WO2014001384A1

WO2014001384A1 - Asphalt composition

Info

Publication number: WO2014001384A1
Application number: PCT/EP2013/063369
Authority: WO
Inventors: Sunil Ashtekar; Chantal Soubigou; Govind Wagle
Original assignee: Shell Internationale Research Maatschappij B.V.; Shell Oil Company
Priority date: 2012-06-26
Filing date: 2013-06-26
Publication date: 2014-01-03

Abstract

An asphalt composition comprising aggregate, bitumen, sulphur, anionic surfactant and bentonite clay is disclosed, wherein the amount of anionic surfactant preferably from 0.05 wt% to 10 wt% and the amount of bentonite clay is preferably from 0.1 to 10 wt%, based upon the weight of the sulphur. Methods of preparing asphalt compositions and asphalt pavements are also disclosed.

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. A 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. The inventors have found that eye and throat irritation can be caused by the presence of sulphur vapour, and have found that by incorporating anionic surfactants such as calcium lignosulphonate into the sulphur-containing asphalt it is possible to reduce the quantity of sulphur vapour and thereby decrease the amount of eye and throat irritation experienced by workers .

Although calcium lignosulphonate and the like is advantageous from the viewpoint of reducing the quantity of sulphur vapour, it is, however, a difficult material to work with and its handling, loading and associated dust management poses a challenge during the production stage of sulphur-asphalt mixtures. It would therefore be desirable to obviate these processing problems associated with the addition of anionic surfactants such as calcium lignosulphonate .

Summary of the Invention

The present inventors have found that anionic surfactants such as calcium lignosulphonate can be more easily incorporated into the sulphur-asphalt mix by combining it with a bentonite clay. Thus, according to the present invention there is provided an asphalt composition comprising aggregate, bitumen, sulphur, an anionic surfactant, and a bentonite 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 premix comprising anionic surfactant and bentonite 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 another embodiment of the invention, the premix comprising anionic surfactant and bentonite 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, anionic surfactant and bentonite clay.

In an alternative embodiment of the invention, instead of incorporating the premix comprising anionic surfactant and bentonite clay into the asphalt

composition, the premix comprising anionic surfactant and bentonite clay can be sprayed into the atmosphere as the asphalt pavement is laid. Accordingly, the present invention provides a process for preparing an asphalt pavement, 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; (iv) spreading the asphalt composition into a layer; and

(v) compacting the layer;

wherein sulphur is added in at least one of steps (i), (ii) or (iii); and wherein, a premix comprising anionic surfactant and bentonite clay, is sprayed above the layer in steps (iv) and/or (v) . Such a process also reduces eye and throat irritation experienced by workers during preparation of an asphalt pavement.

The present invention also embraces the use of a premix comprising anionic surfactant and bentonite clay for the purpose of: (i) reducing the quantity of sulphur vapour encountered during the production and/or paving of an asphalt composition comprising aggregate, bitumen and sulphur; and/or (ii) for decreasing the amount of eye and throat irritation experienced by workers when paving 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 surfactant-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, anionic surfactant and bentonite 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 lOOOdmm, more preferably of from 15 to 450dmm (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 inventors encountered the problem of eye and throat irritation in the use of sulphur-modified

bitumen/asphalt comprising substantial amounts of

sulphur. Accordingly, advantageously, the asphalt 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 anionic surfactant is suitably chosen from: the group consisting of lignin derivatives such as

lignosulphonates ; aromatic sulphonates and aliphatic sulphonates and their formaldehyde condensates and derivatives; fatty acids and carboxylates , including sulphonated fatty acids; and phosphate esters of

alkylphenol-, polyalkylaryl- or alkyl- alkoxylates.

In a preferred embodiment, the anionic surfactant is a lignin derivative, more preferably a lignosulphonate.

Lignosulphonates are known and are defined, for example, in Rompp Chemielexikon [Dictionary of Chemistry] , 9th Edition, Volume 3, Georg-Thieme Verlag, Stuttgart, N.Y. 1990, page 2511. Particularly suitable lignosulphonates are the alkali metal salts and/or alkaline earth metal salts and/or ammonium salts, for example the ammonium, sodium, potassium, calcium or magnesium salts of

lignosulphonic acid. The sodium, potassium or calcium salts are preferably used, and the sodium and/or calcium salts are most preferably used.

Lignosulphonates are derived from lignin, which is found in the cellular material of plants, e.g. trees.

Lignins comprise polymeric propylphenol substituted moieties which are interconnected at various positions on the carbon skeleton through a phenoxy group.

