FIRST SEMESTER PhD RESEARCH PROPOSAL

PRESENTATION

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TOPIC:

CORROSION RESISTANCE AND ELECTROCHEMICAL BEHAVIOUR OF

REINFORCED CONCRETE WITH NANO-SILICA

BY

YUSUF, TALIAT OLA

FACULTY OF CIVIL ENGINEERING

UNIVERSITI TEKNOLOGI MALAYSIA

SUPERVISOR

PROFESSOR DR. MOHAMMAD BIN ISMAIL

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1.0 PROBLEM STATEMENT

1.1 Introduction• Corrosion of reinforcement bars is major cause of

deterioration in concrete (Lizarazo-Marriaga and Claisse 2009), (Topçu, Boğa and et al. 2009) and (Zheng and Zhou 2008)

• It has attracted attention with a view to ameliorating the problem.

• Deterioration of Jetty 15years after construction (Moradi-Marani, Shekarchi et al. 2010)

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1.2 The ultimate consequences of corrosion

fractured concrete arising from cracking,• delaminating and spalling of the concrete cover,• loss of bond between the reinforcement and concrete,• reduction in strength and ductility

All these lead to impaired safety and serviceability requirement (Koleva, Copuroglu et al. 2008).

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The propensity to corrode is a major drawback to durability performance of reinforced concrete structures. (Lizarazo-Marriaga and Claisse 2009).

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1.3 Extending Time to Corrosion:

The main approaches are– Providing tighter quality control on materials and

construction practices– Design modifications, such as increased concrete

cover and increase in area of reinforcement steel provision

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• Use of epoxy , fibre-reinforced polymers (FRP)

and galvanized coatings of reinforcement steel• Cathodic protection systems• the use of corrosion inhibitors as admixture in concrete to

prevent or delay corrosion occurrence.

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• Materials that improve quality and durability of concrete could also provide resistance to corrosion of reinforcement. (Lizarazo-Marriaga and Claisse 2009), (Topçu, Boga et al. 2009), (Morris, Vico et al. 2004) (Angst, Elsener et al. 2009)

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1.3.1 Appropriateness of Silica Admixture:• Addition of micro silica to cement has improved the

strength and durability of concrete through filling of the pores spaces to reduce porosity and pozzolanic reactions that contribute to calcium silicate hydrates (C-S-H) formation

• Nano silica is reported to have improved porosity and permeability of concrete (Belkowitz and Armentrout 2010).

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1.3.2 Need To Establish Suitability of Nano Silica:• if nano silica can improve the strength and durability

properties of concrete, it will also be a good corrosion resisting material.

• It would therefore be appropriate to establish the significance of nano silica admixture towards contribution to corrosion resistance behavior of reinforced concrete.

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1.4 Research Questions:• Is addition of nano silica to concrete significant in the resistance

of reinforcement corrosion?• What is the effect of nano silica on concrete pores, capillary

actions, ionic diffusion and pH of concrete?• What are the impacts of nano silica on chloride concentration,

resistivity of concrete and corrosion rate?• What is the level of nano silica addition tolerable to provide

corrosion resistance without impairing on strength requirements of the concrete?

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2.0 Aim and Objectives• The research seeks to find ways of improving the

performance of reinforced concrete with respect to corrosion resistance through the use of nano silica as admixture.

• The potentials of nano silica in the mitigation of occurrence of corrosion will be assessed through comprehensive study of its effects on agents of concrete deterioration and resulting corrosion.

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2.1 The specific objectives of the research • To assess the ability of reinforced concrete produced

with nano silica to improve concrete quality through evaluation of effects on porosity, capillary action, ionic diffusion and pH level within the concrete.

• To investigate the impact nano silica will exert on chloride ion diffusion, resistivity of concrete and corrosion rate and to draw empirical conclusions from experimental results

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• To determine the level of nano silica admixture that will satisfy strength requirement, provide good resistivity as well as corrosion resistance from empirical considerations.

• To recommend appropriate usage of nano silica in reinforced concrete construction

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2.2 Scope of the workCorrosion of concrete reinforcement could result from influence of carbonation of the concrete or chloride ion ingress into the concrete resulting in de-passivation of the reinforcement bars and eventual initiation of corrosion.

