Oil Shale Ash Research Articles

Life cycle greenhouse gas emissions of concrete containing supplementary cementitious materials: cut-off vs. substitution

Existing life cycle assessments of concrete containing supplementary cementitious materials (SCMs) hinge on methodological procedures that might skew the results towards the conclusion that increasing the use of SCMs in concrete always decreases greenhouse gas (GHG) emissions. These procedures relate to the treatment of co-products and selection of functional units. Co-production is typically addressed via cut-off procedures and by-products are always considered to be unconstrained resources, while functional units often do not account for exposure conditions and concrete properties such as strength and workability. To address this limitation, the aim of this study was to investigate the GHG benefits of using SCMs by (1) adopting different approaches to solve multifunctionality (cut-off vs. substitution) and (2) including strength, workability and exposure conditions of concrete in the functional unit. Ontario (Canada) was used as case study, and both SCMs currently used there (i.e., slag, silica fume and metakaolin) and a wide range of alternative cementitious materials used around the world (i.e., fly ash, oil shale ash, calcium carbide residue, volcanic ash, coal bottom ash and rice husk ash) were investigated. The new contribution of this study reveals that different conclusions can be drawn when different methodological procedures are adopted. If the market for SCM is constrained (i.e., by-products are already fully utilized) and the unconstrained alternative on the market is Portland cement, the benefits of using SCM are greatly reduced, or even reversed, if the substitution approach is adopted. In contrast, unconstrained SCMs result in considerable GHG savings unless they significantly reduce the water-to-binder ratio to reach a prescribed strength and require long distance transport.

Preparation and characterization of glass-ceramics from oil shale ash: Effect of basicity and sintering temperature on crystallization behavior, properties, and environmental risk

Oil shale ash is an inorganic by-product generated from the combustion and refinement of oil shale. In this study, it was used as main raw material to produce glass-ceramics. The crystalline phases, crystallization mechanism, bulk density, compressive strength and microstructure of glass-ceramics were studied. Specifically, the leaching characteristics and ecological risk assessment of heavy metals in glass-ceramics were emphasized. The results showed that the increase of basicity reduced the crystallization activation energy, but the surface crystallization mechanism of different samples has not changed. Anorthite and diopside were identified as the main crystalline phases in glass-ceramics despite varying basicity and sintering temperatures. The compressive strength and bulk density increased with the increase of sintering temperature. The compressive strength of VS2 (basicity = 0.3) was higher than that of VS1 (basicity = 0.2) for the same sintering temperature due to more crystals and denser microstructure. Independent of the basicity, a higher sintering temperature promoted the sintering and densification of products. The highest compressive strengths of VS1 and VS2 were 219.14 ± 12.8 and 255.57 ± 15.6 MPa, respectively. In addition, the reliable stability and low potential ecological risk index of heavy metals in the final products make it to be a competitive eco-friendly construction material.

Experimental Research on Mechanical Property and Environmental Safety of an Industrial Residue Waste Subgrade Material

In order to promote the sustainable use of oil shale residues, a novel subgrade material (SOF) composed of silty clay, oil shale ash residue, and fly ash was developed. The aim of this paper is to study the mechanical behavior and environmental impact of SOF, which is regarded as the safety assessment and prediction for the application of this novel material. To this purpose, the road performance, dynamic properties, and environment impact tests are conducted. In terms of the road performance, the test results of SOF exceed the standard requirement, especially for CBR (California bearing ratio), which can maintain good performance at bad conditions of low compaction degree and being soaked for a long time. The dynamic properties under cyclic loadings are better than most of original and stabilized soils. The shear strength parameters and the anti‐damage mechanism are also discussed; research results show that the friction of SOF mostly contributes to shear strength under high stress conditions, while its cohesion tends to play a more important role under low stress conditions. According to the deformation variation, the accumulation settlement of SOF under vehicle loadings after several years is predicted, which is far lower than the limit of expressway and Grade I highway. Furthermore, the chemical stability and toxicity of SOF leachates are environmentally friendly, which are in line with the benchmarks of Class II surface water and Class III ground water. All the experimental results manifest that SOF used as subgrade filling has good application potential and safety.

