Instant Concrete road repair solution
By Mr. Mangesh Dhamele
Dy. Manager. Choksey Structural Engineering

INTRODUCTION
The Durability of road structures depends on the quality of its maintenance & minor renovations. Maintenance keeps the roadway safe, provides good driving conditions & prolongs the life of the pavement, thus protecting the road investment.

Currently in India more than 2000 km of concrete road is in the operation since last few years. Most of the projects completed by NHAI, MSRDC and other state government authorities. Though the quality & procedural aspects, specifications / guidelines clearly mentions in IRC, MoRTH, but still we observes that various minor cracks, potholes and joints edge spalling in the PQC due to various factors which requires maintenance. Maintenance includes the prompt sealing of cracks & filling of potholes to prevent water entering through the surface.

Repairs and rehabilitation of concrete roads are required to have a smooth riding quality as well as avoid inconvenience causing to the vehicles. We need to have a durable repair products to avoid of cost of various factors like :

a) Diverting the traffic for repairs
b) Inconvenience to the traffic
c) Repeatedly cost of repairs by using conventional methods.
REQUIREMENT OF THE PRODUCT FOR REPAIRS OF CONCRETE SURFACE
1) Resistant to abrasion and weather conditions.
2) Skid resistance, non-reflective finish with colour matching with concrete
3) Fast setting so that repaired patch can accept traffic in as little as one hour.
4) Resistance to deicing chemicals & various industrial chemicals
5) Jet fuel and other fuel resistance like petrol, diesel, oil and grease.
6) Good bond between concrete and steel, Impermeable.
7) Flexible enough to accommodate anticipated expansion and contraction.
8 ) Ultra-violet Resistance, User friendly and paintable.
9) Manufacturer of the material should have the good track record & experience in such kind of repair products.
10) Economical

CONVENTIONAL METHODS OF REPAIR CONCRETE STRUCTURES
Though we have developed our specifications and guidelines to lay the PQC up to the international standards, but now considering the deteriorating conditions of the concrete roads, we have to develop the good specifications and proper guidelines / application systems to repair and rehabilitation of concrete surfaces permanently.
Currently following are the various conventional methods we are using for the repairs of concrete road.

1) Repair by fast setting water based cement compound
2) Repair by epoxy mortar, which is non-UV Resistance material.
3) Repairs of PQC by laying bituminous concrete or bitumen in the cracks & potholes.
4) Other conventional methods

NEXT GENERATION FAST SETTING COMPOUND DELPATCH
In 1983, The D.S. Brown Company introduced Delcrete^TM Elastomeric Concrete. The rigid, yet flexible connection Delcrete^TM provided between steel and concrete soon made it the premier solution for bridge and highway spall repair as a permanent repair solution for high performance pavements, which would offer minimum downtime and, at the same time, limit exposure of work crews to traffic.

D.S. Brown engineers formulated Delpatch^TM Elastomeric Concrete from the original Delcrete^TM product. Delpatch^TM a new generation of elastomeric concrete has two main uses. First, it is an excellent patching material for cracks and spalls on airport runways and highways. Second, Delpatch ^TM provides an easy to use solution in retrofitting airport runways with lighting & bridges with expansion joints.

Delpatch vs Others

Description	Epoxy based Material	Cementatious Material	Delpatch – Polyurathan Based Material
Technical properties:
Compressive Strength	60 N/mm2	Max 55 N/mm2 in 28 days time.	80 N/mm2 in one days
Flextural Strength	20 N/mm2	5.5	-
Tensile Strength	10 N/mm2	-	13.44 N/mm2
Impact resistance	Poor	poor	very good Impact resistance
Flexible	Poor	poor	It can deflect up to 10%, and will regain its original shape
Abrasion resistance	Yes	Up to some extent	very good abrasion resistance.
Practicle:
Curing	Doesn’t required curing by water	Curing by water is must, otherwise it develops cracks	Doesn’t required curing by water
Time required to allow traffic	6 – 16 hours	12 – 24 hours	After one hour
Paintable	Yes	Yes	Yes
UV resistance	Poor	good	Very good
Water impermeability	Good	poor	Very good
Economy :
Rate per ltr or Kgs.	Initial cost will be cheaper,	Cheaper than epoxy	Initial cost will be slightly higher
Life cycle cost	Will be high as need to repair frequently	Will be too high as need to repair frequently	Life cycle cost will be cheaper

A. Existing condition before repair:

After construction of PQC, various cracks has developed due to various reasons like

a) Settlement of the sub-base
b) Surface cracks due to high wind-velocity during laying of PQC
c) Late initial cut of PQC

We have found that various major potholes, cracks and joint spalling at various junctions of Jogeshwari Vikhroli Link Road, Mumbai and at Mumbai international airport wherein contractor or government authorities are unable to repair by epoxy, as epoxies are not UV Resistant or by cementatious material and also they are unable to hold the traffic for conventional repairs.

