GB2515726A - Lime composition - Google Patents

Abstract

A lime mixture which cures in air comprising quicklimeA number of lime mixtures and compositions and products formed from them are described. The compositions are air lime mixtures that include quicklime (CaO) and/or quick lime partial hydrate, and a second lime product such as lime hydrate (Ca(OH)2. A method of forming such lime mixtures and compositions by adding water to a quicklime partial hydrate or a mixture of quicklime and/or quick lime partial hydrate, and a second lime product such as lime hydrate are defined. These lime compositions can achieve a physical set typically within five hours. The compositions can be used in construction applications.

Description

LINE CCMPCSTTTCN

The invention relates to lime mixtures and compositions and also to products formed from lime compositions.

Many different compositions useful as plasters, renders and mortars are known. Many of these are based on a lime material, which is extracted from limestone rock.

There are many known benefits associated with using an "air lime" composition. "Air lime" compositions are those which set in air by absorption of carbon dioxide (carbonation set), to form calcium carbonate. Air lime compositions are simple and cheap to manufacture, are alkaline when setting giving anti-mould and anti-pathogenic properties and, when used correctly, have a long lifetime, show good compressive strength, and the set product is a good insulator.

Air lime compositions are prepared by burning calcium carbonate (e.g. at approximately 480°C) to form calcium oxide, often named "quicklime". This is then dry hydrated or slaked with warer to form calcium hydroxide.

This hydration process is highly exothermic, and must be carefully controlled. Quicklime expands significantly in volume on slaking (typically by a factor of about 1.6).

Addition of a certain amount of water in a dry hydration process forms "lime hydrate" which is a dry Ca (OFT)2 powder. Water is added to this powder when it is to be used to form a workable material.

Addition of excess warer in the process known as "slaking" forms "lime putty". The putty is pure Ca(OH)2, and can be used directly without addition of more water (although lime putty is typically aged underwater for a number of months before use) A quicklime "partial hydrate" can be formed by dry hydration using less water than is required to form the lime hydrate, i.e. less than the stoichiometric amount required to hydrate the CaD to Ca (OH) 2 This forms a product in which, at a molecular level, some CaD remains unhydrated and some is hydrated to Ca(OH)2.

Both lime hydrate and lime putty set by carbonation to form calcium carbonate. However, they will only carbonate once dry. The drying process can take months or years, during which time the lime is soft. This limits when lime can be used in construction, and can lead to an increased construction cost. Further, use of either lime hydrate or lime putty materials requires significant skill to ensure that the correct water content is used. Drying rates also need to be carefully controlled to avoid weakening and failing of the material after application to the surface.

The perceived shortcomings of air lime have led to the emergence of other compositions, such as hydraulic lime, cement and gypsum plaster.

Hydraulic lime is formed by burning calcium carbonate with impurities, typically at about 640°C. The resultant impure calcium oxide is slaked to form a dry powder (in a similar way to lime hydrate) . The impurities present mean that addition of water causes the composition to set and calcium silicates to form. The speed of set depends on the impurity level, but is generally quicker than lime hydrate, and the carbonation process does not proceed to completion, i.e. some of the material remains as Ca (OH)2 rather than carbonating fully to calcium carbonate.

Ordinary Portland Cement is a hydraulio lime composition. Hydrating cement powder forms calcium silicate hydrate. The set speed is high, and CO2 absorption is minimal.

Gypsum plaster is a calcium sulphate hemihydrate which sets following addition of water arid drying to form calcium sulphate dehydrate. The source materials are less abundant than calcium carbonate, and the plaster degrades over time.

Each of hydraulic lime, cement and gypsum plaster have quicker set times than pure air limes, but do not have many of the beneficial properties that the air limes possess (as noted above) WO 2011/098814 describes some pozzolan-containing hydraulic set lime compositions.

At its most general, the present invention relates to air lime compositions that harden quickly (preferably less than about 5 hours) after application, forming a strong "physical set". The material subsequently carbonates to form calcium carbonate, in a "chemical set". Accordingly, the benefits of having an air lime plaster, mortar or render can be realised, whilst the compositions do not suffer from the slow set-time traditionally associated with air lime compositions.

The present invention provides compositions and methods to achieve excellent or improved breathability, moisture/humidity, handling and insulative effects. The present air lime also has human and animal health benefits and anti-pathogenic qualities due to the anti-pathogenic environment on the surface of the present air lime compositions when set. In addition, the compositions have environmental benefits in that they only contain lime products to achieve a firm rapidly settinq material. The compositions do not require a carbonation process to form a physical set so they will harden in the absence of 002 from the air.

