1

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

2

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

3

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

4

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

5

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

6

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

7

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

8

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)

9

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

10

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)

11

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)

12

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)

13

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