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ROAD RESEARCH LABORATORY

Ministry of Transport

RRL REPORT LR 290

METHODS OF TEXTURING NEW CONCRETE ROAD SURFACES

TO PROVIDE ADEQUATE SKIDDING RESISTANCE

by

D.E. Weller

and

*D.P. Maynard B.Sc. (Eng) A.M. Inst.H.E.

Construction Methods Section

• Road Research Laboratory

Crowthorne, Berkshire

1970, "

*Cement and Concrete Association, Senior Research Engineer, (Construction Research Department)

Ownership of the Transport Research Laboratory was transferred from the Department of Transport to a subsidiary of the Transport Research Foundation on I st April 1996.

This report has been reproduced by permission of the Controller of HMSO. Extracts from the text may be reproduced, except for commercial purposes, provided the source is acknowledged.

CONTENTS Page

Abstract 1

i. Introduction i

2. Types of broom used for surface texturing 2

2.1 Soft broom 2 2.2 Yard broom 2 2.3 Wire broom 2

5. Details of laboratory experiments 3

3.i Original trials with the accelerated wear machine 3 3.2 Textures produced by the use of rollers 3 3.3 Surfaces having the coarse aggregate exposed and proud 3 3.4 High-speed photography 3

3.4.1 Development of brush units 4 3.4.2 Development of tined units 4

4. Details of site investigations 4

~.I The recommendations for concrete roads constructed in 1964 4

4.2 Use of the wire broom 4 4.3 Use of the modified wire broom 5 4.4 Use of tined units 5 4.5 Use of a no-fines surface layer 6

5. Results of laboratory tests 6

5.1 Original trials 6 5.2 Use of rollers to produce surface texture 7 5.3 Surfaces having the coarse aggregate exposed and proud 8 5.4 High-speed photographic tests 9

5.4.1 Surfaces textured with the wire broom 9 5.4.2 Tined surfaces 9

6. Results of the site trials iO

6.1 Use of the wire broom with four rows of tufts IO

6.1.1 Site 1 IN), trunk road AI, Newark By-Pass iO 6.1.2 Site 2 (W), trunk road AI2, Witham By-Pass ii 6.1.3 Site 3 (CL), Motorway M4, Chiswick-Langley Ii 6.1.4 Site 4 (PL), Motorway M6, Preston-Lancaster ii 6.1.5 Site 5 (DS), Motorway M6, Dunston-Shareshill 12 6.1.6 Site 6 (B), trunk road AI2, Brentwood By-Pass 12 6.1.7 The overall performance of the road surfaces

textured by the wire brooms 12

6.2 Use of the modified wire broom with two rows of tufts, Site 7 (C), Cromwell By-Pass 14

6.3 Use of the rubber tined texturing units 15

6.4 Use of the no-fines surface 16

7. Conclusions

8. Recommendations

9, References

I0. Acknowledgements

ii. Appendix 1 - The measurement of texture depth of a concrete road surface by the sand patch method

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O CROWN COPYRIGHT 1970 E x t r a c t s from the t e x t may be r e p r o d u c e d

p r o v i d e d the s o u r c e i s acknowledged

METHODS OF TEXTURING NEW CONCRETE ROAD SURFACES

TO PROVIDE ADEQUATE SKIDDING RESISTANCE

ABSTRACT

The development of various methods for texturing the fresh surface of high speed concrete roads is discussed. The performance is reviewed of various roads including those textured by the type of wire broom specified in the current Ministry of Transport Specification for Road and Bridge.Works.

The rate of wear and the skidding resistance of slow and fast lane surfaces are examined. An examination is also made of the effect of the initial texture imposed on the rate of change in skidding resistance with increase in speed.

Recommendations are made for future work to continue the development of various methods of texturing.

I. INTRODUCTION

In 1964 a Joint Working Party consisting of members of the Safety and Construction Divisions of the Road Research Laboratory and of the Construc- tion Research Department of the Cement and Concrete Association was formed to investigate the factors affecting the skidding resistance of concrete roads. The work described in this Report was carried out as part of this general investigation and in particular to develop a suitable method of texturing the surfaces of new concrete roads to provide good and durable skidding resistance.

The importance of the texture of the road surface and its influence on the skidding resistance have been stressed by Sabey 1,2,3 and it is now recognised that the surface requires both sufficient roughness (macro- texture) and a sufficient harshness [micro-texture). The rough texture is required to provide drainage channels to assist in th~ removal of the main bulk of water under wet conditions and also to produce deformations of the tyre. The ultimate penetration of the water film can be achieved only by the presence of fine-scale asperities on which high contact pres- sures are developed.

At high speeds it is difficult to penetrate the water film in the time available however sharp the fine texture and at these speeds the rough texture is essential. The irrecoverable energy of deformation, often referred to as hysteresis loss, contributes an increasing proportion of the skidding resistance as the speed increases.

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Before 1964 concrete road surfaces had been textured by brushing with

a soft-bristled broom, in a direction transverse to the line of the road. The depth of texture produced bylthis type of broom became rapidly worn under traffic and it was realised that a more severe method of texturing should be developed. Brakingand stability tests were carried out on grooved surfaces to compare the performance of transverse and longitudinal texturing. These tests showed that transverse texturing led to shorter braking distances and greater rotational stability and therefore transverse texturing is still specified. This direction of texturing also allows water to drain more readily across the surface.

This Report describes the initial tests carried out in the laboratory which led to the inclusion of clauses in the current Ministry of Transport specification 4 relating to the texture depth of concrete surfaces and to the type of broom to be used. The performance of roads textured in accordance with this specification is .examined. Even this texture, however, becomes rapidly worn on the more heavily trafficked motorways and trunk roads and the development of more severe texturing techniques is discussed.

2. TYPES OF BROOM USED FOR SURFACE TEXTURING

The texture depth achieved on post-war concrete roads by brushing the surface with a soft or medium-soft bristled broom has generally not exceeded 0.38 mm (O.OiS in) as measured by the sand-patch method (Appendix i). Although this texture might be satisfactory when new, there is evidence that under increasingly heavy traffic on major roads the life of this texture is limited. It has therefore been necessary to find ways of increasing the texture depth and making it more durable under heavy traffic.

When the work described in this Report was started there was little time available before construction of the roads to be built during 1964 commenced and it was therefore decided not to investigate ~mmediately any radically different techniques of texturing but to evaluate the most suitable method of texturing by brushing.

Tests were therefore carried out to examine the use of the following types of broom.

2.1 Soft broom

This had a 450 mm wide head with 50 mm long horse-hair bristles.

2.2 Yard broom

This broom (shown i n P l a t e l a ) had a 450 mm wide head wi th 150 mm long b a s s b r i s t l e s . Two d e g r e e s o f t e x t u r i n g were c a r r i e d ou t w i th t h i s broom by a p p l y i n g e i t h e r normal or heavy p r e s s u r e .

2 .3 Wire broom

The w i r e broom (shown in P l a t e lb) had a 450 mm wide head w e i g h i n g abou t 1 .4 kg. The s p r i n g - s t e e l - t a p e b r i s t l e s w e r e 2 7 0 vm t h i c k , 1.25 mm wide and were abou t 100 mm l o n g ; t h e y were a r r a n g e d i n 4 rows o f t u f t s .

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3. DETAILS OF LABORATORY EXPERIMENTS

5.i original trials with'the accelerated wearmachine

Concrete Specimens were made and testedon the accelerated wear machineS. The mix proportions were:- aggregate~cement ratio, 6.7 by weight; 35 per cent of sand and a water/cement ratio of 0.45. This mix was similar to that used for trunk road AI, Newark By-Pass, subsequently tested.

The surfaces of the specimens were textured with the soft broom, the yard broom with either normal or heavy pressure and the wire broom.

After the specimens had been cured in water for 28 days they were subjected to test on the accelerated wear machine.

The texture depth and skid resistance value of the surfaces were measured initially and again during and after wear and polish.

3.2 Textures produced by the use of rollers

Two types of roller were used to investigate the process of imposing a texture into the surface of plastic concrete. The first was a light '~ roller having twin drums of expanded metal, each with a diameter of 127 nml and a width of i.I m. This roller (shown in Plate 2) was fitted with a- long handle. The second roller consisted of a steel pipe, 5OO mm ..... diameter and 5.5 m long/ and weighed 44.5 kg per metre, around which sheets of patterned rubber or expanded metal were wrapped.

3.3 S u r f a c e s h a v i n g t h e c o a r s e a g g r e g a t e exposed and p roud ~

Various methods of applying polish-resistant chippings, either -~ untreated or coated with mortar, to the surface of the plastic concrete ~' were tried, using different techniques. The methods included mechanically.spreading the chippings and compacting by hand-held vibrating screeds, rollers and compacting machines.

3.4 High - speed photography

Tests were carried out to examine closely the action of some of the texturing units on the concretesurface by high-speed photography.

The action of the texturing units and of the movement of individual particles of concrete were studied by low-speed projection of the films.

A c a r r i a g e (shown in P l a t e 3 ) w a s d e s i g n e d to r u n on r a i l s s u p p o r t e d from t h e s i d e forms used to c o n t a i n t he c o n c r e t e d u r i n g t h e t e s t . T h e c o n c r e t e was compacted by a v i b r a t i n g s c r e e d and t h e r e s u l t i n g s u r f a c e t e x t u r e d . The t e x t u r i n g u n i t was f i x e d a t t h e f r o n t o f t h e c a r r i a g e i n such a way t h a t the ang le and load a p p l i e d cou ld be a d j u s t e d and f i x e d f o r t he p a r t i c u l a r t e s t . For each a r r angemen t o f t h e u n i t s a l e n g t h o f about 1.25 m o f c o n c r e t e s u r f a c e was t e x t u r e d and most t e s t s were c a r r i e d out bo th on c o n c r e t e s c o n t a i n i n g g r a v e l a g g r e g a t e s and on t h o s e c o n t a i n i n g granite a g g r e g a t e s .

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The action of the texturing unit was filmed from each Side and also from the back of the carriage usinghigh-speedcameras that took I00 or 250 frames per second. The required lighting was providedby quartz-iodine lamps suspended from the carriage. Plates 3 and 4 show texturing units under test.

3.4. I Development of brush units. The action of the wire broom with 4 rows of tufts was filmed and modifications were subsequently made to the broom head to improve the texture produced.

3.4.2 Development of tined units. Consideration was given to the use of tined units to impose a deeper and hence more durable rough transverse text ture than that produced by brushing. The individual tines were designed to form suitably shaped parallel grooves and ridges in the surface of the concrete.

