Aggregate Base Course Research Articles

Dispersion of Standard and Cellulose-Augmented Termiticides in ‘ABC’ Gravel Foundation Fill

Abstract Six different commercial liquid pyrethroid termiticide formulations commonly used in building construction termite control applications to fill materials were individually applied at label rates to the horizontal surface and within perimeter and utility pipe trenches of ‘aggregate base course’ (ABC) gravel fill commonly used for building foundation construction in Arizona. Three termiticides contained finely powdered cellulose additive and three did not. Cellulose-augmented termiticides were retained in significantly greater concentrations in uppermost ABC partitions compared with their counterpart non-cellulose termiticides that contain the same active ingredient. Residues decreased with increasing depth. Cellulose-augmented permethrin applied to the surface of loamy soil from Mississippi and sandy soil from Florida also resulted in decreasing active ingredient concentrations with depth. Additionally, ABC perimeter trenches and trenches around upright utility pipes penetrating through the fill r...

Influence of Aggregate Base Layer Variability on Pavement Performance

The objective of this research was to investigate the variability of base layer construction in hot-mix asphalt (HMA) pavements and to assess the impact of base layer variability or nonuniformity on pavement performance. Subjective acceptance criteria of base layer construction may lead to variable pavement performance and may result in early pavement distresses and failure. Eleven existing HMA pavement projects with aggregate base course layers constructed in the past few years were selected for falling weight deflectometer (FWD) testing and visual distress surveys. In six of these projects, issues with aggregate base performance (stability and uniformity) had been observed and reported during paving of the HMA surface layer. Later, these pavements exhibited various levels of early distresses, including cracking (longitudinal, transverse, and alligator), aggregate base failure, and pavement surface roughness or irregularities (for ride quality). The remaining five HMA pavement projects, for which no issues related to aggregate base layer behavior were reported during construction, performed well after construction. A test section of approximately 1 mi on each project was subjected to FWD testing. The existing HMA pavements that showed early distresses exhibited high levels of spatial variability and nonuniformity in aggregate base course layers, as demonstrated by FWD testing and backcalculated base layer modulus values and distributions. The existing HMA pavements that performed well exhibited low levels of spatial variability and good uniformity in aggregate base course layers, as shown by the FWD test results and the backcalculated base layer modulus values and distributions.

Time Domain Reflectometry Measurements of Road Basecourse Moisture Content

Abstract This paper describes an empirical transform between the propagation time (tp) data obtained from a non invasive Time Domain Reflectometry (TDR) sensor to the percentage moisture content θv within two different road making basecourse aggregate material. Results show that a simple quadratic fit between tp and θv can be given leading to a maximum error in the estimate of 0.55%. It is also shown that the dielectric model underlying each of the basecourses is different enough to warrant the use of a unique quadratic function (i.e. different quadratic coefficients) for each.

Effect of Matric Suction on Resilient Modulus of Compacted Aggregate Base Courses

This research was conducted to investigate the effect of matric suction on resilient modulus of unbound aggregate base courses. The study characterized the water characteristic curves and resilient modulus versus matric suction relationships of aggregate base courses that were compacted at different water contents and between 98 and 103 % of the modified Proctor density. The soil–water characteristic curve (SWCC) and the relationship between resilient modulus (M r ) and matric suction (ψ) were established for different unbound granular and recycled asphalt pavement materials. This relationship is important for predicting changes in modulus due to changes in moisture of unbound pavement materials. Resilient modulus tests were conducted according to the National Cooperative Highway Research Program (NCHRP) 1-28A procedure at varying water contents, and the measured SWCC was used to determine the corresponding matric suction. Three reference summary resilient moduli (SRM) were considered: at optimum water content, optimum water content +2 % and optimum water content −2 %. The Bandia and Bargny limestones are characterized by a higher water-holding capacity which explains why the modulus of limestone was more sensitive to water content than for basalt or quartzite. Limestones tend to be more sensitive to changes in water content and thus to matric suction. The shape of the SWCC depends on the particle size distribution and the cementation properties from dehydration of the aggregates. Material properties required as input to the Mechanistic-Empirical Pavement Design Guide (M-EPDG) to predict changes in resilient modulus in response to changes in moisture contents in the field were determined for implementation in the M-EPDG process. Results show that the SRM was more correlated with matric suction than with compaction water content (for resilient modulus testing). The empirical models commonly used to predict the SWCC such as the Perera et al. (Prediction of the SWCC based on grain-size-distribution and index properties. GSP 130 Advances in Pavement Engineering, ASCE, 2005) and the M-EPDG (NCHRP in Guide for mechanistic-empirical design of pavement structures. National cooperative highway research program. ARA, Inc., ERES Consultants Division, Champaign, IL, 2004) models tend to underestimate the SWCC and cannot provide reasonable estimation. SRM normalized with respect to the SRM at the optimum water content varied linearly with the logarithm of matric suction. Empirical relationships between SRM and matric suction on semi-logarithmic scale were established and are reported.