Following are the few photographs shows deteriorating concrete surfaces and cracks, which requires repair on priority basis to avoid further damage to take place.

Conclusions:
We can conclude with the recommendation of Delpatch should be the material which can be used for such kind of repairs which are critical and important.
This material can be used for following repairs and rehabilitations of:

1. Concrete roads & patches including underpasses
2. Expressways, aprons of airports, where we can not hold the traffic for the sake of repairs of the deterioted patches
3. Nosing wheel areas, where the loads expected more than 150 – 200 tonnes per 2 sq.ft. Area
4. Replacing the expansion joints – which we can complete in one night, actually such kind of practices adopted in US, and other part of the world, where replacement of expansion joint is essential but at the same time, contractor does not have the permission to hold the traffic for longer time.
5. Heavy Industrial floors, shop floors.
6. Light conduits to put lights on the runways.
7. All the surfaces exposed to the sunlight.
8. A top surface of spillways, bucket area of Dams, where water pressure is more, & surface is exposed to sunlight.

The mix design for M35 Grade Of Concrete for pile foundations provided here is for reference purpose only. Actual site conditions vary and thus this should be adjusted as per the location and other factors.

Grade of Concrete : M35
Characteristic Strength (Fck) : 35 Mpa
Standard Deviation : 1.91 Mpa*
Target Mean Strength : T.M.S.= Fck +1.65 x S.D.
(from I.S 456-2000) = 35+ 1.65×1.91
= 38.15 Mpa
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A long time used material in concrete is for the first time fully replaced by a nano material.It is well known in physics and chemistry that a well designed and developed nano material produces better and cheaper cost results than traditional materials, thanks to the stabilization and reinforcement of matter properties at this level: a thousand fold smaller than the older level: “micro” (0.000001 mt).

Micro silica has been one of the world’s most widely used products for concrete for over eighty years. Its properties allowed high compressive strength concretes; water and chemical resistant concretes, and they have been part of many concrete buildings that we see nowadays. Its disadvantage, though, has been its relatively high cost and contamination, which affects the environment and the operators’ health. As micro silica, as a powder, is thousand fold thinner than cigarette smoke. Operators must take special precautions to avoid inhaling micro silica and not to acquire silicosis, an irreversible disease.

In the middle of 2003, a product which could replace micro silica seen the contaminant effects, having the same or better characteristics and at a reasonable cost was on the design table. The goal: silica fulfilling the environ-mental regulation: ISO-14001.

Using tools from physics, chemistry and recent nanotechnology advances, the challenge was fulfilled.Lab tests and production tests proved that the nano silica did not contaminate (because its state), but it also produced better results than micro silica, and a litre bottle of the product was equivalent to a barrel full of micro silica, extra cement and super plasticizing additives.

Because of its innovation the nano silica was tested for over a year in the world’s largest subterranean copper mine to prove its long term characteristics. Cuore concrete takes care of the environment, the concrete and the operators´ health. It is the first nano product that replaced the micro silica.Cuore concrete surpassed the expectations of its design and gave concrete not only the high initial and final resistance but in addition, plasticity, impermeability, minor final cost of work, and cement savings of up to 40%. Also, it lowered the levels of environmental contamination.

In addition, a liter bottle of Cuore concrete equals a whole barrel of micro silica, extra cement and super plasticizers. If before a 2 meters thick beam was required to hold a bridge correctly, now only 75 cm are required. If before 28 days were necessary in order to achieve compressive strengths of 80MPa, now only 1 day is required. The pre stressed beams that before required 3 days to be ready and needed to be cured with water and steam , now require only 1 day and they do not need water.

Moreover, Cuore concrete became one of the first indicators of the properties that the next commercial nano cements in the market will have: nano particles of silica turn into nano particles of cement (nano cement) in the chemical reactions that take place in the concoction of the concrete, Thanks to all these advantages, the entrance of nano silica Cuore concrete into the market modified the concept of what is possible and what is not in the concrete field.

Since 2004, the greatest copper underground mine of the world, has been using nano silica concrete and the use of the micro silica in this deposit has been prohibited.

Properties of concrete with Cuore concrete nanosilica

• In high compressive strengths concretes (H-70), Cuore concrete is 88% more efficient than micro silica, added to concrete and super plasticizers. ( For an average 9,43 Kg. of Cuore concrete Nanosilica, 73Kg. of all the others additives are used).

• The production cost of is drastically lower than using the traditional production method or formulas.

