Water repellent surface impregnation for extension of service life of reinforced concrete structures in marine environments: The role of cracks Jian-Guo Dai a, * , Y. Akira b , F.H. Wittmann c , H. Yokota b , Peng Zhang c a Department of Civil and Structural Engineering, The Hong Kong Polytechnic University, Hung Hom, Hong Kong, China b Life Cycle Management Research Center, Port and Airport Research Institute, 3-1-1, Nagase, Yokosuka 239-0826, Japan c Center for Durability Studies, Qingdao Technological University, 11 Fushun Road, Qingdao 266033, China article info Article history: Received 23 March 2009 Received in revised form 31 October 2009 Accepted 3 November 2009 Available online 10 November 2009 Keywords: Concrete Surface impregnation Crack Chloride penetration Marine environment Long-term effectiveness abstract The enhancement of long-term durability of marine structures is a matter of interest to many researchers. The study presented in this paper examines the effectiveness of a water reducer and chloride barrier sur- face impregnation of the concrete cover of reinforced concrete (RC) structures, exposed to a marine envi- ronment. Specific focuses is on how surface cracks created (1) before impregnation and (2) after impregnation, affect the effectiveness of the surface treatment. The experiments are conducted in an environment which is as close as possible to the real humid subtropical marine environment. A series of reinforced concrete (RC) prisms and concrete cylinders, each treated with various commer- cial surface impregnation agents, were exposed to cyclic sea water shower under an outdoor environ- ment to accelerate the dry/wet cycles for 1 year. Six types of surface impregnation agents, including four types of silane-based water repellent agents and two types of sodium silicate-based pore blockers (water–glass) were applied. Three types of RC prisms were prepared to simulate the different cracking possibilities, which may occur in surface impregnated concrete structures, during their service life. No cracks were introduced in the first prism group, while cracks were introduced before and after surface impregnation, in the second and third groups, respectively. The time-dependent water absorption of all specimens was monitored during exposure to the dry/wet cycles. Finally the specimens were split open to measure the penetration depths of the surface impregnation agents and the chloride penetration profiles. The areas with corrosion evident in the steel reinforcement in the RC prisms were also measured. Sodium silicate-based pore blockers were found to be inefficient in preventing chloride penetration of concrete under simulated marine exposures. The long-term efficiency of water repellent agents used for surface impregnation was found to be highly dependent on the type of agent and whether impregnation was carried out before or after crack formation. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction Chloride-induced corrosion of steel reinforcement is a major concern regarding the durability of reinforced concrete (RC) struc- tures exposed to marine environments. In practice, the time taken for steel corrosion to occur in marine RC structures is short, in com- parison with their designed service life. Thus, there is often a need for supplementary measures to protect such concrete or/and steel reinforcement in such an aggressive environment. Surface treat- ment is commonly used to improve the resistance of such concrete cover against the penetration of aggressive substances, both in new structures and existing structures, whenever the need for further protection becomes obvious. For instance, the surface of repaired structures is sometimes treated in order to extend the service life of repair measures [1,2]. In general, protective surface treatment can be classified into three categories: (a) surface coating, whereby in most cases a thin or thick polymer film is applied, (b) sealing, whereby the surface near the pores is blocked, and (c) surface impregnation, whereby the surface near zone is impregnated with a water repellent agent, leaving the pores open. Recently there has been an increasing acceptance of surface impregnation materials for buildings and highway bridges. The protective surface treatment wins favor in that it does not interrupt construction work, and is hence cost-effective [3,4]. In re- cent years, two types of surface treatments are frequently used in the construction industry. One is a silane-based water repellent agent and the other is a sodium silicate-based pore blocker, which is a Sealant. Both can penetrate concrete pores and react with hy- drated cement particles. In the former case, the reaction product, i.e. a silicon resin, can form a hydrophobic lining on the pore walls. The achievable penetration depth in concrete mainly depends on four factors: the type of hydrophobic agent applied, the water to 0958-9465/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.cemconcomp.2009.11.001 * Corresponding author. Tel.: +852 2766 6026; fax: +852 2365 6389. E-mail address: cejgdai@polyu.edu.hk (J.-G. Dai). Cement & Concrete Composites 32 (2010) 101–109 Contents lists available at ScienceDirect Cement & Concrete Composites journal homepage: www.elsevier.com/locate/cemconcomp