Runway Operability under Cold Weather Conditions. Tire-pavement friction creation by sand particles on iced pavements, and non-contacting detection of sand particles on pavements

Airports that operate under cold weather conditions face major challenges in ensuring that runways, taxiways and aprons provide sufficient tire-pavement friction to the operating aircraft. This thesis is motivated by two practical problems: (1) maintaining or improving the pavement surface conditions in an, for airline companies, acceptable state and (2) accurately reporting the actual surface conditions to the relevant actors (pilots, air traffic control, winter maintenance services). The primary objective of this thesis is to broaden the general knowledge base of these problems. The work can be divided into a practical, a fundamental, and an applied part of the thesis. The practical part includes a field study on how runway surface conditions change in time and the consequences for runway operability. Different situations were documented where the runway surface conditions changed due to snow fall, sand displacement by aircraft, ice deposition, snow compaction, and melting of the contamination layer. These cases highlighted two weaknesses in the current reporting system: (1) the constrained inspection frequency of the runway surface and (2) the limited possibilities to monitor the surface conditions while the runway is open for air traffic. The practical part also included field studies on a new sanding method, based on pre-wetting the sand with hot water. Practical experiences from maintenance personnel were collected, runway surface conditions were documented, and comments from pilots on the reported conditions were investigated. The method provides a solution for the problem that loose sand can be displaced or blown off the runway by the engine thrust of operating aircraft. In addition, the study highlighted some potential negative effects related to the sanding method. The high friction values that are typically measured on surfaces treated with warm pre-wetted sand can create a too optimistic picture of the prevailing conditions for aircrafts. Cases are documented where pilots faced worse conditions than they expected from the provided friction numbers. In 66 % of the cases there were clear indications available that the situation was not as good as suggested by the friction measurements. Another aspect is the risk of Foreign Object Damage (FOD). Maintenance personnel pointed out the importance of proper pavement cleaning prior to the sand application. The fundamental part of the thesis focuses on the role of sand in the creation of tirepavement friction on iced surfaces. The presence of sand particles changes the interaction between the tire, the pavement, the contamination layer, and the atmosphere in which the interaction takes place. Hence, it changes the way friction is created. The interactions were studied on a macroscopic scale by observing tire tracks on sanded, iced runways and by aircraft braking experiments on ice treated with loose and warm, pre-wetted sand. These observations showed that loose sand particles, ones trapped between the tire and the ice, can slide together with the rubber tread and plough into the ice layer. Loose sand particles can pile-up in front of, and under, locked tires (full skid). Such tire lock-ups can occur, even though when aircraft are equipped with anti-skid braking systems because these systems become disabled below a certain threshold speed (ranging between 30 and 45 km/h, depending on the aircraft type). On freeze bonded sand (produced by the warm, pre-wetted sanding method), friction can be provided by both loose particles that plough into the ice and by particles that stay fixed to the ice and force the tire tread to deform. The sand-ice and rubber-ice interactions were also studied on a microscopic scale by etching and replicating the ice surface. These observations revealed that the sliding friction process involved ice deformation in both cases. During rubber-ice sliding friction, the original crystal structure of the ice remained intact during the interaction. However, small scale ice deformation was evident by the formation of dislocations, aligned in rows along the sliding direction, and by the formation of small scale ploughing tracks. In the case of sand-ice interaction, the ploughing of sand particles was accompanied with the formation of cells within the original crystal structure of the ice. This re-crystallization was observed both in the laboratory and in the field. The rubber-ice and sand-ice sliding friction mechanisms were studied quantitatively by using a British Pendulum Tester in a cold laboratory experiment. It was found that the observed variability in friction measurements was significantly larger than the uncertainties introduced by the instrument itself. The variability may be caused by poorly controllable/reproducible, microscopic or nanoscopic surface properties of the ice and rubber. Rubber-ice interaction resulted in appreciable friction coefficients (0.5 ≥ μ ≥ 0.2) at ice temperatures below -5°C. However, it dropped significantly (down to μ = 0.05) over the whole tested temperature range to by the presence of little snow on the ice (less than 1 mm). It demonstrated that friction provided by rubber-ice interaction is very vulnerable to snow contamination. In contrast, sand-ice friction measurements did not show the dramatic drop in friction by the same amount of snow. Hence, the ploughing of relatively large sand particles provided a more robust mechanism of friction, compared to rubber-ice friction. The applied part of the thesis comprises an exploratory study on a non-contacting measurement principle to quantify the amount and distribution of sand particles on a pavement. A static laboratory arrangement was build where sanded pavements were illuminated by a visible laser light source (wavelength: 635 nm) at different angles of incidence. The radiance from the illuminated area was recorded with a digital camera at different angles. The test matrix included dry and iced pavements and different sand application rates. A correlation between the total radiance and sand application rate was only found when there was negligible radiance from the pavement in the scene. The sand detection therefore required a distinction between radiance originating from the sand and the radiance originating from the pavement. However, due to the similarities in optical properties of the sand and the aggregates in the pavement (both originate from crushed rock) and the transparency of ice in the visible range, it seemed unlikely that the distinction can be made on the basis of radiance intensity. An alternative approach was investigated, based on triangulation. Image analysis techniques were used to define a region of interest where the radiance only originates from the sand. Within this region, individual sand particles can be identified and counted. The principle was developed theoretically for flat surfaces and adapted for application on rough surfaces of unknown topography. It was tested on a selected group of images, taken under favourable incidence and camera angles. The algorithm placed the region of interest reasonably well in all analyzed images, resulting in a rather conservative input in the subsequent analyses. The sand detection algorithm had a success rate between 63 and 100 %, depending on the surface contamination. The errors were mainly caused by not detecting particles that were located in the lower parts of the surface topography. Only few mistakes were made by incorrectly identifying particles. Hence, the number of detected particles was a conservative estimate of the actual number of particles located in the region