Geochemical study of stable carbon and oxygen isotopes in landfilled Ca-rich oil shale ash

Geochemical study of stable carbon and oxygen isotopes in landfilled Ca-rich oil shale ash

Geopolymer composites using natural pozzolan and oil-shale ash base materials: A parametric study

The mechanical properties, capillary porosity and microstructure of Geopolymer (GP) composites made using different natural Jordanian base materials were investigated. GP mortar mixtures were prepared using oil shale ash, Jordanian natural Pozzolan and a blend of both considering different salient parameters related to the composition of alkaline activator and GP binder content. GP mortar specimens (40 × 40 × 160 mm3) cast from 36 different mixtures were left to rest in molds for 24 h before unmolded then exposed to 60 °C temperature to cure for 24 h and finally moved to laboratory shelves to cure for the remainder of the curing periods of 7 and 28 days. Compressive and flexural tensile strengths, capillary porosity, and Scanning Electron Microscopy (SEM) pictures of the hardened GP composite were obtained, analyzed, and compared to study the significance of the study parameters. The results indicate a good potential of producing GP composites using Jordanian natural Pozzolan alone or with oil shale ash for masonry and structural applications with strength grades of up to 24 MPa. A very good statistical correlation was established between the compressive strength and capillary porosity for present GP composites. SEM pictures for GP composites confirm the experimentally-measured mechanical and durability properties.

Accelerated carbonation technology granulation of industrial waste: Effects of mixture composition on product properties.

The use of accelerated carbonation technology in combination with a granulation process was employed to produce aggregates from a variety of industrial wastes, which included municipal solid waste incineration fly ash and air pollution control residue, oil shale ash, cement kiln dust, and quarry fines that have been produced in Estonia. Focusing mainly on the effects produced by the content of municipal solid waste incineration ash in the admixtures, the granule compositions were varied in order to tailor granule properties on the basis of CO2 uptake, strength development, leaching behaviour, microstructure, and morphology. All the steps involved in the accelerated carbonation technology granulation process, from mixing with additives to granulation and carbonation treatment, were carried out in the same apparatus - an Eirich EL1 intensive mixer/granulator. The amount of CO2 that was bound ranged from 23 to 108 kg per tonne of waste. The granules that included the optimised mixture of municipal solid waste incineration air pollution control residue, oil shale ash, cement kiln dust, and ordinary Portland cement were characterised by the highest compressive strength (4.03 MPa) and water durability for the size range of 4-10 mm. In addition, the process was found to be effective in reducing alkalinity (pH < 11.5) and immobilising heavy metals (especially zinc) and chloride. The composition and properties of the respective waste materials and mechanisms associated with the characteristics of the resulting granules were also addressed.

Experimental Research on Deformation Characteristics of Using Silty Clay Modified by Oil Shale Ash and Fly Ash as the Subgrade Material after Freeze-Thaw Cycles

To achieve the purposes of disposing industry solid wastes and enhancing the sustainability of subgrade life-cycle service performance in seasonally frozen regions compared to previous research of modified silty clay (MSC) composed of oil shale ash (OSA), fly ash (FA), and silty clay (SC), we identified for the first time the axial deformation characteristics of MSC with different levels of cycle load number, dynamic stress ratio, confining pressure, loading frequency, and F-T cycles; and corresponding to the above conditions, the normalized and logarithmic models on the plastic cumulative strain prediction of MSC are established. For the effect of cycle load number, results show that the cumulative plastic strain of MSC after 1, 10, and 100 cycle loads occupies for 28.72%~35.31%, 49.86%~55.59%, and 70.87%~78.39% of those after 8000 cycle loads, indicating that MSC possesses remarkable plastic stability after 100 cycles of cycle loads. For the effect of dynamic stress ratio, confining pressure, loading frequency, and F-T cycles, results show that dynamic stress ratio and F-T cycles are important factors affecting the axial deformation of MSC after repeated cycle loads; and under the low dynamic stress ratio, increasing confining pressure and loading frequency have insignificant effect on the axial strain of MSC after 8000 loads. In term of the normalized and logarithmic models on the plastic cumulative strain prediction of MSC, they have a high correlation coefficient with testing data, and according to the above models, the predicted result shows that the cumulative plastic strain of MSC ranges from 0.38 cm to 2.71 cm, and these predicted values are within the requirements in the related standards of highway subgrades and railway, indicating that the cumulative plastic strain of MSC is small and MSC is suitable to be used as the subgrade materials.

