Abstract:
Shaped articles of hydraulic cementitious compositions with aggregates and other components, of mortar, grout, and concrete, are produced by admixing super water reducers and silica fume, the last component being the by-product from the manufacture of metallic silicon and ferrosilicon alloys.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a continuation-in-part of our application Ser. No. 718,522, filed Aug. 30, 1976 now U.S. Pat. No. 4,088,808. 
    
    
     BACKGROUND OF THE INVENTION 
     The primary object of this invention is to provide hydraulic cementitious compositions which have improved compressive and tensile strength, and improved bonding properties. This improvement is accomplished by the incorporation into the cementitious formulation the pozzolan silica fume. Silica fume is the by-product, now a waste product, obtained during the manufacture of metallic silicon and ferrosilicon alloys. A pozzolan is by definition a product which reacts with lime at room temperature in the presence of water. Lime is generated during curing of the cement. The use of an efficient pozzolan improves the strength, the density, resistance to water penetration in the cured compositions, and insolubilizes the water-soluble calcium hydroxide. Silica fume is an excellent pozzolan and bonding agent due to its physical and chemical properties as described below. 
     The process of producing metallic silicon consists of feeding a charge of quartz, coal and wood chips to the top of a tall furnace, provided with carbon electrodes extending to the bottom of the furnace. At the high temperature at the bottom, the silicon dioxide is reduced by the carbon to silicon, which melts and is tapped periodically. To produce the ferrosilicon alloys, scrap iron is also added to the charge. 
     The gaseous by-products are carbon monoxide, which oxidizes to carbon dioxide, and silicon suboxide which oxidizes to silicon dioxide, when the gases reach the top of the furnace. The particulates are the silica fume. 
     Typical analyses and properties of the submicron silica fume are: 
     
         ______________________________________SiO.sub.2             96.09%Fe.sub.2 O.sub.3      0.34%MnO                   0.09%Al.sub.2 O.sub.3      0.21%CaO                   0.35%MgO                   0.23%K.sub.2 O             0.59%Na.sub.2 O            0.07%SO.sub.3              0.35%loss on ignition      1.68%Surface area          25.9 m.sup.2 /gramParticle size         0.25-0.02 micronsAverage particle size 0.12 micronsBulk density as generated                 4-6 pounds pcfBulk density (packed) 12-14 pounds pcf______________________________________ 
    
     The extremely fine particle size and high concentration of silicon dioxide in the fume give it the high reactivity towards lime and thus its effectiveness as a pozzolan. Its presence in the cementitious compositions also greatly improves its bonding properties to aggregates and substrates, thus further increasing the strength properties of the compositions as well as providing an efficient mortar. 
     SUMMARY OF THE INVENTION 
     Our application Ser. No. 718,522, now U.S. Pat. No. 4,088,808, describes a process for forming shaped articles of cementitious compositions containing &#34;super&#34; water reducers and pozzolanic fly ash, as well as reinforcing fiber glass fabric or chopped fiber glass. The super water reducers may be selected from the group of polymers consisting of the alkali metal salts of melamine sulfonic acid partially condensed with formaldehyde, the alkali metal salt of naphthalene sulfonic acid partially condensed with formaldehyde (&#34;Lomar D,&#34; Diamond Shamrock Chemical Company), and about 30-90 percent of the alkali metal salt of a high molecular weight condensation product of naphthalene sulfonic acid and the balance 70-10 percent being the alkali metal salt of gluconic acid. 
     It has now been found that the above process can be greatly improved and its usefulness extended by substituting the above described silica fume for the fly ash used previously, as well as by the use of the silica fume along with fly ash. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following specific examples will further illustrate and describe the practice of our invention. The examples are summarized in Table 1. For convenience of comparison the components were recalculated on the basis of 100 parts by weight of the portland cement component (except for examples 9, 10, and 11). The blended dry components were mixed in water, cast into two inch cubes, cured in closed containers for the number of days shown, then dried in air and tested for compressive strength (psi) and for density (pcf). 
     It may be seen from the results summarized in Table 1 that the substitution of silica fume for fly ash, or the use of silica fume along with fly ash, greatly increases the compressive strength of the grouts and concrete. Examples 1 through 4 show this comparison for grey and white portland cements. Examples 1 and 3 were also applied as a mortar on brick. The mortar bond tests showed separation occuring in the brick rather than the mortar, thus showing that the bond exceeded the strength of the brick. For examples 5 and 6 a graded aggregate was used with an appreciable component of fines. Examples 7 and 8 show the comparison when using a light weight expanded clay aggregate. 
     
                                           TABLE 1__________________________________________________________________________Effects of Silica Fume, Compared to Fly Ash, on the CompressiveStrengthsof Grouts and Concrete, Determined on Two Inch Cubes   Example No.   1   2   3   4   5  6   7  8  9  10 11 12 13__________________________________________________________________________Grey Portland   100 100 --  --  100                      100 100                             100                                -- -- 25 100                                            100White Portland   --  --  100 100 -- --  -- -- -- -- -- -- --Lomar D 1.5 1.5 1.5 1.5 1  1   1.5                             1.5                                1.5                                   1  1  1  1Aragonite Sand   150 150 --  --  -- --  -- -- -- 100                                      125                                         350                                            350Morie Sand   --  --  150 150 -- --  -- -- -- -- -- -- --3/8&#34; QuartzAggregate   --  --  --  --  450                      450 -- -- -- -- -- -- --3/8&#34; CrushedTrap Rock   --  --  --  -- --  -- -- -- -- -- 700                                            700Expanded Clay(Fine)  --  --  --  --  -- --  133                             133                                -- -- -- -- --Silica Fume   15  --  15  --  -- 20  20 -- -- 30 30 -- 15Fly Ash --  15  --  15  10 --  -- 20 100                                   70 70 15 --Lime    --  --  --  --  -- --  -- -- 30 9.2                                      9.2                                         -- --Water   29  29  30  30  28 28  49 52 53 60 75 77 61Cure (Days)   28  28  28  28  28 28  28 28 28 28 28 9  9Density (pcf)   140 140 145 140 131                      140 90 95 98 125                                      114                                         156                                            161CompressiveStrength (psi)   21,200       12,800           20,800               14,000                   7,250                      11,800                          9,100                             6,200                                210                                   730                                      4,900                                         4,800                                            9,600__________________________________________________________________________ 
    
     Examples 9, 10, and 11 are unusual in that even in the complete absence of portland cement, but with the addition of lime, a significant strength was obtained with 30% silica fume and 70% fly ash, as compared with 100% fly ash. This strength was very greatly enhanced by admixing only 20% portland cement. Examples 12 and 13 show the effect of silica fume on concrete with very high loading of aggregate. In spite of this high loading, high strength may still be obtained with the use of silica fume. All these formulations show the characteristic glossy surface when cast in a mold with a synthetic polymer glossy release surface. They may also be reinforced with fiber glass scrim or chopped fiber glass and preserve the resulting higher flexural strength thus obtained. 
     It is obvious that many variations of these compositions may be formulated. We wish to encompass all such applications as come within the scope of the appended claims.