Subbase Construction Research Articles

Performance Study of Stabilized Recycled Aggregate Base Material with Two-Gray Components.

This article studies the practical road performance of recycled materials from construction waste, relying on the paving test section of the supporting project for the Qingdao Cross-Sea Bridge. The research focuses on the construction technology and road performance of using recycled construction waste materials in urban road sub-base construction. Through indoor tests such as sieving and unconfined compressive strength tests, relevant technical indicators were obtained and analyzed. Additionally, periodic core sampling, compaction tests, and rebound deflection tests were conducted on-site according to relevant standards to thoroughly investigate the specific effects of using construction waste in practice and to analyze and evaluate the actual feasibility of the materials for road use. The results indicate that the particle gradation of the construction mix in the test section aligns well with the target gradation, and the dosage of the mixing agent meets the design requirements. The 7-day unconfined compressive strength already satisfied the technical requirements for heavy and extremely heavy traffic on highways as specified in the "Technical Specifications for Construction of Highway Pavement Subbase" (JTG/T F20-2015), with the 14-day strength generally reaching 7 MPa. Core sampling revealed good aggregate gradation, smooth and straight profiles, and the thickness and strength of all parts meet the specifications. The compaction levels met the testing requirements, the surface deflection values showed a decreasing trend, and the deformation resistance was good, consistent with the general development patterns of semi-rigid sub-bases.

Modeling of the effect of gradation and compaction characteristics on the california bearing ratio of granular materials for subbase and landfill liner construction

The California bearing ratio (CBR) of a granular materials are influence by the soil particle distribution indices such as D10, D30, D50, and D60 and also the compaction properties such as the maximum dry density (MDD) and the optimum moisture content (OMC). For this reason, the particle packing and compactibility of the soil play a big role in the design and construction of subbases and landfills. In this research paper, experimental data entries have been collected reflecting the CBR behavior of granular soil used to construct landfill and subbase. The database was utilized in the ratio of 78–22% to predict the CBR behavior considering the artificial neural network (ANN), the evolutionary polynomial regression (EPR), the genetic programming (GP), Extreme Gradient Boosting (XGBoost), Random Forest (RF) and the response surface methodology (RSM) intelligent learning and symbolic abilities. The relative importance values for each input parameter were carried out, which indicated that the (CBR) value depends mainly on the average particle size (D30, 50 & 60). They showed a combined influence index of 66% of the considered parameters in the model exercise. This further shows the importance and structural influence of the particles within the D50 and D60 range in a granular material consistency in the design and construction purposes. Performance indices were also used to study the ability of the models. The ANN model showed the best performance with accuracy of 88%, then GP, EPR and RF with almost the same accuracies of 85% and lastly the XGBoost with accuracy of 81%. Also, the RSM produced an R2 of 0.9464 with a p-value of less than 0.0001. These values show that the ANN produced the decisive model with the superior performance indices in the forecast of CBR of granular material used as subbase and waste compacted earth liner material. The results further show that optimal performance of the CBR depended on D50 and D60 for the design of subgrade, subbase, and liner purposes and also during the performance monitoring phase of the constructed flexible pavement foundations and compacted earth liners.

Investigation on utilization and microstructure of fine iron tailing slag in road subbase construction

