Crushed Rock Research Articles

Estimation of permanent deformation behaviour of crushed waste rocks using multistage repeated load triaxial and CBR tests

ABSTRACT Crushed waste rocks (CWR) are widely used to build mine haul roads. However, the permanent deformation in waste rocks layers can result in surface rutting. Realistic prediction of pavement rutting requires models that can accurately capture the permanent deformation behaviour under repeated loading. However, such models are usually based on advanced laboratory apparatus such as multistage (MS) repeated load triaxial (RLT) tests. In this study, a new approach, using MS repeated load California Bearing Ratio (RLCBR) tests, was proposed to estimate the permanent deformation behaviour of CWR. MS RLCBR tests are faster, easier and more often available than MS RLT tests. A series of MS RLCBR and MS RLT tests for different stress levels were therefore carried out on the same material to characterise CWR permanent deformation behaviour. Results showed that Rahman and Erlingsson model that modified by time hardening approach could satisfactorily capture CWR permanent deformation behaviour for MS RLT tests. A new model was proposed and fitted on MS RLCBR test results to predict CWR permanent deformation behaviour. This model performed well in describing MS RLCBR test results and predicting the CWR permanent deformation behaviour. Results indicate that MS RLCBR tests could be an effective alternative to MS RLT tests for estimating the permanent deformation behaviour of CWR.

Effect of particle size on re-crushing characteristics of crushed coal during axial loading

The deformation and re-crushing characteristics of crushed coal and rock directly affect the porosity and permeability distribution of the mining gob and overburden strata movement, which significantly affects the methane enrichment zone and surface subsidence of mining gobs. The effect of particle size on re-crushing characteristics is investigated in this study based on an innovative compression–acoustic emission (AE) positioning method. The main results are as follows: 1) The AE counts and energy are associated closely with three deformation stages, i.e., initial compression, linear compression, and plastic compression. A larger particle deforms more easily and results in more AE counts and energy under the same compression; 2) crushed coal exhibits layered re-crushing characteristics, i.e., particle re-crushing first occurs in the middle layer, and as stress increases, re-crushing shifts gradually to the upper and lower layers; 3) larger particles re-crush more easily, and the re-crushing occurs more severely in the middle layer under the same compression stress; 4) screened results after final compression show and verify the characteristics of layered re-crushing. The lower layer exhibits the least reduction in porosity for each particle size. A larger particle exhibits a greater re-crushing rate under the same compression stress.

Impacts of Lightweight Aggregate Interlayers for Air Convection Embankment on Pavement Thermal Profile and Pavement Performance in Alaskan Permafrost Regions

Crushed-rock air convection embankment (ACE) has been used to mitigate pavement distresses caused by climatic extremes in permafrost regions for more than three decades. This study proposes using lightweight aggregates as cost-effective alternative materials to overcome the shortage of desired crushed rocks needed for ACE in interior Alaska. This paper presents an investigation of the performance of six selected pavement structures: an asphalt pavement typical of the northern region of Alaska and five pavements reinforced with different paving interlayers (i.e., silty sand/gravel, crushed rocks, cellular concrete aggregate, foam glass aggregate, and lightweight expanded clay aggregate). Pavement thermal analyses using Temperature Estimate Model for Pavement Structures (TEMPS) program and ANSYS Fluent software were performed to predict heat transfer patterns and thermal performance for each case. Pavement performance analyses using viscoelastic-based FlexPAVE™ and the elastic-based Alaska Flexible Pavement Design (AKFPD) program were conducted to evaluate the long-term performance and structural stability of subgrade soil with different types of interlayers. The results showed that the lightweight aggregate ACEs improved cooling performance more effectively than the crushed-rock ACE. The lightweight aggregate interlayers could maintain desired thermal insulation in summer and enhance the cooling effect in winter. The modeling results identified the high potential of using lightweight aggregates as alternative ACE materials to improve pavement service life and subgrade stability.

