NZ764106B2 - Composition of a cement additive material as an additive to cementitious mineral admixtures, and utilised as latent hydraulic binders to improve the outcome of cementitious products - Google Patents

Abstract

A composition of a cement additive material to improve durability of cementitious structures, is disclosed. The cement additive composition comprises an admixture of one or more of divalent magnesium metal silicates with capacity to act as a latent hydraulic binder in said composition activated by a hydration process under aqueous conditions, and in particular the divalent metal silicate is magnesium-dominated silicate, preferably comprising mineral groups of olivines, orthopyroxenes, amphiboles, talc and serpentines or mixtures thereof. The composition also comprise chloride ions or brine. Applications of the compositions are also disclosed, in particular to utilize a property of hydration as a major trigger for the latent hydraulic reaction of magnesium silicates, particularly for said olivines, when exposed to water and brines, in order to obtain a cementitious material becoming self healing. a hydration process under aqueous conditions, and in particular the divalent metal silicate is magnesium-dominated silicate, preferably comprising mineral groups of olivines, orthopyroxenes, amphiboles, talc and serpentines or mixtures thereof. The composition also comprise chloride ions or brine. Applications of the compositions are also disclosed, in particular to utilize a property of hydration as a major trigger for the latent hydraulic reaction of magnesium silicates, particularly for said olivines, when exposed to water and brines, in order to obtain a cementitious material becoming self healing.

Description

W0 2019f074373 PCT/N02018/050238 COMPOSITION OF A CEMENT ADDITIVE MATERIAL AS AN ADDITIVE TO CEMENTITIOUS MINERAL ADMIXTURES, AND UTILISED AS LATENT HYDRAULIC BINDERS TO IMPROVE THE OUTCOME OF CEMENTITIOUS PRODUCTS The field of the present invention The present invention concerns a composition of a cement additive material to improve durability of cementitious structures, as defined in the following claim 1.

More specific, the present invention relates to products made from cementitious mineral ures. The mixtures will include a cement ve product, a new ingredient, purposed as a latent hydraulic binder for cementitious mineral admixtures, mortars and concrete structures for industrial applications and for construction purposes. The utilized ingredient will increase the durability of the product over its whole me, and when in contact with external humid, wet or ged aquatic environment.

The invention also s to several applications of the inventive latent hydraulic binder for cementitious products as appearing in claims 6—14.

Background of the invention.

The present invention relates to the field of cementitious als such as nd Cement and geopolymers. The purpose of the ion is to apply divalent ium—iron solid solution silicates (for example the mineral groups e, orthopyroxene, amphibole, talc and serpentine), here called “magnesium silicates”, as latent hydraulic binders for cementitious mineral admixtures, thereby increasing the integrity, volume, weathering and/or lifetime of the cementitious mineral admixture structure.

W0 2019f074373 PCT/N02018/050238 The invention s the integrity— and/or lity enhancement of cementitious structures over time by including/adding magnesium silicates in cementitious l admixtures as a latent hydraulic binder, and to increase its capacity to handle weathering and exposure to flow of water mixtures on and through the cementitious materials.

Ordinary well cement is based on the principles of Portland Cement. As NORSOK D010 and API Spec 10A are the current industrial standards for operations in the oil and gas industry, it was important that that the present invention is able to meet those standards in an affordable manner. Of particular advantage of the present invention is that it easily added to current well cements operations to improve performance and meet standards. Many of the advantages of the present invention are apparent in the application of well cementing and completing, plugging, ary and ent abandonment of wells Alternatives ed to ordinary well s are Geopolymers. These are materials that are visco-elastic. An example of this physical property is the mixture of cornflour and water; it is hard when handled and soft when held. Another example is Bingham Plastic. This behaves like aise (soft when handled, hard when held). r of these products are currently ably priced or particularly standard ly.

Metamorphism is the mineralogical and structural adjustment of solid rocks to physical and chemical conditions that have been imposed at depths below the near surface zones of weathering and diagenesis and which differ from conditions under which the rocks in question originated.

