Experimental Investigation of Early-Age Cracking Behavior in Concrete Slabs Reinforced

This study presents an integrated experimental and numerical analysis of cracking in concrete slabs reinforced with Glass Fiber Reinforced Polymer (GFRP) bars. The primary focus is on early-age cracking caused by plastic shrinkage, prior to examining the long-term cracking performance over the service life of concrete structures. A key objective is to assess the ability of GFRP reinforcement to limit the formation and propagation of plastic shrinkage cracks. To achieve this, nine small-scale slab specimens were subjected to controlled evaporation conditions, simulating the environmental factors that contribute to early-age cracking. Crack development was monitored periodically through imaging, and measurements of crack widths were recorded. The study included comparisons between slabs reinforced with conventional steel bars, those reinforced with GFRP bars, and unreinforced control specimens. Observations indicate that, during the plastic shrinkage phase, neither the timing of crack initiation nor the subsequent crack openings are significantly affected by the presence of reinforcing bars. To explore the underlying mechanisms, six early-age bond tests were conducted for both steel and GFRP bars at 1, 2, and 3 hours after exposure to the controlled evaporation rate. In parallel, concrete strength evolution and setting times were assessed using penetration resistance tests on representative mortar samples. The numerical component employs a three-dimensional Voronoi cell lattice model, which discretizes relative humidity, temperature, and displacement fields to provide a detailed representation of material behavior under the specified environmental conditions. Using the experimentally measured bond properties, simulations indicate that while reinforcing bars do not entirely prevent plastic shrinkage cracking, they do limit crack widths and moderate crack propagation. These findings highlight the partial effectiveness of GFRP and steel reinforcements in controlling early-age cracking, providing insights into their performance during the critical initial hours of concrete curing.