PUBLISHED PROJECT REPORT PPR810. In service performance of SteelFlow, a SteelPhalt ultra-thin surfacing material. P D Sanders and M Militzer

Transcription

1 PUBLISHED PROJECT REPORT PPR810 In service performance of SteelFlow, a SteelPhalt ultra-thin surfacing material P D Sanders and M Militzer

2 Report details Report prepared for: Harsco Steelphalt Project/customer reference: Copyright: Transport Research Laboratory Report date: March 2017 Report status/version: Issue Quality approval: S McRobbie (Project Manager) Approved M Greene (Technical Reviewer) Approved Disclaimer This report has been produced by TRL Limited (TRL) under a contract with Harsco Steelphalt. Any views expressed in this report are not necessarily those of Harsco Steelphalt. The information contained herein is the property of TRL Limited and does not necessarily reflect the views or policies of the customer for whom this report was prepared. Whilst every effort has been made to ensure that the matter presented in this report is relevant, accurate and up-to-date, TRL Limited cannot accept any liability for any error or omission, or reliance on part or all of the content in another context. When purchased in hard copy, this publication is printed on paper that is FSC (Forest Stewardship Council) and TCF (Totally Chlorine Free) registered. PPR810

3 Contents Executive Summary 2 1 Introduction 3 2 Products and trial sites 4 3 Measurements made 5 4 Survey Results Skid resistance performance Non-event carriageways with one-way traffic (Category B2, IL = 0.4) Non-event carriageways with two-way traffic (Category C, IL = 0.4) Non-event carriageways with two-way traffic (Category C, IL = 0.45) Gradient 5-10% longer than 50 m (Category G1, IL = 0.45) Approaches to pedestrian crossings and other high risk situations (Category K, IL = 0.50) Bend radius <500 m - carriageway with two-way traffic (Category S2, IL = 0.50) Assessment of trafficking levels and material ages Summary of material performance 15 5 Conclusions 18 6 References 19 1 PPR810

4 Executive Summary Steelphalt has developed a range of asphalt products using steel slag aggregate. Whilst examples of these materials have been in service for almost two decades, the products are not currently exploited to their full capacity despite their environmental credentials. A contributory factor is that steel slag aggregates do not typically perform as well in laboratory tests designed to examine polish resistance, as they apparently do in-service. In 2014 and 2015 TRL carried out skid resistance monitoring on sites utilising products across the Steelphalt range. The goal of these surveys was to demonstrate the in-service performance of Steelphalt materials in as wide a range of situations as possible. The findings were presented in PPR737 (Dunford, et al., 2015) and PPR773 (Militzer, et al., 2015). The work presented in this report extends the previous studies by carrying out additional skid resistance measurements in Measurements were carried out on six sites including high and low risk locations, all of which comprised the SteelFlow 6 mm material. A number of the sites had significantly higher levels of traffic than those on the previously assessed sites where this SteelFlow 6mm material was used. This report presents the results of the measurements and analyses the performance against the site categories and traffic levels used for the specification of aggregate in HD36. From the work carried out the following conclusions can be me made: Materials laid on sites with an IL of 0.40, low stress sites, provided wide ranging skid resistance values ( SC(50)). The vast majority of these values were above the 0.40 IL and in many cases indicated a very good level of performance. The performance of materials laid on sites with an IL of 0.45 was good with the majority of values well exceeding the IL. The performance of materials laid on sites with an IL of 0.50 could not be fully assessed due to a lack of appropriate data. However, measurements made on category S2 sites (bends) indicated that high levels of performance are possible. The highest observed skid resistance values were measured on the oldest sites, and, sites exposed to the least amount of trafficking. This observation indicates that the combined effect of weathering and trafficking are aiding the materials skid resistance performance. This is similar to the early life effects observed on some thin surface course systems. 2 PPR810

5 1 Introduction Steelphalt has developed a range of asphalt products incorporating steel slag aggregate. Whilst there are examples of these materials that have been in service for almost two decades, the products are not currently exploited to their full capacity despite their environmental credentials. A contributory factor is that steel slag aggregates do not typically perform as well in laboratory tests designed to examine polish resistance, as they apparently do in-service. In 2014 and 2015 TRL was commissioned to carry out skid resistance monitoring on sites utilising products across the Steelphalt range. The goal of these surveys was to demonstrate the in-service performance of Steelphalt materials in as wide a range of situations as possible. The findings were presented in PPR737 (Dunford, et al., 2015) and PPR773 (Militzer, et al., 2015). The results of these previous studies highlighted the strong performance of the SteelFlow 6mm material, although the levels of traffic on the sites surfaced with this material were not high. The material has subsequently been installed on a number of additional sites, some of which have higher traffic levels. The work presented in this report focuses on this material, and includes sites with higher levels of trafficking than were previously assessed. Measurements were carried out on six sites including high and low risk locations, all of which comprised the SteelFlow 6 mm material. This report presents the results of the measurements and analyses the performance against the site categories and traffic levels used for the specification of aggregate in HD36 (2006). 3 PPR810

