WO2014001385A1

WO2014001385A1 - Asphalt composition

Info

Publication number: WO2014001385A1
Application number: PCT/EP2013/063371
Authority: WO
Inventors: Sunil Ashtekar; Chantal Soubigou; Govind Wagle
Original assignee: Shell Internationale Research Maatschappij BV; Shell Oil Co
Current assignee: Shell Internationale Research Maatschappij BV; Shell USA Inc
Priority date: 2012-06-27
Filing date: 2013-06-26
Publication date: 2014-01-03
Anticipated expiration: 2014-12-27

Description

ASPHALT COMPOSITION

Field of the Invention

The invention relates to an asphalt composition and a process for the manufacture of an asphalt composition. Background of the Invention

In the road construction and road paving industry, it is a well-practised procedure to coat aggregate material such as sand, gravel, crushed stone or mixtures thereof with hot fluid bitumen, spread the coated

material as a uniform layer on a road bed or previously built road while it is still hot, and compact the uniform layer by rolling with heavy rollers to form a smooth surfaced road.

The combination of bitumen with aggregate material, such as sand, gravel, crushed stone or mixtures thereof, is referred to as "asphalt". Bitumen, also referred to as

"asphalt binder", is usually a liquid binder comprising asphaltenes, resins and solvents. Bitumen can for example comprise pyrogenous mixtures derived from petroleum residues such as residual oils, tar or pitch or mixtures thereof.

It is known in the art that sulphur can be mixed with bitumen for applications in the road construction and road paving industry. Sulphur-modified bitumen is formulated by replacing some of the bitumen in

conventional binders by elemental sulphur. Sulphur- modified bitumen typically comprises a greater amount of sulphur than bitumen compositions in which sulphur is included as a crosslinking agent for polymer.

One of the problems encountered when using sulphur in bitumen is the unwanted formation of H₂S, resulting from dehydrogenation reactions between bitumen and sulphur at high temperatures.

Even low ¾S emission from sulphur-comprising asphalt, meaning asphalt formulated using sulphur- modified bitumen wherein elemental sulphur has been used to replace part of the bitumen, presents an emission nuisance on road paving projects. This is due to the gradual H₂S gas concentration increase to high levels in the air voids in the loose paving mixture during storage in silos and during truck delivery to the paving site.

The "stored" gas is released when the air pockets in the mixture are opened up as the mixture is dumped from the delivery trucks or as the mixture is subjected to mechanical mixing.

In view of the substantial amounts of sulphur used, especially in sulphur-containing asphalt having high sulphur-bitumen weight ratios, e.g. as high as 1:1, H₂S emission is a serious problem. Therefore, it is necessary to reduce the unwanted formation and emission of ¾S from sulphur-comprising asphalt.

Since bitumen inherently contains low levels of sulphur, emission of ¾S is even a problem for bitumen and asphalt compositions which have not been modified with additional sulphur.

In addition to the unwanted formation of ¾S, another problem encountered when using sulphur in bitumen is the unwanted formation of SO₂.

Yet another problem that may be encountered during the production and paving of sulphur-containing asphalt, especially asphalt prepared using sulphur-modified bitumen, is eye and throat irritation caused by the presence of sulphur vapour. Various attempts have been made to reduce ¾S and SO₂ emissions and sulphur vapour from sulphur-modified bitumen and asphalt compositions. However, further improvements are needed.

Summary of the Invention

It has now been found that significantly reduced H₂S and SO₂ emissions and significantly reduced sulphur vapour can be achieved by incorporating a hydrotalcite anionic clay into bituminous and asphalt compositions.

Thus, according to the present invention there is provided an asphalt composition comprising aggregate, bitumen, sulphur and a hydrotalcite anionic clay.

In another aspect, the present invention provides a process for manufacturing an asphalt composition

according to the present invention, the process

comprising the steps of:

(i) heating bitumen;

(ii) heating aggregate;

(iii) mixing the hot bitumen with the hot aggregate in a mixing unit to form an asphalt composition;

wherein sulphur is added in at least one of steps (i), (ii) or (iii); and wherein a hydrotalcite anionic clay is added in at least one of the steps (i), (ii) or (iii) or is incorporated into the bitumen before step (i) .