The invention provides an air lime mixture comprising quicklime arid a second lime product, preferably substantially free from impurities, especially preferably free from pozzolanic impurities. The mixture may further comprise quicklime partial hydrate. In some situations the mixture comprises quicklime partial hydrate and a second lime product. Preferably the mixture comprises quicklime and a second lime product.

The second lime product is different from the quicklime and partially hydrated quicklime components. This second lime product may be limestone or lime hydrate, for

example.

The mixtures and compositions comprising: i) quicklime; or ii) quicklime and quicklime partial hydrate; or iii) quicklime partial hydrate, and a second lime product, are three distinct proposals which all achieve the benefits described herein, in particular formation of a fast physical set following addition of water. In some situations, mixtures and compositions comprising quicklime partial hydrate are preferred due to low heat production and non-violent reaction on addition of wacer which has safety advantages.

In use, a specific amount of water is added to these mixtures to form a composicion, such as a plaster, mortar, putty, render, casuing mix, or grout.

Surprisingly, the compositions quickly harden to form a strong physical set, and subsequently carbonate over time to form calcium carbonate. The set time can be from as little as a few minutes to several days depending on the composition and is controllable to a degree by varying the ratio of quicklime to second lime product and also the quantity of water in the composition.

The compositions defined herein form a useable set quickly, whilst retaining die benefits associated with air lime compositions. The compositions typically harden to this physical set in less than about 5 hours, preferably less than about 3 hours, more preferably less than about 1.5 hours, at which point it can be used treated in the same way as a common set gypsum plaster.

Preferably, the second lime product is lime hydrate.

That is, a preferred mixture or composition comprises quicklime and lime hydrate.

In preferred mixtures and compositions, the ratio of lime hydrate to quicklime may be from 1:3 to 1:1 by weight. In mixtures and compositions comprising quicklime partial hydrate, the ratio refers to the equivalent amount of pure quicklime.

The present invention also provides a method of using the inventive mixtures and compositions. This may be in the preparation of an air lime plaster, mortar, putty, render, casting mix, or grout. In preferred cases, the method comprises adding a specific quantity of water to a mixture described herein. Alternatively the method may comprise adding a specific quantity of water to quicklime partial hydrare.

In the case of a lime hydrate/quicklime mixture or a quicklime partial hydrate, the ratio of the mixture or partial hydrate to water may be from 60:100 to 75:100 by weight.

The present invention also provides a set air lime composition, i.e. the material is still an air lime but it has aohieved a solid sec. Preferably this material has a hardness that is practically useable, e.g. a hardness similar to a set gypsum plaster, for example having a Moh hardness of above about 1.5, within about 5 hours, preferably within about 3 hours, more preferably within about 1.5 hours of che addition of water, obtainable by performing the method of described herein.

Lastly, the present invention also provides articles incorporating air lime, including for example, air lime plaster board, cast air lime articles, air lime wall grout, or air lime building or pointing mortar. The compositions described herein can also be incorporated as a binder for other aggregace using articles such as wood or hemp blocks or in cast structures such as cob techniques of construction.

The term "physical sec" as used herein refers to strong, hard compositions comprising Ca(OH)2, which carbonate over time to form a calcium carbonate "chemical set". The hardened, physical set is a useable plaster, render or mortar. The physical set typically forms within about 5 hours, preferably about 3 hours, more preferably about 1.5 hours of the compositions being added to water. The physical set typically has a hardness similar to that of a set gypsum plaster, e.g. above a F4oh hardness of about 1.5.

The term "air lime" as used herein refers to lime compositions which set in air with absorption of carbon dioxide. It excludes lime compositions which have a "hydraulic" setting action, i.e. those which set on addition of water, due to die presence of silicates.

Specifically, pozzolanic additives are excluded from the claimed compositions and mixtures (which are air limes, not hydraulic limes) -The invention provides air lime mixtures comprising quicklime arid a second lime product. This second lime product may be aggregate limestone or lime hydrate, for example. The mixture may further comprise quicklime partial hydrate. Tn some situations the mixture comprises quicklime partial hydrate and a second lime product. Preferably the mixture comprises quicklime powder or granulate and powder or granulate of the second lime product as separate components.

