Rapid hardening, ultra-high early strength portland-type...

Compositions: coating or plastic – Coating or plastic compositions – Inorganic settable ingredient containing

Reexamination Certificate

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C106S693000, C106S694000, C106S695000, C106S722000

Reexamination Certificate

active

06758896

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates in a broad aspect to rapid hardening high strength cement compositions and methods for their formation including the formation of special clinkered compositions. More particularly, the present invention is directed to rapid hardening, high strength cement compositions and to low emission methods for their formation which beneficially utilize the formation of special crystals in the cement clinker to significantly enhance the early compressive strength, sulfate resistance, and water impermeability of the cement.
BACKGROUND OF THE INVENTION
The manufacturing of hydraulic cement dates back to the earliest days of the Roman Empire. Pozzolana, a volcanic ash from one of the world's earliest cement kilns, Mount Vesuvius, was mixed with limestone to form a material capable of hardening under water. During the middle ages this ancient Roman art was lost and it was not until the middle of the eighteenth century that natural hydraulic cements were again made by burning mixtures of clay and limestone at high kiln temperatures to produce a clinker which was mixed with water and allowed to set or cure. However, due to the inherent variability associated with natural clay and limestone the exact composition of these natural cements varied widely and performance was unpredictable.
The art became a science in the early nineteenth century when Joseph Aspdin invented a process of carefully proportioning combinations of calcium, silicon, iron and aluminum found in local clay and lime deposits and burning these materials at high temperatures. This patented process resulted in portland cement with more consistent performance named after the stone quarried on the Isle of Portland off the British coast. Portland type cement is still one of the most commonly used structural materials today. In spite of significant advances in the material sciences, even today the basic process for making cement has remained essentially unchanged. Raw materials including limestone, clay, and bauxite are measured and mixed then fired at temperatures in excess of 1500° C. (2700° F.) until a cement “clinker” is formed. The finished clinker is crushed for use as cement and can be mixed with post production ingredients such as gypsum, soluble CaSO
4
anhydride and additional sources of C
2
S, C
3
S and C
3
A to modify properties. Typically, the latter three come from the addition of conventional portland type cement to the clinker.
For convenience of further description, the following standard cement industry abbreviations will be utilized to describe the composition of fired materials:
H-represents water (H
2
O)
C-represents Calcium Oxide (CaO)
A-Aluminum Oxide (Al
2
O
3
)
F-represents Ferric Oxide (Fe
2
O
3
)
M-represents Magnesium Oxide (MgO)
S-represents Silicon Oxide (SiO
2
)
K-represents Potassium Oxide (K
2
O)
N-represents Sodium Oxide (Na
2
O)
S-represents Sulfur Trioxide (SO
3
)
Mn-represent Manganese Oxide (Mn
2
O
5
)
P-represent Phosphorous Oxide (P
2
O
5
)
f-represent fluorine F
cl-represent Chlorine Cl.
Recent advances in our understanding of cement chemistry, the thermal dynamics of cement kiln operation and control, and pioneering breakthroughs in structural analyses using x-ray diffraction crystallography have allowed material scientists and cement manufactures to overcome and minimize many of the variables and problems inherent in cement manufacturing. However, two particularly vexing problems remain to be fully resolved. First, modern commercial cement compositions rely on a mineral composition known as C
3
S silicate and its hydration (water incorporation) rate for early strength. Yet, these compositions inherently contain high concentrations of non-early strength producing C
2
S in their base clinkers which cannot be converted to the more desirable C
3
S. High early strength and rapid setting times relate to the hydration rate of the C
3
S. General purpose portland type cement (usually designated ASTM I) typically contains approximately 50% C
3
S, 25% C
2
S, 12% C
3
A, 8% C
4
AF, 5% C. Thus the total amount of calcium silicates is approximately 75%, with the predominant silicate being C
3
S. The hydration rate of C
3
S and C
2
S significantly differ with the C
2
S component taking up to one year to fully hydrate. Consequently the C
2
S contributes very little or nothing to the early strength of the cement product. This is even further exacerbated if additional C
2
S is added to the clinkered material by supplementation with hydraulic cement during final product formulation. Consequently, the net silicate hydration rate, and therefore the ultimate rate of strength formation, is limited by the C
2
S hydration rate when the aqueous phase (water) is added.
The second perpetual problem associated with all current cement manufacturing processes is the terrible burden placed on the environment. Cement manufacturing is the single most significant source of atmospheric SO
x
(sulfur oxides) contamination. Further, other noxious gaseous emissions are exuded by the ton from the reaction conditions within the cement kiln. What is more, great quantities of fossil fuels are burned to power these huge kilns and plumes of silicon and aluminum particulates are generated by the mixing, packaging and shipping of the raw materials and final cementuous products. Many collateral methods have been developed to reduce these pollutants. However, the clinker formation process is still fraught with potentially disastrous environmental consequences.
There are four primary properties of cement and its products that material scientists continually work to improve: high early strengths, rapid setting time, resistance to degradation, and good expansiveness to offset shrinkage. For example, concrete made from portland cement together with sand, gravel or other mineral aggregate, typically undergoes shrinkage upon drying. This shrinkage is undesirable in that, among other reasons, it gives rise to cracks which ultimately weaken the set concrete.
Cracking results from excessive shrinking and high heats of hydration in thickly poured structures (cement and water react chemically and produce heat unlike plaster and water which merely dries). The shrinkage rate can be controlled through increasing the amount of calcium aluminum sulfate in the clinker which expands upon hydration in the presence of free CaO and CaSO
4
. Early attempts at reducing cracking and thereby increasing overall strength and resistance to chemical attack resulted in the so-called “calcium alumino sulfate” cements based upon 3CaO, 3Al
2
O
3
, CaSO
4
, abbreviated as either C
3
A
3
C{overscore (S)} or, preferably C
4
A
3
{overscore (S)}. Typically, the primary characteristic of C
4
A
3
S cements is their expansiveness. Addition of additives such as C
4
A
3
{overscore (S)} counteracts shrinkage and may or may not produce cements having early high strength. Examples of these calcium alumino cements can be found in U.S. Pat. Nos. 3,155,526 (Klein), 3,860,433 (Ost) and 4,798,628 (Mills).
Resistance to chemical degradation, water permeability and chlorine attack are qualities that result from improved resistance to cracking and chemical neutralization of reactive species by ingredients within the cement matrix. Resistance to sulfate attack is provided by limiting the C
3
A content to less than 5%, or using novel means to eliminate C
3
A through reactions with C{overscore (S)}.
Excepting the Kunbargi patent discussed below, one consistent element of the prior art has been the use of kiln temperatures in excess of 1500° C. This temperature has been believed necessary by those skilled in the art to encourage the production of the desirable stable calcium silicate C
3
S. However, these elevated kiln temperatures which have dominated the sintering process since Mount Vesuvius first erupted have not been without detriment. The temperatures traditionally used to reach sintering temperatures within the kiln result in a significant source of the primary greenhouse gases released during the calcining of CaCO
3
and through the

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