This study explores the fresh and mechanical properties of Highly Flowable Concrete (HFC), that utilizes eggshell powder (ESP) as a cement substitute. HFC eliminates mechanical vibration during placement, minimizing segregation and honeycombs while improving construction quality. Considering the increased interest in sustainable alternatives, eggshell powder’s calcium content makes it a viable substitute for cement. Thus, laboratory tests were conducted on HFC specimens with eggshell powder substitutions ranging from 5% to 20% by cement weight. The mixture’s fresh properties were assessed using slump flow, T500, sieve segregation, and L-box tests. Mechanical performance was examined using compressive and split-tensile strength tests, with specimens tested to failure after 7 and 28 days of curing, respectively. The failure mode of the test specimens was also investigated. The experimental results show that all HFC mixtures containing eggshell powder met the EFNARC fresh properties requirements. Increasing percentages of eggshell powder replacement resulted in improved flowability, reduced segregation, and increased early age strength. The optimal replacement level was found to be 15%. This study provides vital insights into the potential of ESP in improving concrete performance while addressing environmental concerns associated with cement production and paving the way for more sustainable practices in concrete construction.
