Adhesives in the construction industry: Materials and case histories

Adhesives in the construction industry: Materials and case histories

A d h e s i v e s in the Construction Industry: Materials and Case Histories J D N Shaw" Abstract Traditionally adhesives for the construction indus...

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A d h e s i v e s in the Construction Industry: Materials and Case Histories J D N Shaw"

Abstract

Traditionally adhesives for the construction industry have been based on natural products. Over the past four decades many reactive adhesives on formaldehyde base have been developed for use with timber.type products and polymer dispersions produced during and since the I950s are widely used by the building trade today. Fully hydrated Portland cement has been developed and is being extensively used for reinforced concrete structural repairs, often in coordination with epoxy resin or polymer latex bonding.

A wide range of adhesives have been used for many decades in the construction industry. Historically, many of the adhesives used were based on natural products from many parts of the world and were highly effective as adhesives in essentially non-structural applications. As a result of World War I! in the early 1940s, many of the natural product raw materials for adhesive manufacture were not obtainable and consequently, effective adhesives had to be developed based on raw materials which were available or could be synthesized from crude oil or more especially coal. One of the most notable of the early wartime adhesives was the continued development o f phenol/ formaldehyde, resorcinollformandehyde and urea formaldehyde adhesives for wood, in particular for the construction of the Mosquito fighter aircraft. Over the past 4 0 years, reactive adhesives, based on formaldehyde, have continued to be used in the off site manufacture of many timber based building materials including plywood, chipboard, resin bonded structural beams, etc. There are now a range of British Standards covering the technical performance of these adhesives in tests which cover their long term performance in diverse application and service conditions. 1-5 in the 1940s, the first synthetic polymer dispersions were produced and began to be widely used in the manufacture of the first emulsion paints. These were then based almost entirely upon polyvinyl acetate (PVAC) and still it continues to be the basis of many emulsion paints today, although other polymer dispersions such as acrylics and PVAC copolymers are also used. It was realized in the 1950s that PVAC dispersions were also a basis for the formulation of adhesives for a wide range of building materials from adhesives for floor screeds to timber adhesives - in fact, adhesives to bond any slightly porous building materials. By the mid 1960s adhesives based on Polyvinyi acetate had become the most universal adhesive in the construction industry. Once an adhesive becomes so widely used in the construction industry where, on site, the control of "SBDC o n s t ~

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their use may be rather limited compared with adhesives used under controlled factory conditions, problems inevitably occur and, as a result, PVAC adhesives have been used in a number of applications where good 10ngterm performance of the adhesive under severe service conditions was required. These included their use as a bonding agent for external rendering, adhesives for external brick slips and floor screeds in wet service conditions, repairs to damaged precast concrete units, etc. Relatively short.term tests had been carried out to demonstrate the excellent performance of polyvinyl acetate based adhesives in wet service conditions and at that time it was considered that by careful formulation, PVAC adhesives did have sufficient stability to wet alkaline service conditions not to break down when used as external adhesives for bonding to concrete. It is now accepted that PVAC homopolymer adhesives, however carefully formulated, are not adequately resistant to wet alkaline service conditions because in time the polymer breaks down by saponification. Depending upon the precise formulation of the PVAC adhesive used and service conditions, they break down in approximately five to ten years and evidence as to whether the adhesive was used during construction may disappear as the breakdown products are water soluble. It is important to note that PVAC homopolymer adhesives are still considered excellent adhesives for bonding many building materials for service in dry internal applications. 6 Similar adhesives suitable for service in external or wet service conditions based on other polymer dis. persions such as styrene butadiene rubbers, acrylic polymers and copolymers of vinyl acetate with other monomers such as ethylene or vinyl 'Versatate' which are not prone to alkaline saponification are now widely available. In recent years, the repair of concrete structures has become a significant part of the construction industry. Many of the repairs are necessary because the steel reinforcement within the concrete has corroded and expanded causing the concrete cover to crack and eventually fall off if remedial action is not taken. In many cases, the inadequate concrete cover is removed and replaced by conventional concrete or often a polymerbased repair mortar. In a repair situation, the bond CONSTRUCTION & BUILDING MATERIALS Vol. 4 No. 2 JUNE 1990

