Cutback bitumen 1

[yashrai041]

Dear All,

I need to know how to determine the percentage of solvent to make the cutback bitumen of different grade from 80/100 penetration grade straight run bitumen. please help.

Best regards
g

 

[Ron]

I'm not sure why you would want to mix your own cutback asphalt. It will be hard to maintain consistency and quality if field mixed. Most cutbacks are purchased based on the desired characteristics.

Cutbacks are usually sold by their viscosity, not penetration grade. Manufacturers can control quality of the end product. I would suggest that you purchase the cutback from a manufacturer.

 

[yashrai041]

Dear Ron,

thanks for the reply. But i need to know that based on the road surface temperature, i may have to decrease the viscosity of 80/100 penetration grade bitumen to MC70 etc. As you said, it is hard to maintain consistency and quality in the field.In that case I wish to know only the principal behind it.Please help.

thanks in advance
G

 

[Ron]

The percentage of solvent will depend on the viscosity you want to achieve. You'll have to do this by trial and error. I would start with 5% solvent addition by volume. Mix thoroughly. Check viscosity. Adjust from there.

 

[Hoaokapohaku]

The reason to mix a cutback yourself is cost. Another reason is that in some localities cutbacks are no longer available from the former manufacturers because of environmental and liability concerns, yet certain owners and/or agencies continue to insist on their use. I started manufacturing cutbacks about 20 years ago because to purchase the product cost more than double the cost of the ingredients, and all the supplier did was meter both asphalt and fuel into the customer's distributor truck. The company has produced their own specification compliant cutbacks using the proportions I determined ever since.

It is more complicated than just getting the correct viscosity because you must also get the correct cure time for the kind of product you trying to produce, either rapid, medium, or slow set. This requires use of a solvent, or mixture of different solvents, that provide the evaporation rate needed to provide the correct cure properties for the grade of cutback produced. Typical solvents include kerosene (jet fuel), diesel, naptha and gasoline.

When I first determined the required proportioning, I didn't have a lab readily available that could do the required testing so I devised a "down and dirty" method intended to get me close. My intent was to then send in a sample of my product for testing, adjust, retest, etc. However, the "down and dirty" method worked so well we successfully produced spec MC-70, and SC-3000 the first time we sent the products in for testing. The method was simply to obtain a sample of product in the desired grade that is used the same neat asphalt as I intended to use in my manufacture and that was known to comply with the specifications. Then, I heated that sample until it was in a liquid, but still somewhat viscous state and recorded the temperature. Then I poured the material into a small metal funnel and adjusted the flow rate by squeezing the bottom of funnel with pliers until the filled funnel would drain at a rate so that the steady stream of flow would break into a broken flow (or drip) in about 30 to 45 seconds, and recorded the required time. Then, I heated my various lab mixed combinations of asphalt and differing types and amounts of solvents to the previously established temperature and performed my funnel test on each one, adjusting until the flow time matched the flow time of my compliant sample. I determined the proportion of asphalt/solvent in this manner, using the solvents I thought most likely to have provide the correct cure time for the application, then mixed larger batches and applied them in the intended use and verified by visual inspection that the cure time was typical for the product. Then, I finally sent in samples for independent lab testing and certification. All passed, and always have since then.

 

[Hoaokapohaku]

A couple more things in addition to above...

If you try this "down and dirty" method, make sure you get REPEATABLE results using your spec sample before using it for your own mixtures. It might take a little fiddling around and adjusting temperature to accomplish this.

The MC-70 specification range for residue from distillation is 65% to 90% by volume. It's best to stay away from the limits of the range so you will probably find that a successful product will be between 70% and 85% asphalt and the remainder solvent. Keep in mind your neat asphalt probably contains a small fraction of distillate so if you use a 65/35 asphalt/solvent proportion, it is likely to fail to meet specifications.