Road Base Material Research Articles

Magnesium Salt Influenced Strength Behavior of Lime-Fly Ash Stabilized Fine Grained Soil

The fine grained soil subgrade in coastal areas has the characteristics of high underground water level and serious salinization, and the lime-fly ash stabilized soil (LFSS) often used as the road base material. In order to study the effect of magnesium salt on the material strength, 5 % MgCl2 solution was used to simulate the groundwater magnesium salt environment, and specimens with 7 d, 14 d, 28 d, 60 d and 90 d curing ages were tested in MgCl2 solution for 1 d, 5 d, 10 d, 15 d or 30 d. A controlled test was also conducted in purified water. Strength mechanism of LFSS was analyzed; SEM test was taken; and the influence mechanism of MgCl2 medium was analyzed. The results showed that MgCl2 medium, immersing time, and curing age have effects on compressive strength of LFSS. More specifically, although the early strength is low, the strength of LFSS maintains slow and steady growth from 7 d to 90 d. Long-term immersing in both MgCl2 solution and purified water will reduce the strength of LFSS, while the strength of specimen immersed in MgCl2 solution will decrease faster. Reactions between MgCl2 and LFSS destroyed the original gels and crystals, causing a negative impact on the strength of LFSS. However, with the test dose of MgCl2, the reduced strength of LFSS can still satisfy the sub-base requirement of second-class highway in China.

Preparation of road base material by utilizing electrolytic manganese residue based on Si-Al structure: Mechanical properties and Mn2+ stabilization/solidification characterization

Electrolytic manganese residue (EMR) is a potentially harmful industrial solid waste that should be addressed. In the study, the red mud, carbide slag and blast furnace slag were used as stabilization/solidification (S/S) agents to S/S Mn2+, and simultaneous reused it as raw material to prepare road base material. The S/S behavior of manganese, unconfined compressive strength (UCS) of road base material with different Al/Si ratios, leaching test and the S/S mechanisms were investigated. The results showed that the Mn2+ can be well solidified when the S/S agents reach up to 20 %. The 7-day UCS of the road base material was 6.1 MPa with the Al/Si ratio of 0.48, which meets the highway standards. When Al/Si = 0.48, the formation amount of CaAl2Si2O8·4H2O and ettringite increased, which promoted the adsorption and wrap of Mn2+. The content of active AlⅣ and AlⅥ increased after S/S. Mn2SiO4 and Ca4Mn4Si8O24 were produced by the charge balance effect, and the new chemical bond was formed. Meanwhile, the Mn2+ is oxidized to more stable MnO2 to achieve the S/S of Mn2+. This research provides an effective way to solidify Mn2+ and solves the problem of large-scale utilization of EMR and other solid waste.

Modification of Lime‐Fly Ash‐Crushed Stone with Phosphogypsum for Road Base

In order to increase the recycling of phosphogypsum waste, this study explored the feasibility of using phosphogypsum to replace some of the lime and aggregate in the lime‐fly ash‐crushed stone mixture which is a widely used road base material in China. For this purpose, compaction, compressive strength, composition structures, wetting‐drying cycle tests, and shrinkage tests were carried out on the lime‐fly ash‐phosphogypsum‐crushed stone composite to investigate its performance. The results indicate that lime‐fly ash‐crushed stone modified with phosphogypsum has the required strength of the road base material and favourable performances in environment (wetting‐drying cycle) stability. The image processing analysis and shrinkage tests demonstrated that phosphogypsum can significantly improve the compactness and shrinkage performance of lime‐fly ash‐crushed stone mixture. A suitable content of phosphogypsum and a reasonable content of fine aggregate are conducive to improving the roadway engineering properties (i.e., decreasing shrinkage cracks and increasing compressive strength) of lime‐fly ash‐phosphogypsum‐crushed stone composites.

