Definition :
« Compaction » additives have been developped by CECA, for all cold techniques where the cold product is compacted after being laid down. The production of cold mixes, that is by mixing aggregates, water and bitumen emulsion, enables the achievement of base courses and wearing courses for low to medium traffic, for maintenance work, as well as for new construction.
For base courses, grave-emulsion is the leading technique whereas for wearing courses, compacted slurry surfacing or cold mixes produced in fixed plants are more widely used.
In all these existing or emerging techniques, the final compaction step bears a very important influence in the definition of the cohesion : in spite of a good choice in terms of bitumen penetration, for example, a bad compaction will lead to excessive porosity, with poor water elimination and as a consequence a bad cohesion. At present, the parameters that can be adjusted in a bitumen emulsion plant enable a good control of the emulsion reactivity on the aggregates and hence a good coating as well as clear breaking water.
On the contrary, the control of the downstream part of the process, particularly the compaction, is presently only possible using physical parameters such as binder penetration, aggregate sieve curve or working equipment (finisher, grader, roller ). The first two parameters also have an influence on the long term mechanical behaviour of the deposited layer. Playing with these parameters to ease the compaction can lead to other problems, some symptoms being rutting, stripping, fatting up and plating (or peeling). What’s more, the compacting equipment doesn’t prove to be fully efficient for cold products.
As a whole, this shows that road products based on emulsions lack cohesion at an early stage.
Proposed solution :
CECA proposes a new solution which completes the toolbox already available for road makers in order to improve compaction efficiency. The proposed solution doesn’t disturb the standard process, except for the necessity to use STABIRAM® CM 5XX additives. One will claim an increase in cold mix fluidity, an improvement of water drainage under compaction and a decrease in void content, which lead to a better cohesion in an early stage.
Using advice :
One must add the additives, most of them being liquid, in the emulsifying water phase used for emulsion production or in the emulsion after its production. An important point is that these additives have only a small influence on the emulsion reactivity.
Consequently, in order to test the additive effect, it is not necessary to change neither the usual emulsion formulation, nor the nature or the quantity of the emulsifier, nor the nature or the quantity of the acid.
If the additive is added in the emulsifying water phase, one simply has to introduce it after the usual steps of its preparation (ie) after adding the acid, the emulsifier and water. Additional stirring is necessary in order to achieve a proper dispersion. Water emulsifying phase temperature does not need to be altered. The following steps of emulsion production are unchanged.
The additive can also be added into the emulsion (post addition). In such a case, the higher the temperature of the emulsion, the faster the additive solubilisation–under stirring or recycling.
In all cases, the additive causes no additional foaming.
Using the additived emulsion should only slightly modify the rate of wetting water for the aggregates because the emulsion reactivity only undergoes minor changes with the addition of STABIRAM® CM 5XX products. We offer a whole range of additives as their performances depend on the nature of the aggregrate and, to a lower extent, on that of the emulsifier too
Example 1: Water drainage improvement
In the laboratory, in the case of a cold mix application, trials on a giratory shear press emphasize the performances of the additives Stabiram® CM 506 and 508 (2 kg/t ie 0,2 %) on breaking water drainage (cf. chart hereafter) as well as on final porosity.
Formula : Emulsion from Elf Bitumen Penetration grade70/100,
Bitumen content 65%
Emulsifier Stabiram® CM 406, 8 kg/t with phosphoric acid titled 75%
Aggregate : microdiorite 0/10
Added water content : 5%.
The following data show the quantity of drained water after 120 girations
Case 1 :Additive into the emulsifying water phase Case 2Post-addition in the emulsion
Stabiram CM 506® 52% 51%
Stabiram CM 508® 60% 56%
Reference without additive 50% 50%
Stabiram© CM 508 is the most adapted additive for this aggregate. It is even more efficient when added into the emulsifying water phase.
Example 2 : Porosity improvement
A field case study was completed using Stabiramâ CM 510 in the emulsion (post-addition), laying was performed with a finisher. A comparison with the results given by the emulsion without additive highlights an improvement in the mix fluidity, especially under the finisher’s screed. One week after completion of the roadworks, a core test was performed. Samples were dried up and analyzed through gamma rays.
Formula : Emulsion from Elf bitumen penetration grades 20/30 and 300/400,
bitumen content 60%
Emulsifier Stabiram CM 406®, 6 kg/t with hydrochloric acid titled 33%
Aggregate : Hornfels 0/6
Added water content : 6%
Section completed without additive, average porosity (5 measurements): 19,3%
Section completed with additive, average porosity (5 measurements): 16,6%
Bitumen Additives
