Can we get our pavements to live longer

1. Can we get our pavements to live longer? The Rolling stones sings: You can�t always get what you want (2) And if you try sometime you might findYou get what you needThe Rolling stones sings: You can�t always get what you want (2) And if you try sometime you might findYou get what you need

2. Background and Purpose Various pavement design options used on state highways in NZ are developing early rutting in the first 24 months post construction What can we do to reduce pavement/surfacing premature failures (rutting, cracking, heaving, extensive potholing) Identify project reliability levels and risks This paper highlights rutting progression on rehabilitated sites on state highways 2 NZTA and NZIHT - Building and maintaining highways for the future, 2011 Local roads are not necessarily exempt from this phenomenon Design options for new roads and for reconstruction/rehabilitation Local roads are not necessarily exempt from this phenomenon Design options for new roads and for reconstruction/rehabilitation

3. Let�s talk about the challenges Low cost high quality option. Is that possible or just a dream? Reusing existing material with limited investigations Scarcity of good quality basecourse material in the vicinity of the sites New Zealand new pavements and rehabilitation designs are moving more towards the use of modified pavement and recycling/stabilisation Knowledge of material properties by the designer is crucial prior to construction Limited funding 3 NZTA and NZIHT - Building and maintaining highways for the future, 2011 > Limited funding � For investigation, design and construction � In some contracts for example like the Hybrid maintenance ones the contractor is given a lump sum amount to spend per m2 which limits the selection of treatment . > Limited funding � For investigation, design and construction � In some contracts for example like the Hybrid maintenance ones the contractor is given a lump sum amount to spend per m2 which limits the selection of treatment .

4. Let�s talk about the challenges (contd.) Limited field and laboratory testing of pavement materials (recycled & overlays) Cheaper design treatment solutions to meet budget constraints Multiple seals and its impact on pavement performance when recycled Compliance with Austroads guidelines and the NZ Supplements Introduction of impact of vehicles with higher gross mass limit of up to 53 tons (HPMV) on our road network 4 NZTA and NZIHT - Building and maintaining highways for the future, 2011 > Multiple Seals � Multiple layers of seals. I have seen up to 140mm thick multiple layers of chipseal . These are contributing to the early flushing and rutting of the surface > HPMV - The incremental increase in HPMV on already established routes is minimal. However, it will be detrimental on roads that has no HCV in the past and been added to the route. > Multiple Seals � Multiple layers of seals. I have seen up to 140mm thick multiple layers of chipseal . These are contributing to the early flushing and rutting of the surface > HPMV - The incremental increase in HPMV on already established routes is minimal. However, it will be detrimental on roads that has no HCV in the past and been added to the route.

5. Impact on Treatment Design Materials Subgrade: Volcanic ash, silty clay, clayey silt, sand, river run gravel, pumice, scoria and the list goes on Basecourse/Sub-base: Sedimentary (Greywacke, Shell Rock), igneous family (Basalt, Andesite, Rhyolite), etc. Thickness Pavement thickness and layering may be variable throughout a site Variability of Treatments Different historical treatments have been used along the road. i.e. seal patches, localised stabilisation (lime or cement), dig out, rip and remake, scarify, bound and unbound granular overlay Asphalt surfacing at intersections and some high stress areas 5 NZTA and NZIHT - Building and maintaining highways for the future, 2011 Thickness � We have to look at the majority of the pavement structure and design accordingly. Localised weak areas could be treated differently as digouts Mongrel roads countryThickness � We have to look at the majority of the pavement structure and design accordingly. Localised weak areas could be treated differently as digouts Mongrel roads country

6. Project Reliability Definition: The project reliability is the probability that the pavement when constructed to the chosen design will outlast its design traffic before major rehabilitation is required. (Austroads Guide to Pavement Technology Part 2. 2008) Project/Design Reliability levels � Austroads Pavement Design Guide -Table 2.1 85% to 97.5% over the design traffic Project reliability to be chosen by the road agency and designer Currently project reliability levels are not defined in various contracts. Is it 100%? Who is to blame when there is premature pavement or surfacing failure during the first 12 months post construction? 6 NZTA and NZIHT - Building and maintaining highways for the future, 2011 It is unreasonable to expect that a pavement design process can guarantee, with absolute certainty, that a subsequently-constructed pavement will perform to design expectations. There are a number of factors that can have a significant influence on pavement performance. these are but not limited : The construction quality and consistency Material quality not meeting the design chosen values Variable subgrade and pavement thickness along the site The environment and weather impact Because of this lack of certainty, an appropriate measure of the anticipated performance of the proposed pavement is its project reliability which is defined as the probability that ................. : It is unreasonable to expect that a pavement design process can guarantee, with absolute certainty, that a subsequently-constructed pavement will perform to design expectations. There are a number of factors that can have a significant influence on pavement performance. these are but not limited : The construction quality and consistency Material quality not meeting the design chosen values Variable subgrade and pavement thickness along the site The environment and weather impact Because of this lack of certainty, an appropriate measure of the anticipated performance of the proposed pavement is its project reliability which is defined as the probability that ................. :

