The former RIBA president marvels at majestic brute power, gravity-defying lightness and the poetic economy of form.

I’ve always been fascinated by the two extremes of concrete. On the one hand, its sheer brute power, unmatched by any other material, and perhaps best epitomised by the Nazi U-Boat pens on the French Atlantic coast – built to withstand bombs and still indestructible today. On the other hand, it can be used to create structures of such lightness that they seem to be floating. I have always loved this poetic economy, and it holds valuable lessons when we need to find less carbon-intensive ways of building.

My first choice is one of the most monumental concrete structures ever built, but also a precursor to some of the lighter and more poetic. The Hoover Dam is a classic example of the material at its most primeval and powerful, built to hold back the full force of the Colorado River. The sheer quantity of concrete used is staggering: three million m3, enough to make a slab 1km by 1km and as high as a house.

The aim wasn’t primarily aesthetic, but architects were bowled over by the way concrete could create this sweeping monolithic surface – industrial but on a geological scale. It showed how it could work in combination with form, weather and light to spellbinding effect.

At the Salk Institute, the research laboratory set on a bluff overlooking the Pacific in La Jolla, California, Louis Kahn’s use of concrete is more consciously aesthetic, but it speaks to the surface and finish of the Hoover Dam. The pozzolanic mix has a warmth and smoothness to it, with the colour and texture changing subtly in different lights. Salk has a mysterious primal quality that only great architecture can produce: that ability to bring sky and Earth together in a particular way that we humans find awe-inspiring.

The Hoover Dam’s beauty also lies in its geometric clarity, with a form derived entirely from engineering logic – a horizontal arch locked into the sides of the canyon by the weight of the water. I studied engineering before changing to architecture, and I still love the idea of finding poetry in the purity in the logic of structure. It’s there in the shape of power station cooling towers too.

The hyperboloid gives these structures their strength, allowing for very thin, structurally economic walls. It also creates an iconic silhouette, as well as a majestic space inside – a direct inspiration, as it happens, for Corbusier’s Palace of the Assembly in Chandigardh. There were once 240 cooling towers in the UK, but now only 37 remain. It would be a terrible shame if they were all to disappear.

The most poetic of all engineers of concrete was perhaps Félix Candela. His concrete shells are just astonishing. When you look at a building like the Los Manantiales restaurant in Mexico City, it’s hard to believe that it’s the same material as the U-Boat bunkers. The shell, comprising four intersecting hyperbolic paraboloids, is only 40mm thick. It’s mind-blowing. And it has lasted – the restaurant is still in use today, 70 years after it was built.

As a practice, we have worked with structural engineer Webb Yates, exploring methods for reducing carbon with composite timber and concrete structures. In its structure for the Solera factory in Valencia, designed by Fernando Olba, the composite is with steel, though not in the familiar prestressed or post-tensioned form where the steel is hidden.

As well as creating the floor plate, 150mm-deep hollowcore concrete planks with a 100mm topping act as the compressive top chord of a truss carrying a massive factory floor load, with exposed steel underneath taking the tension. The approach reduced the amount of steel by 30% and concrete by 50%, and has lent a humble electrical components factory a delicate sort of grandeur. 

Sunand Prasad is principal at Perkins & Will, co-founder of Penoyre & Prasad, and a former RIBA president.

Photos Ron Buskirk, Alamy Stock Photo David Cornelius, Simon Webster, Photos: Fernando Olba; via rkett.info