Railway sleepers made of alkali activated fly ash concrete

Abstract

Nowadays, the tracks that comprise the world railway network are estimated to contain nearly three billion sleepers, over 400 million of which are made of concrete. At the same time, over 50% of the world demand for sleepers (around 20 million units per year) was for the concrete version; and between 2% and 5% of the concrete ties that are laid on tracks every year are to replace or renew worn elements. Concrete durability, however, depends on many factors. And in this context it should be noted that the characteristics of the in-plant industrial process involved in manufacturing precast concrete units differs in a number of ways from in situ construction, vesting these units with properties that distinguish them, in terms of durability, from in situ concrete under the conditions generally prevailing on construction sites. Generally speaking, it is widely admitted that the activation process of fly ashes allows obtaining a material with similar cementing features to those characterising Ordinary Portland Cement. Actually, the alkali activation of fly ashes is a singular procedure by which the powder originated in the power plants is mixed with certain alkaline dissolution and cured under a certain temperature to make solid materials. Contrary to conventional concrete, however, this new type of concrete can attain high strength over a very short time (1 day) and do develop excellent durability properties.