Subbase Layers Research Articles

Effect of compaction on the hydraulic conductivity of granular subbase layers in road pavements

Effect of compaction on the hydraulic conductivity of granular subbase layers in road pavements

Unsaturated hydraulic property of recycled concrete aggregates blended with autoclaved aerated concrete grains for unbound road base and subbase materials in Vietnam

Roadbed materials of base and subbase layers are frequently unsaturated caused by rainfall, drainage, and evaporation. However, the movement of water in these layers is still poorly understood because of lacking data on unsaturated properties such as the water retention curve (WRC) and unsaturated hydraulic conductivity (K). This study, therefore, recycled concrete aggregates (RCA) blended with autoclaved aerated concrete (AAC) grains (% of substitution on the mass basis from 0 to 50%) were used to examine the WRC and K for unbound roadbed materials in Vietnam using the evaporation method. Natural aggregates (NA) and Toyoura sand were used as control and reference material. Results showed that compared to NA100% and RCA100%, the water capacity of RCA mixed samples was much improved by blending AAC grains. Toyoura sand showed higher water capacity at saturation compared to RCA100% and NA100%, but quickly became lowest when matric potential exceeds 10 kPa. Toyoura sand showed the highest saturated hydraulic conductivity, but decreased dramatically around 10 kPa, while other tested samples remained higher K. The original van Genuchten – Mualem model was well fitted for Toyoura sand and underestimated for other tested samples, but showed an agreement with estimated conductivity parameter ranging from – 3.0 to -4.4.

Penentuan Biaya Preservasi Berdasarkan Analisa Nilai Pemicu IRI PCI dan Lendutan Perkerasan pada Jalan Nasional di Sulawesi Utara

Samratulangi Street, R.W. Monginsidi Street, Bethesda Street and Pierre Tendean Street are national roads in North Sulawesi. At first glance, these four roads are in good, moderate and slightly damaged condition. Based on their status, these road sections were examined to see the relationship between IRI, PCI and Deflection and calculate the cost of preservation measures. Functional conditions on four national roads from 3.81 to 8.53 for IRI and 69 to 100 for PCI, while Structural Conditions range from 91.4 µm to 542.5 µm for maximum deflection, 120.55 µm to 4602.99 µm for the surface layer, 14.7 µm to 447.4 µm for the base layer, 20.1 µm to 259.9 µm for subbase layer, and 22.4 µm µm to 66.7 µm for subgrade layer. While the elastic modulus of the surface layer ranges from 536.06 Mpa to 270302.05 Mpa, the elastic modulus of the top layer is 40.53 MPa to 3111.77 Mpa, the elastic modulus of the subgrade layer is 80.54 MPa to 2428.48 MPa, and the elastic modulus of the subgrade layer is 86.89 MPa to 868.84 MPa. Project version preservation cost Rp.33,951,452,569. The functional condition analysis version is Rp.37,164,723,427 difference (Rp.-3,213,270,858), and the structural condition analysis version is Rp.76,977,602,855 difference (Rp.-43,026,150,286). The results are expected to provide information to the road management authority regarding the relationship between the level of damage and the amount of costs.
 Kata kunci - preservation cost, fwd, iri, pci

Sustainable Stabilization of Poorly Graded Desert Sand by Cement Kiln Dust and Salt Water for Using in Backfilling and Subbase Layers

Effective use of natural materials and industrial by products has a direct impact on economy, sustainable environment, and waste management. Poorly graded desert sand (SP) is widely observed in sand dunes and sand seas. Studies were performed to get beneficial use of cement kiln dust (CKD) in soil improvement. But there is a lack of information concerning using of CKD as an improving material for poorly graded sand with the aid of salt water. Salt water is widely available in Egypt from seas and some deep wells, using it will help in saving drink water which suffers from shortage in many countries. The aim of this research is to study the possibility of improving SP using CKD and salt water to be used in backfilling work and subbase layers of roads and pavements. Mixtures of poorly graded sand and various CKD ratios (10%, 20% and 30%) were classified and tested using grain size distribution, compaction, shear strength and California bearing tests. The results were compared with potable water. The results show that adding CKD improves the characteristic properties of SP even with salt water. The study enhances the using of 20% CKD with optimum water content of 9.12% of salt water to have noticeable improvement for SP and to be used efficiently in backfilling and subbase layers.

