Properties and behaviour of structural lightweight (Lytag-sand) concrete

Lytag is a synthetic lightweight aggregate which has been in commercial production for many years. Its production process involves sintering pulverised fuel ash at approximately 1200-1300°C to produce spherical, chemically inert pellets with a porous structure, which is graded into coarse, medium and fine grades. Concrete, produced with Lytag coarse and fine material, has been extensively studied to assess its basic material and structural properties. Few data, however, are available on concrete made with Lytag coarse material and natural sand fines. The aims of this investigation were basically two-fold. Firstly the material properties of Lytag-sand concrete were investigated and an extensive study of various properties such as strength, moduli of elasticity, Poisson's ratio, stress-strain characteristics, shrinkage, moisture movement and creep are reported. Secondly, the structural behaviour of reinforced Lytag-sand concrete T-beams failing in shear and flexure was also investigated. As with all concretes, these properties are affected by the constituents which make up the concrete, in particular the aggregate. With this in mind microscopic examination of several Lytag pellets was carried out using a scanning electron microscope (S. E. M. ) in order to observe some of the physical characteristics of Lytag aggregates in general. An attempt was then made to relate these characteristics to the water absorption of Lytag aggregates. The test results show that concrete strengths of 60 N/mm2 are easily obtainable using Lytag and sand, and that in general a lower cement content is required for Lytag-sand, than for other sand replaced lightweight concretes, in order to achieve a given compressive strength. Shrinkage and creep are comparable with the range of values obtained for concretes made with various dense aggregates but when compared to concretes made with good quality dense aggregates values of the order of 1.5 times the dense concrete values are to be expected.