Question:
Describe about pavement investigation report.
Answer:
During survey surface deterioration due to ageing and weathering was observed at several places along the effected sections of the dual carriage way. At some places the cracks were extended deep down the surface layers. Rut depths generally measured below 6mm.
Coring survey revealed asphalt thickness relatively uniform. On eastbound it ranged between 210mm-385mm and on westbound carriage way from 270mm to 425mm.
As shown by DCP analyses granular sub base thickness ranged from 173-470. The in-situ strength was good measuring between 44% to 150%.
Deflectograh results showed variable deflections along most areas on the road. At most places deflection reading were below 100 microns showing good strength and at only few places the deflectograph readings were higher suggesting weakness at that points.
On the other hand HAMPS survey data however revealed satisfactory ride quality and texture. Skidding resistance was low at only two short distances.
All the above mentioned data suggested that the road was mostly in good condition and problems were related generally to surface related distress.
VCS or Visual Condition Survey was carried out on lane No. 1. Cracking, chip loss, pot holes and rutting features were observed. Rut depths were also satisfactorily measured.
The condition of each carriage is detailed below:
Eastbound Carriageway:
The main defects were longitudinal and transverse cracks, chip loss and potholes.
Eleven locations revealed chiploss which amounted to a total length of 350 m.
Longitudinal cracking are caused by continued tensile stresses on pavements.
Among longitudinal and transverse cracks those having greater width were spaced from one another by 20m or more. Only few transverse cracks were spaced by more than 3m to 10m.
Joint sealant was very poor or missing at many construction joints. Adhesive sealant loss occurs when sealant/asphalt concrete interface can no longer sustain the shear and tensile forces due to traffic and pavement contract that happens cold weather. To prevent water influx joint sealed sealant is highly recommended.
Reflector studs were missing at many places.
Westbound carriageway:
Defects were mostly found to be same as found in eastbound carriageway with few exceptions like sunken patch on lane 1, a blocked drain and missing mark post.
Approximately 13 locations showed extensive chip loss amounting to 300 m of road length.
Joint sealant was either entirely missing or very poor at several places on sealant joints. It is recommended that sealant be applied on these sealant joints to prevent water inflow.
The blocked drain at Mp 15/6 was found to be flooded with water causing water stagnation in the area. The drain needs to be unclogged on priority basis. The missing marker post at 15/3 needs be put in place.
Rut depth was mostly below 6 mm on both the directions indicating that it was a minor problem for most length of the carriageway. However two sections with total length of 370m rut depth above 6mm on eastbound lane a total of 123m accounted for 8 to 9 mm rut depth whereas on westbound lane 247 m accounted for 7 to 12 mm deep ruts.
This stretch mostly constitutes a bridge deck, hence likely cause is the defect in waterproof asphalt layer. Traffic loads lead to elastic deformations on bridge deck. Therefore on decks rolled or compacted asphalt and mastic asphalt are applied
These two lengths of category 2 to 3 rutting continue to be monitored.
Vehicle restraint system consists of corrugated tension and box beams. They generally were rust free and in good condition. Required height of barrier is 610 but on the west bound lane 1 it ranged from 500-710, and needs correction.
Core sample data revealed pavement surface had uniform asphalt thickness. Average thickness was greater than 300 mm throughout.
Asphalt thickness was generally good however de-bonding between layers was found in number of cores.
Crack depths of transverse and longitudinal cracks were usually 100mm in depth.
DCP tests revealed that majority of pavement had adequate sub base. Deflectograph survey was carried out to find the structural condition of wheel paths both offside and nearside of
lane 1 in both directions. At 40 mm depth temperature ranged between 26.4 to 20.8 on eastbound and 21.5 to 20 on westbound carriageway.
Deflections profiles on eastbound indicated deflection ranged from 100 microns to 200 microns suggesting strong pavement. In some cases it was found to be higher.
On westbound carriageway deflection was found more variable reaching more than 200 microns suggesting apparent distress on these locations.
Interpretation from deflectograph data:
In the UK Deflectograph has been the main method of assessing the structural condition of pavements. The results indicated that most of the pavement can be termed as long life pavement. Ninety three present of the carriageway which is eastbound was classified determinate life pavement type. Eighty four percent of westbound carriageway was determined to be LLP and 16% as DLP.
