Crushed Rock Research Articles

Influence of calcium carbonate on green self-compacting concrete incorporating porcelain tile waste as coarse aggregate replacement

The disposal of ceramic tile waste poses a significant environmental challenge in the construction industry. This study aims to explore the influence of calcium carbonate (CC) on the properties of self-compacting concrete (SCC) incorporating porcelain tile waste as a coarse aggregate replacement. The objective is to enhance the performance of SCC while addressing the limitations of recycled ceramic aggregates and achieving the desired strength class. SCC specimens were cast by partially and completely substituting natural crushed rock with varying percentages of porcelain tile aggregates (PTA-0, 25 %, 50 %, 75 %, and 100 %) and cement with calcium carbonate (CC-10 %, 20 %, and 30 %). Workability assessments, mechanical properties, and durability were evaluated and compared against those of reference concrete. The experimental findings revealed that the incorporation of CC and PTA positively influenced the workability, mechanical properties and durability of SCC. Notably, the SCC mixture incorporating 10 %CC and 25 %PTA demonstrated exceptional performance, achieving the highest compressive strength of 64.9 MPa at 28 days. Moreover, even with complete substitution, the compressive strength reduction remained below 5 %. These results highlight the potential of PTA and CC-based SCC mixtures as an efficient and sustainable approach for utilizing porcelain tile waste in high performance concrete production. The findings contribute to addressing environmental concerns, promoting waste management practices, and reducing the reliance on natural resources in the construction industry.

Thermal-deformation behavior of a crushed-rock embankment along a high-grade highway in permafrost regions

Numerous studies have been conducted to investigate the thermal stability of crushed rock embankments (CREs). In this study, we developed an automatic field monitoring system for a CRE during the construction of the Gonghe–Yushu High-grade Highway (GYHH) to explore both the convective cooling and the deformation controlling effect of the crushed rock layer (CRL). We evaluated the thermal-deformation performance of a the CRL based on the long-term field monitoring data. The results reveal that the upper peat layer could slow down the degradation of shallow permafrost. However, the heat absorbed by the black asphalt pavement significantly contributed to the degradation of the permafrost beneath the contrast embankment without the CRL. The CRL had an obvious cooling effect range for the shallow stratum, where an effective cooling zone formed (about 4 m deep in the 4th year after the construction of embankment). Nevertheless, deep permafrost beyond this effective cooling range continued to warm owing to the downward heat flux. Consequently, the total settlement of the CRE decreased by 23% compared with the contrast embankment in the 5th year. This work is expected to provide a reference for the design of the CREs in permafrost regions.

A Perspective into Development of Pavement Design Methods for Low Volume Roads: A Review

The definition of low volume roads (LVRs) is not time static and it varies from place to place around the world. The importance of such roads for providing access, in connecting communities and link farms to markets is well appreciated worldwide. LVRs are credited as the direct source of social economic development in rural communities, growth, reduction of poverty and sustaining livelihood. Nevertheless, the LVR network is growing at an unsatisfactory rate especially in Sub-Saharan Africa. The slow rate in developing LVR network is attributed to the high cost of construction and maintenance. To the author’s perspective, research has a significant role in lowering both maintenance and construction costs and in turn realise a growth in the network size and adequacy. To demonstrate the importance of research in road development, a comparison has been made between the current and the previous pavement design methods for LVRs in Tanzania. The improvement so far has been in the determination of subgrade strength using the Dynamic Cone Penetration (DCP) method instead of the less accurate and more demanding California Bering Ratio (CBR) method; a simpler approach in estimating design traffic load that is also less conservative; encouraging the use of local natural materials which could be marginal for construction instead of the conventional but expensive crushed rock; and improvement in layer design which result to less pavement thickness. While all these improvements enhance saving in pavement cost, it is argued that further development is possible through research especially in local materials and procedures.

