FORM 2 THE PATENTS ACT, 1970 (39 of 1970) & THE PATENTS RULES, 2003 COMPLETE SPECIFICATION (See section 10, rule 13) CONTROLLED DETERIORATION OF NON-REINFORCED CONCRETE ANCHORS" ELECTROMAGNETIC GEOSERVICES AS; of Stiklestadveien 1, N-7041 Trondheim, Norway. The following specification particularly describes the invention and the manner in which it is to be performed. ) Concrete is widely used in contact with water in constructions such as piers, bridge pillars, oil platforms etc. Concrete may also be used to make 5 anchors for releasably tethering a. submarine device at the seabed. Submarine devices are used for many purposes, for example, Sea Bed Logging surveys. These surveys require measuring devices to be tethered on the seabed, remain static during the survey, and be released afterwards so that the expensive device can be reused. 10 The measuring device, to the top of which a floater element is attached, is strapped to a concrete anchor element. The anchor then helps to sink the device in a stable manner and to secure a stable position on the seabed. After the measurements are finished, the device is released and floats to the surface leaving the concrete anchor behind. The concrete anchor is left on the seafloor 15 and apart from the fact that it is a foreign object on the seabed, it may subsequently present an obstacle for fisheries (e.g. trawling) or other industrial activity. Therefore, it would be desirable to develop concrete that will disintegrate within a limited time after contact with water, and, for seawater 20 applications, preferably only in seawater. In order to prevent the concrete anchors forming obstacles for trawling and other activities, the concrete should disintegrate shortly after the end of the useful life of the anchor. A secondary advantage of such an approach would be to ensure recovery of the expensive measuring devices after some time in cases where the release mechanism 25 should fail. The concrete composition should disintegrate into components that are not harmful to the environment and marine life. -2- The hydraulic binder of concrete based on Portland cement is amorphous calcium silicate hydrate (CSH-gel) where some 25% crystalline calcium hydroxide is embedded. Other less abundant minerals exist as well. If sufficient calcium carbonate is added to such a concrete (e.g. as 5 limestone filler), it is known that the concrete will be prone to degradation by sulphate attack at low temperatures (<15°C), even if a so called sulphate resistant Portland cement is used. The binder will actually crumble and turn into a mush since CSH gel is transformed to Thaumasite (a calcium silicate carbonate sulphate hydrate; Ca3Si(OH)6(C03)(S04>12H20) without binding 10 properties. Three components are required to form Thaumasite: 1. Calcium silicate (taken from the cement paste) 2. Calcium carbonate (e.g. addition of limestone filler) 3. Sulphate (usually intruded from the surroundings) The formation of Thaumasite is discussed by Sibbick, T., Fenn, D. and 15 Crammond, N. in "The Occurrence of Thaumasite as a product of Seawater Attack?', Cement and Concrete Composites, Vol. 25, No. 8, December 2003, pp. 1059-1066. The bedding mortar of a recently constructed harbour wall step in South Wales had suffered severe cracking and spalling within 2 years. The reaction products formed included Thaumasite, Ettringite, Brucite and hydrated magnesium silicate. The study proved that concrete with limestone will eventually form Thaumasite in line with the chemical changes outlined above. This reference discusses the undesired formation of Thaumasite and the problems caused thereby. However, the aim of the current invention is to provide a concrete formulation which may be used for seabed anchors, which will cause the anchor to disintegrate substantially shortly after the end of the useful life of the anchor. The useful life of the anchor .after deployment in the sea is of the order of 1 month. It is an object of the present invention to provide a cement formulation that will degrade in a controlled fashion, particularly in sea water. - 3 The present applicants have discovered that the degradation of the binder in a cement can be accelerated somewhat (with respect to standard compositions) by using a cement composition with sufficient limestone filler and high water-to-cement ratio (w/c) to make the resulting concrete very open 5 for diffusion of sulphates. The present applicants have further discovered that concrete formulations which include calcium sulphate in the form of either anhydrite (CaS04), hemihydrate (CaS04«l/2H20) or gypsum. (CaS04«2H20) as an additive, as well as sufficient limestone filler, experience a greatly accelerated 10 rate of degradation. Such concrete will be stable as long as it is stored dry and will only require fresh water to start: the Thaumasite formation. Furthermore, the reaction takes place uniformly throughout the concrete cross-section and an even crumbling is likely to occur. 