Compositions: coating or plastic – Materials or ingredients – Additive materials for inorganic cements which contain a...
Reexamination Certificate
2002-04-29
2004-06-15
Marcantoni, Paul (Department: 1755)
Compositions: coating or plastic
Materials or ingredients
Additive materials for inorganic cements which contain a...
C106S713000
Reexamination Certificate
active
06749682
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to non-electrolytic binders and cements having a retardant admixture to prevent hardening of the binder and more particularly to a method for on-demand control setting of such binders and cements using electrical current to defeat the retardant.
BACKGROUND OF THE INVENTION
Concrete is prepared by mixing cement, water, aggregate, and selected admixtures together to make a workable paste. It is molded or placed as desired, consolidated, and then left to harden. Cement needs moisture to hydrate and cure. The reaction of water with the cement in concrete may continue for many years.
Portland cement consists of five major compounds and a few minor compounds. The composition of a typical Portland cement is:
Cement Compound
Weight Percentage
Chemical Formula
Tricalcium silicate
50%
Ca
3
SiO
5
or 3CaO.SiO
2
Dicalcium silicate
25%
Ca
2
SiO
4
or 2CaO.SiO
2
Tricalcium aluminate
10%
Ca
3
Al
2
O
6
or 3CaO.Al
2
O
3
Tetracalcium
10%
Ca
4
Al
2
Fe
2
O
10
or
aluminoferrite
4CaO.Al
2
O
3
.Fe
2
O
3
Gypsum
5%
CaSO
4
.2H
2
O
When water is added to cement, each of the compounds undergoes hydration and contributes to the final concrete product. Only the calcium silicates contribute to strength. Tricalcium silicate is responsible for most of the early strength (first 7 days). Dicalcium silicate, which reacts more slowly, contributes only to the strength at later times.
The equation for the hydration of tricalcium silicate is given by:
Tricalcium silicate+Water→Calcium silicate hydrate+Calcium hydroxide+heat
2Ca
3
SiO
5
+7H
2
O→3CaO·2SiO
2
·4H
2
O+3Ca(OH)
2
+173.6
kJ
Upon the addition of water, tricalcium silicate rapidly reacts to release calcium ions, hydroxide ions, and a large amount of heat. The pH of the pore water quickly rises to over 12 because of the release of alkaline hydroxide (OH
−
) ions. This initial hydrolysis slows down quickly after it starts resulting in a decrease in heat evolved.
The reaction slowly continues producing calcium and hydroxide ions until the system becomes saturated. Once this occurs, the calcium hydroxide starts to crystallize. Simultaneously, calcium silicate hydrate begins to form. Ions precipitate out of solution accelerating the reaction of tricalcium silicate to calcium and hydroxide ions (Le Chatelier's principle). The evolution of heat is then dramatically increased.
Dicalcium silicate also affects the strength of concrete through its hydration. Dicalcium silicate reacts with water in a similar manner compared to tricalcium silicate, but much more slowly. The heat released is less than that by the hydration of tricalcium silicate because the dicalcium silicate is much less reactive. The products from the hydration of dicalcium silicate are the same as those for tricalcium silicate:
Dicalcium silicate+Water→Calcium silicate hydrate+Calcium hydroxide+heat
2Ca
2
SiO
4
+5H
2
O→3CaO·2SiO
2
·4H
2
O+Ca(OH)
2
+58.6
kJ
The other major components of Portland cement, tricalcium aluminate and tetracalcium aluminoferrite also react with water. Their hydration chemistry is more complicated as they involve reactions with the gypsum as well. Gypsum is added to slow or retard tricalcium aluminate hydration. Oil field cements contain a small amount of gypsum.
