Challenges in the Construction of Concrete Pavements: An Indian National Highway Construction ExperienceAuthor 1: Venkata Joga Rao Bulusu*, Research scholar, IIT Kharagpur, Kharagpur, West Bengal, India

Author 2: Kusam Sudhakar Reddy, Professor, IIT Kharagpur, Kharagpur, West Bengal, India

Author 3: Muppireddy Amarnatha Reddy, Professor, IIT Kharagpur, Kharagpur, West Bengal, India

For the corresponding author*: j4jogs@gmail.com

KEYWORDS: Curing, dowel bar, cracks, slab sliding

Conflict of Interest: None

1. ABSTRACT

The construction of cement concrete pavement is a very complex and sensitive process with many factors influencing the quality of concrete and the quality of finished pavement surface. In this paper, the authors presented the construction related issues faced during the construction of a national highway section in India. The major issues discussed are the edge collapse near horizontal curves in winter season in slip form paving method, uneven surface profile caused due to frequent starting and stopping of paver machine due to the difference in the mix delivery speed and the paver speed, the unexpected random cracking in a section of concrete pavement due to the delayed joint sawing, and the insertion marks of dowel bars in the concrete layer to name a few. The range of reasons that lead to theses challenging situations vary from the slope of super elevation to the frequency of vibration used for the dowel bar insertion. To further complicate the construction process, the variability in the quality of cement and super-plasticizer supplied to the construction site necessitate the frequent adjustments in the mix proportions to match the requirements of strength and workability. The selection of joint sawing time is equally difficult with many variables controlling the setting and hardening of concrete mix. The details of the highway section are: concrete layer thickness is 280 mm and concrete mix is of M40 grade, constructed over dry lean concrete sub-base of 150 mm thickness with a 125 microns’ thick polythene separation sheet used for de-bonding.

2. INTRODUCTION

Concrete pavement construction process is very complex, with many factors influencing the pavement quality in terms of strength and surface finish. The construction of pavement quality concrete (PQC) layer itself has the most complexity involved in the form of mix preparation, laying and curing. The major factors governing the PQC mix can be divided into two groups. (a) Requirements of the mix (functional and structural) (b) Properties of the constituent materials. The functional and strength requirements of the mix include the workability, strength, setting time and method of placement. The PQC mix has to be designed keeping in mind all these requirements for the smooth and continuous laying of the PQC layer. On the other hand, properties of constituent materials like the quality and type of cement available, type and texture of aggregate (coarse and fine) and compatibility of super plasticizer also play a major role in the concrete mix properties both in fresh state and hardened state. In addition to these factors, environmental conditions like temperature, humidity and wind velocity also influence the mix parameters. Once the PQC is placed, compacted and tining texture is applied, the curing and joint sawing remain the challenges. The present paper discusses various challenges faced during the construction and in the initial service life of concrete pavement.

3. CONSTRUCTION CHALLENGES

Concrete pavement construction has many challenges that are to be addressed at an appropriate time to maintain a good quality control and a good surface finish. Some issues may arise after completion of construction, as the field implementation experience is limited and many concrete pavement construction works started in India in the recent past. In the present paper, the authors made an attempt to present the construction challenges and the possible solutions concisely. The issues discussed here varied from challenges in preserving the moisture in concrete, to the deficiencies in the dowel insertion mechanisms, to the problems in cold weather construction, to the improperly executed methods in the construction and curing of dry lean concrete (DLC) layer, to the issues of slab sliding after allowing the traffic on the concrete pavement. A total of sixteen issues are discussed with in the scope of the paper’s guidelines.

The issues discussed here are based on the concrete pavement construction experience of national highway sections with a design thicknesses of PQC and DLC as 280 mm and 150 mm respectively. The mix design for PQC is done in India as per the guidelines given by Indian roads congress (IRC) in the form of IRC:44 (2017) and selection of batching plant is done as per IRC: SP: 96 (2012) for smooth and continuous laying of PQC layer. PQC is typically of M40 grade concrete with 320 kg cement, 70 kg flyash and 146 liters of water per cubic meter of concrete. DLC is of M15 grade concrete mix having a minimum compressive strength of 10 MPa in 7 days. The DLC mix has 120 kg cement and 30 kg flyash per cubic meter, designed in accordance with IRC: SP: 49 (2014). The concrete pavement design is done in India as per the guidelines given in IRC: 58 (2015) and construction is as per the construction specifications given in IRC: 15 (2017). The material specifications and other construction related specifications are followed as per the MoRTH (2013).