Inorganic materials that have pozzolanic or latent hydraulic binding effects are commonly used in itious materials. Hydraulicity is defined as “the ty of limes and cements to set and harden under water whether derived from a naturally hydraulic lime, cement or a pozzolan”. A latent hydraulic binder reacts in more slowly and due to a trigger in a particular manner in order to change the properties of the cementitious products. It will come to a full strength on its own, while very slowly. These have the purpose of either stretching the need for lime clinker in the cementitious mineral admixture, or improve the properties of the cementitious mineral admixture. sure of the state of art.

With regard to the state of art, reference is made to the following patent publications: FR-2.939.429, US-2015/18905, 6/094506 and US-2008/196628. Additionally reference can be made to EP-2246315, CN-10521031, and US-20120137931.

All these documents deal with cement mineral mixtures for ing concrete to defend the cement construction from a reaction with CO2, named a carbonation process. Carbonation is a well-known reaction for all lime-cement mixtures and change its mineral composition from CaO (lime) to CaCO3 (Calcium carbonate) and this happens naturally over time due to weathering. The magnesium silicates will also react with the CO2 and the minerals formed due to carbonation will expand into gaps and cracks of the cementitious structure in order to keep the structure sealed.

In more detail, the mentioned patent FR-2.939.429 ns to the carbonation of magnesium silicates. This is particularly relevant in the injection and sealing of reservoirs containing CO2. 39.429 discloses the use of magnesium-olivine i cement/concrete mixtures for the sealing of drill wells into geological formation rock for the purpose of storing of CO2 in ic formations.

Details of a carbonation process.

Magnesium silicates can be carbonised (e.g. altered by CO2), and therefore will increase the cement-plug lifetime for the cement admixtures in wells when exposed to CO2, particularly those penetrating carbon-dioxide storage (CCS) reservoirs. (FR-2.939.429). That patent shows es of the reaction of olivine with CO2 producing magnesium carbonate, creating a selfhealing cement in actual conditions in the well.

Below is an example of a carbonation s of the magnesium end member olivine reacting with carbon dioxide.

Carbonation: Mg2SiO4 + 2CO2 → 2MgCO3 + SiO2 rite carbon-dioxide Magnesite quartz The carbonation process happens naturally, where CO2 reacts with forsterite.

An object of the present ion is to improve the properties of a cementitious mineral admixture by adding a pozzolanic or latent hydraulic binder that reacts h hydration i.e. with H2O and other aqueous solutions. There are a multitude of ans and latent hydraulic binders used in the cementitious mineral admixtures containing lime (CaO), and water.

Pozzolans es a number of natural and manufactured materials, such as ash, slag etc. The pozzolans impart specific properties to cement. Pozzolanic cements may have superior strength at a later age and may be more resistant to weathering.

Brief Description of the Figures.

FIG 1A discloses a CT scan of a sample before Experiment #1 was performed.

FIG 1B discloses a CT of a sample after Experiment #1 was performed.

FIG 1C discloses measurements of porosity and permeability over time during ment #1 FIG 2A discloses a CT scan of a sample before Experiment #2 was performed.

FIG 2B discloses a CT of a sample after Experiment #2 was performed.

FIG 2C discloses a CT scan of a slice of a sample before Experiment #2 was med.

FIG 2D discloses a CT scan of a slice of a sample after Experiment #2 was performed.

FIG 3 discloses the compressive strength analysis of the sample of Experiment #3.

The present invention.

The present invention pertains to the pozzolanic or latent hydraulic reaction h the ion, i.e. the reaction with water and/or aqueous solutions like seawater or other brines with magnesium silicates (divalent magnesium-iron solid solution silicates, i.e. the mineral groups olivine, orthopyroxene, amphibole, talc and serpentine). In our invention, the sealing properties and ence of the resulting product is independent of carbonisation.

The composition of a cement ve material to improve durability of cementitious structures according to the invention is characterized in that the composition comprises an admixture of one or more of divalent metal silicates with capacity to act as a latent hydraulic binder in said composition activated by a hydration s under aqueous conditions.

W0 2019f074373 PCT/N02018/050238 The preferred features of the composition appear in the following claims 2 — 4. According to a particular preferred embodiment, the composition includes a mixture of Portland cement and water, added olivine in a range of from 2 — 99 % based on weight of total hydraulic solid materials (i.e. not including aggregates).

