Strain hardening cementitious composite (SHCC) for crack width control in reinforced concrete beams

Strain Hardening Cementitious Composite (SHCC) is an innovative material which, due to the special material composition and the addition of fibres, exhibits a controlled microcracking behaviour under tensile stresses. As such it might be a promising material for improvement of durability of concrete structures.

An experimental study was performed aiming to investigate the cracking behaviour of reinforced concrete beams enhanced with SHCC layers in the beam tension zone (hybrid SHCC - concrete beams). Specimens with SHCC layers of different thickness were tested. The hybrid SHCC/concrete beams were compared to regular reinforced concrete (control) beams with the same dimensions and rebar position. Specimens were tested in four-point bending while Digital Image Correlation (DIC) and an image analysis software package (ImageJ) were used to evaluate crack pattern development and crack widths. In the experiments, hybrid beams showed better cracking behaviour compared to control beams, whereas also a higher bending moment capacity was found. The thicker the SHCC layer, the higher the load capacity is. More importantly for the aim of this study, composite beams with a 70 mm SHCC layer showed a better crack width control compared to the reference beams. The maximum crack width exceeded 0.3 mm at approximately 64 kN load, whereas in the control beam it exceeded 0.3 mm at 35 kN load. In hybrid beams with a 30 mm SHCC layer, the benefits were much lower, as expected.

The study indicates that by using a combination of conventional concrete and advanced concrete (SHCC in this case), possibly optimal design of reinforced concrete structures could be achieved by eliminating the crack width as governing design parameter and thus saving on reinforcement needed for crack width control.