Cavitation erosion in suspensions containing sediment and NaCl for cement paste and mortar

Synergistic erosion caused by cavitation, abrasion and corrosion is a common issue for hydraulic and marine structures in rivers and oceans with high concentrations of sediments. Erosive experiments using a vibratory apparatus and a stirring apparatus, are performed on cement paste and mortar subjected to tap water, sediment suspensions (0.01-0.1 -mm sizes and 30-150-kg/m3 concentrations), and sodium chloride solutions (0.5-15%). The experimental results demonstrate that cavitation erosion is the dominant failure mechanism. Micro jet and shock wave accompanied by the collapse of cavitation bubble clouds lead to a broadening of the original micro crack and pore. The cumulative mass losses linearly aggravate with the prolongation of exposure duration entering an acceleration period. The increasing sizes and concentrations of sediments aggravate the synergistic erosion due to the accelerated sediments by bubble collapse and heterogeneous nucleation of sediments. Sodium chloride weakens the cavitation resistance of cement mortar with a threshold value of 1.5% concentration. The mass loss caused by cavitation corrosion increases sharply at concentrations of NaCl smaller than 1.5% and then slowly increases. Chlorine ions penetrate the micro crack and result in the dissolution of the calcium silicate hydrate and the formation of the expanding compound with the enlarged porosity, decreasing the compressive strength. The addition of NaCl and sediment in the suspension aggravates the cavitation erosion and no suppression is observed.