Carbonation resistance of one industrial mortar used as a concrete coating

In aggressive environments, concrete itself may not be enough to protect th e reinforcement against carbon dioxide penetration. This gas reacts with th e portlandite of the concrete to form calcium carbonate. This process leads to a pH reduction and, therefore, promotes the depassivation of the steel reinforcement in reinforced concretes. Therefore, a supplementary protectio n method such as coating with a mortar. as carbonation barrier can be used to provide adequate durability. Experimental data are presented to illustra te the effect of three different testing levels of CO2 on an industrial mor tar applied to a concrete base in order to evaluate its performance as an a nti-carbonation barrier. The results from the coated concrete are compared with the carbonation resistance of the uncoated plain concrete. The carbona tion depth was determined using a phenolphthalein pH-indicator. A clear red uction in carbonation was observed when the mortar was applied. The validit y of the accelerated testing method, which consists of placing the mortar i n a high carbon dioxide concentration chamber for a controlled time, and ca rbonation coefficients to assess coating effectiveness are discussed. The u se of 100% carbon dioxide is highly questionable for accelerated carbonatio n testing. (C) 2001 Elsevier Science Ltd. All rights reserved.