R1.12 Performance Benefits of Fiber-reinforced Thin Concrete Pavement and Overlays

Status:  Active
Project Start Date:  11/01/2017


Structural fibers improve the post-crack performance of concrete (Rollings 1986, Roesler et al. 2003, Kevern et al. 2016) by keeping cracks tight which help reduce the panel fatigue crack (e.g., longitudinal, corner, and transverse cracks) severity and increase the load transfer between concrete slabs (Barman 2014) which decreases joint deterioration and subsequently joint faulting. In the last few decades, transportation agencies have used varieties of structural fibers varying in length, geometry, aspect ratio, (AR) and parent materials. The dosages of fibers used were widely varied; however, without any mechanistic basis: 3lb/cy to 25lb/cy for synthetic structural fibers and 40lb/cy to 80lb/cy for steel fibers. Based on the observed performance of FRC overlays constructed in different parts of the country, it is evident that structural fibers positively influence the performance of concrete overlays. However, because of a lack of significant studies involving companion field sections, neither the quantitative benefits of structural fibers have been identified nor the benefits are accounted for in the existing mechanistic-empirical design procedures. Recognizing this research gap, the National Road Research Alliance (NRRA) has taken initiative to construct seven fiber reinforced concrete test cells and one plain concrete control test cell at the Minnesota Road Research facility (MnROAD) at Albertville, MN. Table 1 presents a summary of the designs and materials used in these cells and the experimental plan is presented in Figure 1. Out of the seven FRC cells, Cells 506 through 806 are thin pavement on grade mainly varying with the fiber content (0% to 0.75% volume fraction); Cells 139 and 239 are ultra-thin (3 inch) and thin (4 inch) concrete pavement on grade (city street design), respectively, mainly varying the panel thickness and an enhanced fiber dosage (See Table 1 for the dosage information); and Cells 705 and 805 are thin unbonded concrete overlays constructed with varied panel sizes and a standard fiber dosage. These cells have been constructed during June - September, 2017. These cells are equipped with different types of sensors for measuring: (i) dynamic strain due to wheel load, (ii) strain induced by the environmental forces, (iii) temperature gradient, and (iv) joint movement, etc. In addition to collecting above-mentioned sensor data, the performance of these cells will be periodically evaluated to trace the distress initiation and propagation. Distresses such as panel fatigue cracking (transverse and longitudinal cracking), transverse joint faulting and other significant distresses (if occurs) will be recorded in the performance evaluation. The International Roughness Index (IRI) will also be measured. It is anticipated that the falling weight deflectometer (FWD) and IRI tests will be conducted monthly or seasonally, as appropriate. The sensor data and periodical distress or performance information will be analyzed annually throughout the duration of this research project (3 years, starting November 2017) to understand the influence of the structural fibers on the development and propagation of fatigue cracking and joint faulting, and on the panel size.

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