Once spalling starts, crack widths at the surface become wider and slab deterioration along cracks increase significantly. 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. 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 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. 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. Most likely, there will be few random or out-of-joint cracking. 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.
After cracking, it becomes active and controls crack widths by restricting crack growth. Reinforcement is basically dormant until the concrete cracks. Steel reinforcing bars and welded wire reinforcement will not prevent cracking. Unrestricted crack width growth leads to spalled edges along out-of-joint cracks when exposed to wheeled traffic, especially hard-wheeled lift trucks. 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. Because of constructability issues and costs associated with two layers of reinforcement, structural slabs-on-ground are not as common as nonstructural slabs. Most structural slabs-on-ground have both top and bottom layers of reinforcement for controlling crack-widths and increasing load capacities. Structural reinforcement is typically placed in the bottom portion of the slab thickness to increase the slab's load capacity. Shrinkage and temperature reinforcement is different than structural reinforcement. This type of reinforcement is commonly called shrinkage and temperature reinforcement. When positioned in the upper or top portion of the slab thickness, steel reinforcement limits the widths of random cracks that may occur because of concrete shrinkage and temperature restraints, subbase settlement, applied loads or other issues. Most slabs-on-ground are unreinforced or nominally reinforced for crack-width control.
0 kommentar(er)