• The research will focus on investigation of influence of Nano-silica on concrete deteriorating agents (porosity, capillary action, ionic diffusion, and PH level), resistivity of the concrete, corrosion detection and corrosion rates measurement using half cell potential and other electrochemical measurements.

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3.0 Rational for carrying out the study• Extension of operational life of structures is of

enormous concern to structural engineers (Tamimi, Abdalla et al. 2008).

• Reinforced concrete if properly constructed would be a durable material that provide a prolong service life (Song and Saraswathy 2007).

• The characteristics of reinforced concrete is the reason for it wide acceptability.

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• The material is faced with durability problems (Topçu et al 2009), (Tamimi et al 2008).

• Corrosion of embedded steel rebar is a major problem. • The critical structures affected are those exposed to– marine environments. – where de-icing salts are used.

• The concrete cover is expected to give the protection (Ismail, Hamzah et al. 2010).

• Understanding of the microstructure of the concrete is paramount in an attempt to modify it properties for

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effective corrosion resistance. • The use pozzolanic materials to blend Portland

cement such as Fly ash, GGBF and silica fume or micro silica have helped to improve durability of concrete .

• Nano modifications of concrete is also possible through the use nano materials .

• Cause of Concrete deterioration leading to corrosion is by ingress of harmful substances due to micro structure and ambient conditions of concrete.

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• Corrosion as a major cause of concrete deterioration (Melchers and Li 2009), (Angst, Elsener et al. 2009) and (Morris, Vico et al. 2004) .

• The economic loss due to corrosion defects (Yu, Shi et al. 2010).

• The implication of corrosion occurrence in terms of economic loss is huge.

• A full scale knowledge is required to address the subject of corrosion .

• Major cause of concrete reinforcement corrosion is connected with the quality of the concrete.

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• Two major ways by which concrete can initiate corrosion processes are:– carbonation – ingress of chloride ions (Ahmad 2003).

• Corrosion of reinforcement can result from carbon dioxide diffusion.

• The ingress of chloride ion into the permeable concrete structure induces corrosion.

• Corrosion from chloride ion ingress is the most critical.

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• Methods to extend the time to corrosion damage– tighter quality control on materials usage and

construction practices– design modifications to increase concrete cover– over reinforcement provision– galvanized coating of reinforcement steel – active and passive cathodic protection systems– use of fibre-reinforced polymers (FRP)– Use of corrosion inhibitors

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• Limitations of– barrier coatings and galvanization– Inhibitors

• Use of Silica to improve the quality of concrete– Silica fume or Micro silica– Nano Silica

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• In conclusion the use of nano silica in concrete formulation will further be justifiable if its use for strength and durability improvement as well as corrosion resistance of the concrete is significantly ensured.

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Brief Literature Review

Author/Year of Publication

Title/Journal Highlight/finding

(Topçu, Boga et al. 2009)

Modelling corrosion currents of reinforced concrete using ANN/ Automation in Construction

Reinforced concrete is a durable and cost effective material.Durability is influenced by environmental conditions and exposure to factors causing carbonation, corrosion, alkali-silica reaction and freezing/thawing.Corrosion of the reinforcing steel resulting from chloride ingress is a major issue in durability of reinforced concrete.This can be prevented through the use of high quality concrete and concrete cover at design stage.They concluded that the use of composite cement with fly ash as against corrosion of reinforcing steel.

(Melchers and Li 2009)

Reinforcement corrosion initiation and activation time in concrete structures exposed to severe marine environment/ Construction and Building Materials

Aggressive nature of chloride is responsible for corrosion of steel reinforcement in marine environment. They found out that data overviewed from reported cases of corrosion investigations suggest that concrete made from blast furnace cements have better corrosion durability properties

(Bertolini, Vennnesland et. al 2008)

Chloride threshold for rebar corrosion in concrete with addition of silica fume

Laboratory tests were conducted on concrete specimen made with ordinary Portland cement and 10% of silica fume.A lower chloride threshold was observed in the bars which were embedded in concrete with silica fume compared to those embedded in concrete with ordinary Portland cement .