Remaining life prediction for DLP sections of carriageway varied from 0.2 years to 13 years. Very low remaining life prediction was found for areas with transverse and longitudinal fissures and was less than 5 years.
Deflections figures makes it necessary to impart overlay thickness from 40mm to 110 mm so as to achieve 20 year design life span. However, the observation is only indicative and needs not to be taken in isolation.
Texture depth in both eastbound and west bound lane 1 were in category 1 to category 2 and none of them was in 3 or 4 categories indicating texture not be of concern presently.
All values from TRACS data indicate that readings have not reached to the levels which could be of concern.
Data did not reveal any cracking in the HAMPS database.
Fretting is of concern if the values go beyond 1.15%. i.e, category 3. Fretting of category 3 was found in 19 out 89 hundred metre lengths in eastbound carriageway (20%) and 43 of 87 hundred metre lengths in westbound carriageway (48%).Most of these values were found in lane 2.
Skidding resistance:
Values for this factor were derived from lane 1. Most of the MSS values are greater than IL level or investigatory level i.e, 0.35 for category site B and 0.45 for category site S1 OR 0.5 for category site Q. In places were category Q is found resurfacing needs to be done.
No noise data was found in database of HAPMS for surveyed sections.
Brief Assessment of Pavement Condition
Pavement construction is largely flexible, with average asphalt thickness more than
300mm. Failure in Asphalt pavements is often an complex process involving low temperature. Investigation of cores showed materials were, on the whole, in good condition.
Foundation was also found to be in good condition as revealed by DCP examination. The thickness of granular sub-base was largely greater than 200mm (ranging from 172mm-
471mm) having good in-situ strength, generally higher than 74% CBR (ranging from 45-150). In-situ subgrade toughness ranged from 14% to 68% CBR, possessing average of 30% CBR, which again indicating a strong foundation.
Most of the surveyed site has ageing HRA surface, apart from few small sections with thin surface patching. Both carriageways had identical visual condition with most of the defects spotted in lane 1.The distresses indicated usual ageing HRA surface, with local chip loss (ranging from moderate to severe) in addition to minor potholes and transverse and longitudinal cracks. Cracking was variable along the site – majority of the lengths had no cracks (800m) remaining areas had occasional full width transverse cracks whereas other (smaller ones) areas had numerous longitudinal and transverse cracks along wheel paths. Ten cores were extracted near cracks which indicated crack depths of 100mm to full depth.
The rut depths were mostly below 5mm – hence rutting is not a substantial problem at present. This is in full agreement with data of TRACS which showed there were no lengths with rut depth of 11mm or greater than that. However, a 12mm rut was found to be on the bridge deck on the westbound lane 1 at with values of Mp 20/3+53m. This rut as a part of two small sections (with total length of 370m) which had rut depths more than areas nearby, with rut depths more than 7mm, nearing category 3. Some of these areas in which these ruts were found showed other types of defects as well like cracking and potholes. To avoid disruptions in traffic in future corrective measures are needed.
In general variable deflections were found along most of the site by the Deflectograph results. Pavement condition was found to be strong because most values were below 100 microns.
Many sections and points had greater deflections (higher than 200 microns) at test temperatures. Most of these areas were adjacent to areas showing significant cracking.
On analysing the deflection data majority of the pavement can be classified as potentially long life pavement (91% in eastbound and 85% in westbound). In case of determinate life pavement areas (9% eastbound and 17% westbound), expected 15th percentile residual life span was variable from 0.2 to 13.8 years and would expectedly need 40mm-100mm thickness cover to get a 20 year designed life. Readings suggested thickness of asphalt in determinate life pavement sections generally higher than 300mm.
As asphalt thickness is satisfactory, other kinds of measures such as inlay can be applied to upgrade this pavement to reach the standards of LLP.However, The interfacial adhesion of asphalt layers in wet conditions can be improved by mixing a silane, amine or rubbery polymer into the bitumen. Nowadays use of reclaimed Aspalt on road pavements is increasing for better use of resources.
HAPMS data indicated texture depth and ride quality was satisfactory all over the site.
Fretting data from TRACS showed most lengths having category 3rd fretting.
But visual survey showed no fretting at these areas indicating TRACS data to be unreliable. All below mentioned proposals for maintenance is therefore mainly based on information gathered from visual survey.
