Concrete and Bitumen Properties in Construction

Posted on May 26, 2024 in Geology

Concrete Properties

Numbness

Numbness is the increase in the volume of sand or concrete over time due to water absorption. It is greater with finer sand or cement particles.

Table of Shock

This test measures the increase in diameter of a truncated cone’s lower base when subjected to 15 shocks (12 mm high for 15 seconds). The consistency index determines the following:

  • 0-30: Dry
  • 30-50: Plastic
  • 50-70: Soft
  • 70-100: Fluid
  • >100: Liquid

Consistometer of Vebe

Useful for very dry or fiber-reinforced concrete, this test measures the time for a truncated cone (Abrams) to deform under vibration. It provides an idea of workability:

  • 30-18 seconds: Extremely dry
  • 18-10 seconds: Very dry
  • 10-5 seconds: Dry
  • <3 seconds: Not recommended

Segregation

Segregation occurs when mixtures separate, particularly with very fluid mixes, high sand content, or improper handling. It can be avoided by:

  • Proper aggregate grading
  • Careful concrete management
  • Using air-entraining additives and fly ash
  • Avoiding excessive vibration
  • Using aggregates with similar densities

Exudation

Exudation, a form of segregation, happens when water rises to the surface. This can lead to plastic shrinkage cracks, compromising impermeability and frost resistance. Factors influencing exudation include:

  • Cement fineness
  • Tricalcium aluminate content
  • Fly ash and air-entraining agents (create stabilizing bubbles)

Concrete with good cohesion resists segregation and bleeding.

Indirect Tensile Strength Test (Brazilian Test)

This test involves compressing cylindrical concrete specimens until they break along a diametral plane. The load is applied at 1.5 N/mm2. Pure tensile strength is approximately 85% of the indirect tensile strength.

Flexural Test

This test measures the flexural strength of concrete by applying a load at 1.6 N/mm2 per minute on two rollers positioned at 1/3 of the specimen’s length. The specimen breaks at the weakest point under maximum bending moment. The indirect tensile test result is typically 45% lower than the flexural strength.

Elongation

Elongation refers to concrete’s ability to withstand stretching without breaking. It depends on the paste’s ductility and its bond with aggregates. Stronger concrete generally exhibits less elongation.

Concrete Specification

A concrete specification should include:

  • Characteristic strength
  • Cement content per m3
  • Cement type, kind, and brand
  • Maximum aggregate size
  • Consistency and aggregate-cement ratio (a/c)
  • Type and amount of additives (if any)

Steel Tension Chart Deformation

A steel tension chart illustrates the relationship between stress and strain. Key points include:

  • Proportional Limit: Stress at which deformation ceases to be proportional to the load.
  • Elastic Limit: Maximum stress a material can withstand without permanent deformation.
  • Yield Strength: Stress causing a 0.2% permanent deformation.
  • Yield Point: Point where stress remains constant or decreases slightly while strain continues to increase.
  • Ultimate Tensile Strength: Maximum stress a material can withstand before breaking.
  • Breaking Stress: Stress at which the material fractures.

Material Properties

  • Elasticity: Ability to return to original shape after removing the deforming force.
  • Plasticity: Ability to deform permanently under stress.
  • Ductility: Ability to be drawn into wires under tension.
  • Malleability: Ability to be hammered or rolled into thin sheets under compression.
  • Strain Hardening: Increase in strength and hardness due to deformation.
  • Brittleness: Tendency to fracture with little or no plastic deformation.
  • Hardness: Resistance to indentation or scratching.

Bituminous Materials

Bitumen

Bitumen is a mixture of natural or pyrogenic hydrocarbons, ranging from liquid to solid forms.

Tar

Tar is produced by the destructive distillation of organic materials like coal, shale, or wood.

Bituminous Material Properties

Viscosity

Viscosity measures resistance to flow. It affects workability, adhesion, and dosage. Bitumen viscosity is determined by the time it takes to flow through an orifice. Tar viscosity is measured using the EVT (Equi-Viscous Temperature) method.

Consistency-Penetration

This test measures the penetration depth of a needle into the material. Penetration decreases with increasing density and viscosity.

Thermal Sensitivity (Softening Point)

This property describes how viscosity changes with temperature. The softening point is the temperature at which the material becomes soft enough for a steel ball to penetrate.

Ductility

Ductility measures the ability to deform under tension without cracking. It is determined by the elongation of a specimen at 25°C and a speed of 5 cm/min.

Brittleness

Brittleness refers to the loss of ductility at low temperatures.

Binder-Aggregate Adhesion

, is a chemical bond and ionic bonding due to the humidity of the aggregates, such as bitumen to a rejection has better adhesion with the siliceous calcareous.