Road Subbase Research Articles

Performance Evaluation of Red Clay Soils stabilized with Bluegum Sawdust Ash and Sisal Fiber as Low-Volume Road Sub-base Materials

The engineering properties of Red Clay Soils (RCS) in tropical regions are frequently inadequate for road construction due to a number of factors, including high compressibility, high creep rates, high plasticity, low strength, and swelling potential. This research project examines the potential of stabilizing RCS using Bluegum Sawdust Ash (BSDA) and Sisal Fiber (SF) to develop a cost-effective and environmentally sustainable material for use in low-volume roadways. Tests were conducted on both unstabilized and stabilized soil samples to evaluate a range of physical properties, including Atterberg limits, compaction, Unconfined Compressive Strength (UCS), and California Bearing Ratio (CBR). BSDA was introduced in increments from 2% to 10% at 2% intervals, with 6% of it being optimal. This resulted in a reduction in the Plasticity Index (PI) from 20.78% to 10.90% and a significant increase in both the UCS and the CBR values. The addition of SF resulted in further enhancement of stabilization, with an increase in the soaked CBR to 28.12% and UCS to 736.011 kN/m³. This triphasic approach, which combines RCS, BSDA, and SF, offers a sustainable and economical solution for the construction of road subbases in civil engineering.

Leaching of per- and polyfluoroalkyl substances (PFAS) from municipal solid waste incineration bottom ash intended for utilization as secondary aggregates in road subbase

Ten samples of mineral fraction derived from waste incineration bottom ash (MIBA) from Denmark (N = 7), Sweden (N = 1), and the Czech Republic (N = 2) underwent targeted analysis of 59 per- and polyfluoroalkyl substances (PFAS) in the solid phase and eluates from a batch leaching test at a liquid-to-solid ratio of 2 L/kg. The solid content, expressed as Σ59PFAS(S), ranged from 0.21 ± 0.03 µg/kg DM to 21.6 ± 1.47 µg/kg DM. The leached amounts, expressed as Σ59PFAS(L), ranged from 204 ± 63 ng/kg DM to 3250 ± 77 ng/kg DM. The results of the leaching tests were normalized to “PFOA-equivalents” (PFOA-eq) and used to estimate the bulk leaching emissions from the utilization of MIBA in typical road construction scenario. The calculated bulk leaching emissions associated with the utilization of 100 thousand tons of MIBA in road subbase were 6–30 g PFOA-eq per 10–21 years (Danish MIBA), 30 g PFOA-eq per 10–22 years (Swedish MIBA), and 271 g PFOA-eq per 14–30 years (Czech MIBA) depending on the effective infiltration and annual precipitation rates. This first approximation of the source term provides invaluable information for assessment of the environmental impact of MIBA utilization beyond landfill applications, pending further validation by subsequent research.

Geotechnical, Mineralogical, Petrographic and Microstructural Characterization of Two Lateritic Gravels from Congo

The recovery of lateritic gravel contributes to the reduction of road construction costs and environmental impact. These materials are of particular interest in road construction because of their abundance, especially in tropical countries, as in the case of Congo. The results obtained on the soils of ʽʽTSANGA and TSIAKIʼʼ show an identical appearance of the two particle size curves, with more fines in the TSANGA sample. Both soils are moderately plastic and their properties predispose them to mechanical treatment (TSIAKI soils) and hydraulic binders (TSANGA soils). The lateritic gravels of TSIAKI can be used as road sub-base for medium traffic while those of TSANGA as sub-base for low traffic. The geotechnical properties of the two samples differ due to the mineralogy, petrography and microstructure which vary from one deposit to another. The SEM microstructure study shows two matrices completely made of kaolinite and the matrix facies are cemented by hematite. X-ray microscopy and SEM allowed the differentiation of goethite and hematite to distinguish the two forms of iron oxides. The TSIAKI soil has a normal iron oxide content (mainly goethite), and has less quartz and kaolinite, which could justify its high CBR index.

