Pavement Base Material Research Articles

Strength and Microstructural Study of Recycled Asphalt Pavement: Slag Geopolymer as a Pavement Base Material

AbstractThe integrated transdisciplinary concepts and technologies for greener and more sustainable innovations for recycling waste materials through geopolymer technique into construction material...

The Performance of Controlled Low-strength Material Base Supporting a High-volume Asphalt Pavement

A lack of proper base and subbase materials in pavement construction is one of the common problems in the tropical region worldwide. In many countries such as Thailand, cementitious materials are usually used for ground improvement. Controlled Lowstrength Material (CLSM) was considered in this study as a pavement base material. The CLSM mixes were prepared by varying cement, fly ash and fine aggregate content. Each mixed component was studied for their physical and chemical properties. After mixing, properties of the CLSM were investigated based on the standard testing of fresh concrete and cement-treated base material. The flowability, setting time and bleeding were checked to ensure that the CLSM were self-compacting. The mechanical properties of hardened CLSM were determined by means of CBR, unconfined compressive strength and resilient modulus tests. The resilient modulus results were used in the analytical design of flexible pavement with CLSM base. The critical traffic data under high-volume road collected by the Thailand Department of Highway was adopted in this study. Results show that the CLSM base considerably increased the performance as well as design life of asphalt pavement compared with the conventional crush rock base pavement.

High calcium fly ash geopolymer stabilized lateritic soil and granulated blast furnace slag blends as a pavement base material

Granulated Blast Furnace Slag (GBFS) was used as a replacement material in marginal lateritic soil (LS) while class C Fly Ash (FA) was used as a precursor for the geopolymerization process to develop a low-carbon pavement base material at ambient temperature. Unconfined Compression Strength (UCS) tests were performed to investigate the strength development of geopolymer stabilized LS/GBFS blends. Scanning Electron Microscopy and X-ray Diffraction analysis were undertaken to examine the role of the various influencing factors on UCS development. The influencing factors studied included GBFS content, Na2SiO3:NaOH ratio (NS:NH) and curing time. The 7-day soaked UCS of FA geopolymer stabilized LS/GBFS blends at various NS:NH ratios tested was found to satisfy the specifications of the Thailand national road authorities. The GBFS replacement was found to be insignificant for the improvement of the UCS of FA geopolymer stabilized LS/GBFS blends at low NS:NH ratio of 50:50. Microstructural analysis indicated the coexistence of Calcium Silicate Hydrate (CSH) and Sodium Alumino Silicate Hydrate products in FA geopolymer stabilized LS/GBFS blends. This research enables GBFS, which is traditionally considered as a waste material, to be used as a replacement and partially reactive material in FA geopolymer pavement applications.

A new approach for determining resilient moduli of marginal pavement base materials using the staged repeated load CBR test method

The selection of marginal materials to construct workable and durable pavement base materials requires an understanding of their resilient moduli properties. Empirical formulations have been developed previously based on quality quarried material with known performance-based behaviour. However, in recent years, there has been an increasing demand to use locally available marginal materials, which do not necessarily meet road authority specification requirements; hence it is imperative to evaluate the performance of these non-standard materials. In this study, the geotechnical properties of two marginal materials, namely limestone (Ls) and sandstone (Ss), were evaluated and compared with a high-quality rhyolite (Rh) crushed rock. In order to improve the performance of the marginal materials, each of Ls and Ss was blended with 20% Rh and 50% Rh. The geotechnical properties of individual and blended materials which were investigated included: particle size distribution, particle density, Atterberg limits, Los Angeles value, modified compaction test, California bearing ratio (CBR) and repeated load triaxial test. A novel test method termed repeated load CBR (RL-CBR) was used to investigate the performance properties of the individual materials and blends. The RL-CBR test was further developed to study the stress-dependent behaviour of the materials, termed as staged RL-CBR test. An in-depth analysis of the staged RL-CBR test confirmed the capability of this test method to determine the resilient modulus of marginal pavement base materials.

