Road and Pavement Work Interview Questions

Road and Pavement Work Interview Questions

Q. What is the asphalt?
Ans. A dark brown to black cementatious material which the predominating constituents are bitumen’s which occur in nature or are obtained in petroleum processing.

Q. What are the main desired properties of asphalt?
Asphalt is a thermoplastic material because they gradually liquefy when they are heated. They are characterized by their consistency at different temperatures. Consistency is the term used to describe the degree of fluidity or plasticity of asphalt at any particular temperature. At a standard temperature consistency of paving asphalt cement is commonly specified and measured by a viscosity test or penetration test.

Asphalt cement is composed almost more than 99.5% of bitumen, which by definitions is soluble in carbon disulphide.

Asphalt cement is heated to a high temperature, which will release the fumes that will flash in presence of spark or open flame. There is an adequate margin of safety, if the flash point of the asphalt is known.

Q. What are the main function of Base and Sub base in asphalt?
Ans. Base and sub base are structural elements of the pavement, in conjunction with the overlying asphalt surface, their purpose is to distribute traffic wheel loads over the sub grade or foundation, to perform this function base and sub base must be built with necessary internal strength properties, In this respect full depth asphalt pavement have a special advantage over pavements with granular bases.

Q. What is the purity of asphalt?
Ans. Asphalt cement is composed almost more than 99.5% bitumen, which by definition is soluble in carbon disulphide.

Q. What is the function of asphalt Base Course?
Ans. A foundation course layer which consisting of mineral aggregate, it bounds together with asphalt material on which successive course are placed.

Q. What is the allowable normal thickness of asphalt layer?
Ans. Normal thickness for Asphalt Base course should be 80mm and for Wearing course 40mm.

Q. What is the stripping test of aggregates?
Ans. The coating of aggregate by bitumen at 150ºC for keeping 1 hour in oven, visually assessment only required for results explanations.

Q. What is the stiffness (Rigidity) and how it to calculate?
Ans. Stiffness is caused that where low penetration asphalt is used. Such low penetration asphalt causes the volume changes making the pavement rigid; such asphalt mixes give higher stability values and low flow values.
Stiffness = Stability/Flow

Q. What is the stability?
Ans. Stability of the test specimen is the maximum load resistance in Kgs. that the standard specimen will develop at 60°C in 30 minutes while remain in water when tested.

Q. What is the “Flow value”?
Ans. The flow value is the total movement or displacement in units of “mm” occurring in the specimen between no load and maximum load during stability test.

Q. What are the “Air voids”?
Ans. The total volume of small pockets of air between the coated aggregate particles thru out a compacted paving mixture.

Q. What is the consistency of asphalt?
Ans .It is the term used to describe the viscosity of fluidity or plasticity of asphalt at any particular temperature.

Q. What is the penetration test?
Ans. It is the measurement of asphalt consistency test, based on this test asphalt cement can be classified into grades such as 40-50, 60-70, 85-100, 125-150, 200-300.The hardest grade is 40-50 and the softest grade is 200-300.

Q. Describe the procedure of penetration test?
Ans. In this test a container of asphalt cement is heated at a standard temperature 25 Degree in a controlled water bath. A prescribe needle weighing 1000 g is allowed to bear the surface of the asphalt for 5 seconds. This distance in unit of 1/10th of mm (0.1 mm) the needle penetrate into the asphalt cement is the penetration measurement.

Q. What is the softening point of bitumen 60° to 70° grade?
Ans. 47°C to 54°C

Q. What is the refusal density?
Ans. It is the density at which we get the highest value of Marshall density with the regular increase of blows.

Q. What is the difference between the theoretical and compacted density?
Ans. Theoretical density based on the Sp.G value and the other is simple density by calculation

Q. What is the overheated and over burnt asphalt? What should be max temperature of asphalt at the batching plant?
Ans. The mixing temperature of asphalt should be 160 5°C at the batching plant but if the temperature is more than 205±5°C it is considered overheated and to be rejected and if the temperature is between 163 to 105°C it can be used if the sample is tested and the over all properties are falling within specified limits.

