Base-course Material Research Articles

Light Weight Deflectometer Evaluation of Low-Volume Road Structural Deterioration under Rapidly Increased Traffic Patterns

When evaluating low-volume road (LVR) condition, there is not a tremendous emphasis on structural capacity, since deterioration is typically caused by environmental factors. However, in cases where LVRs experience rapidly increased traffic loading, structural condition becomes important. The research objective was to determine whether the light weight deflectometer (LWD) can be used as a structural evaluation tool for LVRs. This study explored three major factors that affect measurement of flexible pavement structural capacity: load-induced deterioration (e.g., rutting and cracking), soil moisture, and asphalt temperature. Four full-scale flexible pavement test items were constructed with varying base-course materials and layer thickness typical of LVR. Instrumentation was installed during construction to monitor moisture content, temperature, and ambient weather conditions. Accelerated traffic was applied with a 4-axle military truck. A total of 10,000 cumulative vehicle passes were completed. Falling weight deflectometer (FWD) and LWD testing equipment were utilized to measure pavement structural condition at selected traffic intervals. The LWD was shown applicable for LVRs experiencing accelerated traffic. The LWD is portable and is more efficient for LVRs when high rut depths are permitted. The LWD tracked trends of the FWD; therefore, the LWD, based on these experiments, can be recommended for use in lieu of FWD to assess structural condition in some LVR conditions.

Performance assessment of three alkali-treated fly ashes as a pavement base-course material

Alkali-treated fly ash can efficiently serve as a construction material for various purposes. The efficacy of these alkali-treated fly ash must be critically studied for their proper usage in real-life scenarios. In the present study, the effectiveness of an alkali-treated low calcium fly ash (Class F) as a pavement base course material in the pre and post-construction period of the pavement has been investigated. The low calcium fly ash (Class F) was treated with three different alkalis, namely sodium hydroxide (NaOH), potassium hydroxide (KOH), and calcium hydroxide (Ca(OH)2), to study the influence of alkali type, its dose and curing period on the compressive strength and permeability characteristics of alkali-treated fly ash samples as these properties would prominently influence its behavior as a base course. In addition, the microstructural study of different alkali-treated ash samples was done to correlate the microstructural developments with these engineering properties. It was observed that 12% NaOH-treated fly ash samples, 16% KOH, and 16% Ca(OH)2-treated fly ash samples at 28 curing days show an optimum compressive strength value for a stabilized base material in pavements as per various guidelines. Finally, the usability of these optimized alkali-treated fly ash samples as a base material was investigated through a numerical study of a simple two-layered pavement structure. The surface and interface deformations of the pavement under various loading conditions revealed that these optimized alkali-treated fly ashes serve as a better base course than granular material. Also, of the chosen three alkali-treated fly ashes, optimized Ca(OH)2-stabilized fly ash performs comparatively better than others in terms of compressive strength and resisting deformation for these typical pavements.

Unconfined Compressive Properties of Fiber-Stabilized Coastal Cement Clay Subjected to Freeze–Thaw Cycles

This study aimed to investigate the feasibility of using polypropylene fiber-cement-stabilized coastal clay as base-course material or foundation material for city sustainable development by assessing its mechanical performance. The influence of the number of freeze–thaw cycles and curing ages on the mechanical properties of ordinary cemented clay (OCC) and polypropylene fiber-cemented clay (PCC) was investigated by using unconfined compressive test. The experimental results show that the addition of fiber with 1% content can increase the strength as well as the ductility of cemented clay by 12.5% and 15.6%, respectively. The strength of PCC and OCC at 22d age was 1.5 times than at 7d age. Under differently timed freeze–thaw cycles, the mechanical performance of PCC is improved, and, better than that, OCC improves by 11.8% in strength, 16.5% in strain and by 5% in degree of damage, indicating that fiber can improve the freeze–thaw resistance of cemented clay. The frost resistance of PCC and OCC increases with the increase in curing age. Finally, the variation of strength of OCC was explained through the change of micro-structure while the strength enhancing mechanism of polypropylene fiber for cemented clay was also revealed.

