PROPERTIES OF BITUMEN

Adhesiveness of bitumen to a surface depends upon both the nature of the surface and the state of the bitumen. For an adhesive to act it must be able to wet a surface. In a fluid state bitumens can wet a dry solid surface and good adhesion will result, but the presence of water will prevent adhesion. The temperatures of the solid and the bitumen also influence the bond, as will any dust on the surface of the solid and the nature of the solid itself. Even after a bitumen bas been successfully applied, the bond can be decreased or even destroyed by the entrance of water into the bitumen-solid interface.

A number of additives to improve adhesion of bitumens to solid surfaces have been proposed. These compounds have a powerful wetting and adhesive action, and when present in small amounts in bitumens they displace water from the solid surface and permit a good bond. They also prevent any deterioration of the bond should water ever reach the interface. The creation and maintenance of a good adhesive bond between bitumen and a solid is an essential requirement for satisfactory performance.

The water resistance properties of bitumens depend upon the degree of impermeability and water absorption inherent in them. Even a very thin layer (1/64 inch) in a continuous film provides an excellent water barrier. In practical applications the degree of impermeability will be affected by the nature of the filling materials and the continuity of the bituminous coating. For waterproofing and roofing applications, fabrics or felts are used to build up a membrane to provide and maintain continuous waterproofing films.

Under certain conditions water may be absorbed by the bitumen itself or by minute quantities of inorganic salts or fillers in it. The normal solubility of water in bitumen is in the order of 0.001 to 0.01 per cent by weight and is so small as to be negligible. The presence of water soluble salts in any quantity will result in a large capacity for water absorption by osmosis. For this reason oil refineries de-salt the crude oil before refining it. Fillers also can absorb certain quantities of water, the amount varying with the composition and granular size of the material. As a result it bas been found that bitumens in permanent contact with water absorb it in varying amounts, and various claims as to the relative water absorption properties of coal-tar pitch and asphalt have been made.

Results of recent tests on asphalt and coal-tar pitch have reported water absorptions of 0.5 to 2.4 grams/sq ft for commercial coal-tar pitches and 2.0 to 3.9 grams/sq ft for commercial asphalts after one year. This rate of absorption is very low and there is very little difference between the two. It is more significant that the rate of water penetration into the bitumen is also very low.

The viscous or flow properties of bitumens are of importance, both at the high temperatures encountered in processing and application and at the low temperatures to which bitumens are subjected in service. Flow properties are complex and are further confused by changes in the colloidal nature of the bitumens that occur with heating. When the temperature is high enough for the bitumen to be liquid, the rate of shear is directly proportional to the shearing stress. As the temperature drops, how ever, these flow properties are complicated by elasticity and other effects. This has necessitated empirical tests, which. are used by the producer and consumer to measure the consistency of the bituminous materials at temperatures comparable to those encountered in the service life of the bitumen. Among the most common of these tests are the penetration and softening point tests and various indices using them.

The penetration test measures the depth of penetration in tenths of millimetres that a weighted needle achieves in a bitumen after a known time at a known temperature. The most common combination of factors is a weight of 100 grams applied for 5 seconds at a temperature of 77°F. The penetration is a measure of hardness, and typical values obtained are approximately 10 for hard coating grade asphalts, 15 to 40 for roofing asphalts, and up to 100 or more for certain waterproofing materials.

The softening point test measures the temperature in degrees Fahrenheit at which a steel ball falls a known distance through the bitumen when the test assembly is heated at a known rate. The usual combination of factors is a ¾-inch diameter steel ball weighing 3.5 grams sinking 1 inch through a 5/8-inch diameter ¼-inch thick disc of bitumen held in a brass ring, with the whole assembly heated at a rate of 9F degrees per minute. The resulting measured temperature is not the melting point, but merely gives a measure of flow under controlled conditions. The softening point value is used to grade bitumens into groups. Typical values would be up to 240°F for coating grade asphalts, from 140°F to 220°F for roofing asphalts, and down to approximately 115°F for certain waterproofing materials.