7. Pavement Life Assessment NZTA Standard Professional Services Guidelines PSG/5 - Pavement Life Assessment version 1, March 2009 Currently adopted in some state highway network contracts. It is considered by many to be a good guiding tool for pavement life assessment. It is recommended that a meeting between the Contractor/Consultant/NZTA Highways and Network Operations Group (HNO) take place before the guidelines are implemented For example in the hybrid model, the contractor being the designer of the pavement, shall demonstrate the design robustness of the pavement and material meet the design traffic The pavement life assessment should be against the following criteria: Pavement Design Pavement Material Pavement Layer Compaction Pavement Layer Stiffness 7 NZTA and NZIHT - Building and maintaining highways for the future, 2011 The relevance of this guideline is that it could lead to improvement in design and quality of the finished product, thereby enhancing the pavement life. This PSG/5 could be rolled over to other road controlling authorities contracts. Pavement Design � To check whether the design exceeds the design traffic Pavement Material � The contractor shall assess samples of pavement materials proposed for use that are compliant with NZTA specs Design life � Has the design life been met following PC testing (FWD and HSD rutting)The relevance of this guideline is that it could lead to improvement in design and quality of the finished product, thereby enhancing the pavement life. This PSG/5 could be rolled over to other road controlling authorities contracts. Pavement Design � To check whether the design exceeds the design traffic Pavement Material � The contractor shall assess samples of pavement materials proposed for use that are compliant with NZTA specs Design life � Has the design life been met following PC testing (FWD and HSD rutting)

8. Potential Causes of Rutting Inadequate pavement thickness Marginal basecourse/subbase Weak and variable subgrade Ingress of water through the pavement surfacing or shoulder Structural overloading of pavement (exacerbated in asphalt pavement, by high pavement temperature - shoving) Poor construction quality control, particularly compaction, water content and drainage efficiency Densification of upper pavement layers including chip roll- over 8 NZTA and NZIHT - Building and maintaining highways for the future, 2011 I have listed a number of factors that contribute to pavement rutting. The main ones are:I have listed a number of factors that contribute to pavement rutting. The main ones are:

9. Examples of Rutting NZTA and NZIHT - Building and maintaining highways for the future, 2011 9 These are photos of rutting for different state highways. You will notice that when the rutting bowl is large it is an indication that the subgrade is overstrained. However, densification of the basecourse plays an important part in the development of the rutting in the early life of the pavement. Where asphalt is the surfacing we need to ensure that the surface deflections before surfacing do not exceed 1.3mm as the asphalt will struggle to resist the tensile forces caused by bending and results in premature fatigue cracking. (photo at the bottom right)These are photos of rutting for different state highways. You will notice that when the rutting bowl is large it is an indication that the subgrade is overstrained. However, densification of the basecourse plays an important part in the development of the rutting in the early life of the pavement. Where asphalt is the surfacing we need to ensure that the surface deflections before surfacing do not exceed 1.3mm as the asphalt will struggle to resist the tensile forces caused by bending and results in premature fatigue cracking. (photo at the bottom right)

10. Case Studies Three AWT Treatment case studies related to rutting progression have been assessed; Unbound Overlay � State Highway 2, Wellington Cement Modified Overlay � State Highway 53, Wellington Foamed Bitumen Stabilised Overlay � State Highway 49, Ruapehu 10 NZTA and NZIHT - Building and maintaining highways for the future, 2011

11. Case Study 1- Unbound Overlay 11 NZTA and NZIHT - Building and maintaining highways for the future, 2011

12. Case Study 2 � Cement modified overlay 12 NZTA and NZIHT - Building and maintaining highways for the future, 2011

13. Case Study 3 � Foamed bitumen stabilised overlay 13 NZTA and NZIHT - Building and maintaining highways for the future, 2011