Laboratory Evaluation and Design of Construction and Demolition Wastes for Granular Base

Using recycled aggregate from construction and demolition (C&D) wastes as a construction material is a potential method for solving the disposal of C&D wastes, which can reduce the exploitation of natural aggregate. In this study, extensive laboratory tests were carried out to investigate the reliability of the C&D wastes used as road base material. Meanwhile, the gradation design and the dominant aggregate size range were considered, and a physical disposal method was proposed to enhance the structural performance of the recycled material by replacing the skeleton of the recycled aggregate (RA) with high‐quality limestone. The test results showed that (1) given the high absorbency and fragility of C&D wastes, its RA was not enough to provide the strength and stability required by the base; (2) the compaction characteristics of the RA are quite different from that of the limestone aggregate, but the final compaction effect is basically the same; (3) the replacement treatment proposed in this study is an effective approach to improve the performance of the recycled granular base because the breakage rate decreased by at least 28.2% and the mechanical properties increased by approximately 50% compared with that of the untreated specimen; and (4) when the limestone content reached 75%, the California bearing ratio and the resilient modulus of the graded B specimen exceeded 120% and 200 MPa, respectively, satisfying the pavement requirement in medium traffic.

Mechanical Properties of Lime-Fly Ash-Sulphate Aluminum Cement Stabilized Loess

Lime-fly ash stabilized loess has a poor early strength, which results in a later traffic opening time when it is used as road-base materials. Consideration of the significant early strength characteristics of sulphate aluminum cement (SAC), it is always added into the lime-fly ash mixtures to improve the early strength of stabilized loess. However, there is a scarcity of research on the mechanical behavior of lime-fly ash-SAC stabilized loess and there is a lack of quantitative evaluation of loess stabilized with binder materials. This research explored the effects of the amount of binder materials, curing time and porosity on the unconfined compressive strength (UCS), splitting tensile strength (STS), cohesion (c) and friction angle (φ) of lime-fly ash-SAC stabilized loess by a series of unconfined compressive tests (UCT) and splitting tensile tests (STT). The results indicate that an increase in curing time and a decrease in porosity lead to a continuous increase in the UCS and STS for lime-fly ash-SAC stabilized loess. The addition of SAC has a prominent enhancement in the early strength of lime-fly ash-SAC stabilized loess. When the curing time, porosity, and binder content were constant, the UCS and STS increase with increasing SAC content; For a stabilized loess with 30% binder content and 5% SAC content after 1 day of curing, the UCS was greater than 0.7 MPa, which meets the requirement of opening traffic, so lime-fly ash-SAC stabilized loess could be used as an excellent maintenance material for road-base; In accordance with the analysis of testing data, empirical relationships between the UCS and STS of lime-fly-SAC stabilized loess and key effect factors (binder materials content, curing time and porosity) were developed, which can provide references for reasonably selecting the amount of binder materials, compaction degree and curing period to meet the required strength of practical engineering. Finally, based on the Mohr-Coulomb theory and the above empirical relationships, a simpler method for calculating the c and φ of stabilized loess was proposed, with which, the shear strength parameters can be determined only by UCT or STT.

