Different Methodologies for Repair of Cracks in PQC in Concrete Pavements

Dr. Yash. P. Gupta, Technical Advisor, COWI - DIPL Consortium, Naini

Bridge Project, Allahabad, India And (Ex) Material Consultant Allahabad By

Pass Project, Allahabad

Large scale construction of Bridges & Highways is going on in India and

World over. They are mostly made as rigid pavements using Pavement

Quality Concrete (PQC). On one hand, concrete is a very good and strong

material, but it develops cracks due to temperature, shrinkage, creep etc.

Until unless enough precautions are taken, some cracks do come up on

concrete surface. Prominent cracks should be repaired for better

performance and longer life of Highways/pavements. To repair these cracks,

several materials and procedure have been developed. The efficiency of

these materials and procedures depend on the type of crack, weather

conditions and applicator efficiency.

In this paper various procedures of crack repair are described. However, any

procedure in general should be first tried on pilot basis and then depending

upon its success, repairing of cracks be done at site. A procedure of injecting

low viscosity Epoxy Material is an excellent material. It is discussed here and

can be used for the repair of cracks.

Why Concrete Cracks

First it is necessary to understand why the concrete cracks. There can be

many reasons why the concrete cracks. These need to be understood from

its reaction and setting pattern point of view. The main reason is improper

concrete mix design and laying / jointing practice related to the inherent

nature of concrete to change volumetrically due to moisture, reaction and

thermal effects etc. The incidence of cracks can be minimized by improving

concrete mix design, laying time weather condition and jointing practices

with timely saw cutting and properly managed curing.

Concrete roads, properly designed and constructed, should require little, if

any, maintenance over its design life. Still, proper and timed maintenance

may extend the life of the pavement even beyond designed service life.

Concrete pavements undergo stress and strain due to traffic and climatic

effects. However, as long as sub grade is properly compacted, any

variation/change in support (due to moisture-changes) has little effect on

performance. Proper weather during construction and laying / jointing

practice will eliminate most premature distresses. Otherwise, some

shrinkage cracking may appear before the road is opened to traffic.

Normally, there is no reason why a concrete road should not perform well

during the designed life span if properly laid and cared through

maintenance.

Identification and Location of Cracks on PQC Surface

A. Identification of Affected Area

The relevant pavement is surveyed and effected portion marked with a

marker. The area can be struck with a hand held hammer to further

qualify and quantify the crack. The dull and hollow sound is emitted

from the unsound concrete whereas metallic sound is emitted from

sound concrete. The boundary of area to be treated should be marked

and as far as possible rectangular and normally about 50 mm should

be taken into the sound concrete to make sure that all unsound

concrete is included. Cracks and its location can be identified from top

surface of PQC and some from sides. Then judge the extent of cracking

in concrete by any one of following methods.

1. Visual Survey of the effected PQC Surface. This should preferably

be done after rains or after washing the surface with water.

2. Measure the width of cracks at top of PQC surface by using

thickness gauges.

3. NDT: Non destructively estimate the extend of cracking by using

NDT technique. Commonly adopted NDT technique is Ultrasonic

Pulse Velocity Measurements using UPV meter.

4. Core Drilling: Take cores at the apparent location of cracks which

are seen from top, upto full depth of PQC. Generally cores can be

taken of 100 or 150 mm in diameter.

B. Classification of Cracks and Repair Methods

The cracks may be classified in following categories:

a. Small Hair Cracks (< 1mm) - seen mainly at top.

b. Medium / Partial or half depth cracks

c. Full depth cracks

d. Many checker cracks in any one panel of PQC.

e. Pot holes and Corner damages

f. Settlement of panel or Multiple cracks near expansion joints.

Such Surface Cracks develops in PQC due to temperature difference,

late joint cutting, and defective curing of PQC etc. The cracks will allow

water / mud /debris going into the cracks and widens them further.

Medium or Full depth cracks

Some typical Medium or Full depth cracks are shown in Figures 1.

Figure 1: Typical Cracks in PQC Pavement Surface

Settlement of panel or Multiple cracks near expansion joints:

Such cracks normally develop because of poor compaction or poor Concrete Mix Design.

Some typical cracks are shown in Figure 2.

Figure 2: Typical Panel Settlement or near panel Cracks

Visually examine all such cracks and decide which crack is to be

repaired on the basis of width, depth and its pattern. In general hair or

micro cracks do not affect much the structural integrity of PQC much.

Thus remedial works or repair of such cracks may not be necessary.

However, partial / half depth cracks should be repaired. About full

depth cracks and many checker cracks, it must be decided on the case

to case basis after looking at the site and analyzing the condition

depending upon its width, length and number of cracks in a panel as to

what treatment is to be given.