Experimental and Numerical Research on Utilizing Modified Silty Clay and Extruded Polystyrene (XPS) Board as the Subgrade Thermal Insulation Layer in a Seasonally Frozen Region, Northeast China

For strengthening sustainability of subgrade life-cycle service performance and storing industry solid wastes in seasonally frozen regions, compared to previous research of modified silty clay (MC) which consisted of oil shale ash (OSA), fly ash (FA), and silty clay (SC), we identified for the first time, the variations in the thermal insulation capability of MC with different levels of dry density and moisture content. Taking into consideration the effects of 0–20 freeze-thaw (F-T) cycles by a laboratory test, and by the numerical simulation of coupling moisture-temperature, while considering the effects of F-T cycles, the thermal insulation capability of the MC board and the XPS board were studied quantitatively. The testing results show that the thermal conductivity of MC and SC gradually decreases as the number of F-T cycles increases, and that of the XPS board increases with the increased number of F-T cycles, and tend to be of a constant value of 0.061 W/m/K after 17 F-T cycles. The specific heat capacity of the solid particles of the MC, SC, and XPS board does not change regularly as their moisture content, and the number of F-T cycles change, and their variations are in the range of the test error (2%). Simulation results show that MC has the advantage of the thermal insulation property to reduce the frost-depth of 0.21 m, and the thermal insulation property of the composite layer consisting of the MC and XPS board is greater to reduce the frost-depth of 0.55 m, so that it can protect both the SC and sand gravel of the experimental road from the frost heave damage. The research methods and results are very significant in accurately evaluating the thermal insulation capacity and the sustainability of MC and the composite layer consisting of the MC and XPS board, strengthening the stability of the subgrade and increasing the availability of industrial waste.

Influence of waste products from electricity and cement industries on the thermal behaviour of Estonian clay from Kunda deposit

The influence of two different oil shale ashes formed, respectively, at pulverized firing and at circulated fluidized bed combustion of Estonian oil shale (OS) at electricity production, and clinker dust (CD) formed at cement production on the thermal behaviour of Estonian clay from Kunda deposit, and, for comparison, on the illitic clay from Fuzerradvany (Hungary) was studied. Composition of clay with 40% of previously fired at 1050 °C clay (grog) was used as a basement one. In the blends studied the fired clay was partly or totally replaced with OS ash or CD additives. Experiments were carried out under non-isothermal condition up to 1050 °C using a Setaram Setsys 1750 thermoanalyzer coupled with Pfeiffer Omnistar Spectrometer at the heating rates of 1.25, 2.5, 5 and 10 °C min−1 in an oxidizing atmosphere containing 79% of Ar and 21% of O2. The differential isoconversional method of Friedman was applied to calculate the kinetic parameters. Depending on the origin of the additive the thermal behaviour of blends following the two-step route differentiated remarkably from the same characteristics of clays. The value of activation energy along the reaction progress varied for illitic clay and its blends with OS ash and CD additives more than based on Kunda clay, but, contrary, the average activation energy values for blends based on Kunda clay are, as a rule, bigger than based on illitic clay.

The influence of oil shale in situ mining on groundwater environment: A water-rock interaction study

Oil shale samples were obtained from Nong'an oil shale ore-bearing area which was located in the southeastern uplift of Songliao basin, China. The XRD test for oil shale identified the minerals in it and a series of water-rock interaction experiment between oil shale-water and oil shale ash-water were carried out to the study the release of organic matter from groundwater during oil shale in-situ exploitation. The content of phenol, BTEX, TOC and TPH in oil shale and oil shale ash aqueous solution were determined. The phenol and TOC in oil shale aqueous solution were higher than that of oil shale ash aqueous solution, conversely, more BTEX and TPH were existed in oil shale ash aqueous solution. The reaction temperature had significant influence on phenol, TOC and TPH in oil shale aqueous solution, which was not obvious in oil shale ash aqueous solution. Besides, the TOC average content in oil shale aqueous solution gradually increased along with the reaction time. The results show that not only oil shale in situ mining process make groundwater organic pollution aggravate but also continuous pollution of groundwater caused by the residual oil shale ash still exist.

