The materials which plays major role in highway construction are:
a) Soil
b) Bitumen
c) Cement
d) Stone
e) Concrete
f) Sand
Requirements:
a) Soil:
i) It should be clean and coarse.
ii) It should be free from any organic or vegetable matter;
iii) It should be chemically inert.
v) It should not contain salts which attract moisture from the atmosphere.
vi) It should be well graded, i.e., it should contain particles of various sizes in suitable proportions.
vii) It should be strong and durable. It should be clean and free from coatings of clay and silt.
b) Bitumen:
i) The bitumen should not be highly temperature susceptible
ii) During the hottest weather the mix should not become too soft or unstable
iii) During cold weather the mix should not become too brittle causing cracks.
iv) The viscosity of the bitumen at the time of mixing and compaction should be adequate. This can be achieved by use of cutbacks or emulsions of suitable grades or by heating the bitumen and aggregates prior to mixing.
v) There should be adequate affinity and adhesion between the bitumen and aggregates used in the mix.
c) Cement:
i) The color of the cement should be greenish grey.
ii) Cement should give a cool feeling when hand is thrusted into the cement bag
iii) Cement should give smooth feeling when rubbed between two fingers
iv) When cement is thrown into a bucket of water it should float for some time and then sink
v) There should not be presence of lumps
d) Stone:
i) It should be descent in appearance and have uniform colour.
ii) It should be durable i.e. it should resist atmospheric action and should be long lasting
iii) For a good stone, the crushing strength should be more than 100 N/mm2
iv) Stones should be such that they can be dressed easily and economically.
v) For a good building stone, the specific gravity should be more than 2.7
vi) The percentage of water absorption of water by weight after 24 hours should not exceed 60%.
vii) Minerals in stones should be such that it should catch fire easily.
viii) Stones should be well seasoned before use.
e) Concrete:
i) It should have good workability so that it can be easily handled and placed in position.
ii) It should be dense and compact.
iii) It should have enough compressive strength.
iv) It should be durable.
v) It should be resistant to fire.
vi) It should be impermeable.
vii) It should form hard surface capable of resisting abrasion.
viii) It should have minimum shrinkage.
ix) It should be economical.
f) Sand:
i) It should be clean and coarse.
ii) It should be free from any organic or vegetable matter;
iii) It should be chemically inert.
iv) It should contain sharp, angular, coarse and durable grains.
v) It should not contain salts which attract moisture from the atmosphere.
vi) It should be well graded, i.e., it should contain particles of various sizes in suitable proportions.
vii) It should be strong and durable. It should be clean and free from coatings of clay and silt.