A preliminary study of the engineering properties of dorbank

Dorbank, a naturally indurated, pedogenic layer, is found over vast expanses of arid and semi-arid parts of southern Africa. Although considered a nuisance to local farmers, dorbank is relatively easy to rip from the soil profile to clear the way for agricultural developments. Its strategic position just beneath the topsoil in the soil profile, as well as its consistency which is often close to that of rock, raises the question of its engineering capabilities. In this study the properties of unbound, mechanically crushed dorbank gravels were investigated in the context of exploiting dorbank for road-building purposes. Moreover, the study investigated the pedogenic variance of dorbank for possible indicators of engineering quality. Dorbank samples were taken from three different regions in the Karoo - the vicinity of Vanrhynsdorp, Aggeneys and the Vaalputs radioactive waste disposal facility near Springbok. Samples were subjected to two stages of investigation. Firstly, the pedogenic nature of dorbank was determined. Different morphologies of dorbank and their relation to the soil type in which they were found were described, whereafter cementing agents were selectively dissolved from dorbank while noting the resulting effect on its structural strength. Polished dorbank sections were additionally analysed with scanning electron microscopy (SEM), coupled with energy-dispersive x-ray (EDX) spectroscopy to identify minerals that are deleterious to roadworks and to understand the chemical enrichment of dorbank by cementing agents. Secondly, the unbound granular qualities of dorbank were tested to establish its use as a material in the structure of a flexible pavement or as a gravel wearing coarse. Dorbank samples were crushed with a small jaw crusher from which the particle size distribution (PSD), the flakiness index (FI), pH, electrical conductivity (EC), Atterberg limits, linear shrinkage (LS), maximum dry density (MDD), optimum moisture content (OMC), soaked California Bearing Ratio (CBR) and direct shear strength (DST) of remoulded samples were determined. The strength and durability of particles that fell within the 13.2 to 19.0 mm size fraction were evaluated with the Treton impact test, the aggregate pliers test (APT) and the accelerated weathering test (AWT). Dorbank samples presented as platy and as massive morphologies in transported sandy soils. Platy dorbanks were found to occur in silty sands, and massive dorbanks in medium to coarse sands. Dorbanks were often found overlying calcrete horizons and containing calcerous veins, which cause adverse discontinuities in the macro- and micro-morphology of dorbank. From the selective dissolution test with NaOH and HCl, and with quantitative SEM-EDX analyses, samples were confirmed to be petroduric in nature. Dorbank fell short of the South African road-base material requirements, particularly due to its low CBR and low durability. Furthermore, dorbanks were found to be almost cohesionless from the DST results (c' = 3 to 7 kN/m2) and non-plastic from the Atterberg limit test results. The aggregate strength and grading coefficient of dorbank from the Vanrhynsdorp and Vaalputs regions satisfy the requirements for use as a gravel wearing coarse, although possible corrugating, ravelling and a high re-gravelling frequency and dustiness can be expected. Finally, the study concluded that platy dorbank performs better in strength tests, but weather more quickly in the accelerated weathering test. The lack of cohesion and its non-plastic behaviour are likely due to the suppression of the activity of clay, which in turn is due to cementation and the aggregation of clay minerals. Further investigation of dorbank gravels, modified with the addition of fines, is suggested.

Compaction and CBR Characteristics of Sandy Clay Stabilised with Fibre-Mixed Binder

Soil chemical stabilization is an effective yet comparatively economical ground improvement method which involves injecting or blending a binder into the existing soil to enhance the geotechnical properties (e.g. strength and stiffness) for load-bearing purposes. The technique is especially beneficial for road construction works on clayey soil of limited load-bearing capacity such as rural roads. It required thick road base is critical to ensure long-term stability and performance. An endeavour is therefore undertaken to examine the effectiveness of a proprietary fibre-mixed binder in stabilizing soils (sandy clay) nature to serve as road base material. Kaolin was mixed with sand as the base soil at ratios of 0, 25 and 50% sand addition. The fibre-mixed binder was added at dosages of 1.5, 2.5 and 3.5% as recommended by the proprietor. Standard compaction test was first carried out to determine the optimum water content for each kaolin-sand mix. Then left to cure for 1, 3, 7 and 28 days before subjected to the California Bearing Ratio (CBR) test. From the test results, it was found that 2.5% binder addition was sufficient to attain the minimum CBR requirement of 30% for supporting a conventional flexible pavement, as per JKR standard. However, the 100% clay sample required higher binder dosages. Clearly sand particles in the soil contributed to the formation of skeletal scaffolding of the soil matrix, bound and supported by the fibre-mixed binder for enhanced strength properties. This was evident in the compaction test where 50% sand addition reduced the optimum water content by almost half compared to the 100% clay. Moreover 3-day curing could adequately strengthen all samples to attain the minimum CBR requirement (JKR standard), irrespective of the binder dosage used. In conclusion, it could effectively strengthen sandy clay soils within 3 days with dosages as low as 2.5%.

Challenge of adopting relatively low strength and self-cured geopolymer for road construction application: a review and primary laboratory study

ABSTRACT In road construction industry, more sustainable construction materials are required. Currently, for modern road pavement rehabilitation and construction, cement is often used as a stabilising agent. With the rapid growth of road traffic and freight, cement usage substantially increases in amount of CO2 emissions. Hence, how a geopolymer, defined as a future sustainable construction material, can be alternatively used in the road pavement. This paper aimed to reveal the possibility of using geopolymers in road construction. A literature review process and a primary laboratory study were performed. The newly developed concept of a relatively low strength (LS-GP) and self-cured geopolymer may be practical when used as a road stabilising agent. The lower strength requirements of a road construction material in comparison to those of normal concrete application could ease any difficulties with geopolymer production. The available technology for geopolymers cured at an ambient temperature condition could enhance such a possibility. Results from the primary laboratory study confirmed such a concept. An applicable level of alkaline solution concentration led to an increase in strength. While, a high calcium content in standard road base material can rapidly react with alkaline activators, such that a self-cured geopolymer could be used.

