Re-stiffening Over-digested Rubber Bitumen Binders
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Solution Overview
Problem
Over-digested rubber modified bituminous binders in South Africa face challenges due to their low viscosity and reduced stiffness, which limits their application window and handling, and existing methods fail to effectively re-stiffen them for continued use without compromising elastic properties.
Innovation Solution
A method involving the admixing of a reactive, stiffness-inducing organic additive, such as a reactive elastomeric terpolymer, with over-digested rubber modified bituminous binder at elevated temperatures to increase the softening point and improve stress resilience and storage stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If crumb rubber is digested in bitumen using high temperatures and extended agitation time, then elastic properties are enhanced, but viscosity decreases below specification and the binder becomes over-digested
Solution Approach 1:
The patent changes the chemical composition parameters of the binder by adding specific additives (polyphosphoric acid, viscosity modifiers, stiffening agents) to adjust the viscosity and stiffness of over-digested rubber modified bitumen, transforming it from a waste product into a usable binder that meets specification requirements
Solution Approach 2:
The patent recovers over-digested rubber modified bitumen that would otherwise be discarded as waste or blended into new batches, by treating it with additives to restore its properties, thereby eliminating disposal costs and reducing material accumulation
2Ease of operation
If the binder is over-digested to reduce viscosity for easier handling, then handling ease improves, but the application window closes and performance deteriorates
Solution Approach 1:
The patent uses temperature and additive composition as control parameters to maintain the binder in an optimized state during storage and transport, allowing it to be handled easily when needed while preserving its performance characteristics and extending the effective application window
3Strength
If more crumb rubber is added to bitumen, then elastic properties increase, but the binder becomes heterogeneous and storage stability decreases
Solution Approach 1:
The patent introduces intermediary substances (dispersants, viscosity modifiers, and reactive additives) that facilitate uniform distribution of rubber particles throughout the bitumen matrix, reducing heterogeneity and improving storage stability while maintaining the high elastic properties provided by the rubber content
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The re-stiffened binder exhibits enhanced softening point, reduced elasticity at high temperatures, and improved stress resilience, allowing for extended usage and better performance in asphalt applications.
Implementation Method 1
admixing a reactive, stiffness inducing organic additive with the over-digested rubber modified bituminous binder at elevated temperatures to increase the softening point
Data Source
AI summary
A method of re-stiffening an over-digested rubber modified bituminous binder includes admixing a reactive, stiffness inducing organic additive with the over-digested rubber modified bituminous binder to produce a re-stiffened rubber modified bituminous binder with an increased softening point. The admixing takes place at an elevated temperature of at least 185° C. A rubber modified bituminous binder suitable for both asphalt and seal surfacing applications that includes a digested rubber bituminous admixture with a softening point of at least 55° C. and a dynamic viscosity at 190° C. of less than 2000 mPa·s. A method of sealing or paving a surface includes applying a layer which includes a rubber modified bituminous binder to the surface, the rubber modified bituminous binder being in the form of a digested rubber bitumen admixture with a softening point of at least 55° C. and a dynamic viscosity at 190° C. of less than 2000 mPa·s.