 Recently the Canning Dam has been subjected to considerable <unk> of the upper parts of the dam and upper gallery . Investigations have shown that <unk> was due to strong AAR ( alkali aggregate reactivity ) in the concrete . AAR results in swelling of the concrete , which may cause secondary <unk> stresses , localised map cracks , and , ultimately structural cracks . In addition , the concrete tensile strength and elasticity significantly decreases . Many old concrete dams are known to suffer from AAR , including <unk> Dam in Tennessee and <unk> <unk> dam in Italy among others . 