The invention further provides a process for

preparing an asphalt pavement, wherein asphalt is

prepared by a process according to the invention, and further comprising steps of:

(iv) spreading the asphalt into a layer; and

(v) compacting the layer.

In an embodiment of the invention, the sulphur and the hydrotalcite anionic clay are added together; the sulphur is in the form of pellets and the hydrotalcite anionic clay is incorporated in the sulphur pellets.

Accordingly the invention further provides sulphur pellets comprising a hydrotalcite anionic clay. These pellets are advantageously used in a process according to the invention.

In another embodiment of the invention, the

hydrotalcite anionic clay is incorporated into the bitumen during or before step (i) . Accordingly, the invention further provides a bitumen composition for use in preparing an asphalt composition comprising aggregate, bitumen and sulphur, the bitumen composition comprising bitumen and a hydrotalcite anionic clay.

The present invention also embraces the use of a hydrotalcite anionic clay for reducing H₂S and SO₂ emissions from a bituminous composition wherein the bituminous composition comprises from 20 wt% to 99.9 wt% of bitumen and from 0.01 wt% to 10 wt% of a hydrotalcite anionic clay.

The present invention also embraces the use of a hydrotalcite anionic clay for the purpose of reducing ¾S and/or SO₂ emissions from an asphalt composition

comprising aggregate, bitumen and sulphur.

The present invention also embraces the use of a hydrotalcite anionic clay for the purpose of reducing sulphur vapour from an asphalt composition comprising aggregate, bitumen and sulphur.

The use may comprise any of the methods described herein and/or may comprise incorporating sulphur pellets and/or a hydrotalcite anionic clay-containing bitumen composition described herein into a sulphur-containing asphalt composition. Detailed Description of the Invention

The asphalt composition according to the invention comprises aggregate, bitumen, sulphur and a hydrotalcite anionic clay.

The aggregate is suitably any aggregate that is suitable for road applications. The aggregate may

comprise coarse aggregate (retained on a 4mm sieve) , fine aggregate (passes a 4mm sieve but is retained on a 63μηι sieve) and/or filler (passes a 63μηι sieve).

Typically, the asphalt composition comprises at least 1 wt% of bitumen, based on the weight of the asphalt composition. An asphalt composition comprising from about 1 wt% to about 10 wt% of bitumen is preferred, with a special preference for asphalt compositions comprising from about 3 wt % to about 7 wt % of bitumen, based on the weight of the asphalt composition.

The bitumen can be selected from a wide range of bituminous compounds. The bitumen that can be employed may be straight run bitumen, thermally cracked residue or precipitation bitumen, e.g. from propane. Although not necessary, the bitumen may also have been subjected to blowing. The blowing may be carried out by treating the bitumen with an oxygen-containing gas, such as air, oxygen-enriched air, pure oxygen or any other gas that comprises molecular oxygen and an inert gas, such carbon dioxide or nitrogen. The blowing operation may be

conducted at temperatures of 175 to 400°C, preferably from 200 to 350°C. Alternatively, the blowing treatment may be conducted by means of a catalytic process.

The bitumen for use herein is preferably a paving grade bitumen suitable for road application having a penetration of, for example, from 9 to 1000 dmm, more preferably of from 15 to 450 dmm (tested at 25°C according to EN 1426: 1999) and a softening point of from 25 to 100°C, more preferably of from 25 to 60°C (tested according to EN 1427: 1999).

The asphalt composition may comprise, based on the weight of the bitumen, at least 10 wt% sulphur,

preferably 20wt% sulphur, more preferably at least 40wt% sulphur .

