Effects of Aggregate Packing Density on the Mechanical Properties of Ultra-High Performance Concrete

Cement is a remarkable construction material that allows for the formation of complex geometric forms while still providing adequate strength properties to be used as a structural material. This research focuses on Ultra-High Performance Concrete (UHPC) which is a specialized class of cementitious material that exhibits exceptional strength and durability properties when compared to standard concrete. UHPC achieves these properties through a combination of high cement content, high particle packing density, low water-to-cement ratio, and the additional of special admixtures such as superplasticizer. These components all serve the purpose of increasing UHPC strength and mechanical properties by helping achieve much high material densities than other forms of concrete.
In this study, aggregate material evaluation and testing was conducted for use in the mix design of the UHPC mixes that were carried out and tested. Each mix employed the same general UHPC mixture design with the only difference being the aggregate proportions of #4, #8, and #10 nominal size aggregates. The purpose of using a UHPC mix design that was independent of aggregate proportioning was to evaluate the effects of varying aggregate particle packing densities. Increased particle packing density of UHPC provide improved mechanical performance by decreasing the distance between particle within cured UHPC, thereby producing significant increases in compressive strength, tensile strength, durability, and service life of UHPC when compared to standard concrete. For this study, particle packing densities of 0.509, 0.521, 0.540, and 0.552 were employed and evaluated on the basis of compressive strength and tensile strength to determine the optimum UHPC mix design.