The iron tailing slag is solid waste produced during the iron ore refining process and is considered a potential hydraulic material that can be used in road construction. This study focused on fine iron tailing from a location in Hebei, China, to prepare road subbase specimen with a high proportion of fine iron tailing. The research investigated the effects of raw material ratios and additives on the 7-day unconfined compressive strength and elastic modulus of the specimens, as well as their mechanisms of action. A series of single-factor experiments were conducted using a controlled variable approach, including the mass ratio of slag to fly ash (SFR), cement content, and calcium oxide content. It was found that under the conditions of an SFR of 6:1, a calcium oxide content of 4 %, a cement content of 5 %, and a water-resistant base stabilizer additive of 0.02 %, the eco-friendly road subbase specimen achieved a 7-day unconfined compressive strength of 1.97 MPa and an elastic modulus of 286 MPa, demonstrating good mechanical properties. Additionally, a linear relationship was observed between the cement content and the 7-day unconfined compressive strength of the specimen: Rc = 0.253w + 0.793. Using characterization techniques such as X-ray Fluorescence Spectroscopy (XRF), X-Ray diffraction (XRD), Scanning Electron Microscope & Energy Dispersive Spectroscopy (SEM-EDS), and Fourier Transform Infrared Spectroscopy (FTIR), a dense structure was observed in the slag-based road subbase specimen, composed of needle-rod hydrated calcium silicate (C-S-H) gel, hydrated calcium aluminate (C-A-H), hydrated calcium silicoaluminate (C-A-S-H), flake-like hydrated magnesium silicate (M-S-H) gel, and a system containing a large amount of Forsterite. Finally, the study examined the impact mechanisms of five additives—Na2CO3, Na2O·2SiO2, triethanolamine (C6H15NO3), CaSO4, and a water-resistant base stabilizer—on the compressive strength and elastic modulus of the slag road base specimen. It was concluded that the water-resistant base stabilizer significantly improved strength and reduced water absorption. The road subbase specimen can be used by simply mixing at room temperature and pressure, offering broad prospects for industrial application. This technology provides a paradigm for the comprehensive utilization of fine iron tailing and the preparation of new road subbase materials.

Use of Paper Ash and Lime as a Sustainable Stabilized Materials for Lateritic Soil

This research investigates the effectiveness of paper ash and lime for stabilizing lateritic soils in road construction applications. We assessed varying concentrations of paper ash and lime (0%, 3%, 6%, and 9%) to evaluate their effectiveness for soil stabilization. Initial analyses, including grain size distribution through wet sieving, specific gravity, moisture content, and Atterberg limits, were conducted to classify the soil. Following this, strength and compaction tests utilized standard proctor compactive energy, a method well-suited for field application. The findings indicated a general reduction in Atterberg limits (liquid limit, plastic limit, and plasticity index), an increase in maximum dry density (MDD), and a decrease in optimum moisture content (OMC) with increased concentrations of paper ash and lime. A thorough analysis of the results, along with a comparison to established standards, demonstrated significant improvements in soil properties. Specifically, the study found that 6% paper ash provided optimal stabilization, while 9% lime was effective as a stabilizing agent. These materials are suitable for use in the construction of subgrades and subbases for roads, aligning with AASHTO standards.

Analysis of road construction waste generation in developing economies: A focus on surfacing and sub-base construction projects in Sri Lanka

The motivation for this study was to develop simplified tools to estimate material wastage during road construction projects. In developing countries, there is a lack of information about material wastage factors (MWFs) in road construction projects. The purpose of this study is to reveal the MWFs of materials used in road construction. To investigate MWFs, statistics were collected from a sample of 58 road contracts concluded in the southern province of Sri Lanka, comprising 245 road construction projects. Of the selected sample, 80% of the road projects utilized wearing course (asphalt concrete), aggregate base course (ABC), cationic slow setting emulsion 1 (CSS1) and sand. The mean MWFs were calculated only for ABC, wearing course and CSS1 as 8.69%, 5.21% and 6.8%, respectively, because the authors could only achieve acceptable precision levels for these three types of materials. The coefficient of variation (CV) for all these three types of materials ranged from 25% to 3%. Based on collected data, this study proposes equations to predict waste generation for CSS1 and wearing course. Implementing the derived equations to predict waste generation can aid in efficient planning and help construction companies to move towards more sustainable practices.

