Innovation and emerging best practice in the concrete sector will increase in 2008, along with the launch of 'green' cement are just some of the developments ahead, according to the 2008 edition of the IRISH CONSTRUCTION INDUSTRY OVERVIEW.

Performance parameters are no longer restricted to concrete's 28 day compressive strength - the material's other properties often take priority in mix design over and above compressive strength.

The increased use of high performance concretes, flowing concretes and self-compacting concretes is set to continue in 2008, providing a range of framing options and design/construction solutions to suit the project's exact needs.

2008 will also see the advent of a new "green cement" in a bid to reclaim some of the ground lost to the more environmentally-friendly cement available in the market, as recently pointed out in Irish Construction Industry Magazine.

High Performance Concretes

There are no definitive rules for the design of high performance concretes (HPCs) but, generally speaking, they usually contain low water contents and relatively high powder contents. Cement replacement materials, such as pulverized fuel ash (pfa) and ground granulated blastfurnace slag (ggbs) have been used in concretes for a long time, and their inclusion is nearly always required in HPCs.

Other ultra-fine materials are frequently included, such as microsilica and limestone powder, to provide ternary and even quaternary blends of powder content.

The consistency of HPCs are generally of a high workability and flow, enabling faster and easier pumping and placement of the concrete, reducing labour and producing better off-form finishes.

Flowing concretes

In order to maintain cohesion and reduce bleed, sand contents of between 45 and 50% (dependent upon sand gradings) are incorporated into the mix. Relatively low water contents are required, achieved by including a polycarboxylate based superplasticiser, which also imparts the required high workability.

Self-compacting concrete

SCC contains relatively high powder contents. This is required to eliminate bleed (segregation) of the concrete and maintain its cohesion. Powder (or binder) contents are usually of the order 500 to 550 kg/m possible, with judicious mix design, to produce SCCs of up to 100

When placing SCCs, remember that the material should not be allowed to "free-fall", since this will entrap air in the concrete which will not expel itself and, consequently, leave unsightly blemishes on struck surfaces. maximum, although the optimum is 10 to 14 mm.

This article is an extract from IRISH CONSTRUCTION OVERVIEW 2008 - TO READ FULL ARTICLE CLICK HERE TO SUBSCRIBE!