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1. (WO1998049115) HIGH PULP DENSITY, FAST SETTING AND HIGH EARLY STRENGTH BACKFILL METHOD AND MATERIAL
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HIGH PULP DENSITY FAST SETTING AND HIGH EARLY STRENGTH
BACKFILL METHOD AND MATERIAL

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is directed to method and material for underground mine backfill with high pulp density fast setting and high early strength backfill. More particularly, it is directed to high crystal water content, fast setting and high early strength binding material which is mixed with mine tailings, sands, ground sands, industrial solid waste materials, or their mixture, and water to make a high pulp density backfill slurry with 65 - 85% pulp density. More particularly still, the slurry is then sent to the mine stope through a pipeline either by gravity or by pumping. The backfill slurry in the stope solidifies quickly to form a backfill body with high early strength. The backfill body reaches more than 70% of its final strength in about 12 to 72 hours. The present backfill method may be widely used for upwards, downwards, and other mining applications.

2. Prior Art As presently practised around the world, an important problem of using Portland cement as binding material for mine backfill is to reconcile the requirements of backfill body strength and the requirement for transportation of the backfill slurry.

In order to increase the backfill body strength, the ratio of water to cement has to be low on the one hand, but on other hand, to increase flowability of the backfill slurry, much more water has to be used. The typical water to cement ratio is between 0.3 and 0.6 for Portland cement in order to get proper hydration, which is a relatively small ratio of water needed for hydration. But in order to meet the requirements for slurry transportation, pulp density of the slurry has to be less than 65 - 70% , to make it easily transportable to the mine stope through a pipeline. The excess amount of water in the backfill slurry will have to be removed in the stope. Coarse aggregates such as sands, ground sands of coarse fractions from tailings are usually used in order to make dewatering easier. In addition to this problem, the cement backfill body takes 7 - 28 days to reach the required strength. As a result, a long waiting period is necessary in order to continue mining Hie ores beside the backfilled body. The cycle of drilling, blasting, ore transportation and backfill is prolonged.

There are other problems facing existing and traditional Portland cement backfill methods:

1. A large amount of cement in the slurry is carried away by water during the dewatering process. This not only causes environmental problems, but also decreases the strength of the backfill body.

2. Large spaces between the backfill body and the roof of the stope cannot be fully filled due to slurry volume loss during dewatering. Multiple backfilling procedures are often required to fill up this space.

3. In order to create high permeability in the backfill body, only the coarse fractions of the tailings can be used as aggregate. Tailing utilization efficiency is therefore low, at less than 40% . The large quantity of unused fine tailings has to be disposed of on land at the surface, which causes environmental problems on mine surfaces.

4. The making of ground sands or purchase of sands to make up aggregates is costly, if the amount of tailings available is not sufficient for backfill.

5. Due to the long solidifying period of the backfill body of between 7 and 28 days, means delay before the next mining operation may begin, thus production efficiency is lowered.

In order to solve the technical problems listed above, some mines have tried paste backfill. The binding material is still Portland cement, but the pulp density of the slurry has to be increased to more than 80% . Less water needs to be removed from this paste slurry in the mine stope. As a result, the strength of the backfill body increases. However, due to the poor flow characteristics of the paste, it raises a lot of transportation problems and it can only be used in large vertical height mines where gravity flow is used. Special mixing equipment such as 'double axis mixers' have to be used for mixing and special positive displacement pumps for paste slurry transportation are required. The main problems associated with this method are: (a)

A pressure filter is required for making paste, where capital cost is high and the process is complex, (b) Pipeline blockage occurs quite often due to too high pulp density, so that the paste slurry transportation through a pipeline is very difficult; (c) Both curing periods and operation cycles of mining are too long, since Portland cement is used as the binding material; (d) Operating costs are high due to high cement consumption; (e) It is difficult to fill up all of the space in a stope, because of the poor flow characteristics of the paste.

In order to solve the above problems, research on new binding materials and low pulp density backfill methods have made progress in China. Chinese patents ZL90 103141.0 and ZL91 103829.9, to Henghu Sun et al., have disclosed a new process for metal mine backfill. These processes use so-called 'high water content' materials to replace Portland cement as binder to form a low pulp density slurry with 15 - 70% pulp density. The "high water content" material binder is made of two equal parts termed A and B materials. Both slurry A containing the A binding material and slurry B containing the B binding material are sent to the mine stope through two separate pipelines. The two slurries are then mixed together at a place close to the mine stope for backfill. After 30 minutes, the backfill slurry solidifies in the stope without losing any water.