Heat is evolved with cement hydration. This is due to the breaking and making of chemical bonds during hydration. The heat generated is shown in
FIG. 1
as a function of time. Stage I hydrolysis of the cement compounds occurs rapidly with a temperature increase of several degrees. Stage II is known as the dormancy period. The evolution of heat slows dramatically in this stage. The dormancy period can last from one to three hours. During this period, the concrete is in a plastic state which allows the concrete to be transported and placed without any major difficulty. This is particularly important for the construction trade who must transport concrete to the job site. It is at the end of this stage that initial setting begins. In stages III and IV, the concrete starts to harden and the heat evolution increases due primarily to the hydration of tricalcium silicate. Stage V is reached after approximately 36 hours. The slow formation of hydrate products occurs and continues as long as water and unhydrated silicates are present.
Water-reducing and set-controlling admixtures are classified by ASTM C 494 into seven types:
1. Water-reducing
2. Retarding
3. Accelerating
4. Water-reducing and retarding
5. Water-reducing and accelerating
6. Water-reducing, high-range
7. Water-reducing, high-range, and
retarding
The materials that generally are available for use as water-reducing and set-controlling admixtures fall into one of eight general classes:
1. Lignosulfonic acids and their salts
2. Modifications and derivatives of lignosulfonic acids and their salts
3. Hydroxylated carboxylic acids and their salts
4. Modifications and derivatives of hydroxylated carboxylic acids and their salts
5. Salts of the sulfonated melamine polycondensation products
6. Salts of the high molecular weight condensation product of naphthalene sulfonic acid
7. Blends of naphthalene or melamine condensates with other water-reducing or set-controlling materials, or both
8. Other materials, which include: (a) inorganic materials, such as zinc salts, borates, phosphates, chlorides; (b) amines and their derivatives; (c) carbohydrates, polysaccharides, and sugar acids; and (d) certain polymeric compounds, such as cellulose-ethers, melamine derivatives, naphthalene derivatives, silicones, and sulfonated hydrocarbons.
These materials may be used singly or in combination with other organic or inorganic, active, or essentially inert substances to control cement set.
Many of the admixtures used for specific purposes in concrete are used as grouting admixtures to impart special properties to the grout. Oil-well cementing grouts encounter high temperatures and pressures with considerable pumping distances involved. Grout for preplaced aggregate concrete requires extreme fluidity and nonsettling of the heavier particles. Nonshrink grout requires a material that will not exhibit a reduction from its volume at placement. A wide variety of special purpose admixtures are used to obtain the special properties required.
For oil-well cementing grouts, retarders are useful in delaying setting time. Bentonite clays may be used to reduce slurry density, and materials such as barite and iron filings may be used to increase the density. Tile grouts and certain other grouts use materials such as gels, clays, pregelatinized starch, and methyl cellulose to prevent the rapid loss of water. It is standard procedure to add more retardant than is actually needed to allow enough time for placing the grout, sometimes up to 20,000 feet deep in a well to avoid set problems. This procedure sometimes results in a loss over the control of the set, either the set is too rapid due to complex chemistry down hole, or set does not occur as planned requiring waiting days at sometimes millions of dollars of cost per day.
Binders or cements which require electrolytic reactions and acidic conditions to harden are well known in the prior art. For example, a zinc phosphate hydrate cement is produced by combining a metal oxide zinc powder with an acid such as phosphoric acid. When these two components are intermixed, rapid setting occurs and a high quality zinc hydrate cement will be formed.
U.S. Pat. No. 5,252,266 to Brabston et al. teaches electric current induced hardening of binders and cements that rely on electrolysis to effect a pH change around either the cathode or anode thereby changing the surrounding salts to a pH bindable with metal oxides or other additives.
U.S. Pat. No. 5,268,032 to Malone et al. also relies on electrolysis to form an acid or base that reacts with metal oxide to initiate formation of a metal oxide phosphate. Fibers are used to add flexural and tensile strength.
Although these prior art cements have found wide accept
Marcantoni Paul
UT-Battelle LLC
Wilson Kirk A.
LandOfFree
Controlling the set of carbon-fiber embedded cement with... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Controlling the set of carbon-fiber embedded cement with..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Controlling the set of carbon-fiber embedded cement with... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3359913