Behaviors, product characteristics and kinetics of catalytic co-pyrolysis spirulina and oil shale

• Oil shale restrained the thermal decomposition of organic matters in spirulina. • HZSM-5 and CaO promoted the deoxygenization and aromatization of co-pyrolysis. • The minimum E value of catalytic pyrolysis was achieved at 1HZSM-5/3CaO. • A significant synergistic effect was achieved at the percentage of 30% oil shale. The catalytic co-pyrolysis behaviors, kinetics and products distribution of spirulina (SP) and oil shale (OS) were studied by thermogravimetric analysis (TGA) and pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). Results indicated that OS delayed the thermal decomposition of organic matters in SP; there existed inhibition for aromatics production under 310 °C and synergistic effects at high temperatures, and a maximum synergistic effect was achieved with 30% OS. HZSM-5 and CaO enhanced the deoxygenation and aromatization reaction, resulting in a prominent decrease of acids and phenols. With the increase of CaO ratio, the relative content of aliphatic hydrocarbons increased from 9.57% to 17.48%, while the relative content of aromatics increased first and then decreased, and the maximum yield of aromatics (15.92%) was obtained at 1CaO/3HZSM-5. The appropriate CaO/HZSM-5 mass ratio contributed to the production of desired pyrolysis product. The kinetic parameters were determined by using Friedman and Flynn–Wall–Ozawa (FWO) method. As the oil shale blending ratio increased, the average activation energy (E) of mixtures decreased from 278.84 kJ/mol to 192.53 kJ/mol (from 265.51 kJ/mol to 189.63 kJ/mol), related to the catalytic decomposition of organic matter by alkaline earth metals in OS ash. The minimum E value of catalytic pyrolysis 5SP/5OS was achieved at 1HZSM-5/3CaO (257.29 kJ/mol and 269.62 kJ/mol). This paper could offer significant pyrolysis knowledge for obtaining high-grade oil from SP and OS with HZSM-5 and CaO.

Long-term mineral transformation of Ca-rich oil shale ash waste

Power generation and other industries using solid fossil fuels like coal, lignite, oil shale and peat are responsible for producing large quantities of solid residues that are often chemically reactive and/or unstable and are disposed in holding ponds and deposition sites. Stability and long-term behaviour of such deposits are typically studied in short-term laboratory experiments that cannot describe nor predict long-term changes taking place in these materials. Here, we study long-term (>40 years) transformations, in highly alkaline conditions, of the Ca-rich ash deposit in Estonia composed of oil shale processing residues from the Eesti power plant. Detailed mineralogical, chemical and micromorphological analyses using X-ray diffraction, X-ray fluorescence, 29Si nuclear magnetic resonance, scanning electron microscopy and other methods were applied in order to identify the composition of the waste with a focus on formation and transformation of semicrystalline phases in the deposit. The results show progressive formation of calcium-silicate-hydrate (C-S-H) type phase at the expense of silicate minerals and amorphous glass phases with increasing depth and age of the sediments, from about 25% in the upper part of the depository to over 60% in the oldest-deepest part. This demonstrates that over time the high alkalinity of the ash is responsible for initiating natural alkali-activation. The formation of C-S-H-type phases increases the mechanical strength of the sediment and ensures long-term stability of waste deposits. These findings may encourage the use of these ashes in binder or other construction material production or as construction aggregates.

Measurement of radioxenon and radioargon in air from soil with elevated uranium concentration

Among the most important indicators for an underground nuclear explosion are the radioactive xenon isotopes 131mXe, 133Xe, 133mXe and 135Xe and the radioactive argon isotope 37Ar. In order to evaluate a detection of these nuclides in the context of a nuclear test verification regime it is crucial to have knowledge about expected background concentrations. Sub soil gas sampling was carried out on the oil shale ash waste pile in Kvarntorp, Sweden, a location with known elevated uranium content where 133Xe and 37Ar were detected in concentrations up to 120 mBq/m3 and 40 mBq/m3 respectively. These data provides one of the first times when xenon and argon were both detected in the same sub soil gas. This, and the correlations between the radionuclides, the sub soil gas contents (i.e. CO2, O2, and radon) and uranium concentration in the pile, provide very interesting information regarding the natural background and the xenon concentration levels and can most likely be used as an upper limit on what to be expected naturally occurring.