Q. Why the loss of stability test is done in hot mix?
Ans. To know the durability of asphalt.

Q. What are the tests to be performed after taking the sample from site?
Preparation of Marshall molds
Sp.Gravity of molds (Gmb)
Stability of molds
Loss of stability of molds
Extraction of bitumen
Grading of Aggregate (Extracted sample)

Q. What is the variable speed of bitumen extraction machine?
Ans. The variable speed of extraction speed of extraction apparatus should be up to 3600 R/Min

Q. Which chemicals are used to extract the bitumen from the bituminous mixture?
1. Trichloroethaylene
2. Trichloroethane
3. Methylene chloride
4. Benzene
5. Ammonium carbonate

Q. If the grading is out or aggregate content is more what you will do?
Ans. 1 m x 1 m sample by jack hammer for extraction, stop the plant and take the sample from hot bin aggregate and done the individually grading, if the problem is coming than check the hot bin sample source if the problem is coming also now than check the plant using sieves, check the computer functioning if again ask for calibration, if not than take the trial and modify the plant trial.

Q. What is the use of silicons in hot mix?
Ans. Silicons are added to asphalt under certain conditions to reduced the effects of moisture, it may be added to hot asphalt to prevent foaming while in storage, used to prevent hardening of asphalt concrete in storage, to prevent slumping and segregation of the mixture during transportation and tearing of the mix during lay down.

Q. What is the use of rubber in asphalt?
Ans. Natural synthetic and reclaimed rubber in the form of powder, crumbs, pellets, and latex has been used in asphalt to alter certain properties, usually in amounts ranging from 1 to 5% materially changes the properties of asphalt. The purpose for using the rubberized asphalt has been to obtain a material possessing improved elasticity, increased adhesion and greater resistance to fracture at low temperature.

Q. What is the Cut Back asphalt and what are the different types of this?
Ans. The viscosity of which has been reduced by a volatile diluents. The volatile gets the evaporated and the binder develops the binding properties. The viscosity of cut back asphalt and its rate of hardening the road depend upon the quality of bitumen and volatile petroleum solvents.

Q. What are the main types and their function of cut back of asphalt?
Rapid Curing (RC)
Medium Curing (MC)
Slow Curing (SC)
Raid Curing (RC) It composed asphalt cement and naphtha or gasoline-type diluents of high volatility.
Medium Curing (MC) It composed of asphalt cement and kerosene-type diluents of medium volatility.
Slow Curing (SC) It composed of asphalt cement and oil of low volatility.

Q. What is Tack Coat of asphalt?
Ans. It is very light application of asphalt, usually asphalt emulsion diluted with water, it provides a bond between an existing pavement and an asphalting layer, which is too being placed over it.

Q. What is the rate of application of Tack Coat?
Ans. < 0.25 liters/M²

Q. What is a Prime coat?
Ans. A prime coat is an initial application of low viscosity emulsified or cut back asphalt to an absorbent surface, it is used to prepare an untreated base for an asphalt surfaces. It penetrates into the base and plugs the voids, hardens the top and helps bind it to the over lying asphalt course.

Q. What are the applications of Prime coat?
Water proofing the surface of the base
Reducing the capillary voids
Coating and bonding loose mineral particles
Hardening or toughening the surface
Promote adhesion between the base and the overlying asphalt course.

Q. What is the range of rate of application of Prime Coat?
Ans. 0.65 to 1.75 liters/M².

Q. In case of the excessive spray what should be done?
Ans. In this case when asphalt is not entirely absorbed by the base with in 24 hours the excess should be removed with just enough sand to prevent pick up under traffic.

Q. If spray on wet surface, what will be the side effect?
Ans. It will strip off; in this case extend the curing time and normally 24 hours required for curing period after initial spray

Q. How to recognize the RC-2 from MC-1?
RC – 2: It gives the smells of gasoline as bitumen is diluted with gasoline and it is thinner than MC-1and when it is dried it is faster than MC-1.
MC – 1: It gives the smells of kerosene as bitumen diluted with kerosene is called MC-1

Q. What is the Seal Coat? How many types of seal coat?
Ans. Actually a seal coat is a thin surface treatment that may or may not be covered or combined with aggregates.
1. Fog Seal
2. Slurry seal

Q. What is Fog seal?
Ans. It is a light application of emulsified asphalt usually without aggregate cover. The main purposes of fog seal are
Reduced entrance of air and water into the pavement.
Prevent raveling of a pavement.

Q. What is the slurry seal?
Ans. It is the mixture if slow setting Asphalt emulsion, Fine Agg, Mineral filler and water the mixer is poured into the pits and cracks in the pavement.

Q. What is the surface treatment of asphalt?
Ans. A sprayed on application of asphalt to a wearing surface, with or without a thin layer of covering an aggregate is called asphalt surface treatment.

