Silicone Additive for Hot Mixed Asphaltic Concrete
Excellent results have been obtained by adding a Silicone fluid to liquid asphalt prior to mixing with
aggregate. This additive is Dow Corning 200 Fluid 1,000 CS manufactured by Dow Corning Corporation,
Midland, Michigan. With the addition of a few ounces of this silicone into the asphalt tanks, very definite
improvement was noticed in overcoming difficulty of spreading some types of hot asphalt paving mixtures.
When critical conditions such as foaming, flushing, flatting of loads are occurring, and complete drying is
border line this silicone additive will considerably improve the laying of mix by the paver.
Basically, silicone additive improves the laying characteristics of certain type of surface, or fine aggregate
type mixes. Improvement is also noted where there is a predominance of native or natural sand materials used
in a blended state, and also where drying of fines to eliminate internal moisture is borderline. Experience to
date indicates coarse aggregate mixes (base and binder) do not respond as readily as fine aggregate surface
mixes.
No claim is made that silicones provide a cure- all for all surface course laydown problems. Silicone will not
replace drying of the aggregates but does provide some desirable reactions when critical conditions are
encountered. Usually, the two main problems observed when lay-down was unsatisfactory before adding
silicone were:
(a) Some slumping of the mix in the truck.
(b) Behavior of the Paver such as you get when there is moisture in the mix.
Both of these conditions changed to satisfactory after adding silicone. No detrimental effects to the quality of
the asphaltic concrete was found in jobs reported. They passed all standard tests. Tests were made by the
State Highway Commissions before and after treatment and mix was always within specifications.
It is important that the correct quantity of silicone be thoroughly mixed in the asphalt, and good results have
been obtained by diluting two (2) ounces of silicone in two (2) gallons of kerosene or No. 1 diesel fuel. Then
add this mixture to a 10,000 gallon tank of asphalt. This is equivalent to about two (2) parts per million (PPM)
content. Some contractors add this to the asphalt transport trucks before it is pumped into the storage tanks at
the plant. This helps provide the necessary mixing when pumped to the storage tanks. Some State
specifications require that silicone be added at the refinery and be thoroughly mixed by mechanical means.
Dow Corning Corporation definitely specifies #200 Fluid Q 1000 CS (Centistrokes) viscosity for use with hot
asphaltic mixes. Even though other viscosities are available, the 1000 CS viscosity should be used!
Iowa Manufacturing Company does not stock or sell this product, but will supply upon request the addresses
and phone numbers of Dow Corning Branch Offices, where this product can b( purchased.
Mat Surface Before Adding Silicone Compound
Mat Surface After Adding Silicone
Compound
Figure 8
Figure 9
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