Gradation effects on the mechanical response of crushed stone aggregate

A study was conducted to evaluate the effects of varying the gradation of aggregate base course (ABC) on material performance. Five different gradations consistent with a range of common ABC were selected. Experimental trials were performed to classify the materials and assess the performance differences between the five gradations. The gradation was found to affect the behaviour of the aggregate in that coarser gradations gave better strength and resilience values under conditions most similar to those found in the field. From research and experience during the laboratory testing, it was concluded that the coarsest blends became too difficult to realistically work with and they also lacked the stability of the well-graded combinations. It was also observed that as the amount of fines in the specimens exceeded 8–12% by mass, the fines governed the behaviour of the material. Results are interpreted using previously published work on specific surface, ‘ideal’ gradations and micromechanical models for the response of granular materials.

Modeling Effect of Geocomposite Drainage Layers on Moisture Distribution and Plastic Deformation of Road Sections

AbstractThe effect of geosynthetic layers on moisture distribution and plastic deformation of paved and unpaved road sections is studied using numerical simulations. The geosynthetic layers consisted of, from top to bottom, a transport layer, a geonet, and a nonwoven geotextile (referred to as a geocomposite capillary barrier drain by previous researchers). Two geotextile types were modeled as the transport layer: woven fiberglass and nonwoven polypropylene. The numerical models were verified against published results obtained from a soil-geotextile column. Inclusion of the geosynthetic layers at the interface of the aggregate base course (ABC) and subgrade increased suction in the subgrade and decreased it in the ABC during a simulated rainfall event. The woven fiberglass geotextile led to higher suctions in the ABC compared with the nonwoven polypropylene geotextile. The geosynthetic layers decreased the plastic deformation in both paved and unpaved road sections through combined mechanistic and hydraul...

Water quality with storage in permeable pavement basecourse

The harvesting, storage and reuse of stormwater from permeable pavement reservoirs provides an opportunity to alleviate water shortages in urban areas. Reservoirs may be filled with a range of basecourse aggregate materials that provide structural support to the pavement. The materials have the potential to affect the quality of stored water. This research investigated changes in water quality when water was stored in two types of basecourse aggregate. Synthetic stormwater was placed in permeable pavement reservoir models filled with dolomite aggregate or quartzite aggregate or control reservoirs with no aggregate. The influence of residence time was investigated by monitoring stored water quality for up to 144 h. Conductivity and pH increased in both aggregate-filled reservoirs. Total suspended solids and turbidity also increased in the aggregate-filled reservoirs, before falling to levels significantly lower than the control reservoirs. Levels of phosphorous and organic nitrogen were significantly lower in the aggregate-filled reservoirs after 144 h. Total zinc, copper and lead were reduced by 94–99% in the aggregate-filled reservoirs compared with the controls after 144 h storage.

Evaluating the Impact of Coarse Aggregate Content on Properties of Cement Treated Base

This paper mainly presents the study on the properties of cement treated aggregate with different coarse aggregate content. The test specimens which contain 75%, 70%, 65%, 60% and 55% of coarse aggregates were made and the 7d, 28d, and 90d unconfined compressive strengths (UCS), 28d thremal shrinkage coefficient, as well as 90d anti-erosion performance were tested. Results show that with the increase of coarse aggregate, the maximum dry density (MDD)of the cement treated aggregate mixture increased slowly at first to reached the peak value and then decreased rapidly; The optimum moisture content (OMC) declined with the increase of coarse aggregate content; In order to enhance the UCS of cement treated aggregate, coarse aggregate of mixture can be increased to some extent, but too much coarse aggregate will increase the void of the specimen and lead to lower UCS; Increasing the content of coarse aggregate is able to decrease the thermal shrinkage coefficient and erosion quantity of 30 min of the specimens. This is favourable to enhance the cracking resistance and anti-erosion performance of cement treated aggregate base course.

