Subbase Materials Research Articles

Neural network-based model for prediction of permanent deformation of unbound granular materials

Abstract Several available mechanistic-empirical pavement design methods fail to include predictive model for permanent deformation (PD) of unbound granular materials (UGMs), which make these methods more conservative. In addition, there are limited regression models capable of predicting the PD under multi-stress levels, and these models have regression limitations and generally fail to cover the complexity of UGM behaviour. Recent researches are focused on using new methods of computational intelligence systems to address the problems, such as artificial neural network (ANN). In this context, we aim to develop an artificial neural model to predict the PD of UGMs exposed to repeated loads. Extensive repeated load triaxial tests (RLTTs) were conducted on base and subbase materials locally available in Victoria, Australia to investigate the PD properties of the tested materials and to prepare the database of the neural networks. Specimens were prepared over different moisture contents and gradations to cover a wide testing matrix. The ANN model consists of one input layer with five neurons, one hidden layer with twelve neurons, and one output layer with one neuron. The five inputs were the number of load cycles, deviatoric stress, moisture content, coefficient of uniformity, and coefficient of curvature. The sensitivity analysis showed that the most important indicator that impacts PD is the number of load cycles with influence factor of 41%. It shows that the ANN method is rapid and efficient to predict the PD, which could be implemented in the Austroads pavement design method.

Utilization of Waste Materials for the Strengthening of Pavement Subgrade-A Research

From a long period in road construction soil is used as subgrade, sub-base, and base material. While constructing a road in the weak soil areas or subgrade has poor strength, in such cases the improvement of soil is necessary. The improvement of the soil is thru by swapping by the stronger soil or stabilization with the waste material. Dispose of these waste materials is essential as these are causing hazardous effects on the environment. With the same intention, the literature review is undertaken on the utilization of waste materials for the stabilization of soils and their performance is discussed. The waste material is one of the best solutions to the improvement of submerged properties in an economical manner. This review paper presents a brief exposure to the stabilization of soil with waste material like agriculture waste, constructional waste, and industrial waste materials.

EFFECTS OF MECHANICALLY STABILIZED GRADED ASSORTED COARSE-GRAINED SOILS IN THE PERFORMANCE OF UNPAVED ROAD: A CASE STUDY IN GOFFA ZONE, SAWLA AREA

Road network development in Ethiopia is booming, radiating from Addis Ababa towards North-South directions, and East-West directions, due to the good economic growth of the country. However, there are challenges always facing by the pavement designers, and materials engineers for every road project, specifically the unpaved roads in Goffa Zone. It was because, most parts of the existing unpaved road sections within the study area are heavily damaged, and lack of proper maintenance. The source of good quality of sub-base course materials limited and becoming depleted. It is for this reason that the research study focused on the investigation of the effects of mechanically stabilized graded assorted coarse-grained soils. Disturbed and undisturbed samples from different quarry sites were considered and tested in the laboratory. Laboratory test for each location performed, and the results served as control values of the engineering properties of natural soils. The Disturbed samples tested for Gradation, Atterberg's Liquid Limit Tests, and Compaction, while, the undisturbed sample tested for the CBR strength, using ASTM manual. The results of the assorted materials for the sub-base course was analyzed and compared with the AASHTO and ERA Standard Specifications.

EFFECTS OF MECHANICALLY STABILIZED GRADED ASSORTED COARSE-GRAINED SOILS IN THE PERFORMANCE OF UNPAVED ROAD: A CASE STUDY IN GOFFA ZONE, SAWLA AREA

Road network development in Ethiopia is booming, radiating from Addis Ababa towards North-South directions, and East-West directions, due to the good economic growth of the country. However, there are challenges always facing by the pavement designers, and materials engineers for every road project, specifically the unpaved roads in Goffa Zone. It was because, most parts of the existing unpaved road sections within the study area are heavily damaged, and lack of proper maintenance. The source of good quality of sub-base course materials limited and becoming depleted. It is for this reason that the research study focused on the investigation of the effects of mechanically stabilized graded assorted coarse-grained soils. Disturbed and undisturbed samples from different quarry sites were considered and tested in the laboratory. Laboratory test for each location performed, and the results served as control values of the engineering properties of natural soils. The Disturbed samples tested for Gradation, Atterberg's Liquid Limit Tests, and Compaction, while, the undisturbed sample tested for the CBR strength, using ASTM manual. The results of the assorted materials for the sub-base course was analyzed and compared with the AASHTO and ERA Standard Specifications.

