Road Construction Technology

Activities involved in road construction (Manual §3.2):

Tools, equipment and plants used in road construction (Manual §3.3):

For a bituminous road the key items are the hot-mix plant, bitumen distributor, chip spreader, mechanical paver, tippers, and smooth-wheeled + pneumatic rollers. For a cement-concrete road they are the batching & mixing plant, transit/truck mixers, concrete paver-finisher, needle (poker) vibrators, screed/float, joint-cutting machine, and curing equipment.

Manual.pdf §3.2 and §3.3, book pp.206-208; Lecture 22-24 (§4.1-4.2 of these notes).

Activities involved in road construction (Manual §3.2):

Otta seal is a bituminous surface treatment made by placing a layer of graded aggregate (not single-sized as in ordinary surface dressing) on a thick application of a relatively soft bituminous binder; the binder is drawn up through the aggregate by rolling and by traffic, producing a flexible mosaic. It is the standard low-cost surfacing for Nepalese district roads.

Materials — hard, strong, durable graded aggregate with aggregate impact value ≤ 30%, Los Angeles abrasion ≤ 40%, flakiness index ≤ 30%, plasticity index < 5%, graded as per specification; binder MC 3000 or MC 800 cutback bitumen.

Equipment — bitumen distributor, storage tank with heating device, chip/aggregate spreader, pneumatic-tyred roller and mechanical broom.

Construction steps

1. Remove dust and foreign matter from the base with a mechanical broom / hand brushes and an air compressor.
2. Apply the prime coat at the specified rate.
3. Spray the bituminous binding agent generously over the prepared surface with the distributor.
4. Spread the graded aggregate uniformly with an aggregate spreader.
5. Roll with a pneumatic-tyred roller to embed and realign the chippings and to start drawing the binder up through the aggregate.
6. Because of the fines in the aggregate, two or three days of rolling or of traffic are needed for the binder to coat all the particles.
7. During the first few weeks the aggregate dislodged by traffic is swept back into the wheel paths.
8. After about three weeks the surface is swept with a mechanical broom to remove all loose aggregate.
9. For a double Otta seal, the second layer is constructed in the same way two to three months after the first.

Manual.pdf §3.2 (book p.206) and §3.8 — Construction of Otta seal (book p.219).

Tools, equipment and plants used in road construction (Manual §3.3):

For a bituminous road the key items are the hot-mix plant, bitumen distributor, chip spreader, mechanical paver, tippers, and smooth-wheeled + pneumatic rollers. For a cement-concrete road they are the batching & mixing plant, transit/truck mixers, concrete paver-finisher, needle (poker) vibrators, screed/float, joint-cutting machine, and curing equipment.

Double Bituminous Surface Dressing (DBSD) — materials and construction

Surface dressing = a thin bituminous surface treatment in which a bituminous binder is sprayed on the prepared base and immediately covered with single-sized stone chippings which are then rolled in. It provides a waterproof, dust-free, skid-resistant wearing surface and protects the base from abrasion, but adds no structural strength.

• SBST — Single Bituminous Surface Treatment (one binder + one chipping application).
• DBST / DBSD — Double Bituminous Surface Treatment / Double Bituminous Surface Dressing (two successive applications, the second with about half the binder and half the chipping size).

Materials: bitumen of grade 80/100 or 180/200 (or a cationic emulsion); cover aggregate with Los Angeles abrasion < 35%, aggregate impact value < 30%, flakiness index < 25% and water absorption < 1%.

Equipment: bitumen heating/storage unit, bitumen distributor (sprayer), chip spreader, 5-8 t smooth-wheeled or pneumatic-tyred roller, and mechanical brooms.

Construction procedure (SBST)

1. Clean the existing surface with mechanical brooms and repair pot-holes, ruts and depressions.
2. Apply the prime coat at the specified rate if the base is pervious, and cure it for at least 24 hours with no traffic.
3. Spray the bitumen uniformly from the distributor at the design rate.
4. Spread the cover aggregate of uniform gradation before the binder sets.
5. Roll with a pneumatic-tyred roller (starting from the edges, moving to the centre, overlapping one-third of the roller width) to press the chippings into the binder.
6. Sweep off the excess chippings within 24-48 hours and open to traffic.

Construction procedure (DBST / DBSD) — carry out a complete SBST as above; sweep away the loose aggregate; apply a second binder application of about one-third to one-half of the first; spread aggregate about half the size of the first application; roll with a pneumatic-tyred roller; and again broom off the excess within 24-48 hours.

Quality control: binder temperature; aggregate tests (LAA, impact value, flakiness index, plasticity index); gradation; rate of application of binder and aggregate; and binder tests (penetration, viscosity, ductility).

Manual.pdf §3.3 (book p.207) and §3.7 (book p.218); Lecture 22-24 §4.8.

Mass Haul Diagram (MHD) — a graphical representation of the cumulative earthwork volume (cut positive, fill negative, after applying the shrinkage/swell correction) plotted against chainage, drawn immediately below the longitudinal profile. It tells the contractor how much material must be moved, how far, and in which direction, and lets the average haul, free haul and overhaul be measured.

Characteristics of the mass haul diagram

1. Rising curve = cut (excavation exceeds fill); falling curve = fill.
2. A steep slope means a large quantity of earthwork per unit length; a flat slope means little earthwork.
3. The difference of ordinates between any two points = the net volume of cut over fill (or vice-versa) between those points.
4. Points of zero slope (maxima and minima) are the points where the work changes from cut to fill or fill to cut, i.e. the grade points where the formation line crosses the natural ground.
5. Any horizontal line that cuts the curve at two points is a balancing line: cut and fill between those two balance points are equal, so that length is self-balancing.
6. A loop above the balancing line means the haul is from left to right (convex loop); a loop below means the haul is from right to left.
7. The area enclosed between the curve and the balancing line = haul (volume × distance, m³·m or station-yards); dividing it by the maximum ordinate gives the average haul distance.

Sketch: longitudinal profile on top (CUT – FILL – CUT), mass curve below with the balancing line, free-haul line and the loops marked.

Shrinkage — earth taken from a cut or a borrow pit occupies a smaller volume after it is compacted in the embankment, because the compacted density is higher than the in-situ density. The volume of cut is therefore multiplied by a shrinkage factor (typically 0.80-0.90, i.e. 10-20% shrinkage) before it is plotted on the mass haul diagram.

Swelling (bulking) — rock and some hard materials occupy a larger volume after excavation than in place, because of the voids created by breaking; the swell factor may be 1.20-1.40 (20-40% swell).

Both corrections must be applied to the volumes before the mass curve is drawn, otherwise the balance points and the haul quantities will be wrong.

Manual.pdf §3.4 — Mass haul diagram, book pp.208-210.

Mass Haul Diagram (MHD) — a graphical representation of the cumulative earthwork volume (cut positive, fill negative, after applying the shrinkage/swell correction) plotted against chainage, drawn immediately below the longitudinal profile. It tells the contractor how much material must be moved, how far, and in which direction, and lets the average haul, free haul and overhaul be measured.

Characteristics of the mass haul diagram

1. Rising curve = cut (excavation exceeds fill); falling curve = fill.
2. A steep slope means a large quantity of earthwork per unit length; a flat slope means little earthwork.
3. The difference of ordinates between any two points = the net volume of cut over fill (or vice-versa) between those points.
4. Points of zero slope (maxima and minima) are the points where the work changes from cut to fill or fill to cut, i.e. the grade points where the formation line crosses the natural ground.
5. Any horizontal line that cuts the curve at two points is a balancing line: cut and fill between those two balance points are equal, so that length is self-balancing.
6. A loop above the balancing line means the haul is from left to right (convex loop); a loop below means the haul is from right to left.
7. The area enclosed between the curve and the balancing line = haul (volume × distance, m³·m or station-yards); dividing it by the maximum ordinate gives the average haul distance.

