“Their ideas are expressed in cyclopean reinforced concrete forms, massive far beyond utility (and indeed the flats were never meant to be cheap).”
The Buildings of England” Nikolaus Pevsner and Simon Bradley
The buildings are constructed of reinforced concrete for the most part, but there are some areas where pre-stressed concrete was needed.
The terrace buildings have a simple structure of reinforced-concrete load-bearing cross-walls and floor slabs. The use of cross-walls simplified the construction work. A cross-wall forms an internal flat wall which needed painting but not plastering which was a further saving in time and cost. The junctions between walls and slabs provide the stiffness to ensure each block has longitudinal stability.
The tower blocks have an entirely different form of structure. Each block was formed of pre-cast structural reinforced concrete units which were designed to form framework round the outside face of the buildings.
This was the main structure; internal walls were to provide further secondary stability and some load bearing capacity.
The concrete throughout the estate was made with Pen Lee crushed granite, which Nikolaus Pevsner in “The Buildings of England” described as “used in tough masculine forms on a mighty scale”.
Two grades of structural concrete were used with 28-day cube strengths of 34 N/mm2 and 42 N/mm2. For the most part, all batching and mixing of concrete was carried out on site.
Work on the buildings began in 1963. The Barbican estate, as eventually built, employed concrete in a much more monumental way than was envisaged in the comparatively delicate designs in the 1959 Report. This was made possible by using in situ reinforced concrete as the method of construction. The opportunity was provided by the engineers’ adoption of deep beams spanning between wide-spaced cross-walls, which Chamberlin Powell & Bon exploited as a feature, particularly in the more exaggerated forms of the external balconies.