Testing and Preservation of Stone and Artificial Stones

introduction

In the intricate world of civil engineering, the enduring beauty and structural integrity of stone, both natural and artificial, stand as timeless testaments to human craftsmanship. In our comprehensive exploration, we delve into the critical realm of 'Testing and Preservation of Stone and Artificial Stones.' This blog post uncovers the indispensable techniques, methods, and insights essential to ensure the longevity and resilience of these building materials. From historical monuments to contemporary structures, the significance of safeguarding these materials goes beyond aesthetics; it's the cornerstone of architectural longevity and cultural preservation. Join us on this insightful journey into the methods that uphold the durability and beauty of these foundational elements in civil engineering.

testing of stone

Smith test on stone

To determine the presence of soluble matter in stone

In materials science or geology, determining the characteristics of a stone may involve tests for hardness, density, abrasion resistance, or mineral composition. Common tests could include the Mohs scale for hardness, specific gravity tests, or various laboratory analyses to identify the stone's mineral content.

Compressive Strength test on stone:

3 cubes of 50 mm are taken, and the average is reported (IS: 1121, Part-1)

The compressive strength test on stone is a fundamental and common method used to determine the ability of a stone material to withstand loads or pressure applied perpendicular to its surface. This test is crucial in evaluating the durability and suitability of a stone for various construction or architectural purposes.

Sample Preparation: The stone specimen is typically a cube or cylinder cut from the larger stone. The surfaces need to be prepared by grinding or smoothing to ensure they are parallel and even.

Testing Machine: A specialized testing machine, like a universal testing machine, is used to perform the compressive strength test. This machine applies a gradually increasing load to the stone specimen until it fractures.
Test Procedure: The prepared stone sample is placed in the testing machine. A load is applied at a constant rate until the stone fails. The maximum load it withstands before failure is recorded.
Calculating Compressive Strength: Compressive strength is calculated by dividing the maximum load at failure by the cross-sectional area of the stone specimen.

Interpreting Results: The results obtained from the test are essential in determining the stone's ability to endure compressive forces. Engineers and architects use this data to assess the stone's suitability for construction applications. Higher compressive strength typically indicates a more durable stone.

Different types of stones have varying compressive strengths. For example, granite, a common dimension stone, generally exhibits high compressive strength. Other stones like limestone or sandstone might have lower compressive strength but can still be suitable for various construction purposes depending on the context.

attrition test on stone:

It is carried out in a Deval Testing Machine.

60 mm size stones are taken and rotated for 5 hours at 30 - 33 rpm

Rate of wear = (% of weight passing 1.5 mm sieve / Weight of sample ) * 100

NOTE

a) Rate of wear < 3% = Good Quality
b) Rate of wear = 3% = Medium (tolerable)
c) Rate of wear > 3% = Bad quality or cannot be used in stone masonry

The attrition test on stone is a method used to determine the resistance of stone aggregates to wear and tear caused by friction or impact during their use in construction. This test is crucial in assessing the durability and quality of stone aggregates for various construction applications, such as road construction and concrete production.

Sample Preparation:

Preparation of Test Specimens: Small-sized stone aggregates are selected and cleaned. These stones are usually between specific size ranges and are free from dust or impurities.

Drying Process: The selected stone aggregates are dried in an oven to remove any moisture content that might influence the test results.

Testing Procedure:

Los Angeles Abrasion Machine: The test is usually performed using a machine called the Los Angeles abrasion machine. This apparatus consists of a hollow steel drum with an interior diameter and length specified by standards. Inside the drum, a specific number of stone aggregates are placed.

Rotating Drum Test: The drum is rotated at a specific speed for a set number of revolutions. During rotation, the stone aggregates inside the drum collide against each other and the walls of the drum, simulating the abrasive conditions the stones would face during their usage in construction.
Sieving and Analysis: After the specified number of revolutions, the stone aggregates are removed from the machine. They are then sieved to separate the finer particles and dust produced during the test.
Calculating the Abrasion Value: The amount of wear and tear or abrasion that the stone aggregates undergo is assessed by measuring the difference in the weight of the stone aggregates before and after the test. This value is used to determine the abrasion resistance of the stone aggregates.

Hardness test on stone:

This test is done in the Dorry Testing Machine

Coefficient of hardness = 20 - (loss in weight in gram / 3 )

NOTE

a) Coefficient of hardness < 14 = Poor hardness
b) 14 < coefficient of hardness < 17 = Medium hardness
c) Coefficient of hardness > 17 = Very hard

The hardness test on stones is a method used to assess the resistance of a stone material to scratching or indentation. Hardness is a fundamental property that determines a stone's durability and its ability to withstand wear and tear.

There are various methods used to test the hardness of stones, and one commonly used scale is the Mohs scale of mineral hardness, which ranks minerals based on their scratch resistance against a set of standard minerals.

The Mohs scale, developed by Friedrich Mohs in 1812, consists of ten minerals arranged in increasing order of hardness:

Talc
Gypsum
Calcite

Fluorite
Apatite
Orthoclase Feldspar

Quartz
Topaz
Corundum

Diamond

The test involves trying to scratch a stone surface using these standard minerals. For instance, if a stone is scratched by orthoclase feldspar but not scratched by calcite, its hardness is roughly between 3 and 6 on the Mohs scale.

However, the Mohs scale has limitations, especially when testing materials that are harder than the reference minerals on the scale. For more accurate testing, other methods are employed, such as the Vickers hardness test, Rockwell hardness test, or Brinell hardness test. These tests involve using standardized equipment to measure the force required to make an indentation in the stone surface.