Lignosulphonate may be produced from lignin by a sulphite process, in which suitable feedstock such as wood is digested at 140-170°C with an aqueous solution of calcium bisulphite in acidic conditions. A benzylic cation is formed under the stated conditions, which is quenched by the sulphite ion to produce a sulphonated derivative which is separated.

R = H, alkyl, aryl

Ri = H, neighbouring lignin unit

R2 = neighbouring lignin unit

Details of this process are described, for example, in Monomers, Polymers and Composites from Renewable Resources; M. N. Belgacem, A. Gandini; Elsevier, 2008, 225-241.

Depending on the nature of the reaction conditions the lignosulphonate produced can contain carbohydrate components which are chemically linked to the

lignosulphonate molecular framework. This material finds commercial applications as sugared lignosulphonate, which may for example have a carbohydrate content as high as 35wt% depending on manufacturing conditions. Alcoholic fermentation of a sugared lignosulphonate mixture or selective chemical treatment by ultrafiltration can be used to remove sugar content to produce a de-sugared calcium lignosulphonate.

Lignosulphonates useful as anionic surfactants in the context of the invention may be sugared

lignosulphonates or de-sugared lignosulphonates and may be derived from softwood or hardwood feedstocks. For example, sugared lignosulphonates derived from hardwood and de-sugared lignosulphonates derived from softwood have been found to be of particular use.

Preferably, the carbohydrate content of the

lignosulphonates, as determined by TAPPI test method T

249 cm-85 (involves an acid treatment followed by gas chromatography analysis), may be at most 35wt%, more preferably at most 15wt%, even more preferably at most 5wt% .

In some embodiments of the invention, the

lignosulphonates may have a sulphur content in the range of from 4 to 8 wt%, and/or a sulphur content in the +6 (sulphonate) oxidation state in the range of from 4 to 8wt%. The molecular weight of the lignosulphonates may vary considerably and may lie, for example, in the range of from 7000 to 35000 Daltons, preferably 12,000 to

28,000 Daltons.

The term lignosulphonates also encompasses mixed salts of different ions such as potassium/sodium

lignosulphonate, potassium/calcium lignosulphonate or the like, in particular sodium/calcium lignosulphonate.

In another embodiment, the anionic surfactant is an aromatic sulphonate. Examples of aromatic sulphonates are alkylnaphthalene sulphonates and condensates thereof;

preferably the alkyl group contains 1 to 10 carbon atoms.

Typical counter-ions are: proton, sodium, potassium, calcium, isopropropyl ammonium, ammonium, alkanolamine etc. Exemplary alkylnaphthalene sulfonates include metal salts and organic salts of alkylnaphthalene sulfonates such as sodium diisopropylnaphthalene sulfonate,

butylnaphthalene sodium sulfonate, nonylnaphthalene sodium sulfonate, sodium dibutylnaphthalene sulfonate and sodium dimethylnaphthalene sulfonate. Also, alkylbenzene sulphonates are preferred, in particular wherein the alkyl contains 1 to 20 carbon atoms, such as 1 to 12 carbon atoms. Suitable

alkylbenzene sulphonates may be provided as a mixture of alkylbenzene sulphonates with a range of alkyl carbon atoms, preferably 10 to 16 carbon atoms, with the mean number of carbon atoms preferably being in the range of from 1 to 12. The alkylbenzene sulphonates may be linear or branched, with linear alkyl preferred for enhanced biodegradability . A particularly preferred alkylbenzene sulphonate is dodecyl benzene sulphonate, e.g. as its sodium salt.

Aliphatic sulphonates may, for example, be chosen from sulphonates of the formula R-SO₂-O-R', wherein R is Cs-Ci₆ alkyl or alkenyl and R' is a counter-ion selected from: proton, sodium, potassium, calcium, isopropropyl ammonium, ammonium, alkanolamine .

Fatty acids and carboxylates may, for example, be chosen from carboxylic compounds of formula RCOOH, wherein R is C8-C₂₂ alkyl or alkenyl and optionally their carboxylates or salts. Preferably R is an alkyl group. It is preferred that R is a C15-C₂₀ alkyl or alkenyl group, more preferably a C15-C18 alkyl or alkenyl group, and especially a C15-C18 alkyl group. For example, the fatty acid may be stearic acid. Alternatively, R may be a C₂₁-

C₂₂ alkyl group, e.g. the carboxylic additive may be behenic acid. The fatty acids may be sulphonated.