Use of repurposed whole textile for enhancement of pavement soils

The common availability of recycled textile from clothing represents an untapped resource which can be used as soil reinforcement. Recent efforts to use fibers as soil reinforcement have mostly concentrated on adding thin long fibers to natural soils. The techniques when applied to production often encounter mass production issues such as the difficulty in preventing localization, entanglement of the fibers and adhesion between the fiber and soil matrix interface. This experimental study uses small amounts (0.5%, 0.75% and 1.0%) of repurposed textile from polyester clothing cut into small pieces to reinforce a poorly graded sand. The California Bearing Ratio (CBR) test was used to quantitatively assess the strength characteristics of sand reinforced by adding whole textiles. The results of the laboratory program indicate a significant increase in CBR numbers and offers insight into the possible increase in other strength parameters such as ultimate bearing capacity. The increase in CBR values changes the suitability of the reinforced sand from subbase soils only, to also include base soils within pavements. During laboratory procedures localization and entanglement of textile reinforcement during mixing was not observed which suggests minimal difficulties when implementing the technology during construction applications. The results indicate that the use of the technique can lead to cost savings associated with the use of low-cost aggregates within a pavement base and subbase, thinner base and subbase layers, smaller footprints related to steeper slopes, and decreased periodic maintenance requirements of pavements.

Stress-Dependent Behavior of Lightly Stabilized Industrial Waste Subbase Using Falling Weight Deflectometer

Abstract Pavement layers exhibit stress-dependent behavior, characterized by using a laboratory resilient modulus (Mr) test. However, the field behavior of such materials seldom matches with the laboratory because of changes in the state of stress, material matrix, and loading patterns. In this study, the nonlinear behaviors of three innovative fly ash-based lightly stabilized industrial waste mixes that are proposed to replace the granular subbase of flexible pavement are characterized and compared in the laboratory and field for the first time. Nine full-scale pavement test sections were constructed with three varying thicknesses of waste mix subbase layers, namely, fly ash + 5 % lime (FAL), 70 % copper slag + 30 % fly ash (CFA) and 80 % fly ash + 20 % granulated blast furnace slag (FAG). Repeated load triaxial tests on lab samples and multiload falling weight deflectometer (FWD) tests (40 kN, 55 kN and 70 kN) on test sections conducted for three years post-construction were used to extract the nonlinear behavior of Mr and the FWD backcalculated modulus (EFWD) of subbase layers. Effects of curing and traffic damage on the nonlinear parameters of EFWD were investigated. Stress-dependent conversion factors based on two different constitutive models were established to convert Mr to EFWD at different points of the subbase service life. Stabilized waste mixes exhibited stress hardening with increasing bulk and deviatoric stresses both in the field and laboratory. Curing increased EFWD and reduced the effect of stresses on the EFWD. In contrast, traffic damage imparted the opposite effect, as the stabilized waste mixes transformed into a cracked and blocky mass. The results of this study will allow practitioners to predict the field performance of waste mix subbase with great accuracy, resulting in a reliable design and possible cost savings.

Comparative study for global warming potentials of Chinese and Norwegian roads with life cycle assessment

Mitigation of GHG emission is increasing concerned in the research field of road engineering. The quantitative assessments of integral road structural designs in different countries would shed light on the implementation of sustainable road development and global warming controlling. The study referred to the European E6 and the Yanqing-Chongli expressway to quantify the GHG emissions for Norwegian and Chinese roads, and investigate the critical procedures and factors in resulting in the differences of GHG emissions. The data inventory and research framework for life cycle assessment (LCA) were established according to their applied materials, structural design and construction techniques. Moreover, the quantification of GHG emission was conducted as considering the surface layers, base layers, subbase and frost protection layer. The comparative results indicate that the Norwegian road generated extra 1.43 t equivalent CO2 more than Chinese road during the 20-year service life, and the surface layers are the most source of GHG emission in road structure, which occupied 65.75% for Chinese road and 43.19% for Norwegian road. Additionally, the materials extraction phase caused the largest proportion of GHG emission in Chinese road case, while the road construction phase was verified as the capital GHG contributor in Norwegian road case with 108.27 t equivalent CO2 emitted. The obtained results in the comparative study could provide the practical references for low-carbon road construction and promising strategies for globalization development.