However, there are some problems associated with this method: (i) The ratio between A and B has to be exactly at one. Changing of this ratio may prevent the slurry from solidifying; (ii) The A and B slurries have to be transported through two separate pipelines. This directly increases the capital cost of the mining process; (iii) Since the two slurries have to be mixed at a place close to the backfill stope in the mine, satisfactory mixing requires that the pulp density of the slurry must be less than 70%; (iv) Due to the low solids content in the slurry, more binder material is needed if high strength is required. This increases the cost of the backfill.

United States Patent No. 5,141,365 issued August 25, 1992 to Smart discloses that a void in a mine is backfilled by a backfill slurry comprising water, an inert filler, e.g. mine tailings, and a binder, e.g. cement, lime or slag, to which a gelling agent, e.g. sodium silicate, is added just before placement. The salient feature of this patent is that the backfill slurry is made of tailings, water, Portland cement, lime and slag.

United States Patent No. 4, 101,333 issued July 18, 1978 to Wayment discloses a method of backfilling in underground mine operations by a mill tailings slurry which is dewatered to provide a material with a controller water content to permit the dewatered material to be used as a backfill without requiring any substantial dewatering after placement and which material can, when desired, be mixed with selected quantities of cement to provide a mortar for backfilling or surface covering.

The salient feature of this patent is using de- watered tailings for mine backfill. The dewatering of the backfill slurry underground in the mine is not necessary. Portland cement is mixed with prepared backfill aggregate to make a backfill slurry.

Both of the above two United States patents use Portland cement as binding material, and have the common disadvantage discussed above.

United States Patent No. 5,340,235 issued August 23, 1994 to Milliken discloses a method for hydraulically backfilling empty mined salt cavities. The method comprises combining at least one pozzolanically active waste material with an effective amount of an alkaline earth metal in the form of an alkaline earth metal hydroxide or alkaline earth metal oxide and saturated brine to form a pozzolanic mixture, wherein the relative proportions of said pozzolanically active waste material, alkaline earth metal hydroxide or alkaline earth metal oxide and saturated brine are sufficient for reaction under atmosphere conditions in said salt cavity to form a stable, low porosity, load bearing pozzolanic cement; and hydraulically depositing said pozzolanic mixture in the empty salt cavity.

United States Patent No. 5,464,473 issued November 7, 1995 to Shiao discloses a backfill for an engineered barrier used to contain radioactive waste has a predetermined amount of clayic material and a predetermined amount of a reinforcement material with hydrophobic surface characteristics. The reinforcement material may include hydrophobic compounds selected from group consisting of organic polymers or inorganic materials on which a layer of hydrophobic compounds is formed. The hydrophobic reinforcement material results in the backfill maintaining a very low water permeability while providing high mechanical strength and other properties suitable for use in a repository of radioactive waste.

United States Patent No. 4,059,963 issued November 29, 1977 to Wayment discloses a method of backfilling in underground mine operations by a mill tailings slurry which is dewatered to provide a material with a controlled water content to permit the dewatered material to be used as a backfill without requiring any substantial dewatering after placement and which material can, when desired, be mixed with selected quantities of cement to provide a mortar for backfilling or surface covering.

United States Patent No. 4,746,249 issued May 24, 1988 to Haigh et al. discloses an aqueous slurry of backfill material e.g. slimes, includes a settable material and an activator therefor, e.g. pulverized fuel ash and lime, and a lubricant e.g. clay and a plasticizer, e.g. a lignosulphonate so that the slurry can be pumped over long distances but will then set to develop high early strength.

