ENHANCING SERVICE LIFE OF PRESTRESSED CONCRETE STRUCTURES BY USING FLY ASH AND CORROSION INHIBITORS

摘要

Seven-wire strands in pretensioned concrete (PTC) structures can undergo chloride-induced focalized corrosion. The corrosion products occupy the space between the wires of the strands and do not exert expansive stresses onto the surrounding concrete. Hence, propagation of such corrosion cannot be identified/ detected on time using visual observation of concrete surfaces and can lead to catastrophic failure. This scenario necessitates technologies to significantly enhance the chloride-resistance and corrosion-resistance of PTC systems. This paper quantifies the role of pulverised fuel ash (PFA; fly ash) and corrosion inhibiting admixtures (CIAs) in enhancing the probabilistic service life. For this, lollipop specimens with embedded prestressing steel (five in each category) were prepared and subjected to wet-dry exposure using simulated concrete pore solution containing 3.5% NaCl, and the chloride threshold (Cl_(th)) was determined. Also, the synergistic effects of chloride diffusion coefficient (D_(cl)) and Cl_(th) on the corrosion-free service life of PTC systems are demonstrated. The paper also demonstrates the need for specifying both strength and durability requirements (say, "Mx-Dy" concrete). Such an approach can aid engineers and designers in making informed choices of materials to achieve protection of PTC systems against chloride-induced corrosion and to achieve service life of 100+ years with minimal maintenance/repair cost.