Anglo-Dutch pavement evaluation

International Survey Glass reinforced c e m e n t aids floods project A novel use of glass reinforced cement has speeded up a river control s c h e m e in the UK. The job involved a 300 m stretch of waterway which had caused problems to local residents because of its tendency to flood. The plan was to provide it with a concrete channel, 200 m m thick at the base, 3.5 m wide, and with banks lined to a height of 1.8 m. The problem was to find somewhere for the river water to go while the work was going on. Diversion elsewhere was not practicable because of the built up nature of the site, and the noise of pumps, which would have had to run for several months, was also considered unacceptable. Sandbagging would have been an alternative, but would have been laborious, and time consuming. Local contractor, Clugston Construction, c a m e up with an alternative, using prefabricated sections of glass

reinforced cement. The sections are 1.2 m long and 1.92 m m wide and designed to take a flow of 2 m 3. In normal use, as for example in irrigation schemes, the sections are bolted together through a rubber gasket, but Clugston found that for this temporary flow diversion they were able to get by lining the section with polyethylene sheet. While the water flows through the temporary channel this provides, the contractor has been able to concrete half the bed. The temporary channel is then moved onto the concreted section while the other half of the bed slab is completed. The sections, manufactured by Velmac UK Ltd, using Cemfil AR glass fibre reinforcement supplied by Fibreglass Ltd, weigh only 70 kg, and can be easily repositioned by two men. So successful was the technique that a second set of GRC sections has been delivered to extend the area on which the contractor can work.

Further information: Pilkington Brothers PLC, Prescot Road, St Helens, Merseyside, WAIO 3TT

Pfa for water retention

Biwater Shellabear from the site batching plant had far

A concrete reservoir in the UK has used pulverised fuel ash in its construction, with excellent results. At Highwood reservoir, the consultants, Rofe Kennard and Lapworth, permitted the use of pfa in the specification of the two grades of concrete - a minimum 28 day cube strength of 15 N / m m 2 for the mass concrete and concrete binding, and a 28 day strength of 25 N / r a m 2 for the reinforced concrete. In fact the pfa concrete produced by contractor

higher compressive strengths. The pfa, from Pozzolanic Lytag Ltd, enable the contractor to reduce the water/cement ratio whilst maintaining high workability. The floor slab was easily placed from dumpers, and the cohesiveness of the mix was sufficient for the 6.5 m high wall sections to be placed in one operation without any segregation. Early strength of 16-16 kM/mm 2 gained in one day permitted the tight scheduling of site operations required by the programme.

Anglo-Dutch p a v e m e n t evaluation Sir William Halcrow and Partners, UK, and Netherlands Pavement Consultants (NPC) have agreed to co-operate on a project basis for pavement evaluation work in UK and overseas. Marketing will be aimed at highway and airfield authorities and both parties will work together under the name Halcrow Pavements Group. The Group's evaluation techniques will be based primarily on the use of the Falling Weight Deflectometer (F'WD). The FWD measures deflection of the pavement surface resulting from the local application of a test load. The test load is applied by a weight falling on a 300 m m diameter plate which rests on the pavement. Springs attached to the upper side of the plate onto which the

weight falls are designed to influence the application of the load such that a moving wheel load is simulated. Deflections are measured by geophones at varying distances from the plate and are processed by computer to derive strength parameters for the pavement layers. These, together with traffic data, are then used to predict residual life and, where necessary, the thickness of a strengthening overlay. In addition to the pavement evaluation techniques described below, the Group will provide services including overall pavement m a n a g e m e n t systems, full pavement condition surveys, material investigations, pavement failure investigations and full consultancy services for pavement rehabilitation and strengthening projects. Both parties have proven skills in this field. During its