Phosphate esters of alkylphenol-, polyalkylaryl- or alkyl- alkoxylates may, for example, be chosen to

comprise in the range of from 1 to 30 carbon atoms, e.g.

5 to 25 carbon atoms or 10 to 20 carbon atoms.

The amount of anionic surfactant is preferably from 0.05 wt% to 10 wt%, based upon the weight of the sulphur. More preferably the amount of anionic surfactant is from 0.1 to 8wt%, even more preferably from 0.2 to 5wt% and most preferably from 0.7 to 3wt%. Sufficient anionic surfactant should be incorporated to achieve the desired reduction in sulphur vapour and eye and throat

irritation, but larger quantities will incur greater expense. For the avoidance of doubt, the "anionic

surfactant" is described herein as a component which may comprise or consist of one or more of the anionic

surfactant types or anionic surfactants mentioned herein.

Preferably, the anionic surfactant may represent the entirety of anionic surfactant present in the relevant context, but this is not essential. For example, by way of illustration, in embodiments of the invention from 0.05 wt% to 10 wt% (or a more preferred range as

specified above) based upon the weight of the sulphur of an anionic surfactant comprising a sulphonate group, e.g. calcium lignosulphonate, may be present in an asphalt composition, with there being no limitation on the amount of other anionic surfactants present.

The asphalt and bitumen compositions of the present invention also comprise a bentonite clay, preferably in a level of from 0.1 wt% to 10 wt%, more preferably in a level of from 0.1 wt% to 5 wt%, even more preferably in a level of from 0.1 wt% to 1 wt%, by weight of the sulphur.

The anionic surfactant and the bentonite clay are incorporated into the process of the present invention as a premix. The advantage of using a premix incorporating both the anionic surfactant and the bentonite clay, is to facilitate the handling of the anionic surfactant. As mentioned above, the handling, loading and associated dust management of anionic surfactants such as calcium lignosulphonate can pose a significant challenge during the production stage of sulphur-asphalt mixtures. By combining the anionic surfactant with a bentonite clay in a single premix, the processability of the anionic surfactant is significantly improved. In addition, the presence of bentonite clay improves the dispersability of the anionic surfactant within the sulphur.

The premix comprising anionic surfactant and

bentonite clay may be incorporated in a number of

different forms, e.g. as a powder, a liquid, a dispersion in an aqueous solvent or a dispersion in an organic solvent such as glycol.

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.

The asphalt composition may comprise an aminic compound selected from carbamides, thiocarbamides , carbamates and thiocarbamates , and mixtures thereof. The asphalt composition preferably comprises from 0.01 wt% to 10 wt% of the aminic compound. Preferred aminic compounds include urea, N, ' - (bishydroxymethyl ) urea, N, ' -dimethyl urea, N, ' trimethyl urea, 1,1-dimethyl urea, 1,3-diethyl urea, 1 , 3-dimethyl-l , 3-diphenyl urea, benzyl urea, tert- butyl urea, phenyl urea, 1, 3-diphenyl urea, 1,3-carbonyl dipiperidine , 1,3-dipropyl urea, 1,3-dibutyl urea, l-[3-

( trimethoxysilyl ) propyl ] urea, methyl carbamate, ethyl carbamate (also known as urethane) , tert-butyl carbamate, phenyl carbamate and propyl carbamate.

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 premix comprising anionic surfactant and bentonite 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 premix of anionic surfactant and bentonite clay.

Hot bitumen is then added to the hot aggregate-sulphur- anionic surfactant-bentonite clay mixture. In a second embodiment, hot aggregate is mixed with hot bitumen, and the sulphur, anionic surfactant and bentonite 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 premix of anionic surfactant and bentonite clay and the resulting hot bitumen-sulphur-anionic surfactant-bentonite clay mixture is mixed with hot aggregate to obtain a sulphur- comprising asphalt mixture.

Alternatively, in the asphalt manufacture process the premix of anionic surfactant and bentonite clay may be added separately. For example, the premix of anionic surfactant and bentonite 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 premix of anionic surfactant and bentonite clay are added together; the sulphur is in the form of pellets and the premix of anionic surfactant and bentonite clay is incorporated in the sulphur pellets. The sulphur pellets preferably comprise from 0.05 to 10 wt% of the anionic surfactant, based upon the weight of the sulphur. The sulphur pellets preferably comprise from 0.1 wt% to 5 wt% of the bentonite clay, based upon the weight of the sulphur. The sulphur pellets are suitably prepared by a process wherein liquid sulphur is mixed with the premix of anionic surfactant and bentonite clay and optionally additional components such as carbon black and amyl acetate. The mixture is then shaped and/or pelletised.