The amount of sulphur in the asphalt composition is preferably from 10 to 200 wt%, based upon the weight of the bitumen, preferably from 20wt%, more preferably from

40wt% and preferably to 100wt%, more preferably to 80wt%. The presence of sulphur in the asphalt paving mixture can improve the strength and rutting resistance of the paving mixture and it is important to include sufficient sulphur to realise these advantages. Additionally, incorporating increased amounts of sulphur can decrease the cost of the paving mixture. However, too much sulphur can decrease the workability of the paving mixture.

The sulphur may be incorporated into the asphalt composition in the form of sulphur pellets. Reference herein to pellets is to any type of sulphur material that has been cast from the molten state into some kind of regularly sized particle, for example flakes, slates or sphere-shaped sulphur such as prills, granules, nuggets and pastilles or half pea sized sulphur. The sulphur pellets typically comprise from 50 to 100wt% of sulphur, based upon the weight of the sulphur pellets, preferably from 60wt% and most preferably from 70wt%; and typically to 99wt%, and preferably to 95wt% or to 100wt%. A more preferred range is from 60 to 100wt%.

These sulphur pellets may contain carbon black and, optionally, other ingredients, such as amyl acetate and wax. Carbon black may be present in amounts up to 5%wt, based on the pellet, preferably up to 2%wt. Suitably, the content of carbon black in the sulphur pellet is at least 0.25%wt. The content of other ingredients, such as amyl acetate and wax, typically does not exceed an amount of 1.0%wt each. When wax is present, it may be in the form of, for example, slack wax or wax derived from a Fischer- Tropsch process. Examples of suitable waxes for use herein are Sasobit (RTM) , a Fischer-Tropsch derived wax commercially available from Sasol, and SX100 wax, a

Fischer-Tropsch wax from Shell Malaysia.

An example of a suitable sulphur pellet for use herein is Thiopave (RTM) pellets commercially available from Shell Canada.

The asphalt and bitumen compositions of the present invention also comprise an anionic clay, preferably in a level of from 0.05 wt% to 10 wt%, more preferably in a level of from 0.1 wt% to 8 wt%, even more preferably in a level of from 0.2 wt% to 5 wt%, by weight of the sulphur.

The hydrotalcite anionic clay for use herein has a crystal structure which consists of positively charged layers, columns, etc., between which are anions and water molecules, and which are built up of specific

combinations of metal hydroxides. In the hydrotalcite anionic clays the brucite-like main layers built up of octahedral alternate with interlayers in which water molecules and anions, more particularly carbonate ions, are distributed around the cavities between the

octahedral. Among the natural hydrotalcite anionic clays are pyroaurite, hydrotalcite, stichtite, reevesite, eardleyite, sjogrenite, mannaseite and barbertonite . The main layers of these and many others generally synthetic, members of the group are built up of specific

combinations of metal hydroxides derived from on the one hand divalent cations of metals such as Zn, Mn, Fe, Co, Ni, Cu and in particular Mg and on the other from

trivalent cations of metals such as Mn, Fe, Co, Ni, Cr and in particular Al . Alternatively, monovalent and trivalent metal cations may be combined in the form of, for instance, lithium and aluminium cations in

[Al₂Li (OH) ₆] ⁺A^~.bH₂0 (see Clays and Clay Minerals, 3_0, pp. 180-184, 1982) . The interlayers contain anions such as N0₃ ^~, OH^~, CI^", Br^", I^", S0₄ ^2", Si0₃ ^2", Cr0₄ ^2", HP0₄ ^2", Mn0₄ ^~, HGa0₃ ^2", HV0₄ ^2", C10₄ ^", B0₃ ^2", monocarboxylates such as acetate, dicarboxylates such as oxalate, alkyl

sulphonates such as lauryl sulphonate and in particular C0₃ ^2".

A detailed description of hydrotalcite anionic clays is given in Min. Mag. 3_9, 377-389 (1973) .

