Damage Prognosis of Aging Reinforced Concrete Structures through Visual Screening and Rebound Hammer Test

Abstract

Periodic monitoring of concrete quality of Reinforced Concrete (RC) structure is essential for maintaining structural performance, ensuring regulatory compliance and continuously tracking many different causes of quality deterioration processes to ensure serviceability of aging RC structures. In this research, visual inspection of an aging RC building of Chattogram is performed according to an ACI protocol. The findings of visual screening are indicative of significant deterioration of concrete strength over the period of 40 years’ service life of the building. A non-destructive rebound hammer test (RHT) is conducted on different RC elements and results of in-situ concrete strength of the building indicates an average 13% reduction from reference strength. Current concrete compressive strengths of two other selected buildings of Chattogram are also indicative of high inconsistency between their field test results and audit records of strength. One of the major objectives of this research is, therefore, aimed at establishing reliable basis of RHT data for estimating in-situ concrete strength of RC structures. A comparative analysis of time variable strengths is performed for three laboratory scale RC beam specimens cast with two concrete strengths, 20 MPa and 22 MPa. The concrete compressive strengths determined by RHT tests of the beams is well correlated by empirical expressions of time variation of strength, and the empirical laws can be used to provide a reliable estimate of strength by 3% to 4% less than reference strengths. A selected RC structure is modelled for 3D pushover analysis considering design strength of concrete of 4 ksi and also with a randomly chosen 30% reduction of concrete strength. A comparative evaluation of their capacity curve shows that the maximum capacity of RC structure with concrete strength of 2.5 ksi is substantially low as compared to the same structure modelled with baseline strength of 4.0 ksi. The degradation of concrete strength is shown to have significantly reduced global capacity of the structure. There is also increased numbers of plastic hinges formed in the structure modeled with concrete of 2.5 ksi, particularly beyond the Collapse Prevention (CP) state of the capacity curve. A simply supported RC beam is also modelled to assess other associated effects of concrete strength degradation on crack formation and propagation. The accumulation of fracture strain and formation of cracks are more concentrated near the failure zone of the RC beam modelled with lower strength of concrete.