The previous work on brooms had shown that textures which contained particles of aggregate in the surface were more durable than those com- posed only of the surface laitance and it was therefore essential that the tines should induce the aggregates into the ridges. The factors investigated included the shape and spacing of the tines, their stiffness and the angle of contact with the concrete.

A commercial product suitable for pilot tests was a rubber-tined lawn rake and some initial tests were carried out with a 250 mm wide unit (Plate 4). Texturing units of different patterns cut from sheets of neoprene (Table I) were also investigated.

4.1

4. DETAILS OF SITE INVESTIGATIONS

The recommendations for concrete roads constructed in 1964

It was recommended that commercially available wire brooms similar to those used for the laboratory tests {see 2.3) should be used to texture the surface of concrete roads to be constructed in 1964. It was further recommended that the surface should be textured to an average texture depth of not less than 0.65 mm (0.025 in) with a minimum texture depth at any point of 0.50 mm (0.020 in).

A number of concrete specimen blocks textured with the wire broom to the required texture were made and distributed for the guidance of the authorities responsible for the construction of the roads.

4.2 Use of the wire broom

Four of the roads constructed in 1964 and textured by hand with the specified wire broom were either major trunk roads or motorways and tests were carried o~t at these sites to determine whether the recommendations for texture had been met and to measure the effects of the imposed texture on skidding resistance. Tests were also repeated at intervals during the four years following the opening of the roads to traffic. Results are

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a l s o c o n s i d e r e d from a fu r the r . .mo to rway and a t r u n k r o a d b o t h c o n s t r u c t e d in 1965 and h a v i n g s u r f a c e s t e x t u r e d w i t k t h i s t y p e o f _ w i r e broom.

The sideway force coefficient in the line of traffic was measured at 50 and 80 km/h with the Road Research Laboratory's special car fitted with a smooth tyre. The skid resistance value was measured with the portable tester and where it was possible to carry out high-speed skidding tests the braking force coefficient was measured at speeds up to 130 km/h 6.

An attempt was also made to obtain a subjective impression of these coarser textures.

Details of the individual sites are shown in Table 2.

4.3 Use of the modified wire broom

In 1965 a slip-form paver was used for the first time in this country to construct the AI, Cromwell By-Pass, in Nottinghamshire. The Contractor developed and built a subsidiary machine to texture the surface and to apply the curing compound. This machine (shown in Plate 5) was fitted with two brush units approximately i, m wide, each with two rows of tufts of steel tape. Plate 6 shows a broom head of this type but operated manually.

To assess the skidding resistance and texture depth of the surface ,. given by this treatment measurements were made before the road was opened to traffic and were repeated after the road had been trafficked for 6, 18 and 30 months.

Some difficulties were experienced with the use of the prototype brushing machine and modifications had t0 be made toensure uniform pressure to the brush heads in order to obtain a uniform texture of the surface. The contractors have since developed a brushing machine that incorporates a wire-guidance system of control.

4.4 Use of tined units

In o r d e r t o a s s e s s t h e d u r a b i l i t y o f t i n e d c o n c r e t e s u r f a c e s u n d e r the action of heavy traffic, sixteen cores of approximately 150-mm diameter were cut from slabs constructed and textured in the laboratory and reset into the surface of a motorway. The samples were bonded by epoxide resin into holes drilled into the road surface in the line of traffic (Plate 7). Similar specimens were subjected to freeze~thaw tests in the laboratory.

Both g r a v e l and g r a n i t e c o n c r e t e samples were i n c l u d e d i n t h e s e t r i a l s , and t h e i r p e r f o r m a n c e s a f t e r one y e a r u n d e r t r a f f i c i n d i c a t e d t h a t f u l l - s c a l e t e s t s cou ld be c a r r i e d out on a ma jo r road . The f r e e z e / t h a w specimens showed no d e t e r i o r a t i o n a f t e r 80 d a i l y c y c l e s o f f r e e z i n g fo l l owed by s a l t thawing. To t e s t w he the r t h e s u r f a c e s would have a c c e p t a b l e r i d i n g q u a l i t y two t r i a l l e n g t h s were c o n s t r u c t e d .

A c o n c r e t e c o n t a i n i n g g r a v e l a g g r e g a t e was t e x t u r e d w i t h t h e u n i t f

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having curved tines at 15 mm pitch and a concrete containing granite aggregate was textured with theunit having flat chamfered tines at the same pitch. Both of the trial lengths had acceptable riding quality and it was decided to use the flat tined unit to texture a length of a major trunk road. A 180 m straight length of AI2, Kelvedon By-Pass was textured by hand with a 0.9 m wide unit.

Following these trials the units were modified by stiffening the tines to improve the penetration. The earlier laboratory trials had been carried out on more workable concrete. The tines were fitted with spring-steel stiffeners and the unit was fitted with a light vibrator.

This modified tined unit was used to texture a 180 m length of concrete surface at AI, Long Bennington By-Pass. The texture was imposed by hand wi-th a Im wide unit with the tines set at a pitch of32mm. This wider spacing was considered necessary as at this site aggregate of 38 mm maximum size was used.

4.5 U.se era no-fines surface lazer

To examine the effectiveness of a road constructed with a porous no-fines surface a 180 m length of a minor road was constructed at Eakring in Nottinghamshire. Details of the construction and performance of this road after six months' traffic have been reported elsewhere7.

S. RESULTS OF LABORATORY TESTS

5.1 OriBinal trials

The results of the tests are given in Table 5 and plotted in Fig.l.

The wire brushed surfaces had, at all times during test, a greater texture depth than the other surfaces and even after Wear the average texture depth, 0.43 nun, was greater than that of the best of the other surfaces before wear.

The average texture depth of all the surfaces decreased by approximately O.12 mm during test.

The Skid resistance values measured with the portable tester showed only small differences between the treatments. This was to be expected as the skid resistance value is mainly dependent upon the fine texture or state of polish of the surface which would not be significantly different between specimens made from the same mix. However, the wire brushed surfaces had a slightly higher average value than the other surfaces both before and after wear and polish.

A close visual examination before and after wear showed that the wire broom had displaced some of the coarser sand particles so that they protruded into the ridges of the texture (Plate 8). This could explain the better performance of the wire brushed surface.

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Since these tests the regime of test adopted with the accelerated wear machine has been modified and the current regime is more Severe. In order to assess more Closely the correlation between the behaviour of specimens tested in the laboratory and the corresponding performance of similar road surfaces the series of tests on specimens textured with the various brooms has been repeated and these results are given in Table 4 and plotted in Fig.2.

The severity of the different regimes of test are not discussed here but these repeated tests placed the various surfaces in the same relative order of merit.

5.2 Use of rollers to produce surface texture

Light roller. The expanded metal forming the twin drums was of the flattened type having a diamond shaped mesh with apertures 21 mm x 6 mm. When rolled over a concrete surface a pattern was produced which was characterised by protruding 'fins' that were formed through the apertures in the expanded metal. Repeated passes of th~ roller over the surface emphasised the texture since the rolling.action tended to bring mortar to the surface and this helped to increased the height of the fins (Plate 9).

Although the appearance of this texture was considered to be generally satisfactory, there were two defects. The first was the formation of a" ridge of mortar at the side of the roller which became more pronounced with subsequent passes of the roller. In places the height of this ridge was as much as 9mm. The second defect was that the fins which were formed consisted mainly of weak mortar and therefore theywould probably be worn down fairly quickly by traffic.

Tests carried o~t using only one of the two drums but covered with 'a textured rubber sheeting (Plate i0) produced a correspondinggrooved texture in the concrete only after several passes over the same area. ridge was again formed along the edge of the-roller and this increased in size with successive passes.

The most striking feature of this work was the marked variability in the depth of texture due either to slight irregularities in the level of the plastic concrete or small variations in the concrete.

A close examination of the texture where the depth was greatest showed that the ridges contained some of: the intermediate sized (9mm - 4.Smm) aggregate. This is considered to be desirable as the durability of ridges comprising only weak cement paste would probably be poor.

S t e e l ~ i p e R o l l e r . The s t e e l p i p e was f i t t e d w i t h two t y p e s o f expanded m e t a l shown i n P l a t e 11. The f i r s t t y p e was a g e n e r a l p u r p o s e mesh h a v i n g diamond s h a p e d a p e r t u r e s 3 0 mm long and 12 nun w i d e . One l e n g t h was f i t t e d w i t h t h e l o n g e r d i m e n s i o n s o f t h e a p e r t u r e s a l o n g t h e p i p e and a n o t h e r l e n g t h w i t h them a r o u n d t h e p i p e . The s e c o n d t y p e was a f l a t t e n e d mesh h a v i n g a p e r t u r e d i m e n s i o n s s i m i l a r t o t h e f i r s t and a r r a n g e d w i t h t h e l o n g e r d i m e n s i o n s a round t h e p i p e .

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The texture produced by..the general purpose expanded metal was more uniform and had a greater texture depth than that produced by the flattened type. Thel lack of uniformity in this case was due to the reduced rigidity of the mesh and the consequent sagging which occurredbetween the support- ing straps. The reduced texture depth was no doubt due to the increased area of steel stripwhich is inherent in the flattened form. of expanded metal.

Each of these patterns, however, was considered to be preferable to that produced by the light expanded metal roller described above since the latter produced a pattern that was basically a series of small protruding fins of mortar that were formed in the small apertures of the mesh. With the larger mesh sizes used on the heavier steel pipe, the texture was basically a diamond shaped pattern of grooves.

As in the case of the light roller, a small ridge of concrete was formed along the side of the pipe as it was rolled forward and this seems unavoidable if the concrete surface is to take the full weight of the roller or pipe.

Various patterns of rubber sheeting were tried on the pipe and for this work the pipe was arranged to span the 3m wide bays with the ends supported on the side forms in order that the ridges and depressions mentioned above would be avoided. The most satisfactory result was achieved with a ribbed pattern of: rubber (Plate 12) which was the same as that previously tried on the light roller. In this case, however, a far deeper texture was achieved, the average depth of groove being about 4.5 mm - 6 mm (Plate 13). The rubber sheeting was tried with the grooves running circumferentially round the roller and also with the grooves running longitudinally along the pipe (Plate 12), but there appeared to be no difference between these two arrangements in their effect on the quality of the pattern produced in the concrete.

Other less severely textured patterns of rubber sheeting were tried but the texture depths produced were considered to be insufficient.

5.3 Surfaces having the coarse aggregate exposed and proud

Preliminary tests in which 9 mm granite chips were spread by hand and tamped into a carefully levelled freshly compacted concrete slab were unsuccessful as the chips did not adhere to the surface. The effect of precoating the chippings with mortar to improve the bond was examined but the result was only slightly more satisfactory. The replacement of the tam. ping screed with the expanded metal roller (detailed in 3.2 and 5.2) to embed the chippings was not successful, the chippings merely being pressed into the concrete without being gripped sufficiently.