Repair Materials for Crack

The material, techniques / System for repair the PQC cracks should be such

which will have durability of minimum 10 – 15 years or as per the designed

life of pavement. Otherwise water may penetrate from these cracks and

reach sub-grade and embankment level causing settlement. This will

ultimately damage the pavement. Hence it is necessary that a methodology

and guidelines for the repairs & rehabilitation of such cracks in PQC be

developed. Normally the repair material should remain flexible enough to

accommodate anticipated expansion & contraction, water-tightness etc.

Repaired cracks should not be rigid otherwise the cracks may appear again

in the same panel at adjacent panels.

Following are some of the material used in crack repair.

1. Very Low Viscosity Epoxy Material

2. Epoxy Modified Mortar

3. Polyurethane based coating over Epoxy Mortar

4. Elastomeric Concrete

5. Fiber Reinforced Concrete.

Details of some of these materials are given here:

1. Very Low Viscosity Epoxy Material

It is a free flow epoxy grout material designed for grouting gaps of low

width like 0.5 to 10 mm. This epoxy repair compound or free flowing

epoxy resinous grouting material or similar product is a very low

viscosity liquid of around 10 poise or so. Epoxy compound like

RESICRETE of SWC or CONVEXTRA EP10 (M) of FORSROC which is

normally supplied as two-component product consisting of base and

hardener can be used. This should normally have viscosity of 2-4 poise

at ambient temperature. The Compressive strength of such material

should be at least 60-70 MPa or 1 ½ times the Compressive strength of

concrete used for PQC.

2. Epoxy Modified Mortar

Epoxy mortar is a common material used for repair of concrete

surfaces in general, especially for the pot holes in rigid pavements.

However, 100 % epoxy based mortar is little brittle in the long run;

hence in case of repairs of pavements, its modified products should be

used such that the resultant material is not rigid.

The Epoxy Mortar we can modified by:

o Adding about 5 % Poly-sulphide polymer in the epoxy resin as it

basically needs to modify the formulations of epoxy based

mortar. Many companies have started manufacturing Epoxy Poly-

sulphide mixed based mortar.

o It will not only improve the life of mortar but also it gives

flexibility which is required in the repair mortar used for the

pavements.

o By adding Poly-sulphide polymer, it improves the UV resistance.

3. Polyurethane based coating over Epoxy Mortar

As epoxy mortars are non-uv resistance, but still it is a good high

strength material, so use polyurethane based coating on the repaired

surface of mortar which is exposed to UV or direct sunlight. This

coating will protect the existence of epoxy mortar till the time the

mortar remain intact & not start to loose its property of non-brittleness.

PU coating should normally be of about 300 micron thickness.

4. Elastomeric Concrete

This is an epoxy modified cement concrete used in repairs not only in

PQC crack repairs but also in structures and concrete surface. For PQC

Crack repairs Elastomeric concrete is a useful material.

5. Fiber Reinforced Concrete

Fiber reinforced concrete is a concrete having small size aggregate

(say 6 mm or so) or Cement sand mortar. It is mixed with any one of

the different type of fiber given below which are generally used in

construction. Poly propylene Fibers are more appropriate for this

purpose. Though, there are several types of fibers available as given

below. Normally fiber concrete can also be used as a thin top layer or

bearing surface over the cracked PQC pavement after treatment of

cracks.

a. Steel Fibers

b. Carbon fibers

c. Glass Fibers

d. Poly propylene Fibers etc.

Repair Method of PQC in Pavements

Repairs can be classified into following categories:

a. Partial Depth repairs (Transverse as well as Longitudinal) of PQC.

b. Repairs of longitudinal cracks by using U type anchorages / stitching.

c. Repairs of the pavements especially for the areas where aggregates

are exposed due to various reasons like after concreting sudden rain

started or due to more tear & wear of concrete etc.

d. Re-surfacing of Pavements by Fiber Reinforced Concrete / Mortar for

betterment.

e. Cross Stitching / stapling of panels / cracks: Repair the cracks by

putting dowel bars with caps & tie bars so that it can have some space

to have movements.

f. Repairs of Potholes and corner spalls in concrete pavements etc

Repair of minor Cracks (<1 mm wide)

These are very low (small) width cracks or hairline cracks. Such cracks

generally do not affect the performance of road surface. Thus these cracks,

unless the severity level increases, need not be repaired. Further observe

these cracks over a period of time for enlargement.

Medium Cracks (generally 1 to 5 mm wide)

If cracks are not moving then a very low viscosity epoxy resin may be used

for its repair with or without fine sand to bond the crack faces. V shaped

‘joint wells’ are made with 3 to 5 mm saw blade. Also make 8 to 10 mm

diameter grout holes at regular interval. Then pump the epoxy bonded into

holes using a grout gun.

