PRE-STRESSED CONCRETE RAILWAY SLEEPERS

Sleepers are members generally laid transverse to the rails on which the rails are supported and fixed, to transfer the loads from rails to the ballast and subgrade below. Sleepers perform the following functions:

i. To hold the rails to correct gauge (exact in straight and flat curves, loose in sharp curves and tight in diamond crossings).

ii. To hold the rails in proper level transverse tilt i.e., level in turnouts, crossovers, etc., and at 1 in 20 tilt in straight tracks, so as to provide a firm and even support to rails.

iii. To act as elastic medium in between the ballast and rails.

iv. To distribute the load from the rails to the index area of ballast underlying it or to the girders in case of bridges.

v. To support the rails at a proper level in straight tracks and at proper super elevation on curves.

vi. Sleepers also add to the longitudinal and lateral stability of the permanent track on the whole.

vii. They also provide means to rectify track geometry during service life.

For good performance of sleepers to fulfill the above functions or objectives an ideal sleeper should possess the following characteristics:

i. The sleepers to be used should be economical, i.e., they should have minimum possible initial and maintenance costs.

ii. The fittings of the sleepers should be such that they can be easily adjusted during maintenance operations such as easy lifting, packing, removal and replacement.

iii. The weight of sleepers should not be too heavy or excessively light, i.e., they should have moderate weight, for ease of handling.

iv. The design of sleepers should be such that the gauge, alignment of track and levels of the rails can be easily adjusted and maintained.

v. The bearing area of sleepers below the rail seat and over the ballast should be enough to resist the crushing due to rail seat and crushing of the ballast underneath the sleeper.

vi. The sleeper design should be such as to facilitate easy removal and replacement of ballast.

vii. The sleepers should be capable of resisting shocks and vibrations due to passage of heavy loads of high-speed limits.

viii. The design of the sleepers should be such that they are not damaged during packing processes.

ix. The insulation of rails should be possible for track circuiting, if required, through sleepers.

Prestressed concrete is the concrete in which permanent internal stresses are deliberately introduce, usually by tensioned steel, to counteract to the designed degree, the stresses caused in the member in service.

Pre-tensioning is the method of prestressing concrete in which the tenons are tensioned before concreting. Where as post-tensioning is the method of prestressing concrete in which prestressing steel is tensioned against the hardened concrete. Initial tension is the maximum stress induced in the prestressing tenon at the time of the stressing operation and initial prestress is the stress in the concrete at transfer. Although the first experiments were made in USA and the first patent for prestressed concrete was issued in 1988 for P.H. Jackson of Sanfransisco, it was developed in Europe. French, German & Danish engineers tried various ways of prestressing concrete, but none was successful till 1930 when in France, the high strength steel wire was used for prestressing concrete. After 1950s, actually, the prestressed concrete has found its major uses in fabricated constructions where it can be shop controlled & tested. Lift slab constructions were precast or cast on-site. Today it can be well seen that prestressed concrete is finding its varied uses in various types of constructions.

Prestressed concrete sleepers are now being increasingly used by most of the railways throughout the world in preference to timber ones because of scarcity of timber and the inherent technical advantages of concrete sleepers for use with long welded tracks carrying heavier axle loads and designed for greater speeds. The superior structural properties of concrete sleepers add considerably to the overall stability and better performance of the total track-structure. Concrete sleepers with their elastic fastenings also provide better safeguard for important track parameters, such as, gauge, cross levels form of twist, alignment etc. as compared to other types of sleepers. Of the several types of concrete sleepers in use, survey indicates that a majority of them, as much as 70% are monoblock prestressed concrete sleepers. Till today, more than 120 million of these type of concrete sleepers have been load on the track all over the world. About 15 million prestrressed concrete sleepers are produced per annum by the various railways of the world out of which pretensioned sleepers alone account for over 70%.

INTRODUCTION
CLASSIFICATIONS OF SLEEPERS
DESIGN CONSIDERATION FOR PRESTRESSED CONCRETE SLEEPERS
USES AND APPLICATION
B.I.S. SPECIFICATION
RAW MATERIALS
REVERSE BEND TEST
CONSTIUENTS OF CONCRETE
GENERAL PRINCIPLES OF MIX DESIGNS
DESIGN OF HIGH STRENGTH CONCRETE
REQUIREMENTS FOR PLAIN AND REINFORCED CONCRETE EXPOSED
TO SULPHATE ATTACK
MINIMUM CEMENT CONTENT REQUIRED IN CEMENT CONCRETE TO ENSURE DURABILITY UNDER SPECIFIED CONDITIONS OF EXPOSURE FOR
PRESTRESSED CONCRETE
MODERN DEVELOPMENTS IN THE DESIGN & CONSTRUCTION ASPECTS
DESIGN CONSIDERATIONS FOR PCC SLEEPERS
SALIENT FEATURES OF PCC SLEEPERS
SLEEPER DENSITY
MARKET SURVEY
PRESENT MANUFACTURERS OF PRESTRESSED CONCRETE RAILWAY SLEEPERS
PROCESS WISE EQUIPMENT DESCRIPTIONS
PRESTRESSING APPARATUS
APPARATUS FOR TESTING
METHODS OF MANUFACTURE AND TESTS FOR ACCEPTANCE
MANUFACTURING PROCESS
TESTING ARRANGEMENT FOR STATIC BENING STRENGTH TEST
FOR PRESTRESSED MONOBLOCK CONCRETE SLEEPERS FOR BG AND MG
DETAILED PROCESS OF PRESTRESSED RAILWAY CONCRETE SLEEPERS
PROCESS FLOW DIAGRAM
PLANT LAYOUT
SUPPLIERS OF RAW MATERIALS
SUPPLIERS OF PLANT & MACHINERY (GLOBAL)
SUPPLIERS OF PLANT & MACHINERY
PROJECT ECONOMICS
BASIS FOR RAW MATERIAL COMPUTATIONS

APPENDIX – A :

1. COST OF PLANT ECONOMICS
2. LAND & BUILDING
3. PLANT AND MACHINERY
4. FIXED CAPITAL INVESTMENT
5. RAW MATERIAL
6. SALARY AND WAGES
7. UTILITIES AND OVERHEADS
8. TOTAL WORKING CAPITAL
9. COST OF PRODUCTION
10. PROFITABILITY ANALYSIS
11. BREAK EVEN POINT
12. RESOURCES OF FINANCE
13. INTEREST CHART
14. DEPRECIATION CHART
15. CASH FLOW STATEMENT
16. PROJECTED BALANCE SHEET