Laboratory experiments and modelling of the geochemical interaction of a gabbro-anorthosite with seawater and supercritical CO2: A mineral carbonation study

The potential for mineral carbonation of carbon dioxide (CO2) in a plutonic mafic rock is addressed in this work through a set of laboratory experiments on a gabbro-anorthosite sample from the Torrão - Odivelas Massif (Portugal). The experiment was conducted in two stages under pressure (8 MPa) and temperature (313.15 K) conditions similar to those expected around a CO2 injection well. Stage-I simulated dissolution conditions, with a crushed rock sample (1–3 mm) exposed for 30 days to CO2 supersaturated seawater (0.576 M). Stage-II favoured carbonation conditions; cubic rock specimens (8 cm3) were brought in contact with the Stage-I seawater subsaturated in CO2 (0.095 M).A multi-analytical methodology was applied to follow the mineralogical and geochemical evolution of rock and seawater during both stages. At the end of Stage-I, the aqueous phase showed a marked increase in iron (Fe), magnesium (Mg) and calcium (Ca) ions and milder increase in silicon (Si) and aluminium (Al) ions. At the end of Stage-II, a decrease in Si and Al concentrations was observed while the Fe, Mg, Ca concentrations still increased, albeit at a lower rate. No significant geochemical variations were detected in the bulk solid phase. The bulk X-ray diffraction (XRD) analyses detected halite as a new mineral phase, while the grazing-XRD design revealed the presence of dolomite. Moreover, the elemental distribution mapping demonstrated the spatial association of carbon with magnesium indicating magnesite crystallisation. The geochemical model developed in CrunchFlow code was able to reproduce the experimental observations and simulate the chemical behaviour for longer time periods.Overall, the experiments and model point towards a mineral carbonation potential in the Torrão - Odivelas Massif, with further studies being required to upscale the laboratory results to field scale.

Numerical optimization on differential adjusting measures for asymmetrical degenerated warm permafrost railway embankment

Affected by climate warming and shady–sunny slope effect, the permafrost foundation under the railway is undergoing a significant asymmetric degradation process; research on the corresponding regulating or strengthening measures is urgently needed. Based on a well developed of numerical model, we analyzed the ‘thermal repair’ effect of three redesigned differential thermal reinforcement on the partially degraded permafrost embankment with steps. The results show that, when used as a strengthening measure, the method of laying crushed rock revetment (CRR) with different thicknesses on the sunny and shady slopes cannot completely eliminate the residual warm permafrost regions formed in the previous thermal erosion. When the TCRR scheme is adopted for reinforcement, although horizontal region from the evaporation section of thermosyphones (TPCTs) to the right side of the embankment is remarkably cooled, permafrost under the sunny slope is still deteriorating. In the long run, both ETCRR and TCECRR reinforcement schemes can produce a large range of ‘cold core’ right below the whole embankment. However, from the perspective of the simultaneous functioning range and cold storage capacity, the TCECRR scheme is signally more efficient. The thermal insulation materials in the above composite strengthening measures can not only resist the heat input in the warm season, but also improve their working efficiency by maintaining the temperature difference between the evaporation section of the heat pipe and the external environment in cold season. The addition of crushed rock revetment in TCECRR has played its thermal semiconductor effect and further improved the comprehensive thermal repair efficiency of the composite measures.

Arctic ecosystem restoration with native tundra bryophytes

ABSTRACT Bryophytes are ecologically essential to northern ecosystem restoration after disturbance. In this study, native bryophytes were used to revegetate two Arctic restoration sites. Different propagation types (small, medium, large fragments) and substrates (crushed rock, lake sediment, processed kimberlite in Canada; volcanic silt loam and crushed lava rock in Iceland) with two erosion control treatments (with and without cheesecloth) were evaluated. After two growing seasons, large bryophyte fragments resulted in the greatest density and total and live cover with erosion control and medium fragments resulted in the highest density and species occurrence without erosion control. Erosion control significantly increased live cover, total cover, species occurrence, and density, including a tempering effect on soil volumetric water content and temperature. Substrates with more heterogeneous surfaces (crushed rock, volcanic silt loam, crushed lava rock) yielded higher live cover, density, and spontaneous colonization than more homogeneous substrates (processed kimberlite, lake sediment) and can be more suitable for use in arctic ecosystems revegetation. The positive outcomes in both Canada and Iceland led to the conclusion that bryophyte propagation with large to medium fragments, erosion control with cheesecloth, and substrates with heterogeneous surfaces would be effective restoration approaches where bryophyte revegetation is a focus.