Hydrogen generation in crushed rocks saturated by crude oil and water using microwave heating

Fossil-based hydrogen (H2) production, such as steam methane reforming (SMR), typically occurs at surface facilities using hydrocarbons as a major feedstock. Such approach generates significant amount of byproduct carbon dioxide (CO2) and requires the costly carbon capture and geological storage. Here we propose a novel approach to generate hydrogen within petroleum reservoirs using the remaining/unrecovered oil and gas. To validate this scientific proof-of-concept, we use microwave (MW) heating to initiate the reactions of crude oil, water, and/or catalysts in crushed rock samples. A maximum of 63% ultimate hydrogen content is obtained in generated gas mixtures, while CO2 is always less than 1%. Besides hydrocarbon cracking, additional hydrogen is generated by water-gas shift reactions. Water-oil ratios in rocks also affect hydrogen yield, with 1:1 appearing as an optimal ratio. Furthermore, we find that iron catalysts can accelerate reaction rate but has limited effects on ultimate hydrogen yield. Metal minerals in rocks may act as natural catalysts to enhance hydrogen generation. Overall, this work demonstrates the technical feasibility of in-situ hydrogen generation directly from petroleum reservoirs.

Environmental and health impacts of atmospheric CO2 removal by enhanced rock weathering depend on nations’ energy mix

AbstractEnhanced Rock Weathering is a proposed Carbon Dioxide Removal technology involving the application of crushed silicate rocks, such as basalt, to agricultural soils with potential co-benefits for crops and soils, and mitigation of ocean acidification. Here we address the requirement of diverse stakeholders for informative studies quantifying possible environmental and health risks of Enhanced Rock Weathering. Using life-cycle assessment modelling of potential supply chain impacts for twelve nations undertaking Enhanced Rock Weathering deployment to deliver up to net 2 Gt CO2 yr−1 CDR, we find that rock grinding rather than mining exerts the dominant influence on environmental impacts. This finding holds under both a business-as-usual and clean energy mix scenario to 2050 but transitioning to undertaking Enhanced Rock Weathering in the future with low carbon energy systems improves the sustainability of the Enhanced Rock Weathering supply chain. We find that Enhanced Rock Weathering is competitive with other large-scale Carbon Dioxide Removal strategies in terms of energy and water demands.

Experimental investigation on hard rock fragmentation of inserted tooth cutter using a newly designed indentation testing apparatus

This investigation aims to explore the effects of stress conditions and rock cutting rates on hard rock fragmentation through indentation tests on a newly designed triaxial testing apparatus. This apparatus was designed to realize a triaxial loading and indentation test of cylindrical specimens using inserted tooth cutter. The boreability and crushing efficiency of granite rock was investigated by analyzing the change rules of the thrusting force, penetration depth, characteristics of chippings and failure patterns. Several quantitative indexes were used to evaluate rock boreability in this investigation. The granite rock samples all had a chiselled pit and a crushed rock core. Under initial stress conditions, only flat-shape chippings were stripped from the rock surface when the thrusting force reached 20 kN. The rock cutting special energy had a close correlation with the initial stress conditions and inserted tooth shape. Moreover, a thrusting force prediction model was proposed in this paper. The contribution of this study is that for the first time the influence mechanism of the initial triaxial stress conditions on rock fragmentation is investigated using an inserted tooth and the newly designed testing apparatus. This study has a crucial importance for practical underground hard rock crushing in geoengineering.

Properties and Microstructures of Crushed Rock Based-Alkaline Activated Material for Roadway Applications.

The worldwide demand for roads to serve global economic growth has led to the increasing popularity of road improvement using cement. This, in turn, has led to increased demand for cement and the associated problem of CO2 emissions. Alkaline-activated materials (AAMs) could be an alternative binder for relatively low strength construction and rehabilitation as a cement replacement material. Compared to other applications, the lower strength requirements of road construction materials could ease any difficulties with AAM production. In this study, crushed rock (CR) was used as a prime raw material. The mechanisms and microstructures of the hardened AAM were investigated along with its mechanical properties. The results showed that CR-based AAM with an optimum mixture of 5 M of NaOH concentration, an SS/SH ratio of 1.00, and a liquid alkaline-to-binder (L/B) ratio of 0.5 could be used for roadway applications. At this ratio, the paste samples cured at room temperature (26 ± 3 °C) had an early compressive strength (3 days-age) of 3.82 MPa, while the paste samples cured at 60 °C had an early compressive strength of 6.45 MPa. The targeted strength results were able to be applied to a cement-treated base (CTB) for pavement and roadway applications (2.1 to 5.5 MPa).

