NO-PIGMENT ADDED COLORED CONCRETE INTERLOCK BLOCKS – NOVEL APPROACH USING RED SAND

The potential use of Sri Lankan Red Earth (RE) in manufacturing concrete interlock blocks (CIBs) was investigated as an alternative for sand as well as for a coloring agent. The demand for the use of CIBs for pavement construction has been increased recently in the world. Higher durability, resistance to freeze-thaw cycles and de-icing salt, low maintenance cost, ease of placement and removal, availability, and the aesthetic appeal are some advantages of CIBs. Continuous supply of sand, which is the fine aggregate and one of the main raw material, to fulfill the increased demand is the main obstruction confronted by the CIBs manufacturers. The present study suggested the application of RE as a 100% replacement for the river sand to manufacture CIBs. RE is a reddish brown color soil, which is mainly consisted with quartz coated with Fe-Al oxides in a clayey matrix. A series of RE based concrete inter lock blocks (RECIBs) were manufactured by changing the cement (C): Red Earth (RE): rock chips/gravel (RC) ratios to identify the most strongest and durable mixture. The strength (UCS) of commercially available CIBs (CCIBs) and RECIBs were measured at 28 days curing time by the uniaxial compressive strength apparatus. The water absorption capacity (WAC) and the density (D) of CCIBs and RECIBs were calculated following the ASTM C140. Micro-structural characteristics of RECIBs and CCIBs were observed using stereo microscope and scanning electron microscope. RECIB 02 (C:RE:RC = 1: 2: 3 = 17%: 33%: 50%) has the highest strength and the lowest water absorption capacity compared to CCIBs (UCS_RECIB = 13.8 MPa, UCS_CCIB = 11.72 MPa, WAC_RECIB =132.36 kgm^-3, WAC_CCIB = 144.29 kgm^-3, D_RECIB = 2251.35 kgm^-3, D_CCIB = 1983.98 kgm^-3). Image analysis indicated the presence of higher numbers of micro voids in CCIBs compared to RECIBs, which increase the WAC while reducing the relative UCS and density of CCIBs. In addition, RECIBs have reddish brown color compared to the grey shades of CCIBs. The presence of clay minerals in RECIBs facilitates a better temperature regulation than ordinary CIBs. Hence, Sri Lankan RE can be used as an efficient natural replacement for river sand in manufacturing reddish brown color CIBs for sustainable concrete productions.

Key words: Red earth, colored concrete interlock blocks, compressive strength, durability