EFFECTS OF ENVIRONMENTAL EXPOSURE ON CARBONATION-INDUCED DETERIORATION OF OUTDOOR AND INDOOR SIDES OF FINISHED AND NONFINISHED REINFORCED MORTARS

Abstract

The indoor and outdoor surfaces of the peripheral walls of buildings are constantly exposed to different temperature and humidity conditions. Because various finishing materials are often applied to external reinforced concrete peripheral walls and rooftop slabs, carbonation-induced deterioration progresses at different rates on the indoor and outdoor sides of such structures. Therefore, an apparatus was developed to simulate environmental exposure by simultaneously applying different temperature and humidity conditions to the indoor and outdoor surfaces of mortar specimens and the effects of mortar temperature and moisture content on the rates of carbonation and rebar corrosion were investigated. In addition, two types of insulations were applied to external mortar surfaces and the effects of such materials on the rates of carbonation and rebar corrosion were examined.

The major findings of the investigations are summarized as follows:

(1) Carbonation can be controlled by applying an insulation layer and high-gas-permeability polystyrene insulation to external mortar surfaces. In addition, in the externally insulated test specimens, the summertime increase in concrete temperature was suppressed, and the moisture content was higher than that of the pristine mortar test specimen; therefore, carbonation was also controlled on the indoor side. However, in winter, all the specimens were maintained at a high temperature, and the resulting moisture content of both the indoor and outdoor sides were low owing to accelerated carbonation.

(2) In both summer and winter, rebar corrosion increased with both increasing mortar temperature and moisture content in the vicinity of the rebar, regardless of whether insulation materials had been applied to the external mortar surface.

(3) Even when the external mortar surface did not directly come into contact with rainwater, the wintertime mortar moisture content increased when the indoor surface was cold owing to condensation and water penetration from the outdoor surface. As a result, the half-cell potential of the rebar in the carbonated mortar decreased and the corrosion- current density increased.

(4) In summer, the insulation-induced suppression of the increasing mortar temperature effectively controls both outdoor and indoor concrete carbonation. In winter, on the other hand, the heat insulation effect may accelerate carbonation. However, preventing moisture condensation effectively controls rebar corrosion. Therefore, applying insulation materials to external surfaces can effectively extend the life of reinforced concrete structures.