International survey

International Survey Fast flooring Recent visitors to Mowlem N. West's Wirral Leisureland site got a glimpse of one of the latest techniques for laying ground supported concrete floor slabs. A number of visitors intending to view the system in action were surprised when they arrived in the afternoon to find that much of the first bay (approximately 2,000 m 2 of 175 mm deep slab) had already been cast. The speed of construction was mainly due to a new piece of laser-levelled flooring equipment used by subcontractors Ward Bros. (and supplied by John Kelly Lasers Ltd). It is mounted on twin axles and has four-wheeled Transportation of laser screed. The carriage slews for ease of drive and four-wheeled steering. loading The extremely mobile carriage supports a counter-balanced telescopic boom with a reach of more than 6 metres. At the end of this f boom is a 3.66 metre wide screed carriage assembly. Laser beam receivers mounted at each end of the carriage detect a pre-levelled laser light emitted from an indepenent source positioned on site. An onboard computer then autoatically and instantaneously adjusts the carriage level to follow the laser reference plane. This automatic adjustment is carried out five times a second using the machine's hydraulics. During operation the boom is first extended and then lowered. The screed carriage is then drawn across Fig 2 Laser screed operating at periphery of main floor area to be cast the newly placed concrete. One pass of the carriage assembly will level the batching plant at about 0.9 kg is aimed at so that the addition of and compact approximately 22.3 m 2 per cubic metre of concrete. The the fibres can reduce it to a more of floor slab in about two minutes presence of the fibres will produce manageable 75 mm slump. Usually a lower slump, but the 'placeability' the 19 mm long steel fibres are (for floors up to 300 mm deep). The equipment can be used for of the concrete is unaffected. When added at the batching plant at the standard reinforced slabs or, as in using steel fibre reinforcement a rate of 50 kg per cubic metre of this instance, in conjunction with a standard concrete mix can also be concrete. Plasticisers may be used both types of fibre fibre reinforcement. Both poly- used. As with polypropylene fibres with ropylene and steel-fibre reinforce- a slump of about 125 mm minimum reinforcemenL A typical mix design for a standard strength concrete ents have been used successfully using a fibre type reinforcement is with the laser screed. shown in Table 1. This report on the laser.leveUed Polypropylene reinforcement can The concrete is compacted and be used with a standard concrete flooring equipment was submitted levelled at such speed that no side mix. In the case of Wirral by R. Grew, School of Architecture formers are required. Power floating and Building Engineering. The Leisureland a Grade 30 concrete if required can usually be carried out was used. The fibres are added at University of Liverpool, UK.

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CONSTRUCTION & BUILDING MATERIALS Vol. 5 No. 3 SEPTEMBER 1991

International Survey within a few hours. Construction joints at about 6m centres are then cut into the surface of the slab the following day. Eliminating formwork, mesh reinforcement and convenional construction joints obviously produces a large cost and time saving over traditional long strip flooring methods. A typical industrial floor slab of 1,000 m 2 would normally require perhaps 5 to 6 working days to complete. The same slab would require only about 2 working days to complete using the laser screed system. Mowlem found that not only did the system increase site productivity but calculations indicated a saving of up to £]/m 2 by omitting formwork and related costs. Another £]/m 2 could also be saved if the floor loadings required heavy reinforcement to be used. Laser guidance and levelling systems are also now being introduced in conjunction with graders, crawler dozers and pavers with many benefits. Precision levelling and control to within _+ 5mm is obtained by tilt dozers or graders fitted with the system. This prevents overdigging of the site thus reducing the import and export of fill materials.

Table 1 A typical mix design Concrete requirements: compressive strength @ 28 days Mix Design:

Cement (OPC) 20 - 5ram aggregate Sand Free water Plasticiser (Conplast P509)

390kg/m s 1190kg/m 3 680kg/m 3 175 kg/m 3 121/m 3

Water/Cement Ratio Slump (prior to addition of fibres)

0.45 max. 125 mm

Slump after addition of fibres

Fig 3

Fig 4

40 N.mm ~.

75 mm

Screed carriage shown pnor to concrete floor surface being levelled off with a wide float

Machinable ceramic replaces asbestos

Readymix delivery of concrete to main working

A silica-based machinable ceramic with excellent thermal shock resistance to 1100°C (2000°F) which can be used as a replacement for asbestos bearing materials is now available from Aremco Products Inc. Aremcolox 502-1250 has a low coefficient of thermal expansion of 0.3 x ]0-6/°F making it a suitable replacement for asbestos insulation, RF fixtures, furnace links, melting troughs, hot press dies, and high temperature microwave insulation. The material is easily machined or drilled with conventional tooling with no post curing required. Aremco Products Inc., p.o. Box 429, Ossining, NY 10562, USA. Fax: +1-914-762-1663

