Dr. Rakesh Kumar, Head & Senior Principal Scientist, Rigid Pavement Division, CSIR - Central Road Research Institute, New Delhi

Rakesh Kumar
After 2014, the speed of the construction of cement concrete road for national highways and expressways, in cities and even at village level has significantly increased due to the policy adopted by the Government of India. India has a road network of more than 5.6 million kilometre, comprising of a mix of modern and narrow national highways, besides expressways, state highways, project roads, urban roads, rural roads, including unpaved roads [https://en.wikipedia.org/wiki/Indian_road_network]. Figure 1 shows the length-wise percentage of different type of roads in India as on March 2016. About 2 percent of the total road length in our country is made up of cement concrete however, reliable data on it is not available. Figure 2 presents a comparative share of concrete pavement in total motor-able roads in India with respect to a few most developed countries in the world.

Cement Concrete Pavement

The share of cement concrete road in total road length in India will be increasing at a faster rate as the construction of cement concrete road is being encouraged by the GOI due to numerous technical added advantages such as a longer service life with a little to no maintenance cost for the first 10 years or so, etc. As per a report, in 2018-19, about 5000 km of cement concrete road has to be constructed for national highways alone.

Cement Concrete Pavement

A gigantic amount of cement, high-quality aggregates, potable water, and other materials are used in the construction of concrete roads. Due to the ban on mining of sand, manufactured and/or crushed stone dust is being ruthlessly used, without a strict quality control. The heart of a cement concrete pavement is the concrete itself. The performance of concrete determines the performance of the concrete road. But the performance of the concrete mainly depends on the quality of materials used and the workmanship at the time of construction. A poorly designed, but well-constructed cement concrete road generally outperforms a properly designed but poorly constructed pavement.

Premature concrete pavement surface defects such as scaling, pop-outs, crazing, map cracking, shrinkage cracking, and loss of texture etc., have become the commonly reported pavement distresses on a newly constructed cement concrete road in India, especially in the last few years. Among all the surface defects, the problem of scaling draws a quick attention of the road users as well as road authorities as it affects riding comfort as well as safety of the road users moving at high speed [Rakesh Kumar, 2018].

Cement Concrete Pavement F3

Scaling is deterioration of the upper concrete slab surface, and loss of surface mortar and mortar surrounding the aggregate particles. It may occur anywhere over a pavement slab [Miller and Bellinger, 2003]. Normally, the depth of scaling varies from 3 mm to 13 mm [FHWA-HRT-13-092, 2014, N.J. Delatte 2014, ACI 224.1R]. Scaled concrete surface gives a very ugly look of the concrete slab (Figure 3). It is measured as the square meters of affected area and expresses in the percentage of the total slab area. Scaled surface may be of the light, moderate and severe type. In the case of severe scaling, more surface areas are lost and coarse aggregates are clearly exposed and projected from the surface (Figures 4-5). It is common to observe scaling problem of varying severity in several pavement slabs. Severe scaling is considered as a type of functional distress as it affects riding quality and safety of the traffic.

A scaled concrete pavement slab surface should not be mistaken for an "exposed aggregate finished concrete surface", which is a type of decorative concrete and not a surface distress. Exposed aggregate finished surface concrete is obtained by using either a special technique/method which may involve use of a surface retarder or similar chemicals or special tools for removing the mortar around the aggregate in order to expose the coarse aggregate. Exposed aggregate finished concrete surface can uniformly be ensured for the entire stretch of slabs or for the entire surface area. Scaling surface distress is also an aesthetic problem which could occur anywhere on the pavement slab, even locally at a few spots in an entire stretch of the road.