According to an essential aspect of the invention, there is disclosed application of a composition of a cement additive material ing to the preceding claims as a latent hydraulic binder for cementitious mineral admixtures, mortars and concrete structures for industrial applications and for construction purposes, as appearing in claims 6—1 1.

A method for making cement structures in accordance with the present invention is described in claims 12 and 13.

Further disclosure of the invention, an example: Olivine group minerals (Mg,Fe)zSiO4 are silicates with magnesium and iron as major cations, while calcium and minor ts may substitute in the nt cation sites. While reactions between crystalline minerals and H20 are generally regarded as slow, the magnesium silicates do react even at room temperatures. Fine powders of e, when mixed with water may increase the pH of the water to over 9. This is the origin of the term “ultrabasic rocks” and the end—member of the reactions utilized in our invention.

The hydration reactions described here happen at the very low end of the pressure— and temperature range generally discussed in rphic petrology. Diagenesis, weathering and very low grade metamorphism are the main processes. In mical ons, an added g on a reaction can be geochemical instabilities, where minerals or solutions not in equilibrium seeks to react towards a steady state. In our invention, we are ing anthropogenically induced geochemical instabilities to induce low, very low grade metamorphism, diagenesis and weathering. Over time, even olivine grains covered in an aqueous solution and left at room ature will weather to alteration minerals.

W0 2019f074373 PCT/N02018/050238 Below is shown some of the reactions of end—member olivines (forsterite and fayalite) when hydrated in reaction with H20. It may occur according to these but not limited to the following reaction equationsz. 3Mg23i04 + SiOz + H20 —> 205(OH)4 rite Quartz water Serpentine 2 MngiO4 + 3H20 —> Mggsi205(OH) + Mg(OH)2 Forsterite water Serpentine Brucite 3F€2$i04+ 2H20 —> 2F6304 3SiOz + 2H2 Fayalite water Magnetite aqueous silica hydrogen The purpose of the present invention is to utilize a similar reaction pattern of magnesium silicates in hydration reactions (with water (H20) and associated aqueous solutions (e.g. brines)), in that the composition is used as enhancers in cementitious l admixture materials, as a pozzolan, a latent hydraulic binder, as a filler, for the use of producing amorphous silica in the latent reaction, and to provide a natural anti—fouling agent in itious concrete and/or mortar ures in general.

As disclosed above the present invention is a cement additive material that is a pozzolanic or latent hydraulic binder of made from magnesium silicates that improve the properties of a itious mineral admixture and the outcome of the products made from the ure.

Our product is a cement additive material that is a latent hydraulic binder that is activated through hydration, and is intended for cementitious mineral admixtures for the purpose of increasing the integrity of the d structures produced over time. The product may also be used for its faster, pozzolanic effects.

While a function of t that is a cement additive is that the magnesium silicate material is as a filler in the cementitious l admixture material, the latent hydraulic binder reaction by the magnesium silicates will at low—, very low metamorphosis, diagenesis and weathering W0 2019f074373 PCT/N02018/050238 reactions of the magnesium silicate with water form reactive products such as magnesium silicate hydrates, amorphous silica and hydrogen. These reactions and alterations the original minerals causes the reactive products to expand into gaps, pores and other pressure shadows in the cementitious structure with amorphous and crystalline alteration als.

The minor elements of naturally occurring magnesium silicates and traces from accessory minerals, ning elements like Nickel, Zinc and Chromium may in addition improve the interactions with steel, notoriously corroded in contact with corrosive water and brines. ium silicate ps frequently are vegetation free, and we are suggesting this is grounds to e magnesium silicates due to the t of minor amounts of anti—biofouling agents.

For accessory minerals, we are using the standard definition to one skilled in the art of between 0.05 % and 3 % by volume of rock. For the present invention, this range is ably between 0.1% and 1 %.

Adding magnesium silicate minerals to the cement or geopolymer admixture will therefore provide a long term and ide free way to provide anti fouling properties to cement and concrete structures. Trace ls containing Zn, Cr and other heavy metals will appear as microscopic distinct points in a larger blend of ls enhancing the anti—fouling properties on the cement surface while being a negligible contributor to macroscale environmental COl’lCCI'l’lS .