Evaluation of the Structural Performance of Lime-Stabilized cubitermes sp Termite Mound Soil as a Sub-Base Layer for Sustainable Pavements

The scarcity of road materials that can be used directly in the sub-base layer of a road without preparation has led to the use of non-conventional materials. This study describes the feasibility of using hydrated lime-treated cubitermes sp termite mound soils for road construction, based on laboratory tests. Tests of Atterberg limits, dry density, CBR, compressive strength, static modulus and measurement of sinking of the material under traffic were carried out with different proportions of lime (0%, 3%, 5%, 6%, 7%, 9%). The results obtained show that the mechanical properties of soil-lime mixtures improve up to the point of lime fixation at 6% and that above 6% lime, the mechanical properties decrease. The traffic simulation at the rut shows that for the 6% lime mix, microcracks appear from 20.000 cycles and that the average settlement is 2 mm. The friction of the grains under the stresses developed by the passage of the wheel reduces the mechanical bonds of the soil-lime mixture. The rigidity of the material leads to the induced slab effect, which gives the material good behavior in hot weather, without strain or rutting. The mechanical connections during the setting of the soil-lime mixture reduce the friction of the grains under the stresses developed by the wheel. Lime welds the fines into much larger, more or less impermeable particles on the surface, which reduces the crumbling of the material by attrition, a major cause of pavement deterioration. The optimal mix can be used as a sub-base layer or wearing course for low-traffic earth roads (T1 < 300) and for the treatment of the upper parts of embankments. All these results are consolidated by X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses.

Modelling of Temperature Effects on Flexible and Rigid Pavements

Abstract: One of the most crucial elements impacting the rigid and flexible pavements performance is temperature. This significance necessitates specific care and interest in research to create design and analytical processes that take temperature issues into account. The variation in temperature is modelled using ANSYS v19.2 finite element method software. At any assigned depth in different layers of pavement, the stresses and deformation were obtained using solution of axisymmetric problem for an applied temperature of 45ºC. In flexible pavement the temperature stress variation was found to be 2.512 N/m² at top of bituminous concrete to 0 N/m² to the bottom of compacted subgrade layer, vertical deformation was found to be 0.013m at top of bituminous concrete to 0.0089m bottom of compacted subgrade layer. In the rigid pavement the temperature stress found to be 6.23 N/m² at top of concrete and-1.64 N/m² at bottom of subbase layer and horizontal deformation should be maximum and minimum of 0.0542m-0.0102m.

Effect of self-cementing properties on the mechanical behaviour of recycled concrete aggregates in unbound pavement layers

Recycled concrete aggregates (RCA) are increasingly being used in unbound pavement base and subbase layers, while the influence of their self-cementing properties on the mechanical behaviour has not been thoroughly studied. In this paper, the self-cementing properties, permanent deformation and resilient deformation behaviour of two RCA, NRCA (New RCA, crushed recently) and ORCA (Old RCA, crushed long time ago), showing significantly different self-cementing properties, after curing for different times (1, 180, 360 and 720 days), were investigated by pH value measurements, calorimeter tests and repeated load triaxial tests (RLTT). The results show that the self-cementing properties can significantly improve the mechanical behaviour of RCA, which is comparable to that of lightly treated materials. The permanent strains of NRCA, showing strong self-cementing properties, decrease to a very low value quickly after curing for 180 days, and then stabilize. While the resilient modulus of NRCA increases continuously with curing time, up to the studied curing time (720 days), 4.3 times larger than that curing for 1 day. It was also found that the traffic loads can damage the bonds between particles formed due to the self-cementing properties. On the contrary, for ORCA, showing negligible self-cementing properties, curing has no influence on the mechanical behaviour.