The long-term re-cementation of recycled concrete aggregate in road sub-base and its impacts on pavement performance

Recycled concrete aggregate (RCA) can be used as a pavement sub-base or base material, but the re-cementation of RCA raises concerns about its engineering properties and its impacts on pavement performance. This study investigated the long-term re-cementation phenomenon of RCA that has served for 13 years in road pavements, and the effects of this phenomenon on the RCA’s physical, chemical and mechanical properties. Subsequently, the study also examined the impacts of RCA re-cementation on pavement response and performance using a novel random modulus field technique. It was found that the RCA modulus rises roughly in a power law with the increase of service time, indicating a continuous re-cementation process of this material. The re-cemented RCA particle has a porosity of about 7.8 %, anticipated to be lower than that of new unbound RCA. The net-shaped structures were found near the air voids, which is caused by the newly generated cementation crystals in re-cementation. The new mortar has a lower hardness value than that of the ordinary concrete mortar, but the overall strength of the re-cemented RCA is comparable to that of the cement-treated base. In a pavement structure, re-cementation decreases asphalt layer strain and subgrade strain, helping lower the bottom-up cracking and permanent deformation. However, severe re-cementation increases the risk of reflective cracking. In addition, large-size re-cemented particles increase the variations of pavement responses and thus bring additional uncertainties to pavement performance predictions. To mitigate this concern, limiting the fine aggregate (<0.6 mm) content in RCA is an effective solution since this component is closely related to re-cementation.

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.

Research on the Configuration of Multi-Component Solid Waste Cementitious Materials and the Strength Characteristics of Consolidated Aeolian Sand

Developing green, low-carbon building materials has become a viable option for managing bulk industrial solid waste. This paper presents a kind of all solid waste cementitious material (SWCM), which is made entirely from six common industrial wastes, including carbide slag and silica fume, that demonstrate strong mechanical properties and effectively stabilize aeolian sand (AS). Initially, we investigated the mechanical strength of waste-based cementitious materials in various mix ratios, focusing on their ability to stabilize river sand (RS) and aeolian sand. The results show that it is necessary to use alkaline solid waste carbide slag to provide a suitable reaction environment to achieve the desired strength. In contrast, the low reactivity of coal gangue powder did not contribute effectively to the strength of the cementitious material. Further orthogonal experiments determined the impact of different waste dosages on the strength of stabilized AS. It was found that increasing the amounts of carbide slag, silica fume, and blast furnace slag powder improved strength, while increasing fly ash first increased and then decreased strength. In contrast, higher additions of desulfurization gypsum and coal gangue powder led to a continuous decrease in strength. The optimized mix is carbide slag—desulfurization gypsum—fly ash—silica fume—blast furnace slag powder in a ratio of 4:2:2:3:3. The experimental results using SWCM to stabilize AS indicated a proportional relationship between strength and SWCM content. When the content is ≥20%, it meets the strength requirements for road subbases. The primary hydration products of stabilized AS are C-(A)-S-H, AFt, and CaCO3. Increasing the SWCM content enhances the reaction degree of the materials, thereby improving mechanical strength. This study highlights the mechanical properties of cementitious materials made entirely from waste for stabilizing AS. It provides a reference for the large-scale utilization of industrial solid waste and practical applications in desert road construction.

Influence of Ceramic Waste and Cement on the Mechanical and Hydraulic Properties, and Microstructure of the Road Sub-Base Layer

This study examines cement and ceramic waste (CW) for the sub-base layer of roads. This innovative method can do away with the risks associated with improper disposal of industrial waste. To achieve this objective, several proportions of cement and CW were used, ranging from 1.5 to 2% and 5% to 15%, respectively. The aim of the work was to examine the influences of CW and ordinary Portland cement (OPC) on the unconfined compressive strength (UCS), permeability, consolidation, and microstructures of untreated and treated soil of road sub-base layer. The Guelph permeameter, UCS, permeability, and one- dimensional consolidation were among the laboratory and in-situ tests that were examined; the microstructures were characterised using SEM, infrared (IR), and mercury intrusion porosimetry (MIP). The findings indicated that the high permeability of the natural soil caused harm to our road soon after construction. Applying 5 to 15% CW reduced permeability by approximately 100% and settlement by around 43%. Furthermore, under wet and immersed conditions, mixing CW and OPC with soil raised UCS by approximately 182% and 20 times, respectively. This study demonstrated that by enhancing the geotechnical properties of soil, CW and OPC combined with it could be used as a road sub-base layer material.

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.

