EFFECT OF SOME HYDROPHOBIC ADDITIVES ON THE PHYSICOCHEMICAL PROPERTIES OF HARDENED CEMENT AND MORTAR PASTES

Abstract

In the present investigation,the effect of some hydrop­ hobic admixtures on the physicochemical properties of the hardened Portland cement pastes and mortars was studied . Three hydrophobic admixtures were used ,these are stearic acid , palmetic acid and com oil . Various ratios of the admixtures were used , namely; 0.25 , 0.45 , 0.75 and 1.5% by weight of the dry cement , this in case of cement pastes , and the used WIC ratio was 0.30 , whereas, in mortars, the used ratios were • 0.45,1.5 and 2.5 % by weight of cement, mortar mixes were prepared using cement /sand ratio of 1 I 3 and WIS ratio of 0.12 Each paste was cured at a relative humidity of about I 00 % for

the first 24 hours and then under water for the rest of hydration time intervals (3,7 and 28 days) . After each hydration time, each hardened paste was tested for compressive strength , combind water content. free lime content , bulk density , total porosity and water absorption . For sh1dying the phase ' composition , morphology and microstruch1re of the hydration

products , this was carried out by X-ray diffraction analysis and Scanning Electron Microscope . IJ1 addition , the pore structure and surface area of the hydration products were detennined using N 2 - sorption technique .