Utilizing expansive soil treated with phosphogypsum and lime in pavement construction

This study investigated the use of phosphogypsum (PG) in the long term as a construction material, especially in pavement structures. This study aimed to investigate the effect of increasing PG percentages on the geotechnical parameters of Expansive Soil. Extensive laboratory tests were conducted on both natural and PG-stabilized soil mixtures to examine their compaction properties, consistency limitations, swelling and linear shrinkage, pH values, and unconfined compressive strength (UCS), California bearing ratio (CBR), scanning electron microscopy (SEM), and X-ray Diffraction (XRD). The results showed that the PG addition would significantly reduce soil plasticity, linear shrinkage, and swell potential. Despite these improvements, the study concluded that treating the soil using PG only did not affect its physical properties sufficiently to be considered as a pavement subbase. As an alternative, lime was supplemented to the soil-PG mixture and noticed that a blend of 30% PG and 4% lime significantly improved soil strength, thereby rendering it appropriate for utilization as a pavement subbase layer. The Mechanistic-Empirical Pavement Design Guide (MEPDG) was utilized to assess the performance of pavement sections formed with PG-treated and untreated soils. As a result, this study contributes to the development of an environmentally sustainable PG waste management system while also demonstrating its potential uses in roadway construction.

Hydraulic design of granular and geocomposite drainage layers in pavements based on demand-capacity modeling

In this paper, a new approach based on the demand-capacity model is developed for hydraulic design of granular and granular-cum-geocomposite drainage layers in pavements. The demand is given by the intensity-duration curve obtained from the Intensity-Duration-Frequency curve, which is geographic location specific and corrected for climate change. The capacity curve corresponds to critical infiltration rates and critical durations for a drainage layer which is influenced by the hydraulic and geometric characteristics. The design is acceptable if the capacity curve exceeds the demand curve. The design framework is illustrated for typical geometries of highway pavements with three granular gradations and three geocomposites. Based on the developed framework, hydraulic equivalence is defined and evaluated for the drainage layers. The permissible reduction of granular layer thickness for hydraulic equivalence is evaluated if geocomposite is embedded in the subbase layer of pavements. For an optimum gradation based on hydraulic and structural characteristics, the thickness of granular layer with geocomposite could be reduced by 30% compared to the granular layer without geocomposite, which showed similar hydraulic performance. The significance of drainage layer thickness with geocomposite is shown based on the demand for storage to satisfy the drainage requirement for rainfall events of high intensities and long durations.

Experimental study on foam concrete as a sub-base layer of rigid pavement

Rigid pavement consists of three main layers, the base, sub-base and subgrade. Engineers mainly prefered choosing rigid pavement for heavy load road construction because the concrete mixture in this type of pavement has advantages in terms of strength, durability and design life. However, rigid pavement also has several disadvantages: relatively high construction and maintenance costs. As time goes by, researchers have developed several modified concrete mixtures; one of them is foam concrete. Foam concrete has strength similar to concrete in general but with a lighter mass and more affordable construction cost. This study examines foam concrete’s mechanical properties and properness as a sub-base layer on a rigid pavement. The research was conducted experimentally in the lab with five different densities of foam concrete mixture. The results showed that sample with a density of 1.0 g/cm3 has passed the minimum compressive and flexural strength values at 0.896 MPa and 0.0059 MPa respectively. This also indicates that increasing the density of a foam concrete mixture may increase its compressive and flexural strength but also lose its advantage of being a lightweight material as more density means more weight. Thus, it can be concluded that using foam concrete as a sub-base layer of rigid pavement is more advantageous in implementing rigid pavement construction.

Life Cycle Assessment for Substitutive Building Materials Using the Example of the Vietnamese Road Sector

Road construction usually relies on the utilization of natural aggregates as building materials. However, increasing pressure for sustainable roads highlights the importance of replacing natural materials with industrial byproducts. The scope of the present study was to identify feasible secondary raw materials for road subbase construction, and to investigate their environmental footprint in the context of Vietnam. This work examines road subbase alternatives such as manufactured sand (m-sand), granulated blast furnace slag (GBF), electric arc furnace slag (EAF), construction and demolition waste (CDW), and fly ash (FA). Based on the life-cycle assessment (LCA) approach, the environmental footprints of the alternative waste-based layers were compared with one another and with the corresponding conventional layers. The study comprises following working steps: (i) a comprehensive literature review of the respective materials, (ii) general chemical and soil mechanical analysis of road subbase substitutes, and (iii) LCA of the material alternatives in the context of the Vietnamese road construction sector. The results for the road subbase layer indicated that CDW and FA had lower impacts—particularly in the impact categories global warming potential and mineral resource scarcity. The overall LCA analysis for the road subbase layer highlighted that the greatest footprint contribution was involved in the construction material transportation processes. Thus, sourcing of materials closer to the site or the use of low-emission transport alternatives is needed.

