Resistance to deformation (bending): UNI 9724/5
This test is carried out on samples 12 cm long, 3 cm wide and 2 cm high. The samples are placed on the rounded edges of two blades 100 mm apart and a gradually increasing load is applied by a third blade in the middle until breaking occurs. The breaking load of flexion (bending), R, is expressed in MPa (or N/mm' where 1 MPa = 10.2 kgf/cm^2) from the formula
R = (3 P l) / (2 b h^2)
in which P = load of breaking of the sample, in Newtons; l = distance between the supporting blades, in mm; b = the width of the sample in mm; h = height of sample in mm. The test is usually carried out with load applied perpendicular to the natural splitting planes of the rock.
Porphyry - Breaking strain under indirect traction through flexion, average value: 22.5 MPa.
Coefficient of linear thermal expansion
This represents the variation in length of the test samples, expressed in mm/(m°C ), caused by a change in temperature of 1°C. The dilatometer containing the sample is attached to a thermostat and brought first to a temperature of 0°C and then to 50°C. The expansion is measured by the gauge which has a feeler in contact with the transmission bar (in silica). To calculate, it is assumed that the coefficient of linear thermal expansion of the silica is ALFA° = 0.5 x 10-61/°C. It is essential that all the rock parts used in budding have the opportunity to expand whatever their coefficient of expansion by means of the addition of suitable expansion joints.
Porphyry - coefficient of linear thermal expansion, average value: 5.55 x 10^6/°C.
Coefficient of normal elasticity
This is usually obtained by testing samples with a cuboid shape, the base being 5 cm by 5 cm and the height 20 cm.
Alternatively a cylindrical sample with diameter of at least 5 cm and height: diameter ratio of about 3 may be used. The Samples are subjected to compression along their longitudinal axis while measurements of deformation are taken by a couple of electrical extensimeters placed longitudinally in diametrically opposed points from the lateral surface of the sample. The load is applied with constant rate of 0.4 MPa/sec, in a direction perpendicular to the preferred splitting plane of the rock.
The elasticity is therefore defined as the ratio between the variation of the axial face and the consequent unit longitudinal deformation and is expressed in MPa (=N/mm2) or GPa. With the results obtained it is possible to draw a force- deformation (stress - strain) graph from which s obtained the modulus of elasticity tangent Et (measured at a stress corresponding to 50% of the breaking strain) and the elasticity secant modulus Es (measured between the value zero of the stress and 50% of the breaking strain).
Porphyry - Elasticity tangent modulus Et: 66180 MPa. Elasticity secant modulus Es: 59360 MPS.
Impact test
This is measured as defined in article 3 of the law R.D. 2234 of 16.11.1939 determining the minimum fall height, expressed in cm, of a steel sphere with mass 1 kg which, hitting the centre of the samples which are 20 x 20 cm squares, 3 cm thick, resting on a bed of sand 10 cm thick, produces breaking. The rock may demonstrate strength or weakness to impact and thus resistance to sudden impact.
Information, such as the resistance to impact and Knoop microhardness tests, facilitates the assessment of the behavior of the rock used in paving and steps, i.e. in places particularly exposed to impact from objects and the passage of people and vehicles.
Porphyry: impact test, minimum fall height average value: 62 cm.
