Abstract The present state of development in the field of construction is a culmination of the investigations conducted on concrete over the past 80 years. There are two major issues to be dealt within the construction industry, namely depletion of natural resources and societal problems due to pollution. Numerous investigations are carried out on concrete in order to make it eco-friendly the environment is not affected much. Aggregates are the volume fillers in concrete, which consume 70–75% of the volume. Nowadays, natural sand is completely replaced with manufactured sand (M−Sand) based on the previous literatures. Thousands of varieties of sea shell elements are available in the coastal region of Tamil Nadu. In this study, crushed and uncrushed cockle shells are used as replacement material for coarse aggregate in the preparation of M40 grade eco-concrete (0% to 30% at an interval of 5%). It is observed that the increment in cockle shells reduces the density of concrete and the compressive strength of eco-concrete shows better results at 25% replacement of uncrushed cockle shells, whereas crushed shell elements reduce the strength properties linearly by increasing the replacement percentage. It is concluded that eco-concrete produced with cockle shell elements is most preferable in the production of light weight blocks/pavers.