The properties of Portland cement-limestone-silica fume mortars

This work has studied the influence of the combined action of silica fume a nd limestone on strength development, porosity, pore structure and morpholo gical features in the system where 15 wt% of cement was substituted by fine ly ground limestone. Silica fume was added in amounts of 0, 2, 5, 8, 11 and 15 wt% on a cement basis, respectively. Tt has bean established that limes tone addition considerably increases the total porosity of mortars. However , if introduced together with silica fume up to 8 wt% of silica, porosity d ecreases. More than 8 wt% of silica increases the porosity again. The cemen t mortar containing 8 wt% of silica fume shows the highest compressive stre ngth, the minimum value of the total porosity, and its pore size distributi on curve shows a discontinuous pore structure. Limestone is taken up to the system and reacts with aluminate and ferrite phases from cement. Approxima tely 5 wt% is available for reaction after 120 days hydration or mortars co ntaining no silica fume. The quantity of limestone incorporated is affected by the silica fume content. The replacement of Portland cement by 15 wt% o f silica fume causes reduction both in the amount of cement and in the free CH content available for limestone chemical activity, and in this conditio n limestone acts only as a filler addition. (C) 2000 Elsevier Science Ltd. All rights reserved.