There are two types of the modified bitumen one is Polymer Modified Bitumen (PMB) And other is Crumb Rubber Modified Bitumen (CRMB). It has been seen that now a days the mobile plant are available, which can convert VG10 straight run normal bitumen in to CRMB Bitumen at site with a capacity of conversion of 6-8 Ton Per Hour. In such way The CRMB-60 Bitumen produced can be used successfully for bituminous specification both in the rainfall areas and also have an aggregate tend to strip in water. CRMB is cheaper than PMB and it can be manufactured at site form the straight run VG10 bitumen as per requirement continuously through mobile conversion units. The design of the bituminous specification shall be as per IRC-SP53-2002, which is generally used for all type of the designs and job mix formula. Using CRMB is not going to consume more bitumen because of the design of bituminous specification as the parameters of Marshal Stability, Voids and flow value are affected as under.
1. Marshal Stability- is going to increase with the use of CRMB Bitumen.
2. Voids- the value is not going to change with the use of CRMB as the bitumen and Crumb Rubber Modified is also having the same density.
3. Flow value – The range of the flow value is 3 – 4.5. We design the mixes with normal flow value from is 2-4 with normal VG30 bitumen. We design the mixes with normal flow value from 3 to 3.5 and also it has been observed that it is not going to change the quantity of the bitumen for a particular mix.
Crumb Rubber Modifier (CRM) is made of asphalteens and other additives which is blended with the straight run bitumen VG10 to produce CRMB. CRM is normally added12% in 88% VG10 bitumen by weight to give 100% CRMB.
CRM is to be checked for mesh, ash and moisture. It should pass minimum 95% through 600 micron mesh, ash 7-8% and moisture less than 1%. These parameters can be checked through third party tests only for the material being used at site.
VG10 Bitumen can be arranged through Refineries or can be imported also, as per Financial aspects of the procurement.
The CRMB can be produced depending upon the requirement by installation of mobile Unit plants at sites and the CRMB-60 should give the following parameters as per specifications:-
1. Softening Point = Minimum 60 Degree Celsius.
2. Penetration = Less than 50
3. Elastic Recovery = Minimum 50%
4. Separation = Maximum 4 Degree Celsius.
5. Flash Point = Minimum 220 Degree Celsius.
One of the programmable logic control mobile unit is completely fitted in one container of size 8*40.This unit will be installed near the plant having one input tank 40 Ton capacity on one side through which the input will be fed and on other side two 40 Ton capacity tanks for collection of CRMB, one directly connected with the plant and the other for storage purposes. Basically the hot bitumen will be collected in the reaction vessel fitted with Mass flow meter intimating the quantity of the bitumen being fed. On one side of tank CRM. Hopper will be fitted with screw conveyor system for feeding of CRM to the Reaction Vessel. The bitumen with the CRM in the reaction vessel will be mixed though twin blade agitator having speed of 440 RPM. The CRMB after mixing is passed though High Shear Mill, which is further mixing the CRMB at 3000 RPM to ensure that none of the lump of the CRM is Left and it comes as a homogeneous mix. The CRMB so produced is collected in the output tanks. All the controls in the unit are computerized and displayed in the PLC. room. A hard copy of the production using quantity of VG10 and CRM can be generated though the system. It has been discussed that the reconciliation of the stocks are always matching in the specified ratio.
The mobile unit that will be installed at the above site is capable to produce the CRMB continuously even in two shifts daily 100 Ton per Day.