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DURABLE STRUCTURESLNEC Lisbon 31 May - 1June 2012

PROGNOSIS OFINTERNAL EXPANSIVE REACTIONS

IN CONCRETE STRUCTURES

J. Custdio, A. Santos Silva, D. Soares, A. Bettencourt-Ribeiro


Contents

Introduction

IER Prognosis Methodology

Case Study

Conclusions

ICDS12 International Conference DURABLE STRUCTURES: from construction to rehabilitation LNEC Lisbon Portugal 31 May - 1 June 2012

LNEC

ICD

S12


Introduction Concrete chemical deterioration in building and civil infrastructures

Soft water attack Acid attack Sea water attack Sulfate attack Biochemical attack Reinforcement corrosion Internal expansive reactions (IER)

Alkali-silica reaction (ASR) Internal sulphatic reaction (ISR)


Alkali-silica reaction (ASR) Reaction between alkali hydroxides in concrete pore solution and certain siliceous

minerals present within some aggregates; producing a hydrophilic gel that expands in the presence of water causing disruption of concrete.

Distress signs Cracking Surface discolouration Surface deposits (gel exudation, efflorescence) Irreversible movements, displacements, deformations Pop-outs, delamination, disintegration

Requirements for initiation and progressionSufficiently alkaline

solution in the concrete pore

structure

Aggregate/aggregate combination

susceptible to attack by alkaline solution

Supply of water sufficient to maintain the reaction and enable the gel to

exert an expansive force


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Internal sulphatic reaction (ISR) Reaction between sulphate ions and anhydrous or hydrated calcium aluminates

present in the cement hardened paste, resulting in the formation of ettringite. The formation secondary or delayed ettringite has an expansive character that can cause the disruption of concrete.

Distress signs Cracking Surface deposits Irreversible movements, displacements and deformations Delamination and disintegration

Requirements for initiation and progressionHigh temperatures

during concrete early ages

Sufficient amount of Ca(OH)2 in the

concrete pore solution

Sufficient amount of water

Cement with a high alkali, SO3and C3A content


Internal expansive reactions (IER) Consequences

Reduction of material strength properties. Uneven or differential concrete swelling of the structure. Reduction in service life of affected concrete structures.

New structures Methodologies can be followed to avoid IER (e.g., LNEC E 461-2007).

Existing structures No effective way of stopping ASR and ISR, however, in some cases they can

be slowed down through rehabilitation works. Appraisal of an affected structure involves,

Condition survey Diagnosis Prognosis MitigationPrognosis


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In Portugal the problem is very realand totally justifies the

growingconcern about the development ofthese reactions in concrete structures.


Methodology Prognosis of IER

Laboratory testing of samples taken from affected structure Microscopical examination

Petrographic and SEM/EDS current condition of concrete and IER evolution on core samples before and after expansion tests.

Mechanical tests Compression test general condition of concrete. Stiffness damage test (SDT) quantify internal damage due to IER,

evolution of the reaction/expansion, expansion level reached to date.

Expansion tests Confirmation of deleterious expansion and potential for future expansion. ASR RILEM AAR-3 (38 C, 95 % R.H., 12 months). ISR LCPC Mthod d'essai 66 (20 C, Water, 12 months).


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Case study

Reinforced concrete bridge built in the late 70's and located in central part of Portugal.

Samples collected from: columns footing, columns, column caps, slab beams, transverse beams, slab and abutment walls.

Visual inspection revealed that the deterioration was mainly located in the massive sections and in areas that have direct contact with water or are subjected to repeated wetting and drying.


Expansion tests ASR

Potential reactivity varies considerably amongst the various areas of the structure.

Highest residual expansion rate and level attained by cores from slab and transverse beams.

Differentiation also occurred in the same structural element This is due to the type and

amount of reactive aggregates present in the concrete in those areas (confirmed by the petrographic examination).

Expansion limit of 0.04 % for new structures


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Expansion tests ISR

Potential reactivity varies considerably amongst the various areas of the structure.

Highest residual expansion rate and level attained by cores from abutment wall. This might be related to the

higher temperature achieved during the concrete cure due to the higher amount of concrete used in this type of structural elements.

Expansion limit of 0.04 % for new structures


Microscopical analysis ASR

ISR

Presence of expansive products resulting from IER.

Degree of development of the reaction: Crystalline products (left)

formed when the reaction is in an early stage of development;

Amorphous products (right) formed in later stages of the reaction and causing the deleterious expansion.


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Compression tests

Results Great variability on the condition of the concrete throughout the structure. fc,exp > fc,ref this is indicative of some degradation. Comparing fc,exp and Ec,exp with fc,est and Ecm,est for sound concrete, the difference is much larger

for the elastic modulus typical of IER damaged concrete. fc not very sensitive to IER (e.g., values of fc for right abutment lie inside estimated range, but

elastic modulus is far from the reference values for sound concrete, indicating deteriorated concrete.

fc,est

Ecm


Stiffness damage tests Test 5 cycles of loading/unloading up to 10 Mpa Performed after expansion tests

Parameters calculated Stiffness, K Energy dissipated in 1st cycle, HD Plastic strain accumulated in 5 cycles, Ac

Results Confirmed large variability of degradation level

in the structure. Showed that most affected areas are the

columns footing and right abutment wall. In line with visual observations of IER distress,

which did not occurred for the compressive strength results.


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Results HD and Ac confirmed that stiffness provides a

good indication of deterioration level even at the relatively low expansion levels.

K, HD and Ac Provide better indication of internal damage due

to IER than compressive strength.

Can provide indication of reaction/expansion evolution in service and with expansion test.

Allow a better interpretation of expansion curves and compressive test results Cores exhibiting small lab. expansions may

exhibit higher mechanical strengths and lower strength variations with expansion test than specimens showing high lab. expansion.

Cores exhibiting large lab. expansions may exhibit high mechanical strengths and low variations in strength with expansion test.


Conclusions This paper presented a methodology for the prognosis of IER in concrete structures,

which allows the determination of the evolution of degradation phenomena, provides data to evaluate the consequences for the structure.

This study showed also that SDT can reveal concrete degree of deterioration achieved to date and consequently

allows a better understanding of the concrete current condition and its potential for further expansion due to IER.

Therefore, a prognosis methodology including SDT enables a more effective decision making in relation to further intervention or monitoring of the structure affected.

The parameters HD and ac, determined using this method, will be used to estimate the amount of expansion reached by cores from an ASR affected structure. The results will be published soon.


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S12


Obrigado!


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