It is known that the most used experimental olivine (San Carlos olivine) with water will metamorphose to talc (Mg3,(Si4010)(OH)2), and quartz minerals below 70°C and to serpentine minerals (for example Mg6,(Si4010)(OH)g) above 70°C while giving the water a higher pH due to the H2 produced in the on and dissolved into water. The higher pH water is naturally and by less oxidizing to iron and steel and reduce the weathering and weakening of cement and associated structures inside and outside to the cementitious mineral admixture. Mixing materials lowers the Gibbs free energy compared to the pure end-members. The initiation of reactions will happen at lower temperatures for magnesium silicates in cementitious l admixtures, than for the pure end—members alone. The AT above initiation of reactions will W0 2019f074373 PCT/N02018/050238 influence the rate of reaction, as the rate be dependent on the temperature as described by the Arrhenius' equation. Therefore, the processes in the mixtures will speed up and/or occur at even lower temperatures than model l end-members. At diagenetic and very low grade metamorphism pressures and temperatures, the magnesium silicates will reduce and/or replace the need for quartz additives that t the growth of unwanted minerals (e.g. promoting Tobermorite in lieu of the high Ca/Si ratio phases).

Structures like road constructions or ngs for homes and offices will decay over time due to weathering and other external factors like climate, as well as due to al structural decay.

Adding magnesium silicates as a cement additive product working as a latent hydraulic binder will reduce weathering by low temperature metamorphism involving hydrous alteration of the magnesium silicates over time.

Our product will have the same outcome as crystalline quartz flour for compressive strength and permeability at higher pressures and temperatures. Alternatively, it may work like slag, which is also a latent hydraulic binder for cementitious mineral admixtures.

The latent hydraulic binder reaction by hydration without calcium in solution in this invention works by altering the minerals to secondary minerals with a lower y and therefore also a higher volume. Due to pressure—gradients on micro , the secondary ls produced will seek to form in voids, pores, cavities and , thereby sealing the cementitious product when it is exposed to aqueous solutions ally and internally. These are particularly important where weaknesses in the cementitious product occurred during the emplacement of the mixtures. Even during curing of the cement l admixture containing our cement ve material, the volume of the cementitious mineral admixture increases, ed to ordinary cementitious mineral admixtures that shrink during curing. Hydration is a major trigger for the latent hydraulic reaction of magnesium silicates, particularly for olivines. By adding ium silicates, the cementitious materials become self-healing when exposed to water and brines.

As the present invention expands in volume during and after curing, it allows for a better sealing t fluids as more of the available space and pores are filled with reactive materials.

W0 2019/‘074373 2018/050238 Used in oil and gas wells, it improves the exposure ence to fluids that are penetrating the structure made up by the cementitious mineral admixture, while potentially creating natural reactive bonding with the side rock and ing the corrosion of steel in the well. Already established methods used in well maintenance and the plugging and abandonment (P&A) process today can still be d by use of this new latent hydraulic binder for cementitious mineral admixtures. This make it easier for the industry to take the new cementitious into use.

The olivines have a particular wetting angle being much smaller than most other solids to water, and the use of this magnesium silicate will change the adhesion of olivine—containing cementitious mineral admixtures to steel and other iron products.

This change in wetting angle ensures a better bonding to steel and iron. This is very useful during construction applications that involve reinforcing bars. It is also useful when using cement with steel tubulars such as used in the oil and gas industry. Additionally, the present invention provides a high buffer capacity; ting the pH from changing in the face of a strong acid (or base). This ts or reduces harm to the integrity of the steel or iron.

Our tests show that cementitious materials that have been produced with pores and res are filled by low temperature metamorphic minerals when the materials are exposed to water and brines.

Thus, there is provided a cement capable of binding suitable aggregate into a concrete that can set and harden underwater.