United States Patent No. 5, 106,422 issued April 21, 1992 to Bennett et al. discloses a rapid-setting self-hardening backfill composition and a method of installation. The composition comprising a minor amount of Class C fly ash as a primary constituent and other filler materials such as Class F fly ash in major amount. When such materials are combined with water in controlled amount, they produce a backfilling material which is flowable and self-leveling for easy installation in utility trenches and similar excavations in street and roadway surfaces to support relatively heavy compressive loads within relatively short periods of time without settling. The self-hardening initially flowable mixtures attain considerable strength for withstanding traffic loads without undue settling in time periods of about 4 hours. The rapid-setting of the composition provides a rapidly attainable strength of the order of about 20 psi within about 4 hours to permit overlaying a wearing course of paving material and reopening of excavated areas of streets and roadways without undue traffic delays and congestion. The backfilling composition ranges in amount from about 2 to 10 parts by weight filler material to about 1 part by weight Class C fly ash with sufficient water to react with both Class C fly ash and filler material. The composition utilizes by-products of coal-fired power stations to form a most economic backfilling material and method of utilization to provide both early strength and precisely controlled permanent strength to permit ready reexcavation.

Other patents disclosing new binder materials for mine backfill are: United States Patent No. 4,992,103, titled Cementitious Composition; United States Patent No.

4,798,628 titled Apparatus Delivering a Rapidly Setting Composition; and European

Patent No. 28639, titled Rapid set composition.

The major differences among the above patents are that different binders are used. In some, binder consumption is very high at 300 - 500 kg per cubic metre. This is only used for special cases in coal mines due to high cost.

SUMMARY OF THE INVENTION

The present invention endeavours to solve the problems described above. Salient features of the method of the present invention are:

Increase of the backfill slurry pulp density to 65 - 85%.

- Use of all types of tailings, natural sands, ground sands and industrial solid waste materials as aggregates.

Use of various proportions of basic binding materials, accelerating reagents, retarding reagents, and suspension reagents to adjust the backfill slurry setting speed, setting time, early strength, flow characteristics and transportation.

- Alteration of binder addition procedures and slurry making procedures to obtain the required results.

Large quantities of tailings and industrial solid wastes can be used for mine backfill.

The making of high pulp density backfill slurry, such that underground de- watering is not required in some cases.

Existing backfill technology can be used for various mine conditions through adjusting of the present method of making the present binding material composition, and the method of producing the new backfill slurry and its transportation procedures.

Using the backfill technology of the present invention, full tailings from a mine mill can be used as aggregates. In prior methods, when using Portland cement as binder, the tailings must be classified to remove fine tailings; only about 40% of the tailings with particle sizes larger than 37 microns can be used as aggregates. In the present backfill technology, all tailings without classification can be used for backfill. Backfill slurry may be made by mixing any kind of tailings with water to make a slurry with 65 - 85% pulp density by weight. It is then sent to the mine stope through one pipeline, rather than two pipelines. The weight of the present binding material added to the backfill slurry is between 0.5 and 20% by weight. If there are no tailings available for backfill, natural sands, ground sands, industrial solid waste materials or a mixture of thereof may be used as aggregates. The natural sands include river sands, sea sands, sands from mountains. The ground sands are made from grinding rock into particle sizes of 0.04 - 5 mm. The industrial solid waste materials could be iron smelter slag, power plant slag and various industrial waste slags.

According to the present invention, there is provided a high pulp density fast setting and high early strength backfill material and method for use in underground mines comprising: one part of mine tailings, natural sands, ground sands, and solid industrial waste materials as aggregate; a binding material of between 0.5 and 20% by weight mixed with water to form a slurry with 65 - 85% pulp density by weight; and transporting the slurry to the stope of a mine through a single pipeline.

Preferably, the present binding material is composed of six groups of components in the following ratios:

Component 1 can be one of, or a mixture of sulpho-aluminate cement clinkers, ferro-aluminate cement clinkers, fluo-aluminate cement clinkers and high aluminate cement clinkers, in any ratio. The concentration of component 1 in the binding material is between 40 - 90% by weight, preferably at 45 - 80% by weight and best at 50 - 70% by weight.

Component 2 can be one of, or a mixture of anhydrite and gypsum, in any ratio. The concentration of component 2 in the binding material is between 5 - 50% by weight, preferably at 10 - 40% by weight and best at 15 - 40% by weight.

Component 3 can be one of, or a mixture of lime and hydroxide lime in any ratio. The concentration of component 3 in the binding material is up to 30% by weight, preferably at 3 - 25% by weight and best at 5 - 20% by weight.

