Gravel Loss Research Articles

Gravel Loss Prediction Model Using Beta Regression

Unpaved roads consist of considerable portions of the roadway network in many countries. These roads play crucial roles in the development of infrastructure systems, advancements of socio-economic activities and improvements of the agricultural and production sectors. Thereby, unpaved roads benefit the underdeveloped, rural, and remote neighborhoods, and act as lifelines for these geographically disadvantaged communities. Frequent and regular maintenance activities keep the roadway system operational at a desired level of service. Resurfacing is one of the major maintenance treatments for unpaved roads. A gravel loss prediction model (GLPM) can evaluate the impacts of varying magnitude of resurfacing treatments on the roadway performance. Thus, a GLPM can provide valuable insights for roadway maintenance budget scheduling and decision-making tasks. In this paper, the backgrounds, input requirements, and output results of three popular GLPMs were reviewed. These models were (i) Highway Development and Management Model 4 (HDM-4), (ii) South African Technical Recommendation for Highways Model 20 (TRH-20), and (iii) Australian Road Research Board (ARRB) Model. In addition, the practicality of roadway resurfacing frequency charts which were developed based on these models was also evaluated. This study determined that the existing GLPMs and the corresponding roadway resurfacing frequency charts were often unreliable and impractical. In this study, a beta regression (BR) analysis methodology was utilized to develop and calibrate a GLPM for Iowa. Because of its simplified yet effective nature, the BR model outperformed the popular GLPMs and offered a practical approach to quantify annual roadway gravel loss.

Field Assessment of Gravel Loss on Unsealed Roads in Australia

The gravel loss is a major limitation for unsealed roads and attracts major maintenance annually. The continual process of gravel loss also makes roads environmentally unsustainable. The unsealed road management faces several issues viz. difficulty to forecast behavior, huge data collection needs, a vulnerability in the service and maintenance practices. The quality of gravel material also plays a major role in the process of gravel loss. In view of this, appropriate revisions to ARRB material specifications are proposed in this paper. The gravel material as per modified ARRB specifications is used on the unsealed road network in the Scenic Rim Regional Council in the state of Qld. Gravel loss monitoring stations are established over the entire region in order to assess the gravel loss and the implication of using better quality gravel. This paper discusses the gravel loss monitoring approaches, data analyses and improved material specification for gravel. It is found that the modified gravel used on unsealed road performs better than conventionally used gravel.

Use of Gravel Loss Prediction Models in the Design and Management of Unsealed Road Pavements

Many countries have large unsealed road networks which are essential for business efficiency, social connectedness, and community safety. These roads are maintained at considerable cost mainly through blading and re-gravelling. The latter is a major component of the maintenance and is determined by gravel loss. Gravel loss prediction models can be used to assess the effect of different wearing courses, which provides useful input into the design and management of unsealed roads. This paper reviews the origins, input parameters, and output of four available gravel loss prediction models, namely, the Transport and Road Research, HDM-4, Australian, and South African models. It was found that the predictive accuracy of the models is in general low and they predict very different gravel loss results. There is also a lack of integration between the design and maintenance, leading to the wearing course properties recommended for design not being directly linked to gravel loss. These findings led to further analysis of the models and the development of re-gravelling frequencies based on traffic, climate (annual rainfall), and material property (plastic factor), which can be used in the selection of the appropriate wearing course material and in the determination of re-gravelling budgets. This presents a simplified approach to the use of existing gravel loss prediction models in the design and management of unsealed roads which mitigates some of the shortcomings in the use of uncalibrated models.

