If you’ve ever poured a concrete patio in the middle of July, somebody probably told you to start early in the morning and keep the hose close. Concrete doesn’t like heat. Now scale that problem up to a dam wall in the Austrian Alps, and a garden hose isn’t going to cut it.<\/p>\n
You need ice. About 1,300 tons of it, if you’re Verbund.<\/p>\n
The Austrian utility finished pouring the last of 25 new concrete blocks on top of the Limberg dam in Kaprun on August 30. The dam already stands 394 feet tall, and the new blocks make up most of a 28.5-foot raise that will take it to 422 feet. Verbund announced the milestone<\/a> on September 2, and according to Swietelsky, one of the builders on the job, it’s the first time a dam in Austria has ever been made taller.<\/p>\n When cement mixes with water, the chemical reaction that hardens it gives off heat. In a thin slab that heat just escapes, but in a block the size of a house the middle stays hot while the outside cools down, and that difference is what cracks it.<\/p>\n So Verbund set a pretty tight window for the fresh concrete going into the new blocks: between 45 and 54\u00b0F. During the warmer months, it mixed roughly 1,300 tons of crushed ice into the batches to stay inside that range. The concrete and the ice were both made on site, below the Mooser dam farther up the valley, and ORF, Austria’s public broadcaster, reports the plant there was turning out about 16 tons of ice a day.<\/p>\n Most of the pouring happened at night, too. That makes sense when you’re trying to keep a warm mix cool, and I’d guess the people driving up the access roads during tourist season didn’t mind having the trucks out of the way either.<\/p>\n The 25 blocks hold about 32,000 cubic yards of concrete between them. Verbund’s own estimate for the whole raise, back when it started, was closer to 42,000 cubic yards, which includes the work that still has to go on top.<\/p>\n Then there’s the prep work. Before any new concrete went down, the old crest had to be roughed up so the fresh stuff had something to grab onto. Verbund did that with water jets running at up to 43,500 psi, which is a long way past anything you’d point at your driveway. Steel bars reaching up to 9.3 feet deep were also set into the old wall to pin the two together.<\/p>\n So is it done? Not quite. The blocks are poured, but nobody can fill the lake any higher just yet.<\/p>\n Dams like this one are built in separate blocks so each piece can shrink a little as it cools without cracking. Once they’ve cooled all the way down, the gaps between them get pumped full of grout so the wall behaves like one solid piece again. ORF reports the new blocks will sit and cool through the winter, with that joint grouting scheduled for next year.<\/p>\n Verbund also still has to pour a 3.6-foot-thick slab across the top, build a 4.4-foot parapet wall and finish work on the spillway. Roman Kohler, who runs Verbund’s dams department, told ORF the raised wall will be “even safer than before” (translated from German).<\/p>\n The job has been running off a 241-ton crane that rolls along the crest on rails. It has a 213-foot boom and is built to stay standing in winds of up to 137 mph when it’s parked, which is a reasonable spec when your work site sits at roughly 5,600 feet. “In the intensive phase, we will have to make up to 15 lifts per hour,” Verbund project manager Christian Rieder said when the crane went up.<\/p>\n ORF puts the cost of the raise at \u20ac66 million. Compare that with Denver Water’s Gross Dam in Colorado<\/a>, which went up 131 feet for roughly $600 million. Those are very different jobs, admittedly, but it does make the Austrian project look pretty cheap.<\/p>\n More water, basically. The Wasserfallboden reservoir behind the dam goes from about 65,800 acre-feet of usable storage to about 76,100 acre-feet, a 15.6% increase. That’s around 3.4 billion gallons of extra water, and ORF says it works out to about as much as the city of Salzburg drinks in a year.<\/p>\n But Verbund isn’t storing it for drinking. It’s storing it as energy.<\/p>\n If you haven’t run into pumped storage before, it’s essentially a giant water battery. When there’s spare electricity on the grid, a plant pumps water uphill into a reservoir, and when power is needed, that water runs back down through turbines.<\/p>\n Raising the dam adds about 30 gigawatt-hours to what the Wasserfallboden reservoir can hold, taking it from roughly 160 to 190 gigawatt-hours. Verbund says that extra slice equals the capacity of three million home solar batteries. Frankly, making an old wall taller seems like a far easier sell than flooding a brand-new valley in the Alps, and I suspect that’s a big part of why Verbund went this route.<\/p>\n There’s a slightly awkward wrinkle here, though.<\/p>\n The plant that’s meant to make the most of all this water is Limberg III, a pumped storage station Verbund built in a cavern deep inside the mountain. It shuffles water between Wasserfallboden and the Mooserboden reservoir higher up, using two 240-megawatt machines. Verbund held the official opening last fall, and about two months later it reported that both generators had failed during commissioning tests.<\/p>\n Verbund says certain rare operating conditions put the rotors under especially heavy loads, and the insulation on the windings couldn’t take it. The manufacturer, Andritz Hydro, has been rewinding both generators inside the cavern around the clock. Verbund’s last detailed status update<\/a> in April said machine 2 should restart in September and machine 1 in December. In early September, ORF reported<\/a> that the rotor for machine 2 was on the move. I couldn’t find a public update confirming whether it’s actually spinning again.<\/p>\n Next door, the older Limberg I plant (160 megawatts) is also offline. A large transformer there failed during black start tests last November. A black start is basically a rehearsal for bringing a plant back up with no outside power at all, which is exactly the kind of scenario you’d want a pumped storage plant to handle. A new transformer has been ordered, and Verbund is aiming to restart Limberg I by the end of the first quarter of 2027.<\/p>\n Add it up and about 640 megawatts of capacity in Kaprun is sitting idle, and Verbund has warned the two outages could knock \u20ac40 million to \u20ac60 million off its group results, mostly this year. If the repair dates hold, both plants should be running again well before the bigger lake is ready for them, which is arguably the one bit of good timing in all of this.<\/p>\n Verbund plans to fill the Wasserfallboden reservoir to its new, higher level for the first time in late summer 2027, and expects to wrap up the whole Limberg raise by the end of that year.<\/p>\n","protected":false},"excerpt":{"rendered":" If you’ve ever poured a concrete patio in the middle of July, somebody probably told you to start early in … <\/p>\nSo why would anyone put ice in concrete?<\/h2>\n
The dam isn’t quite finished yet<\/h2>\n
So what does Verbund actually get out of it?<\/h2>\n
The new power plant underneath is still being fixed<\/h2>\n