered. Six different mixes of geopolymer bricks have been produced, with the fly ash replacement percentage by wollastonite varying from 0% to 60%. A constant alkaline activator environment with 6 M NaOH and NaOH/Na₂SiO₃ molar ratio of 2 has been maintained throughout the experiment. The results showed that the addition of wollastonite greatly enhanced the behaviour of the geopolymer brick samples up to the optimal replacement content of 40%. The sample made up of 60% fly ash and 40% wollastonite had the maximum compressive strength value of 23 MPa after 28 days, which represented a 28% increase compared to the control sample with a compressive strength of 18 MPa. The same mix had the maximum density of 17.2 kN/m³ and the lowest water absorption of 5.6%, showing a 53% decrease compared to the control sample. Durability tests showed that the sample had better resistance to hostile conditions, experiencing a strength loss of only 3.5% under sulphate attack and 5.2% under acidic conditions, whereas the control sample suffered a strength loss of 10% and 12.2%, respectively. A DS18B20 embedded temperature sensor, along with a Raspberry Pi was used to monitor the temperature development inside the brick during the curing process. The optimum mixture had an average temperature of 25.39 °C and a maturity index of 2587.5 °C·h, thus helping in estimating the compressive strength of 24.4 MPa after 28 days, which correlated well with the experimentally achieved values. It is clear from the research work that geopolymer bricks of wollastonite–fly ash, along with IoT sensing technology, have a bright future ahead.