Controlling cracking requires producers to control volume change and use reinforcing correctly. Here are some tips on avoiding the most common crack types:
Craze cracks are shallow, intersecting surface cracks that resemble dried earth. Craze cracks usually develop at an early age and are caused by shrinkage of the drying surface concrete. Factors that contribute to crazing include: high water-to-cement ratio; excessive vibration of formed surfaces; excessive floating or troweling; finishing while there is bleedwater on the surface; sprinkling dry cement on a surface; and poor curing.
Re-entrant corner cracks:
Cracks at re-entrant (inside) corners are caused by stress concentrations at the corner. They are difficult to avoid without changing the angle of the corner. Welded wire fabric or reinforcing bars can be used for corner reinforcement.
Tensile stresses and shrinkage cracks develop when concrete is restrained as it shrinks. Shrinkage reduction through mix proportioning is the first defense against shrinkage cracking. Welded wire fabric or small-diameter reinforcing bars can be used to control crack width.
Tensile stresses during stripping often cause cracking due to low initial strength of the concrete. If this type of cracking occurs often, form design and stripping procedures should be re-evaluated.