Applying Pavement Preservation Principles in Unpaved Road Management with Specific Reference to Fines Preservation and Dust Control

Unacceptable levels of dust are generated on unsealed road networks in most countries. The loss of fines associated with road dust contributes to increased gravel loss and the need for more frequent grader maintenance. By controlling this dust, the rate of gravel loss and maintenance expenditure can be significantly reduced. Research into the performance and benefits of using chemical treatments as part of unsealed road management programs led to the development of multiplier factors that can be used with gravel-loss and blading-frequency prediction models in unsealed road pavement management systems to determine where these treatments can be used cost-effectively. The factors were first validated in a 2-year pilot study before being implemented in a road agency’s computerized road management system. Output from the system indicated that chemical treatments could be cost-effectively used on at least 20% of the agency’s road network, with considerable savings accruing to both the agency and the road user. Subsequent analyses of county road projects in the U.S.A., where chemical treatment programs had been in effect for several years, verified that considerable savings resulted from reduced rates of gravel loss and longer intervals between required grader maintenance. Based on this experience, it is clear that chemical treatments, as part of longer-term unpaved road management programs, can be considered preservation treatments, with additional benefits of dust control leading to safer driving conditions, reduced vehicle operating costs, and improved health and quality of life for people living and working adjacent to the treated road.

Assessment of the Potential for Salt Damage to Asphalt Surfacings when Chloride-Treated Unpaved Roads Are Upgraded to a Sealed Standard

Experience gained during research into chemical dust control/fines preservation has indicated that the reduced maintenance on, and reduced gravel loss from, treated roads justifies the use of these chemical treatments as a cost-effective road maintenance and management strategy. Treatments also serve as a means of preserving layer thickness and integrity in stage construction if upgrading the road to a paved standard is planned. However, the potential for damage to primed bases and bituminous surfacings placed on chloride-treated layers as a result of salt crystallization underneath the surface during hot, dry conditions in arid and semi-arid climates has to be considered. A laboratory test method was therefore developed to gauge the potential for this type of damage. Calcium chloride, a commonly used dust palliative, was used in the experiment. The test, which simulated a worst-case scenario, followed by two field experiments that were evaluated for 36 months, indicated that salt damage to base materials, whether primed or unprimed, and to bituminous surface treatments or thin asphalt concrete layers is unlikely to occur on roads previously treated with calcium chloride. Care should be taken in the choice of surfacing if the electrical conductivity of the top 25 mm of treated material on the road exceeds 0.15 S/m prior to priming the base and placing the surfacing. This limit can be relaxed if laboratory testing, as described in this paper, indicates that salt damage is unlikely.

Evaluating Surface Material Loss for Gravel Road

Gravel roads require a continuous maintenance and regraveling cycle to maintain the required surface quality and the desired level of service. Surface material loss is a way of deterioration of unpaved road by which the reduction of thickness of gravel wearing course by various factors through time. To keep it in mind the responsible body or roads authority should predict the gravel loss in order to account for maintenance or rehabilitation requirement after a given period. This should be based up on regraveling frequency from predicted gravel loss during construction or after the first maintenance. Here main factors included for study are ADT, mean monthly precipitation of locations, plasticity index of surfacing material and absolute value of gradient of the road as independent variables and gravel loss as dependent variable. The road segments selected are Sodo-Gesuba road(29km), Humbo-Menuka(13km) and Sodo zuriya-Gulgula(11km) road segments. The monthly rainfall data from SNNPR meteorological agency was used as secondary data and all other data was collected from field survey. The data collected for modeling are based up on the basic scientific methods and collected data was analyzed by statistical software IBM SPSS statistics 20 and Microsoft Excel 2019 in order to develop a model. The developed model indicates that gradient of the road is critical factor hence its unit change accelerates loss of gravel by 4.7316, a unit change in ADT lead to 0.1225 change in gravel loss, a unit change in mean monthly precipitation of locations lead to 0.1460 change in gravel loss and a unit change in plasticity index of surfacing material lead to -1.3473 change in gravel loss. From regression output R2 also called coefficient of determination which is the proportion of variance in the dependent variable that can be explained by the independent variables, and is equal to 0.985 for model which means gravel loss contributing factors here in this study explain 98.5% of variability of gravel loss and that statistical package strongly reinforced the correlation. Keywords: Gravel loss, Regraveling, gravel resurfacing, absolute gradient, multiple linear regression and modeling DOI : 10.7176/CMR/11-6-02 Publication date : August 31st 2019