between the parent concrete and the repair material is most important. Fully hydrated ordinary Portland cement is itself an excellent adhesive provided that the prepared surface of the parent concrete can be maintained adequately wet to ensure proper hydration o f the cement matrix at this interface. This in practice is often difficult to achieve and an epoxy resin or polymer latex bonding aid is often used to ensure a reliable bond between the repair material and the parent concrete. With an epoxy resin bonding system specifically formulated for bonding green uncured concrete to cured concrete, a bond is achieved which is significantly greater than the shear strength of good quality concrete or mortar. 7.8 Polymer latex bonding aids which are applied to the prepared concrete either as neat coats of latex or as slurries with cement are widely used, since they are more simple to use and cheaper than epoxy resin bonding aids and give a good tough bond which is 'less structurar than that achieved using the right epoxy bonding aid. However, under severe drying conditions, the 'open time' for polymer latex bonding coats can be too short to be a practical method of ensuring a good bond between the repair mortar and the parent concrete.7, s An an alternative to polymer latex slurry bond coats, there are now available factory blended polymer modified cementitious bonding aids based on special spray dried copolymer powders blended with cement, fine sand and other special additives which are simply gauged with water on site and applied to the prepared parent concrete to give a stipple finish. Even when allowed to set overnight, this type of bonding aid gives a good key for the repair mortar and prevents rapid loss of water from the repair mortar, which may result in inadequate hydration and this poor bond to the repair concrete. However, application of the repair mortar whilst this key coat is still tacky is recommended wherever practicable. In some instances, the epoxy bonding aid is required to function as an impermeable barrier between the repair mortar and the parent concrete. In these cases, two coats of the bonding aid are applied and whilst still tacky are dressed with clean sharp sand. 8 This ensures an excellent mechanical key between the two coats and the repair mortar. In the construction industry, adhesives with high bond strength and high compressive strength are often required and two component adhesives based on epoxy resins and to a lesser extent, upon polyester, acrylic or polyurethane resins are used in a very diverse range of applications. It is important to note that the general term epoxy resin covers a range of ambient curing materials which vary from flexible semi-elastic coatings and sealants to epoxy resin based concretes with compressive properties higher than good quality concrete. Virtually all epoxy resins used in the construction industry are based on Bisophenol A or F resins with an epoxy equivalent weight of approximately 200 and a wide range of hardeners or curing agents based on polyamides, polyamidoamines, aliphatic polyamine, cyclo aliphatic amines and aromatic amines modified to give both the curing characteristics at site temper. atures and ultimate cured properties required. Other

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ingredients such as reactive or non reactive diluents, graded fillers and other additives conferring special properties are also incorporated by the manufacturer to give specific properties either in the cure or uncured state. The 'formulation' - the puffing together of the complete recipe - of an epoxy adhesive to meet an engineer's requirements is a complex matter and engineers cannot be expected to completely understand the complex chemistry involved. Epoxy resin adhesives used in the construction industry are often derived from formulations originally developed for high tech applications in the aircraft industry where adhesives can be applied under very controlled application conditions to very carefully prepared susbstrates. Application of adhesives in the construction industry is regrettably far less controlled and formulations have to be developed so that they are as 'user friendly' as possible. This may involve colouring the resin and hardener components so that the properly mixed adhesive has a distinctly different hue from either of the components. Ensuring the mixed adhesive will stick to damp concrete over a wide range of site temperatures 3 ° - 3 0 % C may be a further requirement. One limitation of site applied resin.based adhesives which has certainly restricted their use in the UK, significantly more than in some other countries, is that they lose their mechanical properties at temperatures above approx 6 0 ° - 7 0 ° C and become increasingly subject to rapid creep under load as the temperature rises. 9 It is important to note that the thermal concluc. tivity of resin based materials tends to be significantly lower than for conventional cementitious building materials but nevertheless this loss of strength restricts their use in structural applications to structures where the risk of fire is minimal or where the structure is designed to that loss of structural integrity does not take place owing to loss of strength of the resin material within the time period permitted by the fire regulations. Often resin-based adhesives are used in conjunction with some other form of mechanical fixing which is satisfactory for short-term loads under fire conditions bat under repeated dynamic loading in service may break down rapidly, in fact, a design philosophy of belt and braces if often used when employing resin based adhesives in the construction industry. 10 in this paper, it is not possible to review all structural applications for resin-based adhesives in civil engineering. ~u2 However, four interesting applications involving quite different application techniques or resin formulations are described in detail. • Segmental construction of bridge using stress distributing adhesives • Strengthening of reinforced concrete structures by external bonding of steel plates • Resin injection to repair cracked concrete structures • The development of an adhesive for skid resistant road surfaces

