Other Methods of Hardness Measurement

Dynamic hardness of a material is measured by dropping a small weight from a fixed height on the surface of the sample and measuring its height of rebound. The instrument in which this measurement is made is known as shore sceleroscope.

Yet another method of dynamic hardness measurement was developed by Martel. He used a pyramidal indenter upon which a ram falls to produce an indentation of sample surface under dynamic loading condition. The Martel Hardness Number (MHN) is defined as :

                                        MHN = Wh / V                                    ---------------- (22)

where,    W = weight of falling arm,

h = height of fall, and

V = volume of indentation.

For paving materials the hardness measurement method has been developed in which wear and abrasion of samples is measured. A number of preweighed pieces of concentrate aggregate of bricks are placed in drum which is subsequently rotated for a fixed number of cycles. Due to tumbling in the drum the sample pieces wear and lose weight. The percentage loss of weight is used as a measure of wear or abrasion hardness. This is known as Rattler method.