Engineering and environmental evaluation of silty clay modified by waste fly ash and oil shale ash as a road subgrade material

The objective of this study was to evaluate the viability of utilizing waste fly ash (FA) and oil shale ash (OSA) to modify silty clay (SC) as a subgrade material. First, the modified soils at five different ratios of OSA/FA/SC were prepared. Second, the compaction, Atterberg limits and CBR (California bearing ratio) tests were conducted to determine the optimum ratio of OSA/FA/SC. Third, the static and dynamic mechanical characteristics of the modified soil at the optimum ratio of OSA/FA/SC were measured. Subsequently, the environmental impact of the modified soil subgrade leachates on water was assessed. The results show the physical properties of SC are improved by the addition of FA and OSA. The modified soil at the OSA/FA/SC ratio of 40:20:40 possesses the highest CBR value, propriate physical properties and the balanced usage ratio of FA, OSA and SC. The triaxial tests demonstrate that the static strength parameters and dynamic fracture strength of SC are significantly increased by FA and OSA. The obtained dynamic modulus could be valuable for evaluating the deformation and stability of this modified soil in geotechnical engineering. The main ions and trace elements concentration analysis results indicate that the modified soil leachates have no pollution on Class II surface water and Class III ground water. Based on these results, SC modified by FA and OSA has the potential to be used a viable subgrade material.

Modified oil shale ash and oil shale ash zeolite for the removal of Cd2+ ion from aqueous solutions

ABSTRACTThe present study attempted to prepare modified oil shale ash and oil shale ash zeolite from oil shale ash, which were characterized by X-ray diffraction, scanning electron microscopy, and N2 adsorption–desorption. Detailed kinetics and isotherm studies of Cd2+ adsorption onto modified oil shale ash and oil shale ash zeolite were examined. The adsorption capacity was determined as a function for the adsorption system. The results showed that the adsorption capacity of oil shale ash zeolite was higher compared to modified oil shale ash and that the time required to reach equilibrium was shorter. The kinetics studies showed that Cd2+ adsorption was well fit by the pseudo-second-order kinetics model. Both the Langmuir and the Freundlich isotherms described the adsorption data well. And the maximum monolayer adsorption capacity determined by the Langmuir adsorption isotherm was found to be 108.70 and 169.49 mg/g for Cd2+ adsorption onto modified oil shale ash and oil shale ash zeolite, respectively. It was concluded that Cd2+ in aqueous solutions was more efficiently removed by oil shale ash zeolite, which could be employed as a low-cost and effective alternative adsorbent for wastewater treatment than modified oil shale ash.

Synthesis of Zeolites Materials Using Fly Ash and Oil Shale Ash and Their Applications in Removing Heavy Metals from Aqueous Solutions

Fly ash and oil shale ash generated from power plants can be transformed to suitable materials usable for removal of heavy metals. Due to their high silica content, fly ash and oil shale ash have been considered as the main stone of zeolite synthesis. In this work, we synthesized zeolites from class F fly ash (FA) and modified oil shale ash (MOSA) by alkaline fusion followed by refluxing. Our synthesis process focused on the effect of quantity of NaOH on the crystallinity of the reaction products: Na-P1 and Na-P2 type zeolites synthesized, respectively, from FA and MOSA. The effect of NaOH mass (1, 2, 4, and 8 g) was investigated with the following synthesis conditions: 2 h fusion at 650°C, 2 h agitation, and refluxing for 12 hours. The experimental results demonstrated that the crystallinity of Na-p1 and Na-P2 zeolites increased with increasing the mass of NaOH. The resulting products were characterized with X-ray diffraction, FTIR, and scanning electron microscopy. The reaction products ZV4 and ZM4 synthesized, respectively, from FA and MOSA and containing main zeolite phases with a crystallinity of 92.7% of Na-P1 and 83.6% of Na-P2, respectively, were chosen as adsorbents for the adsorption experiments. Series of experiments were carried out to study the removal of lead, zinc, and chromium by ZV4 and ZM4. The results allowed us to know the optimal conditions of adsorption for the three heavy metals. Adsorption data have been interpreted in terms of Langmuir and Freundlich isotherms. The results showed that lead has a higher affinity for ZM4 than ZV4 and zinc has similar adsorption efficiency for both sorbents that was remarkably reduced for chromium. The results of the present work suggest that zeolites synthesized from MOSA may be considered as effective as those synthesized from FA for heavy metals adsorption.

