Degradation of Concrete Bridges by InternalExpansive Reactions – Portuguese Case Studies

António Santos Silva, Arlindo Gonçalves, Manuela SaltaMaterials Department, Laboratório Nacional de Engenharia Civil,Av. Brasil 101, 1700-066 Lisboa, Portugal

Context

• Several reinforced concrete bridges have shown premature degradation

Context

• An research and experimental program conducted by LNEC

» Internal expansive reactions

» Alkali-silica reaction (ASR)

» Delayed ettringite formation (DEF)

In Portugal the problem is real and justifies the

ng

Context

growingconcern about the development of this type of concrete degradation

The problem

• The diagnosis requires technical expertise

• The distinction between deleterious and • The distinction between deleterious and non-deleterious products (e.g.: ettringite)

• The field symptoms are not exclusive of internal expansive reactions

• Macroscopical aspects

–– element or structure type

– exposure conditions (wetting-drying cycles, permanent immersion, etc.)

Methods of diagnosis and prognosis

permanent immersion, etc.)

– concrete composition

– concrete application

• Microscopical material aspects (lab tests)

• Sampling• extraction of concrete cores in cracked and sound areas

• cores should be deep enough to be representative of the maximum temperatures reached in the concrete elements

• Characterization techniques• Optical microscopy and/or electronic microscopy

Methods of diagnosis and prognosis

• Optical microscopy and/or electronic microscopy

• Chemical analysis (alkalis and sulphates profiles)

• Characterization techniques• Residual expansion tests on concrete cores

• Avoiding the interception with cracks or reinforcement rebars

• Recommended diameter is 10 cm

• Length representative of the interior of the concrete element

0,12

0,08

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

0.18

0.20

0 50 100 150 200 250

tempo (dias)

expa

nsão

(%) 16-32 cm

0-16 cm

� Bridge located in the centre of Portugal (1976-79)Case studies

Diagnosis tests Diagnosis tests –– optical and scanning electron microscopyoptical and scanning electron microscopy

Case study: Bridge located in the centre of Portugal (1976-79)

DEF and ASR expansive products (alkali-reactive qua rtzitic aggregate)

Prognosis testsPrognosis tests-- concrete residual expansion testsconcrete residual expansion tests

0.06

0.08

0.1

Exp

ansã

o (%

)

30 - 50 cm

0.16

0.20

0.24

0.28

Exp

ansã

o (%

)

Case study: Bridge located in the centre of Portugal (1976-79)

Pier pedestal

Exist potential for future concrete expansion due t o ASR and DEF, even in non-cracked areas

-0.02

0

0.02

0.04

0 91 182 273 364

Tempo (dias)

Exp

ansã

o (%

)

0 - 20 cm

0.00

0.04

0.08

0.12

0.16

0 91 182 273 364

Tempo (dias)E

xpan

são

(%)

Pier pedestal

Pier

Case studies� Bridge located in the north of Portugal (1994-97)

Diagnosis tests Diagnosis tests –– optical and scanning electron microscopyoptical and scanning electron microscopy

Case study: Bridge located in the centre of Portugal (1976-79)

ASR expansive products (alkali-reactive granitic an d quartzitic aggregates)ASR expansive products (alkali-reactive granitic an d quartzitic aggregates)

0.03

0.04

0.05

0.06

0.07

0.08

0.09

0.10

Exp

ansã

o (%

)

Interior

Prognosis tests Prognosis tests –– concrete residual expansion testsconcrete residual expansion tests

Case study: Bridge located in the centre of Portugal (1976-79)

0.00

0.01

0.02

0.03

0 28 56 84 112 140 168 196 224 252 280 308 336 364

Tempo (dias)

Exterior

• The internal expansive reactions (ASR and DEF) are aproblem of durability of concrete structures requiring theadoption of appropriate methodologies for its diagnosis andprognosis.

Conclusions

prognosis.

• The diagnosis and prognosis methodology presentedexplains the degradation causes and allows to predict theevolution of the phenomenon and its consequences for thestructure and supports the decisions taken about therepairing options in the structure elements.

•The two case studies presented show that this disease affectsmainly massive elements and concretes with high cementcontents. Furthermore, the cements used do not contain anytype of mineral pozzolanic additions (fly ash, metakaolin, etc.).

Conclusions

• Today is well known that one of the mitigation measures ofASR and DEF during the design and construction of newstructures is the use of type II additions, with or without cementreplacement. The performance of each addition in the mitigationof these reactions depends on its content and pozzolanicactivity. In order to verify the long-term behaviour of differentmineral additions in the mitigation of these expansive reactionsin concrete an important experimental program is beingconducted by LNEC.

Thank you