CONSTRUCTION & BUILDING MATERIALS Vol. 5 No. 3 SEPTEMBER 1991

area

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International Survey Specifying timber preservatives for Europe The BRE claims good progress in the development of the European performance standards covering the durability of wood and wood-based products. These standards are needed to support the structural timber Eurocode (EC5); BRE is deeply involved in the technical c o m m i t t e e and its associated working groups. A new approach to specification of preservative.treated timber will be required when the European standards come into force, in the system laid out in draft standards, the level of treatment will be used to check compliance. A specifier considering durability requirements for a timber commodity will first have to assess its service environment in terms of five hazard classes. Depending on the natural durability of the wood or wood-based material to be used, this will indicate the need for treatment.

Any preservative selected must c o n f o r m to the p e r f o r m a n c e requirements associated with the hazard class and the subsequent t r e a t m e n t must achieve the penetration level required for that class - ten levels are defined. The standards covering these stages also include tolerances in response to treatment and labelling requirements. Because of the wide range of service conditions encountered in Europe, it is likely that national interpretative documents will be needed to assist the specifier. A seminar to report progress on this work is planned for November 1991; there are considerable changes since the seminar held last June. For more information about the new standards, contact Dr Reg Orsler, Timber Division, Building Research Establishment, Garston, Watford WD2 7JR, UK.

Plastic house is a living laboratory

The Fourth RILEM International Symposium on Fibre Cement Composites will be held at the University of Sheffield on 20-23 July 1992. One-page abstracts of unpublished papers have been called for. The following deadlines will apply: Receipt of abstracts - 15 September 1991; Approval of abstracts - 30 September 199]; Receipt of draft papers - 15 December 1991; Receipt of final manuscripts - 15 February 1992. All papers will be reviewed. The final manuscripts will be typed on camera-ready paper to author's instructions. Send three copies of abstracts to: Mrs r'lorma Parkes, SIRIUS, Department of Mechanical and Process Engineering, University of Sheffield, Mappin Street, Sheffield, $1 3JD, UK. Phone + 4 4 (0)742 768555 ext 5169. Fax: +44 (0)742 753671.

Welded SS pipe

A two-storey family house has been inside the wall skin provide for built by GE Plastics in Pittsville, heating and cooling more efficiently At Massachusetts, using high than forced hot air systems. performance engineering plastics. the heart of the house the Total The house will serve as a living Environmental Control (TEC) system laboratory to demonstrate and provides air conditioning, energy investigate potential applications of management and gas and electrical plastic materials in building and control. The system works by construction. The project, known as filtering air from outside, adjusting Living Environments, will investigate it to the required heat and humidity five primary systems: structural and circulating it through the radiant components; utility systems for wall panels. TEC also filters, routing internal service networks; conditions and h e a t s water. domestic equipment such as water Engineering plastics are used for heaters and refrigerators; non- heat exchangers, all heating and structural systems, including doors cooling coils and c o m p o n e n t and fixtures; and finishing systems housings. The walls, roofs, posts and floors to personalise interior and exterior align and bond with mouldings in surfaces and trims. The house has precast walls with universal extrusions to form airtight glass reinforced thermoplastic skins. seals and give speedy assembly. The house will be continually T h e s e e n c l o s e a low density t h e r m o p l a s t i c foam core and remodelled and refitted to explore moulded channels to provide service new ideas, new materials and new distribution. Radiant panels built building processes.

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Fibre c e m e n t composites

Sumitomo Metals, jointly with its subsidiary Sumikin Stainless Steel Tube Co. Ltd., has developed ferritic stainless steel welded pipe and tubes. They are manufactured by use of a 6 kW-class CO2 laser as the welding heat source, with highfrequency preheating when necessary. This is claimed to be the first process of its kind. Welding of pipe by CO2 laser allows deep penetration of welds at comparatively low heat input, resulting in higher toughness and corrosion resistance in pipe weld than can be provided by a conventional TIG or plasma welding process. In addition, the new approach offers easy welding of ferritic stainless steel, which is difficult to

weld by TIG or plasma welding techniques. Applications of these products are expected in heat exchangers and chemical-plant piping.

CONSTRUCTION & BUILDING MATERIALS Vol. 5 No. 3 SEPTEMBER 1991