Sketch: longitudinal profile on top (CUT – FILL – CUT), mass curve below with the balancing line, free-haul line and the loops marked.

Haul = the transport of excavated material from its original position to its final location (also called authorised haul), measured as volume × distance.

Free haul distance = the distance up to which the contractor must move the earth without any extra payment — it is already covered by the unit rate for excavation (commonly 300 m in Nepalese/Indian practice). On the MHD it is shown by a horizontal line whose intercept on the curve equals the free-haul distance.

Overhaul = the haul in excess of the free-haul distance, for which an extra payment is made:

Economic haul distance (limit of economic haul) = the distance beyond which it becomes cheaper to waste the excavated material and borrow fresh material for the fill than to haul it:

Shrinkage — earth taken from a cut or a borrow pit occupies a smaller volume after it is compacted in the embankment, because the compacted density is higher than the in-situ density. The volume of cut is therefore multiplied by a shrinkage factor (typically 0.80-0.90, i.e. 10-20% shrinkage) before it is plotted on the mass haul diagram.

Swelling (bulking) — rock and some hard materials occupy a larger volume after excavation than in place, because of the voids created by breaking; the swell factor may be 1.20-1.40 (20-40% swell).

Both corrections must be applied to the volumes before the mass curve is drawn, otherwise the balance points and the haul quantities will be wrong.

Manual.pdf §3.4, book pp.208-210.

Mass Haul Diagram (MHD) — a graphical representation of the cumulative earthwork volume (cut positive, fill negative, after applying the shrinkage/swell correction) plotted against chainage, drawn immediately below the longitudinal profile. It tells the contractor how much material must be moved, how far, and in which direction, and lets the average haul, free haul and overhaul be measured.

Characteristics of the mass haul diagram

1. Rising curve = cut (excavation exceeds fill); falling curve = fill.
2. A steep slope means a large quantity of earthwork per unit length; a flat slope means little earthwork.
3. The difference of ordinates between any two points = the net volume of cut over fill (or vice-versa) between those points.
4. Points of zero slope (maxima and minima) are the points where the work changes from cut to fill or fill to cut, i.e. the grade points where the formation line crosses the natural ground.
5. Any horizontal line that cuts the curve at two points is a balancing line: cut and fill between those two balance points are equal, so that length is self-balancing.
6. A loop above the balancing line means the haul is from left to right (convex loop); a loop below means the haul is from right to left.
7. The area enclosed between the curve and the balancing line = haul (volume × distance, m³·m or station-yards); dividing it by the maximum ordinate gives the average haul distance.

Sketch: longitudinal profile on top (CUT – FILL – CUT), mass curve below with the balancing line, free-haul line and the loops marked.

Soil-cement stabilised base — materials

• Soil: material passing 4.75 mm > 50%, passing 75 μm < 50%, liquid limit < 40%, plasticity index < 18%.
• Ordinary Portland cement, 2-12% by weight, the exact percentage fixed by laboratory (unconfined compressive strength) tests.
• Clean water for hydration and compaction at OMC.

Equipment — mix-in-place: rotavator/pulvi-mixer or graders (or hand tools for labour-based work), cement spreader, water tanker, smooth-wheeled/vibratory roller; plant-mix: a central mixing plant with cement truck-mixers plus the same spreading and compacting equipment.

Construction procedure

1. Prepare the subgrade / sub-base to the required grade and camber.
2. Pulverize the soil to the required degree of pulverisation.
3. Spread the cement uniformly at the designed rate and dry-mix it with the soil.
4. Add water to bring the mix to OMC and re-mix thoroughly.
5. Spread and grade the mix to the required thickness, level and camber.
6. Compact with a smooth-wheeled (or vibratory) roller to the specified dry density; the whole operation from adding water to finishing compaction must be completed within about 2 hours of adding the cement.
7. Moist-cure for about 7 days by preventing moisture loss (bituminous seal, moist earth cover or wet hessian).

Field controls — degree of pulverisation, cement content, moisture content, field dry density, unconfined compressive strength of moulded specimens, and surface regularity.

Manual.pdf §3.4 (book pp.208-210) and Lecture 22-24 §4.5 (soil-cement stabilisation).

Mass Haul Diagram (MHD) — a graphical representation of the cumulative earthwork volume (cut positive, fill negative, after applying the shrinkage/swell correction) plotted against chainage, drawn immediately below the longitudinal profile. It tells the contractor how much material must be moved, how far, and in which direction, and lets the average haul, free haul and overhaul be measured.

Characteristics of the mass haul diagram

1. Rising curve = cut (excavation exceeds fill); falling curve = fill.
2. A steep slope means a large quantity of earthwork per unit length; a flat slope means little earthwork.
3. The difference of ordinates between any two points = the net volume of cut over fill (or vice-versa) between those points.
4. Points of zero slope (maxima and minima) are the points where the work changes from cut to fill or fill to cut, i.e. the grade points where the formation line crosses the natural ground.
5. Any horizontal line that cuts the curve at two points is a balancing line: cut and fill between those two balance points are equal, so that length is self-balancing.
6. A loop above the balancing line means the haul is from left to right (convex loop); a loop below means the haul is from right to left.
7. The area enclosed between the curve and the balancing line = haul (volume × distance, m³·m or station-yards); dividing it by the maximum ordinate gives the average haul distance.

Sketch: longitudinal profile on top (CUT – FILL – CUT), mass curve below with the balancing line, free-haul line and the loops marked.

Haul = the transport of excavated material from its original position to its final location (also called authorised haul), measured as volume × distance.

Free haul distance = the distance up to which the contractor must move the earth without any extra payment — it is already covered by the unit rate for excavation (commonly 300 m in Nepalese/Indian practice). On the MHD it is shown by a horizontal line whose intercept on the curve equals the free-haul distance.

Overhaul = the haul in excess of the free-haul distance, for which an extra payment is made:

Economic haul distance (limit of economic haul) = the distance beyond which it becomes cheaper to waste the excavated material and borrow fresh material for the fill than to haul it:

Manual.pdf §3.4, book pp.208-210.

Mass Haul Diagram (definition) — a graphical representation of the cumulative earthwork volume (cut positive, fill negative, corrected for shrinkage/swell) plotted against chainage below the longitudinal profile; it shows how much earth has to be moved, how far and in which direction, and from it the average haul, the free haul and the overhaul are measured.

Water Bound Macadam (WBM) — a base/sub-base course of crushed or broken stone whose particles are mechanically interlocked by rolling, the voids being filled with screenings and binding material with the help of water (pioneered by John Loudon McAdam, c.1820).

Materials

• Coarse aggregate — crushed / broken hard stone or gravel of the specified grading (63-90 mm, 53-63 mm or 22.4-53 mm depending on the course); stock 20% extra along the road.
• Screenings — smaller aggregate (13.2 mm / 11.2 mm) to fill the voids.
• Binding material — stone dust, kankar nodules or a suitable plastic soil (PI ≤ 6 for base course, 5-10 for the surface course).
• Water.

Equipment — water tanker, dump trucks, motor grader, three-wheeled 8-10 t power roller (or tandem / vibratory roller), rakes and hand tools.