When chilled sufficiently all bitumens lose their viscous properties and behave as brittle elastic solids. The interval between the softening point temperature and the temperature at which a brittle condition is reached gives a measure of the temperature susceptibility of the material. This can vary a great deal, depending on the crude oil source and the bitumen processing. Successful use of bitumen usually results if a material has been chosen that will be subjected in service to temperatures well within the limits defined by its brittle condition and softening point.

Lack of compatibility between different bitumens is also of importance, and exhibits itself by staining and the appearance of oil spots or large cracks. If a coal-tar pitch and an asphalt are incompatible, one will be softened and the other hardened, the nature and extent of incompatibility depending upon the chemical composition and internal physical structure of the bitumens. The reaction of asphalt towards pitch can be manifested in two ways:

1.      If asphalt is applied over pitch it can soften and flow off, leaving exposed pitch that will weather rapidly.

2.      If pitch is applied over asphalt, the pitch may harden and crack.

These reactions do not always occur and sometimes asphalt can be applied over pitch, or vice versa, with no ill effects. It is considered advisable, however, to avoid contact of the two bitumens if possible, and for this reason asphalt should not be used with tar-saturated felt, nor should tar be used with asphalt-saturated felt. If any doubt exists on the compatibility of bituminous materials, a test bas been devised to establish it (ASTM D1370-58).

To enable bitumens to wet the surface that is to be protected, they are often applied in the hot liquid state. The temperature to which they should be heated depends upon both the consistency of the bitumen and the temperature of the surface to, which it is applied. As a maximum temperature exists, however, above which chemical degradation of the bitumen occurs, it is not advisable to, heat asphalts above 450°F and coal-tar pitches above 400°F. Coal-tar pitches and one grade of asphalt for built-up roofing have a softening point of about 140°F; it is thus possible, by heating these materials even to 350°F or lower, to obtain a liquid that will wet a dry solid surface and enable the bitumen to be applied so that it can act as a waterproofing agent.

It is occasionally desirable to avoid the use of a hot material. At such times bituminous products are used in so-called cold applications, with the bitumen in liquid form as a cutback or an emulsion. (A cutback material is a solution of the bitumen in a suitable solvent.) After application of the bituminous solution to the solid surface, the solvent evaporates leaving the bituminous film to act as a coating. Numerous solvents are sufficiently volatile and are good solvents for bitumens, but many are either too expensive or too hazardous. To control the drying times of the solution, care must be taken in the selection of the bitumen and solvent.

Emulsions are dispersions of very small drops of bitumen in water. A satisfactory emulsion is smooth in appearance, usually brown In colour, and can be made from bitumens having a wide range of consistencies. Emulsions usually contain a mineral material and are often called clay emulsions, although the mineral can also be coal, shale, metallic oxides, portland cement or asbestos. The most widely used is a special clay known as bentonite. An obvious advantage of emulsions over other bituminous products is that they are easy to handle, addition of water being all that is necessary to decrease their viscosity. Curing involves, primarily, a loss of water by evaporation; its stability, however, depends upon many factors such as asphalt concentration, size and distribution of asphalt droplets, freezing of the water and the nature of the stabilizing agent.

DURABILITY OF BITUMEN

Mention bas been made of the changes that bitumens undergo when they are overheated; this is but one of the peculiarities encountered in their handling and service. Among the other factors to be considered are water absorption and photo-oxidation. Bitumens are readily oxidized when subjected to ultra-violet radiation, a process that forms water soluble products and results in a material that is harder and less flexible than it was originally. If it continues until the bitumen can no longer withstand the strains imposed by thermal and structural movement, the material cracks. The loss of volatile materials also causes contractions that frequently cause shrinkage cracks. In the absence of light and heat, however, the rate of oxidation is low and the useful life of the materials can be extended. Light-coloured gravel in built-up roofing construction provides the protection required for satisfactory durability.

GENERAL USES OF BITUMENS

Bitumen is primarily used for paving roads. Its other uses are for general waterproofing products, including the use of bitumen in the production of roofing felt and for sealing flat roofs. It is also the prime feed stock for petroleum production from tar sands currently under development in Alberta, Canada. Bitumen from tar sands is projected to account for 80% of Canadian oil production by 2020.