6 2 Products and trial sites In-service examples of the SteelFlow 6 mm material were surveyed across six trial sites. The sites possessed a range of traffic conditions and ages as summarised in Table 2-1. A summary of the site locations is given in Figure 2-1, and detailed locations are provided in Appendix A. Table 2-1 Summary of trial sites and materials assessed Site No. Location Product Date laid Traffic (CVD 1 ) 1 Green Arbour Rd, Thurcroft, Rotherham SteelFlow 6 mm Jun Meadow Bank Rd, Rotherham SteelFlow 6 mm May Rockley Ln Birdwell, Barnsley SteelFlow 6 mm Feb-2014 < Bents Rd, Barnsley SteelFlow 6 mm Jul-2013 < Wharncliffe Street, Rotherham SteelFlow 6 mm Mar St George's Bridge, Doncaster SteelFlow 6 mm Jun Figure 2-1 Summary of site locations (Ordnance Survey, n.d.) 1 CVD = Commercial vehicles per day 4 PPR810

7 3 Measurements made TRL was commissioned to independently monitor the skid resistance performance of the sites during the skid resistance survey season of A Sideway-force Coefficient Routine Investigation Machine (SCRIM) was used by TRL to make measurements in accordance with HD28 (2015) and British Standard BS :2006 (British Standards, 2006). Three surveys were carried out during 7 th -8 th June, 25 th -26 th July and 26 th -27 th September These survey dates coincided with the Early, Middle and Late period of the skid resistance survey season. The skid resistance measurements made using SCRIM are returned as speed corrected average values for each 10 m section of road. Measurements made during each survey period were aligned for each site, thus enabling an average measurement to be calculated for the SCRIM survey season as a whole, referred to as the Mean Summer SCRIM Coefficient (MSSC). Characterisation by MSSC is designed to account for some of the long term fluctuations occurring in skid resistance measurement by reducing the effect of within year seasonal variation. It is well understood that measurements made at different times of year will provide different results; measurements made during the winter will generally be higher than those made in the summer (Highways England, Transport Scotland, Welsh Government, The Department for Regional Development Northern Ireland, 2015). This is because the effect of adverse weather in winter is to roughen the surface such that the skid resistance increases whereas the polishing action of vehicle tyres in the relatively calm weather of summer reduces the skid resistance. Even within the skid resistance survey season (May to October) measurements made in the middle of the season tend to be lower than those in the early or late periods. This creates the characteristic U shape in measurements as in Figure 3-1 which presents the individual results for Site 5. The use of an MSSC characterisation therefore allows for a more robust assessment than a single snapshot survey and provides a good baseline for future measurements. Figure 3-1 Example of seasonal variation 5 PPR810

8 Following the methodology defined in PPR737, PPR773 and in accordance with HD28 (2015), site categories and the appropriate Investigatory Level (IL) were assigned to each 10 m section of road. Table 3-1, which is reproduced from HD28, shows the different sites categories and their assigned ILs. Table 3-1 Investigatory levels for different categories of site (Reproduced from HD28) A B C Q K R G1 G2 S1 S2 Site Category and Definition Motorway Non-event carriageway with one-way traffic Non-event carriageway with two-way traffic Approaches to and across minor and major junctions, approaches to roundabouts and traffic signals Approaches to pedestrian crossings and other high risk situations Roundabout Gradient 5-10% longer than 50 m Gradient >10% longer than 50 m Bend radius <500 m - carriageway with oneway traffic Bend radius <500 m - carriageway with twoway traffic IL for CSC data (Skid data speed corrected to 50 km/h and seasonally corrected) HD36 (2006) and Interim Advice Note (IAN) 156 (2012) provide a summary of surfacing options for motorways and trunk roads in the UK and advise on current requirements for surfacings. In particular, guidance is provided on the choice of suitable Polished Stone Value (PSV) levels for the coarse aggregate in surfacing materials, depending on the site category, investigatory level and traffic level. The measurements made as part of this study were used to categorise the sites based on their site category, IL and traffic level using the guidance provided within HD36 and IAN156, in particular Table 3.1 of those documents. Following the methodology described in PPR773, it was determined in which regions of that table the Steelphalt products are performing well, since direct measurement of PSV may be inappropriate for these materials. The minimum, average and maximum MSSC for each site category within a site were calculated and compared to the range of required IL. 6 PPR810

