In all sillimanite-containing concrete mixes, nano alumina was introduced at a consistent rate of 2% by mass of cement. At 10–50%, sillimanite took over the role of fine aggregate. To measure the influence of sillimanite and nano alumina additives in concrete, the blending procedures, water binder ratio, and curing methods were all kept constant. The workability analysis was carried out on freshly poured concrete. Concrete was tested for mechanical strength at 7, 14, 18, 56, and 90 days. The samples for the later age tests were immersed in water for 28 days before being removed and kept in the outdoors until the testing days arrived. The UPV test was conducted on concrete cubes that had been cured for 28 days. Non-destructive testing was used to assess the effectiveness of nano alumina and sillimanite in enhancing the density of concrete. The examined strength and UPV data, as well as their correlations, were established.