What are the Highway Materials?
Highway materials are the materials used for the construction of roads and bridges. Different highway materials, like aggregate, bitumen, concrete, steel, etc., can be used to construct various highways. These materials have different properties based on their constituents. These are used for the construction of highways based on the nature of highways and their strength characteristics.
For the construction of rigid pavements, reinforced concrete material is based on its strength characteristics, and water-bound macadam materials, bitumen mix macadam, etc., are used for the construction of flexible pavements. Before selecting any highway materials for construction, different tests on these materials are required to ensure the Geometric design of highways and the design strength of the pavements.
Properties of Highway Materials
The properties of highway materials are to be known before their use for the construction of roads. These properties can be determined with the help of different tests on these materials. Different properties of the highway materials are listed in the GATE CE syllabus, which includes Strength, Hardness, soundness, Group index value, Specific gravity, etc.
Group Index of Soils (G.I)
To classify the fine-grained soils within one group and to judge their suitability as subgrade material, an indexing system has been introduced in HRB classification, termed a group index. Soils are thus assigned arbitrary numerical numbers known as group index (GI). The group index is a percentage function given by the equation G.I = 0.2a + 0.005ac + 0.01bd.
a = (P - 35) < 40
b = (P - 15) < 40
c = (WL - 40) < 20
d = (IP - 10) < 20
- WL = Liquid limit,
- IP = Plasticity Index.
P = Percentage fines passing from 0.074 mm sieve.
0≤G.I≤20 Lower the group →best quality.
Tests on Highway Materials
Tests on highway materials are required to know the different characteristics of the materials. Tests on highway materials are required before the construction of the roads. These tests depend on the type of materials also. For example viscosity test is required to know the strength of bitumen, etc. These tests are important for the GATE exam. Here a few types of tests on highway materials are described below.
Plate Bearing Test
(i) k = P/0.125 kg/cm3
- k = Modulus of subgrade reaction
- P = Pressure Corresponding to a settlement of 0.125 cm.
(ii) ks = k.(Ps/P)
- ks = Modulus of subgrade reaction for soaked condition.
- Ps = Pressure required in the soaked condition to produce the same deformation as deformation Produced by pressure ‘P’ in consolidated condition.
- k = Modulus of subgrade reaction for the consolidated stage.
Δ = 1.18 Pa/E
Δ = Deformation in ‘cm’.
a = Radius of the rigid plate in ‘cm’.
k = P/Δ = E/1.18a
E = Modulus of elasticity of soil subgrade in kg/cm2.
k.a = constant
a1 = Radius of the smaller plate (another plate)
k = k1.(a1/a)
k1 = Modulus of subgrade reaction of another plate of radius ‘a1’ cm.
California Bearing Ratio (CBR) Test
CBR (%) = [ Load or pressure sustained by the specimen at 2.5 or 5.0 mm penetration ] × 100 / [ Load or pressure sustained by standard aggregates at the corresponding penetration level ]
Test for Road Aggregate
(i) Aggregate crushing test
Aggregate crushing value = 100 w2/w1 %
- w1 = Weight of the test sample in ‘gm’
- w2 = weight of the crushed material in ‘gm’ passed through a 2.36 mm sieve.
(ii) Shape Tests
Angularity number = 67 - (100w/CGa)
- Ga = specific gravity of aggregate
- W = mass of mould containing aggregate
- C = mass of mould containing water
(iii) Abrasion Test
(a) Los Angeles Abrasion Test
Coefficient of hardness = 20 - [ Loss in weight in 'gm' /3 ]
Bitumen as a Highway Material
Bitumen is one of the highway materials used in construction as a binding material. It is mixed with aggregate and other ingredients for the construction of flexible pavements. Bitumen properties and different types of bitumen mix are explained below.
- Product of fractional distillation of Petroleum: Gasoline, Naptha, Kerosene, Lubricating oil and Residue – Petroleum Bitumen.
- Cutback Bitumen: Reduced Viscosity Bitumen
N – Numeral [0, 1, 2, 3, 4, 5]
Show progressive thickening from 0 to 5
- Specific Gravity:
Bituminous → 0.97 – 1.02
Tar → 1.1 – 1.5
(i) Determination of Specific Gravity
Ga = 100/[(w1/G1)+(w2/G2)+(w3/G3)+(w4/G4)]
Where Ga = Average specific gravity of blended aggregate mix.
w1, w2, w3, w4 are % by weight of aggregate 1, 2, 3 & 4 respectively. G1, G2, G3 & G4 are specific gravities of the aggregate 1, 2, 3 & 4, respectively.
(ii) Specific Gravity of Compacted Specimen
(a) Gt = 100/[(100-wb/Ga)+(wb/Gb)]
- Gt = Theoretical maximum specific gravity of the mix.
- Wb = % by weight of bitumen.
- Gb = Specific gravity of bitumen.
- Ga = Average specific gravity of aggregates.
(b) Theoretical density γt, per-cent solids by volume
γt = 100 G /Gt
- G = Actual specific gravity of test specimen
- Gt = Theoretical maximum specific gravity.
VMA - (Vv + Vb) = 100 -(G/Wa)
(c) Voids in the Mineral Aggregate (VMA)
- Vb = % of bitumen
- Wa = Aggregate content per cent by weight
- Vv = % air voids in the specimen.
Vv = 100 - γt = 100(Gt - G)/Gt
(d) % Voids Filled with Bitumen (VFB)
VFB = 100Vb/VMA
If you are preparing for ESE/ GATE or other PSU Exams (Civil Engineering), then avail Online Classroom Program for ESE and GATE CE.
Online Classroom Program for ESE/GATE CE
You can avail of BYJU'S Exam Prep Test Series, specially designed for all Civil Engineering Exams.
BYJU'S Exam Prep Test Series ESE/GATE CE
|Other Important GATE Notes|
|Steel||Zero Force Member In A Truss|
|Water logging||Creep of Concrete|
|Lami's Theorem||Moment Area Method|
|Macaulay's Method||Tender in Construction|
|Critical Path Method||Uniformly Varying Load|
Commentswrite a comment