In use, a specific amount of water is added to these mixtures to form a composition, such as a plaster, mortar, putty, render, casting mix, or grout. On addition of water, the quicklime component (and quicklime partial hydrate component if present) forms calcium hydroxide. Surprisingly, the composition quickly hardens to form a strong physical set, and subsequently carbonates over time to form calcium carbonate.

The violent, exothermio reaction which occurs on contact between water and quicklime is calmed and slowed by the presence of the second lime product. It is believed that the heat of this reaction, the rapid expansion of the quicklime as it is hydrated, and/or the interaction of the hydrating quicklime with the second lime product effects the physical set. That is, the reaction between water and quicklime is used to effect a physical set.

Inclusion of quicklime partial hydrate in the mixture or composition significantly reduces the exothermic reaction when water is added (which is beneficial for safety reasons and ease of use) but has the advantage that time taken to achieve a "physical set" is only marginally increased. The eventual physical set that is achieved is comparable in hardness to that obtained with the quicklime mixtures and compositions.

Preferably, the second lime product is lime hydrate.

That is, a preferred mixture comprises quicklime and lime hydrate. A composition comprising calcium hydroxide is formed as water is added.

In preferred mixtures, the ratio of lime hydrate to quicklime may be from 25:75 to 50:50 by weight. Weight ratios of lime hydrate to quicklime from 50:50 to 75:25 are also useful but towards the lime hydrate-rich end of this range, the strength of the physical set achieved by the composition decreases. More preferably the ratio of lime hydrate to quicklime may be from 28:72 or 30:70 to 45:55 or 40:60 or 35:65 by weight. Most preferably, the ratio is about 1:2 by weight. In mixtures comprising quicklime partial hydrate, this ratio refers to the amount of quicklime and quicklime hydrate equivalents, e.g. if a quicklime partial hydrate is used in which the partial hydration is 75% (by weight) of full dry hydration, this equates to addition of a powder consisting of 75 wt.% quicklime hydrate and 25 wt.% quicklime and contributes co the weight ratios accordingly. Hence addition of lOg of 75 wt.% hydrated quicklime partial hydrate corresponds to 7.5g of quicklime hydrate and 2.5g of quicklime.

If the proportion of quicklime in the mixture is too high, the reaction on addirion of water is too violent for use. If the proportion of quicklime is too low, the physical set will not form.

Preferably the quicklime is a fine powder product, e.g. having a particle size less than about 60 mesh, more preferably less than about 200 mesh. In some cases, an aggregate may be added to rhe mixture. Tn some situations the aggregate is added to the dry mixture and iii some cases the aggregate is added to the composition after combining the mixture with water.

The present invention also provides a method of using the inventive mixtures in the preparation of an air lime composition. The method comprises adding a specific quantity of water to a mixcure as proposed herein.

As noted above, the present compositions form a physical set even in the absence of 002, i.e. without carbonation. Subsequent carbonation over time due to exposure to air chemically sets the compositions by conversion of the lime components to calcium carbonate.

However, in some circumstances it may be preferable to inhibit this carbonation to some extent to retain the alkaline, anti-pathogenic properties of the uncarbonated air lime surface.

Further, the invention provides a method of preparing an air lime composition by addition of a specific amount of water to a quicklime partial hydrate.

In the case of the mixtures described above or a quicklime partial hydrate, the ratio of the mixture or partial hydrate to water may preferably be from 60:100 to 75:100 by weight (i.e. between about 60 g and about 75 g of solid composition with 100 ml water), preferably from 63:100 or 65:100 to 70:100 or 67:100 by weight.

Preferably, the ratio is about 65:100 by weight. If the proportion of water is too high, a fully hydrated lime putty is formed which, as noted above takes an undesirably long time to dry and set in use. If the proportion of water is too low, the mixture sets instantly, or can remain as a powder. The preferred ratio oreates a composition that can be applied to a surface before the physical set is formed. Cf course, in some cases, such as where a plaster mould is being used, a rapid set may be acceptable arid less water can be used in these cases.

The invention also provides a method of using an air lime composition comprising preparing the air lime composition according to the method of preparation as described above, said preparation generating heat due to the mixing with water, and subsequently applying the composition to a surface whilst the composition is still above ambient temperature, e.g. above ambient temperature by about 5°C, or about 10°C, or about 20°C, or about 30°C.