Performance Evaluation of Gravel Road Sections Sealed Using Open Graded Premix Surfacing with Bitumen and Bitumen Emulsion as the Binders

In developing countries like India, rural areas lack adequate transportation facilities. The Ministry of Rural Development (MoRD), Government of India (GoI) decided to develop rural roads under Pradhan Mantri Gram Sadak Yojana (PMGSY). The objective of this program is to achieve connectivity to all habitations under different climatic conditions. There are certain disadvantages associated with construction of the rural roads using gravel like dust generation, gravel loss over a period of time due to passage of vehicles and inaccessibility during rains. The best solution to reduce these problems is to seal the gravel roads instead of maintaining it, since many studies showed that the maintenance of unsealed road is more costly than the sealed road over a period of time. Hence, a project has been taken up to give full and all weather connectivity using locally available materials. Up to the surface course, the selected road was constructed using the locally available gravel. Many sealing techniques are available, out of which, open graded premix surfacing (OGPS) was opted in this study. This paper aims at studying the performance evaluation of gravel surface sealed with OGPS. The variables considered in this study are: gravel surface type, primer rate, and binder type. Past researchers found that the roughness, skid resistance and texture depth significantly affect the performance of sealed gravel roads and these three parameters are considered as performance indicators in this study. Eight sets of data were collected at regular intervals starting from November 2013 to March 2015. The surface distresses were also measured. From the analysis it was observed that the roughness on emulsion based OGPS was more when compared to bitumen based OGPS. Emulsion based OGPS resulted in less texture depth when compared to bitumen based OGPS. Skid resistance varied differently with respect to the binder type, type of surface course and priming rate. Even though there is little effect of gravel surface course type on roughness and texture depth, the effect of primer rate on roughness, texture depth, and skid resistance is negligible.

Performance Evaluation of Gravel Road Sections Sealed with Surface Dressing

The rural population of India lack adequate transport infrastructure to access the nearby towns/headquarters. The Ministry of Rural Development (MoRD), Government of India (GoI) decided to develop various rural roads under Pradhan Mantri Gram Sadak Yojna (PMGSY). The main objective of PMGSY is to achieve all weather connectivity to all habitations. Hence, a pilot study was initiated over a 7 km gravel road stretch from “Ghanapur-Palakurthy Public Works Department (PWD) Road to Komatigudem via Ippagudem, and Rangaraigudem” in the Warangal district of Telangana State, India. There are various disadvantages associated with construction using gravel like dust generation and gravel loss over a period of time due to passage of vehicles. The best solution to minimize these problems is to seal the gravel roads. The pilot road considered in this study was constructed using locally available gravel up to the surface course and then sealed using surface dressing. The performance of the road sections were evaluated in terms of roughness, skid resistance, and texture depth. The initial set of data was collected immediately after construction and one month after construction. Later, four sets of pavement performance data was collected after seven months of construction of the surface dressing layer in November 2013, January 2014, April 2014, and June 2014. Altogether, six sets of data were collected. The data was analyzed and important observations are reported in this paper. There is a considerable change in surface texture and skid resistance values after the first one month of construction whereas no significant changes were observed in the roughness values. Further, there is no significant difference in the results of surface texture, skid resistance and roughness values when the pavement sub-sections were evaluated for four times even after seven months of construction of the sealing layer.

The challenges faced by Tanzania`s Road Organization in running Maintenance Management System and Pavement Management System effectively

Running or developing the local MMS or PMS, be it for unsealed or sealed pavements, needs a team of well-trained and experienced road organization staff and appropriate equipment. The data employed to run a gravel roads MMS should reflect the capacity of the road organization personnel to collect them. In this regard, the team should be of adequate size, education and experience. It is, therefore, essential for the benefit of road users, road organization, the environment, and the sustainability of gravel roads to establish the capacity of road organization personnel responsible for running gravel road maintenance management with the intention of meeting social, economic, and political demands.The need to establish the adequacy of Tanzania road organizations in running gravel road MMS and PMS was the reason for conducting the qualitative research aspect of this study. The survey also intended to find out which parameters are readily collected by the surveyed road organizations, so as to include them as variables in formulating a gravel loss prediction model.This paper presents analysis and discussion of the questionnaire responses. The study notes the challenges being faced by road organizations responsible for the maintenance management of gravel road network in Tanzania and attempts to map a way forward.

