Road Base Layer Research Articles

Assessment of dynamic surface leaching of monolithic surface road materials

Construction materials have to satisfy, among others, health and environment requirements. To check the environmental compatibility of road construction materials, release of hazardous substances into water must be assessed. Literature mostly describes the leaching behaviour of recycled aggregates for potential use in base or sub-base layers of roads. But little is known about the release of soluble substances by materials mixed with binders and compacted for intended use on road surface. In the present study, we thus performed a diffusion test with sequential renewal of water during a 64 day period according to CEN/TS 16637-2 specifications, on asphalt concretes and hydraulically bound monoliths, two common surface road materials. It is shown that release of dangerous substances is limited in these hydrodynamic conditions. It was particularly true for asphalt concrete leachates where no metallic trace element, sulphate, chloride or fluoride ion could be quantified. This is because of the low hydraulic conductivity and the low polarity of the petroleum hydrocarbon binder of these specimens. For hydraulically bound materials around 20,000 mg/m2 of sulphate diffused from the monoliths. It is one order of magnitude higher than chloride diffusion and two orders of magnitude higher than fluoride release. No metallic trace element, except small quantities of copper in the last eluate could be quantified. No adverse effect is to be expected for human and environmental health from the leachates of these compacted surface road construction materials, because all the measured parameters were below EU (Council Directive 98/83/EC) or WHO guidelines for drinking water standards.

Contribution to Improving the Quality of Road Base Layers: Concept of Optimum Maximum Diameterand its Application to the Laterite of Sindia (SENEGAL)

The characterization of materials in laboratory follows standards. For the determination of the bearing ratio-CBR, the applicable standard provided a use of a maximum size of 20 mm diameter. But in practice, the laterite is compacted without removing coarse particles. The aim of this research is to get closer to the field realityby testing the materials with all the elements involved in road building layers. To do this, the laterite coming from Sindia quarry, used for many years in road construction in Senegal is studied. The geotechnical characterization focused on lateritic gravel samples from respective granular classes 0/20; 0/25; 0/31.5; 0/40 and 0/63 mm size. In interpreting the results of laboratory tests, the concept of optimal diameter (Dmax) occurred during the study in addition to the terms usually used as optimum water content and optimum dry density.

Mechanical Stabilization of Unbound Layers to Increase Pavement Performance and Incorporation of Benefits into M-E analysis

In recent years there has been a growing body of evidence supporting the performance benefits of incorporating stiff geogrids into unbound road base layers to improve the mechanical properties of the layer with a resulting improvement in pavement performance. This is quite distinct from the common use of geogrids in many countries for the construction of road foundations over weak soils. This paper will review the research evidence supporting the use of geogrids in a stabilization capacity to improve the modulus and subsequent performance of unbound layers by controlling particle movement and reducing deformations. Guidance published by AASHTO recommends that pavement designs incorporating the effect of a geosynthetic need to be based upon experimentally derived input parameters that are often geosynthetic specific. Such an experimental based approach is described in the paper. A description is provided of the steps taken to incorporate the geosynthetics effects into M-E pavement analysis.

Feasibility study of cement-treated 0–8 mm recycled aggregates from construction and demolition waste as road base layer

Recently, both nationally and internationally, cement-treated granular materials (CTGMs) have been widely used as road base layer. However, all the researches on CTGM with recycled aggregates (RA) are limited to the coarse fraction, with a size range of 0–40 mm. In Spain, one of the recycled materials most commonly produced in construction and demolition waste (CDW) treatment plants is a mixture with around 75% of fine recycled aggregates (hereby called FRA), with 5–8 mm nominal maximum size. This material is commonly used in pipe bedding, an application that provides little or no added-value. The intent of this paper is to study the feasibility of using CTGM made with FRA as road base layer. For this purpose, six mixtures have been produced, comprising 0–8 mm FRA and 0–40 mm coarse aggregates, made of mixed recycled aggregates and recycled concrete aggregate. The main mechanical (unconfined compressive strength and modulus of elasticity) and durability (dimensional changes) properties were studied and the effects of size and aggregates’ source were analysed. To the best of the authors’ knowledge, this is the first study on the use of the fine fraction of CDW in the production of CTGM to be used as road base layer. It suggests that it is feasible to produce CTGM with 0–8 mm RA (SC20) from CDW for that purpose. In addition, CTGM with FRA have better mechanical properties and dimensional changes than CTGM with coarse recycled aggregates (SC40).