Further tests were carried out with a hand held tamper fitted with a light vibrating unit. When the tamper was used in a level position it tended to pu!l chippings from the surface; when tilted it gave only a slightly more satisfactory surface.

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The a p p l i c a t i o n o f p r e c o a t e d c h i p p i n g s t o a f r e s h s u r f a c e u s i n g a cement g u n w a s c o n s i d e r e d bu t p r e l i m i n a r y t r i a l s were n o t s u c c e s s f u l Under normal work ing p r e s s u r e t h e a g g r e g ~ t e s e g ~ e g a t e d f r o m t h e cement p a s t e , w h i l s t u n d e r r e d u c e d p r e s s u r e t h e p i p e s became c l o g g e d .

Further tests were carried out in which chippings were spread mechanically from the Road Research Laboratory's gritting spreader over a fresh concrete surface. Granite chippings of 9 mm nominal size were spread at different rates and compacted into the surface by a vibrating beam set at a controlled level. The surface was very patchy with some areas of loose chippings and some areas with chippings completely vibrated into the concrete. Many chippings came away from the hardened surface when it was lightly brushed the following day.

The t e s t s were r e p e a t e d w i t h c h i p p i n g s p r e c o a t e d w i t h m o r t a r a i d a l t h o u g h much b e t t e r a d h e s i o n was o b t a i n e d t h e f i n a l s u r f a c e w a s s t i l l p a t c h y .

The use o f l a r g e r u n c o a t e d g r a n i t e c h i p p i n g s (18 mm) d i d n o t improve t h e p a t c h y a p p e a r a n c e o f t h e f i n a l s u r f a c e . A s l i g h t l y more u n i f o r m s u r f a c e was o b t a i n e d when t h e l a r g e r c h i p p i n g s w e r e p r e c o a t e d . The b e s t s u r f a c e was o b t a i n e d when t h e y w e r e s p r e a d and s u b s e q u e n t l y r o l l e d i n t o t h e s u r f a c e by a 300mm d i a m e t e r s t e e l p i p e s u p p o r t e d f rom t h e s i d e fo rms . The u s e o f r o l l i n g w i t h o u t v i b r a t i o n , however , s t i l l c a u s e d smal l d e p r e s s i o n s a round t h e p e r i m e t e r o f t h e s t o n e s . None o f t h e s e " methods have g i v e n a c o m p l e t e l y s a t i s f a c t o r y s u r f a c e and c o n s i d e r a b l e r e s e a r c h and d e v e l o p m e n t i s r e q u i r e d b e f o r e t h i s t e c h n i q u e can be a p p l i e d to a road s u r f a c e .

5.4 High-speed photographic tests ':

5.4.1 Surfaces textured with the wire broom. The filmed action of the wire broom with four rows of tufts showed that severe disturbance occurred during the texturing process.~ The presence of unnecessary banksof bristles caused excess disturbance of the surface and it seemed that rapid wear of this texture under traffic could be expected. The action of this type of broom on concrete containing granite coarse aggregate caused even more disturbance than when it was used to texture a gravel concrete surface.

The a c t i o n o f a broom h a v i n g o n l y one row o f t u f t s c a u s e d l e s s d i s t u r - bance but was not considered sufficiently effective in forming ridges. A surface that was considered more suitable was produced by a wire broom with two•rows of staggered tufts at 15 mm pitch.

Typical stills taken from the filmedrecords of two brooms are shown in Plate 14.

5.4.2 Tined surfaces. The initial tests with the neoprene tines described in 3.5 and detailed in Table 1 showed that insufficiently deep textures had been achieved either with the unit having 3 mmthick tines (No.13) or with the unit having weakened • tines (NO. 5).

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It was considered that further tests including high,speed photography should be Carried out on the six units which had produced the most satisfactory surfaces~ These were Units I, 2,i 4, i0, 12 and 14. The average texture depths measured on the surfaces of slabs textured with units 1, 4, I0 and 14, which were considered to be the best, were 0.84 mm (0.033 in), 0.79 mm (0.031 in), 2.34 mm (0.092 in) and 1.03 mm (0.041 in) respectively.

Further development was carried out on the shapes and pitch of the tines to improve the uniformity of the textures produced. A minimum pitch of 12 mm was found desirable to avoid disturbance but units with tines set at a pitch of 18 mm or greater produced, on concretes having 18 mm maximum size aggregate, a texture which was considered to have excessive flat area between the grooves. The pitch considered most satisfactory after this series of tests was 15 mm. The modified commercial lawn rake (Plate 4) with chamfered edges to the face of the tines in contact with the concrete, and the unit having straight tines which were also chamfered (shown in Plate 15), both have the tines at this 15 mm pitch.

The application of vibration to the texturing devices has been found necessary to achieve satisfactory penetration into the surface of less workable concretes. Further development work has also been carried out to produce, in the plastic concrete, a series of grooves up to 6 mm deep by the passage of a textured vibrating beam across the surface. A prototype vibrating texturing unit isshown under test in the laboratory in Plate 16 where the concrete surface has been satisfactorily textured 4 hours after compaction.

6. RESULTS OF SITE TRIALS

6.1 Use of the wire broom with four rows of tufts

Some aspects of the results from the individual sites are discussed first and the overall results from the use of the wire broom are then discussed in 6.1.7.

6.1.1 Site 1 (N), trunk road AI, Newark By-Pass. The results of tests carried out at this site are given in Tables 5 and 6.

Sections 1 - 7 were chosen by visual inspection to be typical of the road and measurements of skid resistance value and texture depth were made before the road was opened to traffic. The average values of initial texture depths in these sections ranged from 0.28 mm (0.011 in) to 0.53 mm (0.021 in) and, as explained below, were less than the specified minimum. The range of individual values within a section was about 0.25 mm (0.010 in).

In o r d e r t h a t t h e p e r f o r m a n c e o f a s u r f a c e t e x t u r e d t o the s p e c i f i e d dep th c o u l d be examined two f u r t h e r s e c t i o n s were i n c l u d e d ; S e c t i o n 8 had a h i g h e r t h a n a v e r a g e t e x t u r e dep th and S e c t i o n 9 was the f i r s t s e c t i o n l a i d on t h i s s i t e and had been h e a v i l y t e x t u r e d w i th a ya rd broom b e f o r e the recommended w i r e broom was o b t a i n e d .

10

The average values of texture depth on Sections 8 and 9 were O.53 mm (0,021 in) and 0.79 m m (0.051 in) respectively. ~ese measurements were made in the traffic line of the nearside lane after the road had been opened for two months and measurements made away from the traffic line indicated that traffic had already caused a drop in texture depth of about 0.12 mm (0.005 in).

To examine t h e g e n e r a l b e h a v i o u r of t h e s u r f a c e o f t h i s road t h e ave rage v a l u e s o f on ly t h o s e s e c t i o n s (2, 4 and 8) t h a t were f u l l y t e s t e d t h r o u g h o u t t h i s p e r i o d have been c o n s i d e r e d .

6.1.2 Site 2 (W), trunk road AI2, Witham By-Pass. The results of tests carried out at this site are given in Tables 7 and 8. The texture depth measurements made initially on the six sections chosen as being typical of this surface showed that although in general the texture was slightly greater than that at site 1 (N) it was still less than that specified. The average value of the individual sections ranged from 0.33 mm (O.013 in) to 0.58 mm (0.023 in) with a range of values within sections of up to O.51 mm (0.020 in).

6.1.3 Site 3 (CL), motorway M4, Chiswick-Langley. The results of tests carried out at this site are given in Tables 9 and i0.

The texture depth measurements made initially on the eight sections selected to represent the road showed that all sections had an average value greater than O.56 mm (0.022 in).

The surfaces of a few small areas that had been insufficiently textured were grooved by a multi-blade saw before the road was opened to traffic.

The initial tests and measurements of skidding resistance had to be fitted in with site construction work and were therefore not all made at the same time.

6 . 1 . 4 S i t e 4 (PL), motorwa 7 M 6 , ' P r e s t o n - L a n c a s t e r . R e s u l t s of t e s t s c a r r i e d out a t t h i s s i t e a r e g iven in Tables 11 and 12 .

Sections 1 - 8 were chosen as having surfaces typical of the road and with one exception the sections had mean texture depths of between O.61 nun (0.024 in) and 0.81 mm (0.052 in). Section 4, however, had a mean value of only O.41 mm (0.O16 in), caused possibly by the use of this area by turning construction vehicles.

The few insufficiently textured areas at various: points along the road were grooved with a multi-blade saw before the road was opened to traffic.

Section 9 was a short section textured with a special broom having only two rows of tufts (see 4.3) but unfortunately this section was laid at the end of construction on this site and was unsuitably located for high-speed testing. The area textured by this broom had an initial mean texture depth of 0.90 mm (0.056 in).

The original intention to carry out further tests onthe same sections

]]

after they had carried traffic was not possible to arrange and it was necessary to substitute similar sections in nearby but more suitable loca- tions for high-speed tests.

6.1.5 Site 5 (DS), motorway M6, Dunston-Shareshill. The results of tests carried out at this site are given in Tables 13 and 14. The initial texture depth of the surface of this road was generally above the specified minimum.

6.1.6 Site 6 (B), trunk road AI2, Brentwood By-Pass. The results of tests carried out at this site are given in Tables 15 and 16. Various short sections were laid to examine the effect of the sand content of the mix and of the texture depth of the surface on skidding resistance.

It is not intended in this reportto examine fully the effects of these factors. The results presented refer to the two sections that had the best and the worst performance under traffic. The best section was laid with a mix having a high sand content (38%) and the texture was imposed by heavy pressure on the wire broom. The worst section was laid with a mix having a low sand content (30%) and was textured by lighter pressure. The initial texture, depths of the best section was above the specified minimum.

6.1.7 The overall performance of the road surfaces textured by wire brooms with 4 rows of tufts. The initial texture depth of the various surfaces laid in 1964 are shown plotted in Fig.5 and the values during the four years under traffic are shown in Fig. 4. The texture depths measured during the first three years of traffic of the motorway site 5 (DS) and of the trunk road site 6 (B) both laid in 1965 are shown in Fig. 5 where they are compared to the performance,of sites 1 (N) and 4 (PL). As discussed earlier the initial t~xture depths achieved on sites 1 (N) and 2 (W) were below the specified minimum and were not much greater than those which had been achieved in experimental roads previously with the use of a yard broom. There was a reluctance on these sites to impose the specified texture for fear of producing unacceptable riding quality. These fears were not justified, however, and the surfaces at sites 5 (CL), 4 (PL), 5 (DS) and 6 (B) which were constructed later were textured more deeply and texture depths of over 0.6mm (0.025 in) were achieved.