The hydrotalcite anionic clay preferably has a layered structure corresponding to the general formula

[M²⁺ _mN³⁺ _n(OH)_2m + 2n] A^a" _n/a.bH₂0 wherein M²⁺ and N³⁺ represent di- and trivalent cations, respectively, m and n have a value such that m/n = 1 to 6 and a has the value 1, 2 or 3, and A represents a mono-, di- or trivalent anion and b has a value in the range of from 0 to 10, generally a value of 2 to 6 and often a value of about 4. It is preferred that m/n should have a value of 2 to 4, more particularly a value practically of 3.

Suitable divalent M²⁺ cations are Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺, Zn²⁺, Mn²⁺, Fe²⁺, Co²⁺, Ni²⁺, Cu²⁺ and combinations thereof. Preference is given to Mg²⁺ and Ca²⁺ .

Suitable trivalent N³⁺ cations are Al³⁺, Mn³⁺, Fe³⁺, Co³⁺, Ni³⁺, Cr³⁺, Ga³⁺, B³⁺, trivalent rare earth metal cations such as La³⁺ and Ce³⁺ and combinations thereof. Preferred is Al³⁺, combined or not with La³⁺ and/or Ce³⁺. Suitable A anions are N0₃ ^", OH^", CI^", Br^", I^", C0₃ ^2", S0₄ ^2", Si0₃ ^2", Cr0₄ ^2", HPO4^2", Mn0₄ ^", HGa0₃ ^2", HV0₄ ^2", C10₄ ^", BO₃ ^2", monocarboxylates , such as acetate, dicarboxylates , such as oxalate, alkyl sulphonates, such as lauryl sulphonate, and combinations thereof. Preferred are CO₃ ^2"'

N0₃ ^", S0₄ ^2" and OH^".

Examples are: [Mg₆Fe₂ (OH) ₁₆] C0₃.4H₂0,

[Mg₆Al₂ (OH) ₁₆] C0₃.4H₂0, [Mg₆Cr₂ (OH) ₁₆] C0₂.4H₂0,

[Ni₆Fe₂ (OH) ₁₆] C0₃.4H₂0 [Ni₆Al₂ (OH) ₁₆] C0₃.4H₂0 [Fe₄Fe₂ (OH) ₁₂] C0₃. 3H₂0[Ca₂Al(OH)₆] ( OH ) ₀.75 ( C0₃ ) 0.125 · 2.5H₂0, [Ca₂Al (OH) ₆ } OH .6H₂0,

[Ca₂Al (OH) ₆] OH.3H₂0, [Ca₂Al (OH) ₆] OH .2H₂0, [Ca₂Al (OH) ₆] OH,

[Ca₂Al (OH) ₆] CI .2H₂0, [Ca₂Al (OH) ₆] 0.5C0₃.2.5H₂0,

[Ca₂Al (OH) ₆] 0.5 S0₄.3H₂0, [Ca₂Fe(OH)₆] 0.5 S0₄.3H₂0,

[ (Ni,Zn)₆Al₂(OH)₁₆]C0₃.4H₂0, [Mg₆ (Ni , Fe ) ₂ ( OH ) ₁₆ ] (OH)₂.2H₂0, [Mg 6A1₂(0H)₁₆] (OH)₂.4H₂0, [Mg₃Zn₃ ) Al₂ ( OH ) ₁₆ ) ]C0₃.4H₂0,

[Mg₆Al₂(OH)₁₆]S0₄.xH₂0, [Mg₆Al₂ ( OH ) ₁₆ ] (N0₃)₂.xH₂0, [ Zn₆Al₂ ( OH ) ₁₆ ]C0₃.xH₂0, [Cu₆Al₂ (OH) ₁₆] C0₃.xH₂0, [ Cu₆Al₂ ( OH ) ₁₆ ] S0₄. xH₂0 and [ΜηβΑ1₂ (OH) 16] CO₃. xH₂0, wherein x has a value of from 1 to 6.

The preparation of anionic clays is described in many prior art publications, particular reference being made to US 4,458,026, Acta Acad. Aboensis Math. Phys . , VII, 3 (1933), Helv. Chim. Acta, 25, 106-137 and 555-569 (1942), J.Am.Ceram. Soc. , 42, no.3, 121 (1959), Chemistry Letters (Japan), 843 (1973), Clays and Clay Minerals, 23,

369 (1975), Clays and Clay Minerals, 28, 50 (1980), Clays and Clay Minerals, 34, 507 (1986), Materials Chemistry and Physics, 14, 569 (1986) .