EFFECT OF BASECOURSE AGGREGATE PROPERTIES ON STRENGTH OF FOAMED BITUMEN STABILIZED MATERIALS

Foamed Bitumen Stabilization (FBS) is a treatment for strengthening pavements and improving road performance, either on newly constructed or existing roads. The FBS within pavements is typically used in the basecourse layer, where the basecourse material is mixed with cement, bitumen, and water through a milling operation on site. The performance of the Foamed Bitumen Stabilized basecourse can be highly affected by various parameters such as the cement content, bitumen content, the quality of the operation as well as the basecourse aggregate characteristics. In this research, a collection of existing historical FBS mix design data from New Zealand roads are analyzed. The Indirect Tensile Strength (ITS) of the FBS material made of aggregate sourced from two different regions are compared. The results show that the aggregate percentage of fine particles and the plasticity index contributes to the final strength of FBS material. The obtained results are valuable towards optimizing the FBS mix design based on the basecourse aggregate properties.

Analyzing the Application of Different Sources of Recycled Concrete Aggregate for Road Construction

Because of the environmental, planning, and resource restrictions in the exploration and processing of natural aggregates, interest in better utilizing recycled aggregates in road pavement construction is increasing. Several researchers have investigated the characteristics of recycled concrete aggregate (RCAg) with the aim of understanding its performance as a base-course unbound material. As the pavement design techniques and the properties of re-processed RCAg in each country are non-homogeneous, previous international research on recycled aggregate cannot necessarily be incorporated in New Zealand’s pavement specifications. Moreover, RCAg is mainly sourced from vertical or horizontal concrete demolished structures. These sources of material have different engineering characteristics, and there is a lack of information about their performance. This paper investigates the difference between the properties of these two vertical and horizontal sources, and it evaluates their application as an unbound granular base-course material as opposed to an alternative layer in the pavement, for road construction in New Zealand. The physical properties of RCAgs engineering performance (durability) were evaluated through experimental laboratory-based tests. Also, the characteristics of the tested RCAgs were compared with the specification of base-course materials (NZ Transport Agency M4) in New Zealand, and their appropriateness for high-performing pavement construction layers was assessed. According to the tests results, the tested RCAgs have proven to meet the “premium” base-course grade product, and it is expected that recycled crushed concrete, if production processes are appropriately managed, could have great potential use as a base-course material in road construction and in some cases perform better than common natural aggregates.

Neutralization of high pH and alkalinity effluent from recycled concrete aggregate by common subgrade soil.

Use of recycled concrete aggregate (RCA) as highway basecourse material conserves virgin aggregate, reduces energy consumption and CO2 emissions, and may also decrease costs during construction. However, concerns remain over possible negative environmental impacts associated with high pH(>11) effluent from RCA in contact with water. This study examines the reactive transport of high-pH and high-alkalinity water, modeled on RCA leachate, through model subgrade soils. By developing an understanding of the reactions controlling effluent neutralization, this study aims to quantify the change in pH from the discharge site through surrounding subgrade soils. Four types of subgrade soils with a range of mineral composition, Atterberg limits, and cation exchange capacities (CECs) are examined. They include a clayey sand (SC10), low-plasticity clays (M14, SC25), and a high-plasticity clay (CH38). Batch reaction experiments are used to develop kinetic parameters describing the neutralization of high-pH and -alkalinity leachate by clay minerals through mineral dissolution and reprecipitation. Given this information, a reactive transport model incorporating advection, diffusion, and reaction is used to model the change in pH as a function of distance traveled through model subgrade soils and is applied to laboratory-scale column experiments. The rate at which the high pH front travels is directly related to a soil's clay mineral content. Soils with high CECs effectively delay the propagation of hydroxide front by the dissolution of clay minerals. This study demonstrates that common subgrade soils with moderate clay content will effectively neutralize high pH leachate initially produced by RCA.