Study on distress of airport pavement foundation and solution applied to Noi Bai international airport

The service quality and life of the runway, taxiway and apron pavement system heavily depends on the condition of its foundation, including base and/or subbase layers and subgrade. In the state of water-saturated condition, the strength of foundation would decline significantly, then inducing the downgrade of overall strength of the pavement. In the long term, the impacts from adverse environmental conditions and aircraft wheel loading will mix-up the materials of foundation layers, leading to the degradation of the original physical and mechanical properties of the original designed material. Furthermore, the accumulation of residual deformation and appearance of voids in the granular material can formulate the large holes beneath cement concrete slab. That, in turn, changes the load bearing model of the slab compared to the original design and causes the structural damage of the slab and threatens flight safety. Due to the complication of pavement foundation, the traditional treatment countermeasures usually need a long time for completion, while the airfield system often requires short and high-quality repair time. Therefore, there should be special solutions to satisfy the practical application. The article analyzes the cause, proposes the solutions for pavement foundation treatment and presents an initial application to Noi Bai International Airport. The findings of this study could be critical and significance basis for both academic and practical applications to maintain the service quality of airport construction infrastructure in Vietnam.

Fatigue of Cold Recycled Cement-Treated Pavement Layers: Experimental and Modeling Study

Fatigue is the main design criterion for cold recycled cement-treated mixtures (CRCTMs). However, the literature shows that the fatigue behavior of such mixtures is still not well known. For example, the effect of increasing reclaimed asphalt pavement (RAP) contents is yet a topic of discussion. This experimental and modeling study helps fill knowledge gaps on CRCTM fatigue behavior using long-term curing fatigue tests and three design methods currently being used in different countries. The objectives of this study were: (1) to characterize the mechanical and fatigue behavior of mixtures of RAP, aggregates and cement; (2) to evaluate the fatigue life of pavements with base and subbase layers of such mixtures using the novel Brazilian design method (MeDiNa); and (3) to compare the results with those obtained using the South African Pavement Engineering Manual (SAPEM) transfer functions and the American Association of State Highway and Transportation Officials AASHTOWare Pavement Mechanistic-Empirical Design (PMED) software. The mixtures were tested in the laboratory using flexural static and cyclic tests, and the required parameters to use the methods were obtained. Experimental results and modeling demonstrated a superior fatigue behavior of recycled layers with higher RAP contents. On the other side, layers with lower RAP contents abruptly lost stiffness in short periods, making thicker structures necessary. Therefore, using high RAP contents is not only a sustainable practice, but also a technical benefit. The equivalent single axle loads obtained using the SAPEM were higher than those obtained using MeDiNa, while the PMED ones were higher than both previous methods. Despite the inherent differences, this suggests that MeDiNa is more conservative. It also highlights the importance of calibration based on long-term pavement performance data.

Investigation of the Effect of Natural-Fiber Geogrids on the Bearing Ratio of the Subbase Layer of a Road

Investigation of the Effect of Natural-Fiber Geogrids on the Bearing Ratio of the Subbase Layer of a Road

The effect of RCA pavements on the liquefaction-induced settlement

The use of recycled concrete aggregates (RCA) not only reduces the demand for natural aggregates (NA) but also might improve the behavior of soil under earthquake loading. In this study, the behavior of the pavement constructed using 100% RCA and NA on a sandy soil layer with high liquefaction potential under dynamic loads was investigated by numerical analysis and compared with free field conditions. For this purpose, first, the classical geotechnical properties of 100% RCA and NA materials were obtained, and then the stiffness properties were determined by resilient modulus and permanent deformation tests. In the second stage, three different models were created with pavement with NA and RCA and without pavement on high liquefaction potential sand, and dynamic analyses were carried out by PM4Sand. Numerical analyses show that constructing a subbase and base layers significantly reduces liquefaction-induced settlement on the surface of flexible pavements built on liquefied soils. Moreover, when the case of using RCA instead of NA in the subbase and base layers built on the liquefied soil is examined, the liquefaction-induced settlement values on the surface are obtained either lower or very close. Consequently, this study proposes a new alternative to the use of RCA waste materials instead of NA. It is expected the use of these waste materials will reduce the need for storage space and also reduce the negative environmental effects associated with storage.

