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Effect of Fly Ash BasedPortland Pozzolana Cement
on Chloride Induced Corrosion f R i f t I C tof Reinforcement In Concrete
Bhaskar Sangoju,Ravindra Gettu
and B H Bharatkumarand B.H. Bharatkumar
Indian Institute of Technology MadrasCSIR Structural Engineering Research Centre
Chennai
Sustainability+ve Impact of Concrete
• Concrete has the lowest• Concrete has the lowest embodied energy among all construction materials
• Raw materials are available for significant volumes of concrete to be
d dproduced
• Both the above indicate that any improvement will have significant impact
Ravindra Gettu
Scrivener, 2013, ICI-ICW
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Sustainability-ve Impact of Concrete
• Cement production in the pworld is about 3 billion tonnes
• Cement manufacturing accounts for about 5% of CO2 emissions in the worldworld
• Concrete usage estimates vary from 10 to 30 billion tonnes; Reinforced concrete about 17 billion tonnes
Ravindra Gettu
Sustainability
+ve Impact of Concrete+ve Impact of Concrete
• Construction provides livelihood to a large percentage of the population
• Construction spending continues to increase at the rate of 3-4%
Ravindra Gettu
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Sustainability
-ve Impact of Concrete-ve Impact of Concrete
• Poor construction with concrete can lead to high repair and rehabilitation costs
• Cost cutting often results in bad quality
Ravindra Gettu
Sustainability
+ve Impact of Concrete
• Concrete is a long term investment that is within reach for most
• Can provide security to the user Ravindra Gettu
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Sustainability
-ve Impact of Concrete
• Cities are becoming concrete jungles
• Quality of concrete is not assured for the user Ravindra Gettu
Sustainability
S
Sustainability Success requires maximum positive economic, environmental and social impacts
Ravindra Gettu
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Sustainability
“Simple” Principles for Concrete Construction
• Use less raw materials and energy over the whole life
• Reduce the emissions and waste over the whole life
• Analyse cost effectiveness over the whole life
• Analyse the social impact over the whole lifey p
Ravindra Gettu
Sustainability
“Simple” Principles for Concrete Construction
• Use less clinker and water, and more waste material
• Increase the useful life of the project
• Increase overall cost-effectiveness
• Improve defect tolerance (i.e., lower sensitivity to defects)
Ravindra Gettu
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Is fly ash blended cement (PPC) better than ordinary portland cement (OPC) for p ( )limiting rebar corrosion in concrete due to chlorides?
YES
Methodology of the Study Conducted at SERC & IITM
Evaluation of mechanical and durability parameters of concretes
Accelerated corrosion tests using cracked specimens
Gravimetric weight loss measurements
Simulation of service life
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Materials and Parameters Studied
Cements: OPC and PPC
Polycarboxylic ether superplasticizer (PCE SP)y y p p ( )
Water to cement ratio (w/c): 0.57, 0.47, 0.37
Crack width: 0 mm (uncracked), 0.2 mm, 0.4 mm
Slump:
Concrete without SP: 25-50 mm
Concrete with PCE SP: 125-150 mm
Specimen Developed at CSIR-SERC U-shaped specimen: horizontal beam -100x100x600 mm
two integral vertical stubs -100x150x200 mm
Holes provided in the stub portion to insert two tie rods for inducingcracks in the beam portion
After 28 days of water curing and 30 days of air curing, tie rodsinserted in the beam and tightened to apply a pure bendingmoment in the beam portion (induced flexural cracks)
Rebar 12mm dia.
Tie rods with nuts
Vertical stubTie rods
300150 Vertical stub
Rebar 12mm dia
Side viewSectional elevation
300
100
200
100Horizontal beam Bottom clear cover 20mm
Rebar 12mm dia.
100
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Impressed Voltage Test Setup
Ti d300150
Power supply unitElectric wire
Electric wire
3.5% NaCl solution
300Plastic tub
Vertical stub
Tie rods Electric wire
Cathode plate
Vertical stub
Rebar 12mm dia.
