Pavement System Research Articles

A COMPUTER PROGRAM FOR SLABS WITH DISCONTINUITIES ON LAYERED ELASTIC SOLIDS

A finite element method programmed for a high­ speed computer is presented. The method is based on the classical theory of thin plate. The program is developed for subgrade soil represented as a linear layered elastic solid. Any number of layers can be accommodated. The program is capable of analyzing stress conditions in concrete pavements with the load transfer in the joint, as well as in the supporting subgrade soil, subjected to loads and temperature warping. Multiple-wheel loads can be input and the number of wheels is not limited. Because of the large computer storage space required, the program can handle only two slabs, except for the special option where a four-slab pavement system is loaded symmetrically at the pavement's center. At the joint, the progam considers only the shear transfer and assumes the element transfer to be zero. The results computed using the program were compared with stress transfers across the joint measured in airfield test pavements. The comparisons were very favorable.

STRENGTH CHARACTERIZATION AND A BASIS FOR SAWCUTTING REQUIREMENTS FOR JOINTED CONCRETE PAVEMENTS

In the early life ofa concrete pavement, the pavement's tendency to change its volume due to temperature gradients and/or shrinkage can cause significant stresses due to pavement restraint to movement. Stress concentration on the tip of initial flaws or cracks leads to the propagation of these cracks. To avoid the formation of random cracks, it is common practice in jointed concrete pavement systems to induce cracks by sawcutting at specific joint locations. The spacing and location of the joints are typically determined prior to sawcutting operations. Current sawcut depth and timing requirements are related to the strength characteristics of the concrete pavement. A deficiency in this regard is that strength is not a material constant and it varies with structure geometry and size. It is common knowledge among practitioners and researchers that different test specimens provide different strength values. Also, it is unknown whether the strength obtained from the small specimens is representative of the actual notched pavement strength. New approaches that take into account the geometry and size effects are needed. An approach is presented to characterize concrete susceptibility to crack propagation. Such characterization which makes use of fracture parameters is used to determine sawcut depth and timing requirements for both longitudinal and transverse joints. The effect of slab thickness and aggregate types on those requirements is investigated and is useful in explaining the performance of different methods of sawcutting.

Effect of Pavement Conditions on Urban Road Accidents

Traffic accidents represent a serious problem in Jordan. The major objective of this study was to investigate the effect of pavement conditions on urban road accidents. To achieve the objective of the study, 25 urban pavement sections were selected. A comprehensive data base, including pavement conditions in terms of pavement condition index (PCI), traffic volume, and traffic accidents, for the selected sections, was developed. Regression analyses were carried out to explore possible relationships between PCI and the number of accidents and accident rates. The results of the statistical analysis indicated that urban pavement conditions had a significant effect on accident occurrences and accident rates. The relationship between accidents and PCI had a parabolic shape. The regression models explained 69% and 61% of the variation in accident frequency and rate, respectively. It was found that urban pavement sections with PCI lower than 50 were consistently associated with higher accident frequency or accident rate. Also, a notable increase in accidents was observed for all sections having a PCI greater than 85. The results of the study are comparable with the results found for rural pavement sections. To provide a safe urban environment; therefore, municipal engineers should keep urban pavement in fair conditions and implement appropriate calming measures for good pavement conditions. Keywords: Accident occurrence, Accident rate, Road safety, Pavement condition index (PCI), PAVER system, Pavement management system (PMS), Pavement distresses.

Engineering of alkali-activated permeable pavement composites with agro-industrial wastes

ABSTRACT This study investigates the development of alkali-activated pervious concrete (PC) composites using industrial and agro-waste as primary constituents. The binder was activated with sodium silicate and sodium hydroxide at an activator modulus (Ms) of 1.25, maintaining a sodium oxide dosage of 4.0% relative to the total binder at a water-to-binder ratio of 0.40. Slag and bagasse ash were used as binders, recycled coarse aggregates (from construction and demolition waste) partially replaced crushed granite and waste-foundry sand served as fine aggregates. Mix proportions were optimised for hydraulic conductivity and compressive strength after 28 days of air curing. Four selected mixes were further evaluated for total porosity, splitting-tensile strength, static flexural strength and flexural fatigue performance. Optimal mechanical properties were observed for the corresponding PC mixes at 10% bagasse ash and 50% recycled aggregates. Statistical analyses of flexural fatigue, including S-N curves and two-parameter Weibull distribution, were conducted, along with Kolmogorov-Smirnov analysis and survival probabilities (95%, 50% and 5%). The findings contribute to understanding the engineering behaviour of alkali-activated PCs, supporting the development of permeable concrete pavement systems through effective utilisation of agro-industrial wastes, thereby promoting sustainability and environmental conservation.