Q. What is an asphalt surface treatment? What are the types of surface treatment?
Ans. Asphalt surface treatment is an application of asphaltic material to any type of road pavement surface with or without the cover of mineral aggregates, which produced an increase in thickness of not less than 25mm.
Single surface treatment
Multiple surface treatment
Double surface treatment

Q. What is the mineral filler?
Ans. The mineral filler is consisting of limestone dust, Portland cement or other suitable (inert) mineral matter. It should be thoroughly dried and free of lumps consisting of aggregates of fine particle. It should be pass from the sieve no.30 and 65% passing on sieve no.200

Q. What are the various types of mineral filler?
Ans. There are four different types of mineral filler
1. Limestone dust
2. Kaoline clay
3. Fuller’s earth
4. Short-fibered asbestos

Q. What is the grading range of filler?
Sieve NoPassing %

No. 30​


No. 50​


No. 200​


Q. What is the asphalt laying procedure?
Ans. Hot mix should be laid longitudinally in lane and joint should be cut in straight line or by using the straight edge to maintain the uniformity in lane.

Q. What is the permissible speed of paver while paving the asphalt?
Ans. While paving the asphalt the speed of paver should be 4 to 6 l.m/min.

Q. What is the weight of STR (steel tandem roller)?
Ans. The weight of roller should be in between 8 to 12 Tons.

Q. What is the weight of PTR (pneumatic tandem roller)?
Ans. The weight of PTR should be in between 20 to 25 Tons. And tyre pressure should be in between 6 to 6.3Kg/cm² or 80 to 110 Psi.

Q. What is the permissible speed of roller?
Ans. Roller speed should be 5Km/h.

Q. What should be the FRL (finish road level)?
Ans. FRL should be 15cm below the curbstone.

Q. What is the range of volume of asphalt mold for the unit correction factor?
Ans.509 to 522 cc for 4” (inches) diameter and 2.5 in height.

Q. What is the rolling operation on the asphalt pavement?
Ans. Rolling should start as soon as possible after material has been spread at temperature of 140°C, rolling consist of three consecutive phases.
1. Breakdown rolling
2. Intermediate rolling
3. Final rolling - rolling compacts the material beyond the compaction imparted by the paver, to obtain practically all of the needed density. Final rolling removes roller marks and other blemishes left from previous rolling.
Steel wheeled rollers vibrating by configuration are the two axles tandem rollers weighing 3 to 14 tons or more.
Pneumatic tired rollers have to eight wheels in the front and four to eight heels in the near weighing about 3 to 35 tons for the final rolling combination of steel vibrating and pneumatic tired rollers are used.

Q. What temperature of asphalt is required to stop the rolling?
Ans. No proper temperature has been assigned where the rolling of asphalt can be stopped. Rolling can be stopped only where it is observed that asphalt will probably gives not good results of density even far from the specified values and also if the temperature of asphalt is below than 90C rolling cannot be done in a proper way and asphalt can not be compacted.

Q. What is the limitation of Marshall method of mix design?
Ans. It is applicable to the asphalt mixes having up to 1” maximum size of aggregate.

Q. What are the specified “air voids” for asphalt wearing and base course?
Wearing Course = 4 – 7%
Base Course = 5 – 8%

Q. What is the specified flow for asphalt wearing and base course?
Wearing Course = 2 – 3.5 (Heavy traffic) and 2.4 – 4 (Light to Medium)
Base Course = 2 – 3.5 (Heavy traffic) and 2.4 – 4 (Light to Medium)

Q. What is the minimum value of marshal stability?
Wearing Course = 1000 Kg
Base Course = 1000 Kg

Q. What is the tolerance between the maximum and minimum Sp.G values of the marshall molds?
Ans. 0.02gm/cc

Q. How many blows are given on each side of the moulds?
Ans. The marshall specimen are compacted with “75” blows of hammer on both sides.

Q. What is the compacting temperature while performing the marshall moulds? How it is affects of Gmb.?
Ans. The compacting temperature for marshall mould test is 145± 5ºC.
In case the temperature during the process of making marshall test is higher as compared to 145 ±5°C, higher “Gmb” results are obtained. If it is lower than 145 ±5°C“Gmb” results are obtained.

Q. How much variation allowed in routine results of stability tests compared to design value?
Ans. Marshall stability should not more than looser than ±200 as compared to design value.

Q. What is the permissible time duration between taking out the mold from the water bath and testing the marshall stability?
Ans. Test should be finished in 30 seconds.

