Fig. 4.

SEM image of the specimen cross section (center) with areas where interfacial air voids are found at higher magnification, showing the different phases (S = steel; C = cement paste; AV = air void; D = debonding between steel and concrete; the solid and dotted red boxes highlight the portions reported at higher magnification in (a) and (b), respectively); a interfacial macro-air void, separated from the steel by a thin layer of cement paste of around 20 μm thickness; b multiple small interfacial voids separated from the steel by a layer of cement paste with variable thickness