Investigation of corrosion potential of local reinforced-concrete mixes in harsh environment

Abstract

ABSTRACT Reinforced concrete (RC) is an ubiquitous building material in structural engineering. Corrosion of RC structures is one of the leading reasons for the loss of serviceability and dilapidation of infrastructures. The genesis and extent of corrosion are chief factors in the prediction of the useful service life of RC structures. Concrete structures exposed to harsh environment are vulnerable to deterioration caused by intrusion of chloride ions. A crucial step towards selecting the most apposite repair strategy for distressed concrete structures is to ascertain the corrosion status of reinforcing bars. With the proliferation of RC structures in Bangladesh, especially in coastal and industrial areas, a detailed insight into quantifying corrosion behaviour has been deemed necessary. This research has been undertaken to study the effect of variations in exposure environment, reinforcement cover and mix design parameters on the corrosion of RC structures and finally correlate the findings with other tests results commonly conducted in concrete to provide with tentative optimum mix for future use in development in harsh environment. To measure corrosion status of a RC structure, half-cell potential (HCP) method was used as it is efficient and relatively quick method where the structure remains undisturbed. In this study a total of 108 RC prisms were cast varying the concrete cover (19mm and 38mm), mix proportion (1:1.5:3 and 1:2:4), aggregate type (brick and stone chips), cement type (OPC and PCC) and exposure condition (air, synthetic coastal (NaCl) water, synthetic industrial wastewater). The corrosion potential were measured over a span of 120 days and it was observed that use of OPC, brick chips, lower rebar cover, a mix ratio of 1:2:4 and submergence in synthetic coastal water all contributed to the higher corrosion potentials and weight loss. A significant positive correlation between weight loss of rebars and corrosion potential has been observed. A 5.07% and 4.5% increase in corrosion potential and weight loss of rebar , respectively has been observed using 19mm cover compared to 38mm on an average. Use of brick chips attributed a weight loss of maximum 73.7gm/m corresponding to a potential of -532mV. Keeping other variables same, stone chips corresponded to 3.97 gm/m weight loss and a potential of -509mV. Hence, the feasibility of different concrete mixes in terms of corrosion potential and weight loss data was quantified. Data from weight loss of rebar, permeability and compressive strength of mixes were correlated with corrosion potential to provide a quantitative assessment of the corrosion scenario germane to the parameters encountered in constructional practices.