International Concrete Abstracts Portal

Concrete is a suitable material for arctic offshore oil and gas drilling and for production platforms. In the splash and tidal zone of these structures concrete is subjected to severe frost-salt attack, chemical attack of sea water, and ice abrasion. In the test series, a method for accelerated testing of arctic freeze-thaw durability in sea water was developed. High-strength air-entrained superplasticized concretes made with blended cement were tested. The test was found to be very severe.

Theoretical aspects of concrete resistance to freezing and deicing chemicals are shown in causal terms. Different constituents and concreting procedures result in different concretes. Furthermore, environmental influences cause a series of physical processes that are also presented in the paper. These physical mechanisms cause stresses that may result in concrete damages. The second part of the paper contains a survey of methods for testing the resistance of concrete to freezing and deicing chemicals. The most common methods are presented in a flowchart showing the advantages and disadvantages of a method and its applicability for a particular structure.

The Belgian Public Works Ministry manages about 5200 important bridges--3640 (70 percent) of them are concrete bridges of which 40 percent are reinforced and 30 percent are prestressed. The average bridge has a surface of 1200 mý, 22 m long spans, and is 22 years old. After seven years of systematic inspection, it is possible to make a balance of the noticed shortcomings and of the reasons why they appeared. Dirty concrete surfaces (graffiti, water trails, moss, etc.) occur very often but generally don't influence the good behavior of the structures. Geometric faults are noticed in 2 to 4 percent of the cases, mainly for cantilever bridges. Concrete cracks are very frequent (30 to 80 percent of the concerned structures). Most of them don't affect the safety but have an influence on the durability. Corrosion of reinforcements and prestressing steel also occurs frequently (20 to 80 percent of the concerned structures). Steel in concrete is naturally protected, but two main factors disturb that favorable situation: carbonation of concrete by CO2 reduces the pH of the concrete and also the protective effect, and cracks and lack of closeness in the protective coating lead to penetration of corrosive agents like deicing salts and acid rain. The deicing salts (chlorides) also attack hardened cement and transform the surface of the concrete into gravel. Although all our bridges are provided with a protective waterproofing, water containing salts remains the most aggressive element. The maintenance, rehabilitation, and reinforcement of the bridges are an important technico-economical problem in Belgium.

Permeability, a prime factor related to durability of concrete, was measured by water and gas flow in plain and reinforced concrete. The results are discussed in terms of porosity and pore size characteristics as determined by mix proportions and hydration parameters. 617-387 Development of impact-resonant vibration signature for inspection of concrete structures

A comprehensive review of the literature about durability (D-) cracking due to frost action in portland cement concrete pavements is developed. D-cracking is defined and described and the mechanisms causing the phenomenon are discussed. The idea that D-cracking is moisture oriented is established. It is affected by freezing temperatures that cause enough volumetric change in the moisture that exists in the cement-aggregate matrix and initiates a durability line crack in the concrete. Factors such as physical characteristics of aggregates and mortar, geographic location, maximum size of coarse aggregates, source of aggregates, and use of deicing agents are found to be among the main factors that affect the development of durability cracking. Tests to indicate frost resistance in aggregate are also reviewed. These tests are of two general types: weathering tests such as unconfined and confined freeze-thaw tests, and measurements of a physical property correlated with performance such as porosity, pore size, and absorption tests. The use of petrographic analysis is an absolute necessity to identify frost-susceptible aggregates. Other tests such as ASTM "Test for Resistance of Concrete to Rapid Freezing and Thawing" (C 666), ASTM "Test for Critical Dilation of Concrete Specimens Subjected to Freezing" (C 671), the PCA method, the Iowa Pore Index Test, and particularly ASTM "Evaluation of Frost Resistance of Coarse Aggregates in Air-entrained Concrete by Critical Dilation Procedures" (C 682) are also considered satisfactory methods to predict field durability performance of concrete aggregates. Researchers such as Axon and others, Iyer and others, and Thompson and Dempsey developed some pertinent tests that could be used in this area as well.