Abstract: A formulation for preparing a cementitious product comprising a cementitious material, a siliceous material, and a low bulk density material being substantially calcium silicate hydrate and including unreacted siliceous reactant. A method of forming a cementitious product comprises adding a cementitious material, a siliceous material and a low bulk density material to water to form a slurry, forming a green shaped article from the slurry and curing the article in an autoclave, wherein the low bulk density material is substantially calcium silicate hydrate and includes unreacted siliceous reactant.

Abstract: This invention relates to a formulation with the addition of low density additives of volcanic ash, hollow ceramic microspheres or a combination of microspheres and volcanic ash or other low density additives into cementitious cellulose fiber reinforced building materials. This formulation is advantageously lightweight or low density compared as compared to current fiber cement products without the increased moisture expansion and freeze-thaw degradation usually associated with the addition of lightweight inorganic materials to fiber cement mixes. The low density additives also give the material improved thermal dimensional stability.