Study On The Interfacial Bonds Between The New And Old Concretes

Nowadays, with the increase of the highway transportation load, the cases of damage of pavements and bridge structures have frequently emerged in their service life. The damaged structures are always repaired with mortar and/or concrete. In order to improve the bonding forces of the interface between new and old concrete, the pre-wetting method has been adopted in the practical engineering, but the viewpoints for the effect of pre-wetting interface are different for different researchers. The objective of this paper focuses on studying the influence of various moisture states on the old-new concrete interfacial bond. The main contents of this paper are as follows: This paper presented the influence of common repair materials and primers on the interfacial bonds between new and old concretes under various moisture states. The pull-off test and bending tests were conducted to evaluate the bonding states between new and old concretes. To give insight into the moisture movement near to the interface, the humidity sensor is proposed and applied in this thesis .By this way the influence of the moisture movement on the interface and interfacial bond was explored and analyzed. As the same time, the micro-hardness in the vicinity of the interfaces between new and old concrete intended to explain the corresponding experimental results. In combination with the Chen-Jia-Chong reconstruction engineering, this dissertation showed the influence of anti-cracking and water-proofing admixture (AWA) on the interfacial bonds between new and old concrete. Based on the experimental results, the relationship between content of AWA and interfacial bonds were found and established. Moreover, the optical content of AWA can be obtained according to this relationship.The characteristics of new-to-old concrete ITZ were discussed as well in this paper. By summarizing and comparing the adherence mechanisms in the domestic and international studies on the interface of new-to-old concrete, Some new ideas about the adherence mechanisms of new-to-old concrete both from macro and micro levels were put forward in combination with the experimental results.The experimental results showed that the interface moisture condition is an important factor to influence the bonding force of the interface between new and old concrete. The strongest interfacial bond can be achieved on the oven-dried substrate. The interfacial bond could appreciably enhance when the strength of repair materials increased. Moreover, the interfacial bond could be obviously increased with carbon fiber or polypropylene polymer fiber in to the repair concrete and the higher interfacial bond can be obtained with the addition of polypropylene polymer fiber compared with the carbon fiber. The interfacial bond could be independent of moisture states on the old-new concrete interface when the primers were used. The strongest interfacial bond could be achieved the moment that the addition ratio of AWA was 6 %( by weight).