Восстановление исторических дымовых труб: полный демонтаж и перестройка для сохранения наследия

The scaffold reaches the top of a stack and then keeps going, in a ring, with the open sky inside it. Below the platform there is no chimney at all. There is a stub, a rank of steel bars standing up out of it, and a timber shutter clamped around them. A barrow comes up in the hoist. What went down was a landmark, and what is going back up will be  the same shape  in new material. Which raises the question of why anybody demolishes the thing they are  trying to protect. Why the only repair was to start over The original concrete was failing from the inside. Two problems ran together. The mix carried a high chloride content, and decades of carbonation had lowered the alkalinity that normally keeps embedded steel passive. Once that protection goes, the bars rust. Rust occupies more space than the steel it came from, so it pushes outward until the cover cracks and falls away. A stack losing its cover at height is not a maintenance problem, it is a  falling object  problem. Patching does not reach it. You can repair a face, but you cannot replace the chloride sitting through the full thickness of a wall, and every patch leaves the next section to go. The only durable answer was to take all four down and pour them again, which is what the heritage authority signed off on the condition that the method matched the  original build. A hand poured stack, one lift at a time Each chimney stands 338 feet. They taper as they rise, about 28 feet across at the base and roughly 22 feet at the top, which means the shutter has to be reset slightly smaller on every lift. No pump was used. The concrete went in the way it went in the first time, barrowed to the shutter and tipped by hand, placed in layers and vibrated, then left to gain strength before the formwork climbed and the next layer started. That is the slow part. A pumped pour puts a stack up in a fraction of the time, and it also produces a wall the conservation officers would not accept as a match. The  method itself  was part of what was being conserved, which is an unusual thing for a building to  ask of a crew. Wheelbarrows, bricks and the real count More than 25,000 barrow loads of concrete went into each stack. Four stacks means the true figure for the whole job runs past 100,000 loads, which is the number worth quoting and the one most retellings get wrong by a factor of four. The brickwork ran on its own count. Six million bricks make up the building. About 1.75 million of them were replaced, and they did not all come from the same place or the same process. Roughly  1.3 million  were hand moulded by the Gloucestershire brickworks that supplied the original job, and about 440,000 more were wire cut by a second supplier. So the shorthand is loose. Calling the replacements handmade covers three quarters of them and misses the rest. Work on the stacks started in 2014 and finished in 2017, under the oversight of the national heritage body, on a structure that has been  listed since 1980. The tenants who arrived before any architect A pair of peregrine falcons had been nesting on the site since 2000. They were in the wash tower, and that mattered, because taking a chimney apart during a breeding season would have broken  wildlife law  outright. The solution was a second tower. A crane supported structure went up with a purpose built nest box set at the same height as the birds were already using. It cost more than  135,000 dollars, a licensed consultant designed the move, and the falcons took it immediately. Three chicks fledged in the first season on the new perch, and more than a dozen young have come off it since.  The site’s own account  describes the arrangement, and  the restoration record  covers the concrete and the brick. What the stacks are, and what they are not Old structures rarely give ground easily, whether the trouble is  a concrete pour  or a  cavern underneath. These are not the original chimneys. Every ounce of concrete in them was mixed this century, and the steel inside is new. What survived is the geometry, the taper, the finish and the method, which is a real kind of authenticity and a narrower one than most visitors assume. One of the four now has a lift in it. The north west stack carries a glass car that takes people to a platform about 358 feet above the ground, which is the only way anybody sees the top of these things up close. The falcons still have the better address. They were there before the scheme, they are there after it, and the  chimney rebuild  worked around them rather than the other way about. Whether the next landmark gets the same treatment depends on whether anyone is  willing to pay  for a barrow instead of a pump.