ASTM A911/A911M-21

Standard Specification for Low-Relaxation Steel Bars for Prestressed Concrete Railroad Ties

ABSTRACT
This specification covers uncoated, stress-relieved steel bars for prestressed concrete railroad ties. Analysis of the steel shall conform to the chemical requirements specified by the specification. Mechanical requirements including test method, tensile strength, yield strength, elongation and wrapping test are provided. One test specimen each for the tensile test and the wrapping test shall be taken for every 10 coils or fraction thereof in a lot.
SCOPE
1.1 This specification covers low-relaxation steel bars for use in prestressed concrete railroad ties.  
1.2 This specification is applicable for orders in either inch-pounds units (as Specification A911) or in SI units (as Specification A911M).  
1.3 The values stated in either inch-pound units or SI units are to be regarded separately as standard. Within the text, the SI units are shown in brackets. The values stated in each system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from the two systems may result in non-conformance with the specification.  
1.4 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

General Information

• Status: Published
• Publication Date: 14-Apr-2021
• ICS: 77.140.15 - Steels for reinforcement of concrete
• Technical Committee: A01 - Steel, Stainless Steel and Related Alloys
• Drafting Committee: A01.05 - Steel Reinforcement

Relations

• Refers: ASTM A370-24 - Standard Test Methods and Definitions for Mechanical Testing of Steel Products
• Effective Date: 01-Mar-2024
• Refers: ASTM A370-19 - Standard Test Methods and Definitions for Mechanical Testing of Steel Products
• Effective Date: 01-Jul-2019
• Refers: ASTM A370-17a - Standard Test Methods and Definitions for Mechanical Testing of Steel Products
• Effective Date: 15-Nov-2017
• Refers: ASTM A370-17 - Standard Test Methods and Definitions for Mechanical Testing of Steel Products
• Effective Date: 01-Jan-2017
• Refers: ASTM A370-15 - Standard Test Methods and Definitions for Mechanical Testing of Steel Products
• Effective Date: 01-Nov-2015
• Refers: ASTM A370-14 - Standard Test Methods and Definitions for Mechanical Testing of Steel Products
• Effective Date: 15-May-2014
• Refers: ASTM A370-13 - Standard Test Methods and Definitions for Mechanical Testing of Steel Products
• Effective Date: 15-Nov-2013
• Refers: ASTM A370-12a - Standard Test Methods and Definitions for Mechanical Testing of Steel Products
• Effective Date: 15-Oct-2012
• Refers: ASTM A370-12 - Standard Test Methods and Definitions for Mechanical Testing of Steel Products
• Effective Date: 15-Mar-2012
• Refers: ASTM A370-11a - Standard Test Methods and Definitions for Mechanical Testing of Steel Products
• Effective Date: 15-Nov-2011
• Refers: ASTM A370-10 - Standard Test Methods and Definitions for Mechanical Testing of Steel Products
• Effective Date: 15-Jun-2010
• Refers: ASTM A370-09a - Standard Test Methods and Definitions for Mechanical Testing of Steel Products
• Effective Date: 01-Jun-2009
• Refers: ASTM A370-09ae1 - Standard Test Methods and Definitions for Mechanical Testing of Steel Products
• Effective Date: 01-Jun-2009
• Refers: ASTM A370-09 - Standard Test Methods and Definitions for Mechanical Testing of Steel Products
• Effective Date: 01-Jan-2009
• Refers: ASTM A370-08b - Standard Test Methods and Definitions for Mechanical Testing of Steel Products
• Effective Date: 15-Oct-2008

Overview

ASTM A911/A911M-21 is the standard specification for low-relaxation steel bars designed for use in prestressed concrete railroad ties. Developed by ASTM International, this standard details the chemical and mechanical requirements, testing methods, and quality assurance processes for the manufacture of steel bars that remain stable under stress over time. The purpose is to ensure the structural integrity and durability of prestressed concrete railroad ties, a critical component in modern railway infrastructure.