Re-cementation of Recycled Concrete Aggregate in Pavement Base or Sub-base

Recycled concrete aggregate (RCA) is often used as a pavement base or sub-base material. One unique concern of RCA used for such purposes is re-cementation. Although re-cementation increases the stiffness and bearing capacity of RCA, it may induce cracking if RCA becomes bound or partially bound. Four approaches were used in this study to investigate RCA re-cementation in pavement sub-base, including long-term monitoring of a trial site, test of RCA samples retrieved from the site, performance simulation based on mechanistic-empirical pavement design guide (ME-PDG), and numerical analysis. The trial site reveals that RCA becomes partially bound after 11 years of road use. The bound material exhibits properties similar to those of cement-treated base (CTB). However, due to variations in the content and composition of fines in RCA, the extent of re-cementation is not uniform in sub-base. According to the analysis results generated by ME-PDG, reflective cracking occurs if RCA is assumed to be CTB. Conversely, if bound RCA is non-monolithic, it may not have significantly negative effect on pavement performance. The fine content or composition of fines in RCA may be specified to further reduce the risk of RCA re-cementation.

Potential Applicability of Impact Echo Method on Pavement Base Materials as a Nondestructive Testing Technique

The use of both recycled asphalt pavement and recycled concrete aggregates is increasing considerably in pavement construction. These materials are relatively weak and have to be stabilized with cement or other stabilizers. However, because of product variability and lack of strength and stiffness, their applicability has to be evaluated extensively. Traditionally practiced methods of evaluation might be unreasonable in terms of time, cost, reliability, and applicability. Rapid nondestructive methods, such as the spectral analysis of surface wave, impact echo, pulse velocity, and so forth, have the potential to be inexpensive and less time-consuming, as well as offering low variability of the test results. The objective of the study was to assess the potential applicability of the impact echo method in evaluating recycled pavement base materials. Six combinations (0%–100%, 10%–90%, 30%–70%, 50%–50%, 70%–30%, and 100%–0%) of recycled asphalt pavement and recycled concrete aggregates, respectively, treated by four amounts of portland cement (0%, 2%, 4%, and 6%), were evaluated by impact echo, unconfined compression, and repeated-load triaxial test. From the test results, the range of P-wave velocity was between 5,500 in./s and 18,000 in./s, the compressive strength varied from 10 pounds per square inch (psi) and 415 psi, and the tangent modulus range was from 2.8 kips per square inch (ksi) to 41 ksi. Statistical models based on P-wave velocity data were derived for predicting elastic modulus, compressive strength, and resilient modulus. It was found that impact echo has significant potential in characterizing the strength and stiffness properties of cement-treated recycled base materials, which confirms the effectiveness of recycled materials in pavement applications.

Strength and Stiffness of Stabilized Alluvial Silt under Frost Actions

The Yellow River alluvial silt was stabilized into pavement base materials for cold regions. The stabilizing additives were cement, fly ash, and lime, which were included in a range of combinations and dosages when mixed with the silt. Freeze-thaw cyclic impacts were conducted on the treated samples to assess materials performance of withstanding the frost actions. The tests were conducted on samples cured for 7 days to up to 180 days. Test results show that the cement-fly ash-treated samples outperform the other two stabilization categories with respect to material strength and stiffness developed under both normal and frost conditions. Under the normal conditions, the material unconfined compressive (UC) strength rises to 3.0 MPa on day 28 depending on the cement and fly ash dosage used. If subjected to frost actions, the fly ash inclusions warrant a residual UC strength value of 1.3 MPa and above. The antifrost performance of the cement-fly ash-treated samples is related to thermal buffer capacity of the fly ash particles. Water adsorption and material soundness results agree with the strength and stiffness development. An optimal dosage was 3–6% for the cement and 0.3 for cement to fly ash mass ratio.