Examples of use: The chemical ties of magnesium silicates make the mineral suitable for improvement of the outcome of cementing and plugging of wells that are drills that are trying to reach reservoirs. The minor elements of magnesium silicates and the commonly accessory minerals will improve the interactions with steel. This invention can be used for the management of wells, including, but not limited to open petroleum oirs, inside casing/liner/tubing/conductor, between casing/liner/tubing/conductor and geological W0 74373 PCT/N02018/050238 formation, in open hole as kick—off plug for drilling/kicking off for new well path, as barrier as part of plug and abandonment, as well as permanent plug and abandonment, both conventional and by use of perf and wash technology. Invention can be used in oil producers, new and old, gas producers, new and old, water producers, new and old, injection wells, new and old, Geothermic wells, new and old, water wells, new and old or any combinations of these.

Exploration well, appraisal wells, development wells will also be areas of use for invention.

Well integrity problems due to degraded cement sheaths are a known cause of leaks through active and ned wells. Development of an improved well ng material that hinders leakage through well plugs is likely to have major positive environmental impact, as it improves long—term well integrity and s leakages to the environment. Our invention, as a cement additive material added to cementitious mineral ure materials, magnesium silicates will increase the —plug lifetime for the drilling, abandonment of oil and gas wells in general, but also those penetrating present or future carbon—dioxide e reservoirs.

Current ces on P&A involves massive retrieval (“pulling”) of steel tubulars. This is an environmental work hazard due to the application of rotating methods (cutting/milling) that can threaten workers, all the while very costly in rig time. The reduction of steel corrosion from our product will possibly reduce the amount of steel pulling needed and enable piercing practices currently underway (so—called perforate—wash—cement). Likewise, the acoustic properties of olivine are significantly different from both the surrounding rocks, steel and mud, making logging easier if applied as an annular sealant material. The addition of the cement additive product will make ry wells described above safer for the future by using this ion in the cementitious material also in areas that may become CCS reservoirs, as shown by FR—2.939.429.

This invention is suitable to be used in cement, mortar and/or concrete products to reduce biofouling and corrosion of steel and iron, weathering and carbonation of the cement material (also as a part of concrete).

The corrosion of constructions were concrete containing e.g. Portland cement is widely known and is more prone to this in environment with rough weather and were d to C02 and salt conditions. This intervention will better resist these conditions and hence increase the lifetime of concrete uctions in general. wo 74373 PCT/N02018/050238 In ry Portland cement, it is a requirement that the Cl" ions (e.g. salt water) in the fluid medium added to the e is kept to a minimum. As such, normal seawater, and other water types containing chloride, are not used. In fact, it is normal to use ized water.

Chloride ions reduce the breaking strength of ordinary cement mixtures. The chloride in the water is also known to erode and rust enforcing steel structures. This is particularly a problem when adding marine sediments as aggregates to a cement mixture. rmore, it is a problem when there is scarcity of fresh, low Cl" water for the mixtures.

The concrete industry may then use water that could have been used for potable water. Lastly, using ordinary Portland cement concrete structures and cemented wells in products that will be exposed to seawater and brines after hardening, e.g. harbors, spars, molos, will be prone to deconstruction from the chloride.

In our ion, we have found that the cement additive s the need for a low Cl‘ water medium as the magnesium silicates will strengthen the structures when exposed to chloride ions. This allows seawater and underground brines to be used directly without any removal of the chloride ions.

A chloride concentration of between 0.7 % and 10 % by weight of water would be functional, preferably between 1.2% and 5%. These are common trations of Cl' found in seawater and underground brines.

Additionally, the high pH of the magnesium silicates and their reactions will reduce the amount of oxidation of iron associated with the cement or concrete product. A designed variation of grain sizes will buffer the solids for longer. rmore, if the solids are deformed at a later stage, broken grains will be free to react with chemicals that are available in the potential flow through them. This will increase the protective effect if the final structure needs to self—heal.

Experiment #1.

In an experiment, solid cementitious mineral admixture products were fabricated based on a mixture of 80% Portland cement, and 20% olivine (which is a divalent magnesium—iron solid wo 2019/074373 PCT/N02018/050238 solution silicate) by weight, and water having an ordinary W/C number (W/C 2 water to cement ratio). The fraction of olivine was 0.2 with denatured water added. A solid cementitious mineral admixture cylinder was prepared and flooded by a seawater analog brine for a period of eleven days. The changes of permeability was measured throughout the experiment and the porosity was evaluated before and after the experiment by using a CT scanner. .