On a l l t h e r o a d s t h e t e x t u r e d e p t h s i n t h e s low l ane d e c r e a s e d r a p i d l y i n t h e f i r s t t w e l v e m o n t h s b u t a f t e r t h i s e a r l y f a l l t h e v a l u e s t e n d e d to s t a b i l i s e . On t h e more h e a v i l y t r a f f i c k e d m o t o r w a y , s i t e 3 (CL), t h e r a t e a t wh ich t h e o r i g i n a l wear o c c u r r e d w a s f a s t e r t h a n on t h e o t h e r s , 4 ( P L ) & 5(DS), b u t t h e v a l u e s r e c o r d e d a f t e r a b o u t 2 y e a r s were s i m i l a r . I t i s n o t s u g g e s t e d t h a t t h i s v a l u e w i l l be m a i n t a i n e d i n d e f i n i t e l y b u t i t w o u l d seem t h a t t h e r a t e o f wear on a l l r o a d s a f t e r t h e f i r s t y e a r i s m a r k e d l y r e d u c e d .

T e s t s have n o t been c a r r i e d o u t on t h e f a s t l a n e o f s i t e 1 (N) a f t e r 2 y e a r s . On t h e r o a d s f u l l y t e s t e d t h e t e x t u r e d e p t h i n t h e f a s t l a n e d i d n o t d e c r e a s e s t e a d i l y . There~ were , however , v a r i a t i o n s f rom y e a r t o y e a r wh ich may b% m a i n l y c a u s e d b y t h e d i f f i c u l t y o f c a r r y i n g o u t t h e t e s t on r o u g h e r t e x t u r e d s u r f a c e s .

]2

The results 0f the sideway force coefficients measured at 50 km/h are shown plotted against the period of trafficking, in Figs. 6 and 7. Although.initial measurements before trafficking, were not taken atall sites the genera~ Shape of the curves show that a large decrease occurred in the first few months of trafficking and that after this period, with the exception of motorway M4, site 5 (CL), which carried three times .the traffic of the other roads, both the slow lanes and fast lanes maintained a fairly steady value. Variations from year :to year occurred but these are partly accounted for by the changes attributable toseasonal effects. The values recorded onthe heavily trafficked motorway however, did not stabilise so quickly as the other surfaces and the coefficient (S 50) of the s.low laneof this road may not yet have reached a steady value after 3½ years. Further measurements are planned on all the sites to observe the long-term behaviour of the surfaces. ~

In general, however, the values (S 50) after S years were, for all roads, between 0.40 and 0.50 in the slow lanes and between 0.55 and O.65 in the fast lanes. The fast lane of the motorway constructed in 1965, site 5 (DS), had, however, after 30 months a sideway force coefficient at 50 km/h of about 0.80. The heavily trafficked motorway M4, site 3 (CL), had the lowest values in both lanes and traffic intensity haSothOrefore had more effect than the initial texture depth~ The three,trunk roads and the motorway at site 5 (DS) had gravel coarse aggregates but the motorway at site 4 (PL), which carried Similar traffic to these roads and had similar sideway force coefficients at 50 km/h in the slow lane,~had: been constructed with a richer mix incorporating a crushed gritstone coarse aggregate. The traffic intensity has therefore had more effect than the difference, in the concrete. . ~ : • • ' "

The results of.the braking f0rce tests at 50, '80 and 130 km/h on the roads are shown in Figs. 8 to II.' . . . . . . . ~

On the'two trunk roads, laid in 1964, which both had low texture -.''~ depthsand on the lightly textured surface of the trunk roadlaid in 1965, there was in the slow lane, a considerable reduction in braking force co@fficient at all times with increase in speed. ,The reduction observed between 50 km/h and 80 km/h was similar to that between 80 and 130 km/h. On the slow lanes of the motorways laid in 1964 the reduction in braking force coelfficient with increase inspeedwas much less, particular/y, from 80 to 130 km/h. The motorway laid in 1965, however, ~ hada performance • similar, to that of the .trunk roads. '~

In the slow lanes of the trunk roads and the heavily trafficked motorway,, all laid in 1964, the braking force coefficient measured:at 130. km/h after four years was less than 0.-20. On the other motorway laid that yea~, however, where the richer mix was used the braking force:coefficientat 130 km/h was.still~greater than.O.3 after four years. The difference in the, two motorways which had similar textures when new may be partly the!result ' of much higher traffic on the M4 but it may be that with the higher strength concrete used to construct the: M6 the shape'of texture has, been better preserved . . . . . • . . -., • , . . : " : - . ,-

O f the two roads laid in 1965 the effect of the texture: on the.

]3

r e t e n t i o n o f b r a k i n g f o r c e c o e f f i c i e n t i n t h e s low l a n e w i t h i n c r e a s e in s p e e d was m o s t , m a r k e d on t h e t r u n k r o a d . A f t e r 5 y e a r s t h e h e a v i l y and l ight ly~textured s u r f a c e s had s i m i l a r c o e f f i c i e n t s a t 50 km/h (B50) but a t 1 3 0 k m / h ( B 1 5 0 ) t h e h e a v i l y t e x t u r e d s u r f a c e had a v a l u e o f 0 . 4 0 w h i l e t h e l i g h t l y t e x t u r e d s u r f a c e had a v a l u e l e s s t h a n 0 . 3 0 .

The slow lane of the motorway, however, which at this time had a similar texture depth and brakingforce coefficient at 50 km/h (BSO) to the heavily textured section of the trunk road, had a value at the higher speed (BISO) of less than 0.25.

In g e n e r a l t h e r e d u c t i o n i n b r a k i n g f o r c e c o e f f i c i e n t w i t h i n c r e a s i n g s p e e d was much l e s s t h r o u g h o u t t h e l i f e o f t h e s u r f a c e o f t h e f a s t l a n e and h i g h e r c o e f f i c i e n t s a t a l l s p e e d s have been a c h i e v e d . However, t h e one t r u n k r o a d , s i t e 2 (W), t h a t was t e s t e d a f t e r f o u r y e a r s showed a l a r g e d e c r e a s e i n c o e f f i c i e n t and t h e v a l u e o f 0 . 6 0 a t 50 km/h f e l l t o 0 . 5 4 a t 150 km/h . The l i g h t l y t e x t U r e d s u r f a c e o f t h e t r u n k r o a d , s i t e 6 (B) , l a i d i n 1965 a l s o showed a f t e r 5 y e a r s a l a r g e d e c r e a s e , t h e c o e f f i c i e n t falling from 0.55 at 50 km/h to 0.52 at 150 km/h.

6.2 Use of the modified wire broom with two rows of tufts. Site 7 (C), trunk, road A1, Cromwell. By-Pass.

The r e s u l t s o b t a i n e d f rom measu remen t s made on t h e s u r f a c e a t s i t e 7 (C) t r u n k r o a d A1, Cromwel l By -Pas s , t e x t u r e d , by t h e m o d i f i e d w i r e broom w i t ~ two rows o f t u f t s , a r e l g i v e n i n T a b l e s 17 and 1 8 .

The i n i t i a l m e a s u r e m e n t s o f t e x t u r e d e p t h made b e f o r e t h e r o a d w a s o p e n e d t o t r a f f i c showed t h a t t h e s i x s e c t i o n s t e s t e d r a n g e d in mean t e x t u r e d e p t h f rom 0 . 5 9 mm ( 0 . 0 2 7 i n ) t o 1 .27 mm (0 .050 i n ) . The mean i n i t i a l t e x t u r e d e p t h o f t h e t h r e e s e c t i o n s f u l l y t e s t e d was 1 .04 mm (0 .041 i n ) . T h e r e was, h o w e v e r , a r a p i d d e c r e a s e i n t h i s v a l u e and a f t e r 18 months t h e t e x t u r e d e p t h was l e s s t h a n 0 . 4 0 ram. These r e s u l t s a r e p l o t t e d i n F i g . 12 t o g e t h e r w i t h t h o s e f rom t h e s i m i l a r l y t r a f f i c k e d t r u n k r o a d s i t e 1 (N) l a i d i n 1964 and t h e motorway s i t e 5 (DS) l a i d i n 1955, which were b o t h t e x t u r e d w i t h t h e w i r e broom w i t h 4 rows o f t u f t s . A f t e r 50 months much o f t h e i n i t i a l a d v a n t a g e had been l a r g e l y l o s t .

The s i d e w a y f o r c e c o e f f i c i e n t a t 50 km/h was always s l i g h t l y l e s s t h a n t h o s e o f t h e s u r f a c e s a t s i t e 1 (N) a n d s i t e 5 (DS) (F ig . 13) . A f t e r 30 m o n t h s ' t r a f f i c t h e v a l u e s o f s i d e w a y f o r c e c o e f f i c i e n t a t 50 km/h were 0 . 3 9 and 0 . 5 7 i n t h e s low and f a s t l a n e s r e s p e c t i v e l y .

The b r a k i n g f o r c e c o e f f i c i e n t s a re shown p l o t t e d i n F i g s . 1 4 and 15. In t h e s l o w l a n e t h e r e d u c t i o n i n b r a k i n g f o r c e c o e f f i c i e n t w i t h i n c r e a s i n g s p e e d f rom 50 t o 130 km/h was a lways l e s s on t h e s u r f a c e t e x t u r e d by t h e m o d i f i e d w i r e broom and t h e c o e f f i c i e n t a t 150 km/h (B130) was above 0 . 5 0 i n t h e t h i r d y e a r .

On t h e f a s t l a n e s o f t h e t h r e e - s i t e s a f t e r two y e a r s t h e b r a k i n g f o r c e c o e f f i c i e n t s a t a l l s p e e d s we re above 0 . 4 5 . There was n o r e d u c t i o n in b r a k i n g f o r c e c o e f f i c i e n t f rom 80 to 130 k m / h on t h e s u r f a c e t e x t u r e d w i t h t h e m o d i f i e d w i r e broom,

]4

As already discussed this wire broom with two rows of tufts is now specified as the standard type of wire broom for texturing road surfaces.

On t h e more h e a v i l y t r a f f i c k e d roads even s u r f a c e s t e x t u r e d b y t h i s broom may w e l l r e q u i r e t o be r e t e x t u r e d a f t e r a number o f y e a r s .