Marginal Lateritic Soil Stabilized with Calcium Carbide Residue and Fly Ash Geopolymers as a Sustainable Pavement Base Material

AbstractTwo waste by-products, fly ash (FA) and calcium carbide residue (CCR), are used to develop geopolymer binders for stabilizing marginal lateritic soil as a sustainable pavement base. The liquid alkaline activator is a mixture of sodium silicate solution (Na2SiO3) and sodium hydroxide (NaOH) at a concentration of 10 molars. Unconfined compressive strength (UCS) and scanning electron microscopy (SEM) images of lateritic soil–FA geopolymers at different influential factors (curing times, Na2SiO3∶NaOH ratios, and CCR replacement ratios) are measured. The soaked 7-day UCS of lateritic soil–FA geopolymers meets the strength requirement for both light and heavy traffic pavement specified by the local national authorities. The early 7-day UCS and cementitious products increase with increasing CCR replacement ratio, and the cementitious products are clearly observed at CCR = 30% (the highest CCR replacement ratio tested). However, the CCR replacement ratio providing the maximum 90-day strength is found at 2...

Recycled asphalt pavement – fly ash geopolymers as a sustainable pavement base material: Strength and toxic leaching investigations

In this research, a low-carbon stabilization method was studied using Recycled Asphalt Pavement (RAP) and Fly Ash (FA) geopolymers as a sustainable pavement material. The liquid alkaline activator (L) is a mixture of sodium silicate (Na2SiO3) and sodium hydroxide (NaOH), and high calcium FA is used as a precursor to synthesize the FA-RAP geopolymers. Unconfined Compressive Strength (UCS) of RAP-FA blend and RAP-FA geopolymer are investigated and compared with the requirement of the national road authorities of Thailand. The leachability of the heavy metals is measured by Toxicity Characteristic Leaching Procedure (TCLP) and compared with international standards. The Scanning Electron Microscopy (SEM) analysis of RAP-FA blend indicates the Calcium Aluminate (Silicate) Hydrate (C-A-S-H) formation, which is due to a reaction between the high calcium in RAP and high silica and alumina in FA. The low geopolymerization products (N-A-S-H) of RAP-FA geopolymer at NaOH/Na2SiO3=100:0 are detected at the early 7days of curing, hence its UCS is lower than that of RAP-FA blend. The 28-day UCS of RAP-FA geopolymers at various NaOH/Na2SiO3 ratios are significantly higher than that of the RAP-FA blend, which can be attributed to the development of geopolymerization reactions. With the input of Na2SiO3, the highly soluble silica from Na2SiO3 reacted with leached silica and alumina from FA and RAP and with free calcium from FA and RAP; hence the coexistence of N-A-S-H gel and C-A-S-H products. Therefore, the 7-day UCS values of RAP-FA geopolymers increase with decreasing NaOH/Na2SiO3 ratio. TCLP results demonstrated that there is no environmental risk for both RAP-FA blends and RAP-FA geopolymers in road construction. The geopolymer binder reduces the leaching of heavy metal in RAP-FA mixture. The outcomes from this research will promote the move toward increased applications of recycled materials in a sustainable manner in road construction.

Effect of Soil Drainage on California Bearing Ratio of Soaked Clay

The quality of pavement is affected mostly by the type of subgrade soil, and in many countries, the subgrade soil is clay. The California Bearing Ratio CBR of clay is generally very low which leads to a thicker layer of pavement and sub base materials. This increase in quantities leads to a significant increase in cost. Since the use of the clay as subgrade is inevitable, many private and public institutions searched on a way to increase its CBR, but most of the conducted studies focused on increasing clay CBR by reinforcing the clay either by geogrids or by fibers which are very expensive. One common finding in all the studies was that the CBR of unsoaked clay is higher than CBR of soaked one which means that CBR of clay is affected by its moisture content. In our work, the objective is to increase the CBR of clay by draining it instead of reinforcing it. Drainage can be obtained by adding a layer of granular soil between clay layers. Sand was used as granular soil for the sake of its workability in the CBR mold and for its relatively small particles size. Our aim is to verify if sandy layer can play a drainage role for the clayey soil and to also find the most efficient position of the sandy layer. We collected six soils from different regions to cover as much as possible the different clay types in Lebanon. For each soil, we found CBR values for clay alone and clay with layer of sand and compared them. Identification tests were necessary in order to build our analysis. At the end, from the results and analysis, we found the position of the sandy layer which increases most the clay CBR and we proved that the existence of sandy layer is beneficial for CBR of clay.