The use of oil shale fly ash to improve the properties of Irbid soil

PurposeThe purpose of this paper is to evaluate the possible use of oil shale as a soil stabilizing agent for expansive soils.Design/methodology/approachAn experimental work has been fulfilled to investigate the influence of oil shale ash (OSA) on the geotechnical behavior of the expansive soil of Irbid, Jordan. Three swelling-shrinkage soils were considered in this study along with various percentages of OSA varying at 2, 4, 6, 8, 10 and 12 per cent by dry weight of the soil. A series of laboratory tests were conducted on the soil samples before and after mixing it with OSA. These tests were soil classification, Atterberg limits, compaction test, falling head permeability test, unconfined compression test, free swelling, swelling pressure and California bearing ratio (CBR) test.FindingsLaboratory tests results indicated that OSA is effective in improving the texture and strength of the treated soil by reducing plasticity index, swelling potential and swelling pressure and moderately enhancing soil strength properties including the unconfined compressive strength (qu), maximum dry unit weight (γd-max.) and CBR test.Originality/valueOSA showed potential as a low-cost soil stabilizing agent for swell-shrink soils.

Synthesis of Na-X zeolite from Longkou oil shale ash by alkaline fusion hydrothermal method

Na-X zeolites were synthesized by Longkou oil shale ash with the alkaline fusion hydrothermal method. The effects of fusion temperature, ash to NaOH ratio, solid-liquid ratio, crystallization time and crystallization temperature on the crystallinity of zeolites were investigated. The synthetic products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), 29Si nuclear magnetic resonance spectroscopy (29Si NMR) and N2 adsorption-desorption. The results showed that the conditions to synthesize Na-X zeolite were: Longkou oil shale ash to sodium hydroxide ratio 1:1.2 g·g−1, fusion temperature 600 °C, solid-liquid ratio 1:4 g·mL−1, crystallization time 24 h and crystallization temperature 80 °C. The zeolite with high crystallinity (91.32%) was synthesized: the product exhibiting octahedral particles observed by SEM, and the calculated Si/Al ratio in Na-X zeolite being 1.23 from 29Si MAS NMR spectra, which was consistent with the observation from XRD.

Producing geopolymer composites using oil shale ash

The potential of producing geopolymer (GP) composites using Jordanian oil shale ash (OSA) was investigated. Twelve GP mortar mixtures were prepared using OSA and different proportions of commercially available alkaline activator, composed of sodium silicate and sodium hydroxide. Prismatic specimens (40 × 40 × 160 mm), attained satisfactory workability, were left at laboratory air for 24 hr, then demolded and dry cured at different practical temperatures (60–100 °C) for 24 and 48 hr before left in laboratory air and finally tested for strength and capillary porosity. Furthermore, SEM analysis was carried out on matured GP mortar samples to determine the extent of OSA polymerization and status of pore system. The results indicated the potential of producing GP mortar using OSA with strength grades of as high as 20 MPa. Dry curing at 60 °C for 24 hr imparted the best mechanical and durability properties of OSA‐based GP mortar. The internal pore structure showed excellent correlation with mechanical and durability properties of produced GP composites.

Experimental Research on Resilient Modulus of Silty Clay Modified by Oil Shale Ash and Fly Ash after Freeze-Thaw Cycles

To dispose of the large amount of OSA (oil shale ash) and FA (fly ash) in Northeast China, a novel subgrade material obtained by modifying SC (silty clay) with OSA and FA was produced. First, the effect of F-T (freeze-thaw) cycles and stress states on the resilient modulus of unmodified SC and the modified SC were investigated. Second, the damage ratio was introduced to describe the relationship of resilient modulus versus F-T cycles. Third, the effect of F-T cycles on the microstructure of soils was investigated. The results indicate that in addition to stress state, resilient modulus is significantly influenced by F-T cycles. For unmodified SC, the resilient modulus continually decreases with increasing F-T cycles. As for the modified soil, the resilient modulus decreases sharply after the first F-T cycle and then tends to be stable. The damage ratio and its fitting equation are effectively adopted to describe the variation characteristic of the resilient modulus after F-T cycles. As observed from SEM testing, the effect of F-T cycles on soils is to destroy the initial structure and increase the porosity of soils. It could be concluded that the microstructure change during F-T cycles is the main factor that results in the decrease of the resilient modulus.