Q. What is the procedure for testing the stability and checking the flow value?
Ans. The test specimen are immersed in a water bath at 60°C for 30 minutes testing, lubricate the guide rod with a thin film of oil. Place the specimen in the machine mould and also place the flow meter and apply the load at constant rate the point of failure is the maximum load reading record the load reading and flow reading. The test should be finished within the 30 seconds after removal the specimen from the water bath.

Q. When correction factor is applied in stability test?
Ans. Correction factor is applied according to the volume of asphalt mold or thickness of asphalt mold, it is determined by multiplying the correction factor with obtained stability.

Q. How much variation is allowed in routine results of marshal stability as compared to design value?
Ans. Marshall stability should not vary by more than ± 200 Kgs. from the design value.

Q. What is fall and weight of Marshall hammer?
Ans. Hammer weight = 6.5 Kg and fall of Hammer = 18”.

Q. Define the DBM (Dense Base course Macadam) mix method?
Ans. Dense Base course Macadam) DBM mix is the mix which have coarse aggregate than base course 1-1/2 inch and have a separate method.

Q. What are the different types of mix design methods?
Marshall method (ASTM D 1559)
Haveem method (ASTM 1560 D 1561)
Hubbard Field method (AASHTO T 169 & ASTM D 1138)
Immersion compression method (ASTM D 1075 & AASHTO T 165)

Q. How will you find out the optimum asphalt content while preparing hot mix design?
Asphalt content at maximum stability = 4.83 %
Asphalt content at maximum unit weight = 5.1 %
Asphalt content at median of Air voids = 4.8 %
Optimum Asphalt Content = 4.91

Q. What are the desired properties of asphalt mix design?
Fatigue resistance
Skid resistance

Q. What problems come out if the hot mix contains little asphalt content?
Ans. The hot mix containing little asphalt content will give low stabilities and flow values, air voids will be higher and voids filled with asphalt will be lower. So that the quantity of asphalt should be used which ensures a durable pavement. Therefore much care should be adopted while calculating the optimum asphalt content as little increase or decrease can affect many other properties.

Q. What is the precautionary measure taken if a hot mix results low voids and low stability?
Ans. It is possible to improve the stability and increase the voids of the mix by increasing the amount of crushed material. Care should also be adopted in the use of asphalt content because hot mix having little asphalt cannot be compacted properly.

Q. What is the effect of “Asphalt content percentage on the Sp.Gravity” or Marshall molds (Gmb)?
Ans. Gmb increase with the increase of asphalt content. At optimum asphalt content value of Gmb is maximum and than start to decrease asphalt content increase.

Q. What is the precautionary measure taken if a hot mix results in excessive voids?
Ans. The increasing of the asphalt content can decrease the percentage of air voids. Increasing the mineral filler contents can also reduce voids. Care should be taken that asphalt content may be increased up to certain limits avoid further problems of rutting and bleeding.

Q. What is the precautionary measure to be adopted if the hot mix results low stability but the air voids satisfactory?
Ans. Low stability when voids and aggregate grading are satisfactory may indicate some deficiencies in the aggregate consideration should be given to improve the quality of aggregates. The aggregates may have to be changed and crushed hard materials may be used to improve the stability.

Q. What precautionary measures are adopted if the stability is coming abnormally higher?
Ans. If the stability is abnormally higher it can be controlled by reducing the coarse aggregate and adding the fine aggregates more. Coarse job mix for heavy traffic is the most suitable whereas the less coarser job mix is suitable for medium to light traffic The aggregate gradation and asphalt content must strike a favorable balance between the stability and durability requirements for the use intended. Reducing the asphalt content can also reduce Stability but the care should be adopted not to use little asphalt content to avoid the further problems in the pavement.
Stability can also be reduced in case the percentage of crushed sand may be lowered, but care should be taken not use the excess quantity of natural sand. It is always better to maintain the ration in the mix.
Crushed Sand = 80 and Natural Sand = 20

Q. What is the rea segregation in asphalt mix?
Improper Mix batching
Improper cold feed
Wrong bitumen content

Q. What is the relation between voids filled with asphalt and asphalt content in the hot mix?
Ans. Voids filed with asphalt increase as the asphalt the asphalt content increase, as the asphalt content decrease voids filled with asphalt starts decreasing.

Q. What is the relation between “Gmm & Asphalt content percentage”?
Ans. The asphalt content percentage increase Gmm starts decreasing and with the decreasing of asphalt content Gmm increase.

Q. What is the relation between “Stability & Asphalt content”?
Ans. Stability starts increasing as the asphalt content %ge increase but at certain point stability decrease even with the increase of asphalt content %.