Evaluating the Long-Term Plastic Strain Accumulation in Reclaimed Asphalt Pavement (RAP) Application for Road Subbase Construction: A Cyclic Triaxial Loading Study

Reclaimed Asphalt Pavement (RAP) has gained significant attention in recent years as an environmentally sustainable solution for road construction. However, the main concerns are regarding its long-term performance and the potential impact on the road subbase. This study aims to investigate the behavior of RAP under cyclic triaxial loading conditions, specifically focusing on the accumulation of plastic strain over time. The research methodology involved laboratory testing using a cyclic triaxial apparatus to simulate the stress conditions experienced by RAP in road subbase applications in reference to AASHTO code. Several RAP specimens with varying degrees of compaction were subjected to repeated cyclic loading while monitoring the associated plastic strain accumulation. To provide a comparative analysis, conventional subbase materials were also tested under the same conditions. The findings indicate that RAP exhibits a notable disadvantage in terms of long-term plastic strain accumulation when compared to conventional subbase materials. The cyclic triaxial loading tests revealed a substantial increase in plastic strain accumulation over extended periods, suggesting the potential for long-term deformations and compromised performance of the road structure. This accumulation of plastic strain could lead to increased maintenance requirements and decreased service life of the road. Based on the results obtained, it is recommended that careful consideration be given to the utilization of RAP in road subbase construction in areas subjected to heavy cyclic loading conditions. Additional research and development efforts are necessary to explore potential mitigation strategies and optimize the use of RAP, ensuring sustainable and resilient road infrastructure.

Effect of Metakaolin and Ashcrete blend on the mechanical properties of lateritic soil for sustainable subgrade and subbase construction

Effect of Metakaolin and Ashcrete blend on the mechanical properties of lateritic soil for sustainable subgrade and subbase construction

The influence of fines on the hydro-mechanical behavior of sand for sustainable compacted liner and sub-base construction applications

The influence of fines on the hydro-mechanical behavior of sand for sustainable compacted liner and sub-base construction applications

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.

Performance evaluation of nano-material stabilized pond ash as subbase layer material for roadway pavement

The power capacity of India is heavily coal based. In the session 2021–22 the overall country’s coal production has been 777.31 million tons, with 8.55% positive growth. However, the Indian coal is of lower grade with higher ash content of 24–63%. This results in the generation of 240.27 million tons of Coal Combustion Ash (CCA) during 2021–22. This huge quantity of industrial byproduct mixed with water and stored in ash lagoons in the form of Pond Ash (PA). From this stored ash deposit only 79.18% finds utilization, which by far falls short of the 100% utilization target as strictly recommended by the Ministry of Environment Forest and Climate Change (MoEF & CC). This high volume generation compounded with lower utilization of PA has been consuming about 65,000 acres of valuable land. Moreover the prolonged disposal of PA in ash lagoons causes serious environmental and health hazards. Besides, the extensive use of Conventional Granular Material (CGM) has been alarming, thus necessitating it to be condemned and strict regulations imposed in construction. Emphasis being laid on the utilization of Non-Conventional Granular Materials (NCGM) like CCA. On the basis of the above mentioned circumstances the PA can be converted into a meaningful wealth for the subbase construction of pavement foundation. Therefore, this paper primarily addresses the potential of PA as subbase layer material for roadway pavement foundation. This study utilizes virgin PA as well as in partial replacement of CGM 10%-100% by weight, being stabilized with lime 0%-14% by weight and Nano-Material (NM) 1:1:150–1:1:400 by dosage as a subbase material for the foundation of pavement. Experimental work was carried out in stages to determine the chemical composition of PA, Lime and NM, characterize the PA samples by FTIR and FESEM followed by understanding the behavior of PA with and without any addition of additives as stabilizers. The c and φ ranges 0.88–40.02 kg/cm2 and 32°-53° The soaked CBR is of 19% to as high as 79% for optimum stabilized PA mix. Terrasil and Zycobond whose pH showed alkalinity, were used as nanomaterial, which provided little to zero permeability for the mix. Slake durability test provided medium to high to very high durability for the optimum mix. A comparative analysis was performed to determine the optimum mix providing the best stability. Light Falling weight Deflectometer (LFWD) showed satisfactory deflection. The values obtained satisfied the Ministry of Road Transport and Highways (MoRTH), Government of India.