Analysis of Infiltration and Runoff Based on the Volume of Storage Spaces in Storage Permeable Blocks

Recent climate change has led to an increase in total rainfall in spite of a decrease in the number of rainy days. In addition, the increase in impervious surfaces due to urbanization has resulted in greater surface runoff, resulting in urban flooding and flash floods. To address this issue, low-impact development techniques have been introduced to improve water cycle health within watersheds. Permeable pavements, which serve as roadways while reducing impervious surfaces, have been introduced in new towns and development zones. However, most performance evaluations were based solely on the permeability coefficient of the pavement, with limited research on the water cycle performance of the entire permeable pavement system, including the subbase layer. Therefore, this study aims to analyze the effects of the porosity storage volume of joint-type permeable blocks with storage spaces under the same conditions for two types of permeable blocks. The results showed that increasing the porosity storage volume reduced the equilibrium runoff rate by 70%, and increased the runoff time delay by 2 to 2.5 times.

Alkali-Activated Permeable Concretes with Agro-Industrial Wastes for a Sustainable Built Environment.

This research presents a proposal for alkali-activated permeable concrete composites with the use of industrial by-products, including ground granulated blast-furnace slag (GGBS) and waste-foundry sand, as well as agro-desecrate product, i.e., sugarcane bagasse ash (SBA). GGBS and SBA served as binders, with crushed granite as coarse aggregate and waste-foundry sand as fine aggregate. The novelty of this proposal is in examining the influence of SBA, in combination with slag, on the fresh- and hardened-state properties of the proposed permeable concretes. Experiments were conducted to optimize the SBA percentage based on hydraulic conductivity and compressive and tensile strength after 28 days of air curing. The hardened density, compaction factor (workability), and saturated water absorption were also measured for all the mixes. Furthermore, the control and optimal mixes were subjected to evaluate the microstructure analysis (EDX, XRD, and FESEM) after 28 days of air curing. The mix containing 100% GGBS and 0% SBA served as the reference, with the optimal 10% SBA mix (with 90% GGBS) used for comparative analysis to understand its effect on the properties of permeable composites. The results showed positive or acceptable mechanical performance at a mix ratio of 10% SBA to 90% GGBS as binders. This study aims to enhance the understanding of the engineering behavior of alkali-activated permeable composites, facilitating the rational design of permeable pavement systems through the effective use of agro-industrial waste products, thereby conserving ecosystems while meeting engineering requirements.

Comparative Study on the Performance of Open Graded Friction Course using Hot and Warm Mix Technology

Conventional pavements and parking lots are constructed as impervious structures which leads to large volumes of stormwater runoff. This increases the load of stormwater drains besides the water carries the dirt and debris present on the surface and pollutes the water bodies. Surface detention basins are usually provided to collect the runoff and slow down its rate. But this requires additional land space. So, a solution in this regard is to provide a permeable pavement system that permits the infiltration of the stormwater. Open graded friction courses are provided as the surface course of such pavements. This research aims at assessing the feasibility of using warm mix technology in the production of open graded friction course mixes. The focus was on the benefits that could be acquired by the use of WMA technology in a porous asphalt mix. In this study a chemical additive namely sasobit was used to prepare warm mixes. A comparative assessment between hot and warm porous bituminous mixes was made. The fundamental parameters evaluated includes volumetric properties of the mix, permeability, drain down, Cantabro abrasion loss, and moisture susceptibility. It was found that the warm mix additive was capable of reducing the production temperature and the maximum temperature reduction was obtained in the case of 3% sasobit. About 100C reduction in mixing and 130C reduction in compaction temperature could be achieved. The results indicate that open graded mixes prepared with warm mix technology met the performance criteria and hence it is suitable for application in porous pavements. This reduction in temperature could be translated to reduced fuel consumption for heating the binder and reduced level of emissions. Thus, it leads to better working environment for those involved in road construction.