It has been found that the use of bentonite clay improves the miscibility of anionic surfactants such as calcium lignosulphonate in the molten sulphur prior to the pelletization process.

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 surfactant and the bentonite clay and a second type of sulphur pellet that does not comprise the anionic

surfactant and bentonite clay. This has the advantage that the anionic surfactant and bentonite 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 premix of anionic surfactant and bentonite clay is added to the bitumen before step (i) . The premix of anionic surfactant and bentonite 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 premix of anionic surfactant and bentonite 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 surfactant 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 bentonite clay content of the bitumen composition may be adjusted to be in the range of from 0.1 to 5 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 improved miscibility of calcium lignosulphonate in sulphur when the calcium

lignosulphonate is incorporated into the sulphur together with bentonite, the following experiment was carried out.

In this example, elemental sulphur was obtained from BEB Erdgas und Erdol GmbH, Germany, calcium

lignosulphonate powder was obtained from Lignotech and Bentonite clay was obtained from Merck Chemicals. 100 g 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 of calcium lignosulphonate and/or

0.5 g of bentonite 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 aluminum tray and was allowed to cool. Visual observation was made to check the

miscibility behaviour. It was observed that the

miscibility of calcium lignosulphonate in sulphur

significantly improved when the calcium lignosulphonate was incorporated into the sulphur together with

bentonite.

Example 2

A blend of elemental sulphur and bitumen was heated to 145-148 °C. The bitumen was a 60/70 penetration grade and the weight ratio of sulphur: bitumen used was 30:70. Elemental sulphur granules were obtained from BEB Erdgas und Erdol GmbH, Germany. Required quantities of

lignosulphonate and/or bentonite clay were added while the stirring was continued for 3 hours. Calcium

lignosulphonate powder was obtained from Lignotech and Bentonite clay was obtained from Merck Chemicals.

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 additive to measure % sulphur loss. The results are shown in Table 1 below. Table 1

Table 1 shows that the there is no detrimental effect in terms of amount of sulphur vapour produced when bentonite is used in the bitumen formulation in addition to calcium lignosulphonate. The % sulphur reduction which is achieved when bentonite is used together with calcium lignosulphonate is comparable to the % sulphur reduction which is achieved when calcium lignosulphonate is used alone .

Example 3

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 H₂S/SO₂ emissions.

A sample containing 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 calcium lignosulphonate and 5 mg of bentonite. 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 H₂S and SO₂ components. The results are shown in Table 2 below .

Table 2

Table 2 shows that the level of H₂S is significantly reduced when bentonite and calcium lignosulphonate are used together compared to when calcium lignosulphonate is used alone. In addition, Table 2 shows that the level of SO₂ is reduced when bentonite and calcium lignosulphonate are used together compared to when calcium

lignosulphonate is used alone.

Claims

C L A I M S

1. An asphalt composition comprising aggregate,

bitumen, sulphur, anionic surfactant and bentonite clay.

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

3. An asphalt composition according to Claim 1 or 2 wherein the amount of bentonite clay is from 0.1 wt% to 10 wt%, based upon the weight of the sulphur.

4. An asphalt composition according to any of Claims 1 to 3 comprising from 1 wt% to 10 wt% of bitumen, based on the weight of the asphalt composition.

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

6. An asphalt composition according to any of Claims 1 to 5, wherein the anionic surfactant is selected from the group consisting of lignin derivatives; aromatic

sulphonates and aliphatic sulphonates and their

formaldehyde condensates and derivatives; fatty acids and carboxylates ; and phosphate esters of alkylphenol-, polyalkylaryl- or alkyl- alkoxylates.

7. An asphalt composition according to any of claims 1 to 6, wherein the anionic surfactant is a

lignosulphonate .

8. A process for manufacturing an asphalt composition according to any one of claims 1 to 7, the process comprising the steps of:

(i) heating bitumen;

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

9. A process for manufacturing an asphalt composition according to claim 7, wherein sulphur is added in the form of pellets.

10. A process for manufacturing an asphalt composition according to claim 9, wherein the sulphur pellets and the premix of anionic surfactant and bentonite clay are added together and the premix of anionic surfactant and

bentonite clay is incorporated in the sulphur pellets.

11. A process for preparing an asphalt pavement, wherein an asphalt composition is prepared by a process according to any one of claims 8 to 10, and further comprising steps of :

(iv) spreading the asphalt into a layer; and

(v) compacting the layer.