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Cutback bitumen (liquid bitumen) is that type of bitumen which 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.
Cutback Bitumen is suitable for primer sealing and can also be used in the manufacturing of pre-mix asphalt, which is used in patch repairs. Cutback Bitumen is extensively used in sprayed sealing application, particularly in cooler weather where they provide improved initial stone retention due to their lower viscosity. Typically, a single application of the appropriate Cutback Bitumen is sprayed on to the pavement onto which aggregate is laid.
The advantage of 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.
An application of binder on a granular base is prepared for an asphalt surfacing.
The rate of application may vary from 0.4 – 1.4 liter per square meter, a very light application of binder hand or machine spread to ensure bonding bitumen the existing layer and the new over lay. An application of binder on the road surface by a Bitumen distributor followed by a covering of aggregates/ chippings spread by a hopper gritter.
An application of hot binder on a compacted layer of coarse aggregate in penetration macadam will also ensure the internal bonding.
A maintenance technique where specially tailored for cutback bitumen vs aggregate vs water and/ or mineral filler is mixed in an onsite distributor and spread on an existing road surface at a thickness of 6-12 mm.
It is both preventive and corrective maintenance method for sealing of surface cracks, water-proofing asphalt surfaces and stopping oxidation.
Cutback is defined by a number which indicates the minimum kinematic viscosity (fluidity) of the cutback.
MC 800 medium viscosity (800-1600) penetration of residue (12-150)
DIFFERENT SYSTEMS OF (ROAD CONSTRUCTION AND ROAD MAINTAINANCE WITH MC 800)
Pot hole& patching mix
Medium Curing Bitumen MC-800 conforming to Indian Standards specification IS:217 specification for cutback bitumen shall be used in preparing that patching mix and shall be supplied by a certified manufacturer of this product for proper mixing, the bitumen shall be heated as specified in section 4.
MC cutback bitumen shall be treated with a proper type and amount of an anti-stripping agent by the approved bitumen supplier so that when combined with the proposed job aggregate the resulting mix shall pass the wet coating test, static immersion test and water resistance test as given in APPENDIX-1.the anti-stripping agent shall conform to IS: 14982 the contractor shall furnish the sample of the job aggregate each year to the bitumen supplier for these coating and stripping tests and obtain a certificate that the bitumen material has been treated to suit the job aggregate. This yearly certificate must be on file and shall be available at the asphalt mix plant when required by the engineer. The contractor shall also forward a copy to the engineer. Under no circumstances, the contractor or the department shall be permitted to manufacture the MC cutback by blending paving bitumen and kerosene.
Where crushed gravel is proposed for use as aggregate, not less than 90 percent by weight of the crushed material retained on 4.75 mm sieve have at least two fractured faces routing from crushing operation.
Fine aggregate shall consist of crushed mineral passing through 2.36 mm sieve and retained on 75 micron sieve. It shall be clean, hard, durable and free from dust and soft organic and other deleterious substances. No natural sand shall be permitted. The contractor shall ascertain from the supplier of MC-800 as to how much residual bitumen it contains. for example , if the mc-800 contains 80 percent bitumen and 20 percent kerosene and a total of 6.0 percent MC-800 is used by weight of the mix, the residual bitumen content in the mix will be 4.8 percent.
| Bituminous Material | Aggregate Temperature, °C | Bitumen Temperature, °C |
| MC-800 | 25-65 | 75-95 |
Since the range of aggregate temperature is rather low and the maximum aggregate temperature is restricted to 65°C, it may not be possible to dry the aggregate within this temperature range. Therefore , the aggregate can be processed in a dryer at high temperature and allowed to cool before the bituminous binder is added. Pre-drying the aggregate at high temperatures will also help in reducing the fines (material passing 0.075 mm sieve), which will go into the bag house. The resulting mix then would have fines less than 2 percent as required in the stringent gradation specifications.
High aggregate temperatures while mixing with the cutback bitumen will not only cause excessive loss of kerosene from the cutback but will also pose a safety hazard in the plant pug mill. Proper and adequate venting of the pug mill is necessary. Under no circumstances there shall be any open flame in the vicinity of MC-800 cutback because it contains volatile kerosene.
Since the mix contains volatile kerosene it is not safe to store the loose mix or sealed bags in a closed binding/warehouse. store under an open shed or in a well ventilated warehouse. no open flame or smoking shall be allowed in the vicinity of the stored mix.
Pothole surface shall be cleaned with a stiff wire brush and all loose material including dust shall be removed with a soft brush. Pothole need not to be dry. However, excess water shall be swept off the pothole.
The mix is intended for patching potholes up to 75mm (3 inches) deep. For deeper potholes, patching mix shall be placed and compacted in 75 mm thick layers.
If the pothole is deep and extends to WMM or granular base, it is recommended to apply a suitable tack coat or prime coat as feasible before placing the patching mix. If angular aggregate (normal size 25mm) is used to partially fill deep potholes, the aggregate should be compacted thoroughly and primed with MC-30 before placing the patching mix. Atleast 50 mm thick pothole patching mix shall be placed at the top.
Firstly the outside edge or periphery of the patch shall be compacted with a hand rammer / small compactor and then compaction shall proceed inwards. To prevent initial pick up of the loose mix by the hand rammer either continue to wet the hand rammer with water or place empty plastic lined bags on the loose mix. For deep potholes, place the patching mix and compact in 75 mm thick layers. After compaction, the compacted patch shall be slightly proud of the existing road surface to allow for further compaction by traffic. If there are numerous closely spaced patches, it is preferred to use a small roller rather than a hand rammer. If a roller is used, the mix shall be placed and spread slightly proud of surface so that after rolling the compacted surface shall be flush with the adjoining surface.
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