Adhesives for segmented precast prestressed concrete structures Over the past 25 years, resin adhesives have been used as stress distributing weatherproof joints for post tensioned reinforced concrete structures built from

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precast units. The first reported structures where precast units were bonded together with resin adhesives are Coventry Cathedral constructed in 1 9 6 0 - 6 2 ~3 and Choisy-le-Roi Bridge over the River Seine near Paris constructed in 1962.14 Bridge construction, in particular spectacular long span bridges, is probably the largest tonnage use of structural resin adhesive in civil engineering worldwide. The construction concept using resin adhesives is to cast precast reinforced concretes using a matched moulding technique so that the matching end of one unit treated with a thin easily removed release film is used as the form for the next unit. 28 This technique ensures that units when installed on site match very well and the resin adhesive joint is very thin (generally 1 - 2 mm). n.15 Three main factors influence the choice of resin adhesive joints.

Speed of construction In comparison with conventional OPC concrete, resinbased adhesives develop mechanical strength within much shorter times allowing much more rapid assembly of cast structures, in the famous Sydney Opera House, constructed in 1 9 3 2 - 6 7 , construction time savings of approximately 25 weeks were achieved. 16.~7The whole shell roof structure was made up from curved hollow concrete ribs to form a series of continuous spherical surfaces united from precast segments cast with matching faces and made longitudinally continuous by post tensioning across transverse epoxy joints. To enable a precision design to be accurately set out in the cast yard In addition to the speed of construction, the use of a resin adhesive in the construction of Sydney Opera House enabled the critical 'orange segment' geometry of the curved roof to be carefully checked before assembly up in the air. I~

Appearance Architects often require very thin joints so that they are as inconspicuous as possible and do not detract from the continuous flow lines of their designs. Sir Basil Spence was very aware of this benefit when he used resin bonding for the slender cruciform columns at Coventry Cathedral. In segmental construction, resin adhesives act as a stress distributing layer ensuring a uniform stress distribution across the joints and most importantly because of their dimensional stability and excellent bonding characteristics also ensure a weatherproof joint in long.term service. The stress distributing resin adhesive joint is subject to a relatively low compressive load, generally not more than 10 N mm -2. The ultimate compressive strength of the resin adhesives used is in excess of 75 N mm -2 when tested according to BS 6319, part 2. Experience has shown that creep of resin systems, often of considerable concern to civil engineers, is rarely a problem if the service stress is less than 2 0 - 2 5 % of the ultimate strength of the resin. In the case of segmental construction, the aspect ratio of the stess distributing adhesive layer is such that even at higher stresses, creep should not be a problem. In fact, the first

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bridge to be constructed using resin bonded joints in the OK, the Rawcliffe Bridge, built in 1966 used an epoxy resin adhesive formulation which is known to be much more prone to creep than the epoxy resin adhesive formulations used today. Rawcliffe Bridge with its resin-bonded joints is reported to be in excellent condition today. 18 Since then, a number of bridges have been constructed in the UK using resin bonded segmental construction, including the Byker Viaduct, Tyne & Wear (1979) 15 and Trent River Bridge (1980), East Moors Viaduct, Cardiff (1984) and Stanstead Abbots By-pass (1987).

