Print

Media

Engineering Insights (Jul / Aug 12) Practical Research - Development of Concrete

31 Jul 2012

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

Since Joseph Aspdin obtained the patent for Portland cement in 1824 the concrete industry, driven by commercial and environmental demands, has endeavoured to transfer research accomplishments from the laboratory into practice.

The progress of technical innovation has followed an almost linear path, displaying all the textbook traits of being at times “radical” and at others “incremental”, or to borrow leading competitive strategist Michael Porter’s terminology “discontinuous” and ”continuous”.

The outcomes have made possible a range of high-performance concretes that are transforming building disciplines, and ensuring concrete remains a key contributor to a sustainable built environment.

Almost any type of concrete is now possible, from ultra-strong, self-compacting and bendable, to translucent, depolluting and recyclable.

CONSTITUENT MATERIALS
Advances in cement and admixture technology have been dramatic over recent decades. Huge investment in research has led to improved manufacturing processes and an array of additives that help reduce environmental impacts and allow designers to fully exploit concrete.

Examples of efficiencies in cement manufacture include the use of alternative renewable kiln fuels and the growth of supplementary cementitious materials – industrial by-products or natural materials which when added to cement exhibit cementitious properties. This drive towards reducing energy use and emissions was further embedded with a recent update of NZS 3122 Specification for Portland and Blended Cements, allowing up to 10 per cent mineral addition (supplementary cementitious materials) in General Purpose cement.

While performance enhancing additives are not new (the Romans used animal blood for durability and workability) recent innovation has been prolific. Water reducers, grinding aids, corrosion inhibitors and water proofing agents are just some of the admixtures now used to improve durability and placing times, reduce costs and enhance sustainability credentials.

CONCRETE
Mirroring innovations in its constituent materials, concrete itself is undergoing constant development. The umbrella term high performance concrete captures the features of modern concrete, which include higher strengths, enhanced abrasion resistance and durability, low permeability and diffusion, improved resistance to chemical attack, and greater ease of placement.
One example of high performance concrete is self-compacting concrete, which was used in the NZ Transport Agency’s Tauranga Harbour Link Stage 2 project. Self-compacting concrete flows under its own weight to fill formwork congested with reinforcing steel. Self-compacting concrete’s benefits include a safer work environment with less mechanical vibration, greater flexibility for complex shapes and a homogenous finish.

High strength concrete is the product of sophisticated mix design that includes premium admixtures as well as particle packing to control porosity and permeability. Used in the shear walls of the Burj Khalifa, the world’s tallest building, high strength concrete offers economic benefits through slender and lighter structural elements. 

There has also been recent significant development in the role of fibres in concrete. Fibre reinforced concrete generally refers to concrete containing steel fibres and is predominantly used in industrial flooring applications due to its toughness and ductility. There are even instances where steel fibres have replaced conventional reinforcement in structures.

Advances in concrete technology have also led to some unusual varieties. Bendable concrete is a lightweight composite material that offers good tensile strength and ductility, and is available as a sheet or can be applied via a shot-nozzle. Translucent concrete, available as non-structural blocks or panels, contains randomly embedded glass fibres that allow light transmission.

SEISMIC STRUCTURAL DESIGN
In terms of seismic structural design, reinforced concrete has long been favoured by engineers to express new ideas. This is particularly so in New Zealand, where Canterbury University has nurtured some of the world’s top structural engineers under the guidance of the late Professors Robert Park and Thomas Paulay.

As seismic structural design develops beyond “life safety” towards “building survivability”, recent advances in damage resistant design using concrete systems are leading the way. These advances include the PREcast Seismic Structural System (PRESSS), which uses un-bonded post-tensioning cables and rocking joints within a precast frame to ensure the building returns to upright without significant structural damage, even after a major seismic event.

In response to structural earthquake demands even the humble concrete slab-on-ground for homes is undergoing development. With it now mandatory for all residential floor slabs to contain seismic grade reinforcing mesh, innovative “raft” slab designs are evolving.

Also within the residential space, and on display at the “HIVE” Home Innovation Expo in Christchurch, prefabricated concrete systems for safe and affordable houses are undergoing design enhancements prompted by interest following the Canterbury earthquakes.

SUSTAINABILITY
Recognising the need for sustainable development the concrete industry has implemented innovative economic, social and environmental strategies.  The CCANZ Concrete3 campaign seeks to raise awareness of concrete’s contribution to a sustainable built environment, while the Holcim Awards acknowledge innovative construction projects and future-oriented concepts.

Industry is also seeking new ways to meet the growing demand for products that allow for recycling. Developments centre on the reuse of wash-water from the production of ready mixed concrete and the uptake of recycled waste (e.g. demolition concrete) as aggregate in new concrete. The latter is illustrated by Lion Nathan’s Pride facility in East Tamaki, which incorporates recycled waste glass as aggregate in concrete.

Also on display in Auckland, in the form of North Shore footpaths, is pervious concrete.  Designed to reduce the flow rate of water entering the stormwater system to mitigate flooding, as well as filter out contaminants, pervious concrete provides a structurally sound pavement option.

Depolluting concrete is another emerging innovation. Incorporating nano–sized photocatalyst particles in the primary form of titanium dioxide (TiO2), depolluting concrete accelerates the natural and safe chemical reaction whereby strong sunlight or ultraviolet light creates an electrical charge that breaks down organic materials such as dirt, biological organisms (e.g. algae and mould), and air borne pollutants (e.g. smog). This innovation is helping to keep concrete clean and depolute the air across European cities, most notably in Rome where the Richard Meier designed Jubilee Church is its most striking example.

CONCLUSION
During the almost two centuries since Joseph Aspdin realised the potential of Portland cement, the wider concrete industry has achieved notable efficiencies through a commitment to innovation.

However, as the producer of the world’s most widely used construction material, the industry must maintain this commitment to help balance commercial pressures and ecologically sound practices while the world transitions to a sustainable economy.

The challenges that face concrete are significant, and will require new ways of thinking, new definitions of success and new stakeholder engagement strategies.

Article appeared in IPENZ Engineering Insights (Jul / Aug 2012).