Kalgoorlie Consolidated Gold Mines Pty. Ltd. (KCGM), located in Western Australia, had a big problem. The 24m-long, 41-cm diameter steel support members that hold up its 78.5m-diameter, suspended conical stockpile cover, which protects gold-containing mined coarse ore from weather until it can be processed, required structural strengthening. Corroded by chemicals and damaged by earthmoving equipment, the steel supports exhibited substantially reduced load-carrying capacity, and the company wanted the solution to this problem to last the life of the mine, currently projected through 2029.
KCGM engineers and a team of outside engineering consultants undertook an investigation and analyzed the structure to understand the critical loads, member forces and risks. Conventional solutions, incorporating steel, concrete and grout, were proposed, with costs ranging from AU$8 million to AU$13 million, and each required an extensive activity shutdown period. In search of a less disruptive answer, KCGM contacted composites firm Advantic LLC (Dayton, OH, US).
“We recognized that little guidance exists in the successful design and integration of advanced material solutions in infrastructure applications,” says Advantic president Brad Doudican. “We provided a staged engineering approach as an integral activity within the project delivery program.” After reviewing the existing documentation and studies on the structure, Advantic formulated conceptual solution approaches, and visited the site. Finite element analyses were performed on each critical steel member to investigate the optimized design geometries necessary to achieve minimum material-performance requirements.
The answer? Advantic fabricated 638 “jackets,” each about 1m long, comprising a stainless steel outer skin bonded over an inner, precast polymer structural sleeve made with Advantic’s trademarked Fortis cast epoxy polymer, which contains glass microspheres, making it one-fifth the weight of conventional concrete solutions. The jackets were adhesively bonded to the steel supports, using an acrylic adhesive from Lord Corp. (Cary, NC, US) by mine workers, who followed a detailed work plan devised by Advantic to make the job go smoothly during a scheduled mine shutdown. Designed-in mating flanges made it easy to enclose the steel within the jackets.
Advantic’s solution cost AU$3 million, 63% less than the least-expensive conventional solution, and was installed in a mere 12 days. Says Doudican, “The jackets will not corrode, are impermeable to moisture, were able to withstand the rough field conditions and provide 27 MPa compressive strength at a density of 560 kg/m3. Our cast polymer’s high shear strength transfers load around the damaged areas of the steel members.”