Tensile Stress Under Restrained Shrinkage
(Ring Test — ASTM C1581)

Assessment of concrete cracking tendency under restrained shrinkage using the standard ring test — predicting age at first crack and cracking risk for high-performance and low shrinkage concrete.

Overview

What is the Tensile Stress Under Restrained Shrinkage?

The Restrained Shrinkage Ring Test casts a concrete annulus around a steel ring. As the concrete shrinks, the steel ring restrains it, inducing tensile stress. The test measures the age of first crack and strain development rate in the steel ring — providing the shrinkage cracking tendency under restrained conditions.

This test is critical for evaluating concrete mixes for bridge decks, parking structures and industrial floors where restrained shrinkage cracking is a durability concern. At Global Lab, ring tests are conducted alongside free shrinkage and autogenous shrinkage for a complete cracking risk profile.

Age of First Crack

Exact age at which concrete cracks under restraint — key cracking risk indicator.

ASTM C1581 Classification

High/moderate/low/negligible cracking risk classified.

Steel Ring Strain Measurement

Strain gauges on steel ring detect crack formation with high precision.

SCM & Admixture Comparison

Compares multiple mix options to select lowest cracking tendency.

NABL Certified Reports

All results on NABL-accredited letterhead per ASTM C1581.

Combined Shrinkage Package

Ring test + Autogenous + Drying shrinkage as complete cracking risk profile.

Test in Action

Tensile Stress Under Restrained Shrinkage — Site Images

Steel Ring Instrumented with Strain Gauges

Concrete Cast Around Ring in Controlled Environment

Strain Drop at Crack Formation Detected

Test Procedure

How the Tensile Stress Under Restrained Shrinkage is Conducted

1

Ring Formwork Setup

Steel ring (inner radius 152mm) instrumented with strain gauges. Outer formwork placed.
2

Concrete Casting

Concrete cast in annulus around steel ring. Surface sealed with aluminium tape.
3

Controlled Environment

Ring specimens stored at 23°C, 50% RH per ASTM C1581.
4

Strain Monitoring

Steel ring strain monitored continuously. Sudden drop indicates crack formation.
5

Analysis & Classification

Age of cracking and strain rate recorded. ASTM C1581 Table 1 classification applied. NABL report within 28 days.

Standards & Specifications

Applicable Test Standards

Standard	Title	Scope	Type
ASTM C1581	Standard Test Method for Determining Age at Cracking and Induced Tensile Stress Characteristics of Mortar and Concrete under Restrained Shrinkage	Ring Test	ASTM
AASHTO T334	Estimating the Cracking Tendency of Concrete	Cracking Tendency	AASHTO
ACI 231R	Report on Early-Age Cracking: Causes, Measurement, and Mitigation	Early Cracking	ACI
IS 516	Methods of Tests for Strength of Concrete	Concrete Testing	Indian Standard

Applications

Where is the CAPO Test Used?

Bridge deck concrete cracking tendency assessment before specification

Parking structure deck concrete selection for low cracking risk

HPC mix design optimisation for crack-resistant infrastructure concrete

Industrial floor concrete mix selection for minimal joint cracking

Shrinkage-compensating concrete and SRA admixture effectiveness evaluation

Research on fibre, SCM and admixture effects on restrained shrinkage cracking

Why Choose Global Lab

Our Advantages

NABL Accredited ReportsLegally valid ASTM C1581 cracking tendency certificates.

Continuous Strain MonitoringAutomated data logger detects cracking moment precisely.

ASTM ClassificationHigh/moderate/low/negligible cracking risk for design decisions.

Combined Shrinkage PackageRing + Autogenous + Drying shrinkage tested as a complete shrinkage study.

Pan-India CoverageTesting at all 7 NABL-accredited lab locations.

Mix Comparison ServiceMultiple concrete mixes tested in parallel for cracking risk ranking.

Tensile Stress Under Restrained Shrinkage(Ring Test — ASTM C1581)