In the past, bitumen was used to waterproof boats, and even as a coating for buildings. The Greek historian Herodotus said hot bitumen was used as mortar in the walls of Babylon.  It is also possible that the city of Carthage was easily burnt due to extensive use of bitumen in construction.

Vessels for the heating of bitumen or bituminous compounds are usually excluded from public liability insurance policies.

Most geologists believe that naturally occurring deposits of bitumen are formed from the remains of ancient, microscopic algae and other once-living things. These organisms died and their remains were deposited in the mud on the bottom of the ocean or lake where they lived. Under the heat and pressure of burial deep in the earth, the remains were transformed into materials such as bitumen, kerogen, or petroleum. Bitumens are found also in meteorites, archean rocks, copper, zinc mineralizations, and caves. It is possible that bitumens are primordial material formed during accretion of the earth and reworked by bacteria that consume hydrocarbons.

Bitumen was also used in early photography technology. It was most notably used by French scientist Joseph Nicephore Nipce in the first picture ever taken. The bitumen used in his experiments were smeared on pweter plates and then exposed to light thus making a black and white image.

USES OF BITUMENS AS WATER PROOFING

The desirable qualities of bitumens control the uses to which they may be put; the limitations of the materials control the methods of application and their performance in service. Adhesiveness and waterproofing qualities, combined with low cost, make them useful as a protective agent in both built-up and prepared roofing and in prepared siding. They have wide use also as sealants and adhesives. Combined with other materials, bitumens may be used as vapour barriers and as agents to waterproof and damp-proof structures.

Bitumen is used in many forms depending upon the characteristics and properties desired. Saturated felts, used in built-up roofing as a base for prepared roofing and siding, as underlays for floors, and as a membrane for waterproofing, require a particular grade of bitumen that bas a low viscosity at the saturation temperature. The flash-point should be above the saturating temperature, however, and a reasonably low temperature susceptibility is desirable. In the preparation of asphalt-saturated felt an asphalt having a softening point of approximately 140°F and penetration value of 50 is used.

Prepared roofing products such as shingles and roll roofing consist of saturated felts coated with asphalt. The coating grade asphalts used for this application are high softening point (200 to 240°F) air-blown products with high penetration values of 18 to 30 at 77°F; they have low temperatures susceptibility. Care is taken during manufacture to ensure that the coating asphalt is compatible with the saturant.

Bitumens are widely used to provide a waterproof coating to walls and to construct waterproof membranes in buildings and engineering structures. Hot applied bitumens used below grade, where they are not subjected to high temperatures, are of a type having a low softening point (115 to 145°F) and a high penetration value (up to 85). Where the bitumen is to be used above grade and may be applied to vertical surfaces exposed to direct solar radiation, a type having a higher softening point (200 to 220°F) and a lower penetration value (15 to 25) should be selected. Emulsions and cutbacks that are applied cold are being used to an ever-increasing extent for damp-proofing and waterproofing. They may be used alone or with felts to build up a membrane.

Asphaltic cutbacks and emulsions have their greatest use in road construction and maintenance. With roofing it accounts for about 95 per cent of the asphalt produced in North America. There are still, however, large quantities of asphalt modified by the addition of mineral matter used in the building industry as sealants, acoustical coatings and paints.

SPECIFICATION FOR MODIFIED BITUMINOUS SHEET WATERPROOFING

PART 1 ‑ GENERAL

1.1 DESCRIPTION:

      This section specifies modified bituminous sheet material used for exterior below grade waterproofing and split slab waterproofing.

1.2 MANUFACTURER'S QUALIFICATIONS:

A.  Approval by Contracting Officer is required of products and services of proposed manufacturers, and installers, and will be based upon submission by Contractor that:

1.   Manufacturer regularly and presently manufactures bituminous sheet waterproofing as one of its principal products.

2.   Installer has technical qualifications, experience, trained personnel and facilities to install specified items.

3.   Manufacturer's product submitted has been in satisfactory and efficient operation on three similar installations for at least three years.

