I write in response to the article regarding the gravity platform being constructed for Amerada Hess by Taylor Woodrow (NCE Concrete Engineering supplement, 5 November). The article is somewhat misleading. Reference is made to the use of 10mm-12mm Lytag, whereas the grade used was 4mm-12mm conforming to BS3797.
The article also stated that concrete used for the roof and tower was lighter and cheaper than the concrete produced using Lytag. At least this is half-right, it was lighter! This is not surprising, as the medium density wall concrete also contained a proportion of normal weight aggregate. However, as for the roof cement being cheaper, it is our understanding from Taylor Woodrow that this is incorrect.
Lytag concrete is normally produced with a density around 1,800kg/m3 and strengths of 20N/mm2 -50N/mm2 when using a BS882 sand. To achieve even lower densities it would be necessary to use Lytag fines as well as coarse, as used by Taylor Woodrow in its Concrete Society Award winning oil storage platform for the Harding field.
Finally, contrary to the inference in the article, it is not only possible, but in fact normal practice to pump Lytag concrete, as indeed it was by Taylor Woodrow in this case. The expertise gained over nearly a quarter of a century, and the unique characteristics of a sintered PFA aggregate, combine to give Lytag distinct advantages when placing lightweight concrete by pump is the preferred option.
Andrew Doel, sales manager, Lytag, Ash Resources, West Burton, Retford, Nottinghamshire DN22 9BL.