Effect of cement replacement by fly ash and epoxy on the properties of pervious concrete

Permeable concrete has strong drainage and can recharge groundwater, making it a common semi-rigid road base material. Over the last decade, authors have focused on the properties of porous concrete with pozzolanic admixtures. The number of studies on the mechanical properties of pervious concrete made through the replacement of pozzolanic materials with cement is quite limited. Unfortunately, researchers have not focused on utilizing additional admixtures to improve the properties of pervious concrete made with high volumes of pozzolanic replacement. This paper focuses on the effect of using epoxy to partially replace cement on the mechanical properties of permeable concrete made with a significant amount of cement replaced by fly ash. A comparison between the addition and non-addition (15%) of sand as a partial replacement for gravel was investigated and the effect of increased gravel to sand ratios on the properties of porous concrete was also studied. This paper showed a slight decrease in porosity due to epoxy replacement compared to an increase in porosity by other mechanical properties. There was an increase in strength when epoxy replacement reached above 45% as well as a marginal decrease in strength and modulus of elasticity with (50%) fly ash replacement. There was also an increase in strength due to (15%) gravel replacement by sand of above 40%, with a reduction in strength with increased gravel to sand ratios.

Life Cycle Assessment of Alternative Road Base Materials: the Case of Phosphogypsum

Phosphogypsum (PG) is the most abundant by-product generated by the phosphate fertilizer industry. Formed during the production of phosphoric acid from natural phosphate rock, PG is mostly disposed in stacks or released into coastal regions’ waters. Due to the expected increase in the world PG production – currently estimated to be around 250 Mt per year – and the environmental impacts of actual waste management scenarios, there is a call for a paradigm shift, by considering PG not as a waste but as a resource. About 15% of the total PG production is nowadays used as fertilizer, retarder, road base material or building material. The load of radionucleids and heavy metals contained in PG however questions the sustainability of such valorization routes. This paper aims to compare the environmental impacts of different PG valorization scenarios through life cycle assessment. Based on Moroccan conditions for phosphoric acid production, it discusses the key parameters influencing the assessment as well as assumptions regarding the allocation of emissions and resource use over PG and phosphoric acid.

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.

Synergic effects of electrolytic manganese residue-red mud-carbide slag on the road base strength and durability properties

The present study was designed to prepare the road base material by using electrolytic manganese residue (EMR), red mud (RM) and carbide slag (CS) as main raw materials. The mix was optimized and mechanical properties, durability, strength formation mechanism and environmental behavior were investigated. X-ray diffraction (XRD), Mercury intrusion porosimetry (MIP), 29Si and 27Al magic-angle spinning (MAS) nuclear magnetic resonance (NMR) and electron probe microanalysis method (EPMA) were used for microstructure characterization. The results show that after curing for 7 days, the EMR-RM-CS exhibited the highest unconfined compressive strength (UCS), showed the best durability, the best pore diameter distribution and critical pore size. Hydration characteristics reveal that C-A-S-H gel and AFt are generated in EMR-RM-CS, which is positive to the form of UCS and durability. 29Si analysis demonstrates that the synergy of EMR, RM and CS has the best polymerized structure. Al in the hydrated pastes exists in the form of AlIV and AlVI, and one part of the dominant AlIV is activated and another one is converted to AlVI. The leaching results meet the Chinese groundwater standards which indicate that EMR-RM-CS system can well solidify the heavy metals. The road base material prepared by EMR not only consumes a significant quantity of solid wastes but also provides a new idea for the synergistic utilization of solid wastes.