Efficacy of underground aggregate infiltration beds under a permeable pavement system

Pervious concrete (PC) pavement systems with their underlying aggregate storage beds provide potential strategies to mitigate stormwater runoff and associated flooding issues. Of particular interest is the efficacy of the infiltration capabilities into the soil of the underground storage bed, especially in areas with slow draining soils. This study uses real-time data on the water levels in the storage beds to determine soil infiltration rates at two test sites in Southeast Texas. One of the sites is connected to a rain garden system, with the potential for taking advantage of the low impact development (LID) processes of both systems. It was found that the combined systems allowed water to flow between them possibly adding additional storage during a storm event with the PC system’s void spaces and allowing for additional evaporative processes from the rain garden post the event. The other site has the PC raised above the surrounding grade, which represents potential applications where structures are raised above base flood elevations with connecting paved areas also raised. It was found that this raised system provided both infiltration into the soils from the underground bed and some detention capabilities in the raised portion of the system. These results aid in designing these LID systems in flat areas subject to flooding with slow draining soils such as in much of the coastal Gulf region.

Towards Sustainable Road Construction: Literature Review on Addressing Environmental Impacts and Promoting Green Technologies

Abstract This study investigates the environmental impacts of road construction and explores strategies to promote green technologies in Indonesia. Traditional road construction methods, particularly those using asphalt and cement, have significant energy consumption and greenhouse gas emissions. This study conducted a thorough literature review to investigate green technologies and best practices to reduce emissions during the construction process. The literature review included articles published from 2004 to 2024, drawn from various national and international academic sources, and adopted the PRISMA method. It was found that key strategies include recycled materials, warm mix asphalt technology, permeable pavement systems, green roofs, and energy-efficient equipment. To mitigate these impacts, the study recommends using recycled materials, adopting energy-efficient technologies, implementing sustainable design practices, and conducting life cycle assessments. Although Indonesia has made progress, challenges such as limited funding, technology, and coordination remain. Overcoming these challenges requires increased commitment and funding, capacity building, better coordination, and stricter regulations. Future studies should investigate the development and implementation of innovative green technologies, including advanced recycled materials, more efficient construction equipment, and innovative pavement design techniques.

Enhancing hydraulic and environmental performance of interlocking pervious concrete pavement systems through layer configuration optimization

Enhancing hydraulic and environmental performance of interlocking pervious concrete pavement systems through layer configuration optimization

Utilizing Machine Learning for Predictive Maintenance of Climate-Resilient Highways through Integration of Advanced Asphalt Binders and Permeable Pavement Systems with IoT Technology

This review provides a comprehensive examination of the application of advanced technologies in enhancing the climate resilience of highway infrastructure. The focus is on the integration of machine learning for predictive maintenance, the use of Internet of Things (IoT) devices for real-time monitoring, and the deployment of advanced materials, specifically permeable pavements and modified asphalt binders. The review explores how these technologies work synergistically to create durable, low-maintenance highway systems capable of withstanding extreme environmental conditions. Advanced asphalt binders, such as those modified with styrene-butadiene-styrene (SBS) and nanomaterials, are discussed for their enhanced flexibility, thermal stability, and load-bearing capacity. Additionally, the environmental and structural benefits of permeable pavements are highlighted, particularly their role in stormwater management and reduction of urban heat island effects. Several case studies highlight the successful implementation of these technologies in diverse geographical and climatic conditions, including North Carolina, Australia, and Raipur, India. These cases illustrate the adaptability and environmental benefits of permeable pavements in managing stormwater, recharging groundwater, and mitigating the urban heat island effect. By synthesizing recent advancements and practical implementations, this review emphasizes the importance of integrating predictive technologies and resilient materials to develop sustainable, climate- adaptive highway systems. These insights offer a foundation for future infrastructure policies and technological innovations aimed at enhancing the durability and environmental sustainability of highway networks.

Boundary Layer Modelling of Flow Acceleration and Energy Transfer Effects in Smart Pavement Design

The integration of remote technology into the construction industry has advanced the emergence of smart, self-learning infrastructure across all levels of land transportation design and development. However, energy harvesting capabilities for smart road ventilation purposes have not yet been fully researched as the world gravitates towards energy sustainability. This study thus presents a mathematical investigation of the self-draining design potentials of road pavements, leveraging on energy absorption and conversion to accelerate conductive and convective ventilation of these pavements during wet conditions, as a means of ensuring the skid resistance and safety of such pavements are not compromised. Applying numerical methods with the aid of commercial software code MATLAB®, the classical physics of fluid-surface interaction was used to model accelerated drainage of microflood off paved surfaces through methodical modification of the thickness of the boundary layer associated with the flow regime over the flat road surface. Results indicate significant influences of energy exchange, thermal, and viscous diffusivity on flow acceleration. Alterations in parameters such as the slip factor, thermally induced Brownian motion or phoretic characteristics of the fluid particles at the boundary induce accelerated flow at the surface of the pavement. The findings contribute to the advancement of smart infrastructure by offering practical insights into the potential benefits of integrating energy-harvesting technologies into road pavement systems. By optimizing flow acceleration mechanisms, smart pavements can play a crucial role in improving road safety and sustainability in urban environments.

