Additive for dewaterable slurry and slurry incorporating same

1. A cementitious slurry comprising

a cement,

a plasticiser,

water, and

a mineral additive having fly ash and including one or both of the following components:

i) fly ash having a particle size of up to 10 microns, said fly ash being present in an amount of 30 wt % to 100 wt % based on the weight of the cement in the slurry;

ii) an aluminous material having a particle size of up to 150 microns, selected from the group consisting of hydrated alumina, partially hydrated alumina and unhydrated alumina, said aluminous material being present in an amount of 5-30 wt % based on the weight of the cement in the slurry;

wherein the mineral additive is added in a quantity sufficient to provide a water reduction effect.

2. The cementitious slurry of claim 1 , wherein the fly ash comprises about 25-60% silica, about 10-30% Al 2 O 3 , about 5-25% Fe 2 O 3 , up to about 20% CaO and up to about 5% MgO.

3. The cementitious slurry of claim 1 , wherein the ratio of hydrated alumina to the fly ash is between about 1:1 and 1:10.

4. The cementitious slurry of claim 1 , wherein the cement is selected from the group consisting of common Portland cements, fast setting or extra fast setting cements, sulphate resisting cements, modified cements, alumina cements, high alumina cements, calcium aluminate cements and cements that contain secondary components.

5. The cementitious slurry of claim 4 , wherein the secondary components are selected from the group consisting of fly ash and slag.

6. The cementitious slurry of claim 1 , wherein the cement is in an amount between about 10 and 50% of total dry ingredients.

7. The cementitious slurry of claim 1 , wherein the amount of the plasticiser is between about 0.3 to 3 wt % based on weight of the dry cement.

8. The cementitious slurry of claim 1 , wherein the cementitious slurry contains about 5 to 30 wt % fillers.