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When I started working on geopolymer science some 14 years back, it was very exiting experience. We use to cast samples and eagerly wait for next morning so that we could see the results. We have used variety of waste and by-products such as fly ash, blast furnace slag, steel slag, copper slag, zinc slag, SiMn slag, construction and demolition waste, tailings and so on. We have developed many good products such as self glazed tiles, concrete slabs, bricks and paving blocks which exhibited good properties and meeting specifications. The struggle started when we tried to translate the lab scale process into pilot scale technology. We could get half of the money from Department of Science & Technology, India and put the equal amount from my Institute to set up a pilot plant. This was the first pilot plant in India which can produce ~10tons product per day. We started operating at pilot plant for producing paving blocks from fly ash using the parameters optimized in laboratory and everything failed. The first few weeks we were producing only cracked and broken blocks, thousands and thousands of it. Then we realized that re-optimization of parameters is necessary. One by one we changed the alkali concentration, used super-plasticizer, improved mixing sequence and shifted to vibro-hydraulic compaction. Gradually it started showing good results, rejection rate decreased significantly and we could produce good quality paving blocks. But this was not over, the season changed from winter to summer and we faced problem of flash setting, cracks formation due to evaporation and so on. Again we have to modify the moisture content, curing schedule, addition of retarders and change in alkali concentrations. During rainy season, the setting delayed for long time and we need to put some accelerators and change in moisture content. But the most killing time was winter, we have lost almost 10,000 pieces because of efflorescence. We struggled hard and finally could overcome by ensuring that all the alkali gets consumed and further controlling pore characteristic. From this experience of 1 year, we learned many lessons especially for quality control. We could finally establish a quality control protocol. However, one of the major hurdle was cost, the cost of product was coming higher that the cost of equivalent conventional products. So we have done a life cycle analysis from cradle to gate including energy balance, elemental balance, material balance, etc. We could identify that we are losing money due to material loss, especially excess alkali which remains unreacted and leached out in course of time. So we have further modified the composition, reduced the cycle time to improve productivity and could reduce the rejection to <2%. This has improved the techno-economics and the product was cost effective. Finally we have roped in an industry they started producing paving blocks which meets IS 15658 specification. They have produced more than 1500 tons product which laid at different parts of city and showing no sign of deterioration in 2 years. With all this effort and experience, we could transfer one technology which is running on 100 tons/day scale and in the process of transferring second technology.

Efflorescence Geo polymer Paving block Fly ash