Evaluation on Strength Properties of Lime–Slag Stabilized Loess as Pavement Base Material

This study aimed to investigate the feasibility of using lime–slag stabilized loess as base-course material by assessing its unconfined compressive strength (UCS). Loess stabilized with various mix ratios were compacted and cured to three, five, seven, and 28 days, respectively, for further strength tests. The effects of binder content, lime-to-slag (L/S) ratio, porosity, and curing time on the UCS of stabilized loess were addressed in detail. The test results show that UCS increases with the increase in binder content or curing time, and it gains strength rapidly within the first seven days of curing. At the same binder content, UCS decreases with the decrease in L/S ratio or porosity. Finally, the correlations of UCS with binder content, porosity, and curing time were derived, which exhibited reasonable correlation coefficients R2 (from 0.86 to 0.97).

Imaging and Parameterizing Moisture in Road Sub Course Using Time Domain Reflectometry

This paper presents the experimental results of using a non-invasive time domain reflectometry (TDR) sensor to image and parameterize the moisture content of basecourse materials used in road construction. Imaging, resulting from the amplitude losses of a pulsed signal travelling down TDR transmission lines, is found to produce excellent information on the relative changes in basecourse moisture content to a spatial resolution $\sim 0.25$ % in volumetric moisture content is achieved when model coefficients are separately fitted for each of the two basecourse aggregate types tested.

State-of-the-Art: Prediction of Resilient Modulus of Unsaturated Subgrade Soils

AbstractIn this paper, equations that were proposed in the literature over the past four decades to estimate or predict the variation of the resilient modulus with respect to soil suction for pavement base-course materials and subgrade soils are summarized into three groups: (1) empirical relationships, (2) constitutive models incorporating the soil suction into applied shearing or confining stresses, and (3) constitutive models extending the independent stress state variable approach. Two equations selected from each of the groups (a total of six equations) are used to predict the resilient modulus–soil suction correlations for three compacted subgrade soils. Strengths and limitations of these widely used equations are discussed based on the comparisons between the measurements and predictions. The key objective of the state-of-the-art research summarized in this paper is for assisting practicing engineers to choose suitable equations for the rational prediction of the resilient modulus taking into accou...

Uniaxial compressive strength of hydraulic, graded iron and steel slag base-course material produced at different manufacturers and its increase with curing time

This paper first briefly overviews the production and use of iron and steel slag in Japan and the quality requirements for use in road construction imposed by the Japanese industrial standard, followed by an outline of the mainstream structural design method of asphalt pavement. Then, presented is the compaction properties and uniaxial compressive strength of hydraulic, graded iron and steel slag base-course material produced at five different manufacturers. Series of uniaxial compression tests were carried out on the specimens cured up to 730 days. As the results, it is shown that there are large variations in the density of solids and the compaction properties among those five base-course materials, that those five base-course materials show uniaxial compressive strength in a wide range for each curing time, that the way the uniaxial compressive strength increases with time differs among them, and so on. Its relationship with the resilient modulus for each of the five base-course materials is also referred.

