Raw & Waste materials

STONE DURABILITY

It is the ability of the rock to resist to decay during the period of use in the work. It is linked to:

• Conditions of the rock at the origin
• Physical and mechanical properties of rock
• Extraction methods
• Processing and installation
• Environmental factors

The decay and the durability of a rock can be addressed: subjected to the same mechanical or physical test or performing in situ monitoring

3.1 Ageing tests

1. FREEZING AND THAWING CYCLES

Frost is one of the most important causes among those responsible for the alteration of stone. Its action is closely linked to the presence of water in the pores and fractures and is conditioned by several factors: degree of saturation in water, distribution of the pore size, continuity of pore system and presence of salts. This condition is performed by an automatic system, the specimens pass from freezing conditions in air to conditions of immersion in water according to the a scheme. After the ageing tests the variation in the physical or

mechanical properties of the specimens is measured.

2. THERMAL SHOCK

The increase in T causes dilation of the rock. The rock are characterized by a low conductivity so that the T variation affect above all the superficial part of the material, which expands and contracts more with respect to the internal part.

3. SALT CRYSTALLISATION TEST

Useful for carbonatic rocks. Salts in aqueous solution may come into contact with the stone by: sea salt, salt used in winter on streets, action of atm pollutants. The measurement are made:

• The aqueous solution penetrate into the pores of the stone
• During the dry periods part of the water evaporates leaving a residue with a higher conc
• During the wet periods new water containing salts penetrates into the stone
• The solution reaches saturation
• By decreasing T of water the solution can become critically over-lapping with consequent spontaneous crystallization of the salts

4. REBOUND SCHMIDT HAMMER TEST

5. UTRASOUND PULSE VELOCITY

Measurement the traveltime

of the ultrasound wavelength inside the medium and then we can estimate the velocity.

6. BOWING 6

Different t and humidity in the lower and upper part lead the material to bowing. The bowing is related to the habits of the crystal and to the exposition (presence of sun, humidity in the back part of the faces and windy side of the building). Its happens usually in marble.

3.2 Different kind of cutting→

1. sawing: the motion of the frame is oscillating, with the grift for sawing gneiss and granites→
2. giant disc: the dick is lowered or the block trolley is lifted, characterized by high energy consumption and considerable noise→
3. diamond wire technology: characterized by a high descent speed, it’s characterized by a lower used of energy, lower noise, lower consumption of cutting tools and absence of lime→
4. cutting line used for piastrelle

3.3 Surface finishing treatment

a. HONED SURFACE: flattering of surface irregularities by means of series of increasingly fine

abrasive grinding wheels

b. POLISHED SURFACE smoothing + final phase with alumina. The formation of a vitrified surface layer is obtained

c. FLAMED SURFACE strong heating obtained through the dart of a nozzle by O2 and propane followed by an abrupt coiling

4. Aggregates

It is a inert material and it’s considered a relatively common mineral source. They can be present as Tout-venant used for foundation, as sand, gravel and crushed stone used for concrete and asphalt and as pietrisksand granulates used for railway and roads embankments.

They can be used in different fields: private and public construction, roads, railways, hydraulic works

74.1 Aggregates characterization

The basic features are:

• physical (shape, specific weight, porosity, index of voids)
• chemical (resistance to aggressive agents, solubility, alterability)
• mechanical (impact, wear)
• rheological (behaviour with respect to the binders any additives)

The main tests are

1. PETROGRAPHIC DESCRIPTION : is performed on the classes

obtained from the granulometric analysis.

For each class, homogenous lithology groups are identified. Each group is define by a %. The main problem are presence presence of soft minerals, lamellar or fibrous mineral, hard minerals

2. SHAPE INDEX : is calculated as the mass of the granules having a ration of size, expressed as a % of the total dry mass of the granules examined

3. FLATTERING COEFFICIENT :

4. LOS ANGELES TEST : test used for the determination of fragmentation resistance. The coefficients indicates the % of the test sample passing trough a mesh test sieve of 1.6 mm after the completed test. The aggregate sample is inserted into an apparatus consisting of rotating cylinder, inside which it rolls together with steel balls. The machine must preform 500 rotation at a constant speed which corresponds to a duration of 15 min.

5. MICRO-DEVAL TEST : used to determine the wear resistance. It consists in measuring the wear produced under conditions defined by the friction between aggregates

and abrasive charge inside a rotating drum. The results indicates the % of the sample passing trough a mesh test sieve of 1.6 mm after the completed test.