Performance evaluation of flexible pavements with a lateritic gravel base using accelerated pavement testing

Lateritic gravel is widely used for road construction and its mechanical properties have been explored in numerous laboratory tests. In this study, full-scale accelerated pavement testing was conducted to evaluate the long-term performance of pavements constructed with lateritic gravel as the subbase and base materials. Test Sections were constructed in a test tank and instrumented with temperature sensors, strain sensors, and moisture content sensors. This study investigated two asphalt layer thicknesses (5 cm and 10 cm) and three types of base materials (crushed stone, cement-lateritic gravel, and lateritic gravel blended with crushed stone) for comparative purposes. The test pavements all had a uniform subbase depth of 30 cm of raw lateritic gravel. The development of permanent deformation and cracking was recorded periodically. Based on measurements and observations, this study found that the crushed stone base performed better than the blended lateritic base in terms of rutting and cracking resistance and that rutting development was relatively less in the thicker (10 cm) asphalt layer than in the thinner (5 cm) layer. The cement-lateritic base developed the largest rutting and exhibited the earliest appearance of cracking among the three base types and showed the weakest behavior among these three bases.

Cement-improved lake bed sedimentary soil for road construction

Phayao Lake, the largest lake in the north of Thailand, supplies water for consumption and irrigation in the region. Currently, the lake is faced with serious problems as it is becoming shallow with a consequent decrease in the volume of water. Every year the local government invests a lot of resources to dredge and pump the lake bed of sediments. However, it is difficult to find suitable landfill areas to dump such large quantities of sedimentary soil. The purpose of this study was to improve the engineering properties of sedimentary soil using Portland cement for possible use in road construction. The sedimentary soils were mixed with cement in a 3–10% proportion by weight. The strength and durability of the improved soil were examined using unconfined compression and durability tests, respectively. A long-term strength improvement was observed and well-fitted to a power function. Soil−cement losses due to multiple wet−dry cycles were examined by means of durability tests. Finally, suitable cement percentages for sediment improvement are suggested to achieve the requirements for road base and subbase materials.

Evaluation of Structural Stability by Characterization of Lateritic Soils with Rock Flour along Ibadan-Iwo-Osogbo Highway, Southwestern Nigeria

Failures of different categories of roads shortly after being opened to traffic have necessitated the need for sustainable alternative road building materials. This study determines the potential of rock flour on the geotechnical properties of lateritic soils with a view to establish the optimum content of the rock flour required for effective stabilization and proffer lasting remediation measures to the incessant road failures. Ten bulk lateritic soil samples were collected from ten trial pits at depths of 1.5 m in different locations of the study area. Index and engineering property tests were performed on the soils, both in their natural and stabilized states by adding 2, 4, 6, 8 and 10% rock flour contents. In addition, CBR – UCS model was used to establish a third order polynomial to correlate the soil-rock flour mix. The results show that the plasticity and linear shrinkage of the soils decreased with increase in rock flour contents. The MDD of rock flour stabilized soils increase with the maximum improvement observed at 10% by weight of rock flour with the corresponding decrease in OMC. The load bearing capacities (LBC) of the soils increase with the stabilization mix. It was observed that the values meet the requirements for good quality subgrade, subbase materials and some of the soils for base materials in road construction. The results also reveal the improvement of the soil properties. This is further confirmed by the increase in UCS and shear strength of the soils which optimally improved on addition of 8% rock flour. Moreover, the addition of more than 8% by weight of rock flour caused reduction in UCS and shear strength. These results show the stabilizing potentials of rock flour on lateritic soils especially when added at the optimum level. The CBR - UCS models established are in form of third order polynomial (ax3- bx2 + cx +d) with the R2 values, 0.672 and 0.528 which indicate positive correlation of the soil-rock flour mix. Therefore, rock flour can potentially stabilize lateritic soils solely with addition of 8% recommended as an optimum content for stabilizing lateritic soils for road constructions.