6.3 Use of the rubber tined texturing units

The c o n c r e t e ' u s e d a t t h e s i t e 8 (K) t r u n k r o a d A12, Kelvedon By-Pass (4.4) was too stiff for the tined texturing unit to produce the type of surface obtained in laboratory trials and the resulting texture depth was very much less than anticipated (Plate 17).

Adjacent areas were textured by the wire broomwith 4 rows of tufts and the skidding resistance of the two types of texturewere compared. Measurements of skidding resistance and texture depthwere made before the surfaces were trafficked and after they had carried traffic for 18 months (Table 19)and tests will be repeated after further periods of trafficking.

The initial results showed that untrafficked surfaces of_thetinedand brushed sections had similar properties. Both surfaces had initial texture depths of about 0.75 mm (0.030 in) and both maintained values of sideway force coefficient in excess of 0.60 at 80 km/h and values of braking force coefficient in excess of 0.40 at 130 km/h.

After 18 months traffic the texture depths of both the tined and brushed surfaces had fallen to about 0.25 mm (0.010 in) in the slow lane and to about 0.38 mm (0.015 in) in the fast lane. ~ At this time both surfaces had sideway force coefficients at 50 km/h of just below 0.50 in the slow lane and of just below 0.60 in the fast lane. Although neither surface retained the braking force coefficient satisfactorilywith increase ofspeed the tined surface gave the betterperformance. The reductionin braking force coefficient with increase in speed from 50 to130 km/h off the wire brushed surface was 81% in the slow lane and 50% in the fast lane and the corresponding reduction in the slow and fast lanes of the tined surface was 67% and 25% respectively. " ~ : '

The rubber tined texturing unit with tines at 52 mm pitch and stiffened with strips of mild steel and fitted with two vibrators was tried on a short length of surface at site 9 (LB) trunk roadAl, Long Bennington By-Pass. As at Kelvedon the concrete was too stiff for the unit to give the intended texture and a texture depth of only 0.66 mm (0.026 in) was obtained. The average texture depth of the brushed sections adjacent to this short experimental length was 0.56 mm (0.022 in).

The mild steel supports were replaced by spring steel to improve transmission of vibration to the tines, and this unit was then used to texture a 180 m test section.

The concrete was still too stiff for the tines to produce the required surface and again the texture consisted mainly of shallow grooves separated by flat areas. The average texture depth of this experimental length was 0.64 mm (0.025 in). Tests to measure the performance of the surface under traffic will be carried out periodically.

15

6.4 Use of theno-finessurface

The method used to construct the road with a no-fines surface layer proved to be practicable and the specification adopted could be used for any future similar work 7.

The h a r d e n e d s u r f a c e was g e n e r a l l y u n i f o r m w i t h t h e c h i p p i n g s w e l l b o n d e d t o g e t h e r . Cores were t a k e n f rom the f i n i s h e d r o a d a n d showed t h a t t h e n o - f i n e s l a y e r was w e l l b o n d e d t o _ t h e lower c o n c r e t e .

The n o - f i n e s s u r f a c e gave a s a t i s f a c t o r y s k i d d i n g _ r e s i s t a n c e h a v i n g i n i t i a l s k i d r e s i s t a n c e Va lues o f b e t w e e n 59 and 84 With t h e p o r t a b l e t e s t e r and s i d e w a y f o r c e c o e f f i c i e n t s o f be tween 0 .49 and 0 . 6 0 a t 50 km/h . The s u r f a c e i n i t i a l l y g a v e r a p i d a n d e f f e c t i v e d r a i n a g e and q u i c k l y d r i e d o u t a f t e r r a i n .

A l t h o u g h t h e n o - f i n e s r o a d gave a s a t i s f a c t o r y p e r f o r m a n c e s t r u c t u r a l l y d u r i n g t h e f i r s t two y e a r s u n d e r t r a f f i c , t h e v o i d s g r a d u a l l y s i l t e d up and a f t e r t h r e e y e a r s some f r o s t d a m a g e h a s o c c u r r e d i n a r e a s where s i l t i n g has c a u s e d w a t e r t o be t r a p p e d i n t h e s u r f a c e l a y e r .

7. CONCLUSIONS

1) L a b o r a t o r y t e s t s have shown t h a t t h e most s a t i s f a c t o r y t y p e o f broom f o r t e x t u r i n g c o n c r e t e i s a w i r e b r o o m w i t h two rows o f t u f t s o f s p r i n g s t e e l t a p e b r i s t l e s . A b room o f t h i s t y p e i s s p e c i f i e d ~ i n t h e c u r r e n t M i n i s t r y o f T r a n s p o r t S p e c i f i c a t i o n f o r Road and B r i d g e Works:

2) Measu remen t s made on two motorways c o n s t r u c t e d i n 1 9 6 4 a n d h a v i n g s u r f a c e s t e x t u r e d i n i t i a l l y t o t h e c u r r e n t s p e c i f i c a t i o n h a v e shown , a f t e r 4 y e a r s , . t h a t t h i s rough t e x t u r e has l i m i t e d t h e r a t e o f change in b r a k i n g f o r c e c o e f f i c i e n t w i t h i n c r e a s e i n s p e e d , when c o m p a r e d w i t h t he p e r f o r m a n c e

"obse rved on r o a d s c o n s t r u c t e d t h a t y e a r w i t h : i n f e r i o r i n i t i a l t e x t u r e d e p t h s .

3) Measu remen t s made on s low lanes , h a v e shown t h a t on a l l r o a d s a r a p i d d e c r e a s e i n t e x t u r e d e p t h o c c u r r e d _ d u r i n g t h e f i r s t y e a r . A f t e r two y e a r s a marked d e c r e a s e i n t h e r a t e o f wear has been o b s e r v e d .

On t h e f a s t l a n e s u r f a c e s t h e r e i s n o i n d i c a t i o n o f a s t e a d y change in t e x t u r e d e p t h w i t h t i m e .

The r a t e o f wear o f t e x t u r e has b e e n i n f l u e n c e d m o r e b y : t r a f f i c i n t e n s i t y t h a n by e i t h e r t h e i n i t i a l t e x t u r e d e p t h o r t h e t ype o f mix.

4) The most satisfactory method of obtaining a suitable surface in the laboratory had been by the use of rubber-tined texturing units but so far only limited success has been achieved with this method on site. The stiffness of the concrete at the time of texturing was critical.

5) No technique has yet been developed to produce completely satisfactory surface textures either by the use of rollers or by the application of polish- resistant coarse aggregate chippings to a fresh concrete surface.

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8. RECOMMENDATIONS

1) The rough t e x t u r e s p e c i f i e d fo r h igh Speed c o n c r e t e road s u r f a c e s should be imposed in such a way t h a t p a r t i c l e s o f a g g r e g a t e a r e con t a ined in the a s p e r i t i e s . This would reduce the r a p i d e a r l y wear shown on su r - faces whose t e x t u r e c o n s i s t e d only of weak mor ta r or con ta ined d i s t u r b e d p a r t i c l e s .

2) The use of a s p e c i a l top course of h igh q u a l i t y m o r t a r - r e s i s t a n t to p o l i s h maybe worth c o n s i d e r a t i o n .

3) Fur the r development work s h o u l d b e c a r r i e d out to improve the techniques of producing s u r f a c e t e x t u r e s b y t h e use o f p a t t e r n e d v i b r a t i n g beams and by t i n i n g , r o l l i n g , o r the a p p l i c a t i o n o f ch ippings to the s u r f a c e .

i.

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9. REFERENCES

SABEY, B.E. Road surface characteristics and skidding resistance. Journ: Brit. Gran. and Whin. Fedn. Autumn 1965, ~ (2).

SABEY, B.E. The-road surface and safety of vehicles. Symposium on Vehicle and Road Design for~Safety. Inst. Mech. Engrs. (Auto Div.) July 1968, 1968-9, 183 (SA).

SABEY, B.E. The road surface in relation to friction andwear of tyres. Road Tar, March 1969, 25 (i).

MINISTRY OF TRANSPORT. Specification for Road and Bridge Works. London, 1969 (H.M. Stationery Office).

WELLER, D.E. and MAYNARD, D.P. The use of an accelerated wear machine to examine the skidding resistance of concrete surfaces. Ministry of Transport, RRLReport LR 388 Crowthorne 1970 (Road Research Laboratory).

ROAD RESEARCH LABORATORY. (H.M. Stationery Office).

Research on road safety. London, 1963.

MAYNARD, D.P. The construction of an experimental road with a no- fines concrete surfacing in Nottinghamshire. Cement and Concrete Association TRA 401. London, 1966. (Cement and Concrete Association).

iO. ACKNOWLEDGEMENTS

The authors wish to acknowledge the help given to them by the County Surveyors of Essex, Lancashire, Nottinghamshire and Staffordshire; by the Borough Engineer of the London Borough of Hotmslow, by_ Sir Alexander Gibb and Partners, by Sir Owen Williams and Partners, andby their staffs. They also wish to acknowledge the help given by the contractors Richard- Costain Ltd., W. and C. French Ltd., John Laing Construction Ltd.,

]7

Sir Alfred McAlpine and Son Ltd., R. McGregor and Sons Ltd., A. Monk and Co. Ltd., and by their staffs. Their thanks are also due to the Divisional Road Engineers of the Eastern, East Midland, London Highways, North Western and West Midland Divisions, and to their staffs, and to members of the staff of the Construction Methods and Vehicles Sections of the Road Research Laboratory, and of the Construction Research Department of the.Cement and Concrete Association.

]8

II. APPHNDIX I

The measurement O f t e x t u r e d e p t h o f a c o n c r e t e road surface, by %he sand patch method

This method, described .in outline in Road Note 27!, consists of measuring the area towhich a known volume of sand has been .spread in a standard manner so that the 'valleys' of the texture are filled to the level of the 'peaks'. The ratio, (volume of sand) / (area Of sand) gives a measure of the 'texture depth' of the surface.

The specification prepared for concrete roads laid in 1964-5 required that the mean of ten measurements of texture depth using a 5cc cylinder to measure out the sand shouldbe at least 0.025 in (0.64mm) with not more than one of the ten individual readings being less than 0.O20 in (O.51 mm).

Tests were subsequently carried out, however, to compare the use of this cylinder with the use of a 25 cc cylinder. This comparison was based on tests carried out by ten operators using both sizes of cylinders on eleven concrete surfaces that had widely different textures.

The standard deviation of the results~obtained by iO different operators using both 5 cc and 25 cc of sand at each of ii areas have been plotted against the mean texture depth for each area in Fig.16.. The regression lines relating standard deviation and mean texture-depth for. the two volumes of sand show that the overall standard deviation using 25 cc was only about 60% of the corresponding standard deviation using 5cc. This would imply a reproducibility* of about ~ 25% of the mean value when the 25 cc is used. The use of the 25 cc cylinder has now been specified.