The measurements showed that porosity of the product, when ng the inventive itious mineral admixture was d by as much as 55 %, and permeability went down by 70% after said just eleven days exposed to brine. The experiments show that a more dense and water resistant concrete material is achieved by the present invention.

FIGS 1A and 1B se CT scans of a sample during this experiment. The red denotes voids within the sample in both FIGS 2A and 2B. In FIG 2B the green shows precipitation within the voids of the sample.

FIG 1C discloses the permeability and injection pressure as a function of time over the course of the experiment.

The ements show that the porosity of the t was reduced by 70% and the permeability by 55%. This demonstrates the self—healing ability of the invention when exposed to seawater.

Experiment #1 show that a denser and water resistance concrete material is achieved by the present invention.

Experiment #2.

In another experiment, a mixture of Portland cement and the present invention as in ments #1 and #2 was exposed to CO2 for a period of a week.

FIGs 2A and 2B disclose the CT scans of before and after Experiment #3. The red denotes voids within the sample in both FIGS 2A and 2B. The green arrow in FIG 2A points to large W0 2019I074373 PCT/N02018/050238 number of inhomogeneities. In FIG 2B the green shows precipitation within the voids of the sample.

FIGs 2C and 2D disclose CT scans of slices of the samples that are sed in FIGs 2A and 2B respectively. Notice that the internal crack of FIG 2C has been healed by the end of the experiment as shown in FIG 2D.

Measurements showed that after exposure to CO2, over 90% of the pores were healed by newly formed minerals. Additionally inhomogeneities were nearly eliminated. These affected reduce the porosity of the sample.

Experiment #3.

The test the strength and ties of the invention at different additive tages (20, 35, and 50% relative to total additive + cement) experiments was tested. A cylindrical sample was subjected to increasing amounts of compressive force to the top and bottom over a period of time. The experiment was stopped when the sample was no longer able to support the force that was applied. Each sample was cured for a period of one week before the experiment.

The s of this experiment is shown in FIG 3. The 0% line (black) is regular Portland cement t the invention being added. The percentages are percent additive by percentage weight of the total cement mass. The Portland cement has a very sharp knee once it breaks. This is a Sign that the Portland cement is failing in a brittle (“hard”) manner. By contrast, the results with the invention have a rounded knee. This is a sign that the failure is a rupture in a brittle , but in a cataclastic or rolling manner. Note that each sample at a given percentage was repeated three times.

From the results of this ment, we expect a mixture of 2 — 99% by weight of solids of nt magnesium dominated silicates to be effective.

Cataclasis is here not being used or defined in a manner that is contrary to its standard meaning to one skilled in the art. Cataclasis means ng of grains. Cataclastic flow is W0 2019f074373 PCT/N02018/050238 observed during deformation of samples containing the ion. Above the brittle—ductile transition zone is cataclastic flow the main deformation mechanism accommodating large strains. The deformation mechanism is brittle, but on a scale that make the deformation continuous and spread over a zone. This zone is observed to be broader the more magnesium silicates that were add. Hence, we find a microscopically brittle behavior that produce macroscopic ductile flow. The deformation can be ed as a ductile ism, although taking place within the elastico—frictional regime of ation. The broader this deformation zone is the more is the macroscopic ductile deformation. Cataclasis indicates that the strength of the bounding between cement grains is strong enough to allow grains to crush. Deformation is also accommodated by the sliding and rolling of nts within the deformation zone / deformation part of the cement.

Experiment #4.

In an experiment, the ordinary Portland cement, olivine and water was mixed and left to cure for one week, after which a core was extracted. The cement was left to cure for five more weeks at sixty s and another core was extracted. When compared, there was 50% less porosity between one week and six week curing at 60 degrees C at 1 atm pressure. There was no change in a control sample of Portland cement without the additive of the present invention.