9 4 Survey Results This chapter presents the results of the surveys carried out. The measurements made have been processed as per the methodology stated in Chapter 3. Discussion of the results is presented in this chapter and the conclusions drawn are presented in Chapter Skid resistance performance This section presents the results of the skid resistance surveys; an assessment is made of the skid resistance performance of the material for various site categories. An assessment of the material performance with age is then presented and, finally, the results are summarised by comparing the performance of the sites with the performance requirements laid out in HD36 and IAN Non-event carriageways with one-way traffic (Category B2, IL = 0.4) Figure 4-1 and Figure 4-2 show the distribution of MSSC across all sites for sections that were assigned site category B. For these sections, an IL of 0.4 was assigned and the vast majority of surface assessed was above this limit. A small number of values, approximately 70 m (3.95% of the material assessed), were recorded below the IL, but on the whole the material performed well given that Site 6 sits in the highest trafficking band of HD 36. Assessing the performance of the material by traffic level suggests that areas exposed to greater amounts of trafficking have a tendency to provide lower levels of skid resistance than those exposed to lower traffic levels. However, most of the values measured at the higher traffic level were well above the IL. Figure 4-1 Distribution of MSSC values by site for category B sections 7 PPR810

10 Figure 4-2 Distribution of MSSC values by traffic level for category B sections Non-event carriageways with two-way traffic (Category C, IL = 0.4) Figure 4-3 and Figure 4-4 show the distribution of MSSC across all sites for sections that have been assigned site category C with an IL of 0.4. As with the category B sites, the vast majority of values recorded were above this level with some values reaching The performance of the material with respect to traffic level is similar as is shown in Figure 4-4. However, only two traffic levels were observed on this site category, <250 CVD and 380 CVD, so a full assessment of the effect of traffic level on category C sites is not possible. Figure 4-3 Distribution of MSSC values by site for category C sections with an IL of PPR810

11 Figure 4-4 Distribution of MSSC values by traffic level for category C sections with an IL of Non-event carriageways with two-way traffic (Category C, IL = 0.45) Figure 4-5 and Figure 4-6 show the distribution of MSSC across all sites for sections that have been assigned site category C with an IL of Approximately half of the measurements made were above the IL. Figure 4-5 shows that the south bound lane of Site 5 was performing slightly better than the northbound. An assessment of performance with traffic level was not possible as only one traffic level was observed on category C sites with an IL of Figure 4-5 Distribution of MSSC values by site for category C sections with an IL of PPR810

12 Figure 4-6 Distribution of MSSC values by traffic level for category C sections with an IL of Gradient 5-10% longer than 50 m (Category G1, IL = 0.45) Figure 4-7 and Figure 4-8 show the distribution of MSSC across all sites for sections that have been assigned site category G1 with an IL of Overall the performance of these sections is good with the majority of values measured above the investigatory level for this site category. All of the measurements made on Site 5, which was more heavily trafficked than Site 3, were above the IL whereas a small number of measurements on Site 3 were below the IL. Figure 4-7 Distribution of MSSC values by site for category G1 sections 10 PPR810

13 Figure 4-8 Distribution of MSSC values by traffic level for category G1 sections Approaches to pedestrian crossings and other high risk situations (Category K, IL = 0.50) Figure 4-9 and Figure 4-10 show the distribution of MSSC across all sites for sections that were assigned site category K with an IL of The measured values are all below the IL for this site category. However, making a definitive assessment of the performance of the material is difficult as the available data consisted of only a limited number of observations, made after 3 months in service. Figure 4-9 Distribution of MSSC values by site for category K sections 11 PPR810

14 Figure 4-10 Distribution of MSSC values by traffic level for category K sections Bend radius <500 m - carriageway with two-way traffic (Category S2, IL = 0.50) Figure 4-12 and Figure 4-13 show the distribution of MSSC across all sites for sections that have been assigned site category S2 with an IL of As with the category K sections, the amount of data collected on category S2 sections was relatively small. The results from the S2 sections are nonetheless interesting because they show two levels of performance for the same site. The westbound carriageway is performing well above the investigatory level and is providing very high levels of skid resistance. The eastbound carriageway however is performing less well with all of the values below the IL. This observation is important because it demonstrates that the material is possible of providing very high levels of skid resistance on high stress sites. It is plausible that the cause of this discrepancy is related to the direction of the bend. The bend on the eastbound carriageway is right handed, a vehicle traversing in this direction would therefore receive some load transfer to its nearside wheels. It is possible that this transfer of load could cause an increase in stress on the surfacing in the nearside wheel path (the wheelpath measured by SCRIM), this could therefore cause a greater amount of polishing in this direction than the westbound carriageway, hence the lower level of skid resistance (Figure 4-11). An assessment of performance with traffic level was not possible as only one traffic level was observed on category S2 sites. 12 PPR810