Transportation Planning through Pavement Performance Prediction Modeling for Botswana Gravel loss Condition

Botswana is a Southern African country with an area of about 582,000 sq. km and its small population of about 2 million people. The road transportation network has grown beyond all expectations since independence in 1966. Out of the 18,300 km Botswana Public Highway Networks, gravel road networks are significant in providing access to rural areas where the majority of the population lives. Modelling of gravel loss conditions are required in order to predict their conditions in the future and provide information on the manner in which pavements perform. Such information can be applied to transportation planning, decision making processes and identification of future maintenance interventions. The results of previous attempts to develop gravel loss condition forecasting models using multiple linear regression (MLR) approach have not been reliable. This paper intended to develop accurate and reliable performance models which best capture the effects of gravel loss condition influencing factors using Feed Forward Neural Network (FFNN) modeling technique. As extension of knowledge in unpaved road transportation network, FFNN trained with Levenberg-Marquardt (L-M) method was used to develop gravel loss performance prediction model for Botswana gravel road networks to achieve a reliable result of a higher coefficient of determinant R2 = 0.94 compared with MLR analysis of R2 = 0.74.

Evaluation of Gravel Loss Deterioration Models

Efforts have been made by the Western Cape Provincial Administration in South Africa to improve all aspects of gravel road construction and maintenance. This thrust has resulted in better performance over time, as had been predicted by gravel loss deterioration models. Various internationally recognized gravel loss deterioration models were evaluated, and their predictions of gravel loss were compared with actual measurements of gravel loss. Through an extensive selection and design process and by incorporating various material property, traffic volume, environmental, and geometric parameters, 20 monitoring sections were selected for comparison. This monitoring was done for more than 5 years, starting in 2003. This paper summarizes the various available gravel loss deterioration models, provides a sensitivity analysis, discusses the improved processes, and gives a brief summary of the experimental design that was followed. The experimental monitoring and the analysis of the measured and predicted annual gravel loss as well as the comparison of the measured with the predicted gravel loss are also discussed. The impact of the sensitivity analysis and the comparison between the actual measurements and the predicted gravel loss as determined from the deterioration models are highlighted. Conclusions and suggested adjustments to the models or to the monitoring procedures are made. The two models that gave the best comparisons to the measured results and that would benefit the most by the suggested adjustments are the Technical Recommendations for Highways Manual 20 model and the World Bank Highway Development and Management model.

Chronic offshore loss of nourishment on Nice beach, French Riviera: A case of over-nourishment of a steep beach?