Partial Depth Repairs

The spalling of concrete occurs near the joints mainly due to adjacent slab

load transfer related movement at the joint particularly in summer. The

spalling will occur frequently in mid slab locations and other locations mainly

due to high slump due to w/c ratio, poor construction or failure of earlier

done repairs. Spalls are a localized problem and can be easily repaired with

partial depth repair methods.

Full Depth Repairs

The full depth repairs are necessitated due to Transverse Crack in slab in full

panel width. This crack may be in one lane or both the lanes. The reasons for

such crack are:

Locking of Transverse Joint:

The joint does not function due to non-functioning of dowel bars. These

dowel bars either get misaligned during construction or slurry gets into

sleeves and prevents their movement.

The intermediate crack may be caused due to too much resistance

offered by rough surface of underlying DLC.

The crack may also develop due to thermal changes coupled with large

joint spacing.

In all such cases where cracks are more harmful, then the PQC Panel should

be examined carefully, if the panel is to be repaired or removed. If it has to

be repaired than use the technique of cross stitching method. However, if

that portion of panel is to be removed and then recast the panel as indicated

by Removal of Existing Unsound Concrete.

Some of these repair methods are described here.

I. Repair By Grouting of Low Viscosity Epoxy Material

a. Equipments for Repair

Depending upon the method of repair the following equipments

may be used.

Grouting Pump of capacity about 5-10 Kg/cm2.

Mechanical Grout Mixer

Air Compressor

Injection Ports.

Hand Chisel, trowel, etc.

b. Preparation for Crack Repair

On both sides of crack, the side edges be slightly chiseled

to give a V-shape. If required do chiseling until a hard

concrete is encountered.

Remove loose material from crack area and blow out the dust and debris

from the gap of crack by using a compressor or air blower.

Figure 3: PQC crack showing

the Grout holes

Drill holes in PQC surface in the line of Crack upto depth of

about 150mm & 10 mm diameter @ 300 – 400 mm c/c as

shown in figure 3.

Fix Injection ports (Nipples) of plastic or similar material ie

nozzles of 6-8 mm in diameter and 100mm length into the holes

using appropriate gluing compound like Araldite. Keep the

projection of nozzle outside the PQC to about 20 mm.

c. Repair Procedure

Surface to be repaired may be pre wetted or bring it in SSD

condition.

Apply a coat of primer like acrylic bonding agent using

brush after scrubbing it well on the prepared surface. Allow

the primer to become tacky, which normally takes 10 – 15

minutes or as given in the manufacturer literature.

Push the Compressed air into the crack to flush out the

dust and all foreign material from the crack to the side or

top.

Fill the top of V-grove portion by appropriate Epoxy

modified mortar.

Use the epoxy repair compound or free flowing epoxy

resinous grouting material or similar product of very low

viscosity.

Prepare the mix of the repair material as directed by

manufacturer or Mix them mechanically with Grout mixture

after weighing them in recommended proportions.

Recommended water quantity (if water based) will be

measured and added to polymer component and mix it

thoroughly. The powder component will be mixed until a

homogeneous mix is obtained.

Pressure Inject the above material or appropriate ultra low

Viscosity epoxy liquid first in the middle nozzle from one

side of crack. Continue till it is forced out of next nozzle or

from the side of PQC crack. Then shift the injection

procedure to next nozzle.

After the injection is complete, estimate the consumption

of grouting material or find out the quantity of injected

material. This may be compared with the estimated

quantity.

If possible ask a supervisor from the suppliers of material

to supervise the job as per their recommended procedure

and specifications during the use of product.

Apply the mix within the pot life of repair compound on the

prepared crack.

d. Finishing of Repair Surface of Crack

If sagging on surface occurs during application to PQC

surface, then Polyurethane based coating may be applied

by trowel in smaller thickness in one or two layers.

The applied mortar shall be finished with wooden floats.

When the injection operation is over then cut the projected

portion of nozzles and sealing the portion by Epoxy Mortar.

After completion of repair of the joints, spalls, partial depth

repair, corner repairs, etc sealing of expansion joints

should be done immediately using polyurethane coating

otherwise joints might leak & will create problems in

future.

e. Curing of Repaired Surface

The repaired surface shall be cured by curing compound or

water curing, if required or as recommended by

manufacturer.

II. Repair By Stitching or Cross-stitching of Cracks

Cross-Stitching is a repair technique mostly used for longitudinal

cracks which are in reasonably good condition. The purpose of cross-

stitching is to maintain aggregate interlock and provide added

reinforcement for strength. The tie bars used in cross-stitching prevent

the crack from vertical and horizontal movement or widening. This

technique knits the cracked portions of the slab together and reduces

the chances of crack to grow further.

