Term: Properties of concrete
**Mechanical Properties of Concrete:**
– Concrete has high compressive strength but low tensile strength.
– Reinforcement is essential for concrete elements under tensile stresses.
– Elasticity of concrete decreases at higher stress levels due to matrix cracking.
– Factors influencing ultimate strength include water-cementitious ratio and design constituents.
– Modulus of elasticity of concrete is influenced by aggregates and cement matrix proportions.
– Compressive strength is a key parameter for specification and quality control.
**Thermal Properties of Concrete:**
– Concrete has a low coefficient of thermal expansion.
– Lack of provision for expansion can lead to cracks in concrete structures.
– Moderate thermal conductivity compared to metals and is used for fireproofing steel structures.
– High temperatures can induce chemical changes in concrete, causing structural damage.
**Expansion and Shrinkage in Concrete:**
– Concrete has a very low coefficient of thermal expansion.
– Lack of provision for expansion can lead to cracks in the structure.
– Shrinkage cracks occur due to restrained volumetric changes in concrete members.
– Repeated cycles of expansion and contraction can lead to cracks.
– Shrinkage cracking has a minor structural impact.
**Creep and Water Retention in Concrete:**
– Creep is a permanent material movement to relieve stresses in concrete.
– Concrete under long-duration forces is prone to creep.
– Water retention properties vary among different types of concrete.
– Pervious concrete allows water to pass through, eliminating the need for storm drains.
**Concrete Testing and Other Properties:**
– Engineers specify compressive strength of concrete using tests.
– Early strength tests can predict ultimate compressive strength.
– Physical changes in concrete occur at elevated temperatures.
– Spalling in concrete at high temperatures is driven by vapor pressure and thermal stresses.
– Segregation in concrete and creep and shrinkage are additional considerations in concrete applications.
Concrete has relatively high compressive strength (resistance to breaking when squeezed), but significantly lower tensile strength (resistance to breaking when pulled apart). The compressive strength is typically controlled with the ratio of water to cement when forming the concrete, and tensile strength is increased by additives, typically steel, to create reinforced concrete. In other words we can say concrete is made up of sand (which is a fine aggregate), ballast (which is a coarse aggregate), cement (can be referred to as a binder) and water (which is an additive).