Covering both inch-pound and SI units, this international standard supports global supply chains and is aligned with the World Trade Organization’s Technical Barriers to Trade (TBT) principles. By adhering to ASTM A911/A911M-21, manufacturers and purchasers of steel bars ensure product consistency, high performance, and compliance with best practices in railway construction.

Key Topics

ASTM A911/A911M-21 addresses several essential areas for low-relaxation steel bars for prestressed concrete applications:

• Material Requirements

  • Specifies chemical composition ranges for elements such as carbon, silicon, manganese, chromium, phosphorus, sulfur, and copper.
  • Demands consistent chemical properties throughout each production lot.

• Mechanical Properties

  • Sets minimum values for yield strength (200 ksi [1375 MPa]) and tensile strength (228 ksi [1570 MPa]).
  • Includes requirements for elongation (at least 6%) and reduction of area (minimum 30%).
  • Mandates a wrapping test to ensure ductility and surface integrity.

• Testing and Quality Assurance

  • Requirements for sampling, testing frequency, and test methods (ASTM A370 and E328).
  • Lot-by-lot mechanical testing (one tensile and one wrapping specimen per 10 coils or fraction thereof).
  • Options for additional purchaser-specified testing, inspection, and reporting.

• Dimensions and Tolerances

  • Defines standard nominal diameters and permissible diameter variations.
  • Sets straightness and out-of-roundness limits for bars after uncoiling.

• Product Identification and Packing

  • Details proper marking, tagging, and packaging for traceability and safe handling.
  • Shipping and storage recommendations to prevent mechanical injury or corrosion.

Applications

The primary use of steel bars conforming to ASTM A911/A911M-21 is in the manufacturing of prestressed concrete railroad ties. These ties require high-strength, low-relaxation reinforcing steel to sustain heavy rail loads and resist long-term deformation.

Key application areas include:

• Railway Track Construction: Enhancing the durability and stiffness of rail support systems for both freight and passenger tracks.
• Track Renewal and Upgrading: Providing reliable replacement components that meet modern standards.
• Infrastructure Projects: Used in mass transit systems, high-speed rail lines, and other rail-related civil engineering works.

By specifying low-relaxation characteristics, the standard ensures that the steel maintains its prestressing force over decades of service, minimizing track maintenance and improving safety.

Related Standards

For comprehensive compliance and optimal performance, ASTM A911/A911M-21 references and is complemented by several related standards:

• ASTM A370: Test Methods and Definitions for Mechanical Testing of Steel Products
• ASTM E328: Test Methods for Stress Relaxation for Materials and Structures
• Fed. Std. No. 123: Marking for Shipments (Civil Agencies)
• MIL-STD-129: Marking for Shipment and Storage (Military Agencies)

Manufacturers, suppliers, and purchasers should familiarize themselves with these and other referenced documents to ensure full alignment and certification to industry expectations for steel bars used in prestressed concrete railroad ties.

Keywords: low-relaxation bars, prestressed concrete, railroad ties, steel bars, stress-relieved, ASTM A911, ASTM A911M, railway reinforcement, mechanical properties, international standard