Construction procedure

1. Preparation of the foundation — the subgrade or the lower course is prepared to the required grade and camber, and any pot-holes or ruts are made good.
2. Provision of lateral confinement — shoulders/kerbs are built up first so that the aggregate cannot spread sideways during rolling.
3. Spreading of the coarse aggregate uniformly to a loose thickness that gives a compacted layer not exceeding 75-100 mm.
4. Dry rolling with an 8-10 t roller, starting from the edges and progressing to the centre with a one-third overlap, until the aggregate is well keyed.
5. Application of screenings in three or more thin doses with dry rolling and brooming, so that the voids are filled without forming a crust.
6. Sprinkling of water and wet rolling — the surface is sprinkled, swept and rolled until about half the voids are filled.
7. Application of the binding material as a slurry, in two or more thin layers, each followed by wet rolling and brooming until a wave of grout appears ahead of the roller.
8. Setting and drying — the finished course is allowed to dry overnight (or cured) before the next layer is laid or traffic is admitted.

Quality control — aggregate tests (Los Angeles abrasion, aggregate impact value, flakiness & elongation index), gradation, plasticity index of the binding material, moisture at 90-105% of OMC, and field dry density (98% of MDD for base, 95% for sub-base and shoulders).

Manual.pdf §3.4 (book p.208) and Lecture 22-24 §4.5 (WBM).

Mass Haul Diagram (MHD) — a graphical representation of the cumulative earthwork volume (cut positive, fill negative, after applying the shrinkage/swell correction) plotted against chainage, drawn immediately below the longitudinal profile. It tells the contractor how much material must be moved, how far, and in which direction, and lets the average haul, free haul and overhaul be measured.

Characteristics of the mass haul diagram

1. Rising curve = cut (excavation exceeds fill); falling curve = fill.
2. A steep slope means a large quantity of earthwork per unit length; a flat slope means little earthwork.
3. The difference of ordinates between any two points = the net volume of cut over fill (or vice-versa) between those points.
4. Points of zero slope (maxima and minima) are the points where the work changes from cut to fill or fill to cut, i.e. the grade points where the formation line crosses the natural ground.
5. Any horizontal line that cuts the curve at two points is a balancing line: cut and fill between those two balance points are equal, so that length is self-balancing.
6. A loop above the balancing line means the haul is from left to right (convex loop); a loop below means the haul is from right to left.
7. The area enclosed between the curve and the balancing line = haul (volume × distance, m³·m or station-yards); dividing it by the maximum ordinate gives the average haul distance.

Sketch: longitudinal profile on top (CUT – FILL – CUT), mass curve below with the balancing line, free-haul line and the loops marked.

Tools, equipment and plants used in road construction (Manual §3.3):

For a bituminous road the key items are the hot-mix plant, bitumen distributor, chip spreader, mechanical paver, tippers, and smooth-wheeled + pneumatic rollers. For a cement-concrete road they are the batching & mixing plant, transit/truck mixers, concrete paver-finisher, needle (poker) vibrators, screed/float, joint-cutting machine, and curing equipment.

Manual.pdf §3.4 (book pp.208-210) and §3.3 (book p.207).

Mass Haul Diagram (MHD) — a graphical representation of the cumulative earthwork volume (cut positive, fill negative, after applying the shrinkage/swell correction) plotted against chainage, drawn immediately below the longitudinal profile. It tells the contractor how much material must be moved, how far, and in which direction, and lets the average haul, free haul and overhaul be measured.

Characteristics of the mass haul diagram

1. Rising curve = cut (excavation exceeds fill); falling curve = fill.
2. A steep slope means a large quantity of earthwork per unit length; a flat slope means little earthwork.
3. The difference of ordinates between any two points = the net volume of cut over fill (or vice-versa) between those points.
4. Points of zero slope (maxima and minima) are the points where the work changes from cut to fill or fill to cut, i.e. the grade points where the formation line crosses the natural ground.
5. Any horizontal line that cuts the curve at two points is a balancing line: cut and fill between those two balance points are equal, so that length is self-balancing.
6. A loop above the balancing line means the haul is from left to right (convex loop); a loop below means the haul is from right to left.
7. The area enclosed between the curve and the balancing line = haul (volume × distance, m³·m or station-yards); dividing it by the maximum ordinate gives the average haul distance.

Sketch: longitudinal profile on top (CUT – FILL – CUT), mass curve below with the balancing line, free-haul line and the loops marked.

Haul = the transport of excavated material from its original position to its final location (also called authorised haul), measured as volume × distance.

Free haul distance = the distance up to which the contractor must move the earth without any extra payment — it is already covered by the unit rate for excavation (commonly 300 m in Nepalese/Indian practice). On the MHD it is shown by a horizontal line whose intercept on the curve equals the free-haul distance.

Overhaul = the haul in excess of the free-haul distance, for which an extra payment is made:

Economic haul distance (limit of economic haul) = the distance beyond which it becomes cheaper to waste the excavated material and borrow fresh material for the fill than to haul it:

Shrinkage — earth taken from a cut or a borrow pit occupies a smaller volume after it is compacted in the embankment, because the compacted density is higher than the in-situ density. The volume of cut is therefore multiplied by a shrinkage factor (typically 0.80-0.90, i.e. 10-20% shrinkage) before it is plotted on the mass haul diagram.

Swelling (bulking) — rock and some hard materials occupy a larger volume after excavation than in place, because of the voids created by breaking; the swell factor may be 1.20-1.40 (20-40% swell).

Both corrections must be applied to the volumes before the mass curve is drawn, otherwise the balance points and the haul quantities will be wrong.

Manual.pdf §3.4, book pp.208-210.

(a) Mass haul diagram, equipment and plants [2+6]

Mass Haul Diagram (MHD) — a graphical representation of the cumulative earthwork volume (cut positive, fill negative, after applying the shrinkage/swell correction) plotted against chainage, drawn immediately below the longitudinal profile. It tells the contractor how much material must be moved, how far, and in which direction, and lets the average haul, free haul and overhaul be measured.

Characteristics of the mass haul diagram

1. Rising curve = cut (excavation exceeds fill); falling curve = fill.
2. A steep slope means a large quantity of earthwork per unit length; a flat slope means little earthwork.
3. The difference of ordinates between any two points = the net volume of cut over fill (or vice-versa) between those points.
4. Points of zero slope (maxima and minima) are the points where the work changes from cut to fill or fill to cut, i.e. the grade points where the formation line crosses the natural ground.
5. Any horizontal line that cuts the curve at two points is a balancing line: cut and fill between those two balance points are equal, so that length is self-balancing.
6. A loop above the balancing line means the haul is from left to right (convex loop); a loop below means the haul is from right to left.
7. The area enclosed between the curve and the balancing line = haul (volume × distance, m³·m or station-yards); dividing it by the maximum ordinate gives the average haul distance.

Sketch: longitudinal profile on top (CUT – FILL – CUT), mass curve below with the balancing line, free-haul line and the loops marked.

Tools, equipment and plants used in road construction (Manual §3.3):

For a bituminous road the key items are the hot-mix plant, bitumen distributor, chip spreader, mechanical paver, tippers, and smooth-wheeled + pneumatic rollers. For a cement-concrete road they are the batching & mixing plant, transit/truck mixers, concrete paver-finisher, needle (poker) vibrators, screed/float, joint-cutting machine, and curing equipment.

(b) Prime coat vs tack coat; construction of surface dressing [2+6]

Interface treatment is a thin film of bituminous binder sprayed on an existing surface before a new bituminous layer is laid. There are two types — prime coat and tack coat; the seal coat is a final surface treatment.