Effect of freeze–thaw and wetting–drying cycles on the CBR, shear strength, stiffness and permanent deformation of crushed waste rocks

Waste rocks produced from mining operations are widely reused for the construction of mine haul roads. However, seasonal changes expose mining facilities to repeated freeze–thaw and wetting–drying cycles which can significantly affect the geotechnical characteristics of the materials in situ. In this study, cyclic and monotonic triaxial and California bearing ratio (CBR) tests were conducted to measure the geotechnical properties of crushed waste rocks subjected to freeze–thaw and wetting–drying cycles. Results showed that freeze–thaw cycles caused a reduction of the resilient modulus and shear strength, and an increase of the permanent deformation. A greater water content during freeze–thaw cycles resulted in a significant increase of the permanent deformation. Wetting–drying cycles could contribute to increase the stiffness, CBR and permanent deformation of crushed waste rocks. Predictive models were also developed to estimate the effect of freeze–thaw cycles on resilient modulus and permanent deformation.

Multi-Morphological Characteristics of a Crushed Granitic Rock of Varying Sizes

Crushed rock fragments are usually a mixture of particles with different sizes and morphologies comprising particle shape and surface texture scales. The significant role of particle morphology in the engineering behavior of granular materials has been increasingly appreciated. However, studies on morphology are mainly on particles of similar sizes, and the few studies that reported particles with varying sizes are limited to particle shape scale alone, especially when 3D morphological characteristics are considered. In this paper, we investigate the multi-scale morphological characteristics of crushed rock with a size ranging from sand to gravel by employing a 3D laser scanner and micro-Computed Tomography (μCT) using quantifiers of sphericity, aspect ratio, and roundness for particle shape, and fractal dimension for surface texture. Crushed granitic rock is used as the testing material to elucidate the morphological characteristics of crushed materials, which are not uncommon in geotechnical applications. For the tested crushed granitic rock, as particle size decreases, the overall shape becomes slightly angular, the corner of the particle becomes more rounded, and the surface becomes smoother. Differences in the morphological descriptors for small particles, mainly those with singular mineral composition, have also been observed and might be explained in terms of hardness and fracture features. The observed dependence of morphological descriptors on particle size and mineralogy bears significance for investigations using reconstructed particles of different sizes using 3D-printing techniques and numerical methods.

Removal of atmospheric CO2 by engineered soils in infrastructure projects

The use of crushed basic igneous rock and crushed concrete for enhanced rock weathering and to facilitate pedogenic carbonate precipitation provides a promising method of carbon sequestration. However, many of the controls on precipitation and subsequent effects on soil properties remain poorly understood. In this study, engineered soil plots, with different ratios of concrete or dolerite combined with sand, have been used to investigate relationships between sequestered inorganic carbon and geotechnical properties, over a two-year period. Cone penetration tests with porewater pressure measurements (CPTu) were conducted to determine changes in tip resistance and pore pressure. C and O isotope analysis was carried out to confirm the pedogenic origin of carbonate minerals. TIC analysis shows greater precipitation of pedogenic carbonate in plots containing concrete than those with dolerite, with the highest sequestration values of plots containing each material being equivalent to 33.7 t C ha−1 yr−1 and 17.5 t C ha−1 yr−1, respectively, calculated from extrapolation of results derived from the TIC analysis. TIC content showed reduction or remained unchanged for the top 0.1 m of soil; at a depth of 0.2 m however, for dolerite plots, a pattern of seasonal accumulation and loss of TIC emerged. CPTu tip resistance measurements showed that the presence of carbonates had no observable effect on penetration resistance, and in the case of porewater pressure measurements, carbonate precipitation does not change the permeability of the substrate, and so does not affect drainage. The results of this study indicate that both the addition of dolerite and concrete serve to enhance CO2 removal in soils, that soil temperature appears to be a control on TIC precipitation, and that mineral carbonation in constructed soils does not lead to reduced drainage or an increased risk of flooding.

