Norwegian researchers and manufacturers have worked together to develop new types of concrete, of which high-strength, lightweight aggregate (LWA) concrete and shotcrete are the most well-known and widely-used.
Modern LWA concrete is nearly twice as strong as the concrete normally used to build houses, and almost as strong as - yet 40 per cent lighter than - the high-strength concrete used to build bridges. The use of LWA concrete combined with high-quality aggregates means major cost savings on steel reinforcement and prestressing, making it an ideal material for floating and submerged bridges. LWA concrete has become very popular in the heavy construction sector and is also well-suited for sectors in which structural weight has traditionally been a limiting factor, such as the offshore and concrete element industries.
The virtues of high-strength LWA concrete have been demonstrated on a number of challenging bridge projects in Norway. The Nordhordland Bridge, which crosses the deep Salhus Fjord north of Bergen, combines floating and cable-stayed structures, including the world's longest floating bridge without side anchoring, and was significantly cheaper to build than a suspension span bridge. The steel floating section is 1,246 m in length and rests on ten concrete pontoons constructed out of LWA grade LC 55. The Bergsøysund Bridge is the world's second-longest floating bridge, with a floating span of 830 m.
The Shotcrete Revolution
By the early 1980s shotcrete (also called sprayed concrete) had nearly replaced the risky, labour-intensive method of casting concrete. Norway's global reputation for tunnel construction is greatly due its shotcreting expertise. The country introduced steel-fibre reinforced shotcrete in the late 1970s. Offering superior strength, top durability and excellent fire-retardant properties, steel-fibre reinforced shotcrete can be used to form a long-lasting, single shell lining for tunnels and caverns, reducing the number of bolts necessary for rock support by up to 50 per cent. The continuous development of shotcrete reinforcement techniques has enabled contractors to apply shotcrete to poorer quality rock. Today, shotcrete can be applied as a permanent lining for rock with a Q-value as low as 0.01. A decade ago that value was 0.1.
The wet-process method is the most popular shotcreting method worldwide, as it offers an improved working environment, better quality and reduced costs. It involves a robot-operated system that applies the material at a safe distance from the tunnel face. The development of water-reducing admixtures and microsilica has contributed greatly to the success of the wet-process method, as material quality, reinforcement and thickness can be adjusted to meet a variety of rock conditions and lining needs. Norwegian companies have become primary suppliers of computerized shotcreting robots and admixtures for all types of shotcrete to the international market.
The Norwegian concrete industry conducts ongoing research activity to develop new and improved types of concrete, and relies on the active involvement of related industry and other technology end-users.
Norwegian researchers are actively involved in formulating new rules and standards for the European building market through participation in international technical committees. Recently Selmer (a Norwegian contracting company) and SINTEF Civil and Environmental Engineering (a Norwegian research institute) were named coordinator and project manager, respectively, for the large "EuroLightCon" concrete technology research project funded by the European Union. Established in 1997, EuroLightCon is a three-year project that involves close cooperation between Norwegian, Dutch, German, British, Spanish and Icelandic companies, universities, research institutes and government agencies. The project aims to further develop lightweight concrete technology by testing new aggregates that utilize waste products, by identifying new areas of use for LWA concrete, and by drawing up rules for the dimensioning of reliable structures.
A great deal of Norway's concrete admixture expertise has its origin in the construction of offshore structures and bridges. To create admixtures for high-strength concrete, underwater concrete, and frost-resistant concrete capable of enduring extreme freezing and thawing, innovative Norwegian manufacturers have taken advantage of the numerous deposits of high-quality rock found along Norway's coast, as well as by-products from cellulose production (lignosulphonates) and ferrosilicon alloy production (silica fume). Borregaard Lignotech is the largest global supplier of lignosulphonate-based plasticizers - the world's most widely-used concrete additive. Elkem Materials is a major worldwide supplier of high-quality microsilica made from silica fume, which is used to increase concrete strength, reduce permeability and greatly enhance chloride resistance.
Today's advanced shotcreting methods are made possible by the addition of Norwegian admixtures which give reinforced concrete the desired consistency, adhesiveness and setting time. Rescon, a global leader in the manufacture of environment-friendly admixtures for shotcrete, is delivering non-alkaline accelerators to large projects in Asia, including a major road tunnel project in Japan.
Offshore: The Last Frontier
Norwegian concrete technology received an enormous boost with the development of concrete offshore platforms in the early 1970s. The gravity-based (GBS) Condeep concept was the first of its kind. Since then, 36 Condeep platforms have been built, over half of which are situated in the North Sea.
In order to find petroleum reserves in ever-deeper waters and to exploit small reserves, oil companies have turned to floating platforms constructed with LWA concrete. The use of LWA concrete in tension leg (TLP) platforms enables contractors to attain the critical weight balance between topsides and substructures. Finished in 1995, Heidrun was the world's first TLP platform with a floating concrete hull.
Modified concrete mixtures were developed for the Troll GBS platform and the catenary anchored Troll West Floater. The Troll A platform in the North Sea - the largest offshore development ever - represents the high point of Norwegian concrete technology for the offshore sector. The world's tallest (472 m) GBS concrete platform for petroleum production, it rests on four 369-m elegant concrete columns and is, surprisingly enough, portable.
Although gigantic structures like the Troll platform will most likely not be built again in the North Sea, innovative Norwegian engineering and design companies continue to devise other advanced systems for production, processing and storage based on concrete technology. Among them is the firm Dr.techn. Olav Olsen, which has designed two mixed concrete and steel vessels: the SEMO (Semi Submersible Monohull) for deep-water oil production in rough seas, and the Heavy Lift MPU (Multi Purpose Unit) for decommissioning operations.