To determine the unit weight of hardened concrete and the water absorption of hardened concrete

Object: To determine the unit weight of hardened concrete.

Code:

ACI ASTM C138.

Apparatus:

• Cylindrical mold
  
• weight machine,scale.
  

Theory:

Unit weight is the weight per unit volume of a material. It is usually measured in Unit weight of concrete is used to determine bulk density values used in selecting proportions for concrete mixes. Itis influenced by specific gravity, water content, air content, proportions of ingredients, w/c ratio.Change in density of concrete effect pumpability, placeability, finishability and strength of all types of concrete.

The unit weight is a useful tool in determining the concrete batch yield and air content. Since air adds no weight to the concrete and only occupies a volume, the unit weight of a concrete gives a very good indication of the air content of the concrete.

Unit weight =

Unit weight =

W= weight of hard concrete

V = volume of concrete sample

Volume of cylinder = (cft)

Procedure:

• Find the mass of the cylinder and cubes.
  
• Find the volume of cylinder and cubes by there lateral dimensions.
  
• Now calculate the unit weight by dividing the weight of concrete by its volume.
  

Calculation:

Result:

The unit weight of fresh concrete is found to be .

Object: To Determine the Water Absorption of Hardened Concrete

Standard code:

ASTM C1585 – 13

Apparatus:

• Oven,
  
• trowels,
  
• weight balance.
  

Materials:

• Cement,
  
• fine aggregate,
  
• coarse aggregate,
  
• water.
  

Theory:

Durability of concrete plays a critical role in controlling its serviceability. Furthermore, durability of concrete is mainly dependent on the capacity of a fluid to penetrate the concrete’s microstructure, which was called permeability. High permeability led to the introduction of molecules that react and destroy its chemical stability. Moreover, low permeability of concrete can improve resistance to the penetration of water, chloride ions, and other harmful substances which caused chemical attack. Concrete permeability had a close relationship with the characteristics of its pore structure in the cement paste and the intensity of micro cracks at the aggregate-cement paste interface as well as within the paste itself.

So depending upon the percentage of absorbed water percentage we determine its durability and accordingly recommend the concrete for the usage in the site

Procedure:

• Dry the specimen in a ventilated oven at a temperature of 105 °C to 115°C till it attains substantially constant mass.
  
• Cool the specimen to room temperature and obtain its weight (M1) specimen too warm to touch shall not be used for this purpose.
  
• Immerse completely dried specimen in clean water at a temperature of 27+2°C for 24 hours.
  
• Remove the specimen and wipe out any traces of water with damp cloth and weigh the specimen after it has been removed from water (M2).
  

Calculation of Water Absorption of Concrete:

Water absorption, % by mass, after 24 hours immersion in cold water in given by the formula,

Water Absorption of concrete =

Quality of Concrete Depending upon the Water Absorption Percentage:

Extremely good concrete might be 4 or 5% by mass.

Very good concrete might be 5 or 6%

Typical commercial concrete might be 6 or 7%

Pretty “ordinary” concrete might be 7 to 10%.

If we want to control water absorption, we need to control how much water goes in. For that we have to perform each activity carefully and consider all the things as mentioned above, upon which water absorption can be dependent.

Result:

Water absorption of the given sample of concrete = …………. %