of bitumen to rock:
A precondition for a longer life to water-exposed pavements
As a material in road construction, asphalt satisfies a wide variety of requirements. Its characteristics can be adapted to the application in question by appropriately selecting the type and grain structure of the mineral aggregate, the type and quantity of the bitumen used as binder and the addition of specific filler materials. However these shall only stand the test of time if under exposure to water, adequate adhesion is ensured between the rocks and the bitumen which should fully envelop the same as far as possible.
Today, it is well known that the capacity of bitumen to adhere to the mineral aggregate has a significant impact on the life of pavements and that the stripping of the bitumen layer from the surface of the rocks caused by water is one of the main reasons for roads being damaged. A pavement that has been weakened in this manner will no longer be able to withstand traffic forces and as a consequence the formation of the rocks will disintegrate, which in turn will lead to secondary consequences.
The reason for this reaction pattern is the opposing relationship that bitumen and rock have with water. Rocks are both hydrophilic (attracting water) as well as lipophilic (attracting fat) to varying degrees, while the lipophilic bitumen repels water, in other words, it is hydrophobic. If the affinity of the water to the rock is greater than that of bitumen, there is a danger to the adhesion of the bitumen to the rock surface.
Not all asphalt mixtures are susceptible to the damaging influence of water to the same degree, as has been shown by tests carried out as per the Swiss Standard SN 671 960. In the tests, the samples were subjected to a precisely defined water exposure, and the residual coating level was measured, that is the percentage values of the mineral surface that was still covered with binding material. The image on the right shows the results clearly. Changes in the coating level influence the mechanical properties of the asphalt. Other testing methods produce comparable results.
As can be seen from the adjacent image, coating levels (as per SN 671 960) between 90% and less than 20% may be found without addition of an adhesion agent. The mineral composition of the rock has the greatest impact on the adhesiveness following exposure to water. In this connection, at least to some extent, the higher values are to be assigned to the basic and only mildly hydrophilic rocks, while the lower values are to be allocated more to the acid and more hydrophilic rocks. Deviations from this rule are possible. The type of bitumen only has a minor effect on the coating level (around ± 10%). In comparison to the widely used type 70/100, the type 40/80 has slightly higher values and the type 160/220 shows slightly lower values.
The action of BITHAFTIN ® :
In order to be able to construct stable roads, it must be ensured that the mineral aggregate of the asphalt mixture has the highest possible level of coating irrespective of its mineralogical composition. Values higher than 90% should be aimed for.
When BITHAFTIN ® is added to the bitumen its properties change, such that it binds with the rocks surface better than water. This is possible because BITHAFTIN ® as a cationic-active tenside combines hydrophilic and lipophilic properties in its molecular structure. Due to its lipophilic characteristics, it can dissolve well in bitumen and due to its hydrophilic characteristic it adheres well to the rock surface. This action becomes even more evident when the coating level of the rock without the addition of an adhesive agent gets reduced due to its mineralogical properties. The adjacent diagram shows this relationship clearly.
The action of the adhesion agent BITHAFTIN ® was proved in experiments conducted by the EMPA (Swiss Federal Laboratories for Materials Testing and Research) in the laboratory, in which the addition of 0.2% produced an increase in the coating level by 47% to 90 or 92% (Test Report Numbers 416'698-3 and 416'698-5)
Lower expenditure – higher
As diagram shows, depending on the type of mineral aggregate and the type of bitumen used, it is only necessary to use around 1-3 kg of BITHAFTIN ® per ton of bitumen in order to effectively block the damaging effect of water and in order to obtain proper coating of the mineral aggregate with bitumen, of over 90% (as per SN 671 960). Practice shows that the optimum results are achieved in most cases with an addition of around 2 kg per ton of bitumen, including compensation of variations in the structure of the rock. If the addition level is too low, the desired result becomes uncertain, while excessive additions of more than 0.3% should also be avoided since this produces no additional benefit, in fact there is a danger of a reversal of the action. With the addition of the right quantity of BITHAFTIN ® , an optimum safety will be obtained regarding the quality of the asphalt mixture to be processed.
An addition of 2 kg of BITHAFTIN ® to 1 ton of bitumen increases the cost of a ready asphalt mixture by only 1% at a maximum, but it makes an important contribution to increasing the life of our roads. This is the best possible investment.
Liquid or solid BITHAFTIN ® ?
In order to make the storage, metering of the addition and adequate mixing of BITHAFTIN ® in bitumen for the user as easy as possible, BITHAFTIN ® is also available in liquid as well as solid form, its action being identical. Depending on where – between the refinery upto the asphalt mixer - the addition is to be made, it is up to the user which variant should be used taking into consideration the technical facilities and equipment available. The two types have the following characteristics:
BITHAFTIN ® -BIT,
This variant has proved itself over more than 20 years in practice. BITHAFTIN ® -BIT is supplied in 25-litre plastic canisters, 200 litre metal barrels or loose in tankers. Since BITHAFTIN ® -BIT is alkaline it should be filled and processed in accordance with the relevant specifications applicable to the handling of chemicals. During storage and processing, care should be taken to see that BITHAFTIN ® -BIT starts crystallising and becoming turbid under temperatures of + 5° to 10° C. Careful heating is recommended in such situations. The specifications of the Water Endangerment Category (WGK) shall be applicable with respect to storage.
BITHAFTIN ® -HVP,
BITHAFTIN ® -HVP was developed to make storage and addition easier; it is also frost-resistant. It is supplied in 30 x 30 cm slabs of 10 kg weight, suitable for around 5 tonnes of bitumen. Smaller or larger units may also be supplied to match the requirements of the user, for example the holding capacity of the installation in which the addition is to be done.
BITHAFTIN ® -HVP is packed in special films that do not need to be removed while adding but which quickly dissolve when BITHAFTIN ® -HVP melts in hot bitumen. Just dunk it in, provide for adequate mixing and you are ready to go – a clean and safe operation. In addition, no special regulations have to be followed for storage.
*) A detailed Safety Data sheet as per 91/155 EWG will be attached to the delivery.
**) The product starts to crystallise and to become turbid under +5°C