CONDITION ASSESSMENT OF QUEENSLAND COAL MINE CONCRETE STRUCTURES
Defective concrete: significant area of spalled concrete found on reinforced concrete wall
Failing pedestals: conveyor belt supporting pedestals with corrosion and spalling along a coal conveyor tunnel.
Damage to the Run of the Mine caused by both mechanical impacts during production and ongoing reinforcement corrosion
Queensland Coal Mine Concrete Structures
Queensland, Australia
Infracorr were engaged by a prominent structural engineering firm to assist with auditing all reinforced concrete structures at an open cut coal mine in northern Queensland. On sites like this, concrete deterioration occurs slowly and invisibly below the surface of a structure. By the time visible deterioration is observed the corrosion is already widespread and expensive maintenance of seemingly sound concrete will be required if deterioration is to be halted. As a part of the mine operator’s requirement for 6 yearly audits, Infracorr was engaged to perform concrete testing and a corrosion assessment of the integral reinforced concrete structures at the primary coal processing plant.
CHALLENGES
Mine sites are exposed to aggressive environments and have a number of critical structures which are constantly in operation, therefore allocating time and budget to undertake maintenance works must be carefully considered to minimize the impact of the mine’s operations. In conducting the structure audit, a number of challenges arose including:• Working within a short shutdown period of 7 days to conduct the inspections and testing on the site’s structures
• The concrete structures on the site ranged in age, some up to 40 years old and exhibited varying levels of deterioration and corrosion
• The residual thickness of the Steel Piles and Steel Pile walls both above and below the water needed to be assessed via Ultrasonic Thickness Testing (UTT) so that Jacobs could design the requirements for the structural upgrades for the wharves.
• Obtaining sufficient data for assessment including Identifying where to best undertake testing based on time and cost constraints
• Working safely with and around other trades and operations
SOLUTIONS
Infracorr designed a testing regime that allowed 11 individual structures to be thoroughly examined during the 7-day shutdown period.
The testing regime consisted of:
• Working collaboratively with the structural engineering team, testing works were completed in conjunction with the structural assessment of critical elements
• A 100% visual inspection was undertaken and combined with target testing of ‘at risk’ locations
(as opposed to widespread testing) to ensure best use of the limited time available
• Extensive Half Cell Potential surveys were performed on 25% of the 136 No. beams thus providing significant information upon which to design the ICCP systems.
• Utilising various testing methods, including; visual inspections, delamination testing, concrete cover surveys, half-cell potential testing, corrosion rate testing, resistivity testing, electrical continuity testing, carbonation testing and chloride content testing where deterioration was identified
Infracorr’s audit report detailed which structures were at short and long-term risk and outlined a number of cost- effective remediation options including recommendations regarding the priority of the required works.
Working consultatively with the structural engineering team, Infracorr were able to:
• Identify the most cost-effective short-term solutions to remediate the structures displaying the worst corrosion effects
• The Durability Plan created provided information and recommendations to minimise maintenance during the next 30 years of the design life of the wharves.
• Advise on remediation solutions including; crack repairs, concrete repairs with anodes and cathodic protection
• Detail a plan to extend the potential life of tested structures by 20 years or more
The mine operator’s requirement for
6 yearly structural inspections allowed Infracorr to identify ways in which the early identification of concrete corrosion and sound remediation planning could save costs and maximise productivity in the long run.