Cement/aggregate composition, concrete product and method for making a concrete product

A method for producing a cast concrete product from a cement aggregate composition, said method consisting of the following steps:

• a) milling a mass of red dune sand to reduce the particle size to 45 microns or less;
• b) providing a mass of Portland cement;
• c) mixing 70 parts Portland cement to 30 parts red dune sand with reduced particle size;
• d) providing a mass of other fine aggregate having a nominal particle size of 5 mm, and coarse aggregate having a nominal particle size of about 20 mm, water, and a superplasticizer selected from the group consisting of polycarboxylate ether, polycarbonate, alkyl citrates, sulfonated naphthalene, sulfonated alene, sulfonated melamine, and formaldehyde;
• e) mixing the Portland cement and red dune sand with the other fine aggregate, coarse aggregate, water, and superplasticizer to produce a mass of concrete including 350 kg/m3 Portland cement, 150 kg/m3 ground red dune sand, 650 kg/m3 other fine aggregate having a nominal particle size of 5 mms, 1165 kg/m3 coarse aggregate, 150 kg/m3 water, and 6 liters superplasticizer;
• f) casting the mass of concrete in a shape by placing the cement mix in a mold to produce a molded article;
• g) within 24 hours of casting steam curing the molded article for 12 hours under atmospheric pressure;
• h) steam molding the molded article by placing the molded article inside a curing chamber and maintaining 100% humidity in the curing chamber;
• i) raising the temperature in the curing chamber to about 180° C. within 1 to 2 hours to thereby raise the pressure to 10 bars and maintaining the 180° C. temperature at 100% humidity within the curing chamber for 4 to 5 hours.
• j) releasing the pressure to reach atmospheric pressure within 20-30 minutes and the temperature reduced;
• and
• k) removing the cast product from the curing chamber.