NEW-TO-OLD CONCRETE BONDING - INFLUENCE OF SULFATES TYPE OF NEW CONCRETE ON INTERFACE MICROSTRUCTURE

The durability of new-to-old concrete bonding is a key factor for the construction of durable thin concrete repairs. The new-to-old concrete bonding zone can be compared to the paste-aggregate interface as a fresh cement paste is cast on a hard surface. However, little is known on the influence of very simple construction techniques such as the wetting of the old surface before casting the new concrete. This condition was studied using two different cements: a Canadian type 10 cement and a French CPA 55. The results show that the nature of cement, and especially its sulfates, is a main factor in the microstructure formation of the bonding zone that is sufficient to mask the influence of others parameters like the saturation state of the old surface.