Corrosion is one of the main concerns in the durability of materials and structures. Much effort has been made to develop a corrosion inhibition process to prolong the life of existing structures and minimize corrosion damages in new structures.
Fusion bonded epoxy coating, also known as fusion -bond epoxy powder coating and commonly referred to as FBE coating, is an epoxy-based powder coating that is widely used to protect concrete reinforcing bars. FBE coated bars are covered under BIS 13620/93
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1. INTRODUCTION: -
Corrosion is one of the main concerns in the durability of materials and structures.
Much effort has been made to develop a corrosion inhibition process to prolong the
life of existing structures and minimize corrosion damages in new structures. Carbon
steel is one of the most widely used engineering materials despite its relatively
limited corrosion resistance. Iron in the presence of oxygen and water is
thermodynamically unstable, causing its oxide layers to break down. Corrosion
undermines the physical integrity of structures, endangers people and the
environment, and is very costly. Because carbon steel represents the largest single
class of alloys used, corrosion is a huge concern. The billions of dollars committed to
providing protective systems for iron and steel have provided new ways of combating
corrosion. Migrating corrosion inhibitors (MCIs) are one means of protection for
reinforced concrete structures. Previous studies have established the benefits of
using migrating corrosion inhibitors, the importance of good concrete, and the
significance of the ingredients used to make the concrete. Reinforcing steel
embedded in concrete shows a high amount of resistance to corrosion. The cement
paste in the concrete provides an alkaline environment that protects the steel from
corrosion by forming a protective ferric oxide film. The corrosion rate of steel in this
state is negligible. Factors influencing the ability of the rebar to remain passivated are
the water to cement ratio, permeability and electrical resistance of concrete. These
factors determine whether corrosive species like carbonation and chloride ions can
penetrate through the concrete pores to the rebar oxide layer. In highly corrosive
environments (coastal beaches and areas where deicing salts are common), the
passive layer will deteriorate, leaving the rebar vulnerable to chloride attack, thereby
requiring additional help to prevent corrosion damage
Generally, unless coated steel will readily corrode. However, when steel is placed into
concrete it develops a passive oxide film, due to the high pH of the concrete. This
passive film prevents further corrosion of the steel and there are many examples
where common reinforcing steel in concrete has remained uncorroded for over 100
years. If steel corrodes in concrete it may cause cracking or spalling of the concrete.
Corrosion of reinforcing steel may occur if the pH of the concrete is decreased, either
from chemical attack or from reaction of the concrete with CO2 in the atmosphere. It
may also occur if enough chloride ions reach the bar. These are typically introduced
by into the concrete, from either deicing salts or sea water.
There are many ways to reduce the risk of corrosion- related distress in concrete. The
first layer of defense is the concrete, which should be dense, and cracks should be
minimized. Appropriate concrete cover should also be used.
Reinforcing bars with improved corrosion resistance over traditional carbon steel
reinforcing bars are readily available. When selecting a particular type of corrosion
resistant bar, issues such as level of corrosion resistance, cost, and availability should
be considered. For publicly funded projects, FHWA and other agencies place
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restrictions on proprietary material and “Buy U.S.A” requirements may be in effect
and should be carefully evaluated during the evaluation and purchasing process.
Types of Rebar with Improved Corrosion Resistance:
• Stainless Steel Bars, IS 16651:2017 (Very expensive)
• Galvanized Steel Bars, IS 12594:1988 (Expensive and causing pollution)
• Epoxy-Coated Reinforced Bars, IS 13620:1993 (Most commonly used process)
2. Epoxy-Coated Reinforced Bars
Fusion bonded epoxy coating, also known as fusion -bond epoxy powder coating and
commonly referred to as FBE coating, is an epoxy-based powder coating that is
widely used to protect concrete reinforcing bars (re bar). FBE coatings are thermoset
polymer coatings. The name fusion-bond epoxy is due to resin cross-linking and the
application method, which is different from a conventional paint. The resin and
hardener components in the dry powder FBE stock remain un-reacted at normal
storage conditions.
At typical coating application temperatures, usually in the range of 230 to 240 °C, the
contents of the powder melt and transform to a liquid form. The liquid FBE film wets
and flows onto the steel surface on which it is applied, and soon becomes a solid
coating by chemical cross-linking, assisted by heat. This process is known as “fusion
bonding”.
The chemical cross-linking reaction taking place in this case is irreversible. Once the
curing takes place, the coating cannot be returned to its original form by any means.
Application of further heating will not “melt” the coating and thus it is known as a
thermoset coating.
FBE coated bars are covered under BIS 13620/93 and application will have to be
made to BIS for certification after project commissioning.
3. Fusion bonded epoxy coating application process
Regardless of the shape and type of steel surface to be coated, the FBE powder
coating application has seven essential stages:
State 1: The steel cleaning & surface preparation - Airless (Wheel Blast) Shot
Blasting Process.
Stage 2: Pre-Heating to recommended FBE powder application temperature.