Equipment (all three): mechanical broom or hand brushes for cleaning, bitumen distributor (self-propelled or towed pressure sprayer) with a heating device, chip/aggregate spreader and light rollers.

Construction procedure (common): (1) sweep the surface clean with a mechanical broom and remove all loose material; (2) do not spray in rainy, windy or foggy weather or below 10°C; (3) spray the binder uniformly at the specified rate with the distributor; (4) for a seal coat, spread the cover aggregate before the binder sets and roll it in; (5) allow the specified curing period before opening to traffic or laying the next layer.

Surface dressing = a thin bituminous surface treatment in which a bituminous binder is sprayed on the prepared base and immediately covered with single-sized stone chippings which are then rolled in. It provides a waterproof, dust-free, skid-resistant wearing surface and protects the base from abrasion, but adds no structural strength.

• SBST — Single Bituminous Surface Treatment (one binder + one chipping application).
• DBST / DBSD — Double Bituminous Surface Treatment / Double Bituminous Surface Dressing (two successive applications, the second with about half the binder and half the chipping size).

Materials: bitumen of grade 80/100 or 180/200 (or a cationic emulsion); cover aggregate with Los Angeles abrasion < 35%, aggregate impact value < 30%, flakiness index < 25% and water absorption < 1%.

Equipment: bitumen heating/storage unit, bitumen distributor (sprayer), chip spreader, 5-8 t smooth-wheeled or pneumatic-tyred roller, and mechanical brooms.

Construction procedure (SBST)

1. Clean the existing surface with mechanical brooms and repair pot-holes, ruts and depressions.
2. Apply the prime coat at the specified rate if the base is pervious, and cure it for at least 24 hours with no traffic.
3. Spray the bitumen uniformly from the distributor at the design rate.
4. Spread the cover aggregate of uniform gradation before the binder sets.
5. Roll with a pneumatic-tyred roller (starting from the edges, moving to the centre, overlapping one-third of the roller width) to press the chippings into the binder.
6. Sweep off the excess chippings within 24-48 hours and open to traffic.

Construction procedure (DBST / DBSD) — carry out a complete SBST as above; sweep away the loose aggregate; apply a second binder application of about one-third to one-half of the first; spread aggregate about half the size of the first application; roll with a pneumatic-tyred roller; and again broom off the excess within 24-48 hours.

Quality control: binder temperature; aggregate tests (LAA, impact value, flakiness index, plasticity index); gradation; rate of application of binder and aggregate; and binder tests (penetration, viscosity, ductility).

Manual.pdf §3.3, §3.4, §3.6 and §3.7 (book pp.207-219).

Soil stabilisation = improving the strength, durability and volume stability of a soil by proportioning it with other materials and/or by adding an admixture, and compacting it, so that it can be used as a sub-base or base course.

Methods of soil stabilisation and when each is applicable

Advantages: increases the bearing capacity and shear strength of the soil, prevents changes of soil properties with moisture, prevents cracking, and improves drainage and frost resistance.

Soil-lime stabilised road — materials

• Consistent-quality slaked / hydrated lime, Ca(OH)₂, 4-8% by weight (the exact percentage from laboratory strength tests).
• Clayey or high-plasticity soil to be stabilised.
• Fresh water for moisture control and curing.

Construction procedure

1. Prepare the subgrade to the required grade and camber.
2. Pulverize the soil to be stabilised.
3. Add part of the lime (as dry powder or as a slurry with water) and mix.
4. Allow the mixture to age (mellow) for about a day — the lime breaks down the clay clods so that pulverisation becomes easy — then re-mix.
5. Add the remaining lime and water if necessary and re-mix.
6. Spread to the desired grade and shape.
7. Compact first with a sheep-foot roller and finish with a smooth-wheeled roller.
8. Moist-cure for about 14 days, protecting the layer from drying out.

Field controls — lime content, moisture content, field dry density and surface regularity.

Lecture 22-24 §4.5 (soil stabilisation) and Manual.pdf §3.5, book pp.210-216.

Soil stabilisation = improving the strength, durability and volume stability of a soil by proportioning it with other materials and/or by adding an admixture, and compacting it, so that it can be used as a sub-base or base course.

Methods of soil stabilisation and when each is applicable

Advantages: increases the bearing capacity and shear strength of the soil, prevents changes of soil properties with moisture, prevents cracking, and improves drainage and frost resistance.

Soil-cement stabilised base — materials

• Soil: material passing 4.75 mm > 50%, passing 75 μm < 50%, liquid limit < 40%, plasticity index < 18%.
• Ordinary Portland cement, 2-12% by weight, the exact percentage fixed by laboratory (unconfined compressive strength) tests.
• Clean water for hydration and compaction at OMC.

Equipment — mix-in-place: rotavator/pulvi-mixer or graders (or hand tools for labour-based work), cement spreader, water tanker, smooth-wheeled/vibratory roller; plant-mix: a central mixing plant with cement truck-mixers plus the same spreading and compacting equipment.

Construction procedure

1. Prepare the subgrade / sub-base to the required grade and camber.
2. Pulverize the soil to the required degree of pulverisation.
3. Spread the cement uniformly at the designed rate and dry-mix it with the soil.
4. Add water to bring the mix to OMC and re-mix thoroughly.
5. Spread and grade the mix to the required thickness, level and camber.
6. Compact with a smooth-wheeled (or vibratory) roller to the specified dry density; the whole operation from adding water to finishing compaction must be completed within about 2 hours of adding the cement.
7. Moist-cure for about 7 days by preventing moisture loss (bituminous seal, moist earth cover or wet hessian).

Field controls — degree of pulverisation, cement content, moisture content, field dry density, unconfined compressive strength of moulded specimens, and surface regularity.

Lecture 22-24 §4.5; Manual.pdf §3.5, book pp.210-216.

(a) Factors affecting soil stabilisation

For mechanical stabilisation: mechanical strength of the aggregate, gradation of the blended material, properties (plasticity, fines content) of the soil, presence of deleterious matter such as salts and mica, and the degree of compaction.

For cement / lime / bitumen stabilisation: nature and type of the soil, the content of the stabiliser, moisture content and degree of compaction, the dry density achieved, curing (period and method), and the use of additives.

(b) Mechanical method of soil stabilisation

Mechanical stabilisation is the blending of two or more materials so that the mixture satisfies the required grading, plasticity and strength criteria, followed by compaction. No chemical admixture is used — the basic principle is only proportioning and compaction. Typically a granular material with insufficient fines is blended with a fine soil (which provides the binder), or a fine soil is blended with granular material (which provides the load-carrying skeleton). Its construction sequence is: prepare the subgrade/sub-base → pulverize the soil → add the required proportion of the second material and mix (grader or rotavator) → spread and grade → compact with a smooth-wheeled/vibrating roller.

(c) Construction of a cement-soil stabilised road base

Soil-cement stabilised base — materials

• Soil: material passing 4.75 mm > 50%, passing 75 μm < 50%, liquid limit < 40%, plasticity index < 18%.
• Ordinary Portland cement, 2-12% by weight, the exact percentage fixed by laboratory (unconfined compressive strength) tests.
• Clean water for hydration and compaction at OMC.

Equipment — mix-in-place: rotavator/pulvi-mixer or graders (or hand tools for labour-based work), cement spreader, water tanker, smooth-wheeled/vibratory roller; plant-mix: a central mixing plant with cement truck-mixers plus the same spreading and compacting equipment.