Experimental study on preparation of solidified soil from residue of construction waste

This study investigates the stabilization effect of a new soil stabilizer based on mineral powder, lime powder, dihydrate gypsum, and sodium hydroxide on the residue of construction waste (RCW). The performance of the residue solidified soil (RSS) with different ratios of stabilizer was analyzed both macroscopically and microscopically, in air and water environments.The experiment indicates that the optimal composition of the new stabilizer for specimen a7 consists of 85 % mineral powder, 3 % sodium hydroxide, and 12 % dihydrate gypsum. The water stability coefficients of specimens a3-a10 are all greater than 80 %.The performance of RSS meets the requirements of the Technical standard for application of soil stabilizer (CJJ/T286- 2018) and the technical specificatiopn for application of road solidified soil (T/CECS 737–2020). Therefore, the RSS designed and prepared in this study is a material with sufficient strength that can be used for urban road subbase layers. From a microscopic perspective, the generation of a large amount of ettringite crystals and C-S-H gel is the main reason for the increase in compressive strength of stabilized soil as it ages.The cost benefit analysis of the RSS that meets the strength requirements is carried out. The performance and cost of the RSS is also compared with the ones solidified by Portland cement and sulphoaluminate cement. From the economic point of view, most of the raw materials of the new soil stabilizer are cheap and easy to obtain, and the cost of the new soil stabilizer is much lower than that of Portland cement and sulphoaluminate cement, therefore the RSS should have strong market competitiveness.

Geotechnical Assessment of Selected Lateritic Soils in Southwest Nigeria for Road Construction and Development of Artificial Neural Network Mathematical Based Model for Prediction of the California Bearing Ratio

Investigation of the geotechnical characteristics of eighteen different lateritic soils within southwest Nigeria was carried out to determine their suitability for road construction. To achieve this goal, the lateritic soils samples were subjected to different laboratory tests, including specific gravity, Atterberg limits, grain size analysis, California bearing ratio, and compaction, in accordance with the ASTM standard procedure. The results of the tests showed that the specific gravity varied between 2.55 and 2.81; the linear shrinkage varied between 6.68% and 10.98%; the liquid limit varied between 37.17% and 56.93%; the plastic limit ranged from 19.47% to 37.14%; the plasticity index ranged from 3.81% to 30.29%; the fine sand content ranged from 37.07% to 62..93%; the fines content ranged from 36.4% to 60.9%; the maximum dry density ranged from 1747 kg/m3 to 2056 kg/m3 ; the optimum moisture content ranges from 10.94% to 20.51%; the un-soaked California bearing ratio ranged from 14.7% to 45.6%; and the soaked California bearing ratio ranged from 10% to 31%. Based on these results, all the studied soils can be used as road subgrade, while none except Loc.5/S1 is suitable for road subbase. However, none of the soils meets up with the requirement for road base course. The suitability of laterite for the construction of road depends largely on the California bearing ratio. However, laboratory tests for determining the California bearing ratio is tedious, time consuming and costly. As a result of this difficulty, there is a need to develop soft computing models to predict laterite California bearing ratio from index properties with cheap and simple tests. Thus, the experimental datasets of the eighteen studied lateritic soils were used to create and train artificial neural network (ANN) models to predict California bearing ratio from liquid limits, plasticity index, linear shrinkage, fine sand content and fines content. The proposed ANN models were compared with the multiple linear regression models proposed in this study and various regression based models suggested in the literature via statistical analyses. Based on the model comparison, the proposed ANN models outperformed the rest of the models; they presented the highest R 2 and the lowest RMSE, MAPE and MAE values. Thus, the ANN models are validated. To enhance the practical application of the proposed ANN models, they were transformed into simple mathematical equations, which gave the same predictions as the direct ANN models. Thus, they can be used for practical purposes.

Study of Utilizing Wawonii River Materials as an Alternative Aggregate for Road Subbase

Makalahini menampilkan hasil uji karakteristik material Sungai Bobolio yang berpotensi dimanfaatansebagai alternatif agregat pada Lapis Fondasi jalan. Pengujian karakteristikdilakukan meliputi analisa saringan, pengujian berat jenis dan penyerapan agregat kasar dan halus, pengujian abrasi serta pengujian pemadatan dan CBR Laboratorium.Hasil pengujian berat jenis dan penyerapan agregat kasar dan halus diperoleh berat jenis agregat kasaradalah 2,65 gram/cm3(2,4-2,8 gram/cm3)dan penyerapan 3,31%(maksimal 5%). Adapunberat jenis agregat halus adalah2,51 gram/cm3(1,6-3,2 gram/cm3) dan penyerapan0.42%(maksimal 2%).Pengujian abrasi mendapatkannilai keausan23 %(0-40%). Nilai CBR pada 95 % nilai kepadatan maksimum adalah 20,50 %(min 50%). Hasil pengujian karakteristik menunjukkan seluruhparametermemenuhi spesifikasiBina Marga 2018kecuali nilai CBR. Meskipun nilai CBR tidak memenuhi spesifikasi, material Sungai Bobolio dengan nilai keausan yang baik dapat dicampur dengan material yang berasal dari sumber lain untuk memenuhi nilai CBR yang dipersyaratakan

