Standing on the top floor of the command tower for the Cocoli complex, looking at the new locks on the Pacific side of the Panama Canal, Jan Kop, project coordinator for the design-build consortium Grupo Unidos por el Canal (GUPC), says, “We’re in the final stretch now, we’ve demonstrated that all systems work.”
The Panama Canal Authority (ACP) wanted locks that would function 99% of the time for the next hundred years. “Ninety-nine percent of the time basically means always,” says Kop.
This meant all systems needed back-ups and all the concrete had to be of the highest quality consistent with the requirements of the ACP.
Below us, workers are pouring the last concrete for roads, curbs, and draining system. The locks, already filled with water, would officially be opened on June 26. After that, ships carrying 14,000 containers will be able to transit the canal.
There’s only a small concrete plant left on the site. The much larger concrete batch plant that produced 610 cubic meters of concrete per hour has been dismantled. The tents that once protected aggregate and sand from the sun are now mostly empty. Aggregate was the first big headache. “The first big delay came because the available basalt rock we used to make aggregate generated much more fines than could be anticipated from the ACP tender information,” says Kop.
Pouring five million cubic meters of concrete and installing 250,000 tons of rebar was the cornerstone of the project. ACP wanted GUPC to use an independent test lab for the concrete cores. This work was done by Fall Line Testing & Inspection, a company headquartered in Pittsburgh. “We use ASTM C1202, [Electrical Indication of Concrete's Ability to Resist Chloride Ion Penetration], one of the standard methods to measure concrete’s ability to resist chloride ion penetration,” says Tim Counts, who has worked at the site for Fall Line since 2011.
“The marine concrete that is in contact with salt water has to hold up for a hundred years,” explains Kop. “So you have to prevent the penetration of salt water that will corrode the rebar. However, our marine concrete at first didn’t pass ACP’s interpretation of the C1202 test after 90 days of curing. It needed more time to cure to reach the desired impermeability, but ACP insisted it should be achieved after 90 days, which is not an applicable criterion in these circumstances. The inflexibility of ACP caused considerable delays.”
Professor Klaas van Breugel, concrete expert from the Technical University at Delft in the Netherlands, explains why it is so difficult to pour large volumes of concrete in a hot and humid climate like Panama’s:
“In the center of mass concrete the temperature will increase more than in the surface zones. This puts the central part in compression and the cooling surface in tension,” says van Breugel. “When the center finally cools, compressive stresses turn into tensile stresses. To avoid cracking, temperature differences in the concrete cross section should not exceed certain limits. In case cracking does occur, appropriate reinforcement should be installed to control the width of the cracks.”
To prevent overheating, GUPC embedded the entire production line with cooling systems that had to make sure the temperature of the concrete as delivered would remain below 52˚ F: ice to keep the aggregate cold and insulated agitator trucks for delivery. After the pour, the temperature of the concrete always had to stay below 160˚ F and the temperature gradient between surface and center could not exceed 30˚ F.
The last big setback for GUPC came in August 2015 when the upper lock chamber of the Cocoli complex was filled for the first time with water, while the middle chamber remained empty, a situation that will not occur during the actual operation of the canal. The massive, one-sided, water pressure created several leaks in the concrete lock sill under the two massive steel gates between the lock chambers.
Kop states that the leaks in the lock sill had absolutely nothing to do with the quality of the concrete. “It was a reinforcing steel design issue. There was not enough rebar in a part of the lock sill that had to deal with large forces from the steel doors under this extreme test condition.” On top of that, hydrostatic pressure from below created small cracks in the sill.
GUPC solved the leaking by grouting the cracks, drilling holes and putting more rebar, regular and pre-stressed, deep into the lock sill. They also placed more drainpipes under the sills to eliminate the effects of hydrostatic pressure. Solving this problem caused an extra delay of four months. The costs of the solution were in excess of $40 million. Kop shrugs, “It’s not unusual, in a huge pioneering project like this you go from managing one crisis to the next.”