4. FIELD OBSERVATIONS AND POSSIBLE SOLUTIONS

Even after following the guidelines and specification available in India, there are some issues that arise during construction operations and during the initial service life of the pavement which need to be addressed. The construction issues and the post construction issues are presented in individual sections with description of the issue, possible solution and the relevant field pictures for better understanding of the importance and severity of the problem.

4.1 Challenges in preserving the moisture in concrete mix

Concrete gains strength with time as long as sufficient moisture is available for the hydration of cement during the rapid strength gain period of first 28 days. The loss of moisture due to evaporation caused by high wind velocity, high ambient temperature and low relative humidity in the air may slow down the hydration process as sufficient moisture may not be available for hydration. The loss of surface moisture may lead to partial hydration of cement at the surface, which in turn leads to weaker concrete at the surface. The weaker concrete cannot withstand the traction of tires for a longer period and hence it may lead to loss of mortar/ concrete at the surface, leading to surface unevenness.

To avoid the loss of surface moisture during the first 24 hours, mist spraying can be done in order to keep the surface humid. In locations where the mist spraying facility is not available, the surface of the concrete may be covered using a polythene sheet to contain the moisture by providing protection from wind and to maintain a higher relative humidity. The polythene sheet covering can be done one hour after the initial setting of concrete, as shown in Figure 1, to avoid damaging the texture while placing the sheet. If the polythene sheet is very light in weight and properly applied, it will not damage the texture even if it is laid immediately after the texturing. This polythene sheet covering will be in addition to the curing compound as far as possible and it should not be considered a substitute or replacement. Preventing the loss of moisture from the concrete surface also prevents the occurrence of drying shrinkage cracks.

(a) PQC surface covered to contain moisture (b) Watering PQC under the polythene sheet

Figure 1 PQC layer covered with a polythene sheet

In the places where there is a shortage of water sources, preserving the moisture in the concrete is difficult during the necessary curing period of 14 or 16 days. In such locations, the moisture can be held trapped inside the concrete by covering the concrete (after spraying water) with a good polythene sheet (like the one used for separation of DLC and PQC) which maintains a higher relative humidity near concrete and also reduces evaporation due to wind. This will reduce the required frequency of wetting the surface or required quantity of water to keep the concrete damp.

4.2 Random cracking issues in PQC with delayed joint sawing

The full width transverse cracking may be observed in few places where the joint sawing gets delayed due to various reasons. In such cases, the full width cracks may form even before the joint sawing begins, similar to the crack shown in Figure 2. These cracks have a higher probability of deterioration under the traffic loads, as the dowel bars will not be available at these unplanned joints (for effective load transfer across the slabs).

(a) Full width transverse cracking due to delayed sawing

(c) Machine breaking and removing the cracked slabs

Figure 2 Random cracking due to delayed sawing and slab removal

This type of cracking is often observed during the construction of concrete pavement in the summer season, probably due to higher rate of hydration in warm weather in addition to the higher drying shrinkage. The changes in the mix proportion can also alter the rate of hydration and in turn the effective joint sawing window. If the full width transverse cracks form in the slab, then the slab has to be partially cut to introduce the load transfer devices or has to be completely removed. If delayed joint sawing happens, the cracks will not be limited to a single slab and hence the resultant damage will be substantial.

4.3 Imperfect automatic dowel bar insertion technique

The full width paving concrete pavers come with additional attachment for automatically inserting the dowel bars into the freshly laid concrete using a pair of tongs for each dowel bar, instead of using dowel basket (dowel chair) to keep the dowels in position. The automatic dowel bar inserter has a higher work output (speed of construction) in addition to minimizing the issues of slippage or movement of dowel basket and distortion of dowels in the dowel basket, during the process of pouring the concrete. However, dowel bar inserter has its own setbacks, like leaving the dowel insertion marks in the PQC layer due to inefficient/ insufficient compaction or due to harsh mixes as shown in Figure 3. This not only leaves dowel insertion marks but also leaves the concrete over the dowels to be weak due to insufficient compaction, which may lead to early cracking of PQC slab at these dowel locations.