Preparation and characterization of a red mud-based road base material: Strength formation mechanism and leaching characteristics

The present study was designed to prepare and characterize an eco-friendly road base material using mainly red mud in terms of mechanical properties, hydration and leaching characteristics. The microstructure was characterized by using scanning electron microscopy, X-ray diffractometer, Fourier transform infrared spectroscopy, electron probe microanalysis, Magnetic angle spinning Nuclear magnetic resonance and mercury intrusion porosimetry while inductively coupled plasma emission spectrometer was adopted to characterize the leaching behavior of hazardous compounds. The results showed that the strength of the optimum proportion reached 5.92 MPa and 6.66 MPa after curing for 7 and 28 days respectively and meet the highest strength requirement (class I) of 5–7 MPa for road base in Chinese standards. The results also showed that the strength increased with long term soaking which implies a good durability of RBM against water. The microstructure analysis indicated that predominant hydration products are C-S-H, C-A-S-H, N-A-S-H gels, ettringite and are responsible for strength development in the road base. The leaching results showed that all parameters in specimens cured for 7d and 28d are lower than drinking water GB 5749-2006 standard limits. Therefore, based on strength and environmental performance, red mud-flue gas desulfurization fly ash mix can be used as a road base material. This process is believed to reduce environmental pollution related to red mud and flue gas desulfurization fly ash, lower the road base cost and also save huge disposal fees that is used for safe disposal of these wastes.

Preparation and characterization of cement treated road base material utilizing electrolytic manganese residue

The utilization of electrolytic manganese residue (EMR) in synergy with red mud (RM) and other solid wastes as road base materials (RBM) was investigated in this research. The chemical composition, mechanical properties, the hydration behavior, pore structure and environmental friendliness performance of the RBM with different Ca/Si ratios were investigated. The hydration characteristics were analyzed by XRD, FTIR, TG, 29Si MAS-NMR and SEM-EDX technique; the pore structure was investigated by MIP, and environmental properties were texted by ICP. The results showed that the optimal proportion of Ca/Si is within the range of 0.91–1.17. After curing for 7 d, the unconfined compressive strength (UCS) of RBM can reach the highest strength requirement (class I) of 5–7 MPa for road base in Chinese standards. The best mechanical properties and polymerized structure were obtained for a Ca/Si ratio = 0.95 and the main hydration products are C-A-S-H gel, ettringite (AFt) and CaAl2Si2O8·4H2O, which promote the development of strength. The leaching test results indicated that the heavy metals can be efficiently solidified, and meet the Chinese groundwater standards GB14848-2017. This study provides a direction for the large-scale and effective utilization of EMR.

Efficient road base material from Kazakhstan's natural loam strengthened by ground cooled ferrous slag activated by lime production waste

A scientifically based disposal of all industrial and municipal wastes is the only solution for the problem of the rapid and constant increase in environmental pollution and the associated climate change, with inevitable catastrophic consequences for our planet. The present study proposes such scientifically based method for the use of two types of industrial waste – ground cooled slag of ferrous metal and lime production waste – as a binder for natural loam for road base construction with complete replacement of traditional layers from natural sand and rubble. The axial compression strength of the developed materials in 3-day age samples reached 3.27 MPa, in 28 days–6.95 MPa, 180 days–13.39 MPa, and 550 days–16.44 MPa, very high water and frost resistance, and rather low linear expansion, meeting the demands for 1st class construction materials of the Kazakh norms. It has been established, by a set of modern complementary methods (X-rays diffractometric analysis, X-rays fluorescence analyses, scanning electron microscopy, Energy-dispersive spectroscopy, Atomic absorption spectroscopy laser micro-mass analyses), the synthesis of new formations, mainly amorphous, which are binding the particles of the initial components. The achieved mechanical properties enable the application of these composites also as building materials, such as unburned bricks and blocks with high environmental and economic efficiency.

Recycled concrete aggregate as a road base material

Natural crushed aggregate (NCA) is the most common material for aggregate throughout the world. The consumption of the NCA itself is rising up through the years. Concrete structures and road construction are some of the most consuming aggregate material, especially NCA. Therefore, aggregate such as recycled concrete aggregate (RCA) has become an alternative material for some particular civil construction. The implementation of RCA as road construction material has been raised for a long time ago especially in road base layer. Road base layer as foundation for road pavement must provide an adequate strength to hold the working load on the pavement surface. RCA is more heterogeneous material compared to NCA as the RCA contain many substances, such as aggregate, cement, sand, and some additive substances. Hence, it effects the strength of the RCA as construction material. In this paper, the properties of the RCA are investigated to get the characteristic of the aggregate. Density, water absorption, aggregate crushing value (ACV), compaction, and penetration test (CBR) were conducted in this research. An improvement by using plastic strips as addition also proposed to strengthen the RCA as road base material.