14. Post Construction Assessment There does not seem to be a link between predicted rutting from FWD deflection back calculation and actual rutting measured by High Speed Data (HSD) FWD back-calculation of stiffness and total life is based on Austroads subgrade strain criteria (for modified and unbound pavements) and does not take into account any densification of the basecourse or subbase HSD rutting testing shows that up to15% of the site with unbound overlay could have rutting in excess of 10mm in just one year post construction Current network maintenance contracts require that the 85th percentile rutting shall be less than 5mm twelve months after construction NZTA and NZIHT - Building and maintaining highways for the future, 2011 14 HSD test measures actual rutting of both left and right wheel paths. Whereas FWD measures the deflection on the left wheel path It appears from records of few networks that the 85th percentile rutting of 5mm is generally difficult to achieve with the current overlay/recycling options apart from an overlay with foamed bitumen stabilisation. The other options will struggle to meet these requirements and these requirements might need to be relaxed to avoid moving towards more expensive options. The cement modified overlay seems to be reasonably performing in terms of reducing early life rutting.HSD test measures actual rutting of both left and right wheel paths. Whereas FWD measures the deflection on the left wheel path It appears from records of few networks that the 85th percentile rutting of 5mm is generally difficult to achieve with the current overlay/recycling options apart from an overlay with foamed bitumen stabilisation. The other options will struggle to meet these requirements and these requirements might need to be relaxed to avoid moving towards more expensive options. The cement modified overlay seems to be reasonably performing in terms of reducing early life rutting.

15. Where from here? Post construction and design reliability requirements need to be agreed with the client based on road classification To minimise risk of premature pavement failures, it is recommended that additional investigation in the field and in the lab at design stage to predict the performance of the available material prior to construction Unconfirmed Compressive Strength (UCS) test, currently used on modified pavement, does not accurately predict potential cracking from tension forces at the bottom of the modified layer. However, it will still provide reasonable information on the strength and reactivity of the material with additives Tests such as beam flexure testing and indirect tensile test (ITS) to measure the tensile resistance can be considered during investigation or post construction 15 NZTA and NZIHT - Building and maintaining highways for the future, 2011 Additional Investigation - Additional testing may include reactivity testing of the proposed imported material and existing seal, basecourse/subbase with cement, lime or foamed bitumen. Test pits to be located following the FWD testing and not before it to determine the weak and strong spots of the pavement. A minimum of 1 test pit per direction per lane every 200m is recommended Additional Investigation - Additional testing may include reactivity testing of the proposed imported material and existing seal, basecourse/subbase with cement, lime or foamed bitumen. Test pits to be located following the FWD testing and not before it to determine the weak and strong spots of the pavement. A minimum of 1 test pit per direction per lane every 200m is recommended

16. Where from here? (continued) Further research is required to predict future rutting with different pavement types Develop national database of the treatments used and distribute to the industry Understanding different pavement material behaviour under loading Increase the level of construction quality control, quality assurance and construction monitoring Introduce construction holdpoints at critical stages during pavement layer construction including sealing 16 NZTA and NZIHT - Building and maintaining highways for the future, 2011 Further Research - The research will help in understanding the expected rutting for different treatment types in the first 12-24month post construction and understanding what is the achievable 85th percentile rutting . We can then establish whether the contract requirements of 5mm after 12months is achievable and on what treatments these requirements can be met. Some tips on the CM The Construction monitoring is to ensure that the hold points set up in the contract documents are met. This may include for example checking the degree of compaction of the layers, deflection testing can be used on the basecourse or even subbase if need be. Scala testing of the SG The final acceptance of the basecourse to the specs and the seal design prior to sealing is crucial to the success of the job. As mentioned earlier, where asphalt is the final surfacing for example we need to ensure that the deflections measured before surfacing do not exceed 1.3mm as the asphalt will struggle to resist the tensile forces caused by bending and results in premature fatigue cracking. Premium asphalt mixes with polymers could provide extra resistance to slightly higher deflections to a limited extent Further Research - The research will help in understanding the expected rutting for different treatment types in the first 12-24month post construction and understanding what is the achievable 85th percentile rutting . We can then establish whether the contract requirements of 5mm after 12months is achievable and on what treatments these requirements can be met. Some tips on the CM The Construction monitoring is to ensure that the hold points set up in the contract documents are met. This may include for example checking the degree of compaction of the layers, deflection testing can be used on the basecourse or even subbase if need be. Scala testing of the SG The final acceptance of the basecourse to the specs and the seal design prior to sealing is crucial to the success of the job. As mentioned earlier, where asphalt is the final surfacing for example we need to ensure that the deflections measured before surfacing do not exceed 1.3mm as the asphalt will struggle to resist the tensile forces caused by bending and results in premature fatigue cracking. Premium asphalt mixes with polymers could provide extra resistance to slightly higher deflections to a limited extent

17. Thank you NZTA and NZIHT - Building and maintaining highways for the future, 2011