(a) Fresh dowel insertion marks (b) Dowel insertion marks on cured surface

Figure 3 Dowel insertion marks in fresh and hardened concrete layer

It is a very serious issue and needs to be addressed soon in the construction. The trailing dowel marks will be very distinct if the PQC mix of a particular batch is harsh with very little workability. The vibration frequency of 3000 vpm is usually used for concrete as per the paver information sheet. However, some of the other dowel bar inserter (DBI) system manufacturers tend to use two pairs of tongs instead of one pair with vibration frequencies of 3000 vpm for outer tongs and 6000 vpm for inner tongs. The system with two pairs of tongs is claimed to alleviate the problem of insufficient compaction of concrete above the freshly inserted dowel bar.

4.4 Misaligned dowel bars at construction joints

The misalignment of dowel bars near the construction joint could lead to a pavement failure near the joint as these dowel bars start taking axial loads when the slabs expand or contract. This is due to the relative shift in the axis of movement of the slab and that of the dowel bar. The automated dowel bar inserters usually place the dowel bars in precise position and alignment as they use vibration to insert the dowel bar through the freshly laid concrete using a sophisticated instrumentation and control. In the case of construction joints, the form plate with holes (for dowel bar insertion) is kept at the joint location and dowel bars are driven in to the PQC layer using hammer blows. The hammer blows may lead to misalignment of the bar as the bar tries to penetrate through the path of least resistance in the concrete (aggregate) mix as shown in Figure 4 (a). The mis-aligned dowels cause spalling due to localized stress concentration due to constrained movement. The spalling at a construction joint can be seen in Figure 4 (b).

(a) Dowels driven at the construction joint (b) Slab spalling due to misaligned dowels

Figure 4 Misaligned dowels and the damage caused by them

The better approach for inserting dowel bars at construction joints would be with the help of a vibration generator, which allows the dowel bar to penetrate with ease and allows the fresh concrete to smoothly close in around the inserted dowel bar while appropriately maintaining the axis of the dowel bar. However, this type of system is not available in the construction industry as of today. There will be a great demand for such a system for dowel bar insertion.

4.5 Misplaced joint

In some places the dowel joint is sawed at an offset rom the middle of the dowels, due to improper training and lack of understanding about the purpose of dowel bars, leading to a decrease in the effectiveness of the dowels in load transfer and long term performance of the joint. This misplaced joint will be a weak joint in the concrete pavement due to little or no contribution of the dowel bar in load transfer. Figure 5 (a) shows the marking for transverse joint mis-positioned even though the dowel bar insertion marks are clearly visible (in some cases similar to the one shown here). If the dowel bars are not available for load transfer, the joints will deteriorate fast and hence the slabs are partially cut and removed to introduce the dowel bars as shown in Figure 5 (b).

(a) Marking for joint sawing placed at an offset (b) Slab removal for correction

Figure 5 Mis-placed transverse joint and corrective measures

The advanced equipment like MIT scan can be used to identify the joints with missing dowel bars. An easier method is to insert a marker strip along with the dowel bars to identify the location for sawing the transverse joint.

4.6 Widening the longitudinal joint

The friction slabs on retaining walls and bridges are often manually laid, after constructing the carriage way with a paver, in order to avoid damaging the already constructed crash barrier as the paver has to move close to the crash barrier while laying the PQC. The pavers need extra width than the PQC slab for the crawler type wheels of the paver to move. There is no need for the form work in case of friction slabs as the already constructed crash barrier wall and PQC slab contain the concrete mix from either side acting like a fixed formwork as shown in Figure 6.

Figure 6 Manual pouring of concrete for the friction slab

This forms a very narrow joint between the PQC slab and friction slab, with a width of approximately half the amount of shrinkage in the width direction. So, sealing this narrow joint will be a difficult task. This narrow joint has to be widened along the joint to pour the sealant. However, the joint sawing at this joint is very difficult as the PQC slab edge is not always perfectly straight in longitudinal direction. So, sawing this joint is very difficult with the joint in place and the saw has to follow that path unlike a regular longitudinal joint or transverse joint which is a straight line (formed by the cutting saw). In order to avoid this difficult joint sawing, a thick glue tape can be adhered to the existing PQC slab before pouring concrete for the friction slab and once the concrete hardens the glue tape can be removed and sealant can be poured in that groove.

