Colored Interlock Blocks of Non-Traffic Grade – A Novel Approach Using Red Sand

Concrete interlock blocks (CIBs) have a wide range of applications due to low cost, easy replacements, and aesthetic appearance. The low availability of the main raw material, river sand, to gratify the increased demand is a major concern in CIBs industry. Hence, this study explored the applicability of natural red sand (RE), which mainly consists of fine-grained quartz coated with Fe-Al oxides as an alternative for river sand in non-traffic grade, red color CIB production. Different proportions of cement (C), RE, and rock chips (RC) were used to produce RE-based concrete interlock blocks (RECIBs) following both air drying and water curing methods. The unconfined compressive strength (UCS), flexural strength (F_b) water absorption capacity (WAC) and density (D) of CIBs were measured following standard protocols. Microstructural characteristics were observed by scanning electron microscope. Commercially available CIBs (CCIBs) were used for comparison purposes. RECIBs produced with the ratio of, C:RE: RC = 17%: 33%: 50% showed the highest strength compared to CCIBs (UCS_RECIB = 17.8 N/mm², UCS_CCIB = 11.72 N/mm², F_{b RECIB} = 3.9 N/mm², F_{b CCIB} = 1.68 N/mm², WAC_RECIB =132.36 kg/m³, WAC_CCIB = 144.29 kg/m³, D_RECIB = 2251.35 kg/m³, D_CCIB = 1983.98 kg/m³). Low void spaces, well-connected aggregates and presence of heavy minerals have enhanced the strength of RECIBs. Water cured RECIBs have higher strength compared to air-dried blocks due to the formation of more hydrated products including ettringite and calcium-silicate hydrate phases, which facilitate the integration between aggregates. The present study confirmed RE is a good material that can be used to produce non-traffic grade, red color interlock blocks.