Soil Stabilization using Brick Kiln Dust and waste Coir Fibre

Stabilization of clay soil has been carried out for improving its engineering properties of soil. To stabilize the clayey soil use Brick Kiln Dust of and waste Coir Fibre, an experiment is conducted to evaluate the properties of soil mixing with 10%, 20% &30% percentage of Brick Kiln Dust and Coir Fibre contents of 0.5%, 0.75% and 1.0% by weight of soil sample and then the tests are performed. Tests conducted for clayey soil mixed with Brick Kiln Dust and Coir Fibre are Liquid Limit, Plastic Limit, Compaction (OMC & MDD), and California Bearing Ratio (CBR). Flexible pavements sections were degined for non-stabilized and stabilized subgrades to be standard axles traffic intensities. The preamble of brick kiln dust and coir fiber is analyzed to improve the features of expansion subgrade materials and other sub-base materials. Also design the thickness of pavement when it is stabilized with optimized brick kiln dust and coir fiber. The results reveal that CBR value increased with increase of Brick Kiln Dust and Coir fibre. The soil stabilization treatment significantly improved the engineering properties of the soil, and reduced the pavement thickness and also cost of the project.

A mixture of coal wash and fly ash as a pavement substructure material

Abstract The reuse of waste materials in engineering projects has become the subject of many research efforts worldwide as it provides economical as well as environmental benefits. Coal wash (CW) and fly ash (FA) are example waste materials that can be used as alternative aggregates in transportation infrastructure projects, specifically as base and subbase materials in roads. Class C FA has been extensively used as a stabilizing material due to its hardening potential. However, Class F fly ash, a non-pozzolanic material when used alone, has not been considered in past research projects. In this study, Class F fly ash is mixed with coal wash as a void filler to enhance its compaction efficiency and produce a compact and well interlocked structure. A laboratory testing plan is performed to assess the geotechnical properties of the mixtures with 0%, 7%, 10% and 13% FA content and it includes compaction tests, unconfined compressive strength tests, California Bearing Ratio (CBR) tests, collapse potential tests and permeability tests. The mixture with 7% FA is selected as the optimum mixture and its potential for tensile cracking under service loads is further investigated using four-point bending tests. Also, the resilient modulus and permanent deformations of the mixture are evaluated under different dry-back conditions using multistage repeated load triaxial tests.

Assessment of the physical characteristics and stormwater effluent quality of permeable pavement systems containing recycled materials

This paper evaluates the physical characteristics of two recycled materials and the pollutant removal efficiencies of four 0.2 m2 tanked permeable pavement rigs in the laboratory, that contained either natural aggregates or these recycled materials in the sub-base. The selected recycled materials were Crushed Concrete Aggregates (CCA) and Cement-bounded Expanded Polystyrene beads (C-EPS) whilst the natural aggregates were basalt and quartzite. Natural stormwater runoff was used as influent. Effluent was collected for analysis after 7–10 mins of discharge. Influent and effluent were analysed for pH, Chemical Oxygen Demand (COD), Dissolved Oxygen (DO), Electroconductivity (EC), turbidity, Total Suspended Solids (TSS), Total Dissolved Solids (TDS), Nitrate-Nitrogen (NO3-N), reactive phosphorous () and sulphates (). Both CCA and C-EPS had suitable physical properties for use as sub-base materials in PPS. However, C-EPS is recommended for use in pavements with light to no traffic because of its relatively low compressive strength. In terms of pollutant removal efficiencies, significant differences (p < 0.01) were found in pH, EC, TDS, DO, and across all rigs whereas no significant differences (p > 0.05) were found with respect to TSS, turbidity, COD and NO3-N. Effluent from rigs containing CCA and C-EPS saw significant increases in pH, EC and TDS measurements whilst improvements in DO, TSS, turbidity, COD, and were observed. All mean values except pH were, however, within the Maximum Permissible Levels (MPLs) of water pollutants discharged into the environment according to the Trinidad and Tobago Environmental Management Authority (EMA) or the United States Environmental Protection Agency (US EPA). In this regard, the CCA and C-EPS performed satisfactorily as sub-base materials in the permeable pavement rigs. It is noted, however, that further analysis is recommended through leaching tests on the recycled materials.