4.7 Slab sliding near bridges which are under construction

The problem of slab sliding under the influence of traffic is often observed near the horizontal and vertical curves within a few months of allowing the traffic. The slab sliding occurs when the terminal slab is not properly planned or constructed. This type of condition arises when the PQC layer is constructed before the construction of bridge/ cross drainage work is ready and traffic is allowed on the constructed portion PQC. In such conditions, there is no terminal slab with anchorage and hence the slabs near the end of constructed PQC section start sliding as the braking of heavy vehicles exerts enough force to move the last few slabs. The images in Figure 7 (a) and 7 (b) show the transverse contraction joints which got widened by more than 50mm and 30 mm respectively.

(a) Joint opening by more than 50 mm (b) Dust filled in joint with 30 mm opening

Figure 7 Slab sliding and joint opening up in absence of anchorage

Due to this opening up of the joint, load transfer efficiency will be practically zero when the joints widen as much, as the aggregate interlocking is lost. The moisture ingress through this type of joint will affect the performance of the slabs adjacent to this joint. Ideally, in such cases either the sliding slabs have to be replaced after the construction of cross drainage work is completed or part of slab has to be removed on either side of such widened joint and a new slab is to be reconstructed in that place with dowel bars for load transfer between new and old slabs.

4.8 Opening up of longitudinal joint near horizontal curve

The widening or opening up of longitudinal joint near a horizontal curve is often caused due to the centrifugal force exerted by the heavy vehicles negotiating the curve on the PQC slab of the outer lane (on the outer radius of the curve) as shown in Figure 8. The widening of gap is also partly due to the self-weight of the slab on the (unloaded) inner lane which does not allow it to move and partly due to insufficient number of tie bars at/ near the horizontal curve where the horizontal force is higher than the design value usually considered. This suggests the need for extra tie bars near horizontal curves. The other alternative is to remove the separation sheet to make the PQC and DLC bond together to eliminate the problem of sliding. However, the bonded construction may have issues with the curling of slabs, due to temperature differential across the combined thickness of the slab, as increased self-weight may lead to increased curling stresses. Cross stitching of the slabs on either side of the longitudinal joint will arrest the further sliding of the slabs to a great extent in such cases, though that is only after the occurrence of sliding.

(a) Widened longitudinal joint (b) Joint sealed with adhesive material

Figure 8 Longitudinal joint opening up near a horizontal curve

The outer lane slabs should have a better bond with the DLC layer below to withstand the horizontal drag, as merely providing extra tie bars may lead to sliding of the inner lane as well over a period of time. The slab sliding further aggravates if the dowel bars are not in place to avoid relative lateral sliding between the slabs.

4.9 Sliding of slabs near vertical curves

The widened transverse joints are often observed near the approach to the vertical curve in case of a valley curve as shown in Figure 9 and near the top in case of a summit curve due to the sliding of the slabs under the influence of gravity (self-weight) and traffic loads. The polythene separation sheet provided between the DLC and PQC layers does not offer sufficient friction to prevent sliding. So, there is a higher possibility of slab sliding and opening up of the transverse joint in the places where the length of vertical curve is more or the slope of curve is steep or a combination of both. To avoid such sliding, the separation sheet is not provided under some slabs or all the slabs in case of vertical curves. The joint load transfer efficiency will be affected if the joint opens wide, in addition to the possibility of spalling due to penetration of debris in the joint groove.

(a) Widened transverse joint (b) Joint widened by one inch

Figure 9 Slab sliding on vertical curve leading to widened transverse joint

Some agencies have tried filling the widened transverse joint with high strength and low shrinkage epoxy concrete with smaller aggregate size to improve the aggregate interlocking and hence the load transfer efficiency. However, the long term performance of such treatments is not well understood.