Construction procedure

1. Prepare the subgrade / sub-base to the required grade and camber.
2. Pulverize the soil to the required degree of pulverisation.
3. Spread the cement uniformly at the designed rate and dry-mix it with the soil.
4. Add water to bring the mix to OMC and re-mix thoroughly.
5. Spread and grade the mix to the required thickness, level and camber.
6. Compact with a smooth-wheeled (or vibratory) roller to the specified dry density; the whole operation from adding water to finishing compaction must be completed within about 2 hours of adding the cement.
7. Moist-cure for about 7 days by preventing moisture loss (bituminous seal, moist earth cover or wet hessian).

Field controls — degree of pulverisation, cement content, moisture content, field dry density, unconfined compressive strength of moulded specimens, and surface regularity.

Lecture 22-24 §4.5 (factors, mechanical and soil-cement stabilisation); Manual.pdf §3.5.

Water Bound Macadam (WBM) — a base/sub-base course of crushed or broken stone whose particles are mechanically interlocked by rolling, the voids being filled with screenings and binding material with the help of water (pioneered by John Loudon McAdam, c.1820).

Materials

• Coarse aggregate — crushed / broken hard stone or gravel of the specified grading (63-90 mm, 53-63 mm or 22.4-53 mm depending on the course); stock 20% extra along the road.
• Screenings — smaller aggregate (13.2 mm / 11.2 mm) to fill the voids.
• Binding material — stone dust, kankar nodules or a suitable plastic soil (PI ≤ 6 for base course, 5-10 for the surface course).
• Water.

Equipment — water tanker, dump trucks, motor grader, three-wheeled 8-10 t power roller (or tandem / vibratory roller), rakes and hand tools.

Construction procedure

1. Preparation of the foundation — the subgrade or the lower course is prepared to the required grade and camber, and any pot-holes or ruts are made good.
2. Provision of lateral confinement — shoulders/kerbs are built up first so that the aggregate cannot spread sideways during rolling.
3. Spreading of the coarse aggregate uniformly to a loose thickness that gives a compacted layer not exceeding 75-100 mm.
4. Dry rolling with an 8-10 t roller, starting from the edges and progressing to the centre with a one-third overlap, until the aggregate is well keyed.
5. Application of screenings in three or more thin doses with dry rolling and brooming, so that the voids are filled without forming a crust.
6. Sprinkling of water and wet rolling — the surface is sprinkled, swept and rolled until about half the voids are filled.
7. Application of the binding material as a slurry, in two or more thin layers, each followed by wet rolling and brooming until a wave of grout appears ahead of the roller.
8. Setting and drying — the finished course is allowed to dry overnight (or cured) before the next layer is laid or traffic is admitted.

Quality control — aggregate tests (Los Angeles abrasion, aggregate impact value, flakiness & elongation index), gradation, plasticity index of the binding material, moisture at 90-105% of OMC, and field dry density (98% of MDD for base, 95% for sub-base and shoulders).

Lecture 22-24 §4.5; Manual.pdf §3.5.

Water Bound Macadam (WBM) — a base/sub-base course of crushed or broken stone whose particles are mechanically interlocked by rolling, the voids being filled with screenings and binding material with the help of water (pioneered by John Loudon McAdam, c.1820).

Materials

• Coarse aggregate — crushed / broken hard stone or gravel of the specified grading (63-90 mm, 53-63 mm or 22.4-53 mm depending on the course); stock 20% extra along the road.
• Screenings — smaller aggregate (13.2 mm / 11.2 mm) to fill the voids.
• Binding material — stone dust, kankar nodules or a suitable plastic soil (PI ≤ 6 for base course, 5-10 for the surface course).
• Water.

Equipment — water tanker, dump trucks, motor grader, three-wheeled 8-10 t power roller (or tandem / vibratory roller), rakes and hand tools.

Construction procedure

1. Preparation of the foundation — the subgrade or the lower course is prepared to the required grade and camber, and any pot-holes or ruts are made good.
2. Provision of lateral confinement — shoulders/kerbs are built up first so that the aggregate cannot spread sideways during rolling.
3. Spreading of the coarse aggregate uniformly to a loose thickness that gives a compacted layer not exceeding 75-100 mm.
4. Dry rolling with an 8-10 t roller, starting from the edges and progressing to the centre with a one-third overlap, until the aggregate is well keyed.
5. Application of screenings in three or more thin doses with dry rolling and brooming, so that the voids are filled without forming a crust.
6. Sprinkling of water and wet rolling — the surface is sprinkled, swept and rolled until about half the voids are filled.
7. Application of the binding material as a slurry, in two or more thin layers, each followed by wet rolling and brooming until a wave of grout appears ahead of the roller.
8. Setting and drying — the finished course is allowed to dry overnight (or cured) before the next layer is laid or traffic is admitted.

Quality control — aggregate tests (Los Angeles abrasion, aggregate impact value, flakiness & elongation index), gradation, plasticity index of the binding material, moisture at 90-105% of OMC, and field dry density (98% of MDD for base, 95% for sub-base and shoulders).

Lecture 22-24 §4.5; Manual.pdf §3.5.

Water Bound Macadam (WBM) — a base/sub-base course of crushed or broken stone whose particles are mechanically interlocked by rolling, the voids being filled with screenings and binding material with the help of water (pioneered by John Loudon McAdam, c.1820).

Materials

• Coarse aggregate — crushed / broken hard stone or gravel of the specified grading (63-90 mm, 53-63 mm or 22.4-53 mm depending on the course); stock 20% extra along the road.
• Screenings — smaller aggregate (13.2 mm / 11.2 mm) to fill the voids.
• Binding material — stone dust, kankar nodules or a suitable plastic soil (PI ≤ 6 for base course, 5-10 for the surface course).
• Water.

Equipment — water tanker, dump trucks, motor grader, three-wheeled 8-10 t power roller (or tandem / vibratory roller), rakes and hand tools.

Construction procedure

1. Preparation of the foundation — the subgrade or the lower course is prepared to the required grade and camber, and any pot-holes or ruts are made good.
2. Provision of lateral confinement — shoulders/kerbs are built up first so that the aggregate cannot spread sideways during rolling.
3. Spreading of the coarse aggregate uniformly to a loose thickness that gives a compacted layer not exceeding 75-100 mm.
4. Dry rolling with an 8-10 t roller, starting from the edges and progressing to the centre with a one-third overlap, until the aggregate is well keyed.
5. Application of screenings in three or more thin doses with dry rolling and brooming, so that the voids are filled without forming a crust.
6. Sprinkling of water and wet rolling — the surface is sprinkled, swept and rolled until about half the voids are filled.
7. Application of the binding material as a slurry, in two or more thin layers, each followed by wet rolling and brooming until a wave of grout appears ahead of the roller.
8. Setting and drying — the finished course is allowed to dry overnight (or cured) before the next layer is laid or traffic is admitted.

Quality control — aggregate tests (Los Angeles abrasion, aggregate impact value, flakiness & elongation index), gradation, plasticity index of the binding material, moisture at 90-105% of OMC, and field dry density (98% of MDD for base, 95% for sub-base and shoulders).

Lecture 22-24 §4.5; Manual.pdf §3.5.

Interface treatment is a thin film of bituminous binder sprayed on an existing surface before a new bituminous layer is laid. There are two types — prime coat and tack coat; the seal coat is a final surface treatment.

Equipment (all three): mechanical broom or hand brushes for cleaning, bitumen distributor (self-propelled or towed pressure sprayer) with a heating device, chip/aggregate spreader and light rollers.

