High strength class C fly ash cementitious compositions with controllable setting

A fly ash mortar or concrete made by mixing a Class C fly ash (CFA) cementitious composition with a controllable setting time consisting essentially of:

• at least one Class C fly ash;
• at least one alkali hydroxide;
• a setting retarder and a strength accelerator comprising at least one source of phosphate;
• a second pozzolanic material and
• water,
• wherein the pozzolanic material is selected from the group:
• Class F fly ash, ground granulated blast furnace slag, superfine blast furnace slag, vitreous calcium aluminosilicate, cement kiln dust, and combinations thereof, wherein the second pozzolanic material replaces the Class C fly ash for up to 40 wt. %, wherein the at least one alkali hydroxide, the at least one source of phosphate and the at least one alkali salt are dissolved in water to form an activator solution.

A Class C fly ash (CFA) cementitious composition with a solid activator consisting essentially of:

• at least one Class C fly ash;
• at least one alkali carbonate;
• at least one alkali hydroxide;
• a setting retarder and a strength accelerator comprising at least one source of phosphate;
• and
• water.

A Class C fly ash (CFA) cementitious composition with a controllable setting time comprising:

• at least one Class C fly ash;
• at least one alkali hydroxide;
• a setting retarder and a strength accelerator comprising at least one source of phosphate;
• and water,
• wherein the mortar or concrete has a 28-day compressive strength of at least about 10,000 psi.

A Class C fly ash (CFA) cementitious composition with a solid activator comprising:

• at least one Class C fly ash;
• at least one alkali carbonate;
• a setting retarder and a strength accelerator comprising at least one source of phosphate;
• and
• water,
• wherein the mortar or concrete has a 28-day compressive strength of at least about 10,000 psi.