15 According to the invention, there is provided a Portland cement formulation comprising amorphous calcium silicate, the formulation additionally comprising calcium carbonate and a source of sulphate. The calcium carbonate may represent 10 to 50 wt % of the formulation and may be in the form of limestone, chalk or calcite. The sulphate may 20 represent 6 to 50 wt % of the formulation and may be in the form of a metal sulphate such as calcium sulphate. The composition of the cement is such that items formed from it will undergo disintegration as a result of a chemical reaction between the calcium silicate, the calcium carbonate and the source of sulphate, in the presence of water, to produce thaumasite. The particles in the 25 cement which react to form Thaumasite will preferably be small (e.g. less than 1 mm in diameter) in order to allow the reaction to progress at an appropriate rate. 4 WO 2006/03801-8- PGT/GB2W5W03859 The preferred form of calcium sulphate is anhydrite (CaS04). Anhydrite is better for workability, in particularly if it is nearly "dead burnt" for delayed reactivity. A preferred cement formulation is obtained when the calcium carbonate 5 and source of sulphate are present in amounts which give rise to a molar ratio of S0427CQ32" of between 0.2 and 3.0. Particularly, the calcium carbonate and source of sulphate may be present in a stoichiometric ratio with respect to Thaumasite. The cement formulation may additionally comprise calcium hydroxide. 10 The calcium hydroxide may represent 2 to 40 wt % of the formulation. Preferably, the cement formulation contains no additives which would not decompose into components occurring naturally in the environment, and no organic admixtures. The main components of seawater are in decreasing order; 18,980 ppm 15 chloride (CI"), 10,561 ppm sodium (Na4), 2,650 ppm sulphate (S042~), 1,272 ppm magnesium (Mg2+), 400 ppm calcium (Ca2+), 380 ppm potassium (K4), 140 ppm carbonate (CO32"), 65 ppm bromide (Br), 13 ppm strontium (Sr) and up to 7 ppm silica (Si02). Seawater is in principle saturated with respect to calcium carbonate and is essential for crustaceans, mussels etc in building 20 protective shells. For this reason seawater has pH on the basic side (around 8). Thaumasite, Ca3Si(OH)<;(C03)(S04>12H2, can be said to consist of 27.02% calcium oxide (CaO), 9.65% silica (Si02), 43.40% water (H20), 7.07% carbon dioxide (C02) and 12.86% sulphur trioxide (S03) although it is a calcium salt of silicate, carbonate and sulphate. Thaumasite occurs naturally, 25 and transparent crystals are for instance found in the N'Chwaning Mine, Kalahari Manganese Field, Northern Cape Province, South Africa. Another site is the Bjelke Mine near Areskutan, Jamtland, Sweden. Standard industrial concrete formulations include organic admixtures such as plasticizers, which improve the workability of the concrete and - 5- decrease the water demand. However, since the concrete of this invention is designed to disintegrate, the inclusion of these admixtures is undesirable due to environmental concerns. According to a further aspect of the invention, there is provided a 5 Portland cement formulation as described in any of the preceding aspects, which is mixed with an aggregate, optionally being a light weight aggregate, preferably with a particle size of less than 50 mm. The aggregate may optionally be any of the following: filler, sand, limestone with particle size greater than 1 mm or gravel. 10 The invention also extends to an anchor for releasably tethering a submarine device at the seabed, made substantially from a formulation which will allow the anchor to disintegrate as a result of a chemical reaction between the calcium silicate, the calcium carbonate and the source of sulphate, in the presence of water, to produce thaumasite. The anchor optionally includes a 15 handle for the attachment of a release mechanism, which is preferably made of wood, leather or any other natural and environmentally non-polluting material suitable for the purpose. Alternatively, there may be a central hole for a central release mechanism. The invention also extends to a method of tethering a submarine device 20 at the seabed, which comprises: forming an anchor by mixing a cement or concrete formulation as described in any of the above aspects, respectively, with water, allowing the mixture to harden to form a finished anchor, attaching the submarine device to the anchor, and deploying the anchor and submarine device at a required location at the seabed. This method may be combined with 25 the further steps of releasing the submarine device from the anchor and allowing the anchor to disintegrate as a result of a chemical reaction between the calcium silicate, the calcium carbonate and the source of sulphate, in the presence of water, to produce thaumasite. 6 WQ-a006/038018 PGF/GD2003/003859 The present invention can be put into practice in various ways, some of which will now be described in the following set of example compositions, with reference to the accompanying drawings, in which: Figure 1 is a plot of compressive strength at age 28 days versus water- 5 to-cement ratio for concrete; Figure 2 is a plot of compressive strength evolution for concrete as a function of time and limestone (LS) addition; Figure 3 is a plot of compressive strength evolution for concrete as a function of time and addition of Limestone (LS)/anhydrite (ratio stoichiometric 10 with respect to Thaumasite) The aspect of the invention extending to an anchor made substantially from a formulation as described may be put into practice in various ways, an example of which is described below with reference to the accompanying drawings, in which: 15 Figure 4 is a side view of the anchor; Figure 5 is a section on A-A of Fig. 4; Figure 6 is a plan view of the anchor; Figure 7 is a view of the top surface of the anchor; Figure 8 is a view of the underside of the anchor. 