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Winter 2004/2005

Although topical in consequence of the Latham-inspired initiatives and

increasingly recognised as being a merited solution to the challenge of providing

optimum value, off-site prefabrication is not a new concept. Architecturalprecast concrete panels have been produced off-site for many decades and are

increasingly being specified to clad a wide range of new buildings including commercial and

civic office schemes, residential, retail and leisure developments as well as hospitals and

schools. Despite this trend, there are many building projects that fail to benefit because

the advantages of precast cladding construction are not fully considered early enough.

Off-site prefabricationChairman of the ACA, Stephen Maddalena considers the

advantages of precast cladding

The direct and incidental advantages of

precast cladding construction are many and

varied. Importantly, they valuably contribute

to enhancing quality and safety, to improving

efficiency and productivity and to providing

programme and price certainty.

Designed by Chantrey Davis

and Shepherd Design

and built by Shepherd

Construction, the Discovery

Dock development in Canary Wharf, is

predominantly clad in reconstructed stone

panels supplied and erected by Techrete

(UK) Ltd.

The largely residential development,comprises three blocks; 14 storey, 16 storey

and the 25 storey tower. The panels are in

the main double-punched window units,

and were delivered to the site, following

the installation of the windows at Techretes

factory by Parry Bowen, the curtain wall

subcontractor. Typically 6m x 3m and

weighing up to 9 tonnes the panels were

produced with cut-outs to accommodate

the cantilever support beams for the steel

balconies.

Although there was very good panelrepetition, it was necessary to manufacture

several challenging shapes, which in some

cases resulted in the adoption of a two-stage

casting process.

With such expansive areas of cladding

it was important to minimise panel-

to-panel colour variation and a new

mix was developed by Techrete to

provide as much colour stability as can

be achieved, using natural materials

The panels were fixed to the

reinforced concrete frame, where

the load was transmitted via integralcorbels on the rear of the panels

adjacent to the columns.

The restraint fixing was via channels

typically cast into the underside of

the post-tensioned floor slab, where

accurate positioning of cast-in fixings

has a substantial bearing on the

economic and smooth running of

the cladding system. Insulation and

horizontal fire stopping was also

included within the precast concrete

cladding package.

Rising high at Discovery Dock

continued on page 2

continued on page 3

Design matters

Innovation in production methods and

significant investment in labour and plant

resources enable architectural precast

concrete panels to be provided in an

increasing range of finishes and facings,

shapes and sizes to suit the requirements of

individual projects.

Finishes and facings

A comprehensive range of cladding finishes

is available ranging from lightly textured

reconstructed stone and polished concrete

finishes to coarser washed exposed aggregate

surfaces. Aggregates and cements can be

selected to suit colour preferences. Precasting

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effectively allows the pre-assembly of natural

stone, granite, brick and terracotta tile facings

with a reinforced concrete backing, a single

panel perhaps incorporating 100+ facing

stones or 1000+ bricks.

Natural stones and granites are usedmore economically than with traditional

construction methods as they can be

produced in thinner sections. Panels may

include a mix of finishes and facings that

would otherwise demand separate trades.

Shapes and sizes

Fresh concrete is an extremely mouldable

material allowing complex shapes to be

formed. Panels can economically incorporate

cill, coping, soffit, window reveal and special

sections, especially where repetitive. Large

panels avoid the need for secondary structurefor their vertical support and lateral restraint.

Grid-width units can reduce mid-span

loadings onto the structural slab edge.

Panel sizes are usually limited by site craneage

or transport constraints. Limitations may be

overcome by using low-loader trailers that

allow storey-height panels to be delivered

vertically. Reduced wall thicknesses with

precast cladding panels can increase net

lettable floor area.

Techrete, a leading manufacturer

of architectural precast

concrete in Ireland and the

UK, has invested 5 million

in an extension to its UK works at Brigg,

making it one of the most modern factories

in Europe. This reflects the companys

increasing volume of business in the UK.

Plant director John Stothard commented,

This expansion will create more space for

conventional production, as well as housing

a new robotic plant to streamline the

production of architectural concrete.

A key feature will be a carousel system in which

steel moulds will travel to the operative rather

than visa versa. The aim is that all curing andfinishing will be contained within the building,

thus creating a better working environment

and a controlled curing regime for the panels.

