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.