Page 17 - ICJ Jan 2023

TECHNICAL PAPER COLLECTOR’S EDITION

At first glance concrete seems an unsuitable
material for railway sleepers. It lacks the elasticity of
wood, its tensile qualities differ from those of steel.
When steel and concrete are used for building it is
the steel reinforcement that takes the strain. The
weight of a fast-running and heavily-loaded train
presents, however, quite a different problem from
the static height of a building.

With ordinary reinforced concrete, when subjected
to tension under bending loads, small hair cracks
develop, and although this is not considered
harmful for ordinary reinforced-concrete
structures, it is harmful in the case of railway
sleepers for main lines, as the heavy and repeated
loads will cause these cracks to widen and finally to
destroy the bond between the steel reinforcement
and the concrete. This damage is accelerated by
rain and frost.
The Batch Concrete mixing plant incorporates the
A RECENT INNOVATION
latest equipment for correct proportioning of materials
Pre-stressed concrete is a comparatively recent required.
innovation in standard engineering practice in
this country. In its production a high-tensile steel
of 100 tons per sq. in. ultimate tensile strength rail it supports, thus reducing track maintenance to
is used for the reinforcement, and during the a minimum. By pre-stressing the concrete, surface-
process of manufacture it is subjected to a high- damage to the sleeper under load conditions is
tensile stress which is afterwards used to obtain a avoided.
permanent compressive stress in the concrete. The
initial compression in the concrete ensures that In 1941 permission was given to construct
no hair cracks will develop under the design load an experimental yard at Colwall, Malvern,
conditions and the factor of safety allowed. Worcestershire, to manufacture a type of concrete
sleeper introducing the new technique of pre-
The amount and distribution of compression in stressing. Prestressed concrete sleepers made
the concrete is determined from the load factors in this experimental yard were first supplied to
to which the sleepers are to be subjected. The the Ministry of Works for use on sidings, and
criterion of a perfect sleeper requires the condition the sleepers’ performance was kept under close
that the life of the sleeper is equal to the life of the observation.

18 The Indian Concrete Journal | November 2018