NZ Construction News (Oct / Nov 11) Green Concrete Options for a Rebuilt Central City

01 Oct 2011

Rob Gaimster
Cement & Concrete Association of New Zealand (CCANZ)

The building and construction industry currently finds itself in a period of almost unprecedented adjustment. Consultations, policy announcements and regulatory amendments appear (it seems) on an almost daily basis.

Changes to the Building Code in the areas of practitioner licensing and weathertightness, along with mounting concerns over the nation’s skills and housing shortages, are part of this evolving landscape. However, the Christchurch and greater Canterbury rebuild effort is the chief driver.

Draft Central City Plan
Crucial amongst preliminary planning tools in this area has been the Christchurch City Council’s draft Central City Plan, which closed for comment in mid-September.

Putting questions to one side about restricting building heights to 7-storeys, which many believe may send capital investment elsewhere, as well as the need for internal sound insulation provisions between tenancies, the draft Plan is to be applauded for its ambitious vision.

In particular, the key theme of a “Green City” contains some unique opportunities for innovative concrete based technologies to enhance the urban landscape of a rebuilt Christchurch.

As New Zealand’s Garden City any plan to rebuild Christchurch must place an emphasis on fostering and integrating the natural environment within the urban landscape. In order to realise this vision and celebrate Christchurch as a modern city with a clear commitment to environmental sensibility, landscape and building design must utilise the best in construction material technology.

Locally produced, recyclable concrete lends itself well to low-impact, resource efficient and sustainable urban design across buildings, greenway networks and infrastructure.  As such, the available range of concrete-based construction technologies and systems must be given serious consideration in any design for the “Eco Streets” and “Green Roof and Wall” concepts of the Green City theme.

Eco Streets
Vital to the realisation of eco streets as a means to improve the Avon River/ Ōtakaro corridor and the water / environmental quality of the Central City are three concrete based pavement technologies - pervious concrete, concrete block permeable paving and concrete grid blocks.

Conventional pavements direct rainwater (along with any pollutants) into overloaded drains, streams and rivers, leading to flooding in extreme conditions. These new concrete based pavement technologies offer alternative, sustainable drainage solutions that are available in a range of configurations, colours and shapes.

Pervious Concrete
Pervious concrete can be used to create a structural pavement, which through an interconnected network of voids, drains and filters stormwater, thereby reducing runoff and replenishing groundwater supplies. Through cationic exchange, pervious pavements can trap the pollutants and heavy metals associated with stormwater run-off.

Pervious concrete is low maintenance, quick to install and cost effective, ideal for car parking areas, as well as foot and cycle paths, and has been successfully trialed on Auckland’s North Shore.

Concrete Block Permeable Paving (CBPP) / Concrete Grid Blocks (CGB)
As drainage and pavement systems CBPP & CGB address both flooding and pollution issues. CBPP and CGB allow water to pass through the surface, between / within each block, and into the underlying permeable sub-base where it is filtered, stored and released slowly, either into the ground or to a drainage system. 

CBPP & CGB variants are already used throughout New Zealand, across commercial, residential and industrial applications.

Greening the Roof
Concrete’s durability, structural qualities and design flexibility in the creation of green roofs and walls has the potential to become a distinctive feature of the rebuilt City’s environmental awareness.

To allow plants grown up or on buildings to absorb summer heat, reduce the cost of air-conditioning, improve air quality, as well as act as bio-filters and provide habitat for native birds and insects, urban designers need look no further than the strength and versatility offered by concrete.

Wollaston Estates winery near Nelson and the NZI Building in Auckland exploit the structural and aesthetic potential of concrete to realise unique green roof features. Similarly, the recently completed Hobsonville Motorway Extension near Auckland makes extensive use of large precast concrete panels containing holes for plants to grow through. These green walls provide retaining capabilities and a vertical canvas for natural beatification.

Planning for Tomorrow
Across its other four key themes, Distinctive City, City Life, Transport Choice and Market City, the draft Central City Plan offers numerous instances where the attributes of concrete can help bring to life a revitalized and resilient Christchurch. These include, but are not restricted to, damage avoidance design systems for multi-storey buildings, affordable housing options, as well as shared public spaces for efficient multi-mode transport.

While commercial pressures will inevitably play a part in forming the new city centre of Christchurch, the draft Plan provides an aspirational foundation from which the people of Canterbury can draw strength.