4.   Submit list of installations, include name and location of project and name of owner.

1.3 SUBMITTALS:

A.  Submit in accordance with Section 01 33 23, SHOP DRAWINGS, PRODUCT DATA, AND SAMPLES.

B.  Manufacturer's Literature and Data:

1.   Bituminous sheet.

2.   Primer.

3.   Mastic.

4.   Protection material, temporary and permanent.

5.   Printed installation instructions for conditions specified.

C.  Certificates:

1.   Indicating bituminous sheet manufacturer's approval of primer, and roof cement.

2.   Indicating bituminous sheet waterproofing manufacturer's qualifications as specified.

3.   Approval of installer by bituminous sheet manufacturers.

4.   Water test report.

1.4 PRODUCT DELIVERY, STORAGE AND HANDLING:

A.  Deliver materials to job in manufacturer's original unopened container.

B.  Do not store material in areas where temperature is lower than 10 degrees C (50 degrees F,) or where prolonged temperature is above 32 degrees C (90 degrees F).

1.5 ENVIRONMENTAL REQUIREMENTS:

      Ambient Surface and Material Temperature: Not less than 4 degrees C (40 degrees F), during application of waterproofing.

1.6 warranty:

      Warrant bituminous sheet waterproofing installation against moisture leaks and subject to terms of "Warranty of Construction", FAR clause 52.246-21, except that warranty period is two years.

1.7 APPLICABLE PUBLICATIONS:

A.  Publications listed below form a part of this specification to the extent referenced. Publications are referenced by basic designation only.

B.  Federal Specifications (Fed. Spec.):

UU‑B‑790A............... Building Paper, Vegetable Fiber: (Kraft, Water‑

INT AMD 1                            Proof, Water Repellent and Fire Resistant)

C.  American Society for Testing and Materials (ASTM):

C578-07..................... Rigid Cellular Polystyrene Thermal Insulation

D41-05....................... Asphalt Primer Used in Roofing, Dampproofing and Waterproofing

D2822-05................... Asphalt Roof Cement

D6380-03................... Asphalt Roll Roofing (Organic Felt)

D.  American Hardboard Association (AHA):

A135.4-1995.............. Basic Hardboard

PART 2 ‑ PRODUCTS

2.1 BITUMINOUS SHEET:

A.  Cold applied waterproofing membrane composed primarily of modified bituminous material prefabricated in sheet form designed for below grade exterior and split slab waterproofing. Sheet reinforced with fibers at manufacturer's option.

B.  Thickness of Bituminous Sheet: 1.5 mm (60 mils), plus or minus 0.13 mm (5 mils), and bonded to a 0.1 mm (4 mil) thick plastic sheet.

C.  Provide with a release sheet to prevent bonding of bituminous sheet to itself.

2.2 PRIMER AND ROOF CEMENT:

A.  Furnished by manufacturer of bituminous sheet as required for particular application in accordance with sheet manufacturer's instructions.

B.  Primer: ASTM D41.

C.  Roof Cement: ASTM D4586.

2.3 PROTECTION MATERIAL:

A.  Polystyrene: ASTM C578, Type I or VIII, 13 mm (1/2-inch) minimum thickness.

B.  Hardboard: PS-58, Service Type, 6 mm (1/4‑inch) thick.

C.  Waterproofed Building Paper: Fed. Spec. UU-B-790.

D.  Roll Roofing: ASTM D6380, Class S (smooth), Type III with minimum net mass per unit area of roofing, 2495 g/m² (51 lb/100 ft²).

2.4 PATCHING COMPOUND:

      A factory prepared, non‑shrinking, fast setting, cementitious adhesive compound containing no ferrous metal or oxide.

PART 3 ‑ EXECUTION

3.1 PREPARATION:

A.  Surface Condition:

1.   Before applying waterproofing materials, ensure concrete and masonry surfaces are fully cured, smooth, clean, dry, and free from high spots, depressions, loose and foreign particles and other deterrents to adhesion.

2.   Fill voids, joints, and cracks with patching compound.

B.  Concrete surfaces cured a minimum of seven days, free from release agents, concrete curing agents, and other contaminates.

3.2 APPLICATION:

A.  Priming:

1.   Prime concrete and masonry surfaces.

2.   Application method, amount of primer and condition or primer before installation of bituminous sheet as recommended by primer manufacturer.

