Evaluation of modified-graphite nanomaterials in concrete nanocomposite based on packing density principles

• The Compaction Packing Model was employed to calculate the packing densities of concrete.
• Nanomaterials extends the size range of particulate matter in fresh concrete.
• CNF at 0.04 vol.% of concrete account for 9% of the packing density of UHPC.

Fresh concrete is a dispersion of particulate matter with a broad size distribution in water. Addition of graphite nanomaterials extends the size range of particulate matter well into nano-scale dimensions, which could benefit the packing of particles in fresh concrete and the engineering properties of hardened concrete materials. In order to test this hypothesis, five classes of concrete (normal-strength, high-strength, ultra-high-performance, self-consolidating normal strength, and self-consolidating ultra-high performance concrete) with different packing densities were evaluated. The Compaction Packing Model was used to calculate the packing densities of various examples of these five categories of concrete materials. The packing density was observed to be lowest for normal-strength concrete and highest for ultra-high-performance concrete. In the case of self-consolidating concrete materials, finer particulate matter was found to make a greater contribution towards raising the packing density with increasing compressive strength. In self-consolidating ultra-high-performance concrete, the effect of micro-scale fibers on improving the packing density was found to be about half that of non-self-consolidating ultra-high-performance concrete. A key finding of the analytical investigations was that graphite nanomaterials (carbon nanofibers) at very low dosages (0.04 vol.% of concrete) account for 9% of the packing density improvement in ultra-high-performance concrete nanocomposites. This notable contribution at such low concentration can be attributed to the fine geometry of the nanomaterials. Experimental results were used to validate the correlation between the contributions of graphite nanomaterials to concrete material properties and the corresponding effects on the packing density of the particulate matter in fresh concrete. These correlations indicated that the Compaction Packing Model provides a viable basis for design of concrete nanocomposites.