This test was carried out on four specimens according to ASTM
C109 M[31]; the surface of the specimens was carefully polished
on fine paper in order to remove irregularities. To help transmit
the load to the specimen’s faces uniformly pieces of cardboard
2 mm in thickness were placed on both faces. Compressive
strength measurements were carried out using a five tonne German Bruf Pressing Machine with a loading rate of 100 kg/min