Development Of A Pavement Rutting Model Using Shakedown Theory

Abstract The rutting of flexible pavements during their exploitation is considered to be one of the main problems in UK as well as worldwide. It is a serious mode of distress alongside fatigue in bituminous pavements that may lead to premature failure, as indicated by permanent deformation or rut depth along the wheel load path, and results in early and costly rehabilitation. This kind of pavement distress makes a negative impact to the serviceability characteristics of the flexible pavement, to the residual life of pavement structure and also to the safety and ride quality for traffic. Two design methods have been used to control rutting: one to limit the vertical compressive strain on the top of subgrade and the other to limit rutting to a tolerable amount usually around “12 mm”. Although experimental data and practical experience have been introduced into these design methods through empirical parameters, there is not a simple relationship between the elastic strain and the long-term plastic behaviour of pavement materials. This paper describes a method based on the kinematic shakedown theorem for constructing a mathematical model to predict the long-term behaviour of pavement structures under the action of repeated and cyclic loadings imposed by moving traffic. This method seeks the mechanism from within a class of mechanisms that minimises the shakedown limit load for pavement structures consisting of layers of Mohr-Coulomb materials. The model differs from extant models, in that the cyclic nature of the loading on a pavement is recognised from the outset, and the current method which is based upon foundation analysis, is replaced by a procedure employing shakedown theory that features the capabilities and applications of the developed technique for assessing rutting in flexible pavements. The basic concepts are outlined together with the most recent calculations of the critical design shakedown load. The influence of the design parameters such as, the strength, stiffness and depth of the granular base-course material as well as the consequences of traffic loading (number of equivalent standard axel loads – ESAL’s) are discussed.

Comparing Results between the Repeated Load Triaxial Test and Accelerated Pavement Test on Unbound Aggregate

Unbound granular materials (UGM) are extensively used as basecourse materials around the world as they are capable of bearing relatively high traffic loads and are an economical option in comparison to bound materials. The unbound materials performance as basecourse determines the life-cycle costs of a pavement. The extent to which the repeated load triaxial test can predict the performance of unbound granular materials in the laboratory is an important parameter for road designers. Moreover, the performance of the unbound basecourse materials depends upon the moisture conditions when they are being loaded, gradation curve of the material, in situ density, permeability, and the nature of the aggregate fines (clays). There is a need to find the factors that cause the variation in the performance of the materials both in the laboratory and in-field pavement conditions to enable appropriate selection and use. This research utilizes accelerated pavement tests (APT) alongside repeated load triaxial (RLT) tests to test differently graded unbound granular materials at higher moisture contents. The objective of the research is to find the similarities and contrasts in basecourse material in both tests and to find the root causes of variation in the aggregate performance. If results of the RLT test can truly represent the results from full-scale APTs for basecourse materials, then the pavement materials industry can use the much lower costing RLT tests with confidence knowing it is representative of performance tests from APTs. The accelerated tests are performed on test pavements at the Canterbury Accelerated Pavement Testing Indoor Facility (CAPTIF) with the introduction of surface water, which replicates typical rainfall events. An increase in moisture in the basecourse layers is observed during the APTs due to entry of surface water through the surface seal, which allowed the performance of the basecourse material at higher moisture contents to be assessed. The RLT tests were conducted in parallel with the same basecourse materials at higher moisture conditions. The relative performance ranking of APTs and RLT tests is found to be the same for some materials; however, it differs in some cases. The similarities and differences in the rankings from both procedures are highlighted, and the causes of these similarities and differences are inferred and discussed.

Design of Unbound Pavement Layer Materials Based Upon the Shakedown Concept

This study aims to introduce an alternative design method for unbound pavement layer materials based upon shakedown theory. The kinematic shakedown theorem that describes the ultimate response of an elastic/plastic structure to cyclic loads is used to predict whether stable behaviour in the unbound granular materials layer occurs or excessive rutting will develop. This method seeks the mechanism, from within a class of mechanisms that minimises the shakedown limit load for pavements consisting of layers of Mohr-Coulomb material obeying the associated flow rule. The basic concepts are outlined together with the most recent calculations of the critical design shakedown load. The influence of the of design parameters such as, the strength, stiffness and depth of the base-course material as well as the consequences of load distribution are discussed.