Final comments: In general, the relative increase in volume when e turns into serpentine is 30—40%, and likewise olivine hydrated to other minerals through hydration. Therefore, each percent of magnesium silicate olivine or other divalent magnesium dominated silicate that is added to a cement mixture may increase the volume by up to 0.4 % when hydrated.

It is ed that as little as 2% olivine or other divalent magnesium dominated silicate by weight can give great initial, short term, ons in terms of early buffer capacity, limited volume compensation and some resistance to C02 initially.

We estimate that we will need 8-12 % (by weight of total hydraulic solid materials) e or other divalent magnesium dominated silicate to reduce the shrinkage to 0%. wo 2019/074373 PCT/N02018/050238 Further, it is estimated that a percentage range (by weight of total hydraulic solid materials) of olivine or other divalent ium dominated silicate of between 2% and 99%, preferably between 10% and 99%, more preferably between 10% and 50%, most preferably between 15% and 25%, ideally about 20% will be beneficial for most uses. There will be some technical effects as before described for the cement in the wide interval of 2% to 99 %.

The range of 10—50 % would have the best cost versus benefit, dependent on the nment, and the range of 15 % to 25 % will be ideal for most applications within current industrial practice.

For the ductile s, the higher range from 35%—70% magnesium dominated silicates are preferred.

PATENT

Claims (14)

1. A cementitious mixture for self-healing, wherein the mixture comprises: a) one or more divalent magnesium ted silicate that in neutral or basic aqueous solutions have the capacity to be a latent hydraulic binder comprising 2 % to 99%, or 10 % to 50 %, or 15 % to 25 % of divalent magnesium dominated silicate by weight of total hydraulic solid materials; and b) chloride ions or brine with a chloride concentration of between 0.7% and 10% by weight of water.

2. The mixture of claim 1, wherein the mixture further comprises accessory sulphide and oxide minerals containing one or more of the cations nickel, zinc and

3. The mixture according to any one of the previous claims, n the mixture further comprises mineral group olivines, orthopyroxenes, amphiboles, talc, serpentines, or a mixture thereof as latent hydraulic binder.

4. The e according to any one of the previous claims, wherein the magnesium dominated silicate is mineral groups of es, orthopyroxenes, amphiboles, talc and serpentines or mixtures thereof.

5. The mixture according to any one of the previous claims, n the magnesium ted te is olivine.

6. Use of the mixture according to any one the previous claims to make a cement slurry that is not solidified and/or in constructing solidified cementitious structures.

7. Use of the mixture according to any one of claims 1 to 5 in constructing solidified cementitious structures with antifouling properties extending to the vicinity WO 74373 of the cementitious structure, the surface of the cementitious structure, the contact to metals, the contact to adjacent ancient structures or natural materials.

8. Use of the mixture according to any one of claims 1 to 5 in ucting fied cementitious structures with antiweathering ties.

9. Use of the mixture according to any one of claims 1 to 5 in constructing solidified cementitious structures that deforms by asis to make it more resilient against deformation from fracturing catastrophic failure.

10. Use of the mixture according to any one of claims 1 to 5 in constructing solidified cementitious structures that are self healing.

11. Use of the mixture according to any one of claims 1 to 5 in constructing solidified cementitious structures such that the volume of the structure increases as it cures.

12. Method for making cement structures with improved antifouling and/or selfhealing properties, wherein the method comprises: a) mixing cement with a cement additive that comprises an admixture of one or more of divalent magnesium-dominated silicates with capacity to act as a latent hydraulic binder to a cement e, said cement ve comprises 2 % to 99%, or 10 % to 50 %, or 15 % to 25 % of divalent magnesium dominated silicate by weight of total hydraulic solid materials. b) adding water comprising chloride ions and/or brine with a chloride ion concentration of between 0.7% and 10% by weight of water, in an ordinary water to cement ratio c) blending the cement mixture to a neutral or basic slurry d) making a structure from the cement mixture e) allowing the structure to set. WO 74373

13. The method according to claim 12, wherein the magnesium dominated silicate is mineral groups of olivines, orthopyroxenes, amphiboles, talc and serpentines or mixtures thereof.

14. The method ing to claim 12, wherein the magnesium dominated silicate is olivine. 1 /3 wo