Cementitious compositions and a method of their use

Details Cementitious compositions and a method of their use Cementitious compositions and a method of their use

2002-03-12

2004-08-24

Marcantoni, Paul (Department: 1755)

Compositions: coating or plastic

Coating or plastic compositions

Inorganic settable ingredient containing

C106S725000, C106S726000, C106S733000, C106S737000, C106S823000

Reexamination Certificate

active

06780237

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to materials suitable for use in coating surfaces in particular the surfaces of rock and to a method for the treatment of surfaces employing the materials of the invention.
BACKGROUND OF THE INVENTION
It has been previously proposed to apply a coating of a polymer for example a polyurethane or polyurea to a mine surface by spraying the polymer-forming reactants onto the surface to be coated.
Alternatively the rock surfaces in mines have been coated by spraying an aqueous emulsion of an organic polymer for example a polychloroprene and causing the polymer to coagulate to produce a flexible coating in the form of a film or skin on the surface. This technique has been described in South African Patent No 8203384.
More recently there has been described in WO 98/58886 a composition comprising two parts. One is an aqueous emulsion of an organic polymer such as the copolymer of ethylene and vinyl acetate. The other part is a cementitious composition capable of absorbing at least its own weight of water. The cementitious composition described is an ettringite-forming composition containing high alumina cement, ordinary Portland cement and anhydrite.
In use the two parts are sprayed onto a rock surface of a mine to form a coating. This patent also discloses a dry mixture of solids formed from the cementitious composition and a dried polymer emulsion to which mixture water is added in the mine. Japanese Patent Application No 60-158269 to Takeda Chem Ind Ltd and Ohbayashi Gumi KK describes a film-forming composition containing alumina cement, gypsum and an aqueous dispersion of a high molecular weight material which may be an organic polymer such as styrene butadiene rubber or ethylene vinyl acetate copolymer. The alumina cement comprises calcium aluminates such as CaO.Al
2
O
3
, CaO.2Al
2
O
3
, 12CaO.7Al
2
O
3
as the main components. The compositions are intended to be applied to form a film of several mm in thickness The specification discloses that compositions based on portland cement have been found to be brittle and crack easily because, it says, it is impossible to control the speed of film formation and the flexibility of the film. Alternatively, when compositions containing only alumina cement are used, because the cement is quick setting, the working life especially in the summer is too short even where a retarder is used. In addition the elastic modulus of the resulting film is too high which again means that it is brittle. The specification describes how by using a mixture of an alumina cement and gypsum it is possible to obtain films without defects which are not dependant on the temperature, humidity or water permeability of the substrate. There is no disclosure that by an appropriate selection of the proportions of C12A7, calcium sulphate and polymer a coating having both high early strength and good long term flexibility can be produced, nor is there any disclosure of compositions which inherently have this combination of properties.
PROBLEM TO BE SOLVED BY THE INVENTION
For use in a mine the coatings are required to have an adequate early strength, typically at least 135 psi and also to have adequate long term flexibility. Previously it has typically taken around 24 hours to achieve the adequate early strength. To reduce down time in the mine it is very desirable to reduce the time taken to reach the target figure for early strength. The present invention provides a solution to this problem by providing a composition containing a reactive cement having a C:A ratio of greater than 1:1 such as C
12
A
7
and an organic polymer (which may be in the form of an emulsion or a dry powder), which composition on hydration is capable of achieving a strength at 4 hours of at least 135 psi and a long term flexibility, as measured by its elongation at 7 days of at least 20%.
SUMMARY OF THE INVENTION
According to the present invention there is provided a settable composition comprising
(i) a cementitious composition comprising the following components:
(a) at least 25%, preferably at least 40% of a reactive cement having a C to A or (A+X) ratio of greater than 1:1, preferably greater than 1.2:1, (where X is S* or S or F) for example C
12
A
7
or C
3
A or C
4
AF or an analogue of C
12
A
7
,
(b) from 0 to 10% of lime and
(c) from 5 to 70% preferably 10 to 40% of calcium sulphate, and where the sum of (b) and (c) is at least 15% the % being by weight based on the combined weight of (a), (b) and (c) and where the proportions of the components are such that the composition on hydration is capable of absorbing at least its own weight of water and
(ii) an aqueous emulsion of an organic polymer, the amount of (ii) in relation to (i) being such as to provide a weight ratio of polymer solids to combined weight of (a), (b)) and (c) of from 0.5:1 to 10:1, preferably 0.7:1 to 2:1 or
(iii) an organic polymer in the form of a powder dispersible in water and where the amount of organic polymer is such as to give a weight ratio of polymer solids to combined weight of (a), (b) and (c) of from 0.5:1 to 10:1, preferably 0.7:1 to 2:1 and where the proportions of the components are selected from within the above defined ranges to provide a composition which on hydration will have a tensile strength at 4 hours of at least 135 psi and an elongation at 7 days of at least 20%.
ADVANTAGEOUS EFFECT OF THE INVENTION
The advantage of employing the cement having a ratio of C:A of greater than 1:1 such as C
12
A
7
is that it enables an adequate early strength to be achieved more quickly and at the same time provides good long term flexibility. Previous experience has been that when steps are taken to increase the early strength then flexibility is reduced ie the product becomes more brittle, and conversely, when steps are taken to increase the flexibility, the early strength is reduced. To achieve the defined combination of early strength and longer term flexibility was therefore surprising.
One of the uses of the composition is as a replacement for welded wire mesh and reducing the time to achieve early strength enables the support characteristics of welded wire mesh to be reached quicker.
DETAILED DESCRIPTION OF THE INVENTION
The cement having a ratio of C to A of greater than 1:1 is preferably C
12
A
7
or C
3
A or an analogue of C
12
A
7
. C
12
A
7
is known as the mineral Mayenite and, as its formula implies, is richer in lime than calcium monoaluminate which has the formula CA where C in cement notation represents CaO and A represents Al
2
O
3
. It is widely used in the steel industry where it is employed in the form of a clinker to form slag. It is normally present in high alumina cement as a minor component, where it is typically present at about 10% by weight. As a cement it is very reactive.
By an analogue of C
12
A
7
is meant a material having a formula containing 7A the balance being C (where C is CaO) and other entities such as F or S (where S is silicate). Its analogues include C
11
A
7
.CaF
2
and C
11
A
7
.CaS. These analogues have a C:A ratio of at least 1.2:1. The calcium sulphate may be provided by a calcium sulphate-containing material such as beta-anhydrite, gypsum, or calcium sulphate hemihydrate.
The lime may be quick lime (CaO) or hydrated lime (Ca(OH)
2
) or may be provided by ordinary Portland cement which releases lime on hydration.
Calcium sulphoaluminate has the formula C
4
A
3
S* where C is CaO, A is Al
2
O
3
S is SiO
2
and S* is SO
3
. This is sometimes known as Klein's compound and may also be written as 3CaO.3Al
2
O
3
.CaSO
4
It is not essential that ettringite is formed, although it is preferred. To promote the formation of ettringite it is preferred to include calcium oxide and/or calcium hydroxide which may be provided by ordinary Portland cement to ensure that 3CaO.Al
2
O
3
is present in sufficient amount to form Ettringite during the hydration.
Ettringite is a calcium trisulphoaluminate having 32 molecules of water of crystallization and has the formula 3CaO.Al
2
O
3
.3CaSO
4
.32H
2
O. Ettringite is produced by the

Affiliated with

Also associated with

Rating

Cementitious compositions and a method of their use does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Cementitious compositions and a method of their use, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Cementitious compositions and a method of their use will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3298657