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation:A911/A911M −21
Standard Specification for
Low-Relaxation Steel Bars for Prestressed Concrete
Railroad Ties
This standard is issued under the fixed designationA911/A911M; the number immediately following the designation indicates the year
of original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval.
A superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope* 3. Terminology
1.1 This specification covers low-relaxation steel bars for 3.1 Definition of Term Specific to This Specification:
use in prestressed concrete railroad ties. 3.1.1 lot, n—all the coils of bars of the same nominal bar
size contained on an individual shipping release or shipping
1.2 This specification is applicable for orders in either
order, from the same heat of steel.
inch-pounds units (as Specification A911) or in SI units (as
Specification A911M).
4. Ordering Information
1.3 The values stated in either inch-pound units or SI units
4.1 Orders for low-relaxation steel bars for prestressed
are to be regarded separately as standard. Within the text, the
concrete railroad ties under this specification shall contain the
SI units are shown in brackets. The values stated in each
following information:
system may not be exact equivalents; therefore, each system
4.1.1 Quantity (weight) [mass],
shall be used independently of the other. Combining values
4.1.2 Nominal diameter of bar (inches) [millimetres],
from the two systems may result in non-conformance with the
4.1.3 Core diameter and length of coils (15.1),
specification.
4.1.4 Packaging,
1.4 This international standard was developed in accor-
4.1.5 Supplementary Requirement S1 (if desired), and
dance with internationally recognized principles on standard-
4.1.6 ASTM designation (A911 [A911M]) and year of
ization established in the Decision on Principles for the
issue.
Development of International Standards, Guides and Recom-
4.2 Thepurchasershallhavetheoptiontospecifyadditional
mendations issued by the World Trade Organization Technical
requirements, including but not limited to, the following:
Barriers to Trade (TBT) Committee.
4.2.1 Prior relaxation tests of similarly-dimensioned bars
2. Referenced Documents
(7.6.3),
4.2.2 Inspection and witnessing of testing (Section 12),
2.1 ASTM Standards:
4.2.3 Load-elongation curves for each test (14.2),
A370 Test Methods and Definitions for Mechanical Testing
4.2.4 Special packaging and marking (Section 15), and
of Steel Products
4.2.5 Other special requirements, if any.
E328 Test Methods for Stress Relaxation for Materials and
Structures
5. Manufacture
2.2 Federal Standard:
Fed. Std. No. 123 Marking for Shipments (Civil Agencies)
5.1 The bars shall be made from properly identified heats of
2.3 Military Standards:
steel made by the electric-furnace, the basic-oxygen, or other
MIL-STD-129 Marking for Shipment and Storage
commercially accepted steelmaking process.
5.2 After hot-rolling, the bars shall be cold-drawn and
1 finally stress-relieved by induction heat treatment to produce
This specification is under the jurisdiction of ASTM Committee A01 on Steel,
Stainless Steel and Related Alloys and is the direct responsibility of Subcommittee
the desired mechanical properties and then coiled.
A01.05 on Steel Reinforcement.
Current edition approved April 15, 2021. Published May 2021. Originally
6. Chemical Requirements
published in 1992. Last previous edition approved in 2015 as A911/A911M – 15.
DOI: 10.1520/A0911_A0911M-21.
6.1 An analysis of each heat of steel shall be made by the
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
manufacturer from test samples taken during the pouring of
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on each heat.
the ASTM website.
6.2 The analysis of the steel shall conform to the chemical
Available from DLA Document Services, Building 4/D, 700 Robbins Ave.,
Philadelphia, PA 19111-5094, http://quicksearch.dla.mil. requirements specified in Table 1.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
A911/A911M−21
TABLE 1 Chemical Requirements
7.6.3 If required in the purchase order, relaxation evidence
Element Composition, % shall be provided from the manufacturer’s records of tests on
A
Carbon 0.70–0.90 similarly dimensioned bars.
Silicon 0.10–0.35
7.6.4 The test specimen shall not be subjected to loading
B
Manganese 0.50–0.90
prior to the relaxation test. The temperature of the test
Chromium, max 0.15
Phosphorus, max 0.030 specimen shall be maintained at 68 6 3.5°F [20 6 2°C]. The
