The present invention provides a composition and a process for the preparation of chemical activated cold setting fly ash building construction materials. The chemical activator is an alkaline aqueous solution of 11.2 to 13.6 in pH and 1.25 to 1.40 gm/cc in density which contains admixtures of different concentrations of hydroxyl, sulfate, acetate and chloride bearing chemical salts of calcium, magnesium, sodium, potassium and aluminum in water medium. The reaction of chemical activator solution and the mineral constituents of fly ash mix develop binding property. The binding matrix of chemical activated fly ash mix is mostly hydrous silica and silicate group of phases which on setting under atmospheric condition attains strength suitable for building construction application. Utilization of fly ash of any source by weight ranges from 80 to 99% in manufacture of building materials including heat and acid resistance and toxic waste disposal products.