Characterisation of stabilised red mud waste material for road infrastructure

Red mud is an industrial waste material generated during the extraction of aluminium metal from bauxite ore. It is deposited in a slurry form into the dam which is called the tailing dam near the industry. It is occupying large costly land without uses. Its production is about 9 million tons/year in India. To investigate its potential application in road infrastructure, it was collected from M/s Vedanta Ltd. Lanjhigarh, Odisha. Basic geotechnical characterisation of red mud was carried out in the laboratory. To improve its geotechnical properties, it was stabilised with cement in the range of 3 to 9 % to investigate their potential application in subbase and base layers of road infrastructure. Compressive and durability characteristics of stabilised red mud were also studied. A laboratory study concluded that red mud is a fine-grained silt-size material. Other geotechnical properties are similar to conventional silty soil viz. dry density, and shear strength. Unconfined compressive strength and durability characteristics indicated the suitability of cement-stabilised red mud for the construction of subbase and base layers of road infrastructure as per Indian road congress guidelines. Application of red mud will lead to the sustainable development of road infrastructure and will reduce environmental pollution.

Environmental and technical feasibility of a waste foundry sand applied to pavement granular layers

The foundry industry generates large amounts of residual byproducts, such as waste foundry sand (WFS). This high generation has motivated studies concerning the disposition of WFS, which in turn can be used for road subbases. Nevertheless, paving applications are still limited, especially regarding the behavior of WFS when added to a mixture of crushed materials. Hence, the objective of this study was to evaluate WFS reuse in mixtures with crushed materials, applied as granular layers of granulometric stabilized pavements. The crushed materials and WFS were characterized by size distribution, physical aspects, and different mixtures, and later submitted to mechanical testing. Initial tests were utilized to define mixtures (crushed material + WFS) that fulfilled the technical requirements for road subbases. California bearing ratio and resilient modulus tests indicated that WFS additions up to 12% for “A” grading improved the bearing capacity of the mixture; while in “E” grading, WFS additions up to 38% resulted in no expressive improvement in bearing characteristics. Thus, for both gradings, a structure with high density, strength, and low susceptibility to deformations can be used for road subbase construction without technical issues. Finally, the highest WFS content (38%) mixture was environmentally classified as a Class II A non-inert waste, indicating its environmental viability for road applications.

An Experimental Study of Granular Material Using Recycled Concrete Waste for Pavement Roadbed Construction

Rapid worldwide urbanization and drastic population growth have increased the demand for new road construction, which will cause a substantial amount of natural resources such as aggregates to be consumed. The use of recycled concrete aggregate could be one of the possible ways to offset the aggregate shortage problem and reduce environmental pollution. This paper reports an experimental study of unbound granular material using recycled concrete aggregate for pavement subbase construction. Five percentages of recycled concrete aggregate obtained from two different sources with an originally designed compressive strength of 20–30 MPa as well as 31–40 MPa at three particle size levels, i.e., coarse, fine, and extra fine, were tested for their properties, i.e., the optimum moisture content density, Californian bearing ratio, and resilient modulus. A characterization of the resilient modulus of the mixes under complex stress conditions was performed. The characterized modulus model was used in the nonlinear analysis of the pavement structure under traffic loading using KENALYER software. Consequently, the two critical responses, i.e., the tensile strain at the bottom of the asphalt layer and the vertical compressive strain at the top of the subgrade, were computed and compared for the pavement structures with varying types and percentages of recycled concrete aggregate used in the subbase layer.

A comparative experimental investigation into the chemical stabilisation of sandstone aggregates using cement and styrene-butadiene copolymer latex for road sub-base construction

