Investigation of the Use of Emulsion and Epoxy as an Interlayer in Composite Pavements

Abstract

A composite pavement is a pavement system in which a hot-mix asphalt concrete layer is placed over a rigid (concrete) base layer and it is widely used in road construction and rehabilitation applications. The concrete layer provides high structural load-bearing capacity, while the asphalt layer ensures the required functional performance. The interfacial bonding between the concrete and asphalt layers plays a critical role in the overall performance of composite pavements. Due to the significant difference in elastic moduli, deformation compatibility between the concrete and asphalt layers is limited; therefore, the interlayer bond is more susceptible to shear damage under the combined effects of traffic loading and environmental conditions. Inadequate interlayer bonding results in increased stresses and deflections within the composite pavement structure, leading to premature surface distresses. These distresses are particularly pronounced at intersections as a result of braking and acceleration forces. Consequently, ensuring a strong bond between the concrete and asphalt layers is essential for achieving satisfactory performance in composite asphalt pavements.

In this study, an inclined rigid laboratory test setup was developed to simulate both static and dynamic vehicle loads. The objective was to evaluate the stresses induced by braking loads as vehicles approach intersections and to investigate the mechanical behaviour of composite pavement layers. Furthermore, the performance of different interlayer types was compared with each other and with findings reported in previous studies in order to identify the most effective interlayer configuration. Composite test specimens were prepared using C25-grade cylindrical concrete samples with no interlayer and with a smooth interlayer, as well as specimens incorporating an MC-30 emulsion with a roughened interface and an epoxy interlayer. The results indicated that the highest bond strength and overall performance were achieved on surfaces treated with emulsion-coated rough aggregates and epoxy-applied interfaces.

Keywords: Composite Pavement; Emulsion; Epoxy; Interlayer; Tack Coat

Introduction

Road pavements are generally constructed in three forms: rigid, flexible and composite. Pavements constructed with cement concrete are termed “rigid pavements”¹. Rigid pavements typically consist of a concrete slab constructed over a base layer. Flexible pavements are multilayered structures. They consist of sub-layers made of granular material with high drainage capability and upper layers made of bituminous mixtures that offer high stability and comfortable driving conditions. Flexible pavements consist of sub-base, base and surface course layers².

Composite pavement, also referred to as flexible-rigid superstructure, is a pavement type consisting of two main structural layers (a flexible asphalt surface and a rigid base, typically composed of cement concrete, roller-compacted concrete (RCC), continuously reinforced concrete pavement^3,4. The performance of the pavement structure is of great importance in highways with a high percentage of heavy vehicles, heavy-duty areas such as ports and container terminals, cargo distribution centers and organized industrial zones. In such cases, the performance of traditional flexible pavements is often insufficient. Therefore, composite pavement designs come to the forefront. However, in composite pavements, the performance of the interlayers significantly affects the quality of service. This is because, during braking, a horizontal load approximately equal to half of the vertical load acts on the pavement layer alongside the vertical load⁵.

In the experimental studies to be conducted; a design mode that ensures the composite layers work together (composite action) will be determined by testing different materials and additives for these interlayers, which affect the performance of composite pavements. The mechanical properties and performance of flexible, rigid and intermediate layers will be tested together using the prepared inclined test setup.

It is widely accepted that typical pavement distresses such as bottom-up fatigue cracking and rutting can be effectively eliminated in composite pavements. However, it has been argued that reflective cracking, top-down cracking and delamination can occur. Furthermore, the large modulus difference between the asphalt surface and the concrete base may cause high shear stresses, leading to pavement damage and reduced service life^6,7.

Studies have been conducted to improve the interlayer between the asphalt cement flexible surface and the rigid base^8,9. However, few studies focusing on the performance of the asphalt layer have been reported. Due to the high modulus and elasticity of the underlying rigid base, the mechanical responses of the asphalt layer differ significantly from those of a flexible pavement and require careful examination.

Traffic loads transmitted to the pavement by moving vehicles are complex: one is the vertical load due to gravity and the other is the horizontal load due to the relative motion between the wheel and the pavement surface^10,11. The horizontal load is influenced by various conditions such as temperature, load level, emergency braking, acceleration and deceleration and pavement alignment. Numerous studies have reported that horizontal load is a significant factor affecting the service level and fatigue life of the pavement structure^12,13.

Although horizontal load can be numerically modelled or simulated in full-scale pavement facilities, it remains difficult to simulate real traffic loads characterizing both vertical and horizontal loads in a laboratory setting. The planned study aims to extend the service life of the pavement. An inclined loading test device was developed to simulate the compressive shear strength of the asphalt pavement under moving traffic loads in a laboratory environment. With this test method, the mechanical properties of the pavement under both horizontal and vertical loads have been examined. Different designs for interlayers and the performance of these designs will be investigated in the laboratory. The study aims to enhance the performance of composite highway pavement designs. Additionally, the experimental setup will provide a more realistic simulation of loads originating from highway vehicular traffic.

Methodology

C25 class concrete was used as the sub-base in the composite pavement. The properties of the concrete class are shown in (Table 1). Ready-mix concrete was procured from the plant and poured into 10 cm diameter plastic pipes as seen in (Figure 1). The concrete was allowed to cure for the full 28-day period and was then removed from the molds. Since an asphalt layer would be applied on top after removal from the Molds, iron Molds of 10 cm diameter were also fabricated (Figure 2).

Figure 1: Pouring concrete into Molds

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