Shrinkage cracking of cement treated demolition waste as a road base

This paper presents the shrinkage cracking characteristics of cement treated demolition waste as a road base layer, which was produced by using recycled crushed concrete and masonry aggregates from construction and demolition waste (CDW). The developed method to estimate the crack pattern was based on the structural properties of cement treated demolition waste measured in the laboratory and the average climatic conditions recorded in the Netherlands. The influences of four mixture variables (masonry content, moisture content, cement content and degree of compaction) on the crack pattern were investigated. Results show that the proposed estimation model can predict the crack pattern of cement treated demolition waste comparable to the crack spacing observed in the field. The masonry variation in CDW is a key factor to determine its shrinkage cracking characteristics.

Influence of quality and variation of recycled masonry aggregates on failure behavior of cement treated demolition waste

Cement treatment of construction and demolition waste (CDW) is a good option as a road base layer with a higher load spreading capacity for pavements. However, the quality and variation of recycled masonry in CDW change considerably in practice and this certainly influences the mechanical properties of cement treated demolition waste. This paper presents the influence of quality and variation of recycled masonry aggregates on its failure and indirect tensile strength by carrying out experimental tests in the laboratory and employing lattice modeling to analyze the fracture process. Numerical analysis and experimental results indicate that the masonry content is an important factor to determine the mechanical properties of the mixture. The failure of cement treated demolition waste originates either in the bonding layer between aggregates and matrix or through some low-quality masonry particles along the loading direction.

High-Modulus Geocells for Sustainable Highway Infrastructure

Technological innovation in geosynthetics such as high modulus (stiff) geocells (cellular confinement systems) can help achieve a more sustainable highway infrastructure. Research, testing, field trails, and case studies demonstrate how geocells increase pavement performance on one hand, while achieving sustainable goals on the other. Recent published research and testing of high-modulus Novel Polymeric Alloy (NPA) geocell-reinforced bases are briefly reviewed in this paper. NPA geocells improved strength and rigidity of flexible pavements as indicated by: increased modulus of structural layers, reduced stresses to the lower layers and decreased surface degradation. Field trials validate that NPA geocells improve the modulus of road base layers, even while reducing the structural thickness and utilizing on-site or recycled materials for structural infill. Sustainable roads can be built with less virgin resources and a smaller environmental footprint, while extending the pavement service life and decreasing maintenance.

Effect of styrene–butadiene copolymer latex on properties and durability of road base stabilized with Portland cement additive

This study investigated the effects of the type and amount of Portland cement and carboxylated styrene–butadiene emulsion (Tylac® 4190) on the short-term performance of a road base layer via a laboratory evaluation of stabilized soil-aggregate mixtures. Cylindrical specimens stabilized with Portland cement (0–6%), Tylac® 4190 (5–10%), and a mixture of both these additives were molded, cured for 7, 28, and 60days, and then subjected to different stress sequences to study the unconfined compressive strength, indirect tensile strength, and indirect tensile resilient modulus. The long-term performance (durability) of stabilized soil-aggregate specimens was investigated by conducting wetting and drying (WD) cycling tests on 7-day-cured soil-aggregate specimens stabilized with cement and Tylac® 4190. The results revealed that the additives improved the strength of the specimens, which has been found to be an important quality indicator of road base mechanical properties. Results of tests conducted to assess the specimens’ resistance to WD cycling showed that the addition of a 4% Portland cement–8% Tylac® 4190 mixture resulted in reductions of 86.99% in both water absorption and permeability, volume changes of 88.55%, and weight changes of 92.84% relative to a sample with only 4% cement after 12 WD cycles. This paper also presents the findings of a correlation study conducted for determining the influences of affective variables using nonlinear regression analysis to establish significant prediction models for strength based on mixture parameters.

Modeling in Situ Performance of Cement-Stabilized Granular Base Layers of Urban Roads

This study used a three-dimensional nonlinear orthotropic computational road model to measure the performance of reclaimed and recycled portland cement concrete (PCC) aggregates and reclaimed asphalt pavement (RAP) aggregates stabilized with cement as a base layer in a typical local road structure in the city of Saskatoon, Saskatchewan, Canada. The pavement structure was composed of 45-mm hot-mix asphalt concrete on a 225-mm granular base built directly over an in situ subgrade. The cross section was analyzed with a conventional granular base layer as a baseline and PCC and RAP base layers with 2% cement stabilization. The cement-stabilized PCC and RAP base layers showed improved shear strain and horizontal strain behavior when compared with the conventional granular base layer (which was not cement stabilized). This improvement con-firmed that cement stabilization of reclaimed PCC and RAP materials provided an enhanced primary response. This study demonstrated that typical thin Saskatoon pavement structures were highly dependent on the constitutive properties of base layer material. Stabilizing the PCC and RAP base layers with 2% cement reduced the maximum shear strains at the edge of the pavement structure by 12% and 25%, respectively, compared with the unstabilized conventional granular base layer. It was believed that the increased fracture and cohesion of the residual cementitious materials inherent to recycled granular base, as well as the cementitious binder added, improved structural performance.