According to Stothard, The advantages

are that each product will be finished in a

controlled environment regardless of the

season and external areas will only be used

for storage of completed units. Achieving this

is quite a challenge as much of the equipment

is bespoke and must be adapted for the

special needs of architectural concrete.

The new building and offices are constructed of

Techretes precast concrete sandwich panels,

which provide a complete wall solution.

TECHRETE INVESTS IN UK PLANT

Off-site prefabricationcontinued from page 1

Quality matters

Panels are produced by skilled

craftsmen, motivated by long-

term employment prospects, in a

purpose-built factory environment

using specialist equipment. Each

stage of manufacture is subject

to inspection in accordance with

an independently certified quality

system, and finish and dimensionalaccuracy are checked before

delivery.

Sustainability matters

Precast panel construction produces negligible

waste, just enough concrete being batched

to fill available moulds. And at the end of the

economic life of a building, the precast panels

may be refurbished for re-use or crushed for

recycling.

Functional matters

Precast concrete cladding produced inaccordance with BS 8297:2000 has a life

expectancy of 60+ years and is generally

maintenance-free. Dense concrete is air-

and water-tight, giving superior weathering

performance and corrosion resistance. Joints

between panels are usually filled with sealant.

The thermal mass of concrete serves to reduce

peak heating and cooling loads. Insulation can

readily be incorporated either as a lining to the

internal face of a panel or as a core between

two concrete layers, achieving U-

value requirements of 0.35W/m2

Kand better. In addition, concrete is

an inherent sound insulator, non-

combustible and fire-resistant.

Construction matters

Precast cladding panels are erected

on site by specialist teams trained

in safe handling and fixing, typically

without the need for an external

scaffold. Panels are delivered on

a just-in-time basis, allowing large

areas of the frame to be rapidly enclosed

to give an early start to weather-sensitive

following trades. Window apertures within

the panels can be framed, glazed and sealed

before delivery.

In addition to issues of quality and practicality,

each of the above points correspondingly

contributes financial advantages. Off-

site prefabrication and increased on-siteproductivity, especially using the largest units

that are practical to deliver and handle at site,

facilitate optimum value. Similarly, decreasing

the dependence on site-based activities

helps stabilise the total construction cost and

shortens construction periods, at the same

time reducing financing costs. However, it

should be recognised that all these advantages

can only be attained by early involvement of

the specialist precaster.

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Rising high at Discovery Dockcontinued from page 1

Trent Concrete recently

completed its 2.3m

cladding contract at Belgrave

House, a high-profile office

development at the rear of Victoria Station

on Buckingham Palace Road in London.

The contract was awarded following a

two-stage tender process, with Trents

previous successful cladding work with

contractors Sir Robert McAlpine (on the

new Bull Ring development in Birmingham)

proving influential.

Trent designed, manufactured and erected

350 units in total. In the main these were

two-storey mullions, 7.5m high, with a facing

of deeply profiled natural Portland stone, and

8.5m long spandrels with projecting Portland

stone sills. Trent was also responsible for

600m2 of handset in-situ Portland stone

cladding. In addition, 1000m2 of matching

reconstructed stone cladding for the servicecore and plant room were produced.

This combined natural and reconstructed

stone approach provides a high-quality, cost-

effective solution. Natural stone is used on

the main elevations, whilst reconstructed

stone is used elsewhere and provides an

extremely good imitation of the natural stone

in both colour and texture.

Combined natural and reconstructed Portlandstone for Belgrave House facade

Erection of the 880 or so panels was completed

in approximately seven months, with a month

or so overlap as the double mastic pointing was

applied by a youthful but very professional team

of abseilers. Serious consideration has to be

given to wind conditions at Canary Wharf, when

formulating a programme for this type of system;

crane down-time of 40% is not uncommon.

A further challenge to be addressed was

negotiating the cantilever formwork at rooflevels, this was achieved by using a C hook

which circumnavigated the obstruction and

resulted in a smoother operation than had been

envisaged.

Award for TrentThe Experian Data Centre in Nottingham

is the winner of the Building category

in this years Concrete Society Awards

held at the London Marriott Hotel on

4 November. The judges commented

Viewed from the front, the building is

striking: indeed its innovation is in the

appearance. Low rise, precast, pigmented

concrete units have been differentially

etched and are of various lengths to

provide a bomb-resistant screen with

unspectacular but effective windows. The

building is unobtrusive and entirely in

harmony with the surroundings.

