All the materials, which are used in any civil engineering structures, are to be known as construction material. However, for a geologist more emphasis is to be given on those construction materials exclusive of steel and timber. Availability of construction material has a vital role or bearing on the economic implementation of all the major civil engineering projects. Projects otherwise feasible have been dropped for want of construction material or alternatively the type and design of the structure has to be modified to suit locally available construction materials. In Pong dam at Beas the slopes had to be modified because suitable size of riprap was not available. The slope was modified to suit locally available construction material to be used as riprap. Sand, silt and clay are the most commonly used construction material due to their easy availability along with gravels.
Geologists report for a construction material: A geologist or rather engineering geologist has to determine the following in order to provide information/input for the project:
(i) Geographical location
(ii) Topography of the area
(iii) Geology of the (construction material) deposit
(iv) Groundwater conditions
(v) Quantity available and
(vi) Methods of quarrying.
1. Building materials (Stones): The building stones should be investigated for their following properties:
(i) Durability: It is a prime requirement, which is the capacity for retaining its original size, shape and appearance for a long period of time. Should be resistant to the point of community.
(iii) Texture: Final appearance of desired stone depend upon its texture, mineral composition and uniformity of color and texture.
(iv) Jointing Spacing of joints etc.
(v) Porosity Sound rock with a little porosity helps in easy quarrying and dressing.
(vi) Cleavage and bedding joints
(viii) Crushing strengths Generally depending upon the load it has to take. While for walls a strength of 3,000 psi has been adequate, for beams the required strength should be 30,000 psi or above.
(ix) Cost Availability and transportation costs as in case of marbles etc.
(x) Age It is generally established that older the rock more it is likely to be weathered or prone to weathering.
These are very fine-grained natural or artificial material used in combination with Portland cement. The word is derived from the town of Pozzkoli (Italy) where volcanic ashes were used for this purpose. Natural pozzolanic materials are volcanic tuffs, ashes, siliceous sedimentary rocks (opaline shales, cherts etc.) like clay and shale. The artificial pozzolanic materials include fly ashes smoke residue from chimneys. Pozzolanic materials also retard the alkali aggregate reaction and are claimed cheaper than cement. In Bhakra dam the crushed Dagshai Shale (crushed) was used as a replacement for cement whereas in Hirakud dam China clay, phyllites and Talabira clay were used.
2. Road Metal: For concrete road, pavement and airstrips the material should satisfy the properties of concrete aggregate in addition to its resistance to abrasion. For flexible bitumen roadways the material should satisfy the following condition:
(i) Better cohesion with tar-ferromagnesian preferred.
(ii) No friable, elongated or weathered material.
(iii) Minimum roundness of the aggregate.
(iv) Good abrasion strength
(v) Good crushing strength.
(vi) Low porosity and
(vii) No coating of materials
3. Railway Ballast: The stones chips used along the railway tracks are called as ballasts. These should have
(i) High modulus of elasticity
(ii) Uniform thermal expansion
(iii) Crushing should not produce fine fragments.
(iv) Angular grains are appropriate.
4. RipRap: Broken/chipped stones or boulders are used as riprap on the upstream face of earth dam and embankment used as protective measures against wave action and erosion by water. The source should be as near to the structure as possible. However, in case of Ramganga dam the compressive strength of the availability Lower Shiwaliks were much less than the required strength. The riprap was brought from a distance and by screening the terrace deposits.