Air entraining mortar and process of manufacture

A process and composition of matter for the treatment of mortar or concrete which includes fly ash containing carbon, for the purpose of increasing air entrainment. A small quantity of a soluble alkaline earth oxide is added to the mortar or concrete at the time of mixing. The material is added in form which is immediately available to inhibit the air-adsorptive properties of the carbon in the fly ash.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention relates to the manufacture of mortar or concrete which 
includes a fly ash containing carbon and an air entraining chemical 
admixture which is intended to create tiny air voids in the concrete to 
allow for the expansion of freezing water. 
2. Description of the Prior Art 
Fly ash from pulverized coal fired boilers is a "pozzolan" long used with 
cement, sand, gravel, air entraining chemicals and water to make concrete 
of special handling characteristics, or to reduce the amount of cement 
required. Boiler operating characteristics generally leave varying amounts 
of carbon in the fly ash. High carbon fly ash, with a carbon content of 
over 5%, is generally considered unsatisfactory for use in concrete 
because it tends to lower air entrainment. The small air bubbles formed in 
the mixing and then retained for several hours after pouring of the 
concrete are necessary in most parts of the United States to allow for the 
expansion of freezing water to counteract freeze/thaw scaling problems. 
One way of trying to overcome this problem is to mix in an excess amount of 
the air entraining agent. Even in this event however another problem 
arises during transportation of the product. 
This problem is that of maintaining air entrainment in the concrete during 
its travel from the mixer to the final placement. Loss of entrained air 
could occur even if there is little or no fly ash containing carbon in the 
mixture but the loss is more serious with high carbon fly ashes. 
A search of the prior art has revealed Patent No. 2,880,101 to Ulfstedt 
relating to the manufacture of steam cured light aggregate concrete by 
adding burnt magnesia or dolomite. However, the starting materials as well 
as the end purpose and product in the Ulfstedt patent are different than 
that of the present invention. Ulfstedt is concerned with the manufacture 
of lime silica brick which tends to shrink during steam curing. The slow 
hydrating burnt magnesia which Ulfstedt adds to the concrete mixture is 
relatively insoluble and would be unsuitable for use in the present 
invention which requires a soluble alkaline earth oxide which is 
immediately hydrated in the mix. 
Burley U.S. Pat. No. 4,011,094 shows a composition for patching or grouting 
which includes magnesium oxide or magnesium hydroxide to provide sag 
resistance. 
The following patents disclose the manufacture of light weight concrete by 
adding calcium oxide per se, calcium oxide in the form of a burnt clinker 
or as a mixture of calcium oxide and magnesium oxide to the concrete 
composition: 
______________________________________ 
3,470,005 3,884,710 
3,785,844 3,558,526 
______________________________________ 
The following patents depict the manufacture of hydraulic cements 
containing calcium oxide as an additive: 
______________________________________ 
2,947,643 3,066,031 
______________________________________ 
The following patents are submitted as of general interest: 
______________________________________ 
2,250,107 4,047,962 
2,476,306 4,101,332 
2,517,993 1,006,725 
4,018,617 1,343,929 
4,108,619 2,502,418 
4,038,095 2,836,502 
______________________________________ 
None of the above listed patents are believed to suggest or disclose the 
presently claimed invention. 
BRIEF SUMMARY OF THE INVENTION 
It is an object of the present invention to provide an improved process and 
composition of matter which will increase the ability of mortar and 
concrete with fly ash containing carbon and an air entraining agent, to 
entrain air necessary to reduce freeze/thaw scaling problems. 
It is another object to provide an improved process and composition of 
matter having these characteristics, which helps maintain air entrainment 
in concrete being transported from the mixer to final placement. 
It is a further object to provide an improved process and composition of 
matter of this nature, which is easy and economical to carry out and uses 
readily available materials. 
Briefly, the process of this invention includes the step of mixing a fly 
ash containing carbon and a soluble alkaline earth oxide in a form 
immediately available to inhibit the air adsorptive properties of the 
carbon in said fly ash. In another aspect, the invention comprises the 
steps of providing a mortar including at least fly ash containing carbon, 
cement, sand, water, an air entraining chemical admixture, and a soluble 
alkaline earth oxide in a quantity sufficient to inhibit the 
air-adsorptive properties of the carbon in said fly ash, and agitating 
said mixture to create air entrainment. 
