MISCELLANEOUS USES OF BITUMEN ROAD EMULSIONS

Introduction

REAL Technical Data Sheets have been aimed at the detailed uses of Bitumen Emulsion in the road maintenance and construction industry as outlined in BS 434 Parts I and 2. Primarily these have involved the production of emulsions specifically designed for the requirements of individual processes e.g., rapid-breaking emulsions for surface dressing or medium-breaking emulsions for coated stone.

This data sheet covers some additional uses of emulsions which have relevance in road construction and civil engineering but not necessarily appertaining to trafficked surfaces. Examples of these applications are given below and, whilst the list is by no means complete, they illustrate the impressive versatility of bitumen emulsions.

Grass Growing

For the normal gardener, the promotion of very rapid growth of grass seed is unnecessary but in any new road construction, particularly where there are steep embankments and 'slip' is likely to occur, it is essential to establish a root system of grass as quickly as possible to stabilise the area.

Bitumen emulsion is a very convenient medium for covering the seed bed with a layer of bitumen which assists germination in the following ways :

(a) The bitumen layer prevents evaporation from the surface and keeps the moisture in the soil.
(b) The layer absorbs heat and gives it up slowly thereby creating better temperature conditions for germination.
(c) The seed bed is less likely to become waterlogged, blown or washed away, or be eaten by birds.

An accepted method of application is as follows

(a) The seed bed is prepared in the normal way by producing a fine tilth of soil.
(b) A good grass seed mixture is applied at the recommended rate.
(c) The seed bed is rolled lightly and may be watered if necessary.
(d) Clean sharp sand is evenly applied to a depth of 5-6 mm.
(e) Class K2 or A1 -55 emulsion is applied at a rate of approximately 0.7
(f) The emulsion film is covered with clean sharp sand to a sufficient depth to prevent damage in the early stages, usually 3-6 mm but not greater than 10 mm.
(g) The bed may be lightly rolled.

Blowing Sand Stabilisation

Sand dunes and other areas often require treatment to prevent the surface being eroded by wind. The use of an emulsion stabilises the surface to a depth of 30-50 mm whilst still allowing effective drainage.

The emulsion commonly used is Class K2 or A2-57. This is diluted with 3-4 times its volume of potable water before it is applied to sand, at the rate of 8.5 - 11.0 l/. Care should be taken to ensure that no surplus bitumen remains on the surface.

Slip-Coat

Emulsions are used to create a bitumen membrane between the base and upper layers of concrete, the object being to retain the strength of the upper layer by preventing water seepage into the lower layer. This avoids rigid adhesion between layers of different ages and strengths so that they mature without setting up internal stresses.

Emulsions of classes K1-60, A1-55 or A1-60 are normally preferred. The emulsions may be applied in one application at a rate of 1.8 I/ or in two applications of 0.9 l/ . The latter has the added benefit in that the first application can be employed as a curing agent, assuming that it has been allowed to break completely before the second application is made.

Butt-joint, priming

BS 595, Specification for Hot Rolled Asphalt, specifies that, in transverse joints and longitudinal joints in the case of wearing courses, the vertical face should be coated with a thin coat of asphaltic cement in order to bond the new material to the face. Similarly, in BS 4987, Specification for Coated Macadam, it is recommended that vertical joint faces should be painted with binder. Having to heat the binder and paint on a hot material that is rapidly cooling on the brush can be a messy and tiresome process, and there are available quick drying cold emulsions which perform this function very efficiently and without the inherent problems of hot binder. They may also be used for promoting adhesion between asphaltic material and concrete. Very often the specification may call for a lower penetration bitumen than is usual for road emulsions. The advantage of this technique over the traditional method may be summarised as follows :

(a) No heating is required, thus plant and fuel costs are eliminated.
(b) Safe and easy application. There are no fire hazards or danger of bums to operatives.

The use of emulsions for joint painting is firmly established in the UK.

Protection

Emulsions are used for the protection of exposed or buried concrete and ironwork. In order to import more 'body' to the emulsion and to strengthen the dried film on the surface, a polymer modifier is normally incorporated in the emulsion.

Crack Filling

Bitumen emulsion, possibly polymer modified, is a most effective material for sealing cracks. Most maintenance departments are very aware of the problem of cracking in pavement surfaces and the need to take corrective action as soon as possible and before the underlying road structure is affected by moisture and detritus. The most common types of cracks may be summarised as follows

Reflection cracks - cracks in a wearing course that are caused by reflection of the cracks in the underlying road structure.
Longitudinal cracks - more or less parallel to the centre line.
Transverse cracks - more or less at right angles to the centre line.
Alligator cracks - interconnected and usually indicating failure of the underlying structure.
Slippage cracks - caused by traffic pushing the wearing course against its bond with thebase course.

As has already been stated, it is essential to treat cracking as soon as it appears, otherwise further damaged is likely to occur, especially in high rainfall areas and in winter where the freeze thaw cycle is particularly harmful. The crack must of course be thoroughly cleaned, preferably by compressed air and a steel brush, Fine cracks are treated with the emulsion on its own but larger cracks up to about 6 mm are best treated with slurry mixture of sand and emulsion to which cement may also be added to improve the strength and, reduce the cure time. If traffic is to be allowed on immediately, the surface should be blinded with sand to prevent pick up, but larger cracks may need topping up after 24 hours.

Prolonging the life of or altering the colour of paved surfaces

There are available mixtures of fine aggregates and bitumen emulsions which are stored in containers, usually 25 litre up to 200 litres, which may be painted or squeegeed on to asphalt or macadam surfaces to provide a surface seal. These ready mixed slurries may perhaps be better considered as a cross between a mist coat and a slurry seal and when part of the aggregate is replaced by pigment a variety of colours may be achieved, e.g., grey, red and green. Several coats may be applied depending on the type of traffic but it must be appreciated that these materials are only applied at paint-film thickness and they will not be very resistant to abrasive trafficking and scuffing action. They have been used successfully on motorway hard shoulders and central reservations particularly where, colour is required to differentiate the area from black surfacing and also secondarily for decorative purposes. They provide an economical and colourful means of sealing paved surfaces in low traffic density areas where colour definition or surface renovation is required,

Skid Pans

A surface suitable for skid testing is provided by depositing a film of hard bitumen on a smooth surface. This may be achieved very simply by application of a specialised grade of emulsion. The bitumen emulsified is a harder grade than the 70-300 penetration grades specified in BS 434. The emulsion is sprayed evenly on to the surface and dries to a hard shiny surface with a low resistance to skidding. The surface can be conveniently re-sprayed if the bitumen film should lose its smooth texture with use.