Corner cracking

Corner cracking appears at the corners and is a crack that, together with the two sides of the joints, forms a triangle. Corner cracking usually extends the full depth of the slab. 

Corner cracking is caused by load repetitions combined with a loss of corner support (subbase or subgrade), poor load transfer across the joint, dowel bar restrain near the edge of the slab and ingress of solids into the joint. The loss of support may be created by pumping or warping stresses. 

The temporary treatment, until such time that corner cracking is permanently repaired, consists of cleaning and sealing the crack. Permanent repair consists of full-depth concrete or asphalt patching. 

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Corrosion causes horizontal cracking along the plane of the rebar and the corner cracking around the end rebar. This leads to the loss of concrete cover as shown in Figure 3.8. This is the main consequence of reinforcement corrosion with its subsequent risk of falling concrete and unacceptable appearance. 

The use of HBM eliminates pumping of fines most certainly to appear in jointed concrete pavements after a period of time, if unbound aggregate material had been used and joint maintenance is delayed. Pumping causes edge or corner cracking at the joints. 

The type of load-related distresses considered in the design of jointed reinforced or CRCPs are longitudinal, transverse and corner cracks, crack width and punchouts. 

With the three point loading test, the stresses were concentrated essentially at the corners, and the panel had a tendency to move downwards in a rigid manner. Failure occurred at the corners. Cracks appeared little by little at each corner and suddenly grew more rapidly at one of the corners then an unstable state took place, and the panel collapsed. 

Carbon treatment New baths do not require activated carbon purification. Circulation through a carbon-packed filter tube is recommended to control organic contamination for design and number, consult with supplier. The need for batch carbon treatment is indicated by corner cracking after reflow duU, pink deposits and haze, haloing, or comet trails around the PTH. Carbon-treat about every 1,500 (Ah) per gal. The following is the procedure for batch carbon treatment. 

Inadequate mixing of flame retardant masterbatches has also resulted in corner cracking of large blow moulded drums used for transporting chemicals when drop tested. Following laboratory trials to evaluate potential mixing devices a mixer was retrofitted as a screw extension which solved the problem. 

Corner cracks may also initiate under fatigue loading. In fact this may be the most common form of nucleation. Nonetheless, this problem seems to have received relatively little attention in the open literature. Lefebvre and Dillard [26,27] considered an epoxy wedge on an aluminum beam under cyclic loading. They chose corner angles (55°, 70° and 90°) that resulted in one singularity. A stress intensity factor based fatigue initiation envelope was then developed. 

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