Selective crushing, enrichment by friction properties and hydrophobization for obtaining the sustainable blast furnace slag aggregate for road subbase

Air-cooled blast furnace slag is a metallurgical waste that can be used to produce the slag aggregate for pavement subbase. Slag aggregate is much cheaper than natural stone aggregate, but differs in heterogeneity in strength (from 2 to 40 MPa), tendency to absorb water, and low resistance to freezing-thawing. The paper suggests the use of methods of enrichment by friction properties, selective crushing, and hydrophobization to increase slag aggregate resistance to freezing-thawing cycles, crushing, and water penetration. Selection of the most strength (low porous) 75 % slag aggregate grains due to enrichment by friction properties decreases the total water absorption of the sample from 4.45 % to 3.64 %, decreases the sample mass loss after tests for resistance to freezing-thawing cycles from 5.05 % to 2.82 %, reduces the aggregate crushing value (ACV) from 30.71 % up to 23.80 %. Hydrophobization of the pre-enriched slag aggregate additionally reduces its water absorption to 1.08–––1.3 %.

Properties of road subbase materials manufactured with geopolymer solidified waste drilling mud

In this study, geopolymer was adopted as an eco-friendly binding material to solidify waste drilling mud to fabricate geopolymer solidified waste drilling mud (GSWDM) as a pavement material in the subbase. Using precursor dosage, Na2SiO3 solution dosage, and slag powder (SP) dosage as parameters of mix proportion, the optimal mix proportions of GSWDM were determined through compressive strength tests. Based on a series of tests of unconfined compressive strength, splitting tensile strength, elastic modulus, and compressive resilient modulus, the effects of the SP percentage in the precursor and curing age on the mechanical properties of GSWDM were analyzed. The results indicated that all the mechanical properties of GSWDM were improved with the increasing SP percentage in the precursor. The 28-day unconfined compressive strength, splitting tensile strength, elastic modulus, and compressive resilient modulus of GSWDM were improved by 80.8%, 56.3%, 65.3%, and 76.72%, respectively, when the SP percentage in the precursor increased from 60% to 100%. A nonlinear increase in the mechanical properties of GSWDM was observed as the curing age increased, with a significant increase in the curing age from 7 days to 14 days and a slight increase in the curing age from 14 days to 28 days. Moreover, the microstructure of GSWDM was denser as the curing age and the SP percentage in the precursor grew. The results of this study verified that GSWDM can be used as construction material for road subbase.

Analysis of Kinang Jingkion Material as Road Subbase Layer Using Soil Cement Method

This research aims to analyze the California Bearing Ratio (CBR) and Unconfined Compressive Strength Test (UCS) values as road foundation layers using local materials, namely Kinang Jingkion. The soil and Kinang Jingkion materials for the study were taken from the Apalapsili quarry in Yalimo Regency. Additionally, the additive or soil stabilizer used was matos obtained from the testing of soil characteristics, including sieve analysis or gradation, Standard Proctor Test for light density, and liquid limit test. After testing, it was found that the soil from the Apalapsili quarry is granular soil and can be categorized as A-1-a according to SNI 03-6797-2002. Subsequent testing involved CBR and UCS testing on Mix Designs made of soil and cement with concentrations of 4%, 6%, and 8%. Next, additional Mix Designs were created with compositions of Kinang Jingkion, soil, cement at 4%, 6%, and 8%. Further Mix Designs included compositions of Kinang Jingkion, soil, matos at 2%, and cement at 4%, 6%, and 8%. From the UCS testing results, Mix Designs with soil and cement concentrations of 4% and 6% did not meet the compressive strength criteria, with compressive strength values of 9.26 Kg/Cm² and 17.4 Kg/Cm² respectively. According to SNI 6887-2012, the compressive strength value after 7 days of immersion should be within 25-35 Kg/Cm², while other Mix Designs met the criteria of SNI 6887-2012. CBR testing also utilized the same Mix Designs, and the highest CBR result was obtained from the Mix Design with compositions of Kinang Jingkion, soil, cement at 8%, and matos at 2%, with a CBR value of 112%. According to the 2018 Revised General Specifications, a CBR value of 112% indicates a Class A Foundation Layer.

