Process for manufacturing concrete of high corrosion resistance

Abstract

Concrete having high resistance to corrosion is prepared by using low aluminate (C 3 A) cement, preferably having less than 5 weight percent of aluminate, and, in addition to conventional concrete constituents, at least 10 weight percent of finely divided, reactive silica based on the cement weight. A highly corrosion resistant cement composition comprises, in addition to conventional cement constituents, 70-90 parts by weight of low aluminate cement and 10-30 parts by weight of reactive silica. An additive useful for making concrete highly corrosion resistant comprises 80-90 weight percent of reactive silica, 0-10 weight percent of low aluminate cement, 3-8 weight percent of formaldehyde condensed sodium sulfonate, 3-8 weight percent of lignosulfonate.

We claim: 
     
       1. In a method of manufacturing concrete having resistance to corrosion, which comprises mixing cement, sand.[.,.]. .Iadd.and .Iaddend.water, .[.reactive silica and, optionally, conventional concrete additives,.]. the improvement wherein the cement has a low aluminate content, and at least 10 weight percent of finely divided, .[.nonpozzolanic,.]. reactive silica .Iadd.formed by sublimation and quenching of a silica-containing raw material.Iaddend., based on the weight of the cement, .Iadd.and an effective amount of an additive to reduce the increase in water demand caused .Iaddend.by said silica, .[.is.]. .Iadd.are .Iaddend.incorporated in and distributed uniformly throughout the concrete. 
     
     
       2. .[.A.]. .Iadd.The .Iaddend.method according to claim 1, wherein the cement has an aluminate content of less than 5 weight percent based on the weight of the cement. 
     
     
       3. .[.A.]. .Iadd.The .Iaddend.method according to claim 2, wherein the reactive silica is added to the concrete in an amount of 10-30 weight percent based on the weight of the cement. 
     
     
       4. .[.A.]. .Iadd.The .Iaddend.method according to claim 2, wherein the reactive silica is added to the concrete in an amount of 10-25 weight percent based on the weight of the cement. 
     
     
       5. .[.A.]. .Iadd.The .Iaddend.method according to claim 2, wherein the reactive silica is added to the concrete in an amount of 15-25 weight percent based on the weight of the cement. 
     
     
       6. .[.A.]. .Iadd.The .Iaddend.method according to claim 2, wherein the cement is sulfate resistant cement having an aluminate content of 1.6 weight percent and further containing 55 weight percent of 3CaO.SiO 2 , 20 weight percent of 2CaO.SiO 2  and 15 weight percent of 4CaO.Al 2  O 3 .Fe 2  O 3 . 
     
     
       7. .[.A.]. .Iadd.The .Iaddend.method according to claim 2, wherein the reactive silica is silica fines recovered during purification of flue gases from a melting furnace used in manufacturing ferrosilicon. 
     
     
       8. A cement composition having corrosion resistance, comprising 70-90 parts by weight of cement having a low aluminate content, 10-30 parts by weight of .[.nonpozzolanic,.]. reactive silica .Iadd.formed by sublimation and quenching of a silica-containing raw material .Iaddend.and, .Iadd.an effective amount of an additive to reduce the water demand of the cement composition caused by said silica when employed .Iaddend.to produce concrete .[.optionally, minor amounts of conventional cement additives.].. 
     
     
       9. .[.A.]. .Iadd.The .Iaddend.composition according to claim 8, wherein the cement has an aluminate content of less than 5 weight percent based on the weight of the cement. 
     
     
       10. .[.A.]. .Iadd.The .Iaddend.composition according to claim 9, wherein the reactive silica is silica fines recovered during purification of flue gases from a melting furnace used in manufacturing ferrosilicon. 
     
     
       11. An additive for imparting corrosion resistance to concrete, comprising: 80-90 weight percent of .[.nonpozzolanic,.]. reactive silica .Iadd.formed by sublimation and quenching of a silica-containing raw material.Iaddend.,   0-10 weight percent of cement having a low aluminate content,   3-8 weight percent of formaldehyde condensed sodium sulfonate, and.Iadd./or .Iaddend.   3-8 weight percent of lignosulfonate.   
     
     
       12. .[.An.]. .Iadd.The .Iaddend.additive according to claim 11, wherein the cement has an aluminate content of less than 5 weight percent based on the weight of the cement. 
     
     
       13. .[.An.]. .Iadd.The .Iaddend.additive according to claim 12, comprising: 80 weight percent of .[.nonpozzolanic,.]. reactive SiO 2  fines .Iadd.formed by sublimation and quenching of a silica-containing raw material, .Iaddend.   10 weight percent of sulfate resistant cement containing 1.6 weight percent of aluminate,   5 weight percent of condensed naphthalene sulfonates, and   5 weight percent of lignosulfonate.