• It has an air inclusion of 0% to 1%

• The cone test shows that It preserves the cone shape for more than one hour. (with a relation of H2O/Cement=0.5, adding 0.5% of Nano silica of the metric volume of the cement used, it conserved a its circle shape of 60 cm for two hours, with a lost of only 5%). The nano silica has a plasticity that has been compared to the policarboxilate technology. Therefore the use of super plasticizing additives is unnecessary.

• High workability with reduced water/concrete levels, for example: 0,2.

• Easy homogenization. The reduction of mixing times allows concrete plants to increase their production

• Depending on the cement and the formulations used for concrete (tests from value H-30 to H-70), shows that the material provides compressive strengths between 15 MPa and 75 MPa at 1 day; 40 MPa and 90 MPa at 28 days and 48 MPa and 120 MPa at 120 days.

• Nano silica fully complies with ISO 14001 regulations regarding the environment and health. It preserves operators of the danger of being contaminated with silicosis and does not contaminate the environment.

It successfully passed all the tests and since the beginning of this year it is being commercialized in different parts of the world.

Immediate benefits for the user

1) Cessation of contamination caused by micro silica solid particles.

2) Lower cost per building site.

3) Concrete with high initial and final compressive and tensile strengths.

4) Concrete with good workability.

5) Cessation of super plasticizing utilization.

6) Cessation of silicosis risk.

7) High impermeability.

8 ) Reduction of cement using Cuore concrete Nanosilice

9) Cuore concrete nano sílica on itself produces nano cement.

10) During the moisturizing reaction of the cement, the silica produces CSH particles, the “glue” of the concrete ensuring the cohesion of all the particles.

11) Cuore concrete has a specific surface near to 1,000m2/gr (micro silica has only 20m2/gr) and a particle size of 5nm to 250 nm.

As a consequence of its size, Cuore concrete produces nano cristals of CSH, filling up all the micro pores and micro spaces which where left empty in traditional concrete production.
Former described function reinforces the concrete structure on levels, thousand times smaller then in the case of traditional concrete production. This allows the reduction of the cement used and gives the compression needed to reduce over 90 % of the additives used in the production of H-70 concrete.

Cuore concrete allows to save in between 35% and 50% of the used cement.We do stress that we recommend to change the formula of the concrete in order to take advantage of the characteristics of the Cuore concrete Nano silica particle.

Less material is needed to obtain better results, using Cuore concrete.

The results are the proof.

1) Resistance to compression from 40 to 90MPa in 1 day.

2) Resistance to compression from 70 a 100 MPa (or more) in 28 days.

3) Versatile: produces high resistance even with low addition (1 to 1,5 % of the cements weight) and gives self compacting characteristics with higher proportions (2,5 %).

4) Meets the norms of environmental protection (ISO14001).

5) 70% less use of additives as traditional silica, super plasticizers or traditional fibres.

6) Equal or minor raw material cost as in traditional ??production with super plasticizers, and or fibres.

This useful information is submitted to us by : Pascal Maes

Filler materials are gaining widespread popularity and becoming very important because they help in increasing some of the mix properties and also lower the usage of binder which is usually more expensive
Here is the table showing some common filler materials along with binders

Material	Binder	Filler	Importance of filler
Concrete	cement	gravel, stone , sand	cheaper
Drywall	gypsum	cardboard	tenacity, volume, main part
Particle board	Synthetic Resin, glue	sawdust	tenacity, volume, main part
Plastic explosive	Plasticizer, oil	explosive	explosiveness
Tyre rubber	rubber	Soot	Volume, better mechanic properties
Resin epoxy	epoxy	Microspheres	Improve viscosity of resin

The ACI Code gives approximate formulas for finding shear and bending moments in continuous beams and one way slabs. A summary list of these formulas follows. They are equally applicable to USCS and SI units. Refer to the ACI Code for specific applications of these formulas.

For Positive Moment

1 ) End spans

If discontinues end is unrestrained =  wl²_n /11

If discontinues end is integral with the support=  wl²_n /14

2) Interior spans =  wl²_n/16

For Negative Moment

1) Negative moment at exterior face of first interior support

Two spans = wl²_n /9

More spans = wl²_n /10

2) Negative moment at other faces of interior supports= wl²_n / 11

3) Negative moment at face of all supports for slabs with spans not exceeding 10ft (3m) and (b) beams and girders where the ratio of sum of column stiffness to beam stiffness exceeds 8 at each end of the span₌ wl²_n / 12

4)Negative moment at interior faces of exterior supports, for members built integrally with their supports

Where the support is a spandrel beam or grider =wl²_n /24

Where the support is a column =wl²_n /16

Shear Forces

Shear in end members at first interior support = 1.15 wl_n /2

Shear at all other supports =  wl_n /2

End Reactions

Reactions to a supporting beam, column, or wall are obtained as the sum of shear forces acting on both sides of the support.