Pavement Base Material Research Articles

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.

Cement-Stabilized Phosphogypsum Synergistized with Curing Agent as Sustainable Pavement Base Materials

Cement-Stabilized Phosphogypsum Synergistized with Curing Agent as Sustainable Pavement Base Materials

Study on synthesis and water stability of geopolymer pavement base material using waste sludge

Waste sludge is a typical solid waste generated during construction excavation, which needs innocuity treatment and resource utilization. The development of geopolymer pavement base material using waste sludge is an economic and environmental method to realize the utilization of waste sludge. This manuscript aims to develop a geopolymer pavement base material using waste sludge and further evaluate its water stability under water soaking environment. The geopolymer specimens with different slag and waste sludge contents were prepared. The optimum mix proportion of geopolymer was determined by analyzing the effect of slag content on the ultimate compressive strength (UCS) and elastic modulus. The CO2 emissions and energy consumption of geopolymer was analyzed. The water stability of the geopolymer was further evaluated by analyzing the effects of soaking time on the density, wave velocity, mechanical properties and pore structure. The results show that the geopolymer with 50% slag content has the largest UCS and excellent strength development characteristics. The UCS of geopolymer pavement base material reaches 48.4 MPa and the CO2 emissions and energy consumption were reduced by 58.34% and 88.16% compared to C40 ordinary concrete. The results also show that the density, longitudinal wave velocity and porosity remain stable as soaking time increases. During the soaking process, the proportion of gel pores and transition pores decreases, while the proportion of capillary pores and air pores increases. The UCS of geopolymer pavement base material remains above 40 MPa after soaking for 90 days, showing excellent water stability. The geopolymer pavement base material has the potential application prospect in road engineering and emission reduction, which provides a feasible and cost-effective method for the utilization of waste sludge.

Preparation of pavement base material by using steel slag powder and steel slag aggregate

Preparation of pavement base material by using steel slag powder and steel slag aggregate

Evaluation of asphaltenes a potential alternative for cement in stabilized base courses using asphalt emulsion

Stabilization of pavement base material using asphalt emulsion has been widely used to improve pavement performance. This technology produces a high-quality base course material with decreased energy consumption, carbon footprint, and raw material usage. Cement has been used as a common additive to improve these mixes strength and moisture resistance. However, some drawbacks are also associated with cement, such as negative environmental impacts, high costs, and low-temperature deficiencies. Asphaltenes is a by-product of oil-sand bitumen with little commercial value in current practice. To investigate the impact of asphaltenes on improving the rheological properties of asphalt binder, a series of binder characteristics tests using a dynamic shear rheometer, breaking time and microscopic evaluation is conducted on modified asphalt emulsion with asphaltenes. Asphaltenes is then added to asphalt emulsion-stabilized granular material, to be compared with mixtures prepared with cement. Two asphaltenes and cement-modified mixes are prepared and compared to unmodified mixtures. All mixes are tested for permanent deformation and moisture sensitivity using a Hamburg wheel tracker and flow number test, while the low-temperature properties are evaluated using indirect tensile strength tests. Dynamic modulus is also evaluated to analyze the viscoelastic behavior of the mixes. The results of this study reveal a considerable increase in the rutting resistance of asphalt mixes by adding 1% of both additives (by total weight of mix), and asphaltenes-modification shows less adverse impacts at intermediate and low temperatures than cement-modification.

Research on macro-microscopic mechanical evolution mechanism of cement-stabilized steel slag

In this paper, the chemical composition, phase composition, physical properties and expansibility of steel slag in Xinjiang, China are analyzed, and the feasibility of steel slag as pavement base material is demonstrated. At the same time, through the tests of unconfined compressive strength, X-ray diffraction, scanning electron microscope and nuclear magnetic resonance, the relationship between macroscopic strength and microstructure of cement-stabilized steel slag at different ages is discussed and compared with that of cement-stabilized macadam. The results show that the mechanical properties of steel slag aged more than one year can fully meet the requirements of relevant specifications for all kinds of pavement base. Compared with cement-stabilized macadam, the compressive strength of cement-stabilized steel slag at the age of 7 d, 14 d and 28 d increased by 15.4%, 22.0% and 23.7%, respectively. Due to hydration and pozzolanic action, the C–S–H content in the interfacial transition zone of cement-stabilized steel slag is higher, while the contents of Ca(OH)2 and AFt are lower. Due to the internal curing effect of steel slag, the interfacial transition zone width of cement-stabilized steel slag at the age of 7 d and 28 d decreased by 9.4% and 31.0% respectively compared with cement-stabilized macadam; with the increase of curing time, the adsorption porosity of cement-stabilized steel slag increased, while the amount of seepage pore and migration pore decreased significantly, and the pore span and total porosity decreased by 47.7% and 7.29%, respectively.