4.10 Undeveloped longitudinal joint near shoulder

Longitudinal cracking in the outer lane is one of the frequently observed distress in concrete pavements and it is often attributed to the undeveloped longitudinal joint between the (1.5 m wide) shoulder and the outer lane which makes the effective width of the outer lane’s slab to be wider (5 m instead of 3.5 m). The load induced stresses, in combination with curling stresses will be higher if the width of slab is more. Even though, both the day time and the night time temperature differentials affect the magnitude of stress, it is the night time curling that is observed to have a greater impact on development of such longitudinal cracks. The longitudinal cracks can be repaired using cross stitching technique and by sealing the longitudinal crack. The method of drilling holes and inserting the re-bars for cross stitching can be seen in Figure 10. It is often advised to increase the depth of longitudinal joint near the shoulder to more than the prescribed 1/3rd the slab thickness to enhance the probability of this joint to develop into a full depth joint, to restrict the width of the outer lane’s slab to behave like a 3.5 m wide slab.

(a) Preparation for cross stitching (b) Cross stitching bars placed in drilled holes

Figure 10 Cross stitching a longitudinal joint

4.11 Uneven pavement surface finish

The formation of uneven surface is one of the most observed issue, that leads to an uncomfortable riding surface with high value of International Roughness Index (IRI). It arises when the paver frequently stops and starts during the laying of PQC due to the difference in the speeds of laying and concrete mix delivery to the paver. The images shown in Figure 11 (a) indicate the locations of undulation in the concrete surface. The change in thickness at such locations can be as high as 1.5 cm (Figure 11 (b)), sometimes with unequal thickness on either side of the slab.

(a) The wavy surface finish (b) The thickness reduction at a location

Figure 11 Uneven pavement surface finish

The paver finished surface is supposed to be smooth and uniform in thickness without any localized undulations. However, the stopping and starting of the paver happens with a shock or sudden movement as the system accelerates from rest position and this triggers the suspension system which causes the undulations in the paved surface. The thickness at such locations is generally observed to be less compared to the adjacent section. To avoid surface undulations, the paver should be run with as minimum stoppings as possible and should move at a constant speed.

4.12 PQC layer edge collapse near horizontal curve during cold weather

The concrete pavement construction during winter will have some issues related to delayed setting time and low rate of strength gain. The delayed setting and hardening during winter nights may lead to unstable pavement edge (side face) as the slipform paver does not provide any support till the concrete sets and it may lead to collapse of edge of the PQC layer, particularly the inner edge on a horizontal curve as shown in Figure 12 (a). Similar edge collapse can also occur when tie bars are inserted after laying the PQC as shown in Figure 12 (b). The inner edge on horizontal curve experiences the pull of gravity due to the presence of super-elevation as the edge is unsupported while the concrete is plastic and weak. This creates a tensile stress in fresh concrete and as a result the edge collapse occurs.

(a) Collapse of inner edge of the curves (b) Collapse of edges at tie bar insertion

Figure 12 Edge collapse in cold weather

The edge collapse observed during construction at night in the winter month of December when the air temperature was close to 10 is shown in Figures 12 (a) and 12 (b). This suggests that℃ the concrete pavement construction on horizontal curves during cold winter nights is not advisable without the support of formwork.

4.13 Problems with excessive vibration and higher water content

Laitance, in concrete, is a condition where the cement slurry rises to the surface with higher water content leading to a weaker mortar at the top. This condition arises when the paver stops (or moves at very slow pace) at a location, while the vibrators are running at full speed, leading to excessive vibration and laitance. In the cases of laitance, the damage severity is more as mortar layer at the top may get eroded soon, leaving exposed aggregate surface as shown in Figure 13.

(a) Aggregate surface exposed (b) Visible loss of surface mortar

Figure 13 Exposed aggregates due to loss of mortar at surface

Such surface failure may occur even if the moisture is lost from the fresh concrete, leading to a weak concrete surface finish which may get damaged quickly. Preserving the surface moisture, maintaining just sufficient moisture and maintaining a homogeneous mix are the key to a good and long lasting surface finish.

