Influence of nano-silica addition on properties of conventional and ultra-high performance concretes

الملخص EN

Cementitious and concrete materials are mainly used on a large scale and in huge quantities for roads, dams, bridges and building constructions.

The mechanical behavior of these materials depends to a great extent on structural elements and phenomena which are effective on a micro and nanoscale.

New efforts and possibilities of material engineering on nanoscale may lead to improve mechanical and physical properties as well as durability of composite construction materials.

This paper intends to study the use of Nano-silica with 99.5% silica content and average particle size of 15 nm as addition in concretes with different strength levels.

Besides, comparison between the influence of SF and NS on concrete performance was also addressed.

Therefore, the experimental program was divided into two parts aiming at investigating the effect of NS addition on the properties of conventional and ultra-high performance concretes (UHPC).

Results indicated that nano-silica addition reduced the concrete workability.

The incorporation of nano-silica resulted in a significant early increase in compressive, splitting tensile and flexural strengths of conventional concrete.

Addition of both silica fume and nano-silica by total amount of 10%, may lead to an increase in the 28-day compressive strength of low cement content and high cement content concretes up to 40% and 50 %respectively, over the strength of comparable concretes.

It was observed that the pozzolanic contribution of nano-silica becomes significant from the very early age, compared to silica fume, which begins its pozzolanic reactivity at the age of 7 days or later.

This mechanism explained the outstanding mechanical performance of nano-silica concrete.

Test results also showed that nano-silica may be applied successfully in ultra-high performance concrete, where strength level over 230 MPa was achieved.