15 Figure 4-11 Example of load transfer during cornering Figure 4-12 Distribution of MSSC values by site for category S2 sections 13 PPR810

16 Figure 4-13 Distribution of MSSC values by traffic level for category S2 sections Assessment of trafficking levels and material ages Figure 4-14 and Figure 4-15 show the distribution of MSSC values measured with respect to traffic level and material age respectively. The distribution of MSSC values by trafficking level is as might be expected and shows that the materials exposed to the lowest trafficking levels provide the highest levels of skid resistance. However there is a wide range of skid resistance levels for materials exposed to <500 CVD and this indicates that trafficking level, although a key component, is not the only contributor to skid resistance performance. Figure 4-14 Distribution of MSSC values by traffic level for all site categories 14 PPR810

17 The distribution of MSSC values by material age shows an improvement in material performance with age. This on first inspection may seem counter intuitive; however this is a phenomenon that has been previously observed on more traditional asphalt materials (Greene, et al., 2010). The development of skid resistance with age over this timeframe suggests that that the materials assessed go through similar early life effects to other asphalt materials. A combination of weathering and trafficking combine to remove the low skid resistance bitumen binder from the aggregate particles over the initial stages of service life. This reveals the higher skid resistant aggregate, hence the increase in skid resistance. Interestingly the results show that the oldest sites are the ones exposed to the least amounts of traffic. The observation that the bitumen layer is removed by the polishing action of traffic therefore appears contradictory because the most highly trafficked sites are have been exposed to more vehicles than the lower trafficked, older surfaces. It would be expected for the bitumen layer to therefore be removed through this action, resulting in higher skid resistance levels, but this is not the case. The reason for this behaviour is due to the combined phenomena of weathering and traffic effects. The current thinking is that weathering, which is a time based event, hardens the bitumen making it easier for the traffic to remove with the abrasive action of vehicle wheels. Without this weathering process it is likely that the malleable bitumen would polish and therefore reduce the skid resistance of the surface. If the materials assessed continue to follow the same relationship as other asphalt surfacings, it would be expected that the skid resistance would reduce to an equilibrium level as the newly exposed aggregate is polished by traffic. Figure 4-15 Distribution of MSSC values by material age for all site categories Summary of material performance The measurements of skid resistance made have been compared with the classification of traffic flow, site category and Investigatory Level. This information has been presented in Table 4-1 which demonstrates the performance of the materials against the requirements set out in HD36 and IAN PPR810

18 Note that any apparent discrepancies between the values presented in Table 4-1 and those shown in the earlier histograms are due to the rounding of data and the handling of measurement values in histogram data for example a measured MSSC of will be reported in Table 4-1 as 0.33, but, as it is above 0.33 it will be shown in the 0.34 data bin in a histogram plot. The effect of averaging length on the results is worth consideration. The measurements made have been assessed as 10 m averages whereas the ILs in HD28 are based on 100 m averages. It is possible that the 100 m average measurement may be above IL even if some 10 m measurements within the 100m length fall below IL. Table 4-1 shows that Sites 2, 3 and 6 provided average MSSC values above the IL required for the site categories and traffic levels defined for their locations, however the minimum MSSC values for these sites were below IL. Site 4 performed well against the requirements of the location with both the average and minimum MSSC values above IL. The performance of Sites 1 and 5 was mixed, on the whole site 5 performed well against its requirements but a slight variation in MSSC between the two directions of this site meant that the minimum MSSC measured on the south bound carriageway was below IL. The bend section of Site 1 showed a difference between the east and westbound directions, with the former being below IL. It is possible that these results have been influenced by load transfer, and therefore variations in polishing, of vehicles travelling through the bend in each direction. 16 PPR810