Evaluation of geogrid reinforcement effects on unbound granular pavement base courses using loaded wheel tester

Loaded wheel tester (LWT) was employed in this study to investigate the effect of geogrid reinforcement on unbound granular pavement base materials. In the LWT test, the compacted base course specimen was tested under the repeated wheel loading given by the LWT to simulate the actual service situation, and the rut depths of the base specimen were measured along the loading path. Four types of geogrids with different apertures and stiffness were tested with river sand and gravel base courses. In order to verify the effectiveness of the LWT tests, commonly applied cyclic plate loading tests were also performed on the same geogrids and base materials as comparisons. Three technical indices, the Traffic Benefit Ratio (TBR), the Rutting Reduction Ratio (RRR), and the Rate of Deflection (ROD), were employed in the study for the evaluation of the potential benefits of geogrid reinforcement. It was found that the results from LWT tests were generally in agreement with those from the cyclic plate loading tests, which indicates that the LWT test was an effective method to characterize the reinforcement effects of different combinations of geogrids and base courses. The corresponding technical indices proposed in the study were also valid to evaluate the reinforcement effects of geogrids on the specimens with or without geogrid reinforcement. From both LWT and cyclic plate loading tests, the geogrid-reinforced base courses exhibited significant improvement in rutting resistance comparing to the base courses without geogrid reinforcement.

Laboratory investigation of the strength, stiffness, and thermal conductivity of fly ash and lime kiln dust stabilised clay subgrade materials

The effectiveness of Class-C fly ash (FA) (ASTM C-618) and lime kiln dust (LKD) used in clay pavement base materials stabilisation has been investigated in this research. Proctor compaction test, unconfined compression test, and non-destructive test (Briaud compaction device (BCD) modulus and thermal conductivity) were carried out on the chemically modified soil. Test specimens were reconstituted by static compaction, constructed at optimum water content, and tested at various curing periods. Test results revealed that the addition of Class-C FA up to 20 wt% could effectively increase the dry unit weight from 16.8 to 17.4 kN/m3 (105.0 to 108.3 pcf), improve the unconfined compressive strength (UCS, which increased from 181.2 to 497.2 kPa at the end of 28 days of curing), and raise the BCD modulus up to 40 MPa. The LKD was also found to be a good stabiliser for weak soil, which could raise the UCS and stiffness under relatively small mixing rations (4 and 8 wt%), but the dry unit weight decreased as the LKD mixing ratio increased. The thermal conductivity, however, decreased as the curing time and stabiliser mixing ratio increased. Parallel and series models were employed to understand the upper-and-lower bound of the mixtures' thermal conductivity. A thermal strength coupled empirical model which is based on the non-destructive testing results was developed to predict the UCS gain over curing time. The thermal conductivity and BCD modulus were also incorporated into a novel compaction quality check model. Based on the observed test data and regression analysis, both models were found to yield good results, indicating that they are robust tools for predicting the UCS and dry unit weight of chemically treated pavement base materials.

Experimental Study in Gangue Base-Course Mixture Materials for Pavement

Coal gangue, acting as the solid skeleton of pavement base materials, can efficiently reduce the drying shrinkage. Additionally, similar to fly ash in mixture material, gangue can react with lime (so called pozzolanic reaction), resulting in the formation of pavement base with a certain strength, good water stability and frost resistance, are good overall at the grass-roots level. Many cities in our country has gradually tried to use different kinds of industrial waste residue instead of sand to prepare the pavement base materials. This way, not only the waste residue is recycled, the lack of sand aggregates in road construction can also be overcome, which facilitate technical and economic growths.