Strengthening of reinforced concrete structures by external bonding of steel plates Much of the development of interesting novel structural uses of resin-based adhesives occurred in the early 1960s and their use in the strengthening of load bearing reinforced concrete structures by bonding on a steel plate reinforcement externally is another notable example From published literature, it would appear that the concept was developed almost simultaneously in South Africa and France in about 1965.1~,19.21In South Africa, resin-bonded reinforcement was used for the rapid emergency repair of a road overbridge damaged by the impact of a mobile crane which ruptured some of the steel reinforcement in several beams. 2° Since 1965, extensive testing has been carried out in South Africa, France, Switzedand, Japan, Belgium and the UK. This has demonstrated that resin bonding of fiat steel plates to the external surfaces of structural concrete beams, columns, etc can be a practicable and economic way of strengthening highway bridges and buildings. Because of loss of strength of ambient cured resin adhesives below 100°C, discussed above, the use of resin bond steel reinforcement has been restricted in the UK to the strengthening of highway bridges or other structures where the risk of fire is minimal or to strengthening buildings where the inherent strength of the structure prior to strengthening is considered adequate in the short term under fire conditions. The first structure in the UK to be strengthened using resin bonded steel plates was an eight.storey building in Harlow, Essex in 1966. Owing to a revision of building regulations regarding performance under very high winds, the vertical columns and lift shaft required strengthening which was achieved by bonding steel plates with an epoxy resin adhesive, lu2~° Several bridges including M5 Quinton Bridge (1974), M20/M25 Swanley interchange bridges (1977) 12 and also Brinsworth Viaduct (1983) TM have been strengthened by the use of steel plate bonded adhesive. One aspect which short-term accelerated testing could not fully prove was whether external bonded plates would prove durable in service over many years. It is now 14 years since Quinton Bridges were strengthened and apart from some very small areas of corrosion, the externally bonded reinforcement is still performing well.

Structural repair of crack concrete structues by resin injection Reinforced concrete structures are designed that the inevitable cracking of the concrete is restricted so that

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no cracks at the surface should exceed approx 100/~m thickness. For many reasons, cracking in excess of the design acceptance limits occur rather too often either during construction or during the service life of the structure, if cracks are not sealed or structurally bonded, further deterioration may occur. Before deciding the most appropriate methods/ atedals for repairing/sealing cracks, it is imperative to establish the cause of the cracking and, where a permanent structural bonding of the crack is required, to carry out any other strengthening which may be necessary. It is possible to restore the structure to the original tensile/shear strength of the uncracked concrete by injection with low viscosity epoxy resins specifically developed for repairing cracks, provided the bonding surfaces of the concrete at the crack interface are clean and sound. Cracking is caused by tensile stresses and, if these stresses recur after crack repair, the concrete may crack again. If it is not possible to establish and rectify the cause of the original cracking, it is recommended to cut out along the surface of the crack and treat it as a normal movement joint or, alternatively, to cut out a normal straight movement joint adjacent to the crack and then repair the crack by resin injection. 2'~° In the main, epoxy resin injection systems are used for structural crack repair using gravity, pressure and vacuum injection techniques. Low viscosity polyester and acrylic resins are also used but their bonding characteristics to slightly damp or even wet concrete, a common occurrence when repairing cracked concrete in the UK, are generally inferior to epoxy resin systems specifically formulated for bonding to wet surfaces. The concept of using epoxy resin injection systems as a means of repairing cracked concrete so that when repaired, the concrete again acts monolithically has been established for over twenty years and during that time some major rescues have been carried out. z2 An interesting example was where resin injection proved very effective to rebond a cold joint crack which occurred during construction of a reinforced concrete motorway bridge due to movement of the supporting formwork whilst the concrete was green23 Initially, it was thought that this movement had purely caused this cold joint of width approximately 0.5 mm and sufficient resin was injected to more than fill this crack. Subsequently, it was realised that the movement had also produced voids underneath the reinforcement and further extensive injection of resin was undertaken to completely fill all the voids and the crack. To demonstrate to the engineers that the resin had restored bond across this cold joint crack, a 100 mm diameter core was drilled at an angle of 30 ° to the line of the joint. This was a practical site use of slant shear test developed by Kreigh at the University of Phoenix, Arizona. 24 A modification of this test is now incorporated in BS 6319, part 4 Testing of Resin Compositions for use in construction: The Shear Bond Strength of Resin Based Adhesives for Concrete. The cores taken from the bridge were cut into cylinders and subjected to compressive testing. Compressive strengths of a similar strength to the adjacent monolithic concrete with failure away from the bond line were achieved to the relief of the contractors and engineers concerned.