The 4.5 km-long gravel beach fronting the exclusive resort of the city of Nice, on the French Riviera, in southeastern France, was artificially nourished from 1976 to 2005 to the tune of 558,000 m 3, making this long-term operation one of the most significant for gravel beaches in the world. Nourishment has ranged from nil in certain years (1979, 1980, 1983–85, and 2001–2002) to a peak of over 97,000 m 3 in 2000. Analyses of 50 transects covering the beach highlight no significant change in net beach width over this 30-year period of massive gravel nourishment. A Principal Components Analysis and a Cluster Analysis used to detect patterns in the 87 beach-width measurement dataset show no clear spatial trends in transect groups that can be interpreted in terms of the morphology of the beach and the steep inner shoreface. Significant wave height off Nice shows no change over the period 1979–2005. Since there is no possibility for alongshore gravel leakage on the strongly embayed Nice beach, the relative stability in beach width clearly implies loss of recharged gravel offshore. Gravel loss following nourishment is favoured by: (1) the steep inner shoreface inherited from the geological context of Nice beach at the flanks of the southern Alps, and (2) the practise of artificial beach widening through flattening, in summer, of a narrow (5–15 m-wide) mobile zone of the profile in order to enhance the ‘carrying’ capacity of this highly touristic beach. Beach widening and flattening following nourishment bring close to the very steep inner shoreface zone several cubic metres of gravel for each metre of beach that may be permanently lost downslope during autumn and winter storms. Recharged gravel is redistributed alongshore and offshore leakage is probably enhanced where small narrow submarine canyon heads impinge on the beach, resulting in a very narrow shoreface. Mean beach width shows an oscillating alongshore pattern that may be due to the influence of these canyons as pathways of gravel loss offshore. However, there is no correlation between mean beach width and distance to the 10-m isobath, used as a surrogate for inner shoreface width. Storms are associated with plunging waves that are particularly effective and concentrated, on this almost tideless shore, over the narrow mobile zone of the beach profile where a series of steep reflective berms are built during storms. The high dynamic pressures associated with this narrow zone of concentrated wave breaking, and energy reflection from the steepened profile, are deemed to contribute to the permanent downslope loss of gravel. This situation of long-term gravel loss is probably accepted by the beach management authority because of the low cost of obtaining nourishment material and the advantages derived from a temporarily wider beach in terms of recreational space.

Transient response in longitudinal grain size to reduced gravel supply in a large river

The first extensive dataset on subaqueous bed material grain size in a large river subject to reduced sediment supply is investigated alongside bathymetry, modeled flow, and sediment flux. Results suggest that following sediment supply decline and a shift to a finer sediment supply, the gravel‐sand transition (GST) in fluvial systems extends and subsequently migrates upstream. The non‐abrupt (∼125 km) GST in the Sacramento River corresponds with a hump in the long profile, indicating recent downstream redistribution of sediment that impacts grain sizes. The hump is composed of sediments winnowed from upstream gravel beds that accumulate downstream where slope declines. This increases local sorting values and coarse sediment flux rates in the GST, leading to further gravel loss by burial and net efflux. Thus, in a transient response to sediment supply changes, whether anthropogenic or natural, the GST extends upstream as a longitudinally patchy bed modulated by bedload sheet transport that favors the loss of gravel.

Development of Performance-Based Tests for Nontraditional Road Additives

Nontraditional road additives (chemical stabilizers and dust palliatives) are applied to unsealed roads to reduce dust levels and gravel loss and improve riding quality and all-weather passability. However, the level of research conducted on additives and documentation derived from it are often unsatisfactory. A review of studies revealed that similar procedures were followed, which entailed routine laboratory tests on a locally available material, followed by a field test during which the period of effectiveness was assessed. No documented test methods exist specifically for these additives. Researchers tend to adapt methods developed for cementitious and asphaltic additives or compare before- and after-treatment results on standard indicator tests. Results rarely correlate with field performance, necessitating construction of full-scale experiments before making a decision on applying the additives on a wider scale. Invariably, a new experiment must be constructed each time conditions such as material, traffic, and climate change. A series of performance-based laboratory tests for nontraditional road additives has been developed, and results have been compared with performance in full-scale experiments. Results are compared with untreated controls or traditional stabilizers. The tests have been incorporated into a research protocol as well as a fit-for-purpose certification system for road additives. They are sensitive enough to assess performance at different application rates and to compare the performance of different additives on the same material. Tentative limits for decision making have been developed on the basis of comparisons of test results with performance on full-scale sections.

Gravel beach erosion and nourishment in Nice, French Riviera

Since 1976, beach width measures have been carried out on 50 transects over the 4.5 long gravel beach in Nice (French Riviera). Statistical analyses of beach width highlight very little significant change over the last 30 years in spite of massive gravel nourishment amounting to 558,000 cubic meters. The results suggest that this nourishment may be necessary to stabilise beach width that would otherwise diminish due to chronic gravel loss to the very steep nearshore zone, within a context of cessation of gravel supply by the nearby Var river. The practise of artificial beach widening through flattening of the profile in summer in order to enhance the beach-goer ‘carrying’ capacity of this strongly frequented beach may favour sediment loss by bringing close to the very steep nearshore zone several cubic meters of gravel for each meter of beach that can be permanently lost downslope during autumn and winter storms.

