The Effects Of Sea Water On The Structural Properties Of Metal-Fiber Reinforced Concrete
Authors: Rider Richard G. , Heidersbach Robert H. 
Published: October 2008

Metal-fiber reinforced concrete is a structural material with several unique advantages for offshore applications. This paper describes a series of exposure tests undertaken to evaluate the suitability of metal-fiber reinforced concrete for marine applications. Corrosion exposure tests and freeze thaw tests are discussed.

INTRODUCTION

There are an increasing number of concrete structures being designed and installed offshore in recent years. While concrete has a number of distinct advantages as a construction material its durability is not demonstrated adequately yet for some applications. Corrosion of metal reinforcement has become an increasing concern for onshore bridge decks,l and it is to be expected that corrosion in offshore concrete structures will become an item of increasing concern in years to come.2,3

Comparisons with coastal and onshore applications indicate that the following problems will be of principle importance in determining the durability of offshore structures: freeze-thaw susceptibility, abrasion and fatigue, and corrosion of embedded metal. All of these problems can be expected to be most severe in the tidal, or splash zones on a vertical structure.4

Metal-fiber reinforced concrete is a material having improved fatigue and tensile properties when compared with conventional reinforced concrete.5,6 Published information on the material suggests that it might be an ideal material for some offshore applications where fatigue and abrasion are important. Unfortunately, information on its durability under corrosion and freeze-thaw conditions is very limited. 7,8.

The purpose of this research was to investigate the durability of metal-fiber reinforced concrete for use in marine environment. Conditions of interest included freeze-thaw, corrosion, and corrosion fatigue. Funding limitations prevented investigation of corrosion fatigue but the other conditions were investigated.

EXPERIMENTAL

Concrete structures are intended to be permanent and design lives of 20 years and more are typical.3 A review of existing experimental research into concrete durability indicates that most corrosion tests tend to be short term (relative to design life) and frequently show no measurable metal degradation.1,7,9 No unequivocal method of accelerating corrosion exposure tests (such as raising temperatures) will work for concrete because of the unique interdependence of dissolved oxygen and of the pH of the concrete in determining corrosion rates.2 Elimination of the large sample sizes commonly used .in concrete testing should help10 and this has been tried in at least one instance.11 Problems can occur in trying to make a "small concrete sample12 and these must be accounted for in experimental design. Thus the ideal concrete corrosion exposure sample should be small enough to maximize the surface attacked-area-to-volume ratio,10 yet be large enough to be representative of typical concrete structuralproperties. The same considerations apply for freeze thaw testing, but fortunately, accelerated exposures are valid for freeze-thaw testing.13.

Concrete sample types used in this investigation are summarized in Table 1. The mix parameters were chosen to be typical of those reported for metal-fiber reinforced concrete.15.