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It is reported that after more than ten years in service, the repaired concrete continues to perform as if it were monolithic concrete. Also in 1975, another most interesting crack repair was carried out which involved the glueing together of a massive crack at the mid point of a 50 metre span 4.lane carriageway viaduct being constructed across a river valley caused by falsework settlement during construction. This was a massive concrete balanced cantilever, three m deep over the central support and reinforced with a mat of four layers of 50 mm bars which occupied the top 250 mm. The 100 mm square grid thus formed effectively prevented access for men to compact the concrete into the main part of the structure below. It was decided to place the concrete up to underside of the reinforcement mat which could then be installed on a convenient horizontal construction joint: concreting could then be completed in a second, much smaller pour. The bottom pour was carried out as planned and all appeared to be well. When a very fine vertical crack occurred over the central support column, this was attributed to thermal effects and not considered importanL When, however, it continued to open steadily it was realized that the mass of unreinforced concrete had divided over the piled support and that the two halves were slowly rotating in opposite directions. Evidently, the scaffold cage support was sinking into the weak aluvial ground upon which it was founded. After much anxious consideration, it was decided that if and when this rotation could be halted, then the crack would need completely filling/rebonding with a suitable resin material. It was then realized that resin injection before the crack had been stabilized by carrying out the top pour would not be effective. It was, therefore, decided to complete the construction as originally planned but with additional shear connections between the mass concrete and the top layer of reinforced concrete and then fill the crack with resin. By this time, the crack measured in height about 2.5 m spanning the complete 4-carriageway width of the viaduct approximately 23 m and wedge shaped from zero at the bottom to over 10 mm at the top. In order to gain good access to the crack, a 100 mm core was drilled at the centre of the diaduct following the crack down to the bottom. A piece of plastic pipe was bonded into the core which would project above the surface on the top pour. Injection tubes were also fixed clown both the side walls of the structure. Within 24 hours after placing the top reinforced concrete, the rotation stopped, stabilizing the crack completely. Resin injection of the stabilized crack was carried out by filling the core with clean dry 5 mm aggregate and then pouring in a long pot life epoxy resin system to completely fill both the 45% voids in the aggregate and the crack. The resin was pressured into the complete depth and width of the crack by using a nitrogen gas cylinder. The complete injection operation approximately two hours, the resin being carefully mixed in four litre batches and a total of about 230 litres of resin were used. After an appropriate cure period, in this case approximately three weeks, a very slow curing esin was used and the concrete temperature was below 7°C.

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Cores were taken across the crack. These cores demonstrated total filling even at narrow crack widths and excellent bonding across the crack. Thirteen years later, the injection resin is still holding the viaduct together under very heavy traffic loads.

R e s i n b o n d e d skid resistant road s u r f a c e s In the 1950s, the ElK Transport and Road Research Laboratory carded out some research on improving the skid resistance of urban roads. This work indicated that for refractory grade calcined bauxite aggregates were much more resistant to polishing under traffic than conventional natural road stones and, not unexpectedly, in tests simulating traffic conditions over a period of five years also maintained a much higher level of skid resistance. 25,z6