Aggregate Subgrade Improvements Using Quarry By-Product Fines: A Case Study

This paper presents a case study for constructing aggregate subgrade improvement (ASI) layers using quarry by-product aggregates (QBA)—a quarry mix of large primary crushed rocks (PCR) and sand-sized quarry fines. The construction took place at Larry Power Road in Bourbonnais Township in Kankakee County, Illinois, where the Illinois Department of Transportation (IDOT) placed two QBA mixes for performance evaluation. The first mix (QBA_M1) consisted of 45% quarry by-products (QB) and 55% railroad ballast-sized PCR. The second mix (QBA_M2) consisted of 31% QB and 69% PCR. Two conventional ASI sections with only PCR were also constructed. All sections consisted of a 229 mm (9 in.) QBA/PCR layer topped with a 76 mm (3 in.) thick dense-graded capping layer. Laboratory studies preceded the construction to recommend optimum QB percentages for the QBA materials and construction practice. The quality and uniformity of the construction was ensured through field testing using dynamic cone penetrometer (DCP), lightweight deflectometer (LWD), and falling weight deflectometer (FWD). The segregation potential of the QBA mixes was monitored by visual inspection, aggregate stockpile sampling, and image analysis techniques. Short-term field evaluation of the constructed QBA layers, particularly QBA_M2 with 31% QB, showed no evidence of major segregation. The QBA ASI layers had slightly lower but comparable strength and stiffness profiles to the conventional ASI sections. The use of QBA materials in ASI was therefore field validated in this case study as a sustainable construction practice to provide stable pavement foundation layers.

Tritium contamination of surface and ground waters at the “Dnepr” peaceful underground nuclear explosions site

The article presents results of a study on the tritium content in surface and ground waters in the area of peaceful underground nuclear explosions of the “Dnepr” series. Low-yield thermonuclear explosions (1.8–2.1 kt of TNT equivalent) were carried out inside Mount Kuel’por (Khibiny Massif, Kola Peninsula, Murmansk Oblast, the Russian Federation) in 1972 and 1984. The purpose of the explosions was to crush the ore body (apatite minerals), followed by the extraction of the crushed rock to the ground surface. The main long-term problem generated by these explosions was the flow of tritium-contaminated groundwater onto the ground surface. The area where the explosions took place is actively visited by tourists. Water from local reservoirs, in particular from the Kuniyok River, is used by people for drinking. The purpose of this study was to assess the drinkability of the local waters in terms of activity concentration of tritium. To achieve this goal, 35 water samples were taken in 2019 from wells, boreholes, rivers, streams, lakes and other accessible environmental waterbodies. Activity concentration of tritium in the samples was determined using the Quantulus 1220 low-background liquid scintillation spectrometer. The activity concentration of tritium in the water samples was in a rather wide range: from less than 2 Bq/kg up to 1510 Bq/kg. The maximum value was up to three orders of magnitude higher than the regional background level of approximately 2 Bq/kg. At the same time, the maximum activity concentration was significantly lower compared to the intervention level for drinking water (7600 Bq/kg, according to Sanitary Norms and Rules of the Russian Federation). Based on the results of this study and data obtained by other researchers earlier, it became possible to assess the half-time for decrease of activity concentration of tritium in surface and ground waters in the period 2008–2019. The mean value (± standard error of the mean) of the effective half-time of tritium in water from the mine, the boreholes, and the Kuniyok River was estimated as 4.4 ± 0.2 year. The decrease in activity concentration of tritium in water depended more on ecological processes (dilution with “pure” water) than on physical decay of the radionuclide. In 2019, the estimated value of the effective dose due to ingestion of tritium in drinking water from the Kuniyok River was 0.17 μSv; this was negligible compared to the dose limit of 1 mSv per year for the public.