The relationship between the value 0f texture depth obtained by using the small cylinder and by using the larger cylinder is shown in Fig.17. The regression line relating the values goes very close to the origin and a linear relationship is assumed over the normal ranges of texture depths. It is seen that the use of the 25 cc cylinder gave greater values of texture depth and the revised spe6i'ffd:ag~On~issued in late 1965 therefore required an average texture depth of 0.030 in (O.76 m m) with not more than one of the ten readings less than 0.025 in (0.64 mm).

For the purpose of this report, although, the initial measurements of texture depths on the roads laid in 1964 were made using a 5 cc cylinder, the values of texture depth obtained have been corrected where necessary and all measurements are quoted on the basis of the use of a 25 ca cylinder.

A copy of the current instructions for this method of_test is reproduced on the next pageand describes the equipment, method of use, frequency of test and required texture depth.

*~The limits outside which only 1 in 20 of results may be expected to fall by chance when comparing results by different operators on the same area

19

The M e a s u r e m e n t o f T e x t u r e D e p t h by the Sand Patch Method

Apparatus and m a t e r i a l

This c o n s i s t s of:

(I) A pair of dividers capable of measuring radii up to 6 in (152 mm).

(2) A 6 in (152 mm) rule marked off in i/8 in (3 mm).

(3) A cylinder 3 5/16 in (84 mm) high with an internal diameter of 3/4 in (19 mm)

(4) A flat wooden disc of 2 1/2 in (64 mm) diameter with a hard rubber disc of the same diameter stuck to one face; this rubber facing should be about 1/16 in (1.5 mm) thick. It is convenient to attach to the other face a short spigot or dowel to serve as a handle.

(5) A container for the sand. A 250 cc plastic beaker would be found convenient for this purpose.

(6) A s o f t hand b rush .

(7) A quantity of sand which will pass a No. 52 B.S. sieve and be retained on a No. I00 B.S. sieve (300 vm - 150 vm). Natural sand with a rounded particle shape shall be used.

Preparation of a conversion table

Calculate the exact volume of the cylinder. If the volume of the cylinder is V, the texture depth, TD, will be given by TD = V , R being

R 2

the radius of the sand patch. Prepare a table showing TD for values of R in increments of 1/8 in (3 mm) from 1 in (25 mm) to 6 in (150 mm).

Test procedure

The surface to be measured must be dry and should first be swept with a sof£ brush. Fill the cylinder with sand: when full gently tap the base of the cylinder three times on the road surface and then topup the cylinder with sand and level the top with a straightedge. Pour the sand into a heap on the surface to be tested. In windy conditions the use of a tyre to surround the sand is recommended. Spread the sand over the surface, working the disc with its face kept flat, in a circular motion so that the sand is spread into a circular patch with the surface depressions filled to the level of the peaks.

With the d i v i d e r s measure the r a d i u s of the patch formed by the sand and r eco rd to the n e a r e s t 1/8 in (3 mm). Carry out 10 such t e s t s a t 3 f t (1 m) i n t e r v a l s a long a l i n e p a r a l l e l to the kerb .

20

m

_ I

Frequency Of tests for new construction

A set of tests shall be done each day or for each 2000 ft (600 m) of carriageway builZ, whichevez produces the greater number of results.

Required texture depth for new concrete roads

The average texture depth obtained from the i0 tests should not be less than 0.030 in (0.75 mm) and not more than one of the iO results should be less than 0.025 in (0.63 mm).

.

R E F E R E N C E

ROAD RESEARCH LABORATORY. Instructions for using the portableskid- resistance tester. Department of Scientific and Industrial Research, Road Note No. 27. London, 1960 (H.M. Stationery Office).

21

TABLE 1

THE DIMENSIONS OF THE NEOPRENE TINES

Tine unit

i 6

2 6

3 6

4 6

* 5 6

6 6

7 6

**'8 6

9 6

I0 6

Thickness of tine (ram)

Width of tine

W. max mm

ii

12

13

14

4.5

6

3

6

9

6

4.5

6

9

9

9

9

7.5

9

6

7.5

9

6

W .min mm

3

2.25

2.25

1.5

2.25

2.25

3

3

3

3

1.5

1.5

2.25

1.5

Length of tine L mm

33.5

35

12

38

38

38

12

33.5

Pitch of tines P mm

9

6

6

9

12

9

9

12

33.5

35

35

35

35

36.5

12

15

12

13.5

12

12

Unit 5. Unit 8.

Thickness o£ tine reduced to 3 mm at the root The tines had chamfered )oints

.L ]

W. min

1W. max F

22

<

P.

u~

o

o

o~

o ,°~ ~ m

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o 0

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8 o o

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o

o'>

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• ~ . ; . ; . ; . . . .

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2 3

Ca)

TABLE 3

LABORATORY TESTS TO EXAMINE THE USE OF VARIOUS BROOMS (SERIES 1)

T e x t u r e Depth

Initial After wear After polish

Type of broom average average average average average average

mm in mm in mm in

Sof t O. 28 (0.01 i) O. 15 (0.006) O. 15 (0.006)

Yard with normal 0.38 (0-.015) 0.23 (0.009) 0.23 (0.009) pressure

Yard with h e a v y p r e s s u r e

Wire

O. 43

0.58

(0.017)

(0 .023)

0.31

O. 46

(0.012)

(o.o18)

0.3]

0.43

(0.012)

(0.017)

N.B. The results are the averages of 4 individual results. Except for the wire broomed specimens the range of the 4 individual results was not greater than 0.050 mm (0.002 in). The range of the 4 individual wire broom results was 0.200 nun (0.008 in).

(b) Skid resistance value

Initial A f t e r wear

Type of b room

After polish

average range average range average range

Soft i00 95-107 64 60-66 57 57-58

Yard with n o r m a l p r e s s u r e

Yard with heavy pressure

i01

107

ii0

94-106

104-112

104-117

66

71

71

63-68

68-73

69-74 Wire

57

60

61

55-59

59 -60

56-64

N.B. Tested under wet running conditions

24

(a)

TABLE 4

LABORATORY TESTS TO EXAMINE THE USE OF VARIOUS BROOMS (SERIES II)

Texture Depth

Type of broom

Soft

Yard with normal pres sure

Yard with heavy p r e s s u r e

Wire

Initial

ave rage . mm

0.30

0.51

0.58

1.22

ave rage in

(0 .012)

(0.020)

(0.023)

(0.048)

After wear

average mm

0.23

O. 30

0.36

0.53

a v e r a g e . in

(0.009)

(0.012)

(0.014)

(0.021)

After

average- mm

0.23

O. 33

O. 36

0.51

N.B. The results are the:averages of 4 individual results

polish

average in

(0. 009)

(0.013)

(0.014),

(0.020)

(b) Skid resistance value

Initial After wear After polish Type o f ..... broom average average range average range

Soft

Yard with normal press ure

Yard with heavy pressure

87

95

97

range

|

83-91

94-97

94-101

52

$2

51

51-54

51-53

48-54

41

43

42

40-42

41-45

40-44

Wire I01 95-105 54 52-55 46 44-47

N.B. Tested under dry running conditions for first 50 hours

25

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26 J

TABLE 6

sIDEWAY.FORCE COEFFICIENT AND PERCENTAGE DROP IN BRAKING FORCE 'COEFFICIENT AT SITE I(N) TRUNK. ROAD AI., NEWARK BY-PASS

Sideway force coefficient 50 km/h

Lane

Slow

Section

i ,

2 3 4 5 6 7 8 9

Initial 1 yr 2 y r 4 yr

0.52 0.47 0.52* 0.43 0.53 0.41 0.51" 0.41 0.52* 0.34 0.47 0.40 0.57* 0.42 0.56* 0.44 0.53 0.56* 0.47 0.51" 0.40 0.50 0.49 0.53* 0.43 0.51

Mean 2,4,8 0 .52 0.39: 0..50 0 .43

0 .61 " 0 .66 0 :67* 0 .66 0.6.7

F a s t

3 4 5 6 7 8 9

O. 69* , ,0~'6!; ;~:.-:'~,:~';': 0 . 61 " 0 . 5 8 0 . 6 4 0 .76 * 0 .67 0 .72* 0 .66 0 .68 0.65* 0.50 0.64* 0.68 0.66 0.59* 0.58 0.64

Mean 2 , 4 , 8 0 .64 "-0~64 0 .66

P e r c e n t a g e d rop i n Brak ing f . c o e f f i c i e n t

lO0/_~50-ju130 '~

Initial 1 yr 2 yr 4 yr

/

56 49 62

39 39 59

37 40

29 40 53 27 40

41, 42 58

42 30 20

6 - 2

9 4

9 - 2 7 - 2 4

11 8

* Measurements made a f t e r 2 months ' t r a f f i c k i n g

27 ̧

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28

TABLE 8

SIDEWAY FORCE COEFFICIENT AND PERCENTAGE DROP IN BRAKING FORCE COEFFICIENT AT SITE 2(W) TRUNK ROAD AI2, WITHAM BY-PASS

Lane

Slow

Mean

Fast

Mean

Section

2,4,5

i 2 3 4 5 6

2,4,5

Sideway force coefficient 50km/h

Initial 9mth 21mth 48mth

0.35 O. 40 0.43 0.47

0 . 4 5 0 . 5 6

0.44

0.47 0.45 0.48 0.52 0.44 0.49 0.48 0.51 0.49 0.50 0.53 0.52

0 .48 0.51

O.SO 0.58 0 /56 0 ,64 0.58 0.61 0.58 0.63 0...53 0 .58 0 . 6 1 0.64

0.56 0 . 6 2

I n i t i a l

0.46

0.50 0.50

0.49

0.62

0.65 0.60

0.62

Percentage drop in braking f . c o e f f i c i e n t

1 0 0 ( ~50-~130 ) ~ 5 0

9mth 21mth! 48mth

49 5 3 35 13

22 15

29

16 26 12 14 18

35 52 77 28 20 85 29. 60 24

34 74

29 40 25

1 6 4 47

13 60 17

19 44

29 ̧

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m B " M

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0 ~ ~ 0

0 .,4

(.3 ¢)

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0 0 0 0 0

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0 0 0 0 0

0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0 6666~6~

e~ 0 ~ ~ ~

0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0

0 0 0 0 0

6666 6

0 0 0 0 0 0 0 0

e e e o e e e e

0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0

0 ~ 0 ~ ! ~

~ 0 ~ ~ ~ ~ ~ - ~

0 0 0 0 0 0 0

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0 0 0 0 0 0 0 0 0 0

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34

TABLE 14

SIDEWAY FORCE COEFFICIENT AND PERCENTAGE DROP IN BRAKING FORCE COEFFICIENT AT SITES [DS) MOTORWAY, DUNSTON-SHARESHILL

Lane

Slow

Section Sideway force coefficient

50 km/h

6mth 18ruth 30ruth

0.51 0.50 0.51 0.46

0.41 '0.41 0.48 0.50

0.59 0.57 O. 46 0.57

Percentage drop in braking force coefficient

100/ '~50-~130

k ) 6mth 18mth 30mth

29 14

- 13

Mean 0.49 0.45 0.55 9

0 . 6 7 0 . 6 6 O. 70 O. 70

0.71 0.71 0.74 O. 73

F a s t

0.85 0.88 0.69 0,81

0.81 Mean 0.72 0.68

:- 10 - 5 - 9 '

2

- 5

51 46 39 51 34 52

4 46

32 49

- 8 - 3 - 1 8 - 4 -26 -6 - 1 4 - 6

- 1 6 - 5

35

u~

a, !

