Increasing train speeds, contemporary requirements for reduced track maintenance costs and extended track service lives required the development and use of reinforced concrete and prestressed concrete ties. Railway engineers began to use concrete for their bi-block and monoblock railway ties heavily, following the development of an understanding for design and performance of concrete structures, production of high strength steel wires and preferable economy of prefabricated mass production for reinforced and prestressed concrete structural elements following the first half of 20th Century.
Structural elements of a railway track such as reinforced or prestressed concrete ties have strict production tolerances that are not common for ordinary structural elements. Production of concrete railway ties takes place under strict dimensional control that ensures a nominal design gauge width for the railway track. Design specifications for prestressed monoblock ties frequently specify the gauge width and the shoulder width to be within 1 mm of the design width. However, prestressed concrete ties experience shortenings in length due to transfer of the prestressing force known as instant elastic shortening and shortenings due to concrete shrinkage and concrete creep in time that also relate to ambient relavite humidity.
The author conducted numerous studies on the matter, showed by calculation, and observed experimentally that if unaccounted for, such shortenings can surpass the allowed tolerances in time and result in the rejection of the produced tie for use in the railway track. This paper refers to previous studies by the author that brought international attention on the issue and presents a thorough and a practical evaluation of time related changes in tie lengths for a particular design for prestressed concrete monoblock ties under varying ambient humidity conditions.

Prestressing; railway ties; concrete; shrinkage; creep; elastic shortening; gauge width; shoulder width; production tolerances