Resilient Modulus and Permanent Deformation Responses of Geogrid-Reinforced Construction and Demolition Materials

AbstractExtensive amounts of natural quarry aggregates are currently being used in road and pavement applications. The use of construction and demolition (C&D) materials such as recycled concrete aggregate (RCA), crushed brick (CB), and reclaimed asphalt pavement (RAP) as an alternative to quarry aggregates has generated interest in recent years, particularly as a pavement base or subbase material. However, the resilient moduli responses and performance of these C&D materials reinforced with geogrids under repeated loads have yet to be established. This research investigates the resilient moduli (MR) and permanent deformation characteristics of C&D materials reinforced with biaxial and triaxial geogrids with the use of repeated load triaxial (RLT) equipment. The effects of varying deviatoric stress on the resilient modulus of unreinforced and geogrid-reinforced C&D materials were also investigated. Regression analyses of resilient modulus test results were performed using the two- and three-parameter mode...

Optimization Design and Research on Gradation of ATB-25

The ATB-25 mixture is optimized design base on the Bailey method. The skeleton embeded crowded structure of ATB-25 is better than that of AC-25 through analyzing the Bailey parameters, and the value of high temperature stability is 17.5% higher than that of AC-25, their water resistance are similar. The ATB-25 mixture is more suitable as pavement base materials. The proposed gradations belong to embedded crowed-solid structure which is verified by the calculated Bailey parameters, and the high temperature stability and water stability can be ensured. Combining with the highway pavement engineering project of Qujiang to Nanxiong, It is researched on the design of the mix proportion for asphalt treated base ATB-25 in the paper, and the suitable gradation design scheme is put out for the design and construction of highway pavement in high temperature and heavy duty area. The high temperature stability and water stability of ATB-25 which is designed based on the Bailey method can meet the requirements, and pavement performance can meet the design requirements.

Possible environmental impacts of recycled glass used as a pavement base material

In theory, glass diverted or recovered from the municipal solid waste (MSW) stream can be used as feedstock (glass cullet) in the production of new glass containers. However, post-consumer glass typically contains a mixture of clear and coloured material and is often contaminated with other wastes; characteristics that are impediments to the production of new containers. Sorting and cleaning of glass diverted from MSW to make it feasible for use in bottle industries are also time consuming and costly tasks. There is, however, the potential to use recycled glass as a sub-base material for road pavement construction. Geotechnical investigations to date suggest that use of recycled glass as a roadway sub-base could be cost-effective, and thus preclude the need for expensive sorting. There is, however, the necessessity to further investigate the potential short- and long-term toxicity, health hazards, and/or environmental pollution associated with use of mixed glass cullet as an aggregate, considering conditions during stockpiled storage and after placement. The results of laboratory tests on recycled glass regarding its potential to release pollutants to the environment via leaching are presented herein. Five random samples of crushed glasses were collected from a recycling company in Melbourne, Australia. The parameters tested for each sample were total organic matter, heavy metals, sulfates, chlorides, conductivity, pH and surfactant levels. It wais found that in most cases, the contamination levels were within the State of Victoria's Environmental Protection Agency-specified limits for manual handling, thus indicating that recycled glass could probably be safely used in pavement sub-bases.

Laboratory and Field Evaluation of Cement-Treated Reclaimed Asphalt Pavement Blends as Roadway Base Material

Abstract Reclaimed asphalt pavement (RAP) and granular base materials were collected throughout Texas to evaluate the properties of RAP and RAP blended with virgin or salvage aggregates for roadway base course application. Mixes containing RAP of 100 %, 75 %, and 50 % and treated with Portland cement of different dosages were utilized in a comprehensive laboratory testing program. The factors that affect the properties of cement-treated RAP mixes are identified and a mix design model based on typical RAP and granular base materials in Texas was proposed. The design model was verified by the data from the initial field trial on actual construction projects. The feasibility of using a modulus-based procedure for quality assurance/quality control during construction is discussed.