Cross-stitching uses deformed tie bars drilled across the crack at an

angle of 30-40 degrees. Deformed steel bars of 10-12 mm diameter

are sufficient to hold the crack tightly closed and enhance aggregate

interlock. Full depth holes of 18-20 mm diameter are drilled at a pitch

distance of 300 mm with offset of about 150 mm from the crack. The

holes are drilled alternately from each side of the crack so that it

passes through the crack from left to right, while the next from right to

left. After drilling, the holes are flushed with high pressure air to clean

out any residual dust. Then a high strength epoxy gel adhesive is

injected into the hole. Immediately after injecting epoxy, deformed

steel bars are inserted into each hole. The crack is sealed at the top

with silicon / epoxy modified sealant.

III. Removal / Replacement Of PQC Panel which has large cracks

When any one of the PQC panel has large number of cracks or if it is

settled, then concrete of such panel should be removed fully.

Otherwise ether it is very difficult to repair or it is too costly. In such

cases the following may be resorted:

a. Full panel removal and recasting as given below.

Removal of Existing Unsound Concrete

A minimum of 50 mm deep rectangular cut should be made at the end

of panel which is to be removed. Use saw cutting machine with vertical

faces. Inside this panel mark rectangle, smaller square of size 100 mm

× 100 m and 25-30 mm deep. These are marked to remove in parts.

The smaller square should be chipped off with chisel. If jack hammer is

used, it should not be more than 14 Kg. in weight. After removal of

unsound concrete, a reassurance hammer-striking is done and any left

out unsound area is also removed by enlarging the rectangle. If the

unsound concrete penetrates more than half depth of slab then full

depth of panel should be removed.

Breaking the Old Concrete

A saw cut usually as deep as possible is made to include all unsound

concrete. Once this cut (full depth or partial maximum depth) has been

made, about 100 mm deep cuts are made with circular diamond saw-

cutters. On the surface of cut-out slab some 75 mm × 75 mm or 100

mm × 100 mm square saw cuts are made to facilitate the breaking of

concrete by jack-hammer.

Recasting of Panel Concrete

Once the old concrete is removed the panel can be prepared for

recasting. A typical view is shown in figure 4. The PQC used for

recasting should be used should be of the same grade as of original

grade concrete. While recasting the panel, Dowel bars and tie bars

should be put in panel as shown in figure. Other procedures are as

used in original casting.

References

Jose C. Horta Report on Defects and Distress of Rigid Pavement

Sections: Survey, Rating, Monitoring, Causes and Repair By

Rev.TL.30.10.05

Binod Kumar, Dr. Saroi Gupta, Dr. V. K. Sood, 2004, Restoration

Techniques for Distressed Concrete Pavements, Technical Papers,

Seminar on Design Construction and Maintenance of Cement Concrete

Pavements, New Delhi, 8-10 October 2004, p. IV-101 to 110

Committee of State Road Authorities, Pretoria, South Africa, 1990,

Standard Nomenclature and Methods for Describing the Condition of

Jointed Concrete Pavements, Technical Recommendations for

Highways, Draft TRH19:1989, p. 1 - 49

D. C. De, S. K. Bagui, 2004, Approach to Maintenance of Concrete

Roads, Technical Papers, Seminar on Design Construction and

Maintenance of Cement Concrete Pavements, New Delhi, 8-10 October

2004, p. IVK-1 to 21

S. G. Joglekar, D. C. Saha, 2005, Defects, Repair and Rehabilitation of

Concrete Pavement, Seminar on High Speed Road Corridors, New

Delhi, 23 - 24 September 2007, p. 2:51 - 59

Satander Kumar, 2004, Causes of Distress, Repair end Maintenance of

Concrete Roads, Technical Papers, Seminar on Design Construction

and Maintenance of Cement Concrete Pavements, New Delhi, 8-10

October 2004, p. IV-2 to 14

Mohamed Y. Shahin, 1994, Pavement Management for Airports, Roads

and Parking Lots, Chapman & Hall, New York, London, 450 p.

Dr. V. M. Sharma, 2004, Diagnostic Investigations and Repair of

Cement Concrete Pavements - State of the Art, Technical Papers,

Seminar on Design Construction and Maintenance of Cement Concrete

Pavements, New Delhi, 8-10 October 2004, p. IV-133 to 144

Vikas V. Thakar, 2004, Maintenance and Rehabilitation of Cement

Concrete Pavements - State of the Art, Technical Papers, Seminar on

Design Construction and Maintenance of Cement Concrete Pavements,

New Delhi, 8-10 October 2004, p. IV-111 to 132

J.R. Hodgkinson (June 1982) C&CAA Technical Note 49: Steel

Reinforcement for Concrete Road Pavements, Australia.

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