SaltSMART : reduksjon av saltforbruk ved bruk av tilsetningsstoffer - feltforsøk vinter 2007/08

Som en del av etatsprosjektet SaltSMART utføres det en studie for å øke forståelsen om hvordan tilsetningsstoffer kan redusere saltforbruket. Denne rapporten fokuserer på levetiden av salt på veg

Airplane braking friction on dry snow, wet snow or slush contaminated runways

Airplanes need tire-pavement friction during taxiing, take-off and landing. The presence of snow reduces the friction and therefore there is need to understand how much friction can be expected on the different types of snow. This study analyses the braking performance of Boeing 737 airplanes on snow or slush contaminated runways. Airplane braking performance on runways contaminated with dry snow, wet snow and slush as analysed. The main finding is that airplanes experienced wet snow covered runways more often as very slippery, compared to slush covered runways. The fraction of the landings experiencing the conditions as “poor” or “less than poor” was significantly higher on wet snow (21%), compared to landings on slush (11%). This can be caused due to higher precipitation intensity during wet snow precipitation, or possibly because wet snow, in contrast to slush, is a compressible material that gets compacted and fills the underlying pavement texture

Can calorimetry be used to measure the melting rate of deicers

Chemical deicers are used in winter maintenance of roads and runways to melt ice and restore a bare pavement. The melting rate of these deicers is a fundamental performance factor, but good test methods to quantify the melting rate are still lacking. In this study, we present a method to measure the melting rate with calorimetry. The method provides a good control over heat fluxes and mixing which are crucial factors for the melting. In addition, it has an advantage of testing a deicer ‘as received’ without any sample handling prior to the test. The results showed that the melting rate of CaCl2 and MgCl2 can be clearly distinguished from NaCl. Solving the heat balance for solid deicers requires the deicer concentration in the meltwater to account for the enthalpy of dissolution. The freeze point and solubility concentrations set the physical limits on concentration and were used to assess the uncertainty due to unknown concentration. The extent of the uncertainty did not allow for a distinction between CaCl2 and MgCl2. This showed the need for an improved assumption scheme based on direct measurements. To represent a non-linear melting rate, different single-number metrics were investigated. The time it takes to reach 75% of the melting capacity gave the best characterization of the melting performance

Do We Need a Change in Road Winter Maintenance to Accommodate for Automated Vehicles? A State-of-the-Art Literature Review Considering Automated Vehicle Technology’s Usage of Road Infrastructure During Winter

For automated vehicles to be allowed to join the modern car fleet, and, in the future, replace human drivers, they must be able to handle adverse weather, including snowy conditions. This literature review focuses on how automated vehicles utilize the road and how this use is suitable for winter maintenance strategies. Where global navigation satellite system (GNSS) service is unavailable, automated vehicles need bare roads to perform relative navigation based on real-time data about lane markings, obstacles, and road infrastructure. Snow-covered tracks hinder vehicle navigation and lane marking detection, which might generate wheel slippage that in turn causes emergency stop and challenging friction estimates. Although the entry of automated vehicles into the car fleet does not demand change in the strategies of winter maintenance, it does demand higher level of service than today. Maintaining an entire road network on which autonomous vehicles always can operate is tremendously expensive and likely not feasible. One solution could be to add another maintenance class in a bare road strategy, that is, an automated vehicle maintenance class with a high level of service and a set of operational criteria allowing automated vehicles to operate. The maintenance class should be used for certain main routes where there is a high frequency of automated vehicles. A model that recommends preferable routes to the destination based on current road conditions within the operational envelope should be provided to the automated vehicle system