RESILIENT POISSON'S RATIO OF HYDRAULIC, GRADED IRON AND STEEL SLAG BASE-COURSE MATERIAL FOR PAVEMENT RESPONSE ANALYSIS

This paper discusses resilient Poisson's ratio of hydraulic, graded iron and steel slag base-course material based on a series of repeated loading triaxial compression tests on the specimens compacted with a maximum dry density and an optimum water content a nd cured for 0, 28, 91 and 365 days. It is shown that resilient Poisson's ratio for no cured specimens is stress dependent in such a way that it increases with deviatoric stress and decreases with mean effective principal stress. As curing time increases, however, the magnitude of resilient Poisson's ratio becomes smaller and its stress dependency vanishes: at curing time of one year, resilient Poisson's ratio appears independent on both mean effective principal and deviatoric stresses and can be taken as constant. Resilient Poisson's ratio can be well expressed by a power function of these two stresses. It is indicative that stress-dependency in resilient Poisson's ratio fades away after hydraulicity has sufficiently developed, which may justify the use of a constant value for resilient Poisson's ratio in pavement response analyses.

Test on the Performance of Road Base-Course Made of Steel Slag and Fly Ash

Fly-ash is an industrial waste burning pulverize coal boilers for thermal power plant and large enterprises, the steel slag is too a residue generated waste in steelmaking industrial processes, the average for every ton steel to produce half ton steel slag, steel slag and fly ash discharge amounts is very big, utilization ratio is very low. At present, a large number of steel slag is used of reclamation work, the remaining items is used rarely and large number is left storage. This paper is introduction steel slag and fly ash to do road base-course material, such can make good use of industry residue waste in large amount to reduce exploitation and cut down natural building stones, it is an application for ecological building materials again. Major study the steel slag and fly ash road features, these tests include materials compaction reality among them, mix design, unconfined compressive strength, split tensile strength, resilient modulus and other commonly used performance. Through comparative analysis, this two materials combination has good use of quality, it has greatly better than other materials such as lime-fly-ash stabilize crushed stone and lime-fly-ash soil and other materials. In particular, it has very good performance to reduce road base-course crack, the material has good resistance shrinkage and temperature shrinkage ability. Therefore, the combination of steel slag and fly ash can be done entirely road base-course and extend the road life.

Freezing-induced water migration in compacted base-course materials

Ramped-freezing tests were conducted on three base-course materials with fines contents of less than 7% and compacted at different initial states but always at degrees of saturation near or well below 60%. Three different quarries were studied. The natural fines from crushed gneiss with biotite, limestone, and monzonite were all frost susceptible. Frost heave was relatively small, but significant water intake occurred in all samples during freezing with access to an external water source, regardless of initial saturation level. The frost susceptibility of coarse-grained soils cannot be solely evaluated with respect to frost heave but needs also to consider the amount of water drawn to the freezing front during the freezing process and the consequences of this water during thaw. The normalized heave of the base-course layer of pavements is a practical and efficient indicator of the frost susceptibility of the base-course aggregates. If it is larger than 1%, the base-course material can be considered as frost susceptible leading to a significant increase in the degree of saturation once frozen. Current base-course material specifications based solely on grain-size distribution are not adequate to differentiate materials that are nonfrost susceptible from those that are frost susceptible. Hence, an additional criterion based on the fines frost susceptibility should be considered.

Active Soils of the Niger Delta in Road Pavement Design and Construction

Active soils existing to irreplaceable extents (both laterally and vertically) within the freshwater zone of the Niger delta are known and have been shown to be highly undesirable in their natural forms for road construction. This is because they swell extensively in the rainy season and shrink proportionately in the dry months together with any structure including road pavement constructed with or placed on them. In this paper, four samples of these soils collected from across the Niger delta were subjected to chemical stabilization with slaked-lime and calcium chloride (CaCl2) to reduce swelling potential while resulting mixtures (corresponding to tolerable swelling limits) were stabilized with Portland cement to improve strength. First, swell indicator (i.e. 24-h free swell index) was found to diminish with increasing stabilizer content while for combined plot (independent of location/percentage fines), about 10.7% and 6% slaked-lime and CaCl2 were found to be required to achieve the minimum (2.5% free swell) tolerable, normal or non-swell soil condition. Under this condition and for individual soil materials, addition of cement was found to enhance continual increase in MDD, soaked-CBR and durability index such that the soil becomes better compactible, stronger and more durable with increasing cement content. About 2.6% and 14.6% cement contents were found needed to respectively produce sub-base and base-course materials in roadworks with the latter much more durable than the former. The graphs so obtain could also constitute a complete graphical model for preparing deltaic active soils for use as road pavement materials.