Compressive strength of cement-bound base layers containing ferrochromium slag

In this study, the compressive strength properties of flexible pavement's cement-bound base layers made with FeCr slag have been investigated. The physical and chemical properties of the materials (FeCr slag and cementitious binders) were determined. Cylinder-shaped slag specimens containing 2%, 4%, 6%, 8%, and 10% Portland cement (PC) and silica fume were then prepared and stored for 28 days in a humid room. Nondestructive testing was performed using ultrasonic pulse velocity (UPV), and then unconfined compressive strength (UCS) testing was applied to the samples. The results of both testing methods are discussed comparatively. The test results showed that FeCr slag stabilized with cementitious binders can potentially be used as a road base layer material, in similar applications to traditional cement stabilized materials. Slag+PC mixtures met the required compressive strength properties of standards at 4% and higher PC contents. In this research, a high correlation was found between UCS and UPV test results.

Mixture optimization of cement treated demolition waste with recycled masonry and concrete

Due to environmental reasons and the shortage of natural resources, it is greatly valuable to recycle construction and demolition waste (CDW) as much as possible. One of effective ways to reuse more CDW is to produce a cemented road base material. The recycled CDW however is a mix of recycled masonry and concrete with a wide variation in composition. This implies that the mechanical properties of cement treated demolition waste are not only determined by cement content and degree of compaction, but also by the ratio of crushed masonry content to crushed concrete content. In order to optimize its mixture proportioning, this paper explores the response surface and contour plot of the combined effect of mixture variables on the mechanical properties including the unconfined compressive strength (UCS), the elastic modulus (E) and their ratio. It has been recognized that optimizing the mixture proportioning of cement treated demolition waste should not only consider its material properties, but also needs to take into account its structural behavior as a pavement layer. Analytical results indicate that increasing the degree of compaction is an economic technique to obtain the required strength, but it is not an efficient method to enhance the admissible elastic strain (the ratio of UCS to E) and to improve the flexural rigidity of the road base layer. Obtaining a desired low flexural rigidity certainly needs adjusting of the masonry content and the cement content.

Performance of Full-Scale Test Section of Low-Volume Road with Reinforcing Base Layer of Soil–Lime

The roads of the rice region of Merin Lake in Uruguay are subjected to low annual average traffic. However, the average daily traffic is approximately 100 trucks during harvest time. The local soils, characterized as clayey silts, are unsuitable for such traffic demands and are generally replaced or reinforced by materials found more than 70 km away, with high transportation costs. An investigation of the performance of a full-scale test section of pavement with a base layer of local silty clay soil stabilized with lime was conducted. The design of the test section consisted of soil selection, determination of lime content for stabilization, compaction, and California bearing ratio laboratory tests. Two test sections, each 50 m, were built, with a base layer of selected soil mixed with 3% lime in one section and with 5% lime in the other. After the rice harvest, the performance of the test sections was evaluated by visual observation of the base layer and deflection measures with a Benkelman beam. Despite some construction difficulties, the deflection average values changed from 244 × 10 2 cm immediately after the section was built to 77 × 10 2 cm 4 months later. The use of soil–lime material for base layers of low-volume roads is a technical and economical alternative that provides a significant improvement of the rural road network with socioeconomic benefits.

Plastic deformation behaviour of pavement granular materials under low traffic loading

This paper analyses the permanent deformation performance of an unbound granular material for base layers of low traffic roads. The material has been subjected to repeated triaxial loads. Three models were fitted to express the cumulative permanent strain as a function of the number of load cycles. In general, the predictions of two models previously studied by other researchers proved to be good but in the long-term, they tended to underestimate the measured values. In contrast, a third new model-the sum of two well known models-offered excellent predictions, which in the long term did not tend to either underestimate or overestimate the measured values. The granular material did not give satisfactory results to be used in low traffic volume road pavements.

