Method for producing bituminous compositions

Abstract

This invention relates to bituminous compositions and methods of producing the same. More particularly, the invention relates to the production of bituminous compositions formulated with performance-graded bitumen-containing solvent-free bitumen emulsions which exhibit controllable, temperature-dependent interfacial rheology. When employed in paving applications, these bituminous compositions develop adhesive strength and load-bearing strength properties at rates comparable to traditional hot mix paving compositions and at rates faster than traditional cold mix paving compositions.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS [0001] This application is a continuation of PCT Application No. PCT / US2005 / 002916, filed Jan. 27, 2005, which claims priority from U.S Provisional Application No. 60 / 545,713, filed Feb. 18, 2004.BACKGROUND OF THE INVENTION [0002] 1. Field Of Invention [0003] This invention relates to bituminous compositions, methods of producing the same, and pavement made from said bituminous compositions. More particularly, the invention relates to the production of bituminous compositions formulated with solvent-free bitumen emulsions which exhibit controllable, temperature-dependent interfacial rheology. [0004] 2. Description of the Related Art [0005] Cold mix paving compositions are made by mixing bitumen emulsion with aggregate at ambient temperature (i.e., temperature less than about 40° C.). However, certain problems have traditionally been associated with the use of such compositions where no solvent is present. For example, when one employs a slow-s...

AI Technical Summary

Benefits of technology

[0019] The objects of this invention are met by a method for producing bituminous compositions suitable for use in paving applications, made by controlling temperature-dependent interfacial rheology in a broad range of solvent-free, high-residue bitumen emulsions containing bitumen. To produce the solvent-free bitumen emulsions in these paving compositions, emulsifiers are employed with structural characteristics that impart low interfacial viscosity, low Marangoni effect, and high interfacial bitumen solubility, at elevated temperatures. The use of bitumens in these emulsions with solubility parameters comparable with those of the emulsifier is preferred. The improved combination of emulsifiers, with structural attributes that impart improved control of interfacial stability and rheology in solvent-free bitumen emulsions at elevated temperatures relative to ambient cold mix technologies and at reduced temperatures relative to hot mix technologies, leads to load-bearing road paving compositions with improved densification and accelerated strength development in the compacted state.

Problems solved by technology

However, certain problems have traditionally been associated with the use of such compositions where no solvent is present.

For example, when one employs a slow-setting bitumen emulsion in the construction of load-bearing pavements the pavement is slow to cure and develop sufficient strength values adequate to support heavy traffic and to resist moisture damage.

However, the use of a quick-setting bitumen emulsion often leads to premature breaking of the emulsion during handling and compaction (resulting in the formation of high air voids).

However, these methods suffer from a lack of control of the timing of the pH-shifting chemistry.

In any construction process involving bitumen emulsions, the premature breaking or coalescence of the bitumen emulsions adversely affects performance in production, handling, transport, and other end-use application operations.

Prematurely broken emulsions often fail to adequately coat aggregate and generally result in high-viscosity bitumen-aggregate mixtures which can be troublesome to discharge from trucks, may excessively stick to paving equipment, and which can be difficult to compact to required pavement densities.

Thus, the failure to effectively control the timing of the pH-shifting chemistry commonly leads to premature rupture of the bitumen emulsion and a cascade of undesirable effects on mix processing and pavement applications.

Upon mechanical action of compaction the invert emulsion ruptures to expose the alkaline aqueous phase to the cationic mixing emulsion, thereby shifting the pH of the system and initiating emulsion break.

However, the use of cutter stocks can also result in decreases in the early compressive strength of compacted pavement.

However, approaches of this nature suffer from two drawbacks which make them unsuitable for construction of load-bearing asphalt pavements that exhibit complete aggregate coating, compact to required densities in the field, and develop strength rapidly.

First, at ambient temperatures rapid-setting emulsions do not adequately coat dense-graded aggregates commonly used in construction of dense-graded, load-bearing pavements, because such rapid-setting emulsions tend to break immediately upon contact with mineral aggregate surfaces.

Second, at ambient temperatures the immediate break of a rapid-setting emulsion produces a mix with high viscosity.

The failure to adequately compact leads to low density pavements which fail under traffic due to deformation, disintegration, and / or, pot-hole formation (as water passes through the low density layer into the base where supporting pavement layers are degraded).

Quick-setting emulsions are not suitable for the production of load-bearing asphalt pavement compositions at ambient temperatures for similar reasons.

The use of large volumes of water beyond that present in the emulsion to promote coating of aggregate with quick-setting emulsions is not a feasible technique in the production of load-bearing pavements.

First, load-bearing pavements are much thicker than the non-load-bearing surfaces produced by slurry seal coatings and micro-surfacings.

The thicker load-bearing pavements must be compacted to densify the mixture, as insufficient density can lead to rapid failure of load-bearing pavements due to deformation, disintegration, and pot-hole formation.

Large water volumes prevent compaction in thick, load-bearing pavements to required densities because water is incompressible.

Moreover, quick-setting emulsions develop high viscosity when stressed by high shear rate events such as compaction.

Moreover, the slow-setting nature of the emulsion yields a road paving composition with a controlled coalescence rate, so that the road paving mixture does not increase in viscosity to a point that it is unsuitable for handling, hauling, or compaction.

However, pavement compositions made at ambient-temperature with slow-setting bituminous emulsions are very slow to develop adhesion and cure to strengths sufficient to bear the stress of heavy traffic.

When a hot asphalt-aggregate mixture cools to temperatures below about 85° C., the handling, placement, and compaction of the mixture become extremely difficult and design densities (air voids) cannot be realized.

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