Author/Year of Publication Title/Journal Highlight/finding

(Angst, Elsener et al. 2011) Chloride induced corrosion: Electrochemical Monitoring of initiation stage and chloride threshold values / Corrosion Science

Chloride threshold values are affected by properties of the steel/concrete interface, pore solution chemistry and the potential among others.Above factors are in turn affected by concrete characteristics such as the water/ binder ratio or binder type. Apart from critical chloride content, concrete structures are also affected by the thickness and quality of the concrete coverThe denser the concrete, the longer it will take to reach the chloride threshold .Corrosion rate is also reduced by the use of pozzolanic materials such as fly ash,

(Tamimi, Abdalla et al.

2008)Prediction of Long term chloride diffusion of concrete in harsh environment/

Chloride diffusion is one f the main factors that affect concrete durability.Diffusion of chloride is influenced by many factors including the composition of the concrete and its porosity.High performance concrete showed less diffusivity as compared to normal concrete of the same type.The improved concrete durability in the high performance concrete could be due to the improved homogeneity of the interface between aggregate and cement paste.

(Angst, Elsener et al. 2009) Critical chloride content in reinforced concrete –A review/Cement and Concrete Research

They presented a review summarising the concept of critical chloride content discussing the influencing factors and assessment of available techniques.Parameters affecting the value of critical chloride value are•steel-concrete interface•concentration of hydroxide ions in the pore solution •Electrochemical potential of the steel•Binder type•Surface condition of the steel type

Author/Year of Publication Title/Journal Highlight/finding

•Oxygen availability at the steel surface•Water/ binder ratio•Electrical resistivity of the concrete•Degree of hydration•Chemical composition of the steel•Chloride source•Temperature•Presence of other substances like inhibitors

(Shih, Chang et al. 2006) Effect of nanosilica on characterisation of portland cement composite.

They opined that filling effect and pozzolanic reaction make siliceous materials a major ingredient of high performance cement based composites.It enhances strength and abrasion resistance while reducing permeability and shrinkage.Siliceous materials of higher purity are and finer size are used to further improve Portland cement base composites.Addition of nanosilica in liquid form to cement was done to investigate the characteristics of corresponding cement composites.The optimal mix proportion of cement:water:nanosilica= 1:0.55:0.006 has the highest compressive strength of 65.62MPa at age 56 days which was 43.8% greater than that without nanosilica.Both the surface area and fractal dimension from BET experiment confirm a dense microstructure for the hardened cement composite with addition of nanosilica.NMR analyses showed that the microstructure of Portland/nanosilica blended cement become more stable and stronger bonding

Author/Year of Publication

Title/Journal Highlight/finding

(Roy, Moelders et al. 2006)

Role of an Amorphous silica in Portland cement concrete/ Journal of Materials in civil Engineering

They replaced Portland cement with 10% of Amorphous silica (AS) by weight. AS has a wide range grain size from tens μm to tens of nm.It was found that the concrete behaved partly as a traditional pozzolan, partly crystalline to quartz and the rest underwent structural reorganization without morphological changes.The presence of AS changed the concrete micro-structure, aggregate- paste interface, and pore size distribution.

(Belkowitz and Armentrout 2010)

An investigation of nanosilica in cement hydration process / Concrete Sustainability Conference

They validated proposition that as the silica decreases in size and increases in size distribution, a number of properties begin to improve.As silica diameter increases , the rate of early pozzolanic reaction decreases. The nano silica was found to be more effective than the micron silica due to exposed surface area .It was highlighted that the use of nano silica with a wide distribution can generate a micro structure that can support a greater compressive load.

(Senff, Hotza et al. 2010)

Mortars with nano-SiO2 and Micron-SiO2 investigated by experimental design.

They reported the effect of nano Silica nS and Silica fume SF on rheology, spread on flow table, compressive strength, water absorption, apparent porosity, unrestrained shrinkage and weight loss of mortar up to28days. Mortar with 7% nS showed faster structures formation in the rheological test.The results of compressive strength, water absorption and apparent porosity was significant when the composition ranges were 0-7%, nS 0-20% SF and 0.35- 0.59W/B

Lizarazo-Marriaga and Claisse 2009), (Topçu, Boga et al. 2009), (Morris, Vico et al. 2004) (Angst, Elsener et al. 2009)

Materials that improve quality and durability of concrete could provide resistance to corrosion of reinforcement since these have been linked to influence the occurrence of corrosion in reinforced concrete to a large extent

(Shih, Chang et al. 2006) , (YazIcI 2007) and (Azari, Mangat et al. 1993).