In the mid 60s the Greater London Council, together with Traffic Department of the Metropolitan Police, realized a great number of accidents in London involved skidding and took place within approximately 20 m of road junctions, pedestrian crossings and the approaches to roundabouts, z7 The total cost of these accidents to the community, damage to vehicles and ambulance and hospital costs, loss of earnings due to personal injury or death was found to be remarkably high and the GLC sought to come up with a cost.effective method of bonding caldned bauxite chippings on to perfect sound, primarily bitumous, road surfaces which had lost their skid resistance in the vicinity of road junctions, etc. It was accepted that the conventional surface dressing techniques would not be able to hold the calcined bauxite in place under the braking forces experienced at road junctions for a suffidently long time for their use to be economic. GLC invited resin manufacturers to carry out trials using high performance resin based adhesives to bond calcined bauxite onto the road surface. In summer ] 966, approximately ten different resin bindners, the majority based on tar or bitumen extended epoxy resin systems, were applied in 1 m wide strips across the A23 close to Lambeth Parish Church on a sharp corner approaching a pedestrian crossing. Half the width of the road was treated one Sunday morning and the other half the following Sunday. z° Some of the binder systems had lost the bauxite chippings within two to three days of application and it was thought that this was due to the unsuitable theology of the binder resistance in 'wicking' of the resin up between the chippings leaving insufficient binder in contact with the road surface to hold the calcined bauxite. Modifications to the theology were made to these binders by the incorporation of fillers before the second half of the road was treated. This overcame the rapid loss of chippings from these trial strips. The initial results of these small trials were so promising that early in 1967 the Greater London Council decided to go ahead with full scale trials on six major road junctions where a large number of accidents involving skidding has been recorded. These trials rapidly demonstrated the effectiveness and in the first year, there was over a 50% reduction of accidents involving injury, It was appreciated that the road areas requiring treating with resin bonded non skid surface dressings were all at very busy road junctions and it was, 96

therefore, essential that the treatment could be carried out at night and permit reopening of the roads fully for the morning rush hour. Special lorry mounted two component metering and mixing equipment, connected directly to a special sprayer was developed. This proved very effective and the machines developed 20 years ago are still in use today. In the LIK, bitumen extended epoxy resin skid resistant surface dressings have made a significant contribution to road safety by reducing accidents at busy road junctions, roundabouts, etc and it is now estimated that approximately 500 0 0 0 - 7 5 0 000 square metres of road surfacing are being treated annually. In most situations, the improvements in skid resistance are achieved for in excess of ten years from application. There are, therefore, probably in excess of seven million square metres of treated roads in the ElK today. References 1 BS 4169:1970 Specification for glue laminated Umber sructural members 2 BS 1203:1979 Specification for synthetic resin adhesives for plywood 3 BS 1204: Parts 1 ~ 2:1979 Synthetic resins (phenolic and aminoplastic) for wood 4 BS 6 4 4 6 : 1 9 8 4 Specifications for manufacture of glued structural components of timber and wood based panel products 5 'introduction to the specification of glue laminated members' (Timber Research and Development Association, 1979) 6 BS 5270:1976 (rev. 1988) Specification for polyvinyl acetate (PVAC) emulsion bonding agents for internal use with gypsum building plasters 7 Tabor, L J . 'Twixt old and new' paper presented at 'Structural Faults and Repair '85' ICE Conference, London, UK April 1985 8 Shaw, J D N. (1985) 'Materials for concrete repair' Proc Ist ]nt Conf on Deterioration and Repair of Reinforced Concrete in the Arabian Gulf, Bahrain, October 1985 9 UK Standing Committee on Structurul Safety Fifth report of the committee for the two years ending 30th June 1982 l 0 Tabor, L J. 'Effective use of epoxy and polyester resins in civil engineering structures' Report No 69 (Construction Industry Research and Information Association, 1978) I 1 Hewlett, P C and Shaw, J D N. 'Structural adhesives in civil engineering' in Developments in Adhesives - I edited by W C Wake (Applied Science Publishers, 1977) pp 2 5 - 2 7 12 Malta, G C. 'Structural applications of adhesives in civil engineering' 'Mater Sci Technoi 1 (Hovember 1985) 13 O'Brlen, 1". 'Jointing Structural Precast Concrete Units with Basic Adhesives' RILEM, Paris, September I967 ]4 Ann Ist Technique Batiment Tray Publics Suppl 204 (1964) 15 Smyth, W J R, Benaln, R and Hancock, C J . Tyneand Wear Metro: Byker Viaduct' Proc Inst Civil Engineers, Part 1 68 (1980) pp 701-718 16 Arup, O M and Z~nac C J. 'Sydney Opera House' "Structural Engineering' 47 (March 1969) 17 O'Brlen, 1", 'Resins in construction - 20 years' experience in many different structures' paper presented at FeRFA Seminar 'Resins in Construction - 20 years' experience', London, October 1984 18 Sims, F A. 'Applications of resin in bridge and structural engineering" paper presented at FeRFA Seminar "Resins in Construction - 20 years' experience; London, October 1984 19 Fleming, C J and King, G IE M. 'The Development of Structural Adhesives' RILEM, Paris, September 1967 20 Shaw, J D IN. 'Epoxy resin compositions - materials for the engineer' paper presented at symposium Liquid Polymers, University of Surrey, Guildford, UK, 1972 21 Shaw, J D PI. 'The use of epoxy resin for the restoration of strength of deteriorated concrete structures' Symposium 'Advances in Concrete' Birmingham, 1971 (Concrete Society, London) 22 Gaul, R W and Smith E D. 'Effective and practical structura] repair of cracked concrete' "American Concrete Institute, Special