Construction procedure (common): (1) sweep the surface clean with a mechanical broom and remove all loose material; (2) do not spray in rainy, windy or foggy weather or below 10°C; (3) spray the binder uniformly at the specified rate with the distributor; (4) for a seal coat, spread the cover aggregate before the binder sets and roll it in; (5) allow the specified curing period before opening to traffic or laying the next layer.

Lecture 22-24 §4.6-4.7; Manual.pdf §3.6 — Construction of prime coat, tack coat and seal coat, book p.216.

(a) Mass haul diagram, equipment and plants [2+6]

Mass Haul Diagram (MHD) — a graphical representation of the cumulative earthwork volume (cut positive, fill negative, after applying the shrinkage/swell correction) plotted against chainage, drawn immediately below the longitudinal profile. It tells the contractor how much material must be moved, how far, and in which direction, and lets the average haul, free haul and overhaul be measured.

Characteristics of the mass haul diagram

1. Rising curve = cut (excavation exceeds fill); falling curve = fill.
2. A steep slope means a large quantity of earthwork per unit length; a flat slope means little earthwork.
3. The difference of ordinates between any two points = the net volume of cut over fill (or vice-versa) between those points.
4. Points of zero slope (maxima and minima) are the points where the work changes from cut to fill or fill to cut, i.e. the grade points where the formation line crosses the natural ground.
5. Any horizontal line that cuts the curve at two points is a balancing line: cut and fill between those two balance points are equal, so that length is self-balancing.
6. A loop above the balancing line means the haul is from left to right (convex loop); a loop below means the haul is from right to left.
7. The area enclosed between the curve and the balancing line = haul (volume × distance, m³·m or station-yards); dividing it by the maximum ordinate gives the average haul distance.

Sketch: longitudinal profile on top (CUT – FILL – CUT), mass curve below with the balancing line, free-haul line and the loops marked.

Tools, equipment and plants used in road construction (Manual §3.3):

For a bituminous road the key items are the hot-mix plant, bitumen distributor, chip spreader, mechanical paver, tippers, and smooth-wheeled + pneumatic rollers. For a cement-concrete road they are the batching & mixing plant, transit/truck mixers, concrete paver-finisher, needle (poker) vibrators, screed/float, joint-cutting machine, and curing equipment.

(b) Prime coat vs tack coat; construction of surface dressing [2+6]

Interface treatment is a thin film of bituminous binder sprayed on an existing surface before a new bituminous layer is laid. There are two types — prime coat and tack coat; the seal coat is a final surface treatment.

Equipment (all three): mechanical broom or hand brushes for cleaning, bitumen distributor (self-propelled or towed pressure sprayer) with a heating device, chip/aggregate spreader and light rollers.

Construction procedure (common): (1) sweep the surface clean with a mechanical broom and remove all loose material; (2) do not spray in rainy, windy or foggy weather or below 10°C; (3) spray the binder uniformly at the specified rate with the distributor; (4) for a seal coat, spread the cover aggregate before the binder sets and roll it in; (5) allow the specified curing period before opening to traffic or laying the next layer.

Surface dressing = a thin bituminous surface treatment in which a bituminous binder is sprayed on the prepared base and immediately covered with single-sized stone chippings which are then rolled in. It provides a waterproof, dust-free, skid-resistant wearing surface and protects the base from abrasion, but adds no structural strength.

• SBST — Single Bituminous Surface Treatment (one binder + one chipping application).
• DBST / DBSD — Double Bituminous Surface Treatment / Double Bituminous Surface Dressing (two successive applications, the second with about half the binder and half the chipping size).

Materials: bitumen of grade 80/100 or 180/200 (or a cationic emulsion); cover aggregate with Los Angeles abrasion < 35%, aggregate impact value < 30%, flakiness index < 25% and water absorption < 1%.

Equipment: bitumen heating/storage unit, bitumen distributor (sprayer), chip spreader, 5-8 t smooth-wheeled or pneumatic-tyred roller, and mechanical brooms.

Construction procedure (SBST)

1. Clean the existing surface with mechanical brooms and repair pot-holes, ruts and depressions.
2. Apply the prime coat at the specified rate if the base is pervious, and cure it for at least 24 hours with no traffic.
3. Spray the bitumen uniformly from the distributor at the design rate.
4. Spread the cover aggregate of uniform gradation before the binder sets.
5. Roll with a pneumatic-tyred roller (starting from the edges, moving to the centre, overlapping one-third of the roller width) to press the chippings into the binder.
6. Sweep off the excess chippings within 24-48 hours and open to traffic.

Construction procedure (DBST / DBSD) — carry out a complete SBST as above; sweep away the loose aggregate; apply a second binder application of about one-third to one-half of the first; spread aggregate about half the size of the first application; roll with a pneumatic-tyred roller; and again broom off the excess within 24-48 hours.

Quality control: binder temperature; aggregate tests (LAA, impact value, flakiness index, plasticity index); gradation; rate of application of binder and aggregate; and binder tests (penetration, viscosity, ductility).

Manual.pdf §3.3, §3.4, §3.6 and §3.7 (book pp.207-219).

Surface dressing = a thin bituminous surface treatment in which a bituminous binder is sprayed on the prepared base and immediately covered with single-sized stone chippings which are then rolled in. It provides a waterproof, dust-free, skid-resistant wearing surface and protects the base from abrasion, but adds no structural strength.

• SBST — Single Bituminous Surface Treatment (one binder + one chipping application).
• DBST / DBSD — Double Bituminous Surface Treatment / Double Bituminous Surface Dressing (two successive applications, the second with about half the binder and half the chipping size).

Materials: bitumen of grade 80/100 or 180/200 (or a cationic emulsion); cover aggregate with Los Angeles abrasion < 35%, aggregate impact value < 30%, flakiness index < 25% and water absorption < 1%.

Equipment: bitumen heating/storage unit, bitumen distributor (sprayer), chip spreader, 5-8 t smooth-wheeled or pneumatic-tyred roller, and mechanical brooms.

Construction procedure (SBST)

1. Clean the existing surface with mechanical brooms and repair pot-holes, ruts and depressions.
2. Apply the prime coat at the specified rate if the base is pervious, and cure it for at least 24 hours with no traffic.
3. Spray the bitumen uniformly from the distributor at the design rate.
4. Spread the cover aggregate of uniform gradation before the binder sets.
5. Roll with a pneumatic-tyred roller (starting from the edges, moving to the centre, overlapping one-third of the roller width) to press the chippings into the binder.
6. Sweep off the excess chippings within 24-48 hours and open to traffic.

Construction procedure (DBST / DBSD) — carry out a complete SBST as above; sweep away the loose aggregate; apply a second binder application of about one-third to one-half of the first; spread aggregate about half the size of the first application; roll with a pneumatic-tyred roller; and again broom off the excess within 24-48 hours.

Quality control: binder temperature; aggregate tests (LAA, impact value, flakiness index, plasticity index); gradation; rate of application of binder and aggregate; and binder tests (penetration, viscosity, ductility).

Tools, equipment and plants used in road construction (Manual §3.3):

For a bituminous road the key items are the hot-mix plant, bitumen distributor, chip spreader, mechanical paver, tippers, and smooth-wheeled + pneumatic rollers. For a cement-concrete road they are the batching & mixing plant, transit/truck mixers, concrete paver-finisher, needle (poker) vibrators, screed/float, joint-cutting machine, and curing equipment.

Lecture 22-24 §4.8; Manual.pdf §3.7 (book p.218) and §3.3 (book p.207).