In a preferred embodiment herein the hydrotalcite anionic clay is dodecylbenzene sulphonate organically exchanged anionic clay commercially available under the tradename Pural MG from Sasol. The asphalt composition of the invention may

suitably comprise additional components. In one

embodiment of the invention, the asphalt composition comprises a polymer. A preferred type of polymer is a copolymer comprising one or more vinyl aromatic compounds and one or more conjugated dienes, in an amount of 0.1 to 7 %wt, based upon the weight of the asphalt composition. More preferably the polymer is a linear styrene- butadiene-styrene block copolymer of formula ABA wherein A is a polystyrene block and B is a polybutadiene block.

Another preferred type of polymer is a copolymer formed from monomers including ethylene and glycidyl

methacrylate or glycidyl acrylate, in an amount of 0.1 to 7 %wt, based upon the weight of the asphalt composition. More preferably the polymer is a terpolymer formed from ethylene, alkyl acrylate and glycidyl methacrylate or glycidyl acrylate.

In step (i) of the processes for manufacturing the present asphalt compositions the bitumen is heated, preferably at a temperature of from 60°C to 200°C, preferably from 80 to 150°C, more preferably from 100°C to 145°C, and even more preferably from 125°C to 145°C. Working above 120 °C has the advantage that sulphur is liquid which facilitates the mixing process. Although the skilled person can easily determine the optimal mixing time the mixing time may be relatively short, e.g., from 10 to 600 seconds.

In step (ii) of the process for manufacturing the present asphalt composition the aggregate is heated, preferably at a temperature of from 60 to 200°C,

preferably from 80 to 170°C, more preferably from 100 to 160°C, even more preferably from 100 to 145°C. In step (iii) of the asphalt manufacturing process, the hot bitumen from step (i) and hot aggregate from step

(ii) are mixed in a mixing unit. Suitably, the mixing takes place at a temperature of from 80 to 200°C,

preferably from 90 to 150°C, more preferably from 100 to

145°C. Typically, the mixing time is from 10 to 60 seconds, preferably from 20 to 40 seconds.

Sulphur is preferably added as late as possible in the process, preferably in step (iii) . Sulphur is

preferably added in the form of pellets.

The sulphur and the hydrotalcite anionic clay may be added together, i.e. both in step (i), step (ii) or step

(iii) . In a first embodiment, the hot aggregate is mixed with the sulphur and the hydrotalcite anionic clay. Hot bitumen is then added to the hot aggregate-sulphur- anionic clay mixture. In a second embodiment, hot

aggregate is mixed with hot bitumen, and the sulphur and hydrotalcite anionic clay are added to the hot bitumen- aggregate mixture. This embodiment offers the advantage of producing a stronger sulphur-asphalt mixture strength.

In a third embodiment, hot bitumen is mixed with sulphur and the hydrotalcite anionic clay and the resulting hot bitumen-sulphur-anionic clay mixture is mixed with hot aggregate to obtain a sulphur-comprising asphalt mixture.

Alternatively, in the asphalt manufacture process the hydrotalcite anionic clay may be added separately. For example, the hydrotalcite anionic clay may be added to the bitumen in step (i) and the sulphur may be added in step ( iii ) .

In one embodiment of the invention, the sulphur and the hydrotalcite anionic clay are added together; the sulphur is in the form of pellets and the hydrotalcite anionic clay is incorporated in the sulphur pellets. The sulphur pellets preferably comprise from 0.05 to 10 wt% of the hydrotalcite anionic clay, based upon the weight of the sulphur. The sulphur pellets are suitably prepared by a process wherein liquid sulphur is mixed with the hydrotalcite anionic clay and optionally additional components such as carbon black and amyl acetate. The mixture is then shaped and/or pelletised.

