What is Bitumen Emulsion?
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.
Description of Bitumen Emulsion
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.
Methods of Preparation
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.
bitumen`s strength properties are secured, because there`s no needed to heat. Cold mixing or slightly warm ingredients emulsion mix are use for pavements construction..
Emulsion can used in wet weather even when it is raining.
It possess anti-stripping properties.
There is no wastage during laying and storage.
Emulsions with lower viscosity or thinner consistency improve spreadability and allows better coating of the bitumen on the surface of aggregate.
Less effect on environment, because it`s water base.
It is the least energy intensive of all construction material: there is no need to heat.
Emulsion is not suitable for every work. It depends on aggregate is acidic or basic in nature.
Setting time depending on air temperature, wind velocity also type of emulsion.
There is wide range of curing time. A suitable emulsion mix needs to designed for a particular need. Also we need to determine for each case, optimum quantity of emulsion based on zone, type of emulsion, mix grade and desired mechanical properties.