Typically, the composition will be used within 30 minutes of addition of the water, and a physical set will form within 75 to 90 minutes of addition of the water.

The guantity of water in the composition influences the setting speed so application under conditions which rapidly reduce water content of the composition, e.g. application to a porous substrate or application in warm and dry environments, can significantly increase setting speed (in a similar way to a gypsum plaster) Conversely, application in a damp environment or to a non-porous surface, can increase the time to achieve a physical set.

The present invention also provides a set air lime composition having a hardness similar to that of a set gypsum plaster, e.g. above a Moh hardness of about ii 1.5,withln about 5 hours, preferably about 3 hours, more preferably about 1.5 hours of the mixing with water, the set composition being obtainable by performing the method described herein.

Lastly, the present invention also provides lime articles formed from air lime, including for example, air lime plaster board, air lime wall grout, air lime building or pointing mortar, or any cast air lime articles such as decorative mouldings or structural details.

The invention will now be described with reference to illustrative examples.

Background examples 1 to 5 demonstrate the effect of mixing water and quicklime in the absence of a second lime product.

Quicklime powder was supplied by Shap quarries (owned by Tata Steel) . Quicklime hydrate was "premier hydrated lime" made by Premier Cements, Swansea, S.Wales.

Observation of vigour of reaction on Compooition Oboorvationo o @ mixing with -4 1 ft water (rating o cj out of 10)* Forms workable lime l0Oml water 1 putty in 10-15 5 40g quicklime minutes.

Still a workable lime putty lhr later.

Forms workable lime putty in 5-7 7 l00ml water minutes.

50g quicklime Still a workable lime putty lhr later.

Fast, violent reaction, forms 10 stiff putty that lOOml water 3 sets in 2 minutes.

60g quicklime Never workable.

Damp solid lhr later.

Very fast, violent reaction that 10 lOOml water 4 solidifies to a 70g quicklime damp powder within one minute.

Very fast, violent lOOml water reaction. Dry 10 BOg quicklime powder within 10 minutes.

* Observation of vigour of reaction on mixing with water is a rating out of 10. A grading between 7 and 4 indicates that the composiion is preferred for use on site. A grading of 7 or over indicates that the reaction is too violent for preferred use on site; a grading of 4 or under indicates that the composition is slow to form a physical set so is not preferred for use on site.

However, these violent reaotions and slow setting compositions may be useful in other situations, i.e. not on a worksite. For example a fast set may be preferred in formation of cast air lime articles.

Using guicklime Partial hydrate significantly reduces the exotliermic reaction but only marginally reduces the hardening effect in time but not overall result.

Background Examples 1 and 2 show the formation of

traditional air lime putty. This type of putty takes many months to set fully.

Background Examples 3 to 5 do not form an air lime

putty, and are never workable. The resulting product is lime hydrate.

Examples 1 to 3 demonstrate the effect of mixing water with a quicklime / lime hydrate mixture.

Observation of vigour of reaction on Composition Observations o mixing with I water (rating out of 10) lOOml water Slow reaction. Not 1 40g guicklime unusable but slow to 2 20g lime hydrate form physical set.

lOOml water Reacts quickly and 2 SOg quicklime forms a physical set 7 25g lime hydrate in 2-5 minutes.

lOOml water Good reaction. Forms 40g guicklime warm, workable 5 25g lime hydrate composition in 15 minutes.

Stiff, physical set within 1.5 hrs.

An alkalinity test was performed on the stiff, physical set of Example 3 (about 1.5 hours after forming the composition) . The results show that the physical set is strongly alkaline, indicating that it is hardened Ca(O1-I)2 but has not yet carbonated to calcium carbonate.

Over time, tested monThly over 3 months the alkalinity was found to reduce, indicating that the hydroxide was carbonating, forming a chemical CaCO3 set.

The physical set in Example 2 formed too rapidly for a workable composition to form, e.g. it would set or "go off" too quickly to be practically useable as a replacement for a standard gypsum plaster. However, such a composition can be useful where a workable composition is unnecessary but where a quick-set air lime composition is advantageous, e.g. in the formation of plaster mouldings or plaster board where the composition can simply be immediately poured into a mould after which a rapid set is advantageous.

Examples and Reference Examples 4 to 13 demonstrate the effect of mixing water with a quicklime / lime hydrate / dust aggregate mixture. The "dust" in the test was crushed limestone 2 mm to dust with no fines removed.

