Shaped cementitious products

A process for preparing a dense shaped article, said article comprising a composite material containing fly ash particles bonded together by cementitious reaction products, said composite material having a splitting tensile strength of at least about 200 psi, said process comprising the steps of:

• (a) providing a substantially dry fly ash-containing powder obtained from the dry scrubbing of fly ash-containing flue gas with lime in a spray drying system, said fly ash-containing powder comprising fly ash in intimate admixture with microparticulate crystallites of scrubber reaction materials selected from the group consisting of calcium sulfite, calcium sulfate, hydrates of calcium sulfite and calcium sulfate, calcium oxide, calcium hydroxide and mixtures thereof;
• (b) uniformly contacting said fly ash-containing powder with from about 4 to about 20% by weight of water;
• (c) forming said powder/water mixture into a shaped article by confined compaction at a compaction ratio of from about 2 to 3 to provide a handleable green body;
• said water being added in an amount sufficient to satisfy the short term hydration demands of said powder and further in an amount which in combination with the selected compaction ratio is sufficient to produce a green body having an uncured dry density in the range of from about 95 to about 140 pounds per cubic foot and wherein the interspatial voids between the fly ash particles in said green body are sufficient to accommodate the subsequently formed cementitious reaction products without deleterious expansion of the article;
• and
• (d) curing said green body product in a moist atmosphere to form a shaped article bonded by said cementitious reaction products.

A process for preparing a dense shaped pellet having a splitting tensile strength of at least about 200 psi, said process comprising the steps of:

• (a) providing a substantially dry fly ash-containing powder obtained from a flue gas desulfurization operation in which fly ash-containing flue gas is scrubbed with an aqueous lime suspension in a spray dryer, said powder comprising fly-ash particles coated with microparticulate crystallites of scrubber reaction materials selected from the group consisting of calcium sulfite, calcium sulfate, hydrates of calcium sulfite and calcium sulfate, calcium oxide, calcium hydroxide and mixtures thereof;
• (b) adding from about 4 to about 20% by weight of water to said fly ash-containing powder;
• (c) uniformly distributing said added water throughout said powder;
• (d) rapidly forming the resulting uniform powder/water mixture into pellets in a high energy extrusion type pelletizing mill operated at compaction ratios sufficient to provide a handleable green pellet having a dry uncured density of from about 95 to about 140 pounds per cubic foot and wherein the interspatial voids between the fly ash particles in said green pellet are sufficient to accommodate the subsequently formed cementitious reaction products without deleterious expansion of the article;
• and
• (e) curing said green pellets in a moist atmosphere to allow said cementitious reaction products to form.