100
Horizontal beam Bottom clear cover 20mm
Impressed Voltage Test (Accelerated Corrosion)• U-Shaped specimens were put in 3.5% NaCl solution for 24 hours
to ensure full saturation of the test specimen
• A potential of 10V is applied. The high impressed voltage wasused to accelerate the corrosion process and shorten the testperiod Current passed was recorded for every one hour usingperiod. Current passed was recorded for every one hour usingAuto Data-logger
• Specimens were exposed for the specified durations (22 days) toattain a weight loss of about 20% in the rebars of the uncrackedspecimens with w/c = 0.57 (Holm 1987; Liu and Weyers 1996)
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Photographs of the Test Setup
RCPT test setupRCPT test setup Sorptivity test setup Sorptivity test setup
Impressed voltage (accelerated corrosion) test Impressed voltage (accelerated corrosion) test
Mechanical and Durability Test Results (28 Days) OPC (Control) and PPC Concretes
w/c 0.57 0.47 0.37OPC ConcreteCube comp.strength (MPa) 33.2 44.7 53.7S lit t il t th (MP ) 2 4 3 8 4 0Split tensile strength (MPa) 2.4 3.8 4.0Flexural strength (MPa) 4.1 5.6 6.4RCPT (Coulombs) 2600 2100 1900Sorptivity (mm/min.1/2) 0.097 0.092 0.087
PPC ConcreteCube comp. strength (MPa) 30.7 41.4 51.2S ( )Split tensile strength (MPa) 2.7 3.7 4.6Flexural strength (MPa) 5.0 5.6 6.9RCPT (Coulombs) 861 720 520Sorptivity (mm/min.1/2) 0.060 0.049 0.043
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Mechanical and Durability Test Results (28 Days)OPC (Control) and PPC+SP Concretes
w/c 0.57 0.47 0.37OPC ConcreteCube comp.strength (MPa) 33.2 44.7 53.7S lit t il t th (MP ) 2 4 3 8 4 0Split tensile strength (MPa) 2.4 3.8 4.0Flexural strength (MPa) 4.1 5.6 6.4RCPT (Coulombs) 2600 2100 1900Sorptivity (mm/min.1/2) 0.097 0.092 0.087
PPC ConcreteCube comp. strength (MPa) 30.7 41.4 51.2Split tensile strength (MPa) 2.7 3.7 4.6Flexural strength (MPa) 5.0 5.6 6.9RCPT (Coulombs) 861 720 520Sorptivity (mm/min.1/2) 0.060 0.049 0.043
Corroded Specimens and RebarsOPC (Control) Concrete
Uncracked specimens (0.37 w/c)Uncracked specimens (0.37 w/c)
0 20 2 k d i (0 37 / )k d i (0 37 / )0.2mm pre0.2mm pre--cracked specimens (0.37 w/c)cracked specimens (0.37 w/c)
0.4mm pre0.4mm pre--cracked specimens (0.37 w/c)cracked specimens (0.37 w/c)
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Corroded Specimens and Rebars after CleaningPPC Concrete
Uncracked specimens (0.37 w/c, PPC)Uncracked specimens (0.37 w/c, PPC)
0.2mm pre0.2mm pre--cracked specimens (0.37 w/c; PPC)cracked specimens (0.37 w/c; PPC)pp p ( )p ( )
0.4mm pre0.4mm pre--cracked specimens (0.37 w/c; PPC)cracked specimens (0.37 w/c; PPC)
Gravimetric Weight Loss in Rebars(% reduction)
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Conclusions from the Durability Studies
The chloride ion penetrability (through the RCPT test) of PPCconcrete was nearly 3 times lower than that of the correspondingOPC concrete
Electrochemical measurements indicate a delay in the onset ofcorrosion in PPC concretes even under cracked conditionspossibly due to higher resistivity compared to that ofcorresponding OPC concretes.
Corrosion induced crack widths and weight loss of rebars in PPCconcretes were much lower than those of the corresponding OPCconcretes were much lower than those of the corresponding OPCconcretes. Also, for the given rebar weight loss, the corrosioninduced crack width was lower in the case of PPC concrete
The results show that the reduction in diameter (i.e. due to pitting)was more for OPC concretes compared to PPC concretes
Implications for Service Life Estimation
ti : estimated from diffusion coefficient Dc
spis ttt Service life is assumed as the sum of corrosion initiation and stable corrosion propagation periods
t = initiation period
tsp : depends on corrosion
Concrete Dc (m2/sec)
OPC 7.67×10-13
PPC 3.92×10-13
ti = initiation periodtsp = stable propagation period
current developed -Rodriguez et al. (1994) model; 10% loss in section can be taken as end of stable propagation period (Andrade et al. 1990)
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Implications for Service Life
In terms of service life controlled by chlorideinduced corrosion:
Changing the cement type from OPC toPPC and using a superplasticizerappropriately, for w/c = 0.6, couldincrease the service life by three times.
Changing the w/c from 0 6 to 0 35 and Changing the w/c from 0.6 to 0.35, andchanging the cement type from OPC toPPC and using a superplasticizerappropriately could increase the servicelife by seven times.
Thank you