Concretes containing various supplementary cementitious materials (SCMs) such as silica fume, fly ash, and slag have improved properties. Nanomaterials (a nanometer, nm, is 10 to the minus 9th), new SCMs with possible applications in concrete, have the smallest particle size that is less than 100 nm. Nanomaterials are very reactive because of the particles’ small size and large surface area and have great potential in improving concrete properties such as compressive strength and permeability. This study evaluated the use of a variety of nanomaterials in concrete compared with conventional concrete and concrete containing common SCMs. The potential benefits of using nanomaterials over other SCMs are their high reactivity; the need for smaller amounts, resulting in less cement replacement; and cost-effectiveness.
Concretes containing nanosilica and nanoclay were prepared in the laboratory and compared to concretes containing silica fume, fly ash, slag, or only portland cement. Specimens were tested for compressive strength and permeability. The microstructure of selected concretes with improved compressive strength and permeability were analyzed using an atomic force microscope and nanoindenter to determine the reason for the improvements.
The microstructure of the nanosilica concrete was denser and more uniform than that of the conventional concrete microstructure. In addition, the nanosilica had the largest improvement in both compressive strength and permeability among the nanomaterials tested.
The results of this study indicate that some of the nanomaterials tested have potential in concrete applications. However, further evaluation is required before nanomaterials can be used in concrete. Specifically, they should be evaluated for improved dispersion to achieve uniformity, optimized amounts of ingredients, and cost-effectiveness.