The composition of matter of this invention is for inclusion in a mortar 
and briefly comprises fly ash containing carbon and a soluble alkaline 
earth oxide in a form immediately available to inhibit the air adsorptive 
properties of the carbon in said fly ash. In another aspect, the 
composition of matter briefly comprises a mortar having at least fly ash 
containing carbon, cement, sand, water, an air entraining chemical 
admixture and a soluble alkaline earth oxide in a quantity sufficient to 
inhibit the air adsorptive of the carbon in said fly ash.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
To carry out the process of this invention, a mortar or a concrete is 
prepared by mixing a fly ash containing carbon and a soluble alkaline 
earth oxide such as lime or calcium oxide, magnesium oxide or another 
soluble alkaline earth oxide which is either already hydrated or will be 
immediately hydrated in the mixture. These materials are mixed with water. 
The quantity of such oxides is preferably between 0.1% and 3% of the 
weight of the cement used, or 0.01% to 0.6% of the weight of concrete. 
Instead of or in addition to calcium oxide and/or magnesium oxide, the 
process could include a mixture of fly ash containing carbon with the 
hydrates of either calcium oxide or magnesium oxide. As a low cost 
alternative, waste dusts from the production of calcium oxide or magnesium 
oxide, containing soluble calcium oxide or magnesium oxide, could be mixed 
with the fly ash containing carbon. 
In another embodiment, the process could comprise the steps of providing a 
mortar or concrete which includes at least a fly ash containing carbon, 
cement, sand, water and coarse aggregate in the case of concrete, together 
with an air entraining chemical admixture. The latter is available in a 
wide variety of commercial air entraining agents such as lignins or 
organics. To this mixture is added a soluble alkaline earth oxide chosen 
from the group described above and in a quantity sufficient to inhibit the 
air adsorptive properties of the carbon in the fly ash. Upon agitating 
this mixture to create air entrainment, the soluble alkaline earth oxide 
will help retain the small air voids which are created. 
Any of various mixing sequences could be used in carrying out the process. 
In one sequence, the sand and coarse aggregate are first mixed, the cement 
including the fly ash containing carbon is added, and water is then added 
simultaneously with the air entraining agent and the soluble alkaline 
earth oxide. Mixing takes place during this sequence. Alternatively, the 
water and cement including the fly ash containing carbon could first be 
mixed and the sand, coarse aggregate, air entraining agent and soluble 
alkaline earth oxide added. 
It is important in carrying out the process of this invention that the 
soluble alkaline earth oxide be readily hydrated. This is because the 
additive will have no effect after the mortar or concrete sets, in about 
two hours, as far as air voids are concerned. 
As a composition of matter, the invention may be considered as one for 
inclusion in a mortar or concrete and thus comprising a fly ash containing 
carbon and a soluble alkaline earth oxide chosen from the above described 
group and in a form immediately available so as to inhibit the air 
adsorptive properties of the carbon in the fly ash. Alternatively, the 
composition of matter may comprise a mortar or concrete which, in addition 
to the above listed ingredients also contains cement, sand, water and an 
air entraining chemical admixture. 
The following tests demonstrate the ability of the invention to overcome 
problems of air entrainment and freeze/thaw scaling. 
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I. 
With CaO Additive, 
Control 2-1/2 lbs/cu yd 
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Lab Mix 
Cement 500 lbs/cu yd 
500 lbs/cu yd 
Fly Ash (5% carbon) 
100 lbs/cu yd 
100 lbs/cu yd 
2NS Sand 1150 lbs/cu yd 
1150 lbs/cu yd 
6A pebble 1920 lbs/cu yd 
1920 lbs/cu yd 
H.sub.2 O 262 lbs/cu yd 
262 lbs/cu yd 
Air Entraining 
Agent - Type Darex Darex 
Amount 25 oz/cu yd 25 oz/cu yd 
Initial Tests 
Slump 4" 4" 
Air 5.8% by vol. 8.0% by vol. 