4.2 Treatment of aggregates

The treatment of inert is an essential condition for the valorisation of the product and therefore for a correct use of the reservoir. It takes place in the quarry systems following cycles of:

• Comminution reduction of dimension
• Washing to eliminate the fine particles
• Classification to separate the different size particles

NB aggregates are cheap, the transport is more expensive than the extraction usually there is a temporary deposit near the quarry to reduce the final cost of the transport

5. Physical properties for mineral processing

The following properties are used to separate substances of different nature in order to achieve more or less pure concentrates. Through the knowledge of the properties of materials we have to know which separation methods can be applied to obtain the free

1. Dimension
2. Shape
3. Mechanical strength
4. Density
5. Magnetic properties
6. Electrical properties
7. Elasticity
8. Colour
9. Thermal properties

5.1 Density

Bulk density = the mass of many particles of the material divided by the total volume they occupy. The total volume includes particle volume, inter-particle void volume, and internal pore volume. The bulk density can change depending on how the material is handled or stored.

5.2 Magnetic susceptibility

It's a quantitative measure of the extent to which a material may be magnetized in relation to a given applied magnetic field. Diamagnetic materials are not influenced by an external magnetic field. Paramagnetic materials increase the magnetic field in which they are placed. Ferromagnetic materials can maintain their magnetic charge even when the magnetic field ends.

5.3 Electrical conductivity

It is the reciprocal quantity of resistivity and measures a material's ability to conduct an electric charge. Electrical resistivity quantifies how

strongly the material opposes the flow of electric current 5.4 Yield and recovery R is the recovery and it’s the useful substance recovered through the mineral processing. The grade is the %of the desired substance. 115.5 Sampling It’s used to determine the properties of a material or to define chemical composition, density, dimensional→properties, treatment tests. The sample must be representative same properties as the batch from whichit’s extracted. →EX: core drilling to sample in the vertical direction A sampling error is a statistical error that occurs when an analyst does not select a sample that representsthe entire population of data and the results found in the sample do not represent the results that would beobtained from the entire population. Sampling is an analysis performed by selecting by specific number ofobservation from a larger population and this work can produce both sampling errors and non sapling errors. There are different type of sampling:→1.

1. Fractional collection with a spoon we collect different part of the pile
2. Fractional wagon
3. Core drilling
4. Open spoon
5. Riffle splitter jones in lab
6. Coning and quartering
7. Screening and comminution

A screen is a surface having a multiply of aperture of given dimension. Material of mixed size presented to that surface will either pass through or be retained according to the particle and aperture. Sieving and screening are similar action, the first one is a laboratory activity and the second is industrial one.

Screening is used to separate different materials by granulometry and composition. Efficiency is the amount of material that can pass through the aperture.

The factors that influenced the passage of the grains through calibrated holes aperture, slope of the layer, quantity of feed, the time in which the sieves are moved.

Many screen work with a sloping surface to encourage the movement of the materials. This causes a small decrease in the probability of passing.

common apertures openings have a circular, square, or rectangular shape with smaller rounded sides. Their thickness and the proportion of the opening vary according to the amount of material that the surface will have to treat. Elongated shapes are generally used for fine sieving limited surface subjected to clogging, low efficiency, and expensive maintenance. Different types of screening: 1. FIXED GRID: Grids with bars for coarse screening, used before the primary crusher. The bars are parallel to the flow and very inclined. 2. ROTARY SCREEN-TROMMEL: At the beginning, the fine particles come out, followed by the larger ones. The small blades inside are used to break plastic bags and decrease the size. This type of screen is commonly used in waste treatment. The rotation speed must avoid the centrifugation of the materials, as they should remain attached to the inside wall. It is inclined. 3. DISC SCREEN: Classification is done with the movement of discs that can have different shapes. The discs rotate in

parallel and both move the material both the material is classified. The distance of the discvary from one floor to the other, in the end smaller distance. The maintenance is a problem→4- VIBRATING SCREEN characterized by high frequency, large amplitudes for large opening otherwise the large fragments do not move on the screening surface

NB: FREE GRAIN = liberation size can be estimated from the petrographic studies, especially microscopic examination of thin and polished sections. Free gran is made up of only one substances. Liberation is essential for the separation treatments. It’s connect with the liberation factor

7.1 Comminution

The reduction ratio characterized the comminution. It can be defined as the ratio between a characteristic dimension