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Publication No 21 'Epoxies with concrete' (1963) pp 145 Shaw, J D N. The use of epoxy resins in structural repairs: some interesting case histories' paper presented at Inf Conf on Structural Failure ICSF 87, Singapore Concrete Institute, March 1987 24 Kreigh, J D. 'Arizona Slant Shear Test' J American Concrete Institute 73 No 7 (1976) pp 373-377 25 Giles, G C. 'The skidding resistance of roads and the requirements of modem traffic' Proc Inst Ciu Eng 6 February 1957) pp 2]6-249 26 James, J G. 'Calcined bauxite and other artificial, polishresistant roadstones' Transport and Road Research Laboratory 23

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Report LR 84, C r o w t h o m e , 1 9 6 7 Hatherly, L W, Mahaffy, J H end Tweddle, A. 'The skid resistance of city streets and road safety' J Inst Highway Engrs

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F A. 'The application of epoxy resins in bridge construction with particular reference to Rawcliffe Bridge' paper presented at Resins and Concrete Symposium, Uniuersity of Newcastle-upon.Tynen, April 7973 29 Hugenschmidt, F. 'Epoxy adhesives for concrete and steel' paper presented at First International Congress on Polymer Concretes, London, May 1975 30 Mender, R F. 'Bonded external reinforcement - a method of strengthening structures'. Symposium 'Adhesiues and Sealants in Building~ Plastics a n d R u b b e r Institute, London 1977 Sims,

Acknowledgement

Thispaperwas presentedat a seminar,EngineeringApplicationo[ .~dhesWes,orgardsed jointiy by The InternationalJournal o[ Adhesion and Adhesiues and RAPRA Technology Ltd, held in London.

16 No 4 (]969) pp 3 - 1 2

International Concrete Roads Symposium A programme and registration details are now available for the 6th International Concrete Roads Symposium to be held at the Palado de Congresos, Madrid, Spain, from 8-10 October 1990. It has been organised by Cembureau, the European Cement Association in conjunction with PIARC, the Permanent International Association of Road Congresses and Oficemen, and Agrupacion de Fabricantes de Cemento de Espana. The themes for the symposium are: modern heavy. duty pavements; developments in other areas; and maintenance and rehabilitation. Each session will be devoted to a theme and there will be simultaneous interpretation provided in En§lish, French, German and Spanish. Ten of the accepted papers are from Britain and these cover a wide range of design and construction topics. A programme of technical visits will be arranged on 9 October, comprising motorway sites with concrete pavements under construction or recently completed, one of them widened with roller-compacted concrete. A copy of the full programme, together with an application form, is available from Mr Brian Walker, British Cement Association, Wexham Springs, Slough SL3 6PL, Berkshire. Telephone: 0753 662727. Fax:

0753 663851.

CONSTRUCTION & BUILDING MATERIALS Vol. 4 No. 2 JUNE 1990

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