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This initial test shows that the air entrainment in the mix having the 
calcium oxide was substantially higher than that without this ingredient. 
______________________________________ 
Delay Tests 
40 mins. 
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Slump 3" 4" 
Air 3.3% 7.3% 
Air Loss 43% 9% 
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This delay test illustrates that the air loss is substantially less in the 
mixture having the additive and thus air voids were still present to a 
greater extent. 
______________________________________ 
II. 
Both With CaO Additive 
2-1/2 lbs/cu yd 
Regular (5% Carbon) 
High Carbon (12%) 
Fly Ash Fly Ash 
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Lab Mixes 
Cement 500 lbs/cu yd 500 lbs/cu yd 
Fly Ash 100 lbs/cu yd 100 lbs/cu yd 
2NS Sand 1150 lbs/cu yd 1150 lbs/cu yd 
6A pebble 1920 lbs/cu yd 1920 lbs/cu yd 
H.sub.2 O 262 lbs/cu yd 262 lbs/cu yd 
AEA-Type Darex Darex 
Amount 25 oz/cu yd 25 oz/cu yd 
Initial Tests 
Slump 4-1/2% 4-1/2% 
Air 4.8% 6.0% 
______________________________________ 
The initial test showed that air in the mixture with the high carbon fly 
ash was greater than that with the regular fly ash. This anomalous result 
may be due to extra air entrapped as large bubbles in the fluffy carbon 
particles, rather than to entrainment by the air entraining agent. 
Entrapped air bubbles are of no benefit to concrete, and usually disappear 
very quickly, even before placement of the concrete. 
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Regular (5% Carbon) 
High Carbon (12%) 
Delay Tests 
Fly Ash Fly Ash 
______________________________________ 
Time 75 mins. 40 mins. 
Slump 3-1/4" 3-1/2" 
Air 4.8% 3.9% 
Air Loss 0 35% 
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There was no air loss in the mixture containing the 5% carbon fly ash. The 
test showed that even with the high carbon fly ash some air entrainment 
was obtained using the additive. Past experience had indicated that, with 
this level of air entraining agent, one would not have been able to obtain 
air entrainment with high (12%) carbon fly ash. 
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III. This test was for a lower target strength concrete. 
Control With Additive 
______________________________________ 
Plant Mix 
Cement 360 lbs/cu yd 
360 lbs/cu yd 
Fly Ash 60 lbs/cu yd 
60 lbs/cu yd 
2NS Sand 1530 lbs/cu yd 
1530 lbs/cu yd 
6A pebble 1800 lbs/cu yd 
1800 lbs/cu yd 
H.sub.2 O 275 lbs/cu yd 
275 lbs/cu yd 
AEA-Type Darex Darex 
Amount 25 oz/cu yd 25 oz/cu yd 
Water Reducing 
3 oz/100 lbs. 
3 oz/100 lbs. 
Additive 
Additive of Invention 
None 1.8 lbs CaO/cu yd 
Initial Tests 
Slump 6-3/4" 6" 
Air 6.9% 7.6% 
______________________________________ 
The initial test showed substantially greater air entrainment in the 
mixture with the additive. 
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Delay Tests Control With Additive 
______________________________________ 
Time 25 mins. 20 mins. 
Slump 5-1/2" 5" 
Air 5.6% 7.0% 
Time 50 mins. 30 mins. 
Water Added 3.5 gals/cu yd 
3.0 gal/cu yd 
Slump 8-1/2" 8" 
Air 4.6% 6.9% 
Time 70 mins. 65 mins. 
Slump 8-1/2" 8" 
Air 4.2% 6.0% 
______________________________________ 
These delay tests show that the mixture containing the additive 
consistently maintained air entrainment to a greater extent than the 
control mixture. The invention thus enables mortar or concrete to be made 
with a much higher carbon fly ash content than ever before. 
While it will be apparent that the preferred embodiments of the invention 
disclosed are well calculated to fulfill the objects above stated, it will 
be appreciated that the invention is susceptible to modification, 
variation and change without departing from the proper scope or fair 
meaning of the subjoined claims.