Experimental study on the interface bonding characteristic of polyurethane and pavement materials

As a new grouting material, polyurethane has been used in the repair engineering of longitudinal joint distress of semi-rigid base asphalt pavement. It is necessary to study the bonding characteristics of the interface between polyurethane and road materials. In this paper, the interface characteristics of composite materials were considered from the two materials about pavement material and base material. Shear test and split tensile test were carried out on the specimens with different interface roughness and polyurethane density. Based on the test data, the strength models of shear strength and splitting tensile strength with roughness and density were established. The micro-characteristics of the composite interface were analyzed. Polyurethane formed a dense film at the interface, and the film thickness increases with the increase of density. The failure mode of the specimen was affected by the polyurethane film. In addition, the influence of normal stress is considered in the shear test, and the friction angle of the interface was analyzed. The stress-strain curve characteristics of shear test and split tensile test of two kinds of composite materials were summarized. The failure modes were generally three types: failure along the boundary of polyurethane material, failure along the boundary of base material, and joint failure of polyurethane material and base material along the interface. The research results provide a basis for better understanding the influencing factors and failure modes of the bonding characteristic between asphalt mixture, cement stabilized macadam and polyurethane materials.

Effect of wetting and drying cycles on mechanical strength of cement-natural rubber latex stabilized recycled concrete aggregate

In this study, natural rubber latex (NRL) was used as a polymer additive to modify the durability against wetting and drying (w-d) cycles of the cement-stabilized recycled concrete aggregate (RCA) when used as a pavement base/subbase material. This research investigated the performance of cement-stabilized RCA and cement-NRL stabilized RCA at various dry rubber-to-cement (r/c) ratios against w-d cycles. The weight loss, unconfined compressive strength (UCS), rate of deterioration, modulus of elasticity, and microstructural analysis of the studied samples before and after being subjected to w-d cycles were performed. The r/c ratio of 10% was found to be the optimum r/c ratio for cement-NRL stabilized RCA, which provided the best performance for all test results. The weight loss was found to increase, while the UCS value subsequently decreased with an increase of w-d cycles for all studied samples. At the optimum r/c ratio, the UCS results of cement-NRL stabilized after 12 w-d cycles were still higher than the minimum requirement (UCS > 2.413 MPa) for a high-volume traffic road. In addition, its modulus of elasticity was higher than that of cement-stabilized RCA samples. This indicated that the NRL additive could enhance the ductility of cement-stabilized RCA. The microstructural analysis illustrated that the formation of a stable cross-linked matrix between the cement hydration products and NRL films could improve the durability against the w-d cycles of cement-stabilized RCA as a pavement base material.

Improved Fatigue Performance and Cost-Effectiveness of Natural Rubber Latex–Modified Cement-Stabilized Pavement Base at Raised Temperatures

The increased temperature at the early state of curing affects the fatigue properties of pavement base materials. The fatigue properties of stabilized pavement bases and subbases govern the performance and service life of pavement structures. This research study utilized natural rubber latex (NRL) to enhance the tensile fatigue properties of cement-stabilized base materials at various temperatures. The effects of influence factors such as cement content (3%, 5%, and 7%), NRL replacement ratio (0%, 10%, 15%, 20%, 25%, and 30%), and temperature (25°C, 40°C, and 60°C) on indirect tensile strength (ITS), indirect tensile resilient modulus (IT Mr), and indirect tensile fatigue life (ITFL) were studied in this research. NRL replacement was found to improve the UCS, ITS, IT Mr, and ITFL of cement (C)-stabilized soil up to the highest values at the optimum NRL replacement ratios, which were 20%, 15%, and 10% for cement contents of 3%, 5%, and 7%, respectively. The cement-NRL (C-NRL)-stabilized samples were found to have superior ITS, IT Mr, and ITFL values compared with C-stabilized samples for the same cement content but had the same rate of reduction in ITS due to the raised temperature. For the NRL replacement ratio on the dry side of optimum, the C-NRL-stabilized samples had lower rate of IT Mr reduction than the C-stabilized samples, although they had the same ITS due to the higher toughness. Therefore, the rate of ITFL reduction of C-NRL-stabilized samples was lower than that of the C-stabilized samples. It was proven in this research that the NRL replacement could reduce the thickness (superior IT Mr) of a cement-NRL-stabilized base course for a given traffic volume and service life, and therefore the construction (material and operation) cost by 17.26% benchmarked to a C-stabilized base course. Finally, the cost-effective design method for C-NRL-stabilized bases course was proposed, which will promote the use of NRL as an alternative green additive instead of synthetic polymer.