Sulphur, max 0.035
test gauge length shall be at least 40 times the nominal
Copper, max 0.30
diameter.
A
Carbon in any one lot shall not vary more than 0.13 %.
7.6.5 The initial load shall be applied uniformly over a
B
Manganese in any one lot shall not vary more than 0.30 %.
period of not less than 3 minutes and not more than 5 minutes,
and the gauge length shall be maintained constant; load-
relaxation readings shall commence 1 minute after application
TABLE 2 Mechanical Requirements
of the total load.
Yield strength, min 200 ksi [1375 MPa]
Tensile strength, min 228 ksi [1570 MPa]
7.6.6 Overstressing of the test specimen by application of
Ratio of yield strength to tensile strength, max 0.95
loads beyond the limits stated in Table 3 during the loading
Elongation after rupture in a gauge length of 4 in. 6.0 %
operation shall not be permitted.
[100 mm], min
Reduction of area, min 30.0 %
8. Dimensions and Permissible Variations
8.1 The size of the finished bar shall be expressed as the
TABLE 3 Relaxation Requirements
nominal diameter of the bar in decimals of an inch [millime-
A
f /f Max Stress Losses after 1000 h, %
pi pu tre]. The required initial diameters before cold-drawing, and
0.50 1.0
the final diameters after cold-drawing shall be as follows:
0.60 1.0
Initial Diameter Final Diameter
0.70 2.5
0.591 in. [15 mm] 0.370 in. [9.4 mm]
0.80 5.0
0.614 in. [15.6 mm] 0.394 in. [10 mm]
A
f = initial prestress load, and
pi
0.654 in. [16.6 mm] 0.413 in. [10.5 mm]
f = specified minimum tensile strength.
pu
8.2 Permissible Variations in Diameter:
8.2.1 All bars shall conform to a size tolerance of
60.002 in. [60.05 mm] from the nominal diameter.
8.3 Out-of-Round—The difference between the largest and
7. Mechanical Property Requirements
smallest diameter, measured at the same section, shall not be
greater than 0.002 in. [0.05 mm].
7.1 Test Method—Tests shall be made in accordance with
Test Methods and Definitions A370, including Annex A4,
9. Workmanship, Finish, and Appearance
using full-size bar specimens taken from either end of the coil
9.1 Joints:
of the finished product.
9.1.1 There shall be no welds or joints in the finished bar.
7.2 Tensile Strength—The minimum tensile stre
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: A911/A911M − 15 A911/A911M − 21
Standard Specification for
Low-Relaxation Steel Bars for Prestressed Concrete
Railroad Ties
This standard is issued under the fixed designation A911/A911M; the number immediately following the designation indicates the year
of original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval.
A superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope*
1.1 This specification covers low-relaxation steel bars for use in prestressed concrete railroad ties.
1.2 This specification is applicable for orders in either inch-pounds units (as Specification A911) or in SI units (as Specification
A911M).
1.3 The values stated in either inch-pound units or SI units are to be regarded separately as standard. Within the text, the SI units
are shown in brackets. The values stated in each system may not be exact equivalents; therefore, each system shall be used
independently of the other. Combining values from the two systems may result in non-conformance with the specification.
1.4 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
A370 Test Methods and Definitions for Mechanical Testing of Steel Products
E328 Test Methods for Stress Relaxation for Materials and Structures
2.2 Federal Standard:
Fed. Std. No. 123 Marking for Shipments (Civil Agencies)
2.3 Military Standards:
MIL-STD-129 Marking for Shipment and Storage
3. Terminology
3.1 Definition of Term Specific to This Specification:
3.1.1 lot, n—all the coils of bars of the same nominal bar size contained on an individual shipping release or shipping order, from
the same heat of steel.
This specification is under the jurisdiction of ASTM Committee A01 on Steel, Stainless Steel and Related Alloys and is the direct responsibility of Subcommittee A01.05
on Steel Reinforcement.
Current edition approved Nov. 1, 2015April 15, 2021. Published January 2016May 2021. Originally published in 1992. Last previous edition approved in 20112015 as
A911/A911M – 11.A911/A911M – 15. DOI: 10.1520/A0911_A0911M-15.10.1520/A0911_A0911M-21.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Available from Standardization Documents Order Desk, DODSSP, Bldg. 4, Section D, DLA Document Services, Building 4/D, 700 Robbins Ave., Philadelphia, PA