Skidding resistance was found to be adequate across the site apart from two short lane 1 sections (total length 80m) which are likely to require resurfacing (see section 7.7 for
details). Excluding two short lane 1 sections totalling 80 m, skidding resistance was found to be satisfactory across the site, and the former will likely require resurfacing.
Maintenance proposals
Three major defects were encountered from the visual surveys: localised chip loss which was ranged from form moderate to severe, some area with transverse and/or longitudinal cracks and many potholes. According Scott Shuler there is a strong relationship between chip seal moisture loss and chip loss.
Two maintenance options should be taken into account: Short-term maintenance and long term maintenance
Short Term Maintenance:
Five to Six years (including minimum maintenance for repairs that are considered to be very urgent and could be a safety risk)
Long-Term option for five to fifteen years. It is preferable to delay substantial structural maintenance as cost and time permits but in case cost of routine maintenance becomes unmanageable than it will desirable to carry out more long-lasting maintenance.
Purposes of the short-term and long-term maintenance are explained below;
Short-term maintenance is mean to retain some of the functional properties and postpone any more structural weakening. Repairs include: crack sealing, resurfacing, patching and thin inlays.
Longer Term Maintenance:
To refurbish functional properties and overall improvements in structural performance. Treatments include sealing of cracks, re-surfacing, deep and shallow inlays.
Following treatment methods would applicable in case of severity of defects:
Resurfacing and Patching:
Resurfacing and Patching is suggested for those areas with depict severe chip loss. If the chip loss
Is combined with rutting and or cracking, the ideal choice that should be taken into consideration is resurfacing with fair use of inlay, sealing of cracks, patching and narrow inlays
Crack sealing should be ensued when a roadway or asphalt road is still fair to good condition. In addition to adequate drainage, sealing of cracks is regarded as one of the most important activity in maintenance of roads. Many pavement problems result due to ingress of water in the structure of pavement. If water ingress in prevented, most of the pavements disruptions can be stopped or postponed
Shallow cracks need to be sealed and wide cracks need to be patched to prevent water influx into the below lying layers to delay deterioration. Crack sealing is highly recommended. Fibrescreed type of cracks and sealing treatment is suggested. Additionally, shallow inlays are required in areas with severe cracking.
Many minor potholes were discovered during the visual survey which need to be patched.
Safety reasons necessitate urgent patching. These surface defects are presented on the visual survey sketch in Appendix A with details in Tables 9.1 and 9.2.
Good adhesion and boding properties of asphalt sealing product is a must. They should be elastic and at the same time resist softening. Their application should be easy and should resist weathering, aging and cracking. These sealants should be compatible with asphalt pavements patch. For crack filling asphalt cements and asphalt emulsions in addition to fiberized asphalt are needed. Silicone that is self-leveling, rubberized asphalt and low-modulus rubber asphalt are extensively used for crack sealing. Patching by suing infrared heaters if also suggested as it often is fast track and cheap way for fully deep patching of damaged roads.
Often time’s unfavourable weather conditions like snow or rain makes it necessary to take up emergency repairs on roads. Such repairs are done in shortest period of time and are usually meant for safety of the motorists for the interim period. Surface patches are meant for temporary repairs and are achieved by milling process which helps in removal of decomposed material from deep down.
Skidding Resistance:
Agencies usually monitor friction (Skidding Resistance) of important roadways on annual basis, while 2-5 year cycle may be appropriate for low risk roads. Carriageway falls in the latter category and frequency of monitoring should be same.
Deep inlays
For the long-term results, deep inlay treatment is suggested in those areas that have greater crack presence, along with other flaws such as potholes, greater degree of chip loss and high deflectograph deflections.
References
Andreas T.W., Pasetto, M. (2013), Durability of Building & Construction Sealants Asphalt
pavements on bridge decks, (2014) pp.51-67.
Flintsch.G. W., McGhee K. K., et al, The little book of Tire Pavement Friction, 2012,
Lambert, L. Pavement Evaluation Using a Curviameter and Deflectograph
(2015),
Nikolaides A.,(Ed), 2015 Bituminous Mixtures and Pavements VI,
Shuler, S., Manual for Emulsion-based Chip Seals for Pavement Preservation (2011),
Seo Y., Seong M. K., KSCE Journal of Civil Engineering (2013),
Shaung S., Bamber R.K, et al, Durability of Asphalt Mixtures, (2014), (Page 100-111)
Speight, J.G.,(2016), Asphalt Materials Science and Technology (Page 20)
