Effect Of Lime And Fly Ash On The Strength Of Cement Composite Mortars.

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Effect of lime and fly ash on the strength of cement composite mortars*
FM Wegian†, HM AlSaeid and AA Alnaki Civil Engineering Department, College of Technological Studies, Kuwait

ABSTRACT: Different proportions of lime and fly ash mortars were analysed against increasing percentages of fly ash, lime as a replacement of cement, and water-to-cement lime-fly ash ratios at various ages.The study was carried out to determine the maximum permissible fly ash content and the optimum water-to-lime-fly ash ratio in order to attain required strength levels at specific ages. The study examined the variation in strength with the gradual increase in fly ash quantities to cement-lime mortars. The addition of 7.5% to 22.5% of fly ash and 2.25% to 6.75% of lime in cement mortars can increaseoverall mortar strength.

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INTRODUCTION

As construction is seeing a worldwide boom, especially in developing countries, it is essential to find new and cheaper materials for composite mortars. These materials have to be used in certain proportions to obtain the correct compressive strength as not to undermine the strength of building structures. Hydrated lime, hydraulic lime and fly ashare not new building materials, but understanding suitable mixtures for maximum strength in comparison to lean cement mortars is still in development. Hydrated lime Ca(OH) 2 has been used as a construction material for millennia, particularly in the form of mortars for different mixes (Oates, 1998; Malhotra & Dave, 1999). Hydrated lime is available in many developing countries, but is costly due tothe chemical processing required (Oates, 1998). However, lime has proved to be an excellent construction material for a variety of reasons. First, it improves the workability and plasticity of mortars. Second, it can be used in damp environments. Third, set time and seven-day strengths of lime-cement mortars “can be controlled by the amount and type of cement” (Oates, 1998; Malhotra & Dave, 1999;Fraay & Bijen, 1990). Fourth, because of its high alkalinity, it can resist mould and corrosion.
* Paper S10-050 submitted 19/01/10; accepted for publication after review and revision 10/05/10. Published in AJSE Online 2010, pp. 67-76. Corresponding author A/Prof Falah Wegian can be contacted at fmwm@yahoo.com.

Hydraulic lime is useful for its ability to set under water and in thick wallswhere there is no free air circulation (Ghosh & Chatterjee, 1981). It is typically produced through a mechanised process in which it is ground to a fine powder then mixed with sand. The mixture is left to mature and then re-ground. Such mortars are used for plasterwork. Fly ash is a waste product from thermal powerstations and is obtained as a finely divided residue resulting from the flue gases oncombustion of ground or powdered coals of boilers. Fly ash is widely accepted for its pozzolanic properties as it helps to increase the long-term strength of concrete and mortars (Hondal & Pandey, 1988; Massazza, 1993; Barbhuiya et al, 2009). Its properties of increased workability and surface finish are added advantages. It reduces bleeding, heat of hydration and shrinkage (Fraay & Bijen, 1990).Fly ash has been found to have numerous advantages for use in the concrete industry. Some advantages include improved workability, reduced permeability, increased ultimate strength, reduced bleeding, better surface finish and reduced heat of hydration (ACI, 1966). Fly ash is a useful admixture to cement, as it is cheaper than cement and a recycled material (Gengying & Xiaozhong, 2005). Architectsand builders prefer fly ash because it is similar in colour to cement, meaning that when dry, it looks like cement. Fly ash’s pozzolanic properties are also beneficial in cementation. Silicon dioxide present in the amorphous form in fly ash reacts with Ca(OH2) liberated from cement during the process
Australian Journal of Structural Engineering, Vol 12 No 1

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