Validity of the Lower Zab River Sediments for Road and Asphalt Works - Southwest of Kirkuk/Northern Iraq

In this study, a geotechnical assessment of gravel and sand deposits were conducted on both sides of the Lower Zab River in the southwest of Kirkuk Governorate/Northern Iraq. geologically the sediment related to Quaternary age and tectonically located at the unstable zone. 5 samples were collected from the study area for the purpose of conducting various geotechnical tests on them and their validity for road works to the sub-base layer and the base layer for asphalt works.
 The results of the physical tests were shown by grain size analysis of thes aggregates for the samples of the study area, and it was found that they are identical to class (A) According to the American Standard [1], and suitable for use in road works for the sub-base layer. The moisture ratio ranging between (1.95 - 4.26) %. The tests of flatness and elongation showed that the highest percentage of flat-shaped particles was (29%) and longitudinal-shaped particles (19%).
 The laboratory tests results showed the durability tests such as - Los Angeles test the highest percentage of weight loss was (20.06%), and thus it is valid according to the Iraqi Standard Specification [2] for use in road works. the highest result of test the aggregate impact value of samples is 7.8%, It conforms to the requirements of specifications that must be provided for road works for a sub base layer. Accordingly it is valid for road works. It was found from Proctor test for (5) samples from the study area that the values of the maximum dry density ranged between (2.14-2.28 gm/cm3), and the values of the optimum moisture content ranged between (3.1-2.41%).
 An asphalt typical mixture was designed for the base layer from the aggregate of the first station S1 as represent station consisting of coarse crushed aggregate 12%, medium crushed aggregate 22%, fine crushed aggregate 20%, river sand 40% and the proportion of filler 6%. The results of the asphalt tests for the ideal station S1 showed that the ideal percentage of asphalt from the weight of the mixture in the asphalt mixture is 4.1, which is within the limits of the specification Roads and Bridges [3]. The percentage of asphalt to the weight of the aggregate after adding the ideal percentage of asphalt showed that its value was 4.3%, As for the stability test result (Marshall), it reached 11.4 kN, and the result of the creep test (Marshall) reached 2.9 mm, and the density was 2.362

A probabilistic approach to assess slope stability of roadway shoulders under superheavy traffic operations

Non-conventional Super Heavy Load (SHL) units generally transport heavy loads weighing significantly higher than conventional trucks. Movements of such SHL trailer units with overweight tires and non-generic axle assemblies are detrimental to the structural integrity of sloped roadway shoulders. This research proposes an approach to realistically evaluate stability of roadway shoulders under subjected to SHL units. The developed methodology upgrades conventional Limit Equilibrium Method to a probabilistic approach to consider uncertainties attributed to orthogonal stiffness characteristics of aggregate materials in pavement structures. The proposed novel approach is also capable of assessing complex traffic loads imparted under SHLs. To achieve these objectives, the researchers first developed a field-testing scheme to obtain prominent features associated with the SHL trailer units and their loading configurations, as well as pavement material and road shoulder characteristics for ten overweight corridors in Texas. The field-derived information was then used as inputs in a series of 3D finite element model to characterize SHL-induced forces. Monte-Carlo methods was also deployed to establish a distribution of shear strength factors, within the bounds of laboratory-derived data for base and subbase layers as well as subgrade soils. Eventually, the resisting forces were contrasted with mobilizing forces along failure surfaces to assess stability of pavement shoulders. Results underscored the importance of tire load magnitude, shoulder slope inclination, surface treatment, and moisture management mechanisms in stability studies of roadway shoulders under demanding stress paths in overweight routes. The permutations pertaining to extreme weather events such as flooding, heavy rainfall, and prolonged inundation events also showed the detrimental effect of SHL operations on the stability of sloped shoulders. The proposed approach and synthesized results for Texas SHL corridors provided in this research facilitate realistic evaluation of the potential failure risk of sloped shoulders under SHL operations, considering non-typical nature of SHLs, environmental factors, and unique features of roadway shoulders in such regions.