For granular road sub-base constructed using local aggregates of marginal quality such as sandstone, chemical stabilisation using cement or polymer has been found to improve the key mechanical properties of pavement. There is a knowledge gap on the strength development of sandstone stabilised using only non-ionic styrene-butadiene (SB) polymer for use as a road sub-base. Previous comparative experimental investigations of the relative strength development of sandstone of marginal quality stabilised with non-ionic SB polymer and cement, individually, have also been limited. Therefore, this paper aims to provide an experimental investigation of the relative strength development of sandstone aggregate sub-base of marginal quality stabilised with Portland composite cement (PCC), ordinary Portland cement (OPC) and SB latex copolymer (or polymer), individually. The samples were prepared with different gravel-to-sand (G:S) ratios of 2.1, 1.2 and 0.4, and subsequently, some samples were treated with 3% and 5% cement contents and some others with 0.5–2% polymer contents. Samples were compacted and cured for 3 and 7 days under dry and wet conditions before measuring their unconfined compressive strength (UCS) and indirect tensile strength (ITS). Samples were compacted and cured for 4 days under unsoaked and soaked curing conditions before measuring their California bearing ratio (CBR). It was found for both cement-stabilised and polymer-stabilised samples that the higher the G:S ratio, the higher the UCS, but this trend was steeper for polymer-stabilised samples. For cement stabilisation, 5% was the optimum cement content that provided the sub-base with the highest UCS and CBR values. For polymer stabilisation, 1% was the optimum polymer content that provided the sub-base with the highest UCS and CBR values. The UCS of OPC-stabilised samples was almost 1.15 times that of PCC-stabilised samples for the same G:S ratio, cement content and curing condition. Despite the potential environmental benefit of polymer stabilisation for pavement aggregates, when used individually, cement stabilisation of the sandstone aggregates was able to achieve significantly faster strength development and resulted in generally higher strength properties than polymer stabilisation.

Hydraulic conductivity-based optimum efficiency frontiers for RAP aggregate utilization in subbase construction

• A design chart based on the frontiers is developed to achieve an efficient design. • The efficient design range of RAP replacement ratio was determined to be 25–35% • Hydraulic conductivity and bearing performance related frontiers are developed. • The efficient global optima is determined based on the design parameters. Reclaimed Asphalt Pavement (RAP) aggregate with or without cement stabilization is currently used worldwide as a virgin-aggregate replacement material in subbase construction. Paper presents the multiobjective efficiency analysis conducted on the experimental results from the extensive parametric study in order to identify how the level of hydraulic conductivity and the cement addition affect the RAP utilization. The optimum efficiency frontiers have been identified considering the dual optimization based on a set of multi-objective analyses using the Response Surface Method (RSM). The factors of RAP aggregate replacement range (0–100 %) and cement addition variation (0–4%) were considered along with the responses of hydraulic conductivity, compaction, CBR (California Bearing Ratio) and UCS (Unconfined Compressive Strength). Paper reveals that a specific replacement limit of 25–35% provides an efficient RAP aggregate utilization in terms of the considered parameters. It presents a practical design chart to attain an optimum control on the efficient utilization of RAP aggregate in subbase construction considering the levels of targeted hydraulic conductivity and other considered parameters.

Recycling phosphogypsum in subbase of pavement: Treatment, testing, and application

This study aims to recycle the phosphogypsum (PG) as pavement subbase material. First, the physical and chemical properties of the PG before and after calcination treatment were characterized. Then the mix design, as well as the performance evaluation of the PG mixture, were detailed. Finally, the engineering application and economic analysis of the PG mixture for paving subbase pavement were presented. It is found that incorporation of the calcined PG (CPG) can help form gel structure to stabilize the PG. Meanwhile, addition of lime can neutralize the water-soluble phosphorus contained in the PG to improve the early strength of the CPG-stabilized PG. The optimal mix proportion of the CPG-lime stabilized PG by mass is determined as PG: CPG: lime = 89: 9: 2. In addition, as compared to the PG stabilized with the traditional inorganic binder materials, the CPG-lime stabilized PG has higher unconfined compressive strength (UCS) and better resistance to the water damage and fatigue damage caused by the water content variation. The field cores extracted from the paved CPG-lime stabilized PG subbase were experimentally observed to have a 7 d UCS as high as 3.69 MPa. Moreover, reuse of the CPG-lime stabilized PG is proven to be a highly economic and environment-friendly pathway for subbase paving, of which total cost per unit cube meter is 504.5 % lower than that of the commonly-used lime-fly ash stabilized soil. These findings identify the feasibility of utilizing the PG for pavement subbase construction.