CONSTRUCTION & BUILDING MATERIALS Vol. 1 No. 1 MARCH/APRIL 1987

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International Survey seven years of existence, NPC has been involved in m a n y projects in m o r e than 20 different countries. These projects were related to FWD road and airport pavement evaluation, asphalt mix design, laboratory testing and pavement design using local materials. In the Netherlands, NPC has worked for the Dutch Ministry of Transport and for the principal cities like Amsterdam and Rotterdam as well as provincial authorities. In 1977 Halcrow, with a history of m o r e than 100 years of consultancy, purchased a FWD with the prime object of testing road pavements in the United Arab Emirates and developing an economical design based on the properties of the materials to be used. This work was reported to the International Road Federation Conference in Nairobi in 1980. Since then, the technique of testing airfield and road p a v e m e n t s has been advanced and refined to

Better r o a d s u r f a c e s in S w e d e n Surface treatment of roads with loose gravel is currently used for 40% of roads in Sweden. The result is a safe and relatively c h e a p coating when the gravel is bedded-in, but it also m e a n s speed limits and the risk of broken windscreens during the first week after it has been laid. However the Swedish road authority, V&gverket, is looking into improving surface treatment so that the roads can be cleared and function normally after only one day. Concrete is used to a small extent but it does not stand up well to ground frost. V~igverket is undertaking research in this area and taking into account developments in other countries. One of the best materials from a safety point of view is drainable asphalt, but this is expensive. Since the water drains away, the surface is left dry and the risk of water planing is reduced substantially. Winter roads is another area where V~igverket are investigating new treatment methods. Better information systems are being developed which give quicker information on changes in the road condition. This enables

Guide to testing c o n c r e t e S o m e sections of British Standards BS 1881, have been revised and published. Part 125 Methods for mixing and sampling fresh concrete in the laboratory is a revision of Clause 3 of BS 1881 : Part 1 (now withdrawn) and describes the preparation and batching of the individual materials and the mixing and sampling of concrete in the

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today's high standards. Today, m o r e than ever before, e c o n o m i c conditions require that m a x i m u m benefit is obtained from the funds which are available for pavement maintenance and strengthening. At the s a m e time, rapid growth in the n u m b e r of commercial vehicles and the damaging power of heavier axles d e m a n d ever increasing levels of service from highway pavements. Airfield pavements are also subjected to m o r e severe loadings due to heavier aircraft and the time available for testing and subsequent maintenance and/or strengthening is usually highly restricted.

Further information from Halcrow Pavement Group, Vineyard House, 44 Brook Green, London W6 7BY or from Netherlands Pavement Consultants bv, Postbus 83, 3870 CB Hoevelaken Hogebrinkermeg 19, Netherlands.

salting to be carried out at the right time and to the right amount. Research is also being carried out into using a m o r e effective and environmentally advantageous type of salt. This salt, CMA (calcium m a g n e s i u m acetate), reduces the freezing temperature to --12°C in comparison with - 6 C for the salt currently being used, and furthermore, CMA does not lead to rusting. At present CMA costs 20 times m o r e than the salt now being used but investigations are underway to see if CMA can be produced more cheaply. Another problem V~igverket has to cope with is tracks worn in widely used roads which have been shown to be caused by the studs in winter tyres. It is mainly when the roads are d a m p that the studs free asphalt particles from the road and wear increases dramatically with traffic speed. Since there is little hope of persuading drivers to drive m o r e slowly it has been decided to cover the m o s t highly used roads with a stronger (and m o r e expensive) asphalt which is m o r e resistant to wear from studs.

Details from Pro lnfo Marketing, Box 3066, S-811 03 Sandviken, Odengatan 1 7, Sweden.

laboratory. It c o m p l e m e n t s BS 1881 : Part 101, which covers the sampling of concrete on site. It is recognised that a wide range of concrete mixes has to be prepared in the laboratory so provision is m a d e for modifications to the standard procedure and their detailed reporting. It is not, however, intended to cover special concrete mixes prepared for research. BS 1881 is now in two series: Part 101 onwards with

CONSTRUCTION & B U I L D I N G MATERIALS Vol, 1 No. 1 M A R C H / A P R I L 1987