Non-efflorescing cementitious bodies
A non-efflorescing cementitious body is formed from sources of calcium aluminate, calcium silicate, calcium sulphate and reactive silica, these ingredients being present in such relative proportions that, upon hydration, both monosulphate (C 3 A.CŜ.12H) and hydrated alumina (AH 3 ) are formed. Also disclosed is a hydraulic binder and a paste from which such bodies can be formed and a method for forming such bodies. In addition to exhibiting low efflorescence, these bodies retain satisfactory physical properties, especially good durability to natural weathering conditions.
1. A non-efflorescing cementitious body being formed upon curing of an aqueous paste formed by the addition of water to a pre-mixed dry binder comprising from 10% to 49% by weight of a first ingredient comprising a source of active silica, and a remainder including:
(i) from 40% to 90% by weight of a second ingredient comprising a source of calcium aluminate selected from calcium alumiate cement or clinker and calcium sulpho aluminate cement or clinker, said source of calcium aluminate having at least 25% alumina or a C/A ratio of less than 3;
(ii) from 5% to 55% by weight of a third ingredient comprising Portland cement or clinker as a source of calcium silicate; and
(iii) from 3% to 50% by weight of a fourth ingredient comprising a source of sulphate at least 25% being SO 3 ;
said ingredients being present in such relative proportions that, upon hydration, both mono-sulphate (C 3 A.Cŝ.12H) and hydrated alumina (AH 3 ) are formed.
2. The body according to claim 1 , having a density after complete hydration of at least 1.8 kgm −3 .
3. The body according to claim 1 , wherein, after complete hydration, the body has a volume expansion on exposure to water of less than 5%.
4. The body according to claim 1 , having a porosity after complete hydration of less than 30%.
5. A method of forming a non-efflorescing cementitious body as a coating on a concrete article, said body being formed upon curing of an aqueous paste formed by the addition of water to a pre-mixed dry binder comprising from 10% to 49% by weight of a first ingredient comprising a source of active silica, the remainder including: (i) from 40% to 90% by weight of a second ingredient comprising a source of calcium aluminate selected from calcium aluminate cement or clinker and calcium sulpho aluminate cement or clinker, said source of calcium aluminate having at least 25% alumina or a C/A ratio of less than 3; (ii) from 5% to 55% by weight of a third ingredient comprising Portland cement or clinker as a source of calcium silicate; and (iii) from 3% to 50% by weight of a fourth ingredient comprising a source of sulphate at least 25% being SO 3 ; said ingredients being present in such relative proportions that, upon hydration, both mono-sulphate (C 3 A.Cŝ.12H) and hydrated alumina (AH 3 ) are formed, wherein said body is constituted by a coating on a concrete article, the method comprising coating an exterior surface of a hardened or fresh concrete article with said paste and curing the article and the coating together at a relative humidity of from 75% RH to 100% RH at a temperature of from 0° C. to 50° C. for a period of from 30 minutes to 24 hours.
6. The method according to claim 5 , wherein said concrete article is a member selected from consisting of: roofing tiles, plates, cladding and walls.
7. A hydraulic binder for forming a non-efflorescing cementitious body, comprising from 10% to 49% by weight of a first ingredient comprising a source of active silica, and a remainder including:
(i) from 40% to 90% by weight of a second ingredient comprising a source of calcium aluminate selected from calcium aluminate cement or clinker and calcium sulpho aluminate cement or clinker, said source of calcium aluminate having at least 25% alumina or a C/A ratio of less than 3;
(ii) from 5% to 55% by weight of a third ingredient comprising Portland cement or clinker as a source of calcium silicate; and
(iii) from 3% to 50% by weight of a fourth ingredient comprising a source of sulphate at least 25% being SO 3 .
8. The hydraulic binder according to claim 7 , said ingredients being present in such relative proportions that, upon hydration, both mono-sulphate (C 3 A.Cŝ.12H) and hydrated alumina (AH 3 ) are formed.
9. The hydraulic binder according to claim 7 , said ingredients being present in such relative proportions that, upon hydration, ettringite (C 3 A.3Cŝ.32H) is formed as an intermediate in the formation of said mono-sulphate (C 3 A.Cŝ.12H).
10. The hydraulic binder according to claim 7 , said ingredients being present in such relative proportions that, upon hydration, strätlingite (C 2 ASH 8 ) and calcium hydrosilictes are additionally formed.
11. The hydraulic binder according to claim 7 , said ingredients being present in such relative proportions that, upon hydration, substantially no Portlandite (CH) is formed.
12. The hydraulic binder according to claim 7 , wherein said source of calcium aluminate is a calcium a luminate cement or clinker or a calcium sulpho aluminate cement or clinker.
13. The hydraulic binder according to claim 7 , wherein said source of calcium sulphate is anhydrite, gypsum or hemihydrate.
14. The hydraulic binder according to claim 7 , wherein said source of calcium silicate is Portland cement.
15. The hydraulic binder according to claim 7 , wherein said source of reactive silica is ground granulated blast furnace slag or a pozzolanic ingredient.
16. The hydraulic binder according to claim 9 , wherein said pozzolanic ingredient is a member selected from group consisting of: metakaolin, fly ash, fumed silica and perlite fines.
17. The hydraulic binder according to claim 7 , wherein the binder comprises at least 15% by weight of alumina.
18. An aqueous paste for forming a non-efflorescing cementitious body, formed by the addition of water to a pre-mixed dry binder comprising from 10% to 49% by weight of a first ingredient comprising a source of active silica, and a remainder including:
(i) from 40% to 90% by weight of a second ingredient comprising a source of calcium aluminate selected from calcium aluminate cement or clinker and calcium sulpho aluminate cement or clinker, said source of calcium aluminate having at least 25% alumina or a C/A ratio of less than 3;
(ii) from 5% to 55% by weight of a third ingredient comprising Portland cement or clinker as a source of calcium silicate; and
(iii) from 3% to 50% by weight of a fourth ingredient comprising a source of sulphate at least 25% being SO 3 , said ingredients being present in such relative proportions that, upon hydration, both mono-sulphate (C 3 A.Cŝ.12H) and hydrated alumina (AH 3 ) are formed.
19. The paste according to claim 18 , having a water over binder ratio of between 0.2 and 1.0.
20. The paste according to claim 19 , wherein the water over binder ratio is between 0.28 and 0.68.
21. The paste according to claim 18 , further comprising aggregate, with an aggregate over cement ratio of up to 6.
22. The paste according to claim 18 , wherein the aggregate over cement ratio is up to 2.
23. The paste according to claim 18 , further comprising additional ingredients selected from the group consisting of: pigments, acid and freeze-thaw performance enhancers, frost performance enhancers, rheology modifiers, plasticisers optionally together with accelerator, anti-segregation additives, defoamers, surface enhancement agents, hydrophobic agents, and acid resistance agents, and mixtures thereof.