Properties of Concrete in Contact With Pressurized Hydrocarbons and Sea Water
Authors: Maxson O.G. , Achenbach G.D. 
Published: December 2007

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Introduction

Prestressed-concrete, gravity-founded structures for oil Prestressed-concrete, gravity-founded structures for oil production/storage applications are being designed, built, production/storage applications are being designed, built, and installed in the North Sea. The environmental effects of hydrocarbons on the properties of concrete for this relatively new application are not well known. At the initiation of this study, no investigation into the effects of pressurized hydrocarbons on concrete properties had been pressurized hydrocarbons on concrete properties had been reported in the available technical literature. Limited information has subsequently appeared. The large investments and potentially high costs of failure justified our investigation.

Chemical reactions between mature concrete and hydrocarbons were not anticipated. However, the presence of hydrocarbons could alter the availability of moisture in concrete. The net result of any such effect on the properties of the concrete was uncertain. The role moisture plays in the curing of concrete has been the subject of extensive investigations. Briefly, the ultimate potential strength of concrete is obtained by a low water-to-cement ratio in the initial mix, maximum available water during the curing stage, and minimum free water at the time of the test. Hydrocarbon flooding during the curing stage could alter the strength and related properties of the concrete.

Crude oils from North Sea production typically contain a significant percentage of pentane and low-molecular-weight hydrocarbons. These hydrocarbons are likely to have the greatest penetration and effect on concrete. Our initial experiments involved high-strength concrete subjected to pentane at several different pressures and time intervals. The effects of crude oil, pentane, and sea water on high-strength concrete were then investigated. The preliminary results of an ongoing study of the effects of these same environments on creep and fatigue behavior are included in this paper.

Test Specimens, Apparatus, Procedures, And Facilities

Standard 6- x 12-in. cylinders were cast in cardboard molds using local materials similar to the materials that might be available in England. Type 1 Portland cement at seven bags per cubic yard was used with mined river gravel and mined per cubic yard was used with mined river gravel and mined sand. Comparisons were made between cylinders of the same age from one batch or a minimum number of equivalent batches. Mixing, casting, and testing techniques conformed to ASTM standards. Special 4- x 8-in. cylinders were used for the fatigue tests. All samples received a 28-day fog-room cure before any testing or exposure.

Pressure vessels were constructed to contain two 6- x 12-in. cylinders. The concrete cylinders were flooded with the environmental fluid and pressured with a nitrogen blinks. Special creep racks were constructed to fit inside the pressure vessels with the load maintained by disk springs. pressure vessels with the load maintained by disk springs. Special fatigue machines were constructed to load the cylindrical samples at 4 cycles/min in the pressurized environments.

Permeability was measured on 1 1/2- x 3-in. cores using a 300-psi pressure differential. Permeability tests were made with air, water, pentane, and crude oil.

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