The Study on the Performance of Regeneration Aggregate Pavement Base Material Under Standard Grading Median

In recent decades, with social and economic development, many new buildings and buildings have been built, while many old buildings have been demolished. Therefore, the world should consider how to reuse construction waste. Reuse of construction waste as aggregate to new buildings or road construction is an effective way. The effect of median aggregate regeneration aggregate on the performance of pavement base material was studied in this paper. Recycled concrete aggregate was used to replace 25 %, 50 % and 75 % of natural aggregate by volume, respectively. While the recycled clay brick was used to replace 5 %, 10 %, 15 % and 30 % of natural aggregate by volume. In addition, recycled aggregate composed of recycled concrete and recycled clay bricks in different proportions was used to replace aggregate of road base materials. The maximum dry density, optimum moisture content, unconfined compressive strength and drying shrinkage of road base materials were studied. The results show that the optimum moisture content increases with the increase of recycled aggregate replacement, and the biggest dry density decreases with the increase of recycled aggregate replacement. Recycled aggregate can improve the 7 d unconfined compressive strength of pavement base material and reduce the dry shrinkage rate in a certain range of replacement rate. When the aggregate was 100 % recycled aggregate, with the increase of recycled clay brick content, the 7d unconfined compressive strength of the material decreases and the drying shrinkage would increase.

Laboratory tests, field application and carbon footprint assessment of cement-stabilized pure coal solid wastes as pavement base materials

Solid wastes from coal industry, such as coal gangue (CG), coal bottom ash (CBA) and fly ash (FA) from coal-fired power plants, pose a significant impact on the environment. Thus, it is essential to fully study the potential values of these coal solid wastes (CSW) as construction materials. In this study, cement-stabilized FA, CBA and CG were performed as pavement base materials, and the mechanical properties and environmental benefits were systematically investigated in order to achieve the utilization of CSW in road construction. The unconfined compressive strength (UCS) test, splitting tensile strength (STS) test, ultrasonic test, triaxial test, and field application were conducted. The results show that CBA exhibits a negative effect on the early strength of the mixtures. However, the negative effect gradually decreases with the extension of the curing age. In addition, the relationship models between UCS and STS, between UCS and amplitude, between peak stress, peak strain and confining pressure with different CBARR and cement content were proposed. Based on the Mohr-Coulomb (M-C) failure criterion, the unified function expression and parameter-related function expressions with various CBARR and cement content of the shear stress τ were established. The laboratory tests indicate that the mixture with CBARR of 50% exhibits preferable mechanical performance. Field application and carbon footprint assessment verify that the mixture has great potential to be used as a new eco-friendly pavement base material and meets the technical requirements for heavy traffic of class II highways in China.

Partially replacing cement with rice husk ash (RHA) in cement stabilised macadam (CSM) containing reclaimed asphalt pavement (RAP) for qualified base materials

High silicon dioxide content enables as a cement substitute. This study explored recycling RHA and RAP in cement stabilised macadam (CSM) to produce a pavement base material. Laboratory experiments covering strength, flexibility, shrinkage, and resistance to temperature variation were conducted on CSM with RAP (40% by weight of natural aggregates) and RHA at 0%, 20%, 40%, 60%, and 80% weight of cement. The results indicated that the compressive strength, resilient modulus, and tensile strength of CSM increased with curing time while the increasing rate and strength after curing decreased with the addition of RHA. The resistance to thermal changes, moisture loss, and the freeze-thaw cycle could be maintained by replacing 20 wt.% (or lower content) cement with RHA. These findings suggest that replacing 20 wt.% of cement with RHA and 40 wt.% of natural aggregates with RAP can generate qualified and environmental pavement base material.