In one embodiment of the invention sulphur may be added in the form of two types of sulphur pellets; a first type of sulphur pellet that comprises the anionic clay and a second type of sulphur pellet that does not comprise the anionic clay. This has the advantage that the anionic clay are essentially concentrated in the first type of sulphur pellet and conventional sulphur pellets can be used to make up the rest of the sulphur requirement .

In one embodiment of the invention the hydrotalcite anionic clay is added to the bitumen before step (i) . The anionic clay is thus pre-incorporated into the bitumen to form a bitumen composition by heating the bitumen, e.g. to a temperature of from 60°C to 200°C, preferably from 80 to 150°C, more preferably from 100°C to 145°C, and even more preferably from 125°C to 145°C, and mixing it with the anionic clay. The bitumen composition may be stored at its heated temperature before being used for manufacturing the present asphalt compositions. The bitumen composition may for example be stored for at least 12, 24, 36 or 48, e.g. up to 72 or 96 hours.

Conveniently, the anionic clay content of the bitumen composition may be adjusted to be in the range of from

0.05 to 5.0 wt%, based on the total weight of the bitumen composition . The invention further provides a process for

preparing an asphalt pavement, wherein asphalt is prepared by a process according to the invention, and further comprising steps of:

(iv) spreading the asphalt into a layer; and

(v) compacting the layer.

The invention further provides an asphalt pavement prepared by the process according to the invention.

The compaction in step (v) suitably takes place at a temperature of from 80 to 200°C, preferably from 90 to

150°C, more preferably from 100 to 145°C. The temperature of compaction is desirably kept as low as possible in order to reduce hydrogen sulphide emissions. However, the temperature of compaction needs to be sufficiently high such that the voids content of the resulting asphalt is sufficiently low for the asphalt to be durable and water resistant .

The invention will now be illustrated by means of the following Examples, which are not intended to limit the invention.

Example 1

To demonstrate the effect of adding hydrotalcite anionic clay into molten sulphur, the following

experiment was carried out.

In this example, elemental sulphur was obtained from

BEB Erdgas und Erdol GmbH, Germany. Linear alkyl benzene sulphonic acid modified Pural MG clay belongs to a family of organically modified hydrotalcite clay (aluminum magnesium compound) , was obtained from Sasol Germany GmbH. It was heated at 100-110 °C in an oven under vacuum for 2 hrs to remove the adsorbed water prior to its use.

100 gm of elemental sulphur was taken in a beaker and heated to 140 °C. Once sulphur was melted completely it was stirred using a high shear overhead stirrer at 3800-4000 rpm. To this molten mass, 1.5 g linear alkyl benzene sulphonic acid modified Pural MG clay was added slowly and the stirring was continued for another 20-30 minutes to get a better dispersed mass. The stirring was stopped and the mixture was then poured on an aluminium tray and was allowed to cool. Visual observation was made to check the miscibility behaviour. Good miscibility of the anionic clay and sulphur was observed.

Example 2

Sulphur Vapour Test:

To demonstrate the effect of hydrotalcite anionic clay on sulphur vapour in a sulphur-modified bitumen, the following experiment was carried out.

A blend of elemental sulphur and bitumen was heated to 145-148 °C. The bitumen was a 60/70 penetration grade bitumen and the weight ratio of sulphur: bitumen was 30:70. A required quantity of linear alkyl benzene sulphonic acid modified Pural MG clay commercially available from Sasol was added while the stirring was continued for 3 hours. Evaporated sulphur was collected on a filter paper for 3 hours and its weight was measured gravimetrically to determine the sulphur loss. This was compared with the control experiment with no anionic clay to measure % sulphur loss. Results are shown in Table 1. Table 1

Table 1 shows that 1.5 wt% of anionic clay

significantly reduces the level of sulphur vapour

sulphur-modified bitumen composition. Example 3

Degassing Test for Elemental Sulphur

To demonstrate the degassing effect of anionic clay on elemental sulphur, the following experiment was carried out.