(a) Typical pavement structures

(Semi-rigid pavements have a cement/lime-bound base under a bituminous surfacing; composite pavements have an HMA layer over a PCC slab.)

(b) Construction methodology of Otta seal

Otta seal is a bituminous surface treatment made by placing a layer of graded aggregate (not single-sized as in ordinary surface dressing) on a thick application of a relatively soft bituminous binder; the binder is drawn up through the aggregate by rolling and by traffic, producing a flexible mosaic. It is the standard low-cost surfacing for Nepalese district roads.

Materials — hard, strong, durable graded aggregate with aggregate impact value ≤ 30%, Los Angeles abrasion ≤ 40%, flakiness index ≤ 30%, plasticity index < 5%, graded as per specification; binder MC 3000 or MC 800 cutback bitumen.

Equipment — bitumen distributor, storage tank with heating device, chip/aggregate spreader, pneumatic-tyred roller and mechanical broom.

Construction steps

1. Remove dust and foreign matter from the base with a mechanical broom / hand brushes and an air compressor.
2. Apply the prime coat at the specified rate.
3. Spray the bituminous binding agent generously over the prepared surface with the distributor.
4. Spread the graded aggregate uniformly with an aggregate spreader.
5. Roll with a pneumatic-tyred roller to embed and realign the chippings and to start drawing the binder up through the aggregate.
6. Because of the fines in the aggregate, two or three days of rolling or of traffic are needed for the binder to coat all the particles.
7. During the first few weeks the aggregate dislodged by traffic is swept back into the wheel paths.
8. After about three weeks the surface is swept with a mechanical broom to remove all loose aggregate.
9. For a double Otta seal, the second layer is constructed in the same way two to three months after the first.

Manual.pdf §3.8 — Construction of Otta seal, book p.219; pavement types from §2.1 (book p.113).

Bituminous (asphalt) concrete is the highest quality bituminous surfacing — a carefully proportioned hot mix of coarse aggregate, fine aggregate and mineral filler with a bituminous binder, laid in single layers of 30/40/50 mm. It is dense, impervious and durable and gives the best riding quality and load-carrying capacity.

Material requirements

• Coarse and fine aggregate — hard, durable, clean and cubical; LAA ≤ 30%, aggregate impact value ≤ 24%, flakiness + elongation index ≤ 30%, water absorption ≤ 2%, and satisfactory stripping value.
• Mineral filler — stone dust / hydrated lime / cement passing 75 μm.
• Binder — viscosity-graded paving bitumen (VG-30 / VG-40) or a modified binder; the binder content and the grading are fixed by the Marshall mix design.

Plants and equipment — hot-mix plant (batch or drum) with aggregate dryer and binder heating unit, bitumen sprayer for the tack coat, tippers, mechanical paver-finisher, 8 t smooth-wheeled or 4 t vibratory roller for breakdown rolling, 8-12 t pneumatic-tyred roller for intermediate rolling, tandem roller for finish rolling, and mechanical brooms.

Construction procedure

1. Prepare the existing surface — sweep it clean and correct irregularities such as pot-holes, ruts and depressions.
2. Apply the tack coat at 6.0-7.5 kg per 10 m² (0.60-0.75 kg/m²).
3. Produce the mix in the hot-mix plant with the aggregate and binder heated to the specified temperatures (mixing temperature tolerance ±10°C).
4. Transport the hot mix in covered tippers and spread it with the mechanical paver to the required grade, camber and thickness.
5. Roll the mix thoroughly — the first two passes with an 8 t smooth-wheeled or 4 t vibratory roller (breakdown), then with an 8-12 t pneumatic-tyred roller, and finally a tandem roller to remove the roller marks, all within the specified temperature range.
6. Open to traffic only after the surface has cooled to the ambient temperature.

Quality-control tests — temperature of the binder, of the mix and at laying/rolling; aggregate tests (LAA, impact value, flakiness, stripping); gradation of the mix; binder content by extraction; Marshall stability, flow, density and air-void analysis; rate of spread of the mix; and the field density (degree of compaction) and surface regularity of the finished layer.

Lecture 22-24 §4.9 (construction of bituminous concrete); Manual.pdf §3.10, book p.221.

Bituminous (asphalt) concrete is the highest quality bituminous surfacing — a carefully proportioned hot mix of coarse aggregate, fine aggregate and mineral filler with a bituminous binder, laid in single layers of 30/40/50 mm. It is dense, impervious and durable and gives the best riding quality and load-carrying capacity.

Material requirements

• Coarse and fine aggregate — hard, durable, clean and cubical; LAA ≤ 30%, aggregate impact value ≤ 24%, flakiness + elongation index ≤ 30%, water absorption ≤ 2%, and satisfactory stripping value.
• Mineral filler — stone dust / hydrated lime / cement passing 75 μm.
• Binder — viscosity-graded paving bitumen (VG-30 / VG-40) or a modified binder; the binder content and the grading are fixed by the Marshall mix design.

Plants and equipment — hot-mix plant (batch or drum) with aggregate dryer and binder heating unit, bitumen sprayer for the tack coat, tippers, mechanical paver-finisher, 8 t smooth-wheeled or 4 t vibratory roller for breakdown rolling, 8-12 t pneumatic-tyred roller for intermediate rolling, tandem roller for finish rolling, and mechanical brooms.

Construction procedure

1. Prepare the existing surface — sweep it clean and correct irregularities such as pot-holes, ruts and depressions.
2. Apply the tack coat at 6.0-7.5 kg per 10 m² (0.60-0.75 kg/m²).
3. Produce the mix in the hot-mix plant with the aggregate and binder heated to the specified temperatures (mixing temperature tolerance ±10°C).
4. Transport the hot mix in covered tippers and spread it with the mechanical paver to the required grade, camber and thickness.
5. Roll the mix thoroughly — the first two passes with an 8 t smooth-wheeled or 4 t vibratory roller (breakdown), then with an 8-12 t pneumatic-tyred roller, and finally a tandem roller to remove the roller marks, all within the specified temperature range.
6. Open to traffic only after the surface has cooled to the ambient temperature.

Quality-control tests — temperature of the binder, of the mix and at laying/rolling; aggregate tests (LAA, impact value, flakiness, stripping); gradation of the mix; binder content by extraction; Marshall stability, flow, density and air-void analysis; rate of spread of the mix; and the field density (degree of compaction) and surface regularity of the finished layer.

Lecture 22-24 §4.9; Manual.pdf §3.10, book p.221.

(a) Types of bituminous pavement construction

(b) Construction procedure of asphalt (bituminous) concrete pavement

Bituminous (asphalt) concrete is the highest quality bituminous surfacing — a carefully proportioned hot mix of coarse aggregate, fine aggregate and mineral filler with a bituminous binder, laid in single layers of 30/40/50 mm. It is dense, impervious and durable and gives the best riding quality and load-carrying capacity.

Material requirements

• Coarse and fine aggregate — hard, durable, clean and cubical; LAA ≤ 30%, aggregate impact value ≤ 24%, flakiness + elongation index ≤ 30%, water absorption ≤ 2%, and satisfactory stripping value.
• Mineral filler — stone dust / hydrated lime / cement passing 75 μm.
• Binder — viscosity-graded paving bitumen (VG-30 / VG-40) or a modified binder; the binder content and the grading are fixed by the Marshall mix design.

Plants and equipment — hot-mix plant (batch or drum) with aggregate dryer and binder heating unit, bitumen sprayer for the tack coat, tippers, mechanical paver-finisher, 8 t smooth-wheeled or 4 t vibratory roller for breakdown rolling, 8-12 t pneumatic-tyred roller for intermediate rolling, tandem roller for finish rolling, and mechanical brooms.