4.14 Random cracking in DLC

The joints are provided in PQC layer to avoid the development of random cracks. However, such joints are not provided in the DLC layer leading to random cracking at an interval of approximately 25 to 30 meters as shown in Figure 14. The observed spacing between the random cracks is for the DLC mix having 120 kg of cement and 30 kg of flyash per cubic meter of mix which is designed to have a minimum compressive strength of 10 MPa on 7 days of curing. The problem with random cracking is the faster deterioration of the joint. Apart from this, if the joint in DLC and joint in PQC match at a location then there can be a higher possibility of joint deterioration, due to larger deflections resulting from the possibility of mud-pumping. If joints are provided in DLC at a predefined spacing like 15 m or so, then the PQC joints and DLC joints can be coordinated not to match with each other. These planned DLC joints can also be sealed with a low cost sealant like bitumen, to prevent ingress of moisture and fines from lower layers. Figure 14 (b) shows the transverse crack which is partially deteriorated due to movement of heavy construction traffic on the DLC layer.

(a) Transverse crack across two lanes (b) Partially damaged crack joint

Figure 14 Random transverse cracking in DLC layer

4.15 Problems during the curing of DLC

In majority of the highway projects in India, the concrete pavements are associated with highway widening as well. This results in less right of way available for construction vehicles to move. In such conditions, watering the DLC (after construction) for curing purpose is often done with sprinkler truck moving over the DLC which is just 3 days old (Figure 15 (a)), damaging the DLC layer to some extent depending on the time and location. This damage is not accounted for in the design. Figure 15 (b) shows the proper way of watering the DLC.

(a) Sprinkler truck moving on DLC (b) Watering DLC using a hose

Figure 15 DLC curing methods generally followed

This type of watering for curing was observed frequently on many national highway sections in India. The same type of watering for the purpose of curing was not observed for the pavement

quality concrete layer, for which watering is done from the tanker kept on the side with a water hose. Similarly, DLC is also watered from the side using a hose in the first three days after construction.

4.16 Construction joint issue in DLC laying method

The construction of DLC is done in two passes (strips) of width 5 m each as shown in Figure 16 (a). This method creates a construction joint between the two strips. This is particularly important in the case of bonded section where DLC and PQC are not separated by a polythene separation sheet, as there is a possibility for formation of a reflective crack in to the PQC layer over the construction joint in the DLC layer. The effect of reflective cracking can be minimized by providing the longitudinal joint in PQC to match the longitudinal construction joint in DLC. If the 10 m wide DLC is constructed in single pass, the construction joint and the possibility of reflective cracking in PQC can be avoided. The image in Figure 16 (a) shows the construction of DLC layer in two passes and the image in Figure 16 (b) shows the reflected crack on the PQC surface, above the DLC construction joint.

(a) DLC laying in two passes (b) DLC construction joint reflected on PQC

Figure 16 Joint in DLC leading to reflective cracking in bonded PQC layer

In case of bonded section, reflective cracking should be minimized as the reflective cracks form into a meandering crack, which constrains the free curling of slab there by increasing the possibility of stress accumulation, which may lead to pavement failure.

5. GENERAL DISCUSSION ON FIELD OBSERVATIONS

The construction related issues that may arise, precautions to be taken, and solutions proposed/ selected during the construction of a concrete pavement of a national highway section in India are summarized in to the following points:

1. The moisture loss from the freshly laid PQC surface should be avoided to the maximum extent possible. Covering the pavement surface with polythene sheet (used for separation) minimizes the moisture loss due to wind and to some extent heat. This sheet should be provided without damaging the tining texture provided on the surface and only after spraying the curing compound. Usually 4-5 hours after laying of PQC, when the texture has sufficient stiffness, polythene sheet can be spread over the PQC.

2. Moisture loss due to high wind velocity leads to shallow surface cracks which should be avoided to the possible extent.

3. Joint sawing of PQC layer should be done within the joint sawing window of 10 -16 hours after laying PQC. Delay in joint sawing leads to formation of random cracking in PQC which cannot be repaired later. Longitudinal cracks which are not in the wheel path can be cross stitched as a repair method.

4. They automatic dowel bar insertion mechanism available in the existing pavers should be improved to make the concrete to close the dowel insertion marks. Most of the existing systems leave the concrete over the dowel bar to be not fully compacted and weak. This may lead to longitudinal crack initiation near the dowel bars or may lead to faulting.