Controlled low-strength materials for pavement foundations in road tunnels: feasibility study and recommendations

This paper presents the results obtained during a laboratory and field investigation which focused on the assessment of the feasibility of using controlled low strength materials (CLSMs) in pavement foundations of road tunnels. The CLSM considered in the study, which contained a significant amount of recycled asphalt pavement, was designed by optimizing its flowability and by considering its sensitivity to changes in cement dosage. For comparative purposes, a standard low-strength Portland cement concrete mixture was also included in the investigation. Both mixtures were produced in a Portland cement concrete batching plant and were thereafter subjected to laboratory tests for the evaluation of flowability, consistency, compressive strength, California bearing ratio and resilient modulus. Furthermore, full-scale slabs constructed with the two mixtures were subjected to plate loading tests and to the transit of a fully-loaded heavy vehicle. Obtained results indicated that both mixtures are suitable for the formation of pavement foundations since they exhibit a short-term mechanical behavior which is comparable to that of standard granular sub-base materials. However, the CLSM proved to be superior in terms of its improved flowability, easier long-term excavatability, lower production cost and enhanced sustainability. Finally, recommendations for future applications of cement-bound materials in pavement foundations were provided in the form of preliminary performance-based acceptance criteria.

Geotechnical Study of the Properties of Black Cotton Soil Treated with Cement and Bone Ash as Admixture

Black cotton soils are vulnerable to changes in moisture content; they swell when in contact with water and shrink upon drying up of the water. These changes, therefore, affect the properties of the soils. In order to improve these properties the common methods are modification or stabilization or both. In this paper an attempt was made to assess the effectiveness of black cotton soil blended with ordinary Portland cement (OPC) and bone ash (BA) for soil stabilization. The study was therefore about improvement of the properties of black cotton soil with bone ash admixed with ordinary Portland cement and the determination of the optimum quantity that could be used as road construction material at minimal cost. Bone generated waste from slaughter houses (abattoirs) could be effectively utilized for civil engineering construction works, aiming at minimizing the disposal problems and reducing the environmental hazard. The preliminary investigation on the black cotton soil collected along Gombe-Biu road in Yamaltu (Baure village) Yamaltu Deba Local Government Area of Gombe state Nigeria, shows that the soil belongs to A-7-6 (31) in the American Association of State Highway and Transport Officers and CH in the Unified Soil Classification Systems (USCS), respectively. Ordinary Portland cement (OPC) / Bone ash (BA) blend in stepped concentrations of 0, 2, 4, 6 and 8% and 0, 2, 4, 6, 8 and 10% respectively, by dry weight of soil, were used to treat the soil. Compaction was carried out using three energy levels namely: the British Standard Light, West African Standard and the British Standard Heavy. The liquid limit decreased steadily from 65% for the natural soil to 55.5% at 6% OPC / 6% BA content, while the plastic limit increased from 25% for the natural soil to 39% at 6% OPC / 6% BA treatment. Generally, the maximum dry density (MDD) increased while optimum moisture content (OMC) decreased with higher BA treatment. The UCS values of specimens treated with 6% OPC / 6% BA increased from 752, 779 and 827kN/m 2 for the natural soil to 1688, 2250 and 2667kN/m 2 when cured for 7, 14 and 28 days, respectively. There was an increase in the unsoaked CBR values from 6, 9 and 12% for the natural soil compacted with BSL, WAS and BSH energies to 48, 80 and 85% at 6% OPC / 6% BA content. The soaked CBR values of 4, 7 and 9% for the natural soil compacted with BSL, WAS and BSH energies, respectively, increased to peak values of 43, 71 and 74% at 6% OPC / 6% BA content. The durability of specimens was determined by immersion in water. Based on the results obtained the optimum of 6% OPC / 6% BA treatment on the black cotton soil could be used as sub-base material when compacted with BSH.