Component 4 can be one of, or a mixture of KC1, NaCl, CaC12, MgC12, ZnC12, Na2CO3, K2CO3, Li2CO3, Li containing chemical compounds, Na2SO4, K2SO4, A12(SO4)3, Na2S2O3, NaF, Na3PO4, NaNO3, KNO3, all alkalis, triethanolamine, tri-isopropanolamine, carbamide, in any ratio. The concentration of component 4 in the binding material is up to 8% by weight, preferably at 0.05 - 6% by weight and best at 0.2 - 5% by weight. Component 4 is used as accelerating or/and high early strength reagent.

Component 5 can be one, or a mixture of sugars, molasses, lignosulphonates, tartaric acid, tartrates salts, citric acid, citrate salts, boric acid and borate salt, in any ratio. The concentration of component 5 in the binding material is up to 2% by weight, preferably at 0.05 - 1 % by weight and best at 0.1 - 1 % by weight. Component 5 is used as retarding or/and dispersion reagent.

Component 6 can be one of, or a mixture of bentonite, limestone, flyash, silica fume, slag powder, cement, talc powder, clay powder, bauxite powder, anhydrite, gypsum, lime and hydroxide lime, in any ratio. The concentration of component 6 in the binding material is up to 30% by weight, preferably at 0.1 - 10% by weight and best at 0.5 - 5% by weight.

In another aspect of the present invention, there is provided a method for producing a binding material for high pulp density, fast setting, high early strength backfill, comprising: mixing of the above six groups of components in preselected ratios; and making and grinding the components to pass 100 Tyler mesh. Preferably, the ratios of the six components are:

(a) component 1: 45% - 80% by weight;

(b) component 2: 10 - 40% by weight;

(c) component 3: 3 - 25% by weight;

(d) component 4: 0.05 - 6% by weight, whereby component 4 is used as accelerator or/and high early strength reagent;

(e) component 5: 0.05 - 1 % by weight, whereby component 5 is used as retarder or/and dispersion reagent; and

(f) component 6: 0.1 - 10% by weight.

In yet another aspect, the method of making high pulp density, fast setting and high early strength backfill slurry for underground backfill comprises using one of, or a mixture of mine tailings, natural sands, ground sands and industrial solid waste materials at any ratio as backfill aggregate; mixing the backfill aggregate, water and material together uniformly to make a slurry with pulp density of 65 - 85% by weight; and transporting the slurry to the mine stope through a single pipeline by pumping or by gravity; wherein the ratio of the binding material to the backfill aggregate is between 1:5 and 1 :100 by weight.

A preferred method for preparation of high pulp density, fast setting and high early strength backfill slurry comprises the following steps: mixing one of, or a mixture of mine tailings, natural sands, ground sands and industrial solid waste materials, in any ratio, with water to form a homogenous and uniform sand slurry with a pulp density of 63 - 82% by weight; adding binding material to the sand slurry through a feeder and mixing the slurry for 2 - 8 minutes in a mixture to form a backfill slurry with pulp density of 65 - 85% by weight; wherein the ratio of the newly invented binding material added to the backfill slurry is from 1:5 to 1 : 100 by weight; and transporting the backfill slurry to the stope in the mines through a pipeline by pumping or by gravity.

In another aspect, the preparation of high pulp density, fast setting and high early strength backfill slurry for underground backfill comprises the following steps: mixing one of, or a mixture of mine tailings, natural sands, ground sands or industrial solid waste materials, in any ratio, with water to form a homogenous and uniform sand slurry with a pulp density of 63 - 82% by weight; transporting the sand slurry to a site close to the stope in the mine through a pipeline by pumping or by gravity, at which site, adding binding material to the sand slurry inside the pipeline through a feeder, wherein the binding material added is well-mixed with the sand slurry through a turbulent flow pattern inside the pipeline on its way to the stope; and wherein the formed backfill slurry has a pulp density of 65 - 85% by weight, and the ratio of the binding material added to the backfill slurry is from 1:5 to 1:100 by weight.

