This set of Pavement Design Interview Questions and Answers for freshers focuses on “Highway Materials – Sub Base and Base Course – 2”.
1. What does WBM stand for?
a) Water Based Macadam
b) Water Bound Macadam
c) Wet Bituminous Macadam
d) Wet Bound Macadam
Explanation: WBM stands for Water Bound Macadam. It is used as a base course. It consists of stone aggregates, screening material, and binders that are laid in the respective order.
2. The method of boulder soling is still used and it is laid over the subgrade.
Explanation: The method of boulder soling is an old practice and it is no longer employed. The reason behind this is the fact that these have proved to result in poor performance and the pavement has an undulated surface.
3. Which of the below is not used as an unbound sub-base material?
c) Lime-fly ash
d) Crushed slag
Explanation: Unbound sub-base is basically granular sub-base. It is made using natural moorum, sand, gravel, crushed slag, crushed stone, kankar, laterite and reclaimed crushed concrete/asphalt. The bound sub-base makes use of materials that are chemically stabilized using cement, lime-fly ash or commercial stabilizers.
4. What is the name of the layer laid in between concrete slab and sub-base course in a rigid pavement?
a) Differential layer
b) Differential membrane
c) Separation layer
d) Separation membrane
Explanation: Separation membrane is the layer laid in between sub-base and concrete slab. It serves the purpose of preventing the new layer of the concrete slab from sticking to the lean concrete sub-base.
5. Which of the below IRC codes gives the guidelines for wet mix macadam?
a) IRC 102
b) IRC SP 102
c) IRC SP 100
d) IRC 109
Explanation: IRC 109 is the code that gives guidelines for wet mix macadam. IRC 102 deals with the traffic studies for planning bypasses around towns. Guidelines for design and construction of reinforced soil walls is obtained from IRC SP 102. IRC SP 100 gives the details on the use of cold mix technology in construction and maintenance of roads using bitumen emulsion.
6. In which country was the first macadam road built?
Explanation: The idea of macadam road was pioneered by Scottish engineer John McAdam. The first road to be built using this technique was in the USA between Hagerstown and Boonsborough, Maryland in 1823. It was a 16 km long stretch of road.
7. Sub-base layer with less proportion of ______ will help in serving as a better drainage layer.
a) Coarse aggregates
b) Fine aggregates
d) Crushed slag
Explanation: For drainage to take place properly, there must be sufficient gap or void space available for the water to flow. This is possible only when coarse aggregates are in a higher proportion than the fine aggregates.
8. Base course can prevent subgrade soil movement caused due to ______ in rigid pavement.
d) Slab pumping
Explanation: Slab pumping is caused when the loads deflect the slab. In pumping, materials come out from the subgrade through the cracks. The base course helps in preventing the movement of the subgrade soil by restricting the slab pumping.
9. Resilient modulus is the relevant strength parameter for granular sub-base.
Explanation: Resilient modulus is the ratio of stress to strain for rapidly applied loads. As per IRC 37:2012, the strength parameter for sub-base is taken as the resilient modulus.
10. By which technique can the existing pavement be reused in the sub-base as well as the base course?
b) Asphalt recycling
c) Cold recycling
d) Hot recycling
Explanation: Cold recycling is a process by which the existing flexible pavement can be broken down into a reusable form. There are specific plants for carrying out this process. Hot recycling is used for rehabilitation of damaged flexible pavements.
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