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.