5. PQC slab sliding is observed near horizontal and vertical curves. The transverse joints are slowly opening wider near the approach to a valley curve (vertical curve). The longitudinal joints near horizontal curves are getting widened when traffic is allowed, due to the centrifugal force of the heavy vehicles. So, PQC-DLC bonded construction can be adopted near the horizontal and vertical curves for better pavement performance.

6. When traffic is allowed on partially completed concrete pavement stretch, sufficient care should be taken to avoid sliding of panels due to frequent braking of the vehicles near the end of the partially completed stretch. This can be achieved by providing a terminal slab or anchorage. This is a frequent occurrence near the cross drainage works which are under construction.

7. The frequent stopping and starting of the paver leads to uneven pavement surface and uneven thickness of the slab. So, the paver speed should be suitably adjusted depending on the PQC mix arrival rate to avoid frequent stoppages of the paver.

8. The PQC laid on a horizontal curve should have form work for supporting the inner edge of the pavement against gravity when the PQC mix is in the fresh state. This is particularly important in the case of winter nights, when the concrete needs more time to set, to avoid inner edge collapse of the PQC layer.

9. The random cracking in the dry lean concrete sub-base layer can be avoided by providing joints at 15 m interval. The random crack spacing was observed to be varying between 25 m and 35 m. The joint in PQC and DLC should not match as far as possible for a better pavement performance.

10. For curing the DLC, water should be sprayed from the side instead of spraying from truck plying on the one or two days old DLC to avoid damage to the DLC layer in the wheel path.

11. Laying and compacting of the DLC layer should be done for the entire width of the pavement in single pass to avoid the formation of longitudinal joint in the DLC layer. This method is

particularly advantageous in the case of bonded PQC construction near vertical curves and horizontal curves.

6. Concluding remarks

Following are the concluding remarks proposed from the construction related issues faced during the construction of a concrete pavement of a national highway section in India:

The moisture in concrete should be preserved for attaining the maximum strength for a given concrete mix. As the concrete pavement has a larger exposed surface area to volume ratio compared to other concrete structures, sufficient care should be taken to prevent moisture loss. Covering the concrete layer with a polythene is observed to be preserving the moisture.

The automatic dowel bar insertion systems should be further developed to make the concrete to close-in completely above the inserted dowel bar for better joint performance. Doweled joints should be properly marked and sawed to fully utilize the dowel bars in load transfer.

Concreting during the winter season should be done with caution. Formwork should be provided for inner edges on a horizontal curve to avoid edge collapse during cold weather, due to delayed setting and hardening.

PQC and DLC should be constructed as bonded (without the separation sheet) wherever the possibility of slab sliding is high, to avoid opening-up of the joints.

DLC construction should be done in a single pass to avoid the construction joint between the lanes. The construction joint in DLC reflects in to PQC in the form of crack when both layers are constructed a bonded.

7. Acknowledgements

The authors would like to acknowledge Late Prof. B B Pandey, Advisor, SRIC, Department of Civil Engineering, Indian Institute of Technology Kharagpur for his initiation in the construction of short panel cement concrete pavements (SPCP) in India, involvement and suggestions during the experimental study. The authors are thankful to National Highways Authority of India (NHAI), Government of India for sponsoring the research project on short panel cement concrete pavements (SPCP).

8. References

IRC:15 (2017), Code of Practice for Construction of Jointed Plain Concrete Pavements (Fifth Revision), Published by Indian Roads Congress, New Delhi, India

IRC:58 (2015), Guidelines for the Design of Plain Jointed Rigid Pavements for Highways (Fourth Revision), Published by Indian Roads Congress, New Delhi, India

IRC: SP:49 (2014), Guidelines for the Use of Dry Lean Concrete as Sub-base for Rigid Pavement (First Revision), Published by Indian Roads Congress, New Delhi, India

IRC:44 (2017), Guidelines for Cement Concrete Mix Design for Pavements (Third Revision), Published by Indian Roads Congress, New Delhi, India

IRC: SP: 96 (2012), Guidelines for Selection, Operation and Maintenance of Concrete Batching and Mixing Plants, Published by Indian Roads Congress, New Delhi, India

MORTH (2013) [Ministry of Road Transport and Highways], “Specifications for Road and Bridge Works”, Published by Indian Road Congress, New Delhi, India