Report No. : GEO Report No. 167

Report Title : The 2004 Review on Prevention of Alkali Silica Reaction in Concrete, 2nd Edition (2008), 78 p.

Author : Y.H. Chak & Y.C. Chan

Abstract

Alkali-Silica Reaction (ASR) was first diagnosed on concrete structures in Hong Kong in 1991. Limitation of alkali content in concrete to 3kg/m³ was introduced in 1994 to control ASR. The present review was carried out to see whether and how to update the control approach.

Current practice in the world is to accept the use in concrete of reactive aggregates to various degrees. The risk of ASR is controlled through the prescription of preventive measures taking into account the nature of structures, the service environment of the structure, and the reactivity of aggregates available. In this light, there is room for expanding the control framework in Hong Kong for informed use of reactive aggregates in concrete.

The nature of structures is classified according to the consequence of ASR. Service environment is described in terms of availability of moisture and alkali/chloride from outside the structure. Reactivity is classified by a range of tests including petrographic examination, accelerated mortar test and concrete prism test.

Common preventive measures are limiting alkali content of concrete, addition of supplementary cementitious materials such as pulverized fuel ash and ground granulated blast-furnace slag, and controlling the content of reactive silica in the aggregate assemblage of a concrete.

Knowledge and experience of ASR and its prevention in Hong Kong was reviewed for formulating the preventive measures for the expanded control framework. For the special case of reinforced concrete in marine environment, ingress of chloride ion presents a more immediate and demanding challenge than ASR to the durability of reinforced concrete in marine environment. This is provided for by an existing set of special specification.

The text of the report describes key elements of international practices and shows the rationale behind the proposed expanded ASR control framework for Hong Kong. Appendix H describes the expanded control framework. The other Appendices provide detailed information of local and international experience and practices. Of particular relevance to readers in Hong Kong are Appendix G and Appendix I that describe local experience and practice.

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