While there are several reinforcing options for nonstructural slabs-on-ground, this article focuses on steel reinforcing bars and welded wire reinforcement for crack width control.

The basics

Steel reinforcing bars and welded wire reinforcement will not prevent cracking. Reinforcement is basically dormant until the concrete cracks. After cracking, it becomes active and controls crack widths by restricting crack growth.

If slabs are placed on high quality subbases with uniform support and consist of low shrinkage concrete with joints properly installed with spacings of 15 feet or less, reinforcement is generally unnecessary. Most likely, there will be few random or out-of-joint cracking. If random cracks do occur, they should remain fairly tight because of the limited joint spacing and low concrete shrinkage thereby limiting future serviceability or maintenance issues.

When slabs are placed on problematic subbases with risks of non-uniform support or consist of moderate to high shrinkage concrete or joint spacings exceed 15 feet, then reinforcement is necessary to limit widths of cracks should they occur. As crack widths grow and approach about 35 mils (0.035 inches), the efficiency of load transfer through aggregate interlock diminishes and differential vertical movements across cracks or slab "rocking" can occur. When this happens, crack edges become exposed and edge spalling will likely occur, especially if the slab is exposed to wheeled traffic and especially hard-wheeled lift trucks. Once spalling starts, crack widths at the surface become wider and slab deterioration along cracks increase significantly.

When contraction joints are unacceptable and not installed, shrinkage and temperature reinforcement is required. This design approach is sometimes referred to as continuously reinforced or joint-less slabs and allows numerous, closely spaced (3 to 6 feet), fine cracks to occur throughout the slab.