Stabilization of Recycled Concrete Aggregate Using High Calcium Fly Ash Geopolymer as Pavement Base Material

This research investigated high calcium fly ash geopolymer stabilized recycled concrete aggregate (RCA-FAG) as pavement base material. The effect of recycled concrete aggregate (RCA):high calcium fly ash (FA) ratios, sodium silicate (Na2SiO3):sodium hydroxide (NaOH) ratio, and curing time on the unconfined compressive strength (UCS) and scanning electron microscope (SEM) properties of RCA-FAG samples were evaluated. The maximum dry unit weight of the RCA-FAG sample was 20.73 kN/m3 at RCA:FA ratio of 80:20 and Na2SiO3:NaOH ratio of 60:40. The 7-d UCS of RCA-FAG samples increased as the FA content and Na2SiO3:NaOH ratio increased. The 7-d UCS of the RCA-FAG sample was better than that of the RCA with no FA because FA particles filled in RCA particles, resulting in a dense matrix. The 7-d UCS of RCA-FAG samples passed the 7-d UCS requirement for the low-traffic road. All ingredients met the 7-d UCS requirement for the high-traffic road except the sample with RCA:FA of 100:0 and Na2SiO3:NaOH of 50:50 and 60:40. The 7-d SEM images indicated that spherical FA and RCA particles are bonded together, resulting in the dense matrix for all Na2SiO3:NaOH ratios. The proposed equation for predicting the UCS of RCA-FAG offered a good coefficient of correlation, which is useful in designing pavement base material from RCA-FAG material.

Application of Iron Tailing Sand in Pavement Base

Iron tailings are solid wastes produced after iron ore is refined. Based on the analysis of the development of road engineering in our country, the application status of iron tailings sand in road engineering in recent years is summarized. The optimal moisture content, maximum dry density and compressive strength of iron tailings cement stable macadam are evaluated by using the compaction test and unconfined compressive test. The results show that UNDER the condition OF a certain amount of cement and the content of iron tailing sand is 10%-20%, iron tailing sand can be used as semi-rigid pavement base material in road engineering construction. Finally, the author puts forward his own views on the future research direction.

Analysis of Shear Resistance and Mechanism of Construction and Demolition Waste Improved by Polyurethane

A large amount of construction and demolition waste (CDW) is generated during the construction of projects. In this paper, polyurethane foam adhesive (PFA) was used to improve the mechanical properties of CDW. The large-scale direct shear tests, California bearing ratio (CBR) tests and Scanning electron microscope (SEM) tests were carried out to study the variation regularities of mechanical properties of treated CDW during the laboratory tests. The test results show that the shear strength of CDW increases with the increase of PFA content, vertical pressure and the shear rate. However, the increase of vertical pressure on the shear strength of CDW is smaller than that of PFA, and the improvement of the shear rate is relatively small. The California bearing ratio (CBR) test also proves that PFA can effectively improve the bearing capacity of CDW and reduce the loss of CBR caused by the 4-day soaking. Scanning Electron Microscope (SEM) finds that polyurethane wraps multiple particles and enhances the internal connection, which results in the cohesion between the particles being greatly increased. The study presented in this paper will better assess the shear resistance of improved CDW with PFA as a substitute for pavement base materials in practical engineering applications.

Use of coal ash cement stabilized material as pavement base material: Laboratory characterization and field evaluation

Coal fly ash (CFA) and coal bottom ash (CBA) are coal combustion's primary solid waste products. This solid waste management is a substantial challenge for power plants and local authorities. In order to apply coal ash as a pavement base material, the relationship of the mixture’s mechanical properties with structural design parameters for pavement design and analysis must be explored. No study has investigated the mechanical behavior of the 100% coal ash cement stabilized material (CACSM) as a pavement base layer. Therefore, this study aimed to investigate the structural layer coefficient of CACSM used in the American Association of State Highway and Transportation Officials (AASHTO) 1993 pavement design guide. The study consisted of laboratory material characterization and field evaluation. The mechanical property test revealed that CACSM has a self-healing ability; coal ash appeared to influence the secondary curing of the specimens significantly. Strength towards the ends of stage I and stage II showed the influence of high pozzolanic on the CACSM, which resulted in improved long-term performance. The layer coefficients of the locations in the field test ranged from 0.22 to 0.24. By contrast, for the granular base and cement-treated base, these values were 0.07 to 0.14 and 0.17–0.20, respectively. The study findings show that CACSM as a pavement base is a viable solution that can help develop transportation infrastructure with enhanced concrete durability and lower carbon footprint emissions.