부산 신항만 준설퇴적물로부터 중금속의 연속추출에 관한 연구

In this study, experiments on total digestion and sequential extraction were conducted in order to understand total metal contents, and mobility, bioavaliability and toxicity of metals in marine dredged sediment from Busan New Port. The total concentrations of arsenic and heavy metals in the dredged sediment were relatively low as follows: Al (2.36~2.96 wt.%), As (1.6~3.3 mg/kg), Ba (30.0~33.8 mg/kg), Cd (0.12~0.18 mg/kg), Cr (27.5~35.0 mg/kg), Cu (11.3~15.0 mg/kg), Fe (2.91~3.51 wt.%), Mn (324~408 mg/kg), Ni (18.8~23.8 mg/kg), Pb (23.8~31.3 mg/kg), and Zn (70.0~86.3 mg/kg). In addition, it was found that most of Al (87.5~ 95.9%), As (74.1~93.8%), Ba (71.8~77.6%), Cr (69.5~94.3%), Cu (50.0~78.7%), Fe (70.8~87.6%), Ni (64.5~75.3%), Pb (53.4~64.3%), and Zn (62.5~81.7%) existed in the residual fraction, meaning that those elements might come from natural sources. On the other hand, Cd and Mn were present mainly in the non-residual fraction. Due to low concentrations of toxic heavy metals and high percentage of residual fraction, it could be possible to reuse the dredged sediment for bricks, pavement base material, etc.

Evaluation and Mix Design of Cement-Treated Base Materials with High Content of Reclaimed Asphalt Pavement

Reclaimed asphalt pavement (RAP) and granular base materials were collected from stockpiles throughout Texas to evaluate the feasibility of using mixes containing high RAP content for base course applications. Mixes containing 100%, 75%, and 50% RAP treated with 0%, 2%, 4%, and 6% of portland cement were evaluated in a full-factorial laboratory experiment. For mixes of 75% and 50% RAP, both virgin and salvage base materials were used. Experimental results indicated that besides the cement content, the RAP content and finer aggregate content significantly affected the properties of the RAP mixes, but the effects of RAP type and asphalt content in RAP were limited. To achieve a 300-psi unconfined compressive strength as required by the Texas Department of Transportation, the optimum cement contents were statistically about 4%, 3%, and 2% for mixes of 100%, 75%, and 50% RAP, respectively. Because the achievement of any specified strength or stiffness might not always ensure the durability of a mix, other parameters that might be relevant to performance and long-term durability were evaluated through laboratory testing. These parameters included modulus, indirect tensile strength, and moisture susceptibility as well as cement leaching.

Application of Shakedown Theory in Characterizing Traditional and Recycled Pavement Base Materials

To facilitate the use of recycled materials in pavement construction, a mechanistic-based approach is required to better characterize pavement base materials. This paper demonstrates the application of the shakedown theory to characterize the behavior of traditional and recycled base materials based on laboratory repeated load triaxial RLT tests and full-scaled accelerated loading tests. A new approach that is based on dissipated energy is proposed to explain different shakedown responses of tested materials under repeated loading. The dissipated energy approach illustrated that there are two responses during RLT tests, namely, stable and unstable responses, which are dependent on the loading levels and type of tested material. It was also observed that the transition from the stable to unstable response represents gradual microstructural adjustments of tested materials to accommodate the applied loading. This gradual transition explains the difficulties in identifying some material responses within the shakedown theory based only on the permanent strain rate criteria. Based on the results of this study, a mechanistic-based design procedure to incorporate various recycled materials into pavement bases is recommended.