For slender cylinders, as the height to lateral dimension ratio of the concrete specimen increases, the compressive strength:

Explanation:

• When testing concrete specimens for compressive strength, the height-to-lateral dimension ratio (also known as slenderness ratio) plays a significant role in how the material behaves under load.

• Shorter, stubby specimens (low height-to-diameter ratio) experience greater lateral confinement due to friction at the loading platens.

• This confinement increases the apparent strength as it resists lateral expansion.

• As the height increases relative to the diameter, the confining effect reduces.

• This leads to a more uniform stress distribution but less lateral restraint, causing the measured compressive strength to drop.

• Slender specimens are more prone to column-like failure (buckling or instability) rather than pure crushing.

• This changes the failure behavior and reduces the load-carrying capacity under compression.

• The standard height-to-diameter ratio used in most concrete compressive tests is 2:1.

• Deviating significantly from this ratio (especially increasing it) may result in underestimating the actual compressive strength of the concrete.

Additional Information

• Compressive strength is the maximum load per unit area that concrete can bear without failure when subjected to axial compression.

• It is considered the most essential mechanical property of concrete, as concrete is primarily used to resist compression rather than tension.

• This property helps engineers design structural elements like columns, beams, slabs, and footings safely and economically.

• The standard test is conducted by casting cylindrical or cubical concrete specimens, typically 150 mm × 150 mm × 150 mm cubes or 150 mm diameter × 300 mm height cylinders.

• These are cured under controlled conditions (usually 28 days) before testing.

• The specimen is placed in a compression testing machine, and the load is applied until failure.