Introduction

Tensile strength is the ability of a cement mortar or hardened cementitious material to resist cracking or failure when subjected to tension. Although concrete and cement-based materials are primarily designed to withstand compressive loads, their tensile strength plays an important role in evaluating material cohesion, crack resistance, and overall structural performance.

Tensile strength is also essential in estimating the behavior of concrete under:

• Shrinkage
• Temperature changes
• Flexure
• Dynamic loading

The property of tensile strength of concrete is not of much importance as usually concrete is subjected to compressive stresses. However, determination of tensile strength is important to have an idea about the cohesion between particles. Since tensile strength and compressive strength are closely related, the tensile strength test is used to supplement or estimate compressive behavior.

Test Procedure and Mechanism

In a tensile strength test, a standardized mortar briquette specimen is subjected to a uniaxial pulling force at a constant rate until failure. The specimen is gripped at one end and pulled with a constant strain rate.

Behavior during testing:

1. Elastic elongation phase – Initially, the specimen undergoes elastic deformation where stress is proportional to strain
2. Progressive deformation – Beyond the elastic limit, microcracking begins
3. Fracture – Eventually, the specimen fractures at its weakest cross-section

Based on the applied load at failure, the ultimate tensile stress is calculated using the equation:

σt = Pmax / A
          

Where:

• σt = Tensile strength (MPa or N/mm²)
• Pmax = Maximum load at failure (N)
• A = Minimum cross-sectional area of briquette specimen (mm²)

Objectives and Significance

The main aim of the tensile test is to determine the following properties of the material:

1. Modulus of elasticity – Stiffness of the material
2. Yield strength – Stress at which permanent deformation begins
3. Ultimate tensile strength – Maximum stress the material can withstand
4. Elongation till fracture – Ductility measurement
5. Reduction in area – Deformation characteristics after fracture

This test provides valuable insight into mechanical properties and fracture characteristics. The results are useful in:

• Predicting the cracking tendency of cement mortar
• Evaluating suitability for applications requiring better tensile resistance, such as:
  • Pavements
  • Repair works
  • Tile adhesives
  • Prestressed or composite constructions

APPARATUS

1. Weighing Devices
2. Glass Graduates
3. Briquette Moulds
4. Trowel
5. Storage Tank
6. Rammer
7. Testing Machine