Utilizing recycled PET blends with demolition wastes as construction materials

The rapid growth in plastic and demolition wastes generation by municipal and commercial industries is a significant challenge to developed and developing countries. The substitution of traditional construction materials with recycled materials is a sustainable solution which mitigates landfilling concerns and reduces the need for virgin quarry materials. In this research, an evaluation of the geotechnical and geo-environmental properties of Polyethylene terephthalate (PET) plastic waste and its blends, with two major constituents of construction and demolition (C&D) waste materials was undertaken. Recycled concrete aggregate (RCA) and crushed brick (CB) were blended with 3% and 5% of PET, and the geotechnical properties of six PET blends were evaluated in the laboratory. The experimental programme included particle size distribution, particle density, sieve analysis, flakiness index, Los Angeles abrasion, water absorption, modified Proctor compaction, hydraulic conductivity, and California bearing ratio (CBR) tests. In addition, the response of the PET blends under repeated dynamic loading conditions was investigated using repeated load triaxial (RLT) tests. CBR results of all six PET blends were higher than the minimum CBR requirements for usage as a subbase material. The RLT testing results indicated that PET blends with RCA and CB performed satisfactorily at 98% maximum dry density and at their optimum moisture contents under modified Proctor compaction effort. Furthermore, a geo-environmental evaluation of the PET blends was undertaken which consisted of determination of organic matter content, pH value, total/leachate concentration of the recycled materials for a range of contaminant constituents and the results were compared with requirements specified by environmental authorities. Control samples, 3% and 5% PET blends with RCA and CB satisfied the CBR requirements. Similarly, control samples, 3% and 5% PET blends with RCA were found to be satisfactory for RLT requirements for subbase applications.

Environmental Sustainability by Bulk Utilization of Fly Ash and GBFS as Road Subbase Materials

AbstractThe underutilization of fly ash, in contrast with its generation, and scarcity of natural aggregates paved the way to unconventional construction approaches, thereby ensuring environmental ...

Experimental and Modeling Studies of Resilient Modulus and Permanent Strain of Stabilized Fly Ash

AbstractIn the present investigation, geotechnical properties of fly ash lime (FAL) mixes and fly ash cement (FAC) mixes were studied for their use as a subbase material for flexible road pavements...

Evaluation of permanent deformation of a new pavement base and subbase containing unbound granular materials, crumb rubber and crushed glass

To avoid premature failures in pavement layers, strong aggregates must be selected for pavement constructions that can bear the accumulation of permanent deformations. Otherwise, rutting happens in the pavement layers due to the accumulation of permanent deformations. On the other hand, due to the extensive generation of construction and demolition (C&D) materials around the world, the application of waste materials in civil engineering projects would be considered as an environmentally friendly and cost-effective solution. Although many studies have been performed to examine the performance of the crushed recycle pavement materials, the literature review shows that few studies have been conducted to examine the permanent deformation characteristic of recycled concrete aggregate (RCA) and crushed rock (CR) containing both crumb rubber (R) and crushed glass (CG). In this study, a series of repeated load triaxial (RLT) tests were carried out to evaluate the permanent deformation (i.e. 100000 loading cycles) of RCA and CR incorporating R and CG. The shakedown theory was used to characterize the permanent deformation behaviour of the samples. Also, Werkmeister's criteria were applied to define the shakedown ranges of the samples. The results show that the RCA, RCA +1% R + 5% CG, CR + 1% R + 3% CG and CR + 1% R + 5% CG can be used as base and sub-base material in pavement.

The strength and microstructural behavior of lime stabilized subgrade soil in road construction

ABSTRACT This paper attempts to study the potential of lime on strength and bearing capacity improvement of subgrade soil. The effect of soil type, different lime percentages (3, 5, 7 and 9%) and curing duration (0, 7, 14 and 28 days) on the engineering properties of soil is evaluated by conducting series of laboratory tests such as linear shrinkage, unconfined compressive strength (UCS), split-tensile strength (STS) and California bearing ratio (CBR) test. The result indicates that soil with large clay fractions needs a relatively higher percentage of lime to alter their physicochemical characteristics. Addition of lime reduced the linear shrinkage strains and increased the UCS, STS and CBR value of soil. But beyond an optimum lime content opposite trend is observed. The strength improvement of lime stabilized soil is further enhanced with curing time. Moreover, the micro-structural analyses are performed to understand the mechanisms involved in the lime stabilization process. Change in soil morphology from FESEM (Field emission scanning electron microscope) and apparent formation of some new peaks in XRD (X-ray diffraction) and FTIR (Fourier transform infrared spectroscopy) analysis confirms the formation of cementitious compounds in lime stabilized soil. For particular lime content and curing duration, soil with high plasticity index gives lower strength value. Further, soil treated with 3% lime achieves 7 days target compressive strength value (i.e. 345 kPa). CBR values of soil treated with the optimum lime meet the requirement of subbase materials for low traffic rural roads thus reduce the overall pavement thickness and the construction cost.

