Coloured concrete offers design flexibility

Concrete, Apr 2007 by Shroff, Roger

Concrete is one of the world's most versatile building materials, offering flexibility of design with durability and strength. Recognising the need for specific concretes for certain applications, Lafarge has created two new ranges of mixes.

The colour blend

Artevia colour is a range of proprietary concretes offering a choice of colours and is suitable for use in a variety of applications. The product versatility means coloured concrete is a viable and aesthetically pleasing alternative to other materials, allowing architects to specify coloured concrete at the design stage of a project.

Artevia colour is an integral through colour system, using high-quality synthetic iron oxide pigments supplied from Lanxess, a pigment blend specialist. The liquid colours system offers:

* excellent pigment dispersion

* uniform colour

* 28 standard colours - with colour matching available

* UV-stable, fade-resistant colours.

The colours are produced by Lafarge at the company's national colour centre-based in Sheffield. Using a colour metering system from Pigment Systems Ltd, accurate colour blends are achieved and can be tailored for any cement content.

Along with a range of colour options, it is also available in the following finishes, and can be used in either vertical or horizontal applications:

* exposed aggregate

* polished

* textured surface

* brush or tamped.

Artevia colour can be specified for most concrete applications and Lafarge Readymix has designed a range of suitable proprietary mixes:

* Domestic use paving (ART 1) - this mix provides a durable coloured concrete finish suitable for generalpurpose domestic use. The concrete can be tamped, brushed or trowelled to finish.

* Commercial use paving (ART 2) - offers design solutions for a range of internal and external applications, including parking bays, bus lanes and demarcation zones.

* Commercial use structural (ART 3) - this can create structures that blend with local environments, such as precast components, columns, bridge abutment and parapets and building façades, all enhancing design features.

* Printing (Stamped) concrete (ART 4) - suitable for use throughout spring, summer and autumn.

* Printing (Stamped) concrete (ART 5) - is suitable for winter working.

ART 4 and 5 have been specifically designed for imprinted (stamped) concrete and have surface abrasion values of 'special' as designated in BS 8204(1). They can be used with Artevia stamping tools to provide a range of patterns and surface textures, providing an economic solution to coloured imprinted concretes.

A significant benefit of an integral colour is the saving in labour during installation, and because the colour is applied to the entire matrix, the colour remains even if the surface is chipped or damaged.

Stamped and imprinted concrete

The second new range is Artevia Print, designed specifically for stamped and imprinted concrete applications to receive coloured surface hardeners. Key factors are the inclusion of air entraining agents and fibres as standard ingredients, along with optimum fines content. This simplifies the ordering process and ensures correct concrete can be specified and supplied with confidence.

EM mixes

To ensure the correct grade of concrete is used for the specific purpose of imprinted concrete, Lafarge Readymix has developed a range of IM mixes, designed to comply with Concrete Society guidelines and available with 20mm and 10mm aggregates. CEM I is the preferred option but depending on conditions, blended cements are available.

The Concrete Society's imprinted Concrete - Model Installation Clauses and Guidance Notes recommends the following specification for imprinted concrete:

* Cement type CEM I with an option for blended cement CIIS (35% blast furnace slag) or type CIIA-V (20% PFA).

* Air entrainment to provide resistance to freeze/thaw.

* Fibres 0.6-0.9kg/m^sup 3^ - this produces a more cohesive concrete with reduced bleed, improves surface wear qualities and reduces plastic shrinkage cracking.

* Minimum cement content 320kg/m^sup 3^ - this can be reduced for 20mm aggregates.

* Watencement ratio max 0.60 - some aggregate combinations at lower cement contents, particularly 10mm aggregate may not comply.

* Fines content 50-60%.

Lafarge Readymix has created a simplified and accurate method of specifying all of the above (depending on the required setting time).

Artevia IM mixes have optimum fines content for given aggregate type and size to ensure easy placing and finishing characteristics and are compatible and can be used in conjunction with coloured surface hardeners. Twentythree standard colours of Artevia print are available from national and regional colour centres; a colour matching service is also available.

Concluding remarks

The increasingly versatile product market for coloured concrete makes it an aesthetic alternative to other materials, and allows architects to specify it at the design stage of projects.

Reference:

1. BRITISH STANDARDS INSTITUTION. BS 8204: Screeds, bases and in-situ floorings. 2004.