Mix 1 consists of 1:1:1 of quicklime, lime hydrate and limestone dust by volume.

Mix 2 consists of 1:1:2 of quicklime, lime hydrate and limestone dust by volume.

Test Reagents Observations Medium to hot Ref. Eq. lOOml water reaction. Does not 1 70g mix 1 set.

Medium to hot Ref. Eq. lOOml water reaction. Does not 2 BOg mix 1 set (doesn't stiffen enough) Hot reaction. Forms composition that sets

Example lOOml water

and stiffens well.

4 BOg mix 1 Physical set in about 1.5 hours.

Very hot reaction.

Forms composition Example lOOml water that is workable for bOg mix 1 about 30 minutes, then stiffens to form physical set.

Little reaction.

Ref. eq. bOOml water Powder suspended in 3 bOOg mix 2 liquid after 30 mins.

Warm reaction. Forms Ref. eq. bOOml water but does not stiffen 4 120g mix 2 after 30 mins. No set.

Warm reaction. Forms Example bOOml water composition which 6 140g mix 2 forms physical set in mins.

Test Reagents Observations Warm reaction. Forms composition which

Example 100ml water

forms physical set in 7 160g mix 2 mins.

Warm reaction. Forms Example lOOml water composition which 8 180g mix 2 forms physical set in mins.

Warm reaction. Forms Example 100m1 water composition which 9 200g mix 2 forms physical set in mins.

[Note -"Ref. eq." denotes that this is a referenoe

example

The Examples and Reference Examples demonstrate that the variation of the ratio of the respective mixture oomponents, and the amount of water in the composition, can be used to influence the set time and vigour of reaction according to the desired application, e.g. as noted above, in some situarions such as forming lime composition castings, it may be advantageous to use a composition which sets rapidly, whereas for compositions intended to be a replacement for gypsum plaster, a slower set may be preferable to allow sufficient time to apply the composition to the surface. Preferred ratios within which the surprising physical set of the composition is particularly useful can be seen from the examples herein.

In respect of numerical ranges disclosed in the present description it will of course be understood that in the normal way the technical criterion fcr the upper limit is different from the technical criterion for the lower limit, i.e. the upper and lower limits are intrinsically distinct proposals.

For the avoidance of doubt it is confirmed that in the general description above, in the usual way the proposal of general preferences and options in respect of different features of the mixtures, compositions and methods constitutes the proposal of general combinations of those general preferences and options for the different features, insofar as they are combinable and compatible and are put forward in the same context.

Claims (14)

1. C LA T MS1. An air lime mixture comprising: 1) quicklime; or ii) quicklime partial hydrate; or iii) quicklime arid quicklime partial hydrate, and a second lime product.
2. 2. An air lime mixture according to claim 1, consisting essentially of the second lime product and the i) quicklime, ii) quicklime partial hydrate, or iii) quicklime and quicklime partial hydrate.
3. 3. A mixture according to claim 1 or 2, wherein the second lime product is lime hydrate.
4. 4. A mixture according to claim 3 wherein the mixture comprises or consists essentially of quicklime and lime hydrate, wherein the ratio of lime hydrate to quicklime is from 1:3 to 1:1 by weight.
5. 5. A mixture according to claim 4, wherein the ratio is about 1:2 by weight.
6. 6. An air lime composition comprising a mixture according to any one of the preceding claims and water; wherein the ratio of the mixture of any one of the preceding claims to water is from 60:100 to 75:100 by weight.
7. 7. A composition or mixture substantially as described herein.
8. 8. A method of preparing an air lime composition, the method comprising adding water to either: a mixture according to any one of claims 1 to 5; or a quicklime partial hydrate.
9. 9. A method according to claim 8, wherein the ratio of the mixture or quicklime partial hydrate to water is from 60:100 to 75:100 by weight.
10. 10. A method according to claim 9 wherein the ratio is about 65:100 by weight.
11. 11. A method of using an air lime composition comprising preparing the air lime composition by a method according to any one of claims 8 to 10, said preparation generating heat, and subsequently applying the composition to a surface whilst it is still above ambient temperature.
12. 12. A method substantially as described herein.
13. 13. A set air lime having a Moh hardness greater than 1.5 within 5 hours of the addition of water obtainable by performing the method of any one of claims 8 to 10 or 12.
14. 14. A set air lime according to claim 13, wherein the F4oh hardness greater than 1.5 is achieved within 1.5 hours of the addition of water.