How are concrete roads constructed?

Weather and Seasonal Limitations in Concrete road construction

Concreting shall not be done during extreme weather conditions, e.g., during monsoon months and when the atmospheric temperature in the shade is above 400C or below 40C unless special precautions are taken as specified. IRC: 61-1976 provides guidelines for cement concrete roads in hot weather.

Base preparation for concrete road construction

The base that will receive the cement concrete must be checked for line, grade, and cross-section by the drawing. All deviations from the allowed tolerances must be corrected.

If concrete is to be laid over an absorbent surface, it must be kept moist in a saturated surface dry condition or covered with water-proof kraft/Polyethylene sheeting to prevent water absorption from the concrete mortar.

Formwork repair for concrete road construction

The formwork must be of the proper shape, free of bends and kinks, and sufficiently rigid to maintain its shape and position under the weight and working conditions of the laying and compacting equipment. It must also be set to true lines and levels and securely fastened in place to prevent subsequent disturbance during compaction. Formwork is checked for line and level accuracy, and any deviation greater than 3mm in 3m is corrected. Formwork deviation should be prohibited at the joints.

Flexible Road Construction Method Process in Civil Engineering

What are the fundamental alignment principles?

Masonry pillars shall be erected at appropriate points in the area visible from the road.

The largest area to serve as a reference point for the excavation of the work. Before beginning work, necessary profiles with iron or wooden pegs, strings, or ‘Burjis’ must be created to show the correct formation or alignment levels.

Ground levels must be taken at 5 to 15-meter intervals in uniformly sloping ground and at closer intervals where local mounds, pits, or undulations are encountered. Ground levels must be documented in field books and plotted on plans. The plans must be drawn to a scale determined by the Architect.

Road development Excavation measurements for earthwork

• If the measurements are taken with tape, the length, breadth, and depth must be accurate to one centimeter. If measurements are taken with a staff and a level, the level must be recorded precisely to 5 mm, and the depth of cutting and filling heights must be calculated precisely to 5 mm. The measurements should be calculated to the nearest two decimal places.
• When excavating in the fairly uniform ground, cutting in trenches or barrow pits must be measured.
• Where the ground is not fairly uniform or the site is required to be leveled, levels shall be taken before and after the start of the work, and the quantity of excavation in cutting calculated from these levels shall be billed.
• When measuring from barrow pits or cutting is not possible or practical, excavation should be calculated from filling. The exact measurements of the filling earth should be calculated by taking levels of the Natural ground Level before starting the work, after site clearance, and after compaction of the filling at appropriate intervals, and the quantity of earthwork so computed should be reduced by 10% in the case of consolidation fills, and 5% in the case of consolidation done by machinery to calculate net earthwork quantity.

The deduction is not required in the following situations:

• Heavy machinery consolidation at optimal moisture contents
• Consolidated fillings in confined areas such as beneath floors.

What exactly is a subgrade in road construction

• The formation surface for the width of sub base, which should be 10cm or 15cm on either side of the base course (depending on thickness in drawing), should be cut to a depth equal to the combined depth of such base (stone soling), base and surface courses below the proposed finished level (due allowance being made for consolidation).
• It must be cleaned of all foreign substances and dressed off parallel to the finished profile before being compacted. The density must not be less than 98% of the Modified Proctor Density.
• The finished surface should be uniform, compacted properly, and conform to the lines, grades, and typical cross section shown in the drawings.
• Prior to actual execution, it must be ensured that the material to be used in the subgrade meets the requirements of design CBR. The subgrade should be compacted and finished in accordance with the design strength and other physical requirements.

Sub-grade Preparation Using GSB

The GSB should be graded as a North III with a CBR of at least 20. Stone aggregate shouldn’t be bigger than 22.5 cm or smaller than 10 cm in any direction, and it should be the same height as the base course with a 25 mm tolerance.

After the subgrade is ready, the stone soling will be put down. As the soling work goes on, care should be taken to place stones on the edges and pack them with small stones. The binding material should then be spread out, and consolidation should be done with a vibratory roller (8 – 10 Tons).

As consolidation goes on, surface imperfections will be fixed. The rate must cover the cost of all materials and labor needed for all of the above operations.

The density that needs to be reached must meet CPWD/IRC requirements for the density found in the lab (Proctor Method).

Base (WBM): Macadam that holds water

In the first layer, there is WBM with stone aggregates that range in size from 90 mm to 45 mm. This also has coarse aggregate that has been rolled into place and filled in with screening and binding material with the help of water. This is all laid on a prepared subgrade, sub-base, or coarse aggregate, depending on the situation. WBM base is coarse in one layer, about 100 mm thick when packed, with a grading of I.

The second layer is water-bound macadam with 63 mm to 45 mm stones. This also has coarse aggregate that has been rolled into place and filled with screening and binding material with the help of water. This is all laid on a prepared sub-base or coarse aggregate, depending on the situation. WBM sub-base coarse in one layer with grading II is about 75 mm thick when it is packed down.

No matter how big or small the particles are, they shouldn’t be put in different piles. Instead, the coarse aggregate should be spread out uniformly with no fine material.

Putting in roads Putting down large rocks

Putting in roads Spreading coarse aggregate on a prepared base should be done evenly and in the right amounts with a twisting motion to keep it from getting separated. It shouldn’t be dumped in piles right on the spot where they will be laid, nor should it be moved over a base that is only partly done.

Using templates set up across the road, the aggregates should be spread out uniformly to the right height. First, the levels along the longitudinal direction, up to which the metal will be laid, must be found on-site and followed. The surface of the spread aggregate should be carefully leveled, and any areas that are too high or too low should be fixed by taking away or adding more aggregate, as needed.

The WBM sub-base should usually be built in layers that are 100 mm thick when compacted. No matter how big or small the pieces are, they shouldn’t be separated, and the coarse aggregate should have a uniform size and no fines.

Work on rolling the road for compaction

Putting in roads Work for rolling for After the coarse aggregate has been spread out, it should be compacted to the full width by rolling it with an 8–10-ton three-wheel power roller or an equivalent vibratory roller. During the “Start” phase, light rolling should be done. This should stop when the aggregate is partially compacted but still has enough space for screenings to be added.

Start rolling from the edges, moving the roller back and forth, and adding screenings at the same time until the edges are tightly packed. The roller should move from the edges to the middle of the road, parallel to the road’s center line and overlapping each previous rear wheel track by a half-width. This should keep happening until the rear wheel has rolled the whole road course.

Rolling should be done until the metal on the road is completely keyed and no metal is moving in front of the roller. During rolling, the only water that should be used is a light sprinkle. On very steep curves, rolling should start at the lower edge of the pavement and move gradually up to the upper edge.

Rolling shouldn’t be done if the sub-base or sub-grade is soft or gives way, or if the rolling makes waves in the sub-base or sub-grade because the ground is wet. When rolling causes irregularities that are bigger than 12 mm when measured with a three-meter straight edge, the surface should be broken up, and if necessary, aggregate should be added to or taken away from it. The area should then be rolled until it has a smooth surface that matches the desired cross-section and grade.

The surface should be checked for camber across the slope, and any problems should be fixed in the way described above.