Cement – natural rubber latex stabilised recycled concrete aggregate as a pavement base material

This research investigated the influence of natural rubber latex (NRL) on the performance of cement stabilised recycled concrete aggregate (RCA) as a pavement base material. The influence factors studied included different cement at contents and dry rubber to cement (r/c) ratios. The NRL replacement enhanced the unconfined compressive strength (UCS) and indirect tensile strength (ITS) of cement stabilised RCA. The highest UCS and ITS of cement-NRL stabilised RCA were found at the optimum r/c ratios. Beyond these optimum r/c ratios, the UCS and ITC values decreased although all UCS values were still greater than the minimum requirement for base material. Microstructural analyses indicated the detected cement hydration products and NRL films, which NRL films were found to improve the adhesion and interparticle bonds of RCA particles. However, the excessive NRL additive retarded the cement hydration, whereby the UCS and ITS development was low when the r/c was greater than the optimum value.

Gradation Design of Phosphorus Tailing–Graded Waste Rock Subgrade Filling Using Discrete Element Method

The method of using silt phosphorus tailing instead of traditional sand and filler as subgrade filling has been suggested to greatly improve the comprehensive utilization of solid waste phosphorus tailing. A suitable combination of phosphorus tailing and graded waste rock can be adopted to improve the stability of the structure of filling, which can then improve the soil properties of phosphorus tailing and prevent the formation of quicksand and landslides. In this research, a discrete element model was established by combining a graded mixing method and the concept of equivalent particle size, and the discontinuous gradation design of a phosphorus tailing–graded waste rock mixture was carried out. Using the filling coefficient, different structural types of mixture composition were verified, and the California Bearing Ratio was used to test and analyze the specimens with different mixtures, grading, and structural type. The results show that the porosity of the main skeleton calculated with the model established using the discrete element software Particle Flow Code and the porosity obtained with the tamping test fit well, with the minimum porosity of the optimal main skeleton coarse aggregate being 30.44%. At the same time, by analyzing the effect of filling the porosity of graded waste rock with different mass fractions of phosphorus tailing and by determining the California Bearing Ratio of the corresponding filling structure, it was shown that the skeleton-dense structure with the best gradation of the mixture displayed better road performance and that the phosphorus tailing–graded waste rock system with improved performance can be used as subgrade filling or in the preparation of pavement base material.

Characterisation of road base materials treated by hybrid alkali-activated binders and cationic asphalt emulsions

ABSTRACT Using suitable chemically stabilized materials to solve the moisture-related damages on the road pavement is still essential. This study investigated the influence of cationic asphalt emulsion (CAE) on a hybrid alkali-activated binder (HAB) consisting of fly ash, hydrated lime, and solid sodium hydroxide for the chemically stabilized road base material. Adding CAE to HAB would introduce the water-repellent and elastic properties of HAB. Crushed rock (CR) treated with HAB binder prepared with two concentrations of CAE (HAB-CAEs) was characterized using a test series of compaction, unconfined compressive strength, resilient modulus, and water absorption. The compaction test results showed that CAE could decrease the optimum water content and air voids at the maximum dry density. Using CAE increased the strength of the HAB-CAE-treated CR, resulting in a sufficient compressive strength of the flexible pavement base. In addition, the HAB-CAE-treated CR had a proficient energy absorption under a static loading condition. The addition of CAE to the HAB-treated CR also provided resilient modulus and stiffness values higher than those of the conventional cement-treated base material with less water absorption. Therefore, HAB-CAE could be a viable option as a sustainable pavement base material.

Experimental Study on Subgrade Material of Calcium Silicate Slag

Calcium silicate slag (CSS) is used as a secondary solid waste produced by aluminum extraction technology from high alumina fly ash, and its resource utilization has always been a key issue to be solved. In this study, CSS was used to replace a portion of fly ash (FA) to prepare a new inorganic binder stabilized material for road base. The unconfined compressive strength (UCS), phase composition, microstructure, durability and performance index of the base of the test section of the CSS pavement base material were studied. The results showed that with the increase in CSS content, the UCS of pavement base materials gradually increased. Under standard curing conditions, the UCS increased 6.90~17.24% after 7 days, and 7.90~28.95% after 28 days. The main reason was that as the hydration time increased from 7 d to 28 d, the hydration products C-A-S-H gel and C-S-H gel increased, the [SiO4] polymerization degree increased, the crystal type changed, and the structure denser, which supported the good development of mechanical strength of CSS pavement base material. In addition, the research has been successfully applied to a pilot test in Hohhot, China. The freeze–thaw resistance, water stability and UCS of the CSS pavement base material were tested to meet the requirements of Chinese road construction standards, indicating that the application of CSS in pavement base is feasible.