Mechanical Response of Hot-Mixed Epoxy Asphalt Concrete Steel Deck Pavement Under Thermal and Load

In recent years, fatigue cracking in orthotropic steel bridge deck pavements has become a significant concern, so the investigation of the mechanical response of the pavement layer has become a central focus in pavement structure design. This experiment subjected a full-scale specimen to a constant amplitude dynamic load of 60 kN to 300 kN over 2 million cycles. Throughout the testing, a circulating water bath elevated the temperature of the pavement layer from 15 °C to 50 °C. Key locations were monitored for strain and deflection data, facilitating an investigation into the mechanical response of the epoxy asphalt pavement system under the effects of temperature and load. The results indicate that the maximum transverse strain at the bottom of the steel deck occurs at the U-rib weld aligned with the load center, reaching 190% of the initial loading strain. Meanwhile, the maximum transverse strain on the pavement surface is observed at the U-rib weld adjacent to the loaded area, measuring 167% of the initial strain. The maximum longitudinal strain is lower than the maximum transverse strain. In the load zone, the longitudinal strain between the U-ribs exceeds that at the U-rib weld. Both transverse strain and relative deflection increase as the load intensifies. The relationship between transverse strain and applied load is characterized by an exponential function, while deflection exhibits a cubic relationship with the applied load. Elevated temperatures also contribute to increased transverse strains at both the bottom of the steel deck and the pavement surface, following an exponential trend. Relative deflection is primarily influenced by the applied load and remains relatively unaffected by temperature variations. When accounting for the coupling of load and temperature, the maximum transverse strains at both the bottom of the steel deck and the pavement surface can be modeled as an exponential function of the independent variables: load and temperature.

In Situ Experimental Analysis and Performance Evaluation of Airport Precast Concrete Pavement System Subjected to Environmental and Moving Airplane Loads.

The behavior of airport precast concrete pavement (APCP) involving new design and construction concepts was experimentally analyzed under environmental and moving airplane loads, and the long-term performance of the APCP was evaluated using fatigue failure analysis. The strain characteristics and curling behavior of the APCP under environmental loads were comprehensively analyzed. The APCP slabs exhibited a pronounced curling phenomenon similar to conventional concrete pavement slabs. The dynamic response of the APCP subjected to impact loads was analyzed by performing heavy weight deflectometer tests. The test results confirmed that the vertical deformation of the APCP was small and within the typical range of vertical deformation of conventional concrete pavement. The dynamic strain response of the APCP under moving airplane loads was then analyzed and the strain variation during day and night times was compared. The strains during the day were found to be significantly larger than those at night under airplane loads because of the curling phenomenon of the APCP slabs. Finally, the long-term performance of the APCP was evaluated using fatigue failure analysis based on the obtained behavior. Even using the most conservative fatigue failure prediction model, the service life of the APCP was ascertained to be more than 30 years. Based on the overall results of this study, it is concluded that the APCP, which is designed to reduce slab thickness by placing reinforcing bars in the slabs via reinforced concrete structural design, exhibits typical behavior of concrete pavements and can be successfully applied to airport pavement rehabilitation.