0

Z

c~

xo

oo

r.u

:>

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oo

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X 6~

t.~ r-1

0

°~

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[--,

°~

o~-I

I - - I

,'-4 XO O0 XO

O0 aO

..~ ,,o do

L~ t '~ 0 0

o o o~ 0 0

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'-¢ 0 0

4-~ 0 0 -r.I c~ o

I,,,-I

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t.~ ,~ d d

~ 0

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d o t

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t |

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o~

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6

TABLE 16

SIDEWAY FORCE COEFFICIENT AND PERCENTAGE DROP IN BRAKING FORCE COEFFICIENT AT SITE 6(B) TRUNK ROAD AI2, BRENTWOOD BY,PASS

Lane Section

7 Slow

4

7 Fast

4

Sideway f o r c e c o e f f i c i e n t

•Initial

O. 70

0.53

0.76

0.60

50 km/h

i l m t h 24ruth i r I "

0 . 5 0 0.58

O. 39 O. 52

0.63 0.65

0.54 0.63

3Smth

0 . 4 9

0.43

Percentage drop in braKing.force coefficient

100( ~50-~130 , : so

Initial

21 i

61

O. 61 23

0.5,8 65

llmth

.

46•

9

45

24mth

16

49

i0

31

35mth

4

36

15

40

37 •

38

O0

I

mG

Z

m

[.-, x

k k 0

.,-I

.,-4 O~

br~ ,-4 0

o

o o o

o o o

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0

cO

0

o

o 0 0 o o o o o o o o

o o o o o o o ~ ~ ~ o

o

o

o

o o o o 0 o

o o o o 0 0

0

~ 0 ~ 0 ~

0 0 0 0 0 0

0 0 0 0 0 0

0

0

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~ ~ o

0 0 0 0 0 0

0 0 0 0 0 0

,'4

.,-I

.,-I

I i I

0

r- i

o o o o o o o ~ ~ ~

Lr~

0 0 0 0 0 0 0

0 ~ 0 0 i-4

~D

0 0 0 0 0 0

0 ,--I

0

TABLE 18

SIDEWAY FORCE COEFFICIENT AND PERCENTAGE DROP IN BRAKING FORCE COEFFICIENT AT SITE 7(C) TRUNK ROAD AI, CROMWELL BY-PASS

Lane

Slow

Section

1 2 3 4 5 6

7 ( G r a n i t e )

Mean 3,4,5

F a s t

Mean

1 2 3 4 5 6

2,5

Sideway force coefficient SO km/h

I n i t i a l 6mth 30mth

37 i°:38 0.44 0 .42 0 .38 0 .38

0.41

i

0.61 0.49 0.55 O. 60 0.50 0.52

0.49

P e r c e n t a g e d r o p i n b r a k i n g

18ruth

O. 44 0.44 O. 45 0.44 O. 41 0 .46 0 .41

0.43

0.56

0.57

0.57

0.41 O. 40 0.36

0 . 3 8

0 . 3 9

0 . 5 7

0 .57

f o r c e coefficient

i00 (~50-p130~

Initial 6mth 18mth 30ruth

11

3 20

0

1-2

- 7 - iO

26 13 19 26 37 27 20

27

31 34 52

64

39

- 4 17 7 18

4 6 18

39

• , - t . ~

~ . ~ . ~

0

r..l.1

| >.,

[-I..]

.<

o

Z

[...,

r.=l

Z

O ~ E ! c o

0

0

•

n=l 0 .. 4.~,

h--I

O~

0

• ~ 0 _ _ .

• ~ x O

. -~ o ~ i ~ ~ J

.z=

a o

°r-~

-I~ ° ~

• . P t

r-t

4-) °r-I

i ̧

0

0

o

o

t ~

0

c~

U~ Cxi

CO

0

o ~

t c

0

0

0

aO

0

xO

0

xO

clO aO

o

0

00 Cxl

0

o

~0 t ~

0

c~

aO

o

t ~ xO

0

c~

0

o

c~

O0 Cxl

c~

xO

c~

0

-Ic n:s .Z:

O0

t

o

xO ,

0

• L t ~

xO

O~

0

c~

u') ¢xl" 0

0

CO

t .

O .

' 0

c~

f-~

0

0

° ~

0

~ o ~ ~-~ 0

40

a) yard broom

b) wire I~oom w|i'h 4 rows of tufts

Plate 1. Two of the brooms used in the prel|m|nary tests

41

Plate 2. The light roller in action

42

~ ~ L ~

, !

L,

I

I,

= .

=

~.~.

~ ~ r~

F ¸ ~ - . . . - ~ . ~ - - ,

f

._u - C

O-

o O

-c: O-

~3

I

c Dm

.o_

D U

e~

O D -

4 3

44

c

c

i o

~m

0

0

Ov~ Io Dim

.E

u

- c OI CJ

o O

Oil f ~

Q-

- c

O i

0

..C U

-8 o

E 0 o

~ 4

Q C

U 0 E

I - - . . C

M

0

45

0

Io 0

,8-- t ~

E 0 0

-O Q~

0 E

~L

46

Plate 7. A textured sample set into a road surface 47

a) before wear

b) after wear and polish

Plate 8. The brushed specimens before wear and after wear and polish

48

0

0

Q~ C

m~ .o

0 )

0

o~

& - 0 9J

0 & I -

- 0

a~

®B. . . £ X j.-- Q~

o~

O Q -

49

C L~

-0 D L.

-0

-O -0 ,m 6

-0

> 0 0

2 - 0

0

c 0

o

h-

0 O-

50

E " 0

" 0 ¢: 0 0.. X 0.1

"13

0 U

"~_

0

I-.-

0

51

c

L.

D I

" D

> 0 O

6 1

, . C I "

O D_

52

c~

0

C I m

c

0

P

- 0 Q~

a .

X

- 0 A)

q~

I--.

0

53

a) the wire broom with 4 rows of tufts

54 b) the wire broom with 1 row of tufts

Plate 14. The action of wire brooms

D ~

c:

0~

X

"O

c~

..Q

i m

~D " 0

E

0

55

G) E D .

q~

QJ

Im

- 0

C

0 ~

L.

X

0 ) C

.o

~J

Plate 17. The surface produced at site 8(K) , trunk road A12 r Kelvedan By-Pass, with the rubber tined texturing unit - Full scale.

E E

r "

"10

I I I

0 Soft broom • Yard broom wi th normal pressure

• Yard broom wi th heavy pressure

L~ Wire broom wi th /, rows of tu f ts

1.0

0.8

0-6

Contact pressure = 0 .38N /mm 2 Angle of scuff = 2 ° Abrasive for 50h wear = 2./~ mm to 1.2mm

f l i n t grovel sand Abrasive for 5h polish = fine emery powder

= " - ' - ' - ' - - ~ _....._.__._~ ~ , , ~

o-1. X

,- ~ •

d ~

o.2 . . - _ _ . . _ ~ ~ . . . . _ ~

i • ~ Period of wea r =

0 I I I I ,. Polish I'*

0 10 20 30 /,0 50 55 Hours of tes t on the accelerated wear machine

Fig.1. THE EFFECT OF IHE TYPE OF BROOM ON THE TEXTURE DEPTH (Series 1: Test carried out under wet running conditions)

60

58

E 0.8

1.2

1-0

E J¢:

O "10

=.. 0.6

X

I - -

0.4

0.2

O Soft broom • Yard broom with normal pressure • Yard broom with heavy pressure

Z~ Wire broom with /~ rows of tufts

Contact pressure = 0.19 N/mm 2 Angle of scuff = 2 ° Abrasive for 50h wear = 2.4mm to 1.2mm

flint grovel sand Abrasive for 5h polish = fine emery powder

w

. 0

J L

0

Period of w=ar 1 I I I

10 20 30. 40 - Hours of test on the acceterated wear machine

Fig.2. THE EFFECT OF THE TYPE OF BROOM ON THE TEXTURE DEPTH (Series I ] : Test corried out under dry running conditions)

Wet 4.- polish I'*

50 55 60

59

Site 1 (N)

Section 1"10.

3 D

Z , -

5 D .

6 ~ ? -

8 ~ 9 -

Site 2 (w) il I

I

si te 3

(CL)

Site /,

(PL)

2 - 3 - 4 - 5

6 - ? -

8 -

2 - 3 B

/ , -

5 - 6 -

7 - 8-

I I

I

I I

I I

I I I I I

0-25 0-50 . 0-75 1.00

Approx texture depth (mm)

I I ' l ' - • I I 1 I 0 0.010 0.020 0.030 0.040 0050

Texture depth (thou in)

N.B. The range of aLL the measurements made within each section is p lot ted The average value of only those measurements that were made in the t ra f f ic Line of the nearsid¢ Lane is indicated

I 0<)60

Fig.3. THE INITIAl. TEXTURE DEPTHS OF THE ~ ROAOS EONSTRUETEO IN 196/, AND TEXTURED BY THE WIRE" BROOM WiTH l, ROWS.OF TUFTS

60

0-9

0-8

0"7

0,6 ~ ~ X " X

0.5

- T Q" 0 -4

X

X

"10

P

X (g I - .