Q. What is the relation between “Loss of stability & Asphalt content”?
Ans. With the increasing of asphalt content the loss of stability starts decreasing.

Q. What is the effect of “Gmm on Gse”?
Ans. Higher values of Gmm will give higher values of Gse in the hot mix.

Q.What is the relation between the “Gmb and Air voids”?
Ans. The value of Gmb decreases air voids starts increase.

Q. How to determine the voids in mineral aggregates (VMA%) in hot mix?
Ans. The volume of intergranular voids space between the aggregate particles of a compacted paving mixtures that includes air voids and effective asphalt content, expressed as a %ge of total vol. of sample.

Q. What is the effect of Sp.G of aggregates on the maximum Sp.G of compacted mix (Gmm).
Ans. The higher the Sp.G of aggregates, the higher the Gmm and if the Sp.G of aggregates is less low value of Gmm will be obtained.

Q. What is the effect of “Gmm” on effective Sp.G.
Ans. Higher values of Gmm will give higher values of effective Sp.G.

Q. What precautionary measures are adopted if the asphalt absorption in the hot mix is coming abnormally higher?
1. Sp.G of aggregates from hot bin may be checked and recalculate the combine Sp.Gravity (Gsb).
2. Effective Sp.Gravity of hot mix (Gse) may be checked.
In case of higher absorption either there is an error in Gsb or Gse and probably the erroneous results of Gmm can also affect the asphalt absorption.
Higher the Gmm value, higher values of Gse and obtained for higher value of Gse the value of Gsb may be close to Gse with a little difference between the values of Gse and Gsb higher absorption value.

Q. What is the effect of combined bulk Sp.G (oven dry) on asphalt absorption?
Ans. The combine bulk Sp.G is calculated by the Sp.G of all aggregates used in the hot mix therefore Sp.G of aggregates plays an important role in increasing or decreasing the asphalt absorption in asphalt concrete. The higher the combined bulk Sp.G of aggregates, the lesser the asphalt absorption. The lesser the combined bulk Sp.G of aggregates achieves the higher absorption of asphalt.

Q. What is the asphalt quantity measurement method for required area?
Ans. For Example!
Area = 20m x 10m x 600mm (Thickness)
= 20 x 10 x 0.6
= 120m³
= 120m³ x 2.50 (Density of Asphalt)
= 300
=300 x 100 / 1000
= 30 Tons.

Q. What are the main parts of asphalt plant?
1. Cold bins
2. Cold feed gate
3. Cold elevator
4. Dryer
5. Dust controller
6. Exhaust stack
7. Hot elevator
8. Sieves unit
9. Hot bins
10. Weighing box
11. Mixing unit (Pugmil)
12. Mineral filler storage
13. Hot asphalt cement storage
14. Asphalt weighing bucket

Q. What are the main types of pavement failure?
Bleeding or Flushing:
Due to excess of asphalt, lack of proper rolling or traffic control.
Corrugation and Shooing:
It will be due to instability of asphalt layer, asphalt excess, too much fine aggregate, too much moisture content is in the area and oil spoilage.
Cracking Alligator:
It is the interconnecting cracking forming a series of small polygons. It is due to poor drainage, cut out pavement and wet material.
Cracking Edge:
It is the cracking at base layer without surface distortion caused due to lack of shoulder and poor drainage.
Cracking Joint:
It occur where the shoulder separate from the main line of pavement. It would be due to trap of water between the joint and main line surface. If it were less than ¼ then would be filled with bitumen.
Cracking Random:
It was occur due to deep foundation settlement slightly of some construction error. If it is more than ¼ inch than do some skin patch or filled with emulsified asphalt.
Cracking Reflection:
It is caused due to horizontal movement in the pavement due to expansion and contraction or down beneath may be concrete.
Cracking Shrinkage:
It is caused due to volume change in the asphalt base course and sub grade.
Pot holes:
It occurs during the winter month due to water penetration in the sub base or sub grade or thin layer or few fines in the mix.
It is caused by a dry little surface, dirty, dusty or soft agar, lack of compaction of surface, too little asphalt in the mix or more heat.
Channels or Rutting:
It caused due to heavy load or high tire pressure, sub grade settlement caused by saturation, poor construction methods and weak asphalt mix.
Intact Surface:
It is depression more than 1 inch caused due to settlement of the bed.
Upheaval or Frost boil: It occurs due to expansion of freezing moisture in the sub grade area or swelling in the soil.