Development of underwater housings for the deep sea made of ultra-high performance concrete (UHPC) and long-term testing at the Arctic Sea
The aim of this research is the design and analysis of underwater housings made of ultra-high performance concrete (UHPC) within the Helmholtz Alliance “ROBEX” (robotic exploration of extreme environments) [1]. Due to the extremely corrosive maritime environment, mainly expensive materials such as titanium, ceramics, special stainless steel and aluminum are used so far for the construction of temporary and permanent research stations to guarantee long-term deployment. In this project the suitability of high-strength concrete with compressive strength up to 210 MPa for underwater pressure housings and constructions is examined to provide a low cost and durable alternative especially for large housings in future.
Material Behavior of Ultra-High-Strength Concrete under Multiaxial Stress States
To evaluate new fields of application of concrete structures in any processes where complex stress states occur, and to optimize concrete structure geometries regarding such applications, the material behavior of concrete under multiaxial loading has to be known. With the aim of determining the material behavior of an ultra-high-strength concrete (UHSC), 35 multiaxial stress states with primarily one tensile stress component are examined and the measured stress-strain curves are shown. Using the test results, the arbitrary parameters of a damage-based material law concerning the single-stress ratios are determined. To describe the material behavior for load-induced isotropic and orthotropic damage, an approximation of the calculated arbitrary parameters is deduced. These enable determining the material behavior of the investigated UHSC for any stress ratios. The prediction of the described material law is compared and discussed regarding the measured stress-strain curves and the maximum strength values from the tests.
Long-Term, Deep Ocean Test of Concrete Spherical Structures - Results after 13 Years.
In 1971, a long-term, deep-ocean test was started on 18 pressure- resistant, hollow concrete spheres, 66 inches in outside diameter by 4.12 inches in wall thickness. The spheres were placed in the ocean near the sea floor at depths from 1,840 to 5,075 feet. Over a 13 year period, annual inspections of the spheres using submersibles have provided data on time-dependent failure and permeability. After 5.3 years of exposure, three spheres were retrieved from the ocean for laboratory testing, and after 10.5 years two more spheres were retrieved and tested. This report is the third in a series describing and summarizing the findings from the ocean and laboratory tests. Data on concrete compressive strength gain, short-term implosion strength of the retrieved spheres, and permeability and durability of the concrete were obtained. The data show that concrete exhibits good behavior for ocean applications. High quality, well-cured concrete can be expected to gain and maintain strength when neither deterioration of the concrete matrix nor corrosion of reinforcing steel are problems, even though the concrete becomes saturated with seawater. uncoated concrete has a very low rate of permeation of seawater through the concrete and even this small flow can be prevented by a waterproofing coating.