When assessing stones for construction or ornamental purposes, hardness is an essential factor. Stones with higher hardness are typically more durable and resistant to scratching, making them suitable for various applications, such as flooring, countertops, sculptures, and architectural features.

Each test has its own set of procedures and equipment, but the goal is the same: to determine the stone's hardness accurately. The choice of method depends on the specific requirements, the nature of the stone, and the precision needed for the intended application.

impact test on stone:

It is carried out using an anvil testing machine.

In this test 25 × 25 mm cylindrical aggregate is impacted by a hammer of mass 2 kg and allowed to fall from different heights until the specimen fails.
Toughness coefficient = Height in cm from which specimen fails.

NOTE

a) Coefficient toughness < 13 = Poor toughness
b) 13 < coefficient of toughness < 19 = Moderate toughness
c) Coefficient of toughness > 19 = Very tough

acid test on stone:

It is used to determine the weather resistance capacity of stone

Sharp and firm corners and edges are an indication of sound stone.

crystalline test on stone:

It is used to determine the durability of the stone.

X-Ray Diffraction (XRD): XRD is a powerful technique used to determine the crystal structure of a material. It identifies the arrangement of atoms within a crystal by analysing the diffraction patterns of X-rays that interact with the sample. This method can provide detailed information about the crystallographic structure of minerals or stones.
Polarizing Microscopy: This technique involves the use of polarized light microscopy to observe the internal structure of minerals. The specific properties of crystals, such as birefringence, can be examined to identify and characterize different crystal structures within a stone.
Microscopic Examination: Examining the stone or mineral under a microscope can reveal the presence of crystals, their sizes, shapes, and arrangements. This visual analysis helps in identifying the crystalline nature of the stone.

Chemical Tests: Some chemical tests can indicate the presence of specific minerals or crystals within a stone. For instance, using certain reagents or acids might react differently with different minerals, aiding in the identification of the crystalline components.
Differential Thermal Analysis (DTA) or Differential Scanning Calorimetry (DSC): These techniques can be employed to determine the thermal behavior of minerals or stones, providing information about phase transitions and crystalline structures.

IMPORTANT QUESTION

The crushing strength of a good building stone should be more than:
a) 50 MPa
b) 100 MPa
C) 150 MPa
d) 200 MPa

Sol: The crushing strength of a good building stone should be more than 100 MPa.
So, the correct answer is b).

preservation of stone

Preservation of a stone is essential to prevent its decay. Different types of stones require different treatments for their preservation.

In general, stones should be made dry with the help of a blowlamp, and then a coating of paraffin, linseed oil, light paint etc., is applied over the surface.
This makes a protective layer over the stone. However, this treatment is periodic and non-permanent.
When treatment is done with the linseed oil, it is boiled and applied in three coats over the stone.

NOTES:

In industrial towns, stones are preserved by the application of a solution of Barium hydrate also termed as Baryta (Ba(OH)₂). It works in the following manner:

(Ba(OH)₂) + CaSO₄ → BaSO₄ + Ca(OH)₂

Here baryta reacts with calcium sulphate deposited on the stones and forms insoluble barium sulphate and calcium hydroxide. The calcium hydroxide absorbs CO₂ from the air to form CaCO₃, ppt.

Са(ОН)₂ + С0₂→ CaCO₃ ↓

artificial stones

Where durable stones are not available at a reasonable cost, an artificial stone known as cast stone is used.

Artificial stones are made with cement and natural aggregates of crushed stone and sand with desired surface finish.
Some of the artificial stones available are as follows:

Garlic stone: It is produced by moulding of iron slag and Portland cement. These are used as surface drains.

Concrete block: These are cast at a site in the construction of a pier or are used for steps, windows, sills etc.
Ransom stone: These are prepared by mixing soda silicate with cement to provide decorative flooring. These are also known as chemical stones.
Victoria stone: These are granite pieces with surface hardened by keeping it immersed in soda silicate for 2 months.

Bituminous stone: Granite and diorite are impregnated with prepared or refined tar to form a bituminous stone.
Imperial stone: These are finely crushed granite mixed with Portland cement. These are similar to Victoria stone.
Artificial marble: It can be either precast or cast in situ. These are made of Portland gypsum cement and sand.

uses of stone

S.NO	Name of rock	Use
1	Granite	Abutment of pier
2	Granite & Marble	Facing work
3	Kankar	Hydraulic lime
4	Limestone, Marble, Sandstone	Flooring
5	Gneiss	Paving work
6	Basalt, Trap	Rubble masonry & Foundation work
7	Slate	D.P.C & Roofing material
8	Chalk	Manufacturing of putty
9	Marble, Sandstone	Ornamental or carving work

Uses of rock or stones

importatnt question

Q: The rock has more fire-resisting characteristics is
a) Marble
b) Compact sandstone
c) Limestone
d) Granite

Sol: The maximum fire-resisting capacity is of compact sandstone as it consists of silica.
So, the correct answer is b).

Q: Hardstone is suitable for
a) Arches
b) Roads
c) Rubble masonry
d) Retaining wall

Sol: Hardstone is suitable for rubble masonry. A heavy stone is suitable for retaining work, harbour works, dams etc. And the lightweight stone is suitable for arch masonry.
So, the correct answer is c).

Q: The rock which has maximum compressive strength is
a) Laterite
b) Gneiss
c) Sandstone
d) Granite

Sol: The compressive strength of the rocks is as follows:
i) Gneiss - 2200 to 3700 kg/cm²

ii) Granite - 770 to 1300 kg/cm²

iii) Laterite - 18 to 32 kg/cm²

iv) Sandstone - 650 kg/cm²

Gneiss has maximum compressive strength.
So, the correct answer is b).

To understand the concept for CEMENT in building material do visit the following articles