Construction procedure

1. Prepare the existing surface — sweep it clean and correct irregularities such as pot-holes, ruts and depressions.
2. Apply the tack coat at 6.0-7.5 kg per 10 m² (0.60-0.75 kg/m²).
3. Produce the mix in the hot-mix plant with the aggregate and binder heated to the specified temperatures (mixing temperature tolerance ±10°C).
4. Transport the hot mix in covered tippers and spread it with the mechanical paver to the required grade, camber and thickness.
5. Roll the mix thoroughly — the first two passes with an 8 t smooth-wheeled or 4 t vibratory roller (breakdown), then with an 8-12 t pneumatic-tyred roller, and finally a tandem roller to remove the roller marks, all within the specified temperature range.
6. Open to traffic only after the surface has cooled to the ambient temperature.

Quality-control tests — temperature of the binder, of the mix and at laying/rolling; aggregate tests (LAA, impact value, flakiness, stripping); gradation of the mix; binder content by extraction; Marshall stability, flow, density and air-void analysis; rate of spread of the mix; and the field density (degree of compaction) and surface regularity of the finished layer.

Lecture 22-24 §4.6-4.9 (classification of bituminous construction and BC construction).

(a) Rolled concrete vs normal concrete in road construction

(A third variant used as a sub-base is the cement-grouted layer — open-graded coarse aggregate compacted first, into which a cement-sand grout is poured so that it fills the voids.)

(b) Construction steps of cement-concrete pavement, with materials and quality control

Materials — ordinary Portland or rapid-hardening cement; clean, hard, well-graded coarse aggregate (max size 25-31.5 mm for PQC) and fine aggregate; potable water; admixtures; 125-micron polythene separation membrane; dowel bars, tie bars and joint-sealing compound. The pavement-quality concrete (PQC) is normally M40 with a specified flexural strength (modulus of rupture) of about 4.5 MPa at 28 days.

Plant and equipment — concrete batching & mixing plant, transit/truck mixers or a site batch mixer, weigh-batching device, wheelbarrows, needle (poker) vibrators and screed vibrators, concrete paver-finisher, long-handled steel or fibre brush for texturing, joint-cutting saw and curing equipment.

Construction steps

1. Preparation of the subgrade and sub-base — compacted to the specified density and checked for level and camber; the DLC/GSB sub-base is laid and covered with the polythene separation membrane.
2. Placing the formwork — steel side forms are set to line and level and well secured so that they resist the tamping/vibrating forces.
3. Fixing the joint furniture — dowel bars at expansion/contraction joints (half greased with an expansion cap) and tie bars at longitudinal joints.
4. Batching, mixing and transporting — the ingredients are weigh-batched and mixed in a batch mixer on site or in a central plant and brought to the site.
5. Placing the concrete on the prepared sub-base to the required depth, either by the continuous construction method (all slabs cast one after another) or the alternate bay method (alternate slabs cast first, the intervening bays later).
6. Compaction with a mechanical poker (needle) vibrator and a screed/vibrating beam.
7. Finishing and texturing — floating and belting, then brushing the surface with an approved long-handled steel or fibre brush to give texture depth.
8. Joint forming/cutting — contraction joints are saw-cut to about ¼ of the depth within 6-24 hours; joint grooves are later cleaned and sealed.
9. Curing — the surface is covered with wet jute mats for 24 hours; after the wet covers are removed the slabs are cured by ponding for 14 days.
10. Opening to traffic after 28 days.

Quality control — cement type and tests; maximum size and tests on aggregates (LAA, flakiness, impact value, soundness); gradation; proportioning of the mix and water-cement ratio; slump/workability; flexural strength of beam specimens and compressive strength of cubes; slab thickness, surface regularity and texture depth.

Joints in cement-concrete pavement

• Expansion joint — a full-depth gap of 20-25 mm with a compressible filler and sealant, provided at about 140 m intervals, that allows the slab to expand; load transfer by dowel bars.
• Contraction joint — a groove cut to about a quarter of the slab depth at 4.5 m spacing for plain slabs (up to about 14 m for reinforced slabs), which forces the shrinkage crack to form at a chosen line.
• Longitudinal joint — provided when the slab width exceeds 4.5 m; it takes care of warping and differential settlement, acts as a hinge, and is held by tie bars.
• Construction joint — provided wherever concreting is interrupted; it should be made to coincide with a contraction joint.

Lecture 22-24 §4.10; Manual.pdf §3.11 — Construction of cement concrete pavement, book p.224.

Materials — ordinary Portland or rapid-hardening cement; clean, hard, well-graded coarse aggregate (max size 25-31.5 mm for PQC) and fine aggregate; potable water; admixtures; 125-micron polythene separation membrane; dowel bars, tie bars and joint-sealing compound. The pavement-quality concrete (PQC) is normally M40 with a specified flexural strength (modulus of rupture) of about 4.5 MPa at 28 days.

Plant and equipment — concrete batching & mixing plant, transit/truck mixers or a site batch mixer, weigh-batching device, wheelbarrows, needle (poker) vibrators and screed vibrators, concrete paver-finisher, long-handled steel or fibre brush for texturing, joint-cutting saw and curing equipment.

Construction steps

1. Preparation of the subgrade and sub-base — compacted to the specified density and checked for level and camber; the DLC/GSB sub-base is laid and covered with the polythene separation membrane.
2. Placing the formwork — steel side forms are set to line and level and well secured so that they resist the tamping/vibrating forces.
3. Fixing the joint furniture — dowel bars at expansion/contraction joints (half greased with an expansion cap) and tie bars at longitudinal joints.
4. Batching, mixing and transporting — the ingredients are weigh-batched and mixed in a batch mixer on site or in a central plant and brought to the site.
5. Placing the concrete on the prepared sub-base to the required depth, either by the continuous construction method (all slabs cast one after another) or the alternate bay method (alternate slabs cast first, the intervening bays later).
6. Compaction with a mechanical poker (needle) vibrator and a screed/vibrating beam.
7. Finishing and texturing — floating and belting, then brushing the surface with an approved long-handled steel or fibre brush to give texture depth.
8. Joint forming/cutting — contraction joints are saw-cut to about ¼ of the depth within 6-24 hours; joint grooves are later cleaned and sealed.
9. Curing — the surface is covered with wet jute mats for 24 hours; after the wet covers are removed the slabs are cured by ponding for 14 days.
10. Opening to traffic after 28 days.

Quality control — cement type and tests; maximum size and tests on aggregates (LAA, flakiness, impact value, soundness); gradation; proportioning of the mix and water-cement ratio; slump/workability; flexural strength of beam specimens and compressive strength of cubes; slab thickness, surface regularity and texture depth.

Joints in cement-concrete pavement

• Expansion joint — a full-depth gap of 20-25 mm with a compressible filler and sealant, provided at about 140 m intervals, that allows the slab to expand; load transfer by dowel bars.
• Contraction joint — a groove cut to about a quarter of the slab depth at 4.5 m spacing for plain slabs (up to about 14 m for reinforced slabs), which forces the shrinkage crack to form at a chosen line.
• Longitudinal joint — provided when the slab width exceeds 4.5 m; it takes care of warping and differential settlement, acts as a hinge, and is held by tie bars.
• Construction joint — provided wherever concreting is interrupted; it should be made to coincide with a contraction joint.

Lecture 22-24 §4.10; Manual.pdf §3.11, book p.224.