Another method of providing binding material comprises: mixing components 1 , 2 and 3 as defined above to form another component 7 as a binding material, wherein the concentration by weight of each component in the binding material is as follows: component 1 40 - 90%; component 2 5 - 50%; component 3 3 - 30%; grinding the component 7 to pass 100 Tyler mesh; mixing component 4 with component 6 in a ratio of 1 to up to 5 by weight, then grinding the mixture to pass 70 Tyler mesh and packaging the result separately to form (accelerating reagent) component 8; mixing component 5 with component 6 in a ratio of 1 to up to 5 by weight, respectively, then grinding the mixture to pass 70 Tyler mesh and packaging the result separately to form

(retarding reagent) component 9.

Depending on the distance at which the slurry will have to be transported, a binding material required with a shorter setting time, typically between 5 and 50 minutes, can be made by mixing component 7 with component 8 in a ratio of (95 - 100):(0 - 5); on the other hand, with a longer setting time, typically between 40 and 120 minutes, the binding material can be made by mixing the component 7 with component 9 in a ratio of (97 - 100):(0 - 3), when the slurry transportation distance is long.

A method for making the high pulp density, fast setting and high early strength backfill slurry for underground backfill comprises: mixing one of, or a mixture of mine tailings, natural sands, ground sands and industrial solid waste materials at any ratio with water to form sand slurry with a 63 - 82% of pulp density by weight in a station at the surface before it is transported to underground, then transported to a place close to the backfill stope through a pipeline by pumping or gravity; adding the binding material to the formed sand slurry in a pipeline through a feeding system, and mixing the binding material well with the sand slurry by turbulent flow inside the pipe; wherein the quantity of the binding material added is about 2 - 20% of the sand slurry by weight.

The preparation method for high pulp density, fast setting and high early strength backfill slurry for underground backfill comprises: mixing of mine tailings, natural sands, ground sands and industrial solid waste materials in any ratio, with component

7 (as described above) to form backfill material mixture; then adding water to the above mixture to make a slurry with 65 - 85% pulp density by weight; and transporting the slurry to a place close to the backfill stope through the pipeline by pumping or gravity, wherein (accelerating reagent 8) component 8 (described above) is added in an amount of 0 - 5% the weight of the formed slurry; wherein the backfill slurry is made uniform by the turbulent flow inside the pipe.

Another preparation method for high pulp density backfill slurry comprises: adding one of, or a mixture of natural sands, ground sands or industrial solid waste materials, in any ratio, to low pulp density tailings from mine processing mills to make a denser slurry with 62 - 80% pulp density sand slurry by weight; adding the binding material (described above) to the slurry through a feeding system with a quantity from 2 to 20% of the weight of the formed slurry to form a backfill slurry with 65 - 85% pulp density.

DETAILED DESCRIPTION OF THE INVENTION

EXAMPLE 1

Tailings from a gold mine is concentrated from 20 - 30% solids to above 70% pulp density slurry. The present binding material is added through a measuring and mixing device to the formed tailing sluπy at a ratio of the binding material to the formed tailing slurry being 1 to 30. After mixing for 5 minutes, the slurry is sent to the underground mine through a pipeline. Samples modules (4" x 8") with different setting time are made for testing setting time and compressive strength. The result is shown as below:

The present binding material composition is as follows:

1. Sulpho-aluminate cement clinkers 65%
2. Gypsum 20%
3. Hydroxide lime 5%
4. CaC12 3%
5. Na2CO3 2%
6. LiOH 0.4%
7. Bentonite 4.6%

The initial setting time: 40 minutes
The final setting time: 180 minutes

Testing time: 8 hours 1 day 3 days 7 days
Strength, psi: 19.6 52.3 67.8 87.4 EXAMPLE 2:

A slurry with 75% pulp density by weight is made by mixing natural sands with water.

Mixture 1 is made of sulpho-alumimate cement clinkers and ferro-aluminate cement clinkers at a ratio of 1 : 1

Mixture 2 is made of gypsum and anhydrite at a ratio of 2:8

Mixture 3 is made of hydroxide lime and lime at a ratio of 3:7

The binding material is composed of:

1. Mixture 1 65%
2. Mixture 2 20%
3. Mixture 3 8%
4. K2CO3 0.8%
5. NaCl 0.7%
6. Li2CO3 0.2%
7. Molasses 0.3%
8. Flyash 5.0% The above material is well mixed and ground to pass 100 Tyler mesh to make the binding material, which is then added to the above 75% pulp density sand slurry with amount of 4% of the weight of the formed sand slurry. The mixture is then well mixed for 5 - 8 minutes and filled to experimental modules at 20 °C. The result is shown below:

The initial setting time: 36 minutes
The final setting time: 166 minutes

Testing time: 6 hours 1 day 3 days 7 days 28 days

Strength, psi: 23.2 112.6 157.8 192.5 220.7

EXAMPLE 3:

Mix dry tailings with slag at a ratio of 1 :1. Ground the mixture to 0.04 - 5 mm. Add water into the mixture to make a slurry of 72% solids. Mix sulpho-aluminate cement clinkers and ferro-aluminate cement clinkers at ratio of 1 :1 and grind the mixture to pass 100 Tyler mesh to produce component 1. The proportions for the present binding material are:

1. Component 1 60%
2. Anhydrite 28% 3. Lime 8%
4. Limestone 4%

The materials listed above is ground to pass 100 Tyler mesh to form the binding material. It is then added to the formed sand slurry which is with 72% of pulp density. The quantity added of the binding material is 5% of the weight of slurry. After mixing for 5 - 8 minutes, the slurry is filled to a few modules for strength testing. The result is as follows:

The initial setting time: 50 minutes
The final setting time: 200 minutes

Testing time: 6 hours 1 day 3 days 7 days 28 days

Strength, psi: 18.8 87.8 138.3 167.1 188.9

EXAMPLE 4:

The binding material composed as shown in table 1 , which is ground to pass totally 100 Tyler mesh, is separately mixed with classified tailing and alluvial sand slurries of 68%, 72% and 76% of pulp density. The ratios of the classified tailings alluvial sand to the binding material, Portland cement type 10, Portland cement type 30, slag cement 10 - 90 are 15:1 , 30:1 , 45:1, respectively. The composition and strengths measured are shown in the following table 1 :

EXAMPLE 5:

Mix dry tailing from the mine mill with ground sand at a ratio of the tailing to ground sand being 70:30. This formed mixture is then mixed with water to form sand slurry with pulp density of 70 wt. % . The binding material to be used, which is the same as in example 4, is added and mixed with the sand slurry to form backfill slurry. The backfill slurry is then transported through pipeline to a place where is about 30 - 50 meters from the backfill stope. The accelerating reagents such as sodium carbonate, lithium hydroxide and the suspension such as bentonite are added through measuring devices. The quantities added of sodium carbonate, lithium hydroxide and bentonite are 3%, 0.02% and 5% of the weight of the backfill slurry, respectively. These reagents are well mixed with the backfill slurry by a turbulent flow inside the pipeline. The slurry is then filled to the stope.

EXAMPLE 6:

Add sand, ground sand and ground industrial solid waste material at an equal quantity, to tailing slurry with pulp density of 20 - 30% by weight from the mine mill to make sand slurry with pulp density of 72% by weight. The binding material, same as in example 1, is added to the formed sand slurry. The weight of binder is 6% of the Table 1
weight of the formed sand slurry. After mixing for 5 - 8 minutes to form backfill slurry, the uniformed backfill slurry is transported to the mine through a pipeline by pumping and filled in the stope. The 3 days strength of the sample from the backfill body in the stope is above 80 psi.

EXAMPLE 7:

This is a comparison between the binding material and Portland cement type 10, type 30. Firstly, natural sands are mixed with water to form various pulp density sand slurries of 68%, 70% , 72%, 74%, 76% and 78% respectively. Secondly, the present binding material, Portland cement type 10 and Portland cement type 30 are added into the formed sand slurries with various sand to binder ratios of 15:1, 20:1, 25:1, 30:1 and 35 : 1 , respectively, with a mixing time of 5 - 10 minutes. The formed slurries are poured into 4" x 8" cylinder respectively. The strengths have been measured at a compressive testing, machine in 1 day, 3 days, 7 days and 28 days, which are listed in the following table 2.

Table 2 shows that the compressive strengths of using the present binding material are much higher than the compressive strengths of either using the Portland cement type 10 and type 30. Especially, very high early strengths have been achieved by using the present binding material. And 1 part of the binding material by weight used can replace 3 times of the Portland cement to get nearly the same compressive strength
within 7 days.

Table 2 also shows very good properties of using the present binding material, which can not be achieved with using Portland cement or any other traditional binding material in the raining backfill field.