Qualities of Good Building Stone
Stone is a very common building material where it is available in a large scale. This is mostly used for foundation work, outer wall and dam construction.
The stonework is not as easy as brickwork, it has several drawbacks. It is necessary to check their quality first before using stones in building works. Following are the somes quality of a good building stones.
The stones that are to be used for the work of the face should have a good appearance. They should be able to retain their uniform colour and appearance for a long time.
Colour is an indicator of good building stones. Uniform colour is always desirable for good building stones. It is desirable to use light coloured stones at the face work and also for exposed positions.
3. Crushing Strength
The crushing strength for a good building stone should be higher than 100 N /mm2. Crushing strength values of some of the stones are as given here.
|Rock||Name of Stones||Crushing Strength in N/mm2|
|1. Sedimentary||Sand stone||64|
|Laterite||1.8 to 3.1|
|Shale||0.2 to 0.60|
|2. Igneous||Granite||75 to 25|
|Basalt||150 to 185|
|Dioritc||90 to 150|
|Trap||330 to 380|
|3. Metamorphic||Gneiss||206 to 370|
|Slate||75 to 207|
The stones quarried from quarries cannot be used directly for masonry work as they are quite irregular. It needs to cut or dressed in usable sizes and shapes. This process is known as dressing of stones. So, a good building stone should be such that they can be easily carved, cut, dressed or moulded.
The dressing of stones is an important factor from the economic point of view. If the dressing of stones is very difficult and costly, it should be avoided to use in the building works. Otherwise, labour costs will be increased which will increase the overall cost of construction.
The coefficient of hardness for the stones which are used for road construction must be more than 17. The coefficient of hardness below 14 shows stone of poor hardness. If the coefficient of hardness lies between 17 to 14, then it is said to be medium hardness.
6. Toughness Index
A good building stone should be tough enough. To find out the toughness of a stone, impact test is carried out. If the value of the toughness index is above 19, the toughness of the stone is said to be high, and it indicates the quality of the stone is good.
When this value lies between 13 to 19, is said to be moderately tough. If this value is less than 13, the stone is said to be poor tough, and it indicates the quality of the stone is bad.
7. Percentage of wear
In the attrition test, if the value of wear comes more than 3%, the stone is unsatisfactory. For a good building stone, the value of wear should not be more than 3%.