Compressive Strength of Concrete Testing

Overview of Compressive Strength of Concrete

• The purpose of the session is to determine the compressive strength of concrete using British Standard (BS) and American Society for Testing and Materials (ASTM) procedures.

Key Terminology

• Compression Test: determines the behavior of materials under crushing loads, recording deformation at various loads.
• Compressive Strength: the maximum stress a material can sustain under a crushing load, calculated by dividing the maximum load by the original cross-sectional area.
• Hardness: a measure of a material's resistance to localized plastic deformation, often reported as resistance to scratching or rebound of a projectile.

Background of Concrete Strength

• Concrete strength is considered its most valuable property, but other characteristics like durability, impermeability, and volume stability are also important.
• Strength depends on the physical structure of cement paste and the presence of flaws, discontinuities, and pores.
• Understanding the mechanics of fracture of concrete under stress is crucial to understand the influence of flaws on strength.

Destructive Testing (DT) vs Non-Destructive Testing (NDT)

• Destructive testing (DT) involves high cost, specially made specimens, and does not provide direct information about the concrete in actual structures.
• Non-Destructive Testing (NDT) does not impair the performance and appearance of structures, allows re-testing, and monitors changes with time.
• NDT measures other properties, and estimates strength by calibration.

Non-Destructive Testing (NDT) using Schmidt Hammer

• The Schmidt Hammer test is based on the principle that rebound of an elastic mass depends on the hardness of the surface.
• The test is sensitive to the presence of aggregate and voids underneath the plunger, requiring 10-12 readings over the area to be tested.

Equipment Needed

• Compression Testing Machine with sufficient capacity
• Vernier Caliper
• Schmidt (Rebound) Hammer
• Abrasive (Grinding) stone
• Concrete cube samples