Emulsified Bitumen usually consists of bitumen droplets suspended in water. This dispersion under normal circumstances would not take place, also everyone knows, oil and water don’t mix, but if an emulsifying agent added to water asphalt will remain dispersed. Most emulsions used for surface treatments. That`s enable using lower temperatures (45-70°C). This is much lower than 150-190°C used for hot mix asphalt cements. The lower application temperatures will not damage asphalt and are much safer for field personnel. In bitumen emulsion production, water treated with emulsifying agent and other chemicals. It pumped to colloid mill along with bitumen. The colloid mill breaks bitumen up to tiny droplets. Emulsifying agent migrates to asphalt-water interface and keeps droplets from coalescing. Emulsion then pumped to storage tank.
Bitumen Emulsion, usually having a relatively low average particle size, can be continuously and speedily prepared by a process comprising feeding emulsion components into the first of at least two static mixers, arranged in series. Product passed from first to second mixer maintained at lower temperature (below boiling point of water).
In addition final emulsion product is obtained from outlet of second mixer. Bitumen emulsions of up to 70 wt. bitumen of mean particle size of from 2 to 8 microns are also described.
This invention relates to bitumen;emulsions and a process for preparing them. Bitumen emulsions are well known materials useful in road-making and for other purposes. Their attractions are ease of handling, because of lower viscosity than starting bitumen, and ability to applied at lower temperatures in spraying. There are no environmental problems because in use when emulsion breaks and water present evaporates to leave a film of bitumen where required.
There are two main methods currently used in the preparation of bitumen emulsions.
The first employs a colloid mill and the second a centrifugal pump:
In the process employing a colloid mill, bitumen, water and emulsifier are emulsified at a high shear rate. Process is continuous, but to obtain emulsion with diameter particle size of bitumen at acceptable level, there is a limit on throughput.
Furthermore, process conducted at atmospheric pressure, for emulsion product to emerge at -100°C. It1s found that bitumen cannot be fed to emulsifier at +140°C. Higher temperatures for the bitumen feed require lower temperatures for the water feed.
This causes skin-hardening of the bitumen on contact of the two feeds and emulsification becomes very difficult. This factor causes limitation on types of bitumen which employed in bitumen emulsion manufacture by this way. A recent development, employing pressures slightly greater than atmospheric, involves cooling the product so that it can emerge from the mixer at below 100° C. This entails extra equipment and is difficult to control.
Second method uses centrifugal pump who cannot normally acted under pressure. This has drawbacks of above-referred to colloid mill process. Furthermore, it`s essentially only a batch process.
Water phase has to continually recycled whilst hot bitumen added little by little. The resultant emulsion product has a fairly wide particle size distribution and this leads to unevenness in the surface obtainable in use of the product.