Tradeoffs associated with sediment‐maintenance flushing flows: a simulation approach to exploring non‐inferior options

AbstractSediment‐maintenance flushing flows designed to mimic the action of natural floods in removing the accumulated fine sediments from the channel and loosening the gravel bed have been increasingly proposed as an effective alternative in dam management and a required component of riverine restoration programmes. However, reservoir releases are generally associated with financial and environmental costs, thus it is highly desirable to specify flushing flows as accurately as possible. In this paper we present a simulation approach to evaluating flushing flows and exploring the tradeoffs associated with non‐inferior flushing options. A two‐fraction sediment routing model is used to simulate the gravel‐sand bed response to flushing flows. The results reveal that the sand cleansing effect propagates from upstream to downstream and from surface to subsurface. Under a steady gravel supply from upstream, an equilibrium state of gravel transport and bed degradation is eventually reached in the simulation reach. The flushing flow and sediment transport system investigated in this study involves a transient state variable (bed sand content), a decision variable (flushing flow discharge), a flushing goal (ultimate bed sand content), and three outcomes to be minimized (flushing duration, released water volume, and total gravel loss). A series of numerical simulations are carried out with a range of flows and pre‐flushing bed sediment conditions. The results reveal that the flushing efficiency is higher for the larger flow. However, for flows greater than ∼100 m3/s the flushing duration is less sensitive to the flow discharge, thus the system may be simplified as a bi‐objective one. The gravel loss and water volume are two conflicting outcomes within the non‐inferior flow region. Under a worse bed sediment condition, the feasible flushing options are constrained in a narrower range and also associated with higher costs. The tradeoffs between the conflicting outcomes are quantitatively displayed with the transformed feasible solutions in the objective space. We provide here a general and practical approach permitting a quantitative evaluation of the different flushing options that is appropriate to the level of data typically available. Copyright © 2004 John Wiley & Sons, Ltd.

Gravel Loss Characterization and Innovative Preservation Treatments of Gravel Roads: Saskatchewan, Canada

Recent restructuring of Canadian transportation has significantly increased commercial truck traffic on many rural roads in Saskatchewan, Canada. This increased traffic is having a detrimental effect on performance of the approximately 175,000 centerline kilometers of gravel roads collectively managed by provincial road agencies. The depletion of quality aggregate sources in many Saskatchewan regions is a primary contributor to the detrimental performance. Preservation and optimization of gravel are therefore becoming critical in sustaining an effective and efficient rural road system. Saskatchewan road agencies spend tens of millions of dollars per year purchasing gravel for the gravel road system. Even minor improvements in gravel optimization could significantly reduce the amount of gravel required for an acceptable level of service and save millions of dollars per year for taxpayers. A study was undertaken to quantify typical gravel supply and demand characteristics in Saskatchewan, the factors influencing gravel loss, and innovative means of gravel road preservation. Several rural municipalities were interviewed on their gravel road preservation practices and gravel supply and demand. Test sections were constructed to evaluate relationships between gravel loss and heavy truck loadings and to investigate innovative gravel preservation techniques. The study determined that most rural municipalities suffer from aggregate shortages. Gravel with a larger top size took longer to break down, and higher gravel application rates reduced gravel displacement. Ionic stabilization of gravel roads improved gravel retention and reduced dust, and shoulder reclamation with commercial rock rakes could recover gravel from roadside slopes for reapplication to the road surface.