An Exploratory Study on the Use of Biobinder Derived from Brewer’s Spent Grains as an Asphalt Modifier

The production of asphalt concrete depends on the use of nonrenewable resources, such as asphalt binder and crushed rocks. Nowadays, technologies exist to convert biomass into biofuels and other by-products, which are an alternative to traditional sources of energy. The by-products of biomass conversion are similar to those of petroleum distillation. Several researchers have investigated the use of bio-oils from biomass as asphalt additives, but the potential use of brewery waste has not been considered. In this project, spent grains from a local brewery were converted into bio-oil using an auger reactor. The water in the bio-oil was removed, and the biobinder was analyzed. It was found that the biobinder derived from brewer’s spent grain has an elemental composition similar to other biomass-derived biobinders. Fourier transform infrared (FTIR) spectroscopy identified multiple polar functional groups in the biobinder, including high nitrogen content (4.6% by weight). Also, thermogravimetric analysis and gas chromatography showed a higher thermal degradation rate of the biobinder and loss of volatile components. The biobinder was used to create six blends with 5%, 8%, 10%, 15%, 20%, and 25% replacement of asphalt. The performance of each of the six blends was compared with the performance of control unmodified samples. The modified binder characterization indicated that the biobinder makes the material more susceptible to permanent deformation at high temperatures, and it showed higher aging of the short-term aged residue. However, the biobinder seems to improve relaxation properties at low temperatures, which could be attributed to its high nitrogen content. The findings of this preliminary study suggest that production and use of brewer’s spent grain biobinder are feasible and could be considered a potential feedstock for further development of asphalt biomodifiers.

Evaluation of the effectiveness of secondary support of haulage drifts based on a comparative analysis of the deformation characteristics of protective structures

The object of this study is the processes of managing the state of lateral rocks in the coal rock array with preparatory workings. The influence of deformation characteristics of the protective structures of the preparatory workings on the stability of lateral rocks in the coal rock array has been established. The stable state of the above-the-drift pillars of coal is provided within the deformation resource, which corresponds to the critical level of the specific potential energy of the deformation. The limits of the deformation resource are the range of change in the relative deformation of coal pillars 0.1≤λ≤0.25. When the critical level of the specific potential energy of deformation is passed, at λ˃0.25, there is a relative change in the volume of pillars δλ˃0,1, as a result of which their durability decreases and the state changes. Under such conditions, the residual strength of coal pillars is not enough to limit the movement of lateral rocks, which provokes their collapse. For protective structures made of crushed rock, within the established deformation resource of 0.4≤λ≤0.7, with an increase in static load and cross-sectional area, the specific potential energy of deformation decreases, simultaneously with the relative change in the volume of the embedded material. This is due to the compaction of the crushed rock and an increase in its strength. Regularities of change in the specific potential energy of deformation of protective structures have been established, which, under conditions of uniaxial compression, make it possible to assess, within the deformation resource, their stability. To ensure the stability of lateral rocks in the coal rock array and to preserve the operational condition of the preparatory workings, it is advisable to use protective structures made of crushed rock. This method will limit the movement of the roof and sole in the produced space and avoid collapses.

Microstructure and mechanical behavior of cemented gold/tungsten mine tailings-crushed rock backfill: Effects of rock gradation and content

