Reducing concrete permeability by using natural pozzolans and reduced aggregate-to-pasteratio

Abstract

Durability of concrete structures is mainly achieved with a low-permeability concrete. Permeability depends on both permeability of the bulk cement paste (CP) and that of its interfacial transition zone (ITZ). Even though permeability of CP can be adequately controlled, the effect of ITZ on is not well understood yet. This paper shows that minimizing permeability of concrete requires minimizing permeability of CP by using a supplementary cementing material (SCM) such as natural pozzolans (NP) and minimizing ITZ by reducing aggregate content. This was done by comparing performance of concrete made with ordinary portland cement (OPC) and blended cement (OPC+NP) at the same w/b, and by comparing performance of concrete with different amount of ITZ at the same w/b. All of this was performed through testing of mechanical properties, air permeability, sorptivity chloride ion permeability, and aggregate specific surface. Results show that NP in concrete reduced air permeability by 84% and chloride ion permeability by 66%, but increased sorptivity by 50 to 140%. ITZ has an important effect in all properties tested; especially in air permeability where sensitive reduction of more than a 90% was achieved. ITZ effect seems to be as important as using SCM´s in reducing permeability of concrete.