Elemental sulphur granules were obtained from

Chennai Petro Chemicals Ltd and its adsorbed H₂S content was measured to be around 176 ppm. The gassy elemental sulphur granules were therefore used to check the

suitability of additive/s as degassing agent/s in

controlling the H2 S / S O2 emissions.

A sample weighing 1 g of elemental sulphur granules was taken in a 20 ml vial. This is followed by the addition of approximately 15 mg quantity of organically modified Pural clay. The mixture was heated to a

temperature of 125 °C for 15 minutes under a constant high agitation of the vial prior to its headspace

analysis. These parameters were maintained constant within the instrument capability during all experiments. The headspace was sampled via a 1 ml sample loop kept at 150 °C and injected into GC via a transfer line kept at 160 °C. An Agilent G188 GCMS equipped with a headspace auto sampler oven was used for analyzing H2 S and S O2 components. The results are shown in Table 2 below.

Table 2

Table 2 shows that addition of 1.5 wt% of an anionic clay to elemental sulphur significantly reduces the level of H2 S and S O2 gas which is emitted from the elemental sulphur . Example 4

H₂S/SO₂ Emissions Test for Elemental Sulphur & Bitumen Blend

To demonstrate the effect of anionic clay on ¾S and SO₂ emissions in a sulphur-modified bitumen, the

following experiment was carried out.

Bituminous compositions were prepared according to the following procedure. Bitumen of penetration grade, 60/70 was pre-heated in an oven for 2 hours at 160°C. 28 g of this pre-heated bitumen was placed in a 3 neck round bottom flask followed by addition of 12 g of elemental sulphur granules (gassy granules, supplied by Chennai Petro Chemicals Ltd) while maintaining the stirring rate of 1000 rpm. To test the effect of additive on H₂S and SO₂ emissions, 0.18 g of linear alkyl benzene sulphonic acid modified Pural MG clay was added to the above mix which was maintained at 140°C and the stirring was continued for another 4 minutes. A Drager "Multiwarn" H₂S/SO₂ gas detector was connected to one of the necks of the round bottom flask containing the blend sample which was maintained at 140°C under a continuous stirring rate of 275 rpm. H₂S and SO₂ emissions were measured. The results are shown in Table 3 below.

Table 3

Table 3 shows that the addition of 1.5 wt% of an anionic clay to a sulphur-modified bitumen significantly reduces H₂S and SO₂ emissions.

Claims

C L A I M S

1. An asphalt composition comprising aggregate,

bitumen, sulphur and a hydrotalcite anionic clay.

2. An asphalt composition according to claim 1 wherein the amount of hydrotalcite anionic clay is from 0.05 wt% to 10 wt%, based upon the weight of the sulphur.

3. An asphalt composition according to claim 1 or claim 2 comprising from 1 wt% to 10 wt% of bitumen, based on the weight of the asphalt composition.

4. An asphalt composition according to any of claims 1 to 3, wherein the amount of sulphur is from 10 to 200 wt%, based upon the weight of the bitumen.

5. A process for manufacturing an asphalt composition according to any one of claims 1 to 4, the process comprising the steps of:

(i) heating bitumen;

(ii) heating aggregate;

wherein sulphur is added in at least one of steps (i), (ii) or (iii); and wherein a hydrotalcite anionic clay is added in at least one of the steps (i), (ii) or (iii).

6. A process for manufacturing an asphalt composition according to claim 5, wherein sulphur is added in the form of pellets.

7. A process for manufacturing an asphalt composition according to claim 6, wherein the sulphur pellets and the anionic clay are added together and the anionic clay is incorporated in the sulphur pellets.

8. A process for preparing an asphalt pavement, wherein an asphalt composition is prepared by a process according to any one of claims 5 to 7, and further comprising steps of:

(iv) spreading the asphalt into a layer; and

(v) compacting the layer.

9. Sulphur pellet comprising sulphur and from 0.05wt% to 10wt% of a hydrotalcite anionic clay, based upon the weight of the sulphur.