19111-5098, http://dodssp.daps.dla.mil.19111-5094, http://quicksearch.dla.mil.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
A911/A911M − 21
4. Ordering Information
4.1 Orders for low-relaxation steel bars for prestressed concrete railroad ties under this specification shall contain the following
information:
4.1.1 Quantity (weight) [mass],
4.1.2 Nominal diameter of bar (inches) [millimetres],
4.1.3 Core diameter and length of coils (15.1),
4.1.4 Packaging,
4.1.5 Supplementary Requirement S1 (if desired), and
4.1.6 ASTM designation (A911 [A911M]) and year of issue.
4.2 The purchaser shall have the option to specify additional requirements, including but not limited to, the following:
4.2.1 Prior relaxation tests of similarly-dimensioned bars (7.6.3),
4.2.2 Inspection and witnessing of testing (Section 12),
4.2.3 Load-elongation curves for each test (14.2),
4.2.4 Special packaging and marking (Section 15), and
4.2.5 Other special requirements, if any.
5. Manufacture
5.1 The bars shall be made from properly identified heats of steel made by the electric-furnace, the basic-oxygen, or other
commercially accepted steelmaking process.
5.2 After hot-rolling, the bars shall be cold-drawn and finally stress-relieved by induction heat treatment to produce the desired
mechanical properties and then coiled.
6. Chemical Requirements
6.1 An analysis of each heat of steel shall be made by the manufacturer from test samples taken during the pouring of each heat.
6.2 The analysis of the steel shall conform to the chemical requirements specified in Table 1.
7. Mechanical Property Requirements
7.1 Test Method—Tests shall be made in accordance with Test Methods and Definitions A370, including Annex A4, using full-size
bar specimens taken from either end of the coil of the finished product.
TABLE 1 Chemical Requirements
Element Composition, %
A
Carbon 0.70–0.90
Silicon 0.10–0.35
B
Manganese 0.50–0.90
Chromium, max 0.15
Phosphorus, max 0.030
Sulphur, max 0.035
Copper, max 0.30
A
Carbon in any one lot shall not vary more than 0.13 %.
B
Manganese in any one lot shall not vary more than 0.30 %.
A911/A911M − 21
TABLE 2 Mechanical Requirements
Yield strength, min 200 ksi [1375 MPa]
Tensile strength, min 228 ksi [1570 MPa]
Ratio of yield strength to tensile strength, max 0.95
Elongation after rupture in a gage length of 4 in. 6.0 %
[100 mm], min
Elongation after rupture in a gauge length of 4 in. 6.0 %
[100 mm], min
Reduction of area, min 30.0 %
TABLE 3 Relaxation Requirements
A
f /f Max Stress Losses after 1000 h, %
pi pu
0.50 1.0
0.60 1.0
0.70 2.5
0.80 5.0
A
f = initial prestress load, and
pi
f = specified minimum tensile strength.
pu
7.2 Tensile Strength—The minimum tensile strength of the finished bar, as represented by test specimens, shall conform to the
requirements prescribed in Table 2.
7.3 Yield Strength—Yield strength shall be measured at 1 % extension under load. The load at this extension is recorded as yield
strength and shall meet the requirements of Table 2.
7.4 Elongation—The total elongation after rupture shall not be less than 6.0 % and shall be measured in a gagegauge length of
4 in. [100 mm].
7.5 Wrapping Test—Bars shall withstand being wound around a mandrel with a diameter of five times the bar diameter without
cracking or other surface defects occurring on the outside of the bent portion. The bar shall be bent around the mandrel 1- ⁄2 turns
beginning with a 90° bend.
7.6 Low-Relaxation Text—Bars shall be tested as prescribed in Test Methods E328.
7.6.1 Low-relaxation bars shall meet the mechanical property requirements of this specification, with the added requirements listed
in Table 3.
7.6.2 Yield strength of low-relaxation bars, as described in 7.3, shall not be less than 90 % of the specified minimum tensile
strength of the bar.
7.6.3 If required in the purchase order, relaxation evidence shall be provided from the manufacturer’s records of tests on similarly
dimensioned bars.
7.6.4 The test specimen shall not be subjected to loading prior to the relaxation test. The temperature of the test specimen shall
be maintained at 68 6 3.5°F [20 6 2°C]. The test gagegauge length shall be at least 40 times the nominal diameter.
7.6.5 The initial load shall be applied uniformly over a period of not less than 3 minutes and not more than 5 minutes, and the
gagegauge length shall be maintained constant; load-relaxation readings shall commence 1 minute after application of the total
load.
7.6.6 Overstressing of the test specimen by application of loads beyond th
...