Research on Performance of Cement Stabilized Skeleton-Dense Structure Aggregate Base Course Material

Laboratory tests were conducted to evaluate the performance of cement stabilized “skeleton-dense structure” aggregate and conventional “suspended-dense structure” aggregate. In this study, both of the aggregates above were stabilized by cement with different cement content (2%, 3%, 4%, 5% and 6%). Performances of the prepared specimens were studied in terms of compaction property, 7 day unconfined compressive strength (UCS), thermal shrinkage coefficient and 30 min erosion quantity. Results indicated that the maximum dry density of cement stabilized “skeleton-dense structure” aggregate is bigger than that of cement stabilized “suspended-dense structure” aggregate slightly. On the contrary, the optimum moisture content of the former is slightly smaller than that of the latter one. Along with the increase of cement content, the 7 day UCS and thermal shrinkage coefficient of cement stabilized two aggregates were all increase, and 30 min erosion quantity of cement stabilized two aggregates were all decrease. At the same cement content level, the 7 day UCS of cement stabilized “skeleton-dense structure” aggregate is greater than that of cement stabilized “suspended-dense structure” aggregate, and the thermal shrinkage coefficient and erosion quantity in 30 min of the former is smaller than that of the latter.

Resilient Modulus of Unbound Aggregate Base Courses from Senegal (West Africa)

This paper presents the results of research conducted to investigate the Resilient Modulus (Mr) of unbound aggregates used as pavement layer in Senegal (West Africa) as well as the effect of water content and density on the Resilient Modulus of the materials tested. Four different aggregates was collected from different sites within Senegal and then subjected to repeated load triaxial tests. Test results showed that the Bandia limestone is around 44% stiffer than the basalt, and 71% to 104% stiffer that the Black and the Red quartzites (GNB and GRB). The basalt is 21% to 43% stiffer than the GNB and the GRB. Basalt specimens compacted at Wopt– 2% were 30% stiffer than basalt specimens compacted at Wopt and 40% stiffer than those com- pacted at Wopt+ 2%. The Summary Resilient Modulus (SRM) at Wopt– 2% is 22% higher than SRM at Wopt and 35% higher than SRM at Wopt+ 2% for the GRB and the GNB. The SRM at Wopt– 2% is 30% higher than SRM at Wopt and 40% higher than SRM at Wopt+ 2%, for the Basalt. For the Bandia limestone, the SRM at Wopt– 2% is 81% higher than SRM at Wopt and 126% higher than SRM at Wopt+ 2%. Results show also that the Resilient Modulus increases around 25% when relative density increases from 77% to 119% and the variation is more significant at high stress states than at low stress state. Results of statistical analysis and coefficients of determination (R2) showed that the Uzan and NCHRP models are more suitable to predict the Resilient Modulus of the aggregates tested.

Characterization of Mechanically Stabilized Layer by Resilient Modulus and Permanent Deformation Testing

The majority of roadways in the United States are low volume. Pavement structures for low-volume roads (LVRs) are designed according to empirical procedures that are sometimes verified by a mechanistic-based design process. The flexible pavement structure for an LVR consists of a relatively thin asphalt–concrete wearing course and an aggregate base course constructed on subgrade. An asphalt wearing course provides a good riding surface and moisture protection for the base course. Service life of a thin asphalt pavement depends on material quality and thickness of granular layers. A compelling need now exists for reducing the cost of building and maintaining the national transportation infrastructure. The limited lifespan of most construction materials due to continuing wear and tear requires more creative, innovative, economical, and sustainable roadway design techniques. Geogrid reinforcements in LVRs are seen as a particularly promising solution because they can be designed to provide an equivalent service life through use of less material. The combination of the aggregate and geogrid materials creates an improved or mechanically stabilized layer (MSL) with a significantly increased resilient modulus. The objective of this study was to use existing testing protocol to determine and to evaluate material design parameters for an unbound and a geogrid MSL. To determine the effects of an MSL, a test combination that included AASHTO T307 and NCHRP 598 was conducted on both unbound and mechanically stabilized aggregate specimens.

