Large-Scale Test Setup of Concrete Pavement Slabs Jointed by Carbon Fiber-Reinforced Polymer Dowel Bars as Load Transfer Devices ^†

Abstract

Conventional steel bars are mostly used as the main load transfer mechanism between jointed slabs in rigid pavements; however, they are generally prone to corrosion which reduces the load transfer efficiency at the joints. This study evaluates the performance of steel bars wrapped with Carbon Fiber Reinforced Polymer (CFRP) sheets, introducing a corrosion-free alternative to conventional steel bars while maintaining the required strength. This paper explains the test setup of large-scale shear strength and load transfer efficiency tests that are currently conducted on the slab samples to evaluate the structural performance of the proposed dowel bars and concrete mix designs.

1. Introduction

The performance of jointed concrete pavements is often closely related to the load transfer capacity of dowel bars at the pavement joints. Faulting is frequently seen in pavement joints without dowel bars because the provided load transfer method by aggregate interlock alone is insufficient. Steel dowels are commonly used to enhance load transfer in concrete pavements. However, the issue of high bearing stress and corrosion of steel dowels has a significant impact on their long-term performance. There have been efforts to improve dowel durability using alternative shapes (other than round) to further reduce dowel–concrete bearing stresses and to use alternative materials for improved corrosion resistance. Fiber Reinforced Polymer (FRP) dowel bars are among those alternative materials. They have been given considerable attention because of their high strength and excellent corrosion resistance. There are several benefits of using Carbon Fiber Reinforced Polymer (CFRP) materials in construction, including their lightweight nature, having high strength and greater stiffness per unit weight, improving the strength of concrete, and increasing the life span of facilities [1,2,3].

2. Research Methodology

This study evaluates the performance of steel bars wrapped with CFRP sheets, introducing a corrosion-free alternative to conventional steel bars while maintaining the required strength. This paper explains the test setup of large-scale shear strength and load transfer efficiency tests that are currently conducted on rigid pavement slab samples to evaluate their structural performance of the proposed dowel bars and concrete mix designs.

2.1. Load Transfer Efficiency (LTE) Test

The main function of dowel bars in rigid pavement slabs is to efficiently transfer the applied loads from the loaded slab to the neighboring unloaded slab. As a result, both loaded and unloaded slabs bend. Dowel bars significantly reduce the stresses and deformations that are induced at the loaded slabs compared to concrete pavements without dowel bars. Load transfer efficiency influences the magnitude of reduced stresses and deformations. The LTE can be calculated as per Equation (1) [4]:

$$\mathrm{L}\mathrm{T}\mathrm{E},\mathrm{\%}=\frac{{\mathrm{d}}_{\mathrm{u}}}{{\mathrm{d}}_{\mathrm{l}}}\ast 100$$

(1)

where ${\mathrm{d}}_{\mathrm{u}}$ and ${\mathrm{d}}_{\mathrm{l}}$ are the joint’s vertical displacement for unloaded and loaded concrete slabs, respectively measured on top of the joint’s edge.

The objective of this test is to evaluate the LTE of the steel dowel bars wrapped with CFRP sheets compared to the conventional steel dowel bars.

2.2. Shear Strength Test

The shear test is intended to apply uniform pressure on the dowel bars jointing the concrete slabs. This shear pressure will make the dowel bars reach a sliding failure along the parallel plane to the applied shear pressure. The objective of this test is to evaluate the shear strength of steel dowel bars wrapped with CFRP sheets compared to conventional steel dowel bars. The shear strength test method was adopted from the AASHTO T-253-76 test setup, as shown in Figure 1 [5,6]. To be able to conduct the shear test on the slab specimens, a few modifications were introduced to the AASHTO T253-76 test setup as explained in Section 3.2 below.

3. Results and Discussion

3.1. Load Transfer Efficiency (LTE) Test Setup

Figure 2 and Figure 3 show the LTE test setup details. The concrete pavement slabs were designed as per the general specifications of FHWA [5]. Each slab has dimensions of 2400 mm length, 1000 mm width, and a thickness of 200 mm with four dowel bars of 25 mm diameter embedded in the middle of the slab thickness.

A set of 180 mm thickness rubber pads were placed underneath the slabs at specific locations to simulate the actual soil in a real pavement section (see Figure 3). The physical and mechanical properties of these pads were determined to ensure that they can represent the required soil modulus of subgrade reaction. Additionally, six pancake-loading cells were placed underneath the concrete slabs where the dowel bars are located as shown in Figure 2. The pancake loading cells are used to measure the applied load on both loaded and unloaded slabs during the test. Also, the joint’s vertical displacement for the unloaded and loaded concrete slabs is measured using Linear Variable Differential Transformers (LVDT) attached to the surface of the concrete slabs. Moreover, each slab has eight 38.1 mm (1.5-inch) diameter holes located along the slab edges and matching the holes in the large-scale loading steel frame (see Figure 4 and Figure 5). These holes are used to connect eight different threaded bars to both the loading frame and the slab test sample during the shear test.

3.2. Shear Strength Test Set-Up

The shear test set-up was installed to a large-scale loading steel frame, Figure 4 and Figure 5 show the shear test set-up details.

The shear load is applied on the concrete slab specimen using a 50-ton hydraulic jack fixed underneath the concrete slab. A spreader steel beam is placed between the hydraulic jack and the concrete slab to transfer the point load from the hydraulic jack into a uniform pressure on the slab middle segment. Additionally, the concrete slab is connected to four reaction beams at specific locations on top and below the slab specimen (as shown in Figure 5) to prevent any deflection in the concrete slab and forcing it to fail in shear only.

4. Conclusions and Ongoing Work

This paper presented the testing setup for load transfer efficiency (LTE) and shear strength tests of dowel bars in rigid pavement slabs. In addition, different configurations of CFRP-wrapped steel bars are included to assess their performance. Wrapping of the bars was chosen as an efficient method to protect dowel bars from corrosion and other environmental exposures. The testing setup was successfully completed and confirmed for both LTE and shear strength tests. Currently, the research team is conducting the actual LTE and shear strength tests on the prepared slab specimens. Different concrete mix designs incorporating crumb rubber will be evaluated in the study as well.