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

Abstract

A concrete product is produced by providing red dune sand having a particle size of 45 microns or less and mixing the red dune sand with hydraulic cement in a ratio of about 30% of the cement being replaced by the red dune sand. The cement and red dune sand are then mixed with fine and course aggregate, water and a superplasticizer and cast after pouring into a mold cavity. Then within 24 hours of casting, the cast article is steam cured for 12 hours under atmospheric pressure, demolded and placed in an auto clave at 100% humidity. The temperature in the auto clave is raised to 180 C. within one to two hours and maintained at that temperature for 4 to 5 hours. The temperature also increases the pressure to about 10 bars. The pressure is released to reach atmospheric pressure within 20-30 minutes and the temperature reduced gradually, so that the article can be removed.

Claims

1. 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/m.sup.3 Portland cement, 150 kg/m.sup.3 ground red dune sand, 650 kg/m.sup.3 other fine aggregate having a nominal particle size of 5 mms, 1165 kg/m.sup.3 coarse aggregate, 150 kg/m.sup.3 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.

2. A cement aggregate composition for cast products comprising: Portland cement in an amount of 300 to 400 kg/m.sup.3, red dune sand in an amount of 100 to 200 kg/m.sup.3, fine aggregate 600 to 700 kg/m.sup.3, coarse aggregate 1,000 to 1,330 kg/m.sup.3, water 100 to 200 kg/m.sup.3 and superplasticizer 5 to 7 liters.

3. A cement aggregate composition that comprises: Portland cement in an amount of 350 kg/m.sup.3, about 150 kg/m.sup.3 of red dune sand, about 650 kg/m.sup.3 fine aggregate, about 1165 kg/m.sup.3 coarse aggregate, 150 kg/m.sup.3 water and about 6 liters superplasticizer.

Description

DESCRIPTION OF THE DRAWINGS

(1) The FIGURE is a graph showing the relative compressive strengths of several mixes of concrete.

DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION

(2) This patent covers development and use of red dune sand as a partial cement replacement material in concrete products. It is well established that highly siliceous materials obtained from waste products such as fly ash and silica fume are effective cement replacement materials. They are, however becoming more expensive than cement itself, hence making it economically unattractive. Naturally occurring amorphous silica found in Turkey (Isparta Region) have been shown to enhance the properties of concrete and could be utilized as partial cement replacement materials (Davraz and Gunduz, 2005). Also, less reactive forms of silica such as ground quartz (silica flour) can act as a pozzolan under high pressure steam curing (Mindess, et al, 2003)). However, ground silica from sand dunes have not been tried or suggested as pozzolanic materials for concrete manufacturing. The only known utilization of dune sands in concrete mixtures is its use as a fine aggregate.

(3) Preliminary analysis of red sand obtained from sand dunes around Riyadh, Saudi Arabia had been conducted and it was found that they have high silica content to entitle them as potential materials for partial cement replacement. Initial test results have shown that red sand obtained from sand dunes can be used as cement replacement in concrete manufacturing.

(4) Concrete mixes of different categories were cast to determine the contribution of dune sand to the strength properties of concrete when used as partial cement replacement. The red sand was ground to small particles of less than 45 microns before it is used as cement replacement in concrete mixtures. Three different mixtures were as follows:

(5) (a) Mix 1 (NS): contains normal concrete with only Ordinary Portland Cement, OPC (500 kg/m.sup.3).

(6) (b) Mix 2 (RS): contains OPC (350 kg/m.sup.3) and ground red sand (dune sand, 150 kg/m.sup.3).