Life Cycle Assessment of Natural and Recycled Concrete Aggregate Production for Road Pavements Applications in the Northern Region of Colombia: Case Study

The environmental impacts of natural aggregates (NA) and recycled concrete aggregates (RCA) production for use in road pavements have been evaluated in this study through an attributional life cycle assessment (LCA) from cradle to gate. Such effort is relevant considering the increasing interest of national agencies in applying recycled aggregates for construction and rehabilitation (C&amp;R) of highway infrastructures. The study used site-specific data from two different aggregate production plants, stationary and mobile, both located in the northern region of Colombia. The stationary facility produces NA, and the mobile plant processes a combination of NA and RCA from the demolition of Portland cement concrete (PCC) pavements in the city of Barranquilla. The aggregates produced in the stationary facility are generally used as road base and subbase materials, and in the production of PCC, whereas the recycled mobile plant produces aggregate for subbase and road base mainly. Two scenarios were contemplated in the study. The first scenario involved extraction, hauling, and processing of NA. The second scenario involved aggregate (limestone) extraction, hauling, and recycling of RCA, and finally processing the combination of NA with RCA. The environmental impacts related to the production process of both stationary and mobile plants were evaluated using the computer program SimaPro 8.4.0 and the impact assessment method IMPACT 2002+. The results showed that diesel fuel is the principal energy used in both production processes, and is mainly responsible for the negative impact on respiratory inorganics, global warming, and nonrenewable energy. Results were very sensitive to transportation distances.

Long-term permanent deformation behaviour of recycled concrete aggregate with addition of crumb rubber in base and sub-base applications

The structural behaviour of pavements depends on the permanent and resilient deformations. These deformations are accumulated during the pavement lifetime. Although many studies have been done to explore the use of construction and demolition (C&D) waste materials in road pavement construction, the long-term permanent deformation behaviour (i.e., 100,000 loading cycles) of recycled concrete aggregate (RCA) with an addition of crumb rubber as base/subbase layers has not been studied yet. The aim of this study is to assess whether RCA combined with crumb rubber can be used as the base or sub-base materials or not. Two different crumb rubber sizes were used in this study: a fine type measuring 1–5 mm in diameter and a coarse type measuring 15–20 mm. 0.5, 1% and 2% crumb rubber by weight of the dry aggregate were added to the 20 mm RCA. A series of repeated load triaxial tests were performed to investigate the effects of the sizes and percentages of crumb rubber on the long-term permanent deformation characteristics of RCA incorporating rubber. The results show that only RCA and RCA containing 0.5% fine or coarse rubber can be used as base and sub-base material in pavement in terms of long-term permanent deformation.

New shakedown criterion and permanent deformation properties of unbound granular materials

Unbound granular material specifications for road pavements in Australia are primarily based on physical material specification rather than mechanical characterisation. This simplified approach does not reflect the actual material performance under repeated dynamic traffic loads. There is a little information available on the influence of the local crushed rock properties and compacted layer properties on permanent deformation (PD). This study aims to characterise the local unbound granular materials in Victoria according to their PD behaviour under repeated loads and to develop a suitable shakedown criterion that could describe the PD of the tested materials to simplify the flexible pavement design. Repeated-load triaxial tests were conducted over several samples with a range of moisture contents, gradations, densities, and stress conditions. The laboratory test results showed that PD behaviour was influenced by several factors. In addition, the tested subbase-specified unbound granular materials reflect high PD resistance that is almost equivalent to base-quality unbound granular materials. This may indicate that current requirements for the subbase-quality unbound granular materials are over-prescribe. Moreover, as the existing shakedown criterion was not applicable for the multi-stage repeated-load triaxial test and the local tested materials, a new shakedown criterion and new boundaries are proposed based on the PD behaviour. In the proposed criterion, the shakedown ranges are identified based on the curve angle of the PD vs. logarithm of the number of loading cycles, and this new criterion was validated using several materials from existing literature. The local tested base and subbase materials can be assigned as Range A when PD < 1%, Range B when 1% < PD < 3%, and Range C when PD > 3%. The proposed criterion could provide a useful and quick approach to assess the PD of the unbound granular materials with both single and multi-stages of stresses.