Nanotechnology to Manipulate the Aggregate–Cement Paste Bond Effects on Mortar Performance

Abstract

It is well recognized that the area of contact between cement paste and aggregates, known as the interfacial transition zone (ITZ), is one of the most vulnerable areas of concrete. The microstructure, chemistry, porosity, and mineralogy of this interface affect the adhesion between the aggregate and the cement paste and therefore, under certain conditions, dictate the performance of concrete. The traditional strategy for improving the ITZ has been the addition of pozzolanic materials having a close relation between surface area and particle size. However, the beneficial effects of these additions to the ITZ are diluted because the additives largely end up in the bulk of the cement paste. Research was done to show the benefit and practicality of depositing pozzolanic materials as thin films on the surface of aggregates to improve the ITZ. Preliminary results show that a small dose of these materials can significantly modify adhesion between aggregate and cement paste in the ITZ. The consequence is an overall improvement of the principal mechanical properties and a change in the microstructure of mortar. In particular, mortar made with a 0.0032 silica oxide–cement ratio deposited as a surface coating of just one-third of the total fine aggregates showed an average 35% improvement in compressive, flexural, and tensile strength at early ages along with decreased chloride penetrability. These results clearly indicate that the addition of silica oxides into concrete as thin films on aggregate surfaces has a high potential for improving the overall performance of concrete.