A Comparison of the Pore Structure of Cement and Fly Ash/Cement Mortars Made With Sea Water and Fresh Water
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A COMPARISON OF THE PORE STRUCTURE OF CEMENT AND FLY ASH/CEMENT MORTARS MADE WITH SEA WATER AND FRESH WATER
B.K. MARSH, R.C. JOSHI, AND A. BALASUNDARAM Calgary Fly Ash Research Group, Dept. of Civil Engineering, Calgary, Calgary, Alberta, Canada, T2N IN4.
University of
ABSTRACT Pore structures of portland and blended cement mortars prepared with sea water were assessed by mercury intrusion porosimetry. Comparison is made with similar mortars made with fresh water. Mortars were made using cement containing 0%, 25% or 50% (by volume) of one of two Alberta fly ashes. They were tested after 90 days of continuous immersion in sea water at 5°C or 20°C. Results show that the mortars made with sea water generally contained a much higher volume of fine pores although the porosity was, in some cases, greater than that of mortars made with fresh water. Nevertheless, the volume of larger pores was lower in the mortars made with sea water. The pore structure of the various mortars is discussed in relation to potential durability.
INTRODUCTION Sea water is rarely used as mixing water for concrete because it is usually required that the mixing water be of a quality fit for drinking. Indeed, the use of sea water as mixing water is restricted by British standards (BS 3148) to unreinforced concrete, and Asierican standard (ASTM C94) precludes its use due to its high chloride content. Successful use of sea water for mixing concrete could result in substantial cost-saving in remote coastal areas where the supply of drinking water is limited. Moreover, investigations have shown that, for some types of concrete, mixing with sea water may result in higher compressive strengths than when fresh water is used [1-3]. Whilst strength is an important property, it is well known that many of the engineering properties of concrete and mortar are related to pore structure; this is particularly so in the case of durability in sea water [4]. This paper gives results from an investigation using mercury intrusion porosimeter of the pore structure of mortars mixed with sea water and stored in sea water. They are compared with results from mortars mixed with fresh water but also stored in sea water. The effect of chloride, prominent in sea water, on the pore structure of hardened cement paste has been investigated by Midgley and Illston [5]. By analysis of hardened cement pastes cured in lime water for 28 days, then stored in sodium chloride solution (of sea water concentration), they showed that chloride ion penetration altered the pore size distribution. An increase in the chloride concentration within the paste resulted in an increase in the amount of smaller pores. The current investigation explored the effect of having chloride, in the form of sea water, present at the mixing stage as well as throughout the curing period. The effect of partial replacement of cement by fly ash on any redistribution of pore size was also investigated.
EXPERIMENTATION Mortars were mixed at a water/cementitious-material ratio of 0.6 and a sand/cementitious-materia
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