Evaluation of the effect of marine salts on urban built infrastructure Khandaker M. Anwar Hossain * , Said M. Easa, Mohamed Lachemi Department of Civil Engineering, Ryerson University, 350 Victoria Street, Toronto, Ontario M5B 2K3, Canada article info Article history: Received 29 January 2008 Received in revised form 25 May 2008 Accepted 27 June 2008 Keywords: Sea spray Marine salts Mortars External renders Salt penetration resistance abstract This paper presents the results of a study that evaluated the effects of marine salts on built infrastructures at the Port city of Chittagong in Bangladesh. Specimens made from five different types of mortars (normally used as external renders in built infrastructures such as buildings and bridges) with varying cement contents were exposed to atmospheric environment at 12 sampling stations scattered around the metropolitan area of Chittagong. The performance of the specimens was evaluated based on marine salt deposition and resistance to marine salt penetration. The study also monitored the depo- sition of chlorides and sulfates in wet candle sensors located at 12 stations. The type and amount of salts captured in powdered samples extracted from the mortar specimens as well as from wet candle sensors were determined using ion chromatography. The study showed that the marine salt deposition is significant up to a distance of about 200 m from the seashore. The analysis of deposition and subsequent penetration of marine salts in exposed specimens identified the mortar types that are more resistant to the aggressive potential of the region’s marine aerosol. The results of this study can be very useful for local authorities engaged in selecting protective measures (in terms of external renderings) to improve the durability of infrastructures exposed to marine salts. Ó 2008 Elsevier Ltd. All rights reserved. 1. Introduction Deterioration of the built infrastructure due to marine salts in coastal regions has been, for many years, a significant and ongoing problem. Marine salts adversely affect the durability of the infra- structure and reduce its service life [1,2]. The sea spray, composed primarily of seawater along with particles naturally generated by the action of wind on the seawater surface, introduces ionic species into the atmosphere, principally chlorides and sulfates [3–10]. The air containing sea spray causes accumulative deposition of ions on the external surface of structures that penetrate the interior of the material through ionic diffusion causing its degeneration. Such environments are extremely dangerous to construction materials as salts can penetrate and crystallize inside the material, causing deterioration of the physical infrastructure. Such infrastructure degradation is primarily true with regards to mortars where salt crystallization inside the mortar pores causes an increase in the volume that results in high pressure build up and subsequent destruction of pore structure of the material. Most building materials of mineral origin (commonly used as external renders) cannot resist this pressure. Besides salt crystallization within the pores of the external renders, chemical attacks due to the combined action of the penetration of humidity and the sulfates can also occur. Researches have been conducted on the deteriora- tion of structures exposed to atmospheric aerosol and/or to acid deposition. Some of these researches focused on the mechanism of the interaction between the atmospheric substances and those present in the construction materials [1,4,11–15]. Others were concentrated on the production/distribution of salts from marine aerosols as well as their interaction with structures [16–30]. Some major cities in Bangladesh, a country that has a large coastal area with the Bay of Bengal, are situated on the coastline where the action of sea spray creates hazard for materials and products used in construction. An example is the city of Chittagong (Fig. 1). Chittagong, the second largest city, is the chief seaport and the main centre of export/import in Bangladesh. During the past decade, the city has rapidly expanded with the establishment of heavy, medium, and light industries. This is also associated with a rapid growth in the population. An intense presence of sea spray can be detected along the city’s coastal line and within its greater metropolitan area. A strong marine aerosol with high levels of chloride ions is present in the atmosphere of this metropolitan area similar to other regions of the world. Such adverse environment has caused tremendous damage to local structures, such as build- ings and bridges [31]. Very little research has been conducted to evaluate the destructive effect of marine aerosol on local infra- structure in the context of Bangladesh. The measurement and evaluation of the quantity of airborne sea salt can provide * Corresponding author. Tel.: þ1 416 979 5000x7867; fax: þ1 416 979 5122. E-mail address: ahossain@ryerson.ca (K.M. Anwar Hossain). Contents lists available at ScienceDirect Building and Environment journal homepage: www.elsevier.com/locate/buildenv 0360-1323/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.buildenv.2008.06.004 Building and Environment 44 (2009) 713–722