(Induction heating).
Stage 3: Coating - Fusion Bonded Epoxy Coating.
Stage 4: Curing.
Stage 5: Water Quenching.
Stage 6: Unloading.
Stage 7: Inspection.
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FBE coated Rebar, a kind of construction material, is of high cost-effectiveness and
challenge. FB Rebars can be widespread used in many heavy-industry infrastructure
constructions such as port, highway, railway, and airport and so on. This process of
epoxy coating is environment friendly and accords with the general trend of
sustained economy growth of energy conservation and emission reduction.
4. FINANCIAL ASPECTS: -
A. Land & Building-
The plant will need about 20,000 square feet of covered area for plant
machinery installation and another 20,000 square feet area for storing raw
material for 15 days inventory. Estimated cost of land will be around 1.00
crore, which is considered in the project for Cut & bend plant
B. Machinery & Equipment’s: -
In order to produce around 3000 tons per month, following machines will be
needed:
C. Shot Blasting Machine
Line speed up to 10 Meters per Minute as per diameter of Rebars and surface
scale level. Line speed is considering fresh steel without rust.
D. Abrasive Separator, Rotary Screen Unit & Storage Hopper:
Separator reclaims abrasive from a mixture of spent abrasive, fines, dust and
other contaminants for reuse in the abrasive de -scaling process. The
separator is a 60” Compensating Flow Straight (CFS) Air-wash type. A rotary
screen housed within the separator and mounted on a common shaft with an
in -feed screw conveyor separates oversize contaminants from the media
mixture. The trash is directed by internal screw flights, to a trash discharge
gravity flow drain line.
E. Cartridge Type Pulse Jet Type Dust Collector
The Cartridge Pulse Jet Dust Collector is a continuous automatic type dust
collector of filtering dust-laden air through filter media. The dirty or
contaminated air enters the dust collector through the module inlet. A baffle
plate distributes the air uniformly throughout the housing and drops out
heavy particulate into the hopper. The dust-laden air the passes through
several cartridges which retain the dust particulate on the exterior surface
while allowing clean air to pass through the module outlet.
F. Loading System:
The loading system is mainly consisted of cross transfer system & layering
system.
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i. Layering System:
Seven numbers 2 meters long layering stand, for layering rebars. From
which batch of 18 rebars will be transferred to main process conveyor.
ii. Cross Transfer System of Bars:
It consists of six steel structure holders. From which transfer system will
place rebars on the process conveyor.
G. Roller Conveyor System:
Overall length of the roller table is about 75 m. There are 18 nos. grooves on
each roller. The entire roller conveyor system is designed to run at a variable
line speed from 4 – 11 meters per minute depending upon diameter and
surface scale level of bar.
All rollers in curing and water-cooling tower, and outlet conveyor are made of
special rubber material.
H. Curing Bay:
It’s an intermediate bay between powder booth & water-cooling tower. FB
powder get cured as bar travel through this bay, and its temperature is
dropped with half rollers being submerged in cooled water tank.
I. Water Quenching:
Water cooling tunnel is used for cooling work piece, which mainly consists of
water.
J. Unloading System:
The unloading device consists of pneumatic kick off system and unloading
rack.
K. Kick Off System:
When coated bars reaches end point of conveyors, sensors placed at the end
of conveyor system activate kick off arms, there are 6 nos. of special rubber
coated kick off arms which transfers bars onto unloading rack which is also
provided with special coating to avoid any kind of damaged to coated rebars.
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L. Project requirement:
Capital requirement
Capital requirement will be approximately as under
Capital cost
Rs.
Lakhs
Land * -
Shed 200.00
Equipment 550.00
Office building & others * -
Boundary wall 1300 Feet, 8"X9'high @
1700/ft * -
Hard facing of land 5500m3, @350/cu Mtr * -
Total Capital 750.00
* These costs have been considered in the project for Cut & Bend rebars
center
Working Capital Requirement (P.M.)
Since this operation will be carried out on the material supplied by the
customer, inventory cost is not being considered for working capital
requirements. Operating consumables @ Rs 700/ PMT are considered and
valued at Rs. 21 Lakhs approximately
Other Contingent Expenses like telephone. Conveyance & travelling,
Stationary, Power and water charges, Stationary postage and other misc.
expenses etc. to be considered as lumpsum approx. Rs 15 lakhs/mon. Thus
total working capital requirement for this project is around Rs. 36 lakhs
Land and Building
Total requirement of Land under covered area is approx. 2000 square meters
with EOT cranes of 3 & 5 tons capacity to handle RM & FG bundles. Open area
for storing will be one Acre, which will be common with proposed C&B plant.
Boundary wall and hard-facing of land is already considered in project for C&B
plant
Office building and security will be common between both C&B and FBE
plants, and therefore not considered here
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Treatment of wastage and effluents
The operation will generate steel particle and rust in micro form and will be
collected by dust collection system. This will be disposed off to the
prospective users in foundry or indication furnaces.