Prediction of CBR and resilient modulus of crushed waste rocks using machine learning models

Prediction of CBR and resilient modulus of crushed waste rocks using machine learning models

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.

Thermal and deformational repairing effect of crushed rock revetment acting as reinforcement along Qinghai–Tibet railway in permafrost regions

Due to the particularity and complexity of permafrost subgrade, research on its long-term maintenance and reinforcement under climate warming and engineering activities is of great significance. To mitigate subgrade diseases caused by thermal disturbance during the engineering construction and operation in the initial stage, the crushed-rock revetment (CRR) was additionally paved with a thickness of 1.5 m and 1.0 m on some sunny and shady shoulders of the traditional embankments along the Qinghai–Tibet railway, respectively. The improving effects for thermal and deforming stability are evaluated based on observation data of ground temperatures and embankment deformations at two sites from 2002 to 2014. The results show that a larger uplifting magnitude in the artificial permafrost table (APT), greater ground temperature decreasing amplitudes and reduction ranges of settling rate appear under the shady embankment shoulder in warm permafrost region, and both sides in the cold permafrost region when reinforcing with CRR. However, in warm permafrost region, the laying of CRR on the sunny slope of subgrade may cause considerable thermal disturbance to the underlying permafrost foundation, combined with the resulting additional stress, induce the further expansion of differential settlement. Moreover, the thermal stability strengthening effect of the CRR is closely related to the variation of the APT thickness in the earlier stage, convection intensity inside the CRR, ‘cold energy reserve’ in the deeper permafrost, and amount of solar radiation received by the CRR. More effective reinforcements should be implemented to alleviate the potential threaten beneath sunny embankment slope in warm permafrost regions.

Effect of gradation, compaction and water content on crushed waste rocks strength

We reduced the size of the abstract to 170 words, but we cannot go lower without loosing meaning. We hope it will be ok like this --> Open-pit mining operations generate large volumes of waste rocks. It can be both economically and environmentally attractive to valorise waste rocks in mining infrastructures such as haul roads. However current practice usually consists of using waste rock directly, without any preparation or selection, thus frequently resulting in punctures, dust generation and low durability. The aim of this study was therefore to determine optimal geotechnical properties of crushed waste rocks for use in surface course layer. Crushed waste rocks were characterised in the laboratory. Their strength was evaluated using California Bearing Ratio (CBR) tests. Several compaction energies were used, and he effect of maximum particle size, fines content, and dry density on the strength were assessed. Results showed that these parameters had a significant impact on the performance of the material. The strength was maximum for an optimum FC of around 10%, a high density and in the presence of coarser particles. Two regression models were also proposed to predict the CBR value of crushed waste rocks based on their physical properties.

Risk assessment of the crushed rock structure embankments of the Qinghai-Tibet Railway under a warming climate

On the Qinghai-Tibet Plateau, transportation infrastructure has been greatly affected by permafrost degradation owing to the increasing air temperature caused by climate change. This study presents a risk assessment model for evaluating the viability of the crushed rock embankment under the scenario of climate warming. The results demonstrate that the service life of an embankment is determined by the time it spends at the lowest or low levels of failure risk. At the failure probability threshold of 0.1, the service lives of open crushed rock-based and U-shaped crushed rock embankments are longer than 100 years, those of closed crushed rock-based embankments are about 66 years, and those of crushed rock revetments are less than 40 years. In essence, the longer an embankment has been in service, the stronger its ability to resist climate warming. Based on these results, U-shaped crushed rock and crushed rock-based embankments are the most capable of offsetting the effects of climate warming on permafrost and should account for a higher proportion of independent embankment structures. The same cannot be said for crushed rock revetments, which should only be used as auxiliary engineering measures. Despite this recommendation, regular maintenance should be conducted on the open system crushed rock embankments because the high winds on the Qinghai-Tibet Plateau fill the embankments with sand, which has a negative effect on the long-term stability of the embankments.