Laboratory Performance Comparison of Stabilized Undercut Subgrade Under Cyclic Loading

Abstract This study evaluated the performance of undercut subgrade stabilization measures during construction traffic loading prior to final paving. Twenty-two simulated undercut sections with different stabilization configurations over a typically undercut Coastal Plain clay subgrade were built in a large-scale test pit. The subgrade was placed at a California Bearing Ratio of ∼2–3 % and stabilized with granular layers, granular layers reinforced with geosynthetics, and lime. Granular layers consisted of either aggregate base course (ABC), sandy select fill, or a multi-layer system with both soil types. The four geosynthetics tested were a woven reinforcement geotextile, a woven separation geotextile, and two biaxial polypropylene geogrids. The soft nature of the subgrade and its consequences on the ability to compact the ABC layer show the importance of carefully analyzing the results when viewed on a comparative basis. Cyclic plate loading simulating construction traffic showed that thicker granular layers produced less surface displacement, barring subgrade strength differences from remolding effects. Tests with lime stabilized subgrade showed the least magnitude of deformation over initial and post-rut repair cycles. ABC tests with geotextile showed improvement over unreinforced sections but only when placed at depths approximately equal to the loading plate diameter and after initial displacements mobilized the geosynthetic strength.

Comparison of Georgia Department of Transportation Design Procedure with Mechanistic–Empirical Pavement Design

This research had several objectives: measure the dynamic modulus of commonly used hot-mix asphalt mix types, two aggregate base courses, and two soils that represent high and low values; compare the results of using measured moduli with Mechanistic–Empirical Pavement Design Guide (MEPDG) Level 3 default moduli for the subgrade and aggregate base material; and compare design results using the AASHTO 1972 Interim Guide for Pavement Design currently being used by the Georgia Department of Transportation (GDOT) with the MEPDG results. The research showed that the MEPDG Level 3 default values for resilient modulus of both soil and aggregate materials are significantly higher than the actual values determined from laboratory test results. Use of actual material properties and load spectra resulted in significantly greater structures being recommended than when Level 3 default values were used for the MEPDG design program. On the basis of these results, GDOT is cautioned against using the default values built into the MEPDG software and should conduct a thorough calibration study using Georgia materials before implementing the MEPDG design procedure.

Discussion of “Design Method for Geogrid-Reinforced Unpaved Roads. I: Development of Design Method” by J. P. Giroud and Jie Han

A discussion of an article with the aforementioned title, published in this journal in August 2004 is presented with closure. The discussers mention several aspects of the paper, including the selection of aperture stability modulus for geogrid performance, the typical aggregate base course thickness for design method and other comparisons to unpaved road design methods. The authors respond with appropriate comments on the calibration of the design method, consensus standardized test method, the issue of departing from other design methods, the typical aggregate base thickness for design method development, installation damage and environmental factors, tensioned membrane effect, the base thickness obtained with different unpaved road design methods and current practices. They also comment on the Giroud and Noiray method.

Strength Behaviour of Geogrid Reinforced Shedi Soil Subgrade and Aggregate System

ABSTRACT Shedi soil (Lithomargic clay), a yellowish-white silty soil underlying lateritic soil, is densely deposited along Konkan belt of India. The strength behaviour of Shedi soil under varying moisture content is major problem for road construction projects in this region. In the present investigation, the subgrade is stabilized with geogrid, keeping the geogrid at different positions from top of subgrade, to locate its optimum position. The plate load tests were also conducted at soaked and unsoaked conditions for unreinforeced, reinforced (with Geogrid) subgrade with aggregate base course. An equation has been established based on load-deflection values recorded for subgrade of un-reinforced and reinforced with geogrid at different levels. The deflection values obtained from equation and from the laboratory investigation were compared. In the case of reinforced subgrade with aggregate base course, the theoretical deflection values were computed based on Burmister's theory and compared with laboratory deflection values.

Deformation-Resistance Model for Geogrid-Reinforced Unpaved Road

Unpaved road sections experience degradation and accumulation of plastic deformation under repeated loading. Geogrid placed between subgrade and aggregate base course (ABC) can improve section performance through several mechanisms and lead to reduction in stresses and plastic deformation. An unpaved road design model that includes provisions for mobilization of subgrade bearing capacity under axisymmetric condition is proposed. The model incorporates base course property, mobilization of subgrade bearing capacity with rutting, degradation of base course stress attenuation with cyclic load, and the effect of reinforcement inclusion. An elastic layer method has been used to back-analyze the vertical stresses on subgrade with data from previous cyclic plate load tests performed in the laboratory. The degradation of unpaved sections was expressed as a reduction in base course-subgrade elastic modulus ratio (E1/E2) with an increasing number of cycles or a decrease in stress distribution angle of base course. ...