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&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.

Investigation on the preparation and performance of clinker-fly ash-gypsum road base course binder

Abstract Reflecting cracks of asphalt pavement induced mainly by shrinkage crack of road base course become one of the most common pavement diseases in highway. To compensate the shrinkage of stabilized road base course, a slow setting slight-expansive cement was designed as road base course binder (RBCB) and the properties of road base course with RBCB were investigated. Furthermore, the RBCB’s shrinkage compensation effect, the performance of RBCB stabilized crushed stone and its applications are studied in this article. RBCB has longer setting time and its 28-day strength is almost equal to 32.5 grade Portland slag cement (P.S 32.5). RBCB has slight expansion characteristics, it can effectively compensate the shrinkage of the cement, thus its volume stability under both wetting-drying and drying-wetting scenario is improved. The road base course stabilized by RBCB has higher mechanical properties and substantially lesser shrinkage crack than the ordinary cement stabilizing road base course. RBCB has low construction costs and outstanding performance in practical applications. Hence, it is an effective approach to lessen the pavement cracking by developing slow setting and expansive road base stabilizer compensate the shrinkage of road base materials.

Strength development of recycled concrete aggregate stabilized with fly ash-rice husk ash based geopolymer as pavement base material

This research studies on the usage of fly ash (FA) and rice husk ash (RHA) based geopolymers for improving the compressive strength of recycled concrete aggregate (RCA) to be a lightweight stabilised pavement base material. A mixture of FA from coal-burning power plants and RHA from rice milling process was used as a precursor while the liquid alkaline activator (L) was a mixture of sodium hydroxide solution (NaOH) and sodium silicate solution (Na2SiO3). Various RHA/FA ratios (between 100/0 and 0/100) and NaOH/Na2SiO3 ratios (between 50/50 and 100/0) were used in this study. The FA-RHA-geopolymer stabilised RCA samples, at each NaOH/Na2SiO3 ratio were prepared at the optimum liquid alkaline activator content (OLC) for unconfined compressive strength (UCS) tests. The UCS tests were conducted after 7, 28 and 60 days of curing. The test results indicate that the UCS of FA-RHA-geopolymer stabilised RCA increases as the RHA/FA and NaOH/Na2SiO3 ratios decrease and the curing time increases. Based on the Department of Highways, Thailand, the 60/40 RHA/FA and 60/40 NaOH/Na2SiO3 mix proportions are recommended for both low and high traffic volume roads with a low unit weight of 21.1 kN/m3. This research study confirms the potential of FA-RHA-geopolymer stabilised RCA as an alternative stabilised road base material.

Investigation of shear strength of interface between roadbase and geosynthetics using large-scale single-stage and multi-stage direct shear test

The application of geosynthetics in the road pavement industry as a reinforcement has increased dramatically in recent years. Geosynthetic inclusions can significantly: (i) increase the bearing capacity of the pavement, (ii) prolong the road service life, (iii) reduce maintenance costs, iv) diminish unfavourable large vertical and lateral pavement deformations; and (v) prevent reflective cracking and reduce crack propagation. Although considerable research has been carried out on the interfaces between soils and geosynthetics through large-scale direct shear testing, there is a lack of research in the interfaces between roadbase materials and geosynthetics in pavement engineering. The main innovation of this paper is to investigate the shear strength behaviour of the interfaces existing in a geosynthetic-reinforced pavement. One interface is existing between roadbase and geosynthetic reinforcement for base reinforcement; another one is existing between roadbase and subgrade with geosynthetic reinforcement for subgrade stabilisation. Therefore, a series of laboratory, large-scale direct shear tests was carried out on roadbase materials with and without the inclusion of geosynthetics, under applied normal stresses of 25, 50, 75 or 100 kPa, representing the magnitude of the overburden pressure in the pavement. In addition, theoretical interpretations are developed to back up the experimental results, and to quantify the contribution of different shear strength components mobilised along the interface between roadbase materials and geogrids. Finally, the applicability of multi-stage, large-scale direct shear box testing is assessed by comparing the results obtained with those from conventional single-stage tests obtained in the present experimental study.