0.3

0.2

0.1

0

site Site Site s;te

Stow Lone Fast tone

1 (N) Trunk rood O • 2 (W) Trunk road & • 3 (CL) Motorwoy D • 4 (PL) Motorwoy +~ X

12 24 36

Period of trafficking (months)

Fig.t,. THE EFFECT OF TRAFFIC ONTHE TEXTURE. PROOUC.EO. BY THE WIRE BROOM WITH t, ROWS 00 TUFTS

48

61

1.0

Jl"

Jf & 0.9,

0-8 • x

jr

0.7 , ~

\ X

0.6

E

• - 0"5 ~

X , [ ~ 0.~

0.3 L-------- ~ m b ~ ~ _ _ . . ~ _

0.2 -

0.1

Site 1 (N) Trunk rood Site /, (PL) Motorwoy . Site 5 (DS) Motorwoy Site 6 (B) Trunk rood

?

SLow [one Fost Lone

0 • + X

.1~ . j heavy brushing I"1 • tight brushing

0 12 2L, 36 Period of trafficking (months)

~8

Fig. 5. THE EFFECT OF TRAFFIC OH THE TEXTURE PRODUCEO BY THE WIRE BROOM WITH ~. ROWS OF TUFTS

52

0.9

0"Sk

0"?

x - - - 2 - x

~ o.s ' ~

~ O'4

10 0.3

0.2

0 ° 1

stow tone Fast tane l l l

Site 1 (N) Trunk road O • Site 2 (W)"Trunk road & & Site 3 (CL) Motorway 13 • Site 4 (PL) Motorway, " -I- X

m m

0 12 24 36

Period of traff icking (months)

Fig.6. THE EFFECT OF TRAFFIC ON THE SIDEWAY FORCE COEFFICIENT OF SURFACES TEXTURED BY THE WIRE BROOM WITH t.ROWS OF TUFTS

48

63

0'9

0"8

07

0-6

o 0 -s

~, o.~ g

~ 0"3 "1o

0.2

0.1

0

\ \

\

~ J f

SLow tane

Site1 (N) Trunk road O Site/, (PL) Motorway + Site 5(DS) Motorway A Site 6 (B) Trunk road ,B"

El

l

Fast tane

X A ,ll Heavy brushing • Light brushing,

12 2/, 36

Period of t raf f ick ing (months)

Fig.7. THE EFFECT OF TRAFFIC ON THE SIOEWAV FORCE COEFFICIENT OF SURFACES TEXTURED BY THE WIRE BROOM WITH/. ROWS OF TUFTS

64

0.?

0.6

0"5

"G O.k'

o U

g z,.

2 0.3

.E v

o QI

0"2

0.1 ̧

Site I(N) Trunk road Site 2 (W) Trunk road Site 3(CL) Motorway Site 4 (PL) Motorway

l l l l l l • I e q l l 0

[3 0 + +

0 Firstl year Secondl year I ~ y e a r ~ F o u r t h year

50 80 130 50 80 130 50 80 130 50 80 130

Speed (kin/h)

Fig.6. THE EFFECT OF TRAFFIC ON THE BRAKING FORCE COEFFICIENT OF THE SLOW LANE SURFACES TEXTURED BY THE WIRE BROOM WITH/, ROWS OF TUFTS

65

0"?

0"6

0"5

"~ 0"6 o ~

0 U

u

0.3 ¢...

° ~ 21£

m

0.2

I

I

Site 1 (N) Trunk rood Site L, (PL) Motorway Site 5(DS) htotorway Site6(B) Trunk rood

\

O ~ - ---O + + A m - h A

J3" Heavy brushing [] I"1 Light brushing

q ,

\

0"1 I

First year I Second year Thir~ year I I Fourthyear I I I

50 80 130 50 80 130 50 80 130 50 80 Speed (k m/h)

130

Fig.9. THE EFFECT OF TRAFFIC ON THE BRAKING FORCE COEFFICIENT OF THE SLOW LANE SURFACES TEXTURED BY THE WIRE BROOM WITH t. ROWS OF 1UFTS

66

0.?

0.6

0.5

._u

0 U

u 0

r - a m

P co

0"4

0.3

0"2

Site 1 (N) Trunk road • . . . . 4

Site 2 (W] Trunk road & m m ~

Site 3 (CL') Motorway -- -

Site /, (PL) Motorwoy X X

\ \

%

0.1

Second Third ~ ~ ' [ _ _ ~ r _ _ _ j ~F°urthyear J 50 80 130 50 80 130 50 80 130 50 80 130

Speed (kin/h)

Fig.lO. THE EFFECT OF TRAFFIC ON THE BRAKING FORCE COEFFICIENT OF THE FAST LANE SURFACES TEXTURED BY THE WIRE BROOM WITH/. ROWS OF TUFTS

67

0-8

0"?

0-6

0.5

O

O

a t C

m

0.3

j X

Site 1 (N) Trunk,road

0-2 Site &(PL) Motorway Site 5 (DS)Motorway Site 6 (B) Trunk road

0.1

First year Second year ~ year 0 I I

50 80 130 50 80 130 50 80 130 50 80 130 Speed (k in /h )

Fig 11 THE EFFECT OF TRAFFIC ON THE BRAKING FORCE COEFFICIENT OF THE FAST LANE SURFACES TEXTUREO BY THE WIRE BROOH WITH t, ROWS OF TUFTS

68

T .

E E

v

=.-

( 9 I 0

( 9 t ~

4.w X

( 9

0.9

0.8

0.?

0.6

0-5

0./,

0 .3

0.2

0-1

Initial texture depth 13 • 1.0/.mm

&

&

\

L

F C

" ' - o

Stow tone Fast tone

2 row broom Site?(C) Trunk road I"1 •

/, row broom Site 1 (N) Trunk road 0 • /, row broom Site 5(DS) Motorway & &

0 12 24


Fig.12. THE

36

EFFECT OF TRAFFIC ON THE TEXTURE PRODUCED DY THE WIRE BROOM WITH 2 ROWS OF TUFTS

/.8

69

A 0"8

A 0"7

A

0"6

• )

~ 0.1, ° l

O u

u O

>. 0"3 O

"10 ° l

t / )

• SLow 0-2 Lane

2 row broom Site 7(C) Trunk road (3

l, row broomSite 1 (N) Trunk road O ~ row broom Site 5(~)Mot~way B

0.1

Fast Lane

A

12 2/, 36


Fig.13. THE EFFECT OF TRAFFIC ON THE SIOEWAY FORCE COEFFICIENT OF

SURFACES TEXTUREO BY THE WIRE BROOM WITH 2 ROWS OF TUFTS

/,8

70

0.7

0.6 2 row broom Site ? (C)Trunk road l. row broomSite 1 (N)Trunk road /, row broom Site 5 (DS)Motorway

0 O

O- .... 0

0"5

° ~ t J . m

o

o

O ~ C o _

o (33

0";.

0.3

0.2

"\ \ \

\ \ \ ,

\ \

0-1

0

• Second Third Fourth

50 80 130 50 80 130 50 80 130 50 80 130

Speed (km/h)

Fig.li,.THE EFFECT OF TRAFFIC ON THE BRAKING FORCE COEFFICIENT OF THE SLOW LANE SURFACES TEXTURED BYTHE WIRE BROOM WITH 2 ROWS OF TUFTS

7 ]

0-8

0"?

0-6 /

T /

/ /

/

0"5

o o-~

u

C

"~ 0.3 .a

a l

0.2

0.1

J 2 row broom Site ? (C) Trunk road H ! l, row broom Site 1 (N) Trunk rood O - ~ - Q

4 row broom Site 5 (173) Motorwoy ~ . _ , &

Second year Third year ~ J _ . ~ J. _

50 80 130 50 80 130 50 80 130 50 Speed (kin/h)

Fourthyear

80 130

Fig.15. THE EFFECT OF TRAFFIC ON THE BRAKING FORCE COEFFICIENT OF THE FAST LANE SURFACES TEXTUREO BY THE WIRE BROOM WITH 2 ROWS OF TUFTS

72

.c_

C: 0

'10

0 "10 t - O

0"025

0"020

0"015

0"010

0-005

VoLume of sand

5cc

X-- - - - - ) ( 25cc

• f / I f

.L/

i f

?x

f l

X I o ~

f X / -

X

f f

J f

f

1 f f

0 0.5 1"0 .5 2"0 2-5 mm

I I I I I I 0 0.020 0.040 0'060 0"080 0.100 in

Mean texture depth

Fig.16. THE EFFECT OF THE CYLINDER SIZE ON: THE VARIATION BETWEEN OPERATORS OF THE%.~ND PATCH' METHOD OF OETERMIHIHG TEXTURE DEPTH

3.0

0.120

73

" 0

. m

>.,. , J

U u

J ¢

'10

X

0.100

,_c

0080

0"060

0-0/.0

0-020

o/ J

y, f

/ j -

0 0"6 1"0 1"5 2"0 2-5 mm 3-0 I l I I I I 0 04320 0.0/.0 0.060 0-080 0 "100 in

Texture depth ( 25 cc cyl inder)

Comparison of texture depth measurements made on eleven different surfaces using both the 5cc cylinder and the 25cc cylinder

Fig.17. THE EFFECT OF CVLINOER SIZE ON THE MEASUREMENT OF TEXTURE OEPTH BY THE 'SAND PATCH'METHO0

I 0"120

74

ABSTRACT

Methods of texturing new concrete road surfaces to provide adequate skidding resistance': D.E. WELLER and D.P. MAYNARD B.Sc. (Eng) A.M. lnst.H.E.: Ministry of Trans- port, RRL Report LR 290: Crowthome, 1969(Road Research Laboratory). The development of various methods for tex- turingthe fresh surface of high speed concrete roads is discussed. The performance is reviewed of various roads including those textured by the type of wire broom specified in the current Ministry of Transport Specification for Road and Bridge Works.

The rate of wear and the skidding resistance of slow and fast lane surfaces are examined. An examination is also made of the effect of the initial texture imposed on the rate of change in skiddingresistance with increase in speed.

Recommendations are made for future work to continue the development of various methods of texturing.

ABSTRACT

Methods of texturing new concrete road surfaces to provide adequate skidding resistance': B.E. WELLER and D.P. MAYNARD B.Sc. (Eng) A.M. Inst.H.E.: Ministry of Trans- port, RRL Report LR 290: Crowthorne, 1969 (Road Research Laboratory). The development of various methods for texturing the fresh surface of high speed concrete roads is discussed. The performance is reviewed of various roads including those textured by the type of wire broom specified in the current Ministry of Transport Specification for Road and "Bridge Works.

The rate of wear and the skidding resistance of slow and fast lane surfaces are examined. An examination is also made of the effect of the initial texture imposed on the rate of change in skidding resistance with increase in speed.

Recommendations are made for future work to continue the development of various methods of texturing.

(505) Dd635272 3M 4/70 H.P. Ltd. G1915 PRINTED IN ENGLAND

road research laboratory ministry of transport rrl … · 2016-10-02 · specification 4 relating...

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