Long-Term Strength and Durability of Cement-Treated Coal Mine Overburden Materials in Subbase and Base Layers of Low-Volume Roads

Long-Term Strength and Durability of Cement-Treated Coal Mine Overburden Materials in Subbase and Base Layers of Low-Volume Roads

Performance evaluation of recycled concrete aggregates with geosynthetics as an alternative subbase course material in pavement construction

This study investigates the feasibility of using recycled concrete aggregates (RCA) as subbase materials in roads through laboratory experiments. Various physical tests were conducted on the soil subgrade and RCA subbase, followed by cyclic plate load tests to assess the impact of geosynthetic reinforcement on the bearing capacity of RCA materials. The ultimate bearing capacities of different RCA configurations ranged from 186 to 480 kPa, similar to previous studies on natural and recycled aggregates. The geocell-reinforced section exhibited excellent performance, with a measured ultimate bearing capacity of 480 kPa. The Geocell-Geogrid and Geocell-Geotextile sections showed the highest bearing capacity ratios at 2.58 each, indicating superior performance. Reinforced RCA infills demonstrated improved settlement values under repeated loading, with the geocell-geogrid section effectively reducing permanent settlement. The study concludes that RCA can be a substitute for natural aggregates in road subbase materials, mitigating the environmental impact of construction and demolition waste.

Sustainable utilization of landfill mined soil like fraction in subbase layer for asphalt road applications

The scarcity of natural resources, and energy demand/carbon footprints related to their processing and transportation, has led to the quest for alternate materials for road/pavement construction and other infrastructure development. On the other side, landfill mined soil like fraction (LMSF) forms significant proportion of mined legacy landfill waste that exists at different locations around the world; however, it has found limited applications. The present study explores the utilization of LMSF in development of novel asphalt road subbase layers for resilient road infrastructure. 30–60% of LMSF replacement has been studied, and findings based on gradation analysis, compaction tests and California bearing ratio (CBR) tests are quite encouraging. Most combinations of subbase layers studied exceed the design requirements for low volume roads in Indian scenario (rural and outer urban roads); while 30% LMSF in wet mix macadam satisfies the requirements of Indian and other international codes. The cost-benefit analysis shows significant saving in material cost due to utilization of LMSF in road subbase layer. The potential utilization of low cost and sustainable LMSF in asphalt road subbase layer would allow design of superior roads with CBR exceeding design values, resulting in better life cycle performance of road infrastructure with high resilience to fatigue effects, water inundation and overloading conditions.

Exploring mechanical and microstructural properties of cement-stabilized coal mine overburden materials

The present research explores the suitability of coal mine overburden (OB) material, as secondary aggregate in the sub-base and/or base layer of low-volume roads. As low-volume roads are expected to have less traffic than other types of roads, weak materials like coal mine OB may effectively be utilised in different layers of the road after stabilisation with cement. In that direction, various strength parameters, namely unconfined compressive strength, flexural strength, flexural modulus, and indirect tensile strength have been evaluated after seven days and 28 days of curing on stabilised samples collected from five different mines in Jharkhand. Subsequently, the results have been validated through the non-destructive test and microstructural analysis. Moreover, correlations have also been established between compressive strength, flexural properties, and tensile properties of cement-treated OB (CTOB) samples, which will be beneficial for field engineers to estimate flexural and tensile properties of CTOB mixes from known compressive strength values.

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.

Recycle of discarded masks in civil Engineering: Current status and future opportunities with silane coupling agent modified discarded masks

In recent years, with the heightened of public health protection awareness, masks have become an important protective equipment. The accumulation of discarded masks (DM) poses an impact to environment and resource. Recycling DM has become a prime focus of sustainable development research. This investigation introduces a review of the recycling of DM in civil engineering and presents a novel modification of discarded mask fibers (DMF) to enhance the mechanical property of cement paste. In the review section: (1) The masks are divided into three classes by integrating relevant standards and considering mask protective characteristics; (2) Various disposal techniques for recycling DM are categorized in shredding, hot processing, paper shredding, and crushing; (3) The impact of incorporating DMF in concrete, mortar, asphalt, road subbases and base courses are discussed. The enhancement of applying DMF into composite materials varies depending on the specific application. In the experimental research section, the silane coupling agent (SCA) is introduced as a modification to improve the weak bonding between DMF and composite materials. The SCA-modified polypropylene (PP) fibers were conducted as a control group. The results indicate that the compressive strength of cement paste with both SCA-modified DMF and PP fibers increased by 12.29 % and 26.10 %, respectively. Finally, several future opportunities in recycling of DM in Civil Engineering were drawn.