19 Table 4-1 Summary of material performance Site category A1 A2 B1 Site description Motorways where traffic is generally free-flowing on a relatively straight line Motorways where some braking regularly occurs Dual carriageways where traffic is generally free-flowing on a relatively straight line IL Site Min. Avg. Max. Cat. I.L B NB B SB B Minimum PSV required for given IL, traffic level and type of site Traffic (cv/lane/day) at design life Over 6000 Minimum and average above IL Average above IL, Minimum below IL Minimum and average below IL B2 C G1/G2 K Q R S1/S2 Dual carriageways where some braking regularly occurs Single carriageways where traffic is generally free-flowing on a relatively straight line Gradients >5% longer than 50m as per HD 28 Approaches to pedestrian crossings and other high risk situations Approaches to major and minor junctions on dual carriageways and single carriageways where frequent or sudden braking occurs but in a generally straight line Roundabout circulation areas Bends (radius <500m) on all types of road, including motorway link roads; other hazards that require combined braking and cornering EB C WB C NB C SB C EB C WB C NB C SB C NB G SB G NB G SB G NB K SB K EB S WB S PPR810

20 5 Conclusions From the work carried out the following conclusions can be made: Materials laid on sites with an IL of 0.40, low stress sites, provided wide ranging skid resistance values ( SC(50)). The vast majority of these values were above the 0.40 IL and in many cases indicated a very good level of performance. The performance of materials laid on sites with an IL of 0.45 was good with the majority of values well exceeding the IL. The performance of materials laid on sites with an IL of 0.50 could not be fully assessed due to a lack of appropriate data. However, measurements made on category S2 sites (bends) indicated that high levels of performance are possible. The highest observed skid resistance values were measured on the oldest sites, and, sites exposed to the least amount of trafficking. This observation indicates that the combined effect of weathering and trafficking are aiding the materials skid resistance performance. This is similar to the early life effects observed on some thin surface course systems. 18 PPR810

21 6 References British Standards, BS Methods for measuring the skid resistance of pavement surfaces - Sideway-force coefficient routine investigation machine, London: BSi. Dunford, A., Nicholls, J. C., Viner, H. & Sanders, P. D., PPR737 In service performance of Steelphalt products, Wokingham: TRL. Greene, M. J., Sanders, P. D. & Roe, P., PPR492 Further studies of the skid resistance of asphalt surfaces in their early life, Wokingham: TRL. Highways England, Transport Scotland, Welsh Government, The Department for Regional Development Northern Ireland, HD36/06 - Surfacing materials for new and maintenance construction., London: The Stationary Office. Highways England, Transport Scotland, Welsh Government, The Department for Regional Development Northern Ireland, HD29/08 - Data for pavement assessment, London: The Stationery Office. Highways England, Transport Scotland, Welsh Government, The Department for Regional Development Northern Ireland, IAN156/12 Revision of aggregate specification for pavement surfacing, London: The Stationery Office. Highways England, Transport Scotland, Welsh Government, The Department for Regional Development Northern Ireland, HD28/15 Skidding resistance, London: The Stationery Office. Militzer, M., Viner, H., McRobbie, S. & Greene, M., PPR773 In service performance of Steelphalt products (2015), Wokingham: TRL. Ordnance Survey, n.d. Ordnance survey open data. [Online] Available at: [Accessed ]. 19 PPR810

22 Appendix A Site locations (Ordnance Survey, n.d.) A.1 Site 1 Green Arbour Rd, Thurcroft, Rotherham (Both directions) A.2 Site 2 - Meadow Bank Rd, Rotherham - Approach to M1 roundabout (J34) 20 PPR810

23 A.3 Site 3 - Rockley Ln, Birdwell, Barnsley (Both directions) 21 PPR810

24 A.4 Site 4 Bents Rd, Barnsley (Both directions) A.5 Site 5 - Wharncliffe Street, Rotherham (Both directions) 22 PPR810

25 A.6 Site 6 - St George's Bridge, Doncaster (Both Directions) 23 PPR810

26 In service performance of SteelFlow, a SteelPhalt ultra-thin surfacing material Steelphalt has developed a range of asphalt products using steel slag aggregate. In 2014 and 2015 TRL carried out skid resistance monitoring on sites utilising products across the Steelphalt range. The goal of these surveys was to demonstrate the in-service performance of Steelphalt materials in as wide a range of situations as possible. The work presented in this report extends the previous studies by carrying out additional skid resistance measurements in Measurements were carried out on six sites including high and low risk locations, all of which comprised the SteelFlow 6 mm material. Other titles from this subject area PPR737 In service performance of Steelphalt products. Dunford, A; Nicholls, J C; Viner, H; Sanders, P D PPR773 In service performance of Steelphalt products. Militzer, M; Viner, H; McRobbie, S; Greene, M TRL Crowthorne House, Nine Mile Ride, Wokingham, Berkshire, RG40 3GA, United Kingdom T: +44 (0) F: +44 (0) E: enquiries@trl.co.uk W: ISSN ISBN PPR810