Page 10 - Open-Access-Nov-2020

TECHNICAL PAPER

ENHANCING SERVICE LIFE OF

PRESTRESSED CONCRETE

STRUCTURES BY USING

FLY ASH AND CORROSION

INHIBITORS DYANA JOSELINE*

RADHAKRISHNA G. PILLAI

Abstract Cl th : Critical chloride threshold
PS : Prestressing
Seven-wire strands in pretensioned concrete (PTC) structures RC : Reinforced concrete
can undergo chloride-induced localized corrosion. The corrosion CIA : Corrosion inhibiting admixture
products occupy the space between the wires of the strands and hr : High resistivity
do not exert expansive stresses onto the surrounding concrete. lr : Low resistivity
Hence, propagation of such corrosion cannot be identified/
detected on time using visual observation of concrete surfaces %bwob : % by weight of binder
and can lead to catastrophic failure. This scenario necessitates CE : Counter electrode
technologies to significantly enhance the chloride-resistance and WE : Working electrode
corrosion-resistance of PTC systems. This paper quantifies the RE : Reference electrode
role of pulverised fuel ash (PFA; fly ash) and corrosion inhibiting EIS : Electrochemical impedance spectroscopy
admixtures (CIAs) in enhancing the probabilistic service life. S-C : Steel-cementitious
For this, lollipop specimens with embedded prestressing steel TMT : Thermo-mechanically treated
(five in each category) were prepared and subjected to wet-dry QST : Quenched and self-tempered
exposure using simulated concrete pore solution containing R p : Polarization resistance
3.5% NaCl, and the chloride threshold (Cl th ) was determined. : Corrosion rate during passive-to-active transition
i corr, P-A
Also, the synergistic effects of chloride diffusion coefficient : Probability of the occurrence of depassivation
P dep
(D Cl ) and Cl th on the corrosion-free service life of PTC systems x : Travel length of chlorides (say, cover depth, d)
are demonstrated. The paper also demonstrates the need
t SL : Design service life
for specifying both strength and durability requirements (say,
P o : Target failure probability
“Mx-Dy” concrete). Such an approach can aid engineers : Initial chloride concentration
and designers in making informed choices of materials to Cl i
achieve protection of PTC systems against chloride-induced Cl s : Surface chloride concentration
corrosion and to achieve service life of 100+ years with minimal erfc() : Mathematical error function
maintenance/repair cost. %bwoc : % by weight of concrete
: Compressive strength of concrete
f c
Keywords: Bridge, Chloride threshold, Corrosion, Corrosion Mx-Dy : A notation to specify concrete
inhibitors, Fly ash, Prestressed concrete, Service life.
1. INTRODUCTION
SYMBOLS AND NOTATIONS
Significant proportion of the world’s bridge stock comprises of
PTC : Pretensioned concrete
pre-tensioned concrete (PTC) members, and these important
SLD : Service-life based design
and expensive bridges are expected to be serviceable for a
D Cl : Chloride diffusion coefficient at 28 days ‘deemed-to-satisfy’ service life of more than 100 years. However,
SCMs : Supplementary cementitious materials some of them have started showing signs of premature
PFA : Pulverized fuel ash corrosion-induced distress. Also, because most of the PTC

54 THE INDIAN CONCRETE JOURNAL | NOVEMBER 2020
*Corresponding author : Dyana Joseline, Email: dyanajoseline@gmail.com