Effect of pigments on structural properties of colored reinforced concrete beams

Abstract

The need for colored reinforced concrete (RC) structures has increased in the modern building industry. This paper assesses the effect of white-colored titanium dioxide as well as red- and yellow-colored iron oxide (IO) pigments on the structural properties of RC beams with or without stirrups. The concrete mixtures had a water-to-cement ratio of 0.5, while pigments were added at 1.5 % and 3 % of cement mass. Test results showed that the concrete compressive strength increased with such additions (i.e., about 20 % to 31 % for mixtures containing 3 % pigment rates), given the micro-filler effect that enhanced the binder-packing density and refined the matrix microstructure. The incorporation of pigments had an insignificant influence on the ultimate flexural strength of under-reinforced beams containing stirrups, wherein the load-carrying capacity is controlled by yielding of the tensile steel reinforcement. In contrast, the shear strength of RC beams without stirrups improved with such additions (i.e., about 28 % to 70 % for mixtures containing 3 % pigment rates), particularly the yellow IO having a needle-shaped morphology. In addition to the micro-filler effect, the needles could have acted as nucleation sites to create bridging hydrating compounds that enhanced the aggregate interlock mechanism.