Cement Concrete Pavement F6

Based on the core strength data generated from moderately and severely scaled areas of pavement slabs, it has been found that scaling has insignificant effect on the structural capacity of the pavement. However, keeping in view the functional performance of the pavement, a proper durable repair of the scaled pavement surface is required. Surprisingly, in a few cases of scaling, the recommendation for reconstruction or replacement of scaled concrete slabs was seen in our country. The ground for recommendation is based upon the IRC SP:83, 2008. Table 1 presents the measured parameter, degree of severity, assessment rating, and repair action for scaling distress of concrete pavement as per IRC SP:83.

Table 1. Measured parameter, degree of severity, assessment rating and repair action for scaling distress of concrete pavement
Measured parameter Degree of severity Assessment rating Repair action
Area in square meter expressed in %. r=scaled surface area/ total  slab surface area. 0 Nil, not discernible No action
1 r < 2% Local repair of damaged areas
2 r = 2 – 10 %
3 r = 10 – 20 % Bonded Inlay
4 r = 20 – 30 %
Maximum depth of damage (h) 5 r > 30 % and h > 25 mm Reconstruction of slab

The applicability of reconstruction is highly questionable in Indian condition because it is very uncommon to have a scaled pavement concrete surface with scaled depth more than 25 mm for the pavement concrete mix commonly used (Table 2) for the construction of a pavement slab. Therefore, reconstruction of scaled pavement slab is seldom necessitated. Repair of Scaled Areas of Concrete Pavement Slabs

Cement Concrete Pavement F8

Table 2. Combined aggregate gradation for pavement quality concrete (MoRTH, 2013)
Sieve size, mm Percentage by weight passing the sieve
31.5 100
26.5 85-95
19.0 68-88
9.5 45-65
4.75 30-55
600 8-30
150 5-15
75 0-5

Premature reconstruction of concrete pavement slabs corresponds to an unacceptable waste of materials, work energy, money, and unnecessary emission of greenhouse gases (GHGs). Therefore, proper repair and/or rehabilitation without compromising the overall performance of the pavement should be encouraged. Irrespective of the cause of damage due to surface scaling of pavement slab, it is imperative to establish the extent of the damage and determine the suitability and soundness of the major portion of the concrete slab on which a sound repair could be build. Based on this information, the type and extent of repair are chosen. Scaled areas of concrete pavement slabs can be satisfactorily repaired by a thin concrete or mortar overlay, provided the surface is sound, durable and clean. The surface should be free from dirt, paint or oil and sound. To accomplish this, use of a hammer and chisel, sand blasting, high-pressure water jet etc are used to prepare for resurfacing with a repair material. Numerous patching materials are available for this purpose. Texture and colour of the repair must match with the surrounding concrete.

Among all repair mortar types, polymer modified cementitious mortar has an upper- hand for concrete repair due to its overall compatibility with the parent concrete. Polymer modified cementitious mortar works monolithically with the parent concrete due to similar physical properties such as modulus of elasticity, shrinkage, and coefficient of thermal expansion (COTE). The most widely used polymer mortar for repair of scale is styrene butadiene rubber (SBR) [Wang and Zhang 2015]. Figures 6-12 show different steps starting from cleaning of the surface till measurement of the repaired mortar depth of a repaired scaled pavement slab with suspension type SBR polymer modified cementitious mortar. Quartz sand was used in this mortar.

Measurement Of Depth

The cost of such repair depends on the thickness of the mortar used for the repair of scaled surface, which ultimately depends up on the severity of the scaling. In the present study, it was approx. ₹1000 to ₹1400 per sqm. A simple calculation for the repair of a concrete pavement slab of 4.5 m x 3.5 m with 0.30 m thickness with and without demolition cost is presented in Table 3.