Deformation–Resistance Model for Geogrid-Reinforced Unpaved Road

Unpaved road sections experience degradation and accumulation of plastic deformation under repeated loading. Geogrid placed between subgrade and aggregate base course (ABC) can improve section performance through several mechanisms and lead to reduction in stresses and plastic deformation. An unpaved road design model that includes provisions for mobilization of subgrade bearing capacity under axisymmetric condition is proposed. The model incorporates base course property, mobilization of subgrade bearing capacity with rutting, degradation of base course stress attenuation with cyclic load, and the effect of reinforcement inclusion. An elastic layer method has been used to back-analyze the vertical stresses on subgrade with data from previous cyclic plate load tests performed in the laboratory. The degradation of unpaved sections was expressed as a reduction in base course–subgrade elastic modulus ratio ( E1/ E2) with an increasing number of cycles or a decrease in stress distribution angle of base course. The proposed model has been validated by data from a field study. Computed base course thickness matched well with the test results, but further verification of the method based on field testing is needed before it is accepted as a viable design tool.

Numerical analysis of stress–deformation response in reinforced unpaved road sections

Aggregate base course (ABC) layers of unpaved structures show significant plastic behavior under traffic load, including stress-dependent modulus and structural degradation. Geosynthetic reinforcement is commonly placed between the ABC and the subgrade to improve the performance of unpaved structures. Numerical analyses using the finite element program ABAQUS were conducted to investigate the performance of geogrid-reinforced aggregate over soft subgrade. Elasto-plastic constitutive models were used to model aggregate, subgrade and geogrid layer. Interaction between geogrid and aggregate was simulated as a shear-resistance interface. The reinforcement effects were seen in reducing surface deformation and improving vertical stress distribution on the subgrade layer. A parametric study indicated that ABC thickness and ABC/ subgrade modulus ratio greatly affect the contribution of the reinforcement. As the ABC thickness decreases, or as the ABC/subgrade modulus ratio decreases owing to deterioration or degradation of the ABC layer, the modeled sections show larger deformation, and the benefit due to geogrid inclusion becomes more apparent. Reinforcement with higher tensile modulus and better interface friction coefficient yielded better section performance in terms of less stress on the subgrade and surface deformation.

Numerical analysis of stress-deformation response in reinforced unpaved road sections

Aggregate base course (ABC) layers of unpaved structures show significant plastic behavior under traffic load, including stress-dependent modulus and structural degradation. Geosynthetic reinforcement is commonly placed between the ABC and the subgrade to improve the performance of unpaved structures. Numerical analyses using the finite element program ABAQUS were conducted to investigate the performance of geogrid-reinforced aggregate over soft subgrade. Elasto-plastic constitutive models were used to model aggregate, subgrade and geogrid layer. Interaction between geogrid and aggregate was simulated as a shear-resistance interface. The reinforcement effects were seen in reducing surface deformation and improving vertical stress distribution on the subgrade layer. A parametric study indicated that ABC thickness and ABC/ subgrade modulus ratio greatly affect the contribution of the reinforcement. As the ABC thickness decreases, or as the ABC/subgrade modulus ratio decreases owing to deterioration or degradation of the ABC layer, the modeled sections show larger deformation, and the benefit due to geogrid inclusion becomes more apparent. Reinforcement with higher tensile modulus and better interface friction coefficient yielded better section performance in terms of less stress on the subgrade and surface deformation.

Validated Model for Predicting Field Performance of Aggregate Base Courses

The International Center for Aggregates Research Project 502 focused on pavement layers of unbound aggregate proper representation in mechanistic pavement models. The research team developed models for resilient and permanent deformation behavior from the results of triaxial tests conducted at the Texas Transportation Institute and the University of Illinois. The studies indicate that the unbound aggregate base (UAB) material should be modeled as nonlinear and cross-anisotropic to account for stress sensitivity and the significant differences between vertical and horizontal moduli and Poisson’s ratios. Field validation data were collected from a full-scale pavement test study conducted at Georgia Tech. The validation of the anisotropic modeling approach was accomplished by analyzing conventional flexible pavement test sections using the GT-PAVE finite element program to predict responses to load in the UAB layer and comparing these predicted responses to the measured values. Laboratory testing of the aggregate samples was conducted at the University of Illinois, and characterization models were developed for the stress-sensitive, cross-anisotropic aggregate behavior. With nonlinear anisotropic modeling of the UAB, the resilient behavior of pavement test sections was successfully predicted for a number of response variables. In addition, the stress-sensitive, cross-anisotropic representation of the base was shown to greatly reduce the horizontal tension computed in the granular base compared with a linear isotropic representation.