Hydraulic Conductivity and Bearing Performance Related Optimum Efficiency Frontiers for Reclaimed-Asphalt-Pavement Aggregate Utilization in Subbase Construction

Hydraulic Conductivity and Bearing Performance Related Optimum Efficiency Frontiers for Reclaimed-Asphalt-Pavement Aggregate Utilization in Subbase Construction

Construction and performance evaluation of large stone subbase (LSSB) layers

The most appropriate way to evaluate the engineering properties of large stones is to perform field testing on full-scale pavement systems built with large stone subbase (LSSB) layers because such properties of large stones cannot easily be measured in the laboratory. Although there have been several studies discussing the use of large stones in pavement systems, there is still limited knowledge about appropriate thicknesses, use with geosynthetics and/or with recycled aggregates, and long-term performance of LSSB layers. In this study, several test cells were constructed with LSSB layers with different thicknesses. The cells contained different recycled aggregate base (RAB) layers, and some of the cells contained geosynthetics beneath the LSSB layers. Nuclear density tests and intelligent compaction were performed during construction. A series of falling weight deflectometer (FWD) tests were performed during and after construction. One of the cells contained thermocouples embedded at different depths for soil temperature monitoring. This study showed that the use of geosynthetics was essential for constructing LSSB layers that are not thick enough, and staged construction was not convenient for large stones. In addition, the cells constructed using the thicker LSSB layers provided greater performance. In the short term and the long term, the cells containing the thicker LSSB layers yielded around 2.6 and 1.5 times higher modulus values, respectively.

Potentials of Cement Kiln Dust-Periwinkle Shell Ash Blends on Plasticity Properties of Two Selected Tropical Soils for use as Sustainable Construction Materials

This paper investigated the effect of cement kiln dust (CKD) and periwinkle shell ash (PSA) on the plasticity characteristics of two lateritic soil. Two Soils (termed soil A and B) were collected from two selected locations within Osun State, Nigeria. Air-dried soil was treated with CKD and PSA blend in order of 0, 5, 10, 15, and 20% for CKD and 0, 2, 4, 6, 8 and 10% for PSA by dry weight of soil. The specific gravity of both soils increased with increase in CKD and PSA fillings. The Index properties such as Atterberg’s limit (liquid limit, LL, plastic limit, PL, and plasticity index, PI), percentage fines content of the soils was determined. The index properties results showed that the two soils are clayey soil of low plasticity. There was a general decrease in the Atterberg’s limits (liquid limit, LL and plastic limit, PL). The scan electron microscopy (SEM) and electron diffraction spectroscopy of treated soil revealed the formation of crystalline products of calcium silicate hydrate (CSH) and calcium aluminate hydrate (CAH) which was responsible for strength gain. Based on preliminary investigations, the study concluded that the combination of CKD-PSA blends is a viable stabiliser for the two tropical soils under consideration to be used as sub-base construction.

Lightweight concrete in cement-treated subbase construction

Following the development of transportation technology, steady road infrastructure is needed. The choice of construction type is a crucial point for the expected quality. Road construction consists of flexible and rigid pavement construction. Rigid pavement has higher durability and is produced from concrete, a strong, flexible, and fire-resistant material. Lightweight concrete, containing high amounts of pores, can be produced by using lightweight aggregate or a mixture of lightweight-coarse aggregate fulfilling the requirements for compressive and flexural strength. This study evaluated the compressive and flexural strength of lightweight concrete without coarse aggregate as a rigid pavement material. This study used specimens from type I Portland cement for compressive and flexural strength test, in 0.5 water-cement ratios and the specific gravity of 1.0. The result revealed a compressive strength value of 38.91 kg/cm2 and a flexural strength value of 1.32 MPa. Based on the results obtained, it was concluded that lightweight concrete material fulfilled the general specification criteria for the compressive strength requirements of the cement-treated subbase (CTSB).