Table 3.  Repair cost of a completely scaled pavement slab of 4.5 m x 3.5 m x 0.3 m vis-à-vis its construction cost
Dimensions of the pavement slab (m) Surface area of the slab, m2 SBR cementi-tious mortar repair cost per m2 (Rs.) Repair cost of fully scaled surface of a slab (Rs.) A typical construction cost per slab (Rs.) Repair cost/ construction cost (%) Repair cost/ reconstruction + demolition cost* (%)
4.5x3.5x0.30 15.75 900! 14175 37800 37.5 30
1200!! 18900 37800 50 25

The data presented in the above table is collected from an actual field. It clearly indicates that the repair cost of the scaled pavement slab varies depending on the thickness of the mortar used. Higher the thickness of the repair mortar costlier is the repair. The cost of repair of a scaled pavement slab depends on the degree of severity of the scaling. For a mortar loss depth between 5-8 mm varies from 25 to 30 percent of the reconstruction cost of the slab.

Cement Concrete Pavement F12

Performance of the Repaired Surface

Repair Mortar TextureFigure 13. Loss of repair mortar and texture
The performance of a repaired surface is generally judged by its intactness with the substrate and resistance to surface abrasion. An improper thickness of the repair mortar starts deteriorating (breaking off and texture loss) after few months (Figure 13). On the other hand, a properly placed repair mortar overlay maintains its intactness and texture for a long period. Figure 14 shows a typical repair of scaled surface using relatively a thicker overlay of mortar even after more than one year on a highway on which more than 5000 trucks are plying. Hence, a concrete pavement engineer is required to select a proper thickness and construction practice to ensure satisfactory performance of repaired surface of scaled pavement slabs over the designed life of the pavement. Well designed and constructed pavements generally develop distresses gradually over time under traffic and environmental effects. But use of poor materials, improper mixes and/or poor construction practices cause pavement distresses even before the pavement is put into service, consequently affecting the performance of the pavement.

Summary and Conclusion

Repair of scaled surface areas of a newly constructed concrete pavement slabs is a highly specialized work which requires proper material and workmanship, besides expertise in repair work. A proper selection of thickness of the repair mortar plays a key role in ensuring durability and long-term performance of the repaired areas of the affected pavement. The recommendation of reconstruction of the slabs for distress like surface scaling is not required if the concrete slab is structurally adequate. A moderately to severely scaled pavement slab can be properly repaired to restore the functional performance of the concrete at merely 25-30 percentage of the reconstruction cost by a knowledgeable and expert repair team.

Cement Concrete Pavement F14Figure 14. Repaired scaled surface of pavement slab after 1 year

Acknowledgements

The permission of the Director-CRRI Prof. Satish Chandra to publish this work is gratefully acknowledged. The support and help provided by site engineering, contractor and road owners for the photographs and information regarding the cost of repairing of the scaled surface of pavement slabs are thankfully acknowledged. The help provided by Mr. Adarsh Kumar and Ms. Garima during preparation of the manuscript is gratefully acknowledged.

References
  1. https://en.wikipedia.org/wiki/Indian_road_network, 10 Dec., 2018.
  2. Rakesh Kumar, 2018. Influence of surface scaling on the performance of cement concrete roads, New Building Materials & Construction World, March 2018.
  3. Miller, J.S., and Bellinger, W.Y. 2003. Distress Identification manual for the long-term pavement performance program (4th revised Ed.), FHWA-RD-03-031, Washington, D.C.
  4. Wang, R., and Zhang, L. 2015. Mechanism and durability of repair systems in polymer-modified cement mortar, Advances in Materials Science and Engineering, Vo.2015, Article ID 594672.
  5. IRC SP: 83, 2008. Guidelines for maintenance, repair and rehabilitation of cement concrete pavements.
  6. Federal Highway Administration (FHWA) 2014. Distress identification manual for long term pavement performance program (5th Edn), FHWA-HRT-13-092, May 2014. https://www.fhwa.dot.gov/publications.
  7. Norbert J. Delatte, 2014. Concrete Pavement Design, Construction and Performance, 2ne Edn., CRC Press, London.
  8. American Concrete Institute Committee 224.1R, Causes Evaluation, and Repairs of Cracks in Concrete Structures, ACI 224.1R, Farmington Hills; MI, American Concrete Institute.
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