Econ. Environ. Geol. 2003; 36(5): 365-374

Published online October 31, 2003

© THE KOREAN SOCIETY OF ECONOMIC AND ENVIRONMENTAL GEOLOGY

Concrete Deterioration Near Coastal Area and Characteristics of Associated Secondary Mineral Formation

Hyomin Lee1*, Jin Yeon Hwang1 and Chi-Sup Jin2

1Department of Geology, Pusan National University, Busan 609-735, Korea
2Department of Civil Engineering, Pusan National University, Busan 609-735, Korea

Correspondence to :

Hyomin Lee

hmlee61@pusan.ac.kr

Received: July 24, 2003; Accepted: October 18, 2003

Abstract

Various deleterious chemicals can be introduced to existing concrete structures from various external sources. The deterioration of concrete by seawater attack is involved in complex processes due to various elements contained in seawater. In the present study, attention was paid to the formation of secondary minerals and characteristics of mineralogical and micro-structural changes involved in concrete deterioration caused by the influence of major seawater composition. The characteristics of deterioration occurred in existing concrete structures was carefully observed and samples were collected at many locations of coastal areas in Busan-Kyungnam. The petrographic, XRD, SEM/EDAX analyses were conducted to determine chemical, mineralogical and micro-structural changes in the aggregate and cement paste of samples. The experimental concrete deteriorations were performed using various chloride solutions (NaCl, CaCl, MgCl2) and Na2SO4 solution. The experimental results were compared with the observation results in order to determine the effect of major elements in seawater on the deterioration. The alkalies in seawater appear to accelerate alkali-silica reaction (ASR). The gel formed by ASR is alkali-calcium-silica gel which known to cause severe expansion and cracking in concrete. Carbonation causes the formation of abundant less-cementitious calcite and weaken the cement paste. Progressive carbonation significantly affects on the composition and stability of some secondary minerals. Abundant gypsum generally occurs in concretes subjected to significant carbonation, but thaumasite ({Ca6[Si(OH)6]2 ·24H2O} · [(SO4)2] · [(CO3)2]) occurs as ettringite-thaumasite solid solution in concretes subjected to less significant carbonation. Experimentally, ettringite can be transformed to trichloroaluminate or decomposed by chloride ingress under controlled pH conditions. Mg ions in seawater cause cement paste deterioration by forming non-cementitious brucite and magnesium silicate hydrate (MSH).

Keywords concrete, seawater, deterioration, secondary minerals, carbonation

Article

Econ. Environ. Geol. 2003; 36(5): 365-374

Published online October 31, 2003

Copyright © THE KOREAN SOCIETY OF ECONOMIC AND ENVIRONMENTAL GEOLOGY.

Concrete Deterioration Near Coastal Area and Characteristics of Associated Secondary Mineral Formation

Hyomin Lee1*, Jin Yeon Hwang1 and Chi-Sup Jin2

1Department of Geology, Pusan National University, Busan 609-735, Korea
2Department of Civil Engineering, Pusan National University, Busan 609-735, Korea

Correspondence to:

Hyomin Lee

hmlee61@pusan.ac.kr

Received: July 24, 2003; Accepted: October 18, 2003

Abstract

Various deleterious chemicals can be introduced to existing concrete structures from various external sources. The deterioration of concrete by seawater attack is involved in complex processes due to various elements contained in seawater. In the present study, attention was paid to the formation of secondary minerals and characteristics of mineralogical and micro-structural changes involved in concrete deterioration caused by the influence of major seawater composition. The characteristics of deterioration occurred in existing concrete structures was carefully observed and samples were collected at many locations of coastal areas in Busan-Kyungnam. The petrographic, XRD, SEM/EDAX analyses were conducted to determine chemical, mineralogical and micro-structural changes in the aggregate and cement paste of samples. The experimental concrete deteriorations were performed using various chloride solutions (NaCl, CaCl, MgCl2) and Na2SO4 solution. The experimental results were compared with the observation results in order to determine the effect of major elements in seawater on the deterioration. The alkalies in seawater appear to accelerate alkali-silica reaction (ASR). The gel formed by ASR is alkali-calcium-silica gel which known to cause severe expansion and cracking in concrete. Carbonation causes the formation of abundant less-cementitious calcite and weaken the cement paste. Progressive carbonation significantly affects on the composition and stability of some secondary minerals. Abundant gypsum generally occurs in concretes subjected to significant carbonation, but thaumasite ({Ca6[Si(OH)6]2 ·24H2O} · [(SO4)2] · [(CO3)2]) occurs as ettringite-thaumasite solid solution in concretes subjected to less significant carbonation. Experimentally, ettringite can be transformed to trichloroaluminate or decomposed by chloride ingress under controlled pH conditions. Mg ions in seawater cause cement paste deterioration by forming non-cementitious brucite and magnesium silicate hydrate (MSH).

Keywords concrete, seawater, deterioration, secondary minerals, carbonation

    KSEEG
    Feb 29, 2024 Vol.57 No.1, pp. 1~91

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