Characterization of Restrained Shrinkage in Sloped Ultra-High Performance Concrete-Normal Concrete Composites Using a Distributed Fiber Optic Sensing System

Abstract

Thin-bonded ultra-high performance concrete (UHPC) overlays offer a protective layer to extend the service life of civil infrastructures, such as bridge decks and road pavements. In the outlined applications, a sloped overlay is commonly required to facilitate the drainage of the surface water and mitigate the risk of vehicles skidding, especially in curves. The restrained shrinkage in bonded concrete systems, however, can cause stresses that eventually lead to overlay surface cracks and interface debonding failures. While a transition from NC to UHPC overlays has helped address several performance issues in bonded concrete composites, questions regarding the characteristic of restrained shrinkage in sloped UHPC-NC composites remain. These standing questions motivated the current study, where a set of experimental tests was designed to measure shrinkage in such composites and determine their possible failure modes. For this purpose, non-proprietary UHPC mixtures with specified rheological and mechanical properties were developed, enabling casting slopes up to 20%. The experimental tests systematically covered the effects of key overlay properties, including geometric details (e.g., thickness and slope) and mixture characteristics (e.g., fiber inclusion and binder alternatives). A set of UHPC-NC specimens were cast with the overall dimensions of 180×75×15 cm3 and slopes up to 8%. Integrated distributed fiber optic sensors (DFOS) have been employed to monitor the progressive deformations inside the bonded UHPC overlays. The collected data provided firsthand information on the magnitude and spatial distribution of restrained shrinkage in the sloped UHPC-NC composites over time. By addressing the potential early-age shrinkage issues, this study’s outcome is expected to help maximize the benefits of thin-bonded UHPC overlays.