Rutting prediction of a granular material for base layers of low-traffic roads

This paper analyses the permanent deformation performance of an unbound granular material for base layers of low-traffic roads. The material has been subjected to repeated triaxial loads. The shakedown theory was used to classify the structural response of the unbound granular material to the applications of load cycles. Three models were fitted to express the cumulative permanent strain as a function of the number of load cycles. In general, the predictions of two models previously studied by other researchers proved to be good but in the long-term, they tended to underestimate the measured values. In contrast, a third new model – the sum of two well known models – offered excellent predictions, which in the long-term did not tend to either underestimate or overestimate the measured values.

Incinerator Bottom Ash: Engineering and Environmental Properties as a Cement Bound Paving Material

This paper reports a laboratory study investigating the use of incinerator bottom ash (IBA) as cement bound material (CBM) for use in sub-base and roadbase layers. Engineering properties associated with its use are determined and practical limits on IBA content discussed. It was found that IBA could be practically used in proportions of 40% or more by mass for all CBM categories defined in the UK Highway specification. However, the use of IBA as aggregate in CBM required higher cement contents to achieve the same compressive and tensile strength. Tests carried out to confirm that leachable constituents were bound in the mixture and raised no environmental concern were carried out by comparing the results of tank leach tests with a one-dimensional model. It was observed that despite the tests and models being designed to maximise release of species, that leachates were well within typical regulatory drinking limits.

Kenya Bituminous Materials Study

The causes of premature failures in asphalt surfacings in Kenya have been identified. Two heavily trafficked sites had suffered top-down cracking, associated with severe hardening of the asphalt in the surface of the wearing course, whereas others had deformed plastically. Tests confirmed that reduction of voids in the mix (VIM) to less than 3 percent resulted in a high risk of plastic deformation under heavy traffic. Difficulties arise in designing asphalt mixes for heavily trafficked roads in countries where laboratory equipment is limited. These difficulties include selection of appropriate levels of compaction in the Marshall test and predicting the combined effect of asphalt hardening and secondary compaction. Use of a refusal density test is recommended to determine a reference density to ensure that 3 percent VIM will be retained. The importance of preconstruction field trials to establish the workability of such a mix is emphasized. Acceptable results were most easily obtained with aggregate gradings for binder course or roadbase layers that fell below the Superpave restricted zone. Such materials must be sealed to prevent premature top-down cracking associated with age hardening of asphalt in the layer surface. Performance tests, such as those used in this study, are ultimately required to ensure good performance of asphalt surfacings. Until developing countries can acquire the equipment required for these tests, it is recommended that the procedure described here be used to reduce the large number of premature failures such as those currently occurring in Kenya.

Improvement of marl and dune sand for highway construction in arid areas

Major parts of the Eastern Province of Saudi Arabia are covered with windblown dune sand which is characterized as poorly-graded soil with high permeability. Also, marl, which is available in abundance in this region, has poor strength. It is usually required to use these materials as subgrade layers or as a backfill in base and subbase layers of roads and highways. Because of the low strength characteristics of these materials and the high water table in the region, some sort of stabilization is needed to improve the characteristics of these materials. In this research, slow-setting emulsified asphalt and medium-curing cutback asphalt were used to stabilize both marl and dune sand. Lime and Portland cement ( 2% and 4%) were added to the stabilized soils to accelerate the curing process and to reduce stability loss due to water damage. It was found that the stabilizing agents improved both shear strength and resistance of the analyzed soils to water damage. It was observed that Portland cement was more effective than lime.

96/01500 Overview of coal combustion byproduct (CCB) production and use in the USA

The American Coal Ash Association, Inc. (ACAA) is an organization of producers and marketers of coal combustion byproducts (CCBs). Since 1968, the goal of ACAA has been to gain recognition and acceptance of CCBs as an engineering material on par with competing virgin, processed and manufactured materials by advancing CCB uses that are technically sound, commercially competitive and environmentally safe. The use of CCBs is affected by local and regional factors including production rates, processing and handling costs, transportation costs, availability of competing materials, seasonal adjustments, and the experience of materials specifiers, design engineers, purchasing agents, contractors, legislators, regulators, and other professionals. An annual survey of coal-burning electric utilities is conducted by ACAA to determine the quantities of CCBs produced and used in the USA. In 1993 approximately 88.5 million tons of CCBs were produced in the form of fly ash, bottom ash, boiler slag and byproduct from flue gas desulfurization (FGD). Approximately twenty-two percent of the combined production of these byproducts was used, while the remaining portion was deposited in disposal areas. The major markets for CCBs include cement and concrete products, structural fills, road-base layers, mineral filler in asphalt, grit for snow and ice control, blasting grit andmore » roofing granules, grouting, coal mining applications, and waste solidification and stabilization.« less