The use of tangent stiffness to characterize the resilient response of unbound crushed aggregates

Repeated-load triaxial tests were conducted on crushed granitic base-course material to study the resilient response under different stress paths and compaction states. It has been established that the resilient response of this prestrained unbound granular material is best defined in terms of tangent stiffness (Et) and vertical stress (σv). The data also revealed the existence of a threshold value of tangent stiffness that is essentially dependent on initial confining stress for a given compaction state. When the tangent modulus exceeds this threshold value, a unique relationship between tangent stiffness and vertical stress exists for mobilized shear resistance ratios less than 0.4. This Et–σv relationship is independent of stress path. A simple power law model can be used to predict the resilient response of unbound base-course material and an approximate value of resilient modulus for any desired stress path and initial stress condition. The use of the tangent stiffness – vertical stress model for pavement design appears to be very promising.Key words: granular, material, resilient modulus, triaxial, stress path.

Limit-State Curve of Base-Course Material and Its Relevance for Resilient Modulus Testing

The limit state characteristics of base-course granular materials were obtained using a typical triaxial testing equipment devoted to the measurement of resilient modulus. Accurate monitoring of axial strain during isotropic and anisotropic compression was used to determine the stress conditions where significant irrecoverable strains occur for samples prepared by static compression, Proctor rammer, and vibratory compaction. The limit state curve is highly anisotropic, centered about the q/p=1 line. It is sensitive to sample preparation technique and fines content. The Strategic Highway Research Program (SHRP) procedure corresponds to stress paths during conditioning and repeated loading that remain within the limit state curve of the control base course material containing 3.5% fines. The resilient modulus values reflect henceforth the behaviour of the same material with its original particle contact distribution. The Laboratoires des Ponts et Chaussees (LCPC) procedure is characterized by stress paths that cross the original limit state curve of the Proctor compacted samples. Particle contact distribution changes thus continuously as the limit state curve expands in response to the various stress paths used in this procedure. The resilient modulus values correspond to samples with different fabrics. A simple procedure based on isotropic loading has been proposed for the determination of a simplified limit state curve of base course materials with the intent of specifying the testing conditions for obtaining adequate resilient modulus values.

Influence of fines on frost heave characteristics of a well-graded base-course material

The influence of fines on the frost susceptibility of base-course crushed aggregates was established by laboratory freezing tests simulating closely the thermal conditions in the field. The frost susceptibility of the fines was varied by use of different mixtures of granitic fines and commercially available kaolinite clay. A total of 13 samples with fines content of 5%, 10%, and 15% and kaolinite fractions of 10%, 50%, 75%, and 100% were subjected to four freeze–thaw cycles. The frost susceptibility of well-graded crushed aggregates increases with increasing fines content and increasing kaolinite fraction. From a quantitative point of view, for a given kaolinite fraction, the segregation potential increases linearly with fines content, until the fines create a matrix in which the coarser particles are embedded. For the material studied, this occurs when the fines content is higher than 15%. For a given fines content, it was also established that the segregation potential increases linearly with kaolinite fraction, indicating the importance of mineralogy. It was also established that appropriate thermal testing conditions need to be adopted to prevent undue pore water extraction from the unfrozen soil close to the frost front during laboratory freezing of unsaturated coarse-grained soils.Key words: coarse grained, soil, frost susceptibility, pavements, laboratory, fines.