7 WO 2006/038018 PCT/G1TCW5WB859- The following materials were used in trial concrete mixing. Cement: Norcem Rapid Portland Cement (Industry cement), laboratory cement "IN5" Limestone: 8 plastic bags of Verdalskalk Calcium carbonate, approximately 5 200kg Anhydrite: 1 bucket of Anhydrite, approximately 80 kg Aggregate:- 1 big bag of Norstone sand 0-8 mrri, approximately 300 kg 2 big bags of Verdalskalk, limestone 8-16 mm crushed stone, approximately 10 300 kg 2 bags of FrǾseth sand 0.4 mm, approximately 50 kg Laboratory concretes Proposed laboratory mixes to make concrete cubes and beams are shown in Table 1. The reference concrete is the one used by Spenncon Verdal AS 15 today. Spenncon has previously produced concrete elements approximately 1,000 x 1,000 x 90 mm for EMGS. The composition of the other laboratory recipes is with increasing limestone filler content, ending up with a stoichiometric concrete composition that deteriorates the binder totally. The limestone content is increased in steps of 20% and the cement+ limestone filler 20 + anhydrite mass is kept constant to 410 kg/m3 concrete. The concrete density is proposed equal for all the mixes. The water/cement (w/c) ratios are increasing from 0.45 to 0.81 and thereby the porosity increases as well. - 8 - WO 2006/038018 B€T/GD2005/003859 Table 1: Nominal concrete composition, kg/m3 Mix No 1 2 3 4 5 6 7 8 9 % Limestone 0 20 20 40 40 60 60 80 80 Rapid cement 410 342 342 293 293 256 256 228 228 Water, free 185 185 185 185 185 185 185 185 185 Water/cement-ratio 0.45 0.54 0.54 0.63 0.63 0.72 0.72 0.81 0.81 Limestone filler 0 68 68 117 117 154 154 182 182 Anhydrite 0 0 86 0 .147 0 192 0 228 Ardal 0-8 nun sand 885. 885 840 885 810 885 790 885 770 Fraseth 0-3 mm sand 40 40 40 40 38 40 38 40 37 Verdalskalk 8-16 mm gravel 880 880 840 880 810 880 785 880 770 Density 2400 2400 2401 2400 2400 2400 2400 2400 2400 Cement + limestone 410 410 410 410 410 410 410 410 410 From each mix 100 mm cubes and 100 x 100 x 400 mm prisms were made. The concrete was demoulded after 20 hours and placed in water at 20°C until 7 days age. 5 9 Laboratory procedures Concrete for documentation of properties was mixed in a 60 litre forced action mixer. Each concrete was mixed in two batches to achieve a total volume of 120 litres. 5 The mixing was carried out according to the following procedure: 1. 1 min mixing of dry materials 2. addition of mixing water during 1 min mixing,, 3. addition of excess mixing water to get a slump of approximately 200 mm 10 4. 2 min rest 5. 2 min mixing Fresh concrete properties for each mix were determined according to EN 12350, part 2 (slump), part 6 (density) and part 7 (air content). Compressive strength was determined on 100 mm cubes according to 15 EN 12390 part 3. Curing regimes After 7 days the specimens were stored at three temperature regimes: 1. In laboratory fresh water at 20°C 2. In sea water 5°-9°C 20 3. In concentrated seawater (5 times natural concentration) in laboratory at 5°C CCT/GD20U5ffitt38ST 40- Testing schedule Three cubes were tested for compressive strength after demoulding at 24 hours. Three cubes were tested for compressive strength after 7 days in fresh water of 20°C. The other. test specimens were placed in hardening regime 2 and 3 for 5 later testing. The testing schedule from 1 month after mixing for each mix is shown in Table 2 (the number indicates number of cubes or prisms subjected for testing). Table 2: Testing schedule for all mixes Testing after mixing 1 month 2 months 3 months 4 months 5 months 1 year Bending strength 5°C 2 3 3 3 3 Compressive strength 5°C 3 3 3 3 3 3 3 3 3 3 Hardening conditions A B C B C B C B C B C B C A - Laboratory fresh water at 20°C 10 B - Seawater 5-9°C C - Concentrated (5 times) seawater to increase the deterioration, 5°C Results 15 Fresh Concrete The real compositions of the 9 mixes are shown in Table 3. The workability was measured by standard slump measure according to EN 12350- PC 2. The density and air content was measured according to EN 12350-6 and EN 12350-7, respectively. The density and air content was measured according to EN 12350-6 and EN 12350-7, respectively. 5 12 ECT/CB2005/003859 Table 3: Real composition and fresh concrete results, (surface dry aggregates) Concrete Mix No 1 2 3 4 5 6 7 8 9 Industry cement 400 334 277 286 212 250 170 223 143 Calcium Carbonate 0 67 5.5 114 85 150 102 179 114 srete Anhydrite 0 0 70 0 107 0 129 0 144 a om.n Ardal sand 0-8 mm 856 861 866 865 870 863 863 867 862 bH Fraseth sand 0-4mm 39 39 38 38 38 38 38 38 38 Verdalskalk 8-16 mm 856 861 861 860 865 858 858 862 857 Free water 219 211 208 209 201 208 208 204 207 Water/binder-ratio .55 .631 .750 .731 .950 .835 1.22 .915 1.45 Slump, batch 1, mm 195 180 200 190 190 190 210 200 210 Slump, batch 2, mm 205 190 200 200 200 190 210 200 210 Air content batch 1, % 1.2 1.3 1.2 1.2 1.4 1.3 1.0 1.3 0.9 Air con tent batch 2, % 1.2 1.2 1.3 1.3 1.3, 1.2 0.9 1.3 0.9 13 P€T/GB2005/0038S