Effect of nonlinear stress-dependency and cross-anisotropy on the backcalculation outputs from the TSD deflection slopes and the effect on estimated pavement performance

ABSTRACT The Traffic Speed Deflectometer (TSD) is a mobile vehicle that measures deflection slopes. Deflection slopes have been utilised in previous studies to backcalculate pavement layers’ moduli. However, the nonlinear stress-dependency and cross-anisotropy of unbound granular materials and fine-grained soils were overlooked in those studies. Utilising the Finite Element Method (FEM) based on static analysis in this study to evaluate a three-layered flexible pavement system with specific material properties and layer thicknesses revealed that neglecting the nonlinear stress-dependency of base and subgrade layers underestimated the permanent deformation life of the backcalculated pavement by more than 45%. Neglecting the cross-anisotropy of the base layer with the design anisotropy ratio of 0.5 increased the backcalculated Asphalt Concrete (AC) modulus by more than 21%, increased the estimated permanent deformation life of the pavement by more than 160%, and decreased the backcalculated base modulus by around 28%. Neglecting the cross-anisotropy of the subgrade with the design anisotropy ratio of 0.5 almost increased the estimated permanent deformation life of the pavement by 15%. The results underscore the necessity to consider the nonlinear stress-dependency and cross-anisotropy of unbound granular materials and fine-grained soils in backcalculating pavement layers’ moduli from TSD deflection slopes.

Effects of Mixture Proportions and Molding Method on the Performance of Pervious Recycled Aggregate Concrete.

The use of pervious concrete pavement systems with recycled aggregates is a sustainable and innovative solution to major urbanization challenges such as repurposing construction waste, alleviating urban waterlogging, and reducing heat-island effects. This study aims to investigate the effects of mixture proportions and molding methods on the performance of pervious recycled aggregate concrete (PRAC). To this end, the coarse aggregate size (4.75~9.5 mm, 9.5~16 mm, and 16~19 mm), the molding method (layered insertion-tamping and vibration molding with vibration times of 5 s, 10 s, or 15 s, respectively), and the replacement rate of recycled coarse aggregate (RCA) (0%, 30%, 50%, and 100%, respectively) are considered. The results reveal that the addition of RCA to permeable concrete weakens its permeability. However, the compressive strength of PRAC reaches its maximum value when the RCA replacement rate is 50%. A larger aggregate particle size (16~19 mm) enhances the compressive strength of PRAC, yet decreases the permeability of PRAC. By using vibration molding to fabricate PRAC, an extension to the vibration duration increases the compressive strength, yet concurrently decreases the permeability. Based on the compressive strength and permeability coefficient of PRAC, the optimal mixture proportions and molding method are suggested.

Development and optimization of ultimate performance self-levelling epoxy asphalt concrete (USEA) for prefabricated deck pavement

Developing prefabricated bridge deck pavement systems can fundamentally avoid the drawbacks caused by traditional on-site construction such as poor continuity of the construction process and significant differences in pavement layer performance. Prefabricated bridge deck pavement requires that the bridge pavement is completed with the steel deck together in the factory indoors thus it needs the concrete has better self-leveling characteristics which is rare for existing pavement materials. This article develops the ultimate performance self-levelling epoxy asphalt concrete (USEA) which both have excellent self-leveling properties and comprehensive performance. The study initially established the self-leveling asphalt concrete rolling model based on asphalt film thickness theory and Hertz contact theory and the critical rolling mechanical calculation results states that the aggregate particles and the skeleton amounts are the key elements for fluidity of concrete. Comprehensive the analysis of rolling model and research on the curing reaction process of epoxy resin, the study raises the material configuration of USEA and determine the gradation by the Bailey’s method. To guarantee the better pavement performance of USEA, the study designs the orthogonal test and establish the Entropy-TOPSIS model to optimize the details mortar schemes of concrete. Through the model calculation, the epoxy resin content and the SBS modified asphalt oil-stone ratio are determined as 20 % and 8.0 % respectively. In this scheme, the high temperature stability is 2805 times·mm-1, the low temperature bending strain is 3662με and the fatigue life can reach 1.200 million times. The study provides a material selection for the development of prefabricated bridge pavement system and the technical reference for the development of other self-leveling materials which has constructive practical significance.

Prediction of resilient modulus with pre-post experimental data of undisturbed subgrade soils using machine learning algorithms

The resilient modulus (MR) of subgrade, which shows relationship between stress and unit deformation of a pavement systems under traffic loads, is a design parameter of the pavement structure. Although a cyclic triaxial test apparatus can be used to directly determine the MR of the subgrade in the laboratory, utilizing prediction models based on easily obtainable soil parameters, is a more efficient method when taking time and cost considerations into account. A comprehensive laboratory testing program is designed to create MR prediction models using machine learning (ML) algorithms. 70 undisturbed soil samples are subjected to MR tests, as well as physical and engineering soil properties tests (water content, field density, specific gravity, gradation, consistency limits, unconfined compressive strength, swell pressure, swell percentage). Soil samples are drilled from a highway that has been in operation for over five years.First, a linear model like MLR is used in the study. Next, nonlinear regression models like RF, GBM, LightGBM, CatBoost, and XGBoost algorithms are used. Research findings showed that nonlinear regression models outperformed linear regression models in predicting the MR (R2 > 0.85), with the XGBoost algorithm yielding the best accuracy (R2 = 0.90). Apart from the primary effects such as confining pressure (σ3) and deviatoric stress (σd), it was found that unconfined compressive strength (qu), natural water content (wn), and swelling percentage (SR) are significant parameters in the prediction of MR among all parameters.

