The Influence of Cement Content and Water to Cement Ratio on Capillary Absorption of Root-Pile Mortars

Abstract

For the design of mortar mixes for filling root piles, the Brazilian standard NBR 6122, establishes a minimum compressive strength of 20 MPa (28 days), minimum cement content of 600 kg/m3 and a water to cement ratio between 0.5 and 0.6 and allows the use of water-reducing admixtures; however, the definition of a minimum cement content is a controversial topic about the guarantee of durability. Besides, cement content at these levels, will lead to axial compressive strength higher than 20 MPa, which is the minimum required by the standard, without much technological effort. The present study shows the influence of cement content and water to cement ratio on capillary absorption of mortars. It was found that, cement content, water to cement ratio and grain size distribution have an influence on capillary absorption. The study also demonstrates that it is possible to obtain mortars with low absorption for cement content lower than 600 kg/m3 by controlling the overall grain size distribution and by adding chemical admixtures to control the amount of mixing water. However, for mortars where grain size control is not possible, such as mortars mixed on site, the minimum cement content of 600 kg/m3 should be used to ensure low permeability.