Addition of micro silica to cement has improved the strength and durability of concrete through filling of the pores spaces to reduce porosity and pozzolanic reactions that contribute to calcium silicate hydrates (C-S-H) formation

(Bitaraf and Mohammadi 2008), (Manera, Vennesland et al. 2008), (Melchers and Li 2009), (Angst, Elsener et al. 2011), (Yu, Shi et al. 2010) and (Yildirim, Ilica et al. 2011).

Corrosion of embedded steel rebar is a major problem facing the use of reinforced concrete material. The critical structures affected are those exposed to marine environments and wherede-icing salts are used

(Bola and Newtson 2005),

Corrosion of reinforcement in concrete can be mitigated through the use of corrosion inhibitors

(Tamimi, Abdalla et al. 2008).

The need to extend operational life of structures is of enormous concern to structural engineers

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4.0 Methodology• The experiments will be set up to determine – strength, – chloride content,– chloride ion diffusivity, – PH levels, – porosity, – concrete resistivity,– corrosion rates of reinforced concrete specimens

with varied nano silica contents, water/binder ratio,

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sodium chloride content and environmental conditions.

4.1 Materials• Ordinary Portland cement• processed nano silica, • natural river sand,• crushed stone aggregates• sodium chloride• super plasticizers • high yield reinforcement bars

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4.1 Materials• Ordinary Portland cement• processed nano silica, • natural river sand,• crushed stone aggregates• sodium chloride• super plasticizers • high yield reinforcement bars

reinforcement bars will be require to make reinforced concrete test specimens.

4.2 Testing• The ordinary Portland cement binder blended with

0% to 0.5% nano silica (Shih, Y. J. et al (2006)) will be used to cast 100×200mm cylinders in accordance with ASTM C39.

• The cylindrical specimens will be de-molded after 24 hour and cured for 28days and 180 days after which they will be cut into 50mm slices. They will be cut into 100mm dia. × 50mm. The slices will be epoxy coated

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4.2 Testing• The ordinary Portland cement binder blended with

0% to 0.5% nano silica (Shih, Y. J. et al (2006)) will be used to cast 100×200mm cylinders in accordance with ASTM C39.

• The cylindrical specimens will be de-molded after 24 hour and cured for 28days and 180 days after which they will be cut into 50mm slices. They will be cut into 100mm dia. × 50mm. The slices will be epoxy coated

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Concrete prisms will be produced, conditioned and tested for rapid chloride penetration in accordance with the ASTM C1202 method.

• The electrical resistivity of the specimens will also be measured using the two-electrode method. These tests will be carried out on saturated surface dried specimens.

• Samples for mercury intrusion porosimetry test will be taken from the cured concrete specimens. This test will be used to measured porosity and pore structure of the paste.

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• Electrochemical measurements on the specimens will be carried out to assess the corrosion condition of embedded steel reinforcement.

• Half-cell potential as describe by ASTM C876 will be use to detect the potential of corrosion in the specimens.

• Polarization resistance measurements will also be performed using potentiostat and values use to estimate the estimate the corrosion density.

• The electrical conductance of concrete will also be measured using a conductivity meter.

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• 50mm cube specimens will also be prepared from same mix proportions as above in accordance with ASTM C109 to test the concrete cube strength at age of 7, 28 and 90 days.

• SEM, XRD, NMR and AFM tests will be used to analyze the micro structure of mortar specimen to see the effect of nano silica on the micro structure which might explain the electrochemical behaviors.

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6.0 Expected Outcome of Studies and Contributions• It is expected that replacement of Portland cement

with nano silica will enhance corrosion resistance of reinforcement in concrete through reduction in permeability, porosity, oxygen and carbon dioxide diffusion and chloride ion penetration.

• The corrosion resistance will be comparable to conventional corrosion inhibitor and if so the use of nano silica will be better because nano silica use will also improve strength properties as well as remove problems associated with the use of inhibitors

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• The results of the study will elucidate ways of blending cement with nano silica to achieve better physical and durability requirements of reinforced concrete. The result will contribute to evolving a methodology for an application of nano silica to practical use on construction.

• A reduction in the use of Portland cement resulting from its replacement with some quantities of nano silica will reduce carbon dioxide emission to the atmosphere thereby making the environment better.

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