Architect for the project was Sheppard

Robson, main contractor Bowmer &

Kirkland Ltd and the precaster Trent

Concrete Ltd.

The project also benefited from maximising

the use of precast and specification of alarge-panel scheme. This enabled rapid

construction and the early enclosure of a

weatherproof envelope, allowing follow-on

trades to start sooner.

Client: Belgrave House Development Ltd &

JER Victoria Ltd

Contractor: Sir Robert McAlpine Ltd

Architect: Squire and Partners

Engineer: Whitby Bird and Partners

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Arup Associates design of this

new office block for British

Land incorporates an innovative

solution to the construction of

its facade, albeit founded on the traditional

principle of a load-bearing structure.

The facade includes storey-height panels of

Bavarian limestone and reconstructed stone

finished precast concrete spandrel units, both

acting as structural elements.

The natural stone panels, which serve as

the perimeter columns, were provided by

Stone Cladding International. Each column

was constructed as a set of five solid blocks of

stone that were pre-tensioned with steel tie-

bars to prevent their splaying under load.

The precast concrete spandrel units at each floor level provide the connection between

the stone panels and the steel beams that tie

the facade back to the main structure. The

precast spandrels were manufactured and

delivered by The Marble Mosaic Co Ltd,

typically as 6m-long units. The concrete

mix and surface finish specifications for their

manufacture were developed to match

An Innovative Solution

Architectural Cladding Association 60 Charles Street, Leicester LE1 1FB.

Tel: 0116 253 6161 Fax: 0116 251 4568 Website: www.britishprecast.org/aca

A product association of British Precast

Member CompaniesDecomo UK Ltd, 180-186 Kings Cross Road, London, WC1X 9DE. Tel: 0207 689 8058. Contact: Paul Desmet.

Redland Precast Concrete Products Ltd, 15/F Kai Seng Commercial Centre, 4-6 Han Kow Road, Tsimshatsui, Kowloon, Hong Kong.

Tel: 00852 2590 0328. Contact: Trevor Gregory.

Techrete (UK) Ltd, Warren Court, Feldspar Close, Warren Park Way, Enderby, Leics, LE4 5SD. Tel: 0116 275 0785. Contact: David Kennell.

The Marble Mosaic Company Ltd, Winterstoke Road, Weston-super-Mare, BS23 3YE. Tel: 01934 419941. Contact: Stephen Maddalena.

Trent Concrete Ltd, Colwick, Nottingham, NG4 2BG. Tel: 0115 987 9747. Contact: David Walker.

the appearance of the natural stone. Each

spandrel unit required a number of stainless

steel boxes to be cast-in with exceptional

accuracy to suit the irregular locations of the

fixing positions on both the stone panel and

steel beam.

The stone panels and precast spandrels were

erected by William Hare for Bovis Lend Lease.

With over twenty years experience of providing

architectural concrete solutions on the Continent,

Belgium based Decomo, entered the UK market

in 1998.

With such prestigious projects as the European Parliament Building in

Strasbourg and the Hilton Hotel in Paris to its credit, it was not long

before the companys expertise and flair became recognised by many

leading UK architects and contractors.

An impressive portfolio of completed projects, this side of the Channel,

built up over the last six years, is something Decomo UK Ltd is now

rightly proud of. Amongst these are the Guinness Headquarters in

London, the Fenwick Store in Canterbury and the Royal Academy of

Music in London.

Currently, three major projects are being undertaken, at Wembley

Park Station, Chesham House and the University College, London.

Offering complete design, supply and installation packages, the

companys ethos is based on providing client satisfaction and it is

always striving to give that little bit extra in order to enhance both its

product and service.

This is evident, not only in the extensive range of finishes and colours

available, but also from the substantial investments made in production

facilities, equipment and people.

This year, alone, a new finishing building, covering an additional

3500m2 has been opened in Mouscron, Belgium, where all productionis undertaken. A new office building and showroom is also planned for

construction next year.

In the UK, offices have recently been opened in London, where Paul

Desmet has been joined by Andrew Tyrrell, formerly with Histon

Concrete Products Ltd, to provide closer client support as the

company realises its targets for continued growth in a market which it

believes holds much potential.

Welcome to new member