Rolling Resistance Measurements on Cycleways Using an Instrumented Bicycle

Snow and ice on roads often lead to increased rolling resistance that makes roads less accessible and less attractive for cyclists. Introducing a minimum requirement for rolling resistance in winter maintenance of cycleways may increase the attractiveness of winter cycling. To control the rolling resistance level, an objective measurement method is needed. This article presents a new method for measuring rolling resistance for cyclists by using an instrumented bicycle. The new method utilizes measurements of pedaling power and resistive forces from gravitation, acceleration, and air drag to estimate the rolling resistance. Test results show that the method can measure the coefficient of rolling resistance, Crr, with a precision, represented as the standard error of the mean, between ±0.005 (1 Hz, n = 9) and ±0.001 (1 Hz, n = 220). The accuracy of the method was verified in a test with known rolling resistance and the results yielded a mean accuracy of 96.5%

Effect of Temperature and Prewetting for Ice Penetration with Sodium Formate

Granular sodium formate (NaCOOH) is a popular deicer used at airports. It is mainly used to weaken compacted snow/ice and thereby facilitate mechanical ice removal. Earlier research has developed a set of methods quantifying deicer performance, but linking these test results to operational guidelines is difficult. The main objective of this study is to increase the knowledge of how temperature and prewetting affect the ice penetration performance of granular sodium formate. A new method to evaluate the development of ice penetration process is presented here. Ice penetration tests were performed with single grains on large, optically clear ice cubes, and digital image analysis is used to quantify the initial waiting time, penetration rate and –depth, and melted volume. Eighteen tests including dry and prewetted sodium formate grains were performed at three different temperatures (–2°C, −5°C, and −10°C). Prewetting reduced the initial waiting time (the time it takes before the particles started to penetrate) by a few minutes at −10°C, but at higher temperatures, this reduction was insignificant. The particles penetrated the ice at a constant rate. At −10°C, the particles penetrated at 10–15 mm/hour, while at −2°C this speed is about five times higher. Prewetting does not seem to have a clear beneficial effect on the penetration rate. Suggestions are given on how to capture the results from this study into operational guidelines for deicing operations at airports, using sodium formate as deicer

Bicycle rolling resistance under winter conditions

In many cold regions of the world, the percentage of trips made by bicycle drops drastically during the winter months. To facilitate increased bicycle usage during the winter, we studied the effect of typical winter conditions on bicycle rolling resistance and cycling comfort. An instrumented bicycle was used to measure bicycle rolling resistance under various winter conditions on streets and cycleways in Trondheim, Norway. The rolling resistance was estimated by first measuring propulsive and resistive forces on a moving bicycle and then solving the force equilibrium. Simultaneously, the test cyclist subjectively evaluated the level of cycling comfort, and video recordings were made to document the conditions. Data were collected on 103 road sections, including three levels of service (maintenance standards). The results showed that rolling resistance increased significantly in accordance with increasing loose snow depths. Dry and wet snow leads to a higher rolling resistance than slush does at the same depth. Similarly, increased rolling resistance correlates with reduced cycling comfort. Rolling resistance coefficients (Crr) higher than 0.025 noticeably reduce cycling comfort. The road sections that were maintained with a bare road winter maintenance strategy (using anti-icing chemicals, brushing and/or plowing) provided significantly lower rolling resistance and higher levels of cycling comfort than the sections maintained with a winter road strategy (only plowing and sanding). This study shows that rolling resistance measurements may be used to estimate winter cycling comfort indirectly. Therefore, rolling resistance may be useful for improving winter maintenance operations and controls. Better winter maintenance is essential for increasing bicycle usage in the winter

The effect of rolling resistance on people’s willingness to cycle during wintertime

Harsh winters reduce utilitarian cycling in many cities. Using an online survey, we examined how increasing rolling resistance due to snow and ice affect people’s cycling willingness. The respondents (N = 1318) reported their willingness to cycle on various winter cycling conditions presented in photos. The answers were compared to the rolling resistance levels on the presented conditions, measured in a previous study. Respondents’ cycling willingness dropped from 91.2% at very low to 18.3% at very high rolling resistances. The cyclist’s age, gender, local climate, winter cycling experience and studded tire use affected the cycling willingness significantly. Electric bike usage did not affect cycling willingness. “Summer-only” cyclists did not cycle during the winter due to low temperatures (29%), lacked feeling of safety (27%), bicycle wear (17%), increased travel time (17%) and increased physical effort (10%). Hence, lower rolling resistance and increased use of studded tires can increase the cycling frequency of existing winter cyclists. To recruit new winter cyclists, the surface conditions should not only offer a low rolling resistance but should also be perceived as safe and comfortable