Temperature Effects on Traffic Load-Induced Accumulating Strains in Flexible Pavement Structures

AbstractRutting is a major distress mode in flexible pavements, results from the repetitive loading caused by traffic movement. Pavement deformation consists of both recoverable (elastic) and unrecoverable (plastic) components. The continuous movement of vehicles contributes to the overall deformation in the flexible pavement system, involving all pavement components. In regions with hot climates or in the hot summer season, rutting tends to be more prominent due to the substantial reduction in the viscosity of the asphalt binder. This decrease in viscosity, which is inversely linked to rutting, occurs as temperatures rise, leading to a heightened susceptibility of the Hot Mix Asphalt (HMA) blend to rut formation. However, according to studies, a significant amount of permanent deformation takes place in the unbound layers beneath the asphalt course, it is therefore essential to prioritize attention on these layers. Temperature exerts besides viscosity a substantial impact on asphalt stiffness, leading to the transfer of higher vertical deviatoric stresses to the unbound layers beneath the asphalt course (base, subbase, subgrade). This research presents a study integrating the High Cycle Accumulation (HCA) model into a laminar model to determine permanent deformations in the unbound granular layer of flexible pavements and taking into account the temperature dependent stiffness of asphalt. Rutting depths at the end of the design lifetime were computed, accounting for seasonal stiffness variations. It was shown that the softer asphalt behavior significantly increases the development of ruts in the underlaying soil layers. The findings were compared with results obtained from mean annual temperature and the typical equivalent asphalt stiffness utilized in fatigue tests. Additionally, an analysis was conducted to assess whether the timing of road implementation influences settlements throughout the design lifetime. The results suggest that the sequence of seasons is most relevant during the first year of service, showing a distinct effect at that time. However, with a higher number of axle passes, the initial differences fade away, and the curves start to merge.

Modeling the influences of rainfall conditions on nitrogen removal effects of a permeable pavement system

Permeable pavement systems are important facilities for alleviating runoff pollution. However, few studies have focused on outflow nitrogen processes under varying rainfall conditions. In this study, we proposed a permeable pavement system model that can simulate the nitrogen transformation processes. The model was verified with data on outflow rates and outflow nitrogen concentrations (ammonia nitrogen (NH4-N), nitrate nitrogen (NO3-N), and total nitrogen (TN)) processes for six consecutive rainfall events of a permeable pavement system in Shenzhen, China. Based on the validated model, scenarios were designed to simulate the influences of rainfall conditions on nitrogen removal effects at the single rainfall event and annual scale, respectively. The results indicate that: (i) the model can explicitly describe hydrological and nitrogen processes of the system, and the Nash Sutcliffe Efficiency and percent bias of outflow rates and outflow nitrogen concentrations range from 0.5 to 0.9 and from −22.4% to 24.9%, respectively; (ii) the sensitivity analysis reveals that the empirical coefficient (C) related to evaporation in the gravel layer is sensitive at the annual scale but not at rainfall events scale. Parameters related to mineralization and microbial assimilation (i.e., mineralization rate constant in the gravel layer (k3N,mine), microbial assimilation rate constant of NH4-N, NO3-N, and ON (k1N,bio, k2N,bio, k3N,bio)) are sensitive annually but not at rainfall events scale; (iii) in the single rainfall event simulations, nitrogen removal efficiencies decrease with increasing rainfall return periods but is not significantly affected by rainfall peak coefficients. Nitrogen removal efficiencies improve notably with antecedent dry period extension for single rainfall event with antecedent dry period less than 2 days. In addition, we found that the outflow process significantly affects the outflow nitrogen concentrations process. In annual-scale simulations, extending the antecedent dry period only significantly boosts runoff reduction efficiency and nitrogen removal efficiencies for rainfall events with less than 10 mm.