Fly ash is a byproduct from burning pulverized coal in electric power generating plants. Fly ash brick (FAB) is a building material, specifically masonry units, containing class C fly ash and water. Compressed at 28 MPa(272 atm) and cured for 24 hours in a 66 °C steam bath, then toughened with an air entertainment agent.fly ash–lime–phosphogypsum (FaL-G) hollow blocks are one of the best substitutes for conventional burnt clay hollow bricks or concrete hollow blocks in the construction industry. FaL-G hollow blocks are light in weight and being hollow, impart thermal insulation to the buildings.In this paper, a study based on the results of an experimental investigation on FaL-G hollow blocks is presented.  The compressive strength, water absorption and weight of FaL-G hollow blocks were determined. The durability of these blocks in terms of loss in compressive strength in sulfate environments is also presented in this paper. It is observed that FaL-G hollow blocks have sufficient strength for their use in general building construction.More from ECO BRICKS