Chloride Environment
The resistance of microsilica concrete to the penetration of chloride ions makes it particularly suitable for structures exposed to a chloride environment.
Microsilica concrete is extensively used for marine structures, harbour construction and bridges exposed to saline water.
In particular in areas where de-icing salt is used, e.g. parking structures and bridges, microsilica concrete has proven to be a cost efficient solution to steel reinforcement corrosion problems.
In the harsh ' Sabkha' environment of the Arabian Peninsula steel reinforced concrete structures often deteriorate in a matter of years. Sabkha is an Arabic term describing arid, salt-encrusted soils where the shallow groundwater has a concentration of dissolved salts of three to five times that of sea water. High quality microsilica concrete is considered the most rational approach to mitigate the corrosion problems in these areas.
Long service life
Designing for a specific service life requires knowledge of the parameters determining the ageing and deterioration of concrete structures. Such parameters include environmental loading, structural resistance, transport mechanisms for aggressive materials into and within the concrete as well as deterioration mechanisms of concrete and reinforcement.
The pre-condition, to calculate service life and life cycle costs, is to have a scientifically sound mathematical model taking all these parameters into consideration.
Life-365 is a program to determine life cycle costs of concrete structures. In the initial version it handles parking structures and other structures exposed to de-icing salts. While we feel there are still great inadequacies in the program, such as lack of standardised methods for determination of parameters, lack of third party information for parameter values and lack of correlation to field performance, the principles involved are of sufficient interest to the engineering community to make them available. The basics of the model will be further developed by American Concrete Institute, ACI Committee 365.
Be sure to read the disclaimers in the users manual and to register, before using the program!
Marine environment
Gullfaks C, North Sea
A total of 246 000 m3 of high-strength concrete was needed to build Gullfaks C, one of the world’s largest offshore platforms.
The concrete mix contained Elkem Microsilica to improve the pumpability and reduce segregation.
Gullfaks C is located in the North Sea and has a production capacity of 245 000 barrels of oil per day. The construction of the platform was a major step in the development of offshore structures designed for the North Sea.
Refurbishment of Karmøy Wharf, Norway
At Karmøy in Western Norway, Norsk Hydro has a large aluminium smelting plant. All products are shipped from this plant by sea, and the huge wharf, built in 1968, is essential to the operation. The 270 x 25 metre wharf was built in B300 (30 MPa) concrete. The consequence was that the structure, after only 10 years service in a very exposed location, was due for extensive repairs. In 1980, 22 of the 65 sections of the wharf were repaired by removing all delaminated concrete, cleaning the steel and applying wet shotcrete. In all but 2 of the sections, the shotcrete contained 15% microsilica. In 1986 an additional 7 segments were repaired, this time latex as well as microsilica was used in the shotcrete. The latest round of repairs was performed in 1989, using a dry shotcrete process, with a microsilica dosage of 15%.
The experience from the first repair was that failure occured in the two sections without microsilica. The second and third repairs are still intact.
Extensive analyses have been performed on the repairs. The main conclusions are that those with microsilica had lower chloride content than those without. Chlorides from the original concrete migrated into the shotcrete layer, reducing the overall maximum concentration.
The net effect of using microsilica shotcrete for the repair of this chloride damaged concrete has been a repair with better durability than the original concrete.
Crude Palm Oil Terminal, Indonesia
Elkem Microsilica in combination with ASTM Type II Portland Cement replaced Portland Blast Furnace Slag Cement (PBFSC) for the construction of a terminal for handling crude palm oil on Batam Island, Indonesia. The use of microsilica gave a number of benefits:
- high early strength for prestressed members
- reduction of moulds needed
- easier logistics since only 6% microsilica by weight of cement, compared to all the PBFSC, had to be imported.
The terminal consists of tank farm and a jetty. It will serve tankers up to 35 000 DWT. The project was finished by the end of 1991.
Since the specified cement was difficult to obtain in the area, it was proposed to use microsilica. This solved a logistics problem since the tests showed that the use of 6% Elkem Microsilica gave high early and final strengths with reasonable cement contents.
After extensive testing, it was decided to use microsilica for all offshore concrete that comes in contact with seawater. The concrete volume for this part of the project was 12,000 m3.