Cooling water is recirculated, and no wastage is envisaged. Used machine oil
and grease will be collected and disposed off to agencies engaged in recycling
these materials.
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Cost impact to the project
Considering a house construction project of Site Size: 30x50 feet site house construction
cost (Ground + 1, 3 BHK) up to 2125 Sq. ft built up area With Concrete Blocks, Total
House cost (Rs. 74.37 lakhs) and material cost is as per table below:
Total cost of house ownership 7,437,500
Materials Required Quantity Unit
Material
cost (Rs.)
Cost share
in Mat.
Cost
Overall
Cost
share
TMT Steel 7.6 Tonnes 357,200 29% 5%
Cement 930 Bags 337,590 27% 5%
Plastering M Sand 147 Tonnes 205,800 17% 3%
Concrete M Sand 65 Tonnes 61,750 5% 1%
40mm Jelly 513 Cft 12,825 1% 0%
20mm Jelly 2996 Cft 74,900 6% 1%
6" Concrete Block 3120 Blocks 156,000 13% 2%
4" Concrete Block 1040 Blocks 37,440 3% 1%
Total material cost
1,243,505
Additional FBE coating
@ Rs. 11,000/PMT
7.98 Tonnes 87,780 7.1% 1.2%
Source: https://www.materialtree.com/30-50-house-construction-cost/
From above calculations it may be seen that overall impact on a project of Rs 74 lakhs is
only Rs 87,780/-, which is barely 1.2% of total project cost. But this enhances life of the
structure by more than three times resulting considerable savings in repair and
replacement cost even at current prices. Ideally life of a RCC structure is considered to
be around 20-30 years and by using FBE if the life is even doubled, savings can be
substantial for the customer
Life cycle cost analysis:
Assuming the life of a RCC structure is about 25 years, amount invested today will
become due for reinvestment as the building will have to be demolished and re-
constructed. Assuming annual inflation rate of 4%, present value at inflated rates is
indicated in the table below. Similarly, additional amount spent for FBE coating, if not
spent and invested with annualized returns of 12% will also fetch compounded value
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after 30 years as shown in the table below. Form these tables, it may be seen that using
FBE coated bars is much cost effective compared to using plain bars.
PV % GWT
Period
(Yrs)
FV
1,243,505 4% 25 3,314,981
87,780 12% 25 1,492,266
Saving 1,822,715
194,998* 12% 25 3,314,981
*Present value of replacement
cost of Rs 33.15 lakhs
107,218
is the saving in
life time cost
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Project time line
Sigining of
Consultancy
agreement
(W0)
Preparation
of Project
feasibility
report
(W1)
Application
for land
(W2)
Sanctioning
of land &
initial
payment
(W3)
Bhoomi Pooja &
Civil work
commencement
(W4)
Shed
erection
(W24)
Application
for financial
closure
(W2)
Finalization
of civil
contractor
(W3)
Application for
electric
connection
(W4)
Electric
connection
(W5)
Negotiation
with
equipment
supplier &
Ordering
(W2)
Shortlisting
for sales team
(W2)
Recruitment
(W3)
Training
(W4-20)
Will be used for
C&B
Order
booking
(W27)
Servicing
of orders
(W28)
A
c
t
i
v
i
t
y
Civil work in progress
(W5-10)
Electric wiring
(W20-26)
Receipt of
equipments (W26)
Equipment erection &
Commissioning
(W27-28)
Sales team candidate
search
(W1)
Contacting prospective customers and presentations
(W20-27)
Production of machinary at vendor's place and dispatch
(6 Months)
Total Project duration is 7 months
Details of financial working
Table 1
Capital requirement and working capital needed
Capital cost Rs. Lakhs
Land -
Shed 200.00
Equipments 550.00
Office building & others -
Boundary wall 1300 Feet, 8"X9'high @ 1700/ft -
Hardfacing of land 5500m3
, @350/cu Mtr -
Total Capital 750.00
Int. on Capital 90.00
Working capital Rs. Lakhs
Inventory
Operating expenses (R&M) 30.00
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Table 2
Projected Working results of FBE plant
Break
Even
1308
Income
FromSale of FG@2500/PMT 32.71 50.00 75.00 a
Total Income 32.71 50.00 75.00
Expenses
Operatingexpenses
Labor @800/PMT 10.47 16.00 24.00 b
Operatingexpenses (R&M) @700/MT 9.16 14.00 21.00
Total Operatingexpenses 19.63 30.00 45.00
c
Fixedcost d
Interest@12% oncapital 7.80 7.80 7.80 e
Depreciation@10% onMachinary 4.58 4.58 4.58 f
Staff salaries (includingsecurity) 1.00 1.00 1.00
Total Fixedcost 13.38 13.38 13.38 (a-b-e)
(a-b-f)
EBIDTA 12.08 19.00 29.00
PBT - 6.62 16.62
Epoxy coatingproject
Production/ Mon
2000 3000