Long-term field monitoring of slabs-on-ground reinforced with GFRP bars

The current design of GFRP bar-reinforced slabs-on-ground, according to ACI 440.1R-15 is based on an empirical equation derived from the design of steel-reinforced concrete slabs-on-ground, developed based on the subgrade drag equation proposed in Portland Cement Association code (1990). ACI 440.1R-15 explicitly stipulates that field performance data from the application of FRP bar-reinforced slabs-on-ground is required to validate the equation. This paper reports the experimental outcomes of a comprehensive study on the long-term field monitoring of eight large-scale slab-on-ground specimens. Slabs of plan dimensions 6000 × 1100 mm2, resting on a lean concrete subbase over a compacted soil subgrade and exposed to harsh ambient environment, were monitored for 525 days to study rebar and concrete strain development and concrete cracking. The exposed ambient environment was characterized by averages of 41.7 ℃ with RH 12.8% in summer and 9.5 ℃ with RH 87.7% in winter. The major parameters of the study are reinforcement types (ribbed GFRP, sand-coated GFRP, and ribbed steel), reinforcement spacings (200 mm and 300 mm), slab thicknesses (100 mm and 200 mm), and the presence of a contraction joint. It was observed that all GFRP bar-reinforced slabs developed a transverse mid-panel shrinkage crack within the first 18 days of casting. The maximum average crack widths over the long-term were within the ACI 440.1R-15 and AASHTO LRFD code limit of 0.7 mm, and the maximum strains in rebars in the vicinity of the cracks did not exceed 12.4% of the ultimate strains of the bars. Decreasing the slab thickness from 200 mm to 100 mm did not affect the development of cracking or strain evolution. The presence of a saw-cut contraction was effective in localizing the cracking location.