Evaluation of Lightweight Concrete Perfomance in 55 to 80 Year-Old Ships
R. D. Sturm, N. McAskill, R. G. Burg, and D. R. Morgan
Appears on pages(s):
carbonation; compressive strength; corrosion; cracking (structural); expanded shale; marine environment; performance; reinforcing bars; spalling
Ten concrete ships currently being used as a floating breakwater around the log pond at the Pacific Paper Powell River Plant in British Columbia, Canada, are after approximately 55 to 80 years of marine exposure, showing varying degrees of deterioration. The ships were constructed with a double mat of reinforcing steel and expanded lightweight shale aggregate concrete. Two separate inspections were conducted over the last seven years to evaluate the conditions of the hulls, decks, and other components of five of the ships. Cores taken from various portions of the ships with different exposure conditions were subjected to laboratory analysis and testing, including testing for compressive strength and petrographic examination. Results of these tests indicate that the lightweight aggregate concrete that the ships are constructed of has performed well, considering the harsh marine environment to which they are exposed. All the ships exhibited evidence of spalling induced by the corrosion of embedded steel reinforcement. However, the extent and severity of spalling varies between ships and was influenced by the depth of concrete cover over the reinforcement, the development of structurally-related cracking in the ships' hulls and decks, and the penetration of air, moisture, and salts to the level of the reinforcing steel. Lightweight aggregate concrete in parts of ships not exhibiting delaminations are in generally good condition and the cement matrix exhibits a tight microstructure and apparent low permeability to seawater. The manufactured lightweight aggregate used in the concrete is essentially unchanged proving that it is durable in a harsh marine environment. Compressive strength of the concrete meets or exceeds the designed minimum compressive strength of 35 MPa (5000 psi). Overall, the lightweight aggregate concrete is of excellent quality and has performed well for over 50 years.