Otta Seals and Gravseals as Low-Cost Surfacing Alternatives for Low-Volume Roads: Experiences in South Africa

The geology of the northeastern part of the province of KwaZulu–Natal, South Africa, is predominantly alluvial with vast deposits of sands. Suitable gravel sources are hard to come by, which results in high graveling and regraveling costs brought about by long haul distances and accelerated gravel loss. Most gravel roads carry fewer than 500 vehicles per day of which less than 10% are heavy vehicles. The high cost of regraveling has led to consideration of upgrading such roads to surfaced standard, even though traffic volumes do not justify upgrading. Traditional chip seals are expensive and cannot be economically justified on roads that carry fewer than 500 vehicles per day. The KwaZulu–Natal Department of Transport is actively involved in efforts to identify cost-effective alternative surfacing products for low-volume roads. Field trials were conducted with Otta seals and Gravseals, which have been used successfully in other countries, as low-cost surfacing products for low-volume roads. The Otta seal is formed by placing graded aggregates on a relatively thick film of soft binder that, because of traffic and rolling, works its way through the aggregates. Gravseal consists of a special semipriming rubberized binder that is covered by a graded aggregate. Both Otta seals and Gravseals provide relatively flexible bituminous surfaces suitable for low-volume roads. Cost savings are derived mainly from the broad aggregate specifications, which allow for the use of marginal materials.

Toward Fit-for-Purpose Certification of Road Additives

Chemical stabilizers and dust palliatives are widely used in road construction and maintenance to improve the characteristics and performance of available materials for lower dust levels, improved riding quality, reduced gravel loss, and improved all-weather passability. Numerous products are available to the road industry. However, the level of research and the usefulness of the findings differ from product category to product category. In many instances, no effort has been made to quantify the benefits and cost-effectiveness of additives over longer periods of time (e.g., 5 years), and little attempt has been made to compare the performance of treated roads with the performance of untreated roads for reduced gravel loss and reduced maintenance, the two most important factors in unsealed road management. Only limited information on material requirements and application techniques is available, whereas there is minimal information on rejuvenation. This lack of understanding has culminated in general skepticism in the road industry regarding chemical dust control and stabilization with so-called alternative stabilizers. The situation is aggravated by poor marketing, with many sales representatives having no engineering background, little understanding of the road industry, and insufficient information to provide adequate technical backup. Discussions with road authorities and consulting engineers indicated that a “fitfor-purpose” certificate for each product issued by an independent certification body would contribute to confidence in the use of the products. A certification system would also encourage suppliers to conduct appropriate product research. An internationally recognized certification body in South Africa was therefore approached about developing such a certification system, under the guidance of a steering committee with representation from road authorities, consulting engineers, product suppliers, and academia. Unsealed road additive certification is introduced, the development of control tests for certification is detailed, and a procedure for certification is proposed.

Evaluation of Stabilized Bases, Double Sand Seal, and Slurry Seal Pavement Sections in the Sultanate of Oman

Petroleum Development Oman undertook a study in 1996 to evaluate the use of a sulfonated petroleum product (SPP) as a base/subbase stabilizer and the performance of slurry seal and double sand seal in paving applications. Eight different road sections were constructed for a total length of 23.3 km. They constituted part of Marmul-Thumrait road project where the average traffic is about 150 vehicles per day. The objective was to improve the performance of graded roads and provide a low-cost base suitable for application of a thin bituminous surfacing. All eight sections were constructed with the standard subbase and base layers specified for roads in the Sultanate of Oman. However, major exceptions were as follows: Section 1, a slurry seal surface on normal resheeted base; Section 2, a slurry seal surface on SPP-stabilized base and subbase; Section 3A, unstabilized base and subbase (control section); Section 3B, SPP-stabilized base and subbase with a slushed finish carried out during construction; Section 4A, SPP-stabilized base and subbase with a slushed finish carried out a period of time after pavement construction; Section 4B, SPP-stabilized base and subbase; Section 5, a double sand seal surface on SPP-stabilized base and subbase; Section 6, a double sand seal surface on normal resheeted base. Road sections were monitored monthly for 6 months. The evaluation program included visual assessment of the surface, riding quality, dust generation, gravel loss, rutting, and in situ strength with a dynamic cone penetrometer. There were no differences in gravel loss, dust generation, strength values, or signs of distress between the stabilized and unstabilized sections. For the paved roads, the slurry seal section with SPP-stabilized base and subbase displayed the best performance in terms of less rutting and bleeding.