Full-scale test on emergency pavement repair under aeroplane loading

To investigate the structural response of emergency pavement repairs under aeroplane loading and verify the backfill material and structural applicability, two craters were backfilled. Crater 1 comprised a 2.4 m thick layer of recovered flying objects, 0.4 m of graded crushed rock (GCR), 0.2 m of roller-compacted concrete and a fibre-reinforced plastic (FRP) course. Crater 2 comprised a 2.4 m thick layer of flying objects, 0.6 m of GCR and a FRP course. Static and dynamic loads were applied using two aeroplanes. The results showed that the FRP pavement layer reduced the maximum deflection of crater 2 by 21%. Crater 1 and the concrete pavement were both slightly rigid structures with a strong load-transfer ability. The dynamic deflection basin curves of crater 2 could be fitted using a Gaussian function, while the curves of crater 1 and the concrete pavement were fitted using a quartic polynomial. Under static loading, the earth pressures of crater 2 at −0.6 m, −0.4 m and −0.2 m depths were 4.3, 9.0 and 9.6 times of those of crater 1, respectively. At a depth of −0.2 m, the earth pressure of crater 1 was 0.11 MPa, while that of crater 2 was 1.06 MPa. The results can be used to guide rapid quality inspection and optimisation design of emergency pavement repair structures and materials.

Construction and Current Maintenance of the Reinforced Ballast Layer of the Railway Track

The article presents the ideas for the construction and the current maintenance of the reinforced plastic geogrid top ballast composed of crushed solid rock. Meanwhile, the reinforced ballast material acquires new properties, which lead to the formation of a composite material with new properties. In the reinforced material, only micro-deformations occur under the dynamic load, which is intrinsic to solid rock. In this case, laboratory simulation of reinforced ballast with a cyclic load showed that multilayer stabilization with three geogrids reduces settelment by 67% and does not require cleaning during the entire service life of the reinforced top ballast.The construction and the current maintenance of the composite structure make a real difference from the ballastless structure of the railway track as the work techniques with geosynthetics in the ballast subgrade are properly developed, and they are widely used during the repairs of railway track, because the development of the technology for the creation of reinforced geocomposite will not cause any problem.

Assessing soil index parameters to determine the frost susceptibility of crushed rock aggregates

In Norway, crushed rock aggregates are widely used in all layers of pavement infrastructures. Frost heave severely affected the Norwegian road network during cold winters of 2009/10 and 2010/11, including newly built roads. In 2016, the Frost Protection for Roads and Railways project (FROST) was set up in part to investigate frost susceptibility and frost heave of crushed rock aggregates. Twenty-three frost heave tests were performed on the 0–4 mm fraction with nine types of different rock, in which 2 series were measured at different crushing stages in a production line. The tests succeeded to expand knowledge on the frost susceptibility of crushed rock aggregates, using the segregation potential as frost susceptibility criterion. However, the cost and time necessary for laboratory work were important. Since budget for road construction and rehabilitation are variable, a methodology to estimate the segregation potential using soil index properties was tested. A laboratory investigation was carried out to compare segregation potentials determined in laboratory (SP0 lab) to those calculated using the normalized segregation potential equations (SP0.n), which requires only four soil index parameters: the specific surface area of the fine fraction, the mean grain-size diameter of the fine fraction, the water content, and the liquid limit of the fine fraction, the fine fraction being <75 μm. Results showed a good correlation between the SP0 lab and the SP0.n. Results also showed a strong correlation between the SP0 lab and the crushed rock aggregates with a specific surface area of the fine fraction of <8 m2/g, which was the case for 19/23 samples. High specific surface area estimations (≈12.5 m2/g) found in early stage crushing aggregates are believed to be cause by weak mineral content enrichment and/or grain-surface irregularities in the fine fraction. In conclusion, this study confirms that the estimation of the segregation potential of a crushed rock aggregate from the normalized segregation potential equations is possible and reliable. The relationship developed using the specific surface area to determine the segregation potential is promising and should be validated furthermore to reinforce the relationship.