Project Details
As part of a pre-acquisition survey of a 7 storey office block in central London, through a suite of routine sampling and testing of the concrete frame, OSC identified that all suspended floors comprised HAC pre-stressed concrete beam elements, topped with an in-situ concrete slab.
High-Alumina Cement Concrete loses strength with time due to a process known as conversion. This process, when fully complete, reduces the compressive strength of the concrete from typically 50N/mm2 by more than half, to a generally accepted assumed strength of 21 N/mm2. This strength loss resulted in a number of high-profile collapses of floors and roofs in the 1970s, which led to HAC effectively being banned from new construction.
OSC assisted our Client in establishing the extent that HAC was used in the construction of the slabs, before establishing the beam and slab construction details, sufficiently to enable our engineers to assess the residual capacity of the slabs to identify areas that required strengthening to restore capacity to the structure.