(7) (c) Mix 3 (WS): contains OPC (350 kg/m.sup.3) and silica flour (150 kg/m.sup.3)

(8) The mixes were subjected to normal curing (water cured at room temperature) and special curing (steam curing at high temperature and pressure). Test results showed that there is no strength contribution for either ground red sand or silica flour for the concrete subjected to normal curing. However, a significant contribution to the strength was obtained with these materials when subjected to special curing. The materials used and comparison of the compressive strength for the mixes are shown in Table 1 and the FIGURE, respectively. The NS, RS and WS refer to Normal Mix, Red Sand Mix and Silica Flour Mix subjected to normal curing. The NSA, RSA and WSA refer to Normal Mix, Red Sand Mix and Silica Flour Mix subjected to special curing which include the following steps;

(9) 1. Specimens are steam-cured within 24 hours of casting for 12 hours under atmospheric pressure.

(10) 2. The specimens were then demoulded before being placed in the curing chamber. The humidity inside the curing chamber was maintained at 100% throughout the special curing period.

(11) 3. Specimens were put in a curing chamber (autoclaved) where the inside temperature was increased from ambient to 180 C. within 1-2 hours (this resulted in an equivalent increase in pressure to 10 bar)

(12) 4. The temperature inside the curing chamber was maintained at 180 C. for 4-5 hours.

(13) 5. The pressure was released to reach atmospheric pressure within 20-30 minutes and the temperature reduced gradually

(14) The specimens were tested immediately after this curing process. Test results show that there is clear potential use of the red sand (dune sand) in concrete production. The process to transform the dune sand into partial cement replacement is less energy intensive than cement manufacturing and more environmentally friendly (no release of CO.sub.2 into the atmosphere) The replacement of ordinary Portland cement by ground dune sand of up to 30% can be very economically attractive and will encourage wide utilization of dune sand in concrete manufacturing specially for precast concrete.

(15) TABLE-US-00001 TABLE 1 Constituent materials for three different mixes Mix 1 (NS) Mix 2 (RS) Mix 3 (WS) Cement (kg/m.sup.3) 500 350 350 Ground red sand 0 150 0 (kg/m.sup.3) Silica Flour (kg/m.sup.3) 0 0 150 Fine Aggregate 650 650 650 (kg/m.sup.3) Coarse Aggregate 1165 1165 1165 (kg/m.sup.3) Water (kg/m.sup.3) 150 150 150 Superplasticizer 6 6 6 (liter)

(16) A method for producing a cast concrete product having a compressive strength of at least about 85 MPa from a cement aggregate composition wherein up to about 30% of the cement has been replaced with milled red dune sand having an average particle size of less than 45 microns. The method comprises the steps of: a) Milling red dune sand to reduce the particle size to less than about 45 microns; b) Mixing the milled dune sand from step a. with cement, aggregate and water to produce a cement mix with about 3 parts dune sand to 7 parts cement; c) Casting the cement mix in a shape by placing the cement mix in a mold to produce a molded article; d) Within 24 hours of casting, steam curing the molded article for 12 hours under atmospheric pressure; e) De-molding the molded article and placing the molded article inside a curing chamber and maintaining 100% humidity in the curing chamber; f) Raising the temperature in the curing chamber to 180 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; g) Releasing the pressure to reach atmospheric pressure within 20-30 minutes and the temperature reduced gradually;

(17) A method for producing a cast concrete product from a cement/aggregate composition, said method consisting of the following steps: a) Providing a mass of red dune sand with a 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; d) Providing a mass of fine aggregate having a nominal particle size of 5 mm, and course aggregate having a nominal particle size of about 20 mm, water, superplasticizer; e) Mixing the Portland cement red dune sand with the fine aggregate, course aggregate, water and superplasticizer to produce a mass of concrete; f) Casting the mass of concrete in a predetermined 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 and placing the molded article inside a curing chamber maintaining 100% humidity in the curing chamber; i) Raising the temperature in the curing chamber to 180 degrees C. within 1 to 2 hours to thereby raise the pressure to 10 bars and maintaining the 180 degrees 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 gradually; k) Removing the cast product from the curing chamber;

(18) While the invention has been described in connection with its preferred embodiments it should be recognized that changes and modifications may be made therein within departing from the scope of the appended claims.