A Practical Assessment of Mass Concrete Construction for Wind Farm Projects in Remote Sites

Abstract

Wind Turbine Generator technology deployed in Australia has reached a point where each generating unit is producing power outputs in excess of 7.0MW. The generating unit consists of a steel tubular tower with a hub height in the region of 155m, and three blades with a rotor diameter of over 170m harnessing a sail area of approximately 2.2Ha. This equipment is supported on a reinforced concrete footing platform up to 4m thick, which, to sustain the imposed actions, can comprise upwards of 850 cu.m of concrete and 110 tonnes of reinforcing steel. Overall project size varies, depending on a vast array of factors, from 2 to 180 generating units with lifespans in the range of 30 to 40 years. Whilst today the installed capacity of wind generation is comparatively modest in Queensland, there is a considerable pipeline of projects under development in the range of 50 to 150 turbines each, which will be completed as part of the state’s increasing energy transition. Meeting this future demand will conservatively require the construction of approximately 200 to 250 wind turbines per annum for the foreseeable future. This translates to between 4 and 5 turbine foundations per week. Aggressive estimates for upstream infrastructure needed to sustain an emerging Hydrogen economy will increase this requirement threefold. Given these projects are largely situated in remote and regional communities, the logistical and technical challenges of delivering large volumes of high-quality concrete consistently, across an extended period and seasonal variations, are critical considerations during the planning, design and execution phases of these projects. Wind turbine foundations are highly loaded structures with an exceptionally high fatigue spectrum that require exacting standards in respect of strength, bleed, density, consistently, durability and thermal performance during the maturation process. An inappropriate concrete mix design and execution will result in unacceptable consequences to the durability and long-term structural performance of the footing platforms. Planning prior and during construction becomes vital given the lack of local established infrastructure. The concrete mix designs must be simple, practical, and where possible make use of locally available resources while still meeting exacting performance standards. Each wind farm typically requires minimum two mobile batching plants and the establishment of a reliable constituent supply chain. Concrete placement success is reliant on the timely replenishment of constituents without disruption. These batching plants must be capable of delivering concrete volumes at sufficient rates, and at the appropriate hour, to eliminate the failure of the typically monolithic footings. This paper outlines the technical and constructability challenges faced by repetitive mass concrete pours in isolated regions of Queensland and, more broadly, Australasia. Drawing on the lessons learned from the author’s personal experience in the sector, this paper presents the key issues for consideration to ensure that mass concrete works can be undertaken to a high standard without compromising on program or quality. It looks at key measures that can be deployed to manage potential durability concerns associated with delayed ettringite formation, bleed settlement, thermal cracking and how to recover when planning fails.