3.   Reprime when required in accordance with manufacturer's instructions.

B.  Bituminous Sheet Installation:

1.   Remove release sheet prior to application.

2.   Lay bituminous sheet from low point to high point so that laps shed water.

3.   Treat expansion, construction and control joints and evident working cracks as expansion joints. Apply bituminous sheet in double thickness over joint by first applying a strip of bituminous sheet not less than 200 mm (8 inches) wide, centered over joint.

4.   Lap seams not less than 50 mm (2 inches).

5.   Lay succeeding sheet with laps, and roll or press into place.

6.   Repair misaligned or inadequately lapped seams in accordance with manufacturer's instructions.

7.   Seal seams and terminations in accordance with sheet manufacturer's instructions.

C.  Corner Treatment:

1.   At inside and outside corners apply double cover using an initial strip not less than 280 mm (11 inches) wide, centered along axis of corner.

2.   Cover each strip completely by the regular application of bituminous sheet.

3.   Provide a fillet or cant on inside corners.

4.   Form cants using patching compound

5.   Do not use wood, fiber, and insulating materials for cants.

D.  Projection Treatment:

1.   Apply a double layer of bituminous sheet around pipes and similar projections at least 150 mm (6 inches) wide.

2.   At drains, apply a bead of roof cement over a double layer of bituminous sheet under clamping rings.

3.3 PROTECTION:

A.  Protect bituminous sheet before backfill or wearing courses are placed.

B.  Install protection material and hold in place in accordance with instructions of manufacturer of waterproofing materials.

C.  Permanent Protection:

1.   Vertical Surfaces:

a.   Install hardboard, polystyrene, or roll roofing protection material.

b.   Extend protection full height from footing to top of backfill.

c.   If graded backfill is used, use roll roofing or hardboard.

D.  Horizontal Surfaces:

1.   Install roll roofing protection under concrete wearing courses.

2.   Install roll roofing, hardboard, or polystyrene under earth backfill.

3.   Where no concrete wearing course occurs or when surfaces will bear heavy traffic and will not immediately be covered with a wearing course, use protection specified for vertical surfaces.

E.   Temporary Protection:

      When waterproofing materials are subjected to damage by sunlight and can not be immediately protected as specified, protect waterproofing materials by waterproof building paper or suitable coating approved by manufacturer of waterproofing system used.

3.4 PATCHING:

      Repair tears, punctures, air blisters, and inadequately lapped seams, in accordance with manufacturer's instructions before protection course is applied.

3.5 TESTING:

A.  Before any protection or wearing course is applied, test all horizontal applications of waterproofing with a minimum of 25 mm (1-inch) head of water above highest point and leave for 24 hours.

B.  Mark leaks and repair when waterproofing is dry.

C.  Certify, to Resident Engineer, that water tests have been made and that areas tested were found watertight.

3.6 INSPECTION:

      Do not cover waterproofed surfaces by other materials or backfill until work is approved by Resident Engineer.

ALTERNATIVES OF BITUMEN

The world has become increasingly concerned over the global climate change thought to be caused by greenhouse gases, chief among them anthropogenic carbon dioxide which is released into the atmosphere from burning fossil fuels. This has led to the introduction of bitumen alternatives that are more environmentally friendly and non toxic. Bitumen can now be made from non-petroleum based renewable resources such as sugar, molasses and rice, corn and potato starches. Bitumen can also be made from waste material by fractional distillation of used motor oils, which is sometimes disposed by burning or dumping into land fills.

Non-petroleum based bitumen binders can be made light-colored. Roads made with lighter-colored pitch absorb less heat from solar radiation, and become less hot than darker surfaces, reducing their contribution to the urban heat island effect.

SUMMARY

Some of the more important properties of bitumens have been examined in this Digest. Particular mention has been made of the adhesive, waterproofing and flow characteristics that control the use to which bitumens are placed in construction. An outline has also been given of the various bitumens and the manner in which they are used. Recent studies have produced much information to justify even more research into the properties of bituminous materials. As more becomes available on composition, internal structure, mechanisms of flow, degradation and adhesiveness, a more widespread and even more successful use of this material in construction can be anticipate