Concept: Measurement of air content in fresh concrete: Mainly there are three methods of measuring the air contents of fresh concrete is as follows:
1. Gravimetric Method 2. Volumetric Method 3. Pressure Method Gravimetric Method: ● This method is simple and does not require any special equipment, as such it is the first method used for calculating the air contents in concrete.
● The method
principally comprises the determination of density of fresh concrete compacted by a standard method.
● This density is then compared with the theoretical density of air-free concrete calculated from mix proportions and specific gravities of the constituent materials of the concrete.
Volumetric Method: ● This
method aims at measuring the volume of air in the sample of fresh concrete directly.
● The sample of a known volume of concrete is taken and all air is removed from it by any method and then the amount of water required to restore the original volume is determined.
● This method is tedious and time-consuming.
Pressure Method: ● This is the
most popular and best-suited method for site use. ● It is based on the relation between the volume of air and the applied pressure (at a constant temperature) given by Boyle’s law.
● This meter is directly graduated for the percentage of air and proportions or properties of materials need not be known.
● This meter is not suitable for use with porous aggregates and needs calibration if used at high altitudes.
Explanation: Blaine air permeability method:● It is used for
determining the fineness of Portland Cement measures the specific surface area of fine materials in square centimeters per gram of test sample.