Cutback Bitumen ( Liquid Bitumen ) is Bitumen that is dissolved in a solvent . Typical solvents include Naptha, gasoline and kerosene, white spirit etc. The type of solvent controls the curing time while the amount determines the viscosity of the Cutback Bitumen. Wahal engineer’s manufactured bitumen, which is used for road construction, is semisolid or solid at atmospheric temperature, is brought to certain viscosity value as required for road construction operation by fluxing it with certain petroleum distillates to obtain cutback bitumen. Upon exposure to atmospheric conditions the distillates evaporate.
Cutbacks are divided into three classifications; this classification is based on the rate of curing or hardening after the application.
>> Rapid Curing (RC).
>> Medium Curing (MC).
>> Slow Curing (SC).
They are further defined by a number which indicates the minimum kinematic viscosity (fluidity) of the cutback.
These are bitumens, fluxed or cutbacks with a petroleum distillate such as naphtha or gasoline, which will rapidly evaporate after using in construction, leaving the bitumen binder. The grade of the RC cutback is governed by the proportion of the solvent used. The penetration value of residue from distillation upto 360°C of RC cutback bitumen 80 to 120.
This bitumen fluxed to greater fluidity by blending with a intermediate boiling-point solvent like kerosene or light diesel oil. MC cutbacks evaporate relatively at slow rate because the kerosene-range solvents will not evaporate rapidly as the gasoline-range solvents used in the manufacture of RC cutbacks. MC products have good wetting properties and so satisfactory coating of fine grain aggregate and sandy soils is possible.
These are obtained either by blending bitumen with high-boiling-point gas, oil or by controlling the rate of flow and temperature of the crude during the first cycle of refining. SC cutbacks or wood soils hardens or set way slowly as it is a semi volatile material.
The raw bitumen from the raw material storage tank, which is at 1800C, is taken into the Blowing Column, where the bitumen of desired softening point and penetration is obtained (IF REQUIRED). It is then pumped into the Cutback Mixing Tank where, first the temperature of bitumen is brought down to around 1000 C. by water circulation in the coils provided and then it is fluxed with petroleum distillate for about thirty minutes to obtain the desired grade of Cutback bitumen. The final product is then pumped to the finish material storage tank.
>> Production capacity:- annual production of modified bitumen membranes of 1-3 million Sqm. (16 hours/day, 300days/year with two shifts).
>> Reinforcement:- Polyester, Glass fiber.
>> Modified materials :- SBS, APP.
>> Materials for surface:- sand, scraps of stone, PE membrane, aluminum foil, etc.
>> Specification of products:- Width: 1m, thickness: 2-5mm, length: 7.5 or 10m.
>> Production speed:- 0-30 m/min.
>> Main workshop:- 48× (12-15) ×(6-9)m.
>> Bitumen 80/100.
>> App (Recycled).
>> SBS.
>> Soap Stone Powder.
>> Hdpe Film.
>> Sand/Slate Chips.
The advantage Cutbacks have over Emulsions is a much higher residual Bitumen percent, typically over 80% compares with over 40-65% for Bitumen emulsions. The result is more Bitumen left on the roadway after curing, for the same volume of binder applied.
Cutback bitumen’s suitable for primer sealing, it can also be used in the manufacture of pre-mix asphalt, which is used in patch repairs. Cutback bitumen’s are used extensively in sprayed sealing applications, particularly in cooler weather where they provide improved initial stone retention due to their lower viscosity.
RC: for surface dressing in cold weather and patch repair work.
MC: is used in a premix with less quantity of fines.
SC: are used in a premix with more quantity of fines.