Long-Term Field Monitoring of Slabs on Ground

In the last two decades, lightweight and non-corrosive glass-fiber reinforced polymer (GFRP) bars have been widely used in several applications targeting more than 100 years of service life, faster construction, and life-cycle costs comparable to steel reinforcement. A remarkable example is the world’s largest GFRP bar reinforced structure, the 21.3 km-long flood mitigation channel in Jazan, Saudi Arabia, constructed as a slab on ground. The design of GFRP reinforced slabs on ground is based on empirical equations derived from steel reinforced slab practice. The lack of field performance data, low modulus of elasticity, and creep rupture stress features warrant research on the design aspects of GFRP bars for grade-supported structures. This study, which has the sole objective of reporting the experiment outcomes, involves long-term field monitoring of eight large-scale slabs on ground specimens. Slabs of plan dimensions 6000×1100 mm2, resting on a lean concrete subbase over compacted soil subgrade and exposed to harsh ambient environment, were monitored for 525 days using more than 65 sensors mounted on the GFRP bars and embedded in the concrete. The major parameters of the study are reinforcement type (ribbed GFRP, sand-coated GFRP, and conventional ribbed steel), reinforcement spacings (200 mm and 300 mm), slab thickness (100 mm and 200 mm), and contraction joint. The effect of these parameters on crack widths, crack patterns, and concrete and reinforcement strains were observed. The slabs with both types of GFRP bar and spacing developed a transverse mid-panel shrinkage crack at an early-age, and the maximum widths of the cracks over the long-term were within code limits. The GFRP bars spacing in slabs on grade could be increased from 200 mm c/c to 300 mm c/c without any adverse effect for the 200 mm thick slabs monitored in the field.