Without appropriate and responsible waste management in place, the cursory storage of tailings and waste rocks on the surface can cause devastating damage to the planet's ecosystems. To proactively manage or abolish the damage, some techniques such as mine backfill have been already used repeatedly in mines. Microstructure and strength behavior of cementitious tailings-crushed rock backfill (CTCRB) with gold/tungsten tailings and rock contents (e.g., 10%, 20%, 30%, 40%, and 50%) were conducted in this study by using both UCS (unconfined compressive strength) tests (e.g., peak strengths, stress-strain curves, failure modes) and SEM micro-graphs. Key conclusions were shown that: when gradation and content of crushed rock was considered as 1–3 mm and 50% respectively, the UCS value of gold tailings based backfills was 1.02 MPa. In contrast, the UCS value of tungsten mine tailings based backfills was 1.36 MPa when the amount of crushed rock within the filling matrix became 10%. Tungsten tailings based backfills were more sensitive to crushed rock gradation than gold tailings based backfills. CTCRB's stress-strain curvatures were up-concave in the step of pore compaction. With the increase in the content and gradation of crushed rock, tungsten tailings based backfills showed swelling and crushing in complete destruction. Tailings' particle size, crushed rock content and gradation utterly affected the failure modes of CTCRB. Ettringite/CSH gel was found to be the leading hydration materials in the backfill matrix. The micro-cracks within CTCRB specimens were unfavorably correlated with its UCS data. To conclude, this study's main outcomes could give a significant guide for CTCRB's industrial uses.

Limited access to oxygen reduces the release of harmful trace elements from submerged alum shale debris

Construction and mining activities in acid-producing alum shale regions often produce large volumes of crushed rock. Disposal under groundwater level (e.g., a bog) may minimize oxygen access. In this study, the effect of varying oxygen access on the leaching potential of alum shale was investigated by submerging tunnel construction rock debris in synthetic rainwater under atmospheric (AOC) and low oxygen conditions (LOC) for 52 weeks. The sulphate increase and nitrate decrease in the leachates suggested that pyrite (FeS2) in the alum shale was oxidized, but carbonates originating from calcite dissolution provided sufficient buffering capacity (leachate pH ~7.7 over 52 weeks), resulting in neutral rock drainage. Less available oxygen led to significantly lower production of sulphate and acid from pyrite oxidation, reducing the release of harmful elements. Under LOC, the leaching of Mo, Co, Ni, Zn and Cd was 2–4 times lower than under AOC and the lower buffering requirement diminished the release of Ca as well as divalent cations (Mg, Sr, Mn) likely present as impurities in calcite. Contrastingly, limited pyrite oxidation led to less oversaturation with respect to BaSO4 and lower release of Fe in the LOC leachates. Thus, co-precipitation of 226Ra was inhibited and scavenging of leached V, As and Sb by newly formed Fe(OH)3 was not as dominant as in the AOC systems. Leaching of U was ~20 % higher under LOC likely due to enhanced complexation by dissolved carbonate. In general, element leaching rates were slower under low O2 levels. Characterization of water collected at the disposal site after ~1.2 years of discarding tunnel materials showed that the weathering of debris submerged in the open, water-filled pond occurred similarly to leaching under low oxygen conditions. Overall, these results highlight the importance of minimal oxygen access or anaerobic conditions when acid-producing rock waste is stored under water.

Heat transfer and cold energy capacity properties of crushed-rock layer in cold sandy regions

Addressing the impact of climate warming and anthropic activities, crushed-rock layer (CRL) is a zero-carbon emission technology by using natural cold air to protect infrastructures in permafrost regions. But in cold sandy environment, the issue of its cold energy capacity on account of aeolian sand clogging needs to be solved. Based novel field experiments on Tibet Plateau, the dynamic evolution law and its controlling factors of natural cold energy accumulation of the CRL are quantitatively figured out. Results show that the initially open CRL had a strong forced convection of air in the first two winters, while the cooling effect was failure after the third winter. The filling of aeolian sand caused heat transfer mode of the CRL to change from forced convection to natural convection in cold season, losing the ability of “thermal semiconductor” aimed to mitigate permafrost degradation. The closed CRL represented weak natural convection in cold season and thermal insulation in warm season, which had better long-term cooling effectiveness than other conditions in the aeolian environment. As the thickness of the aeolian sand filling increased, the maximum Rayleigh number and natural convection time of the closed CRL decreased. Accumulation of cooling energy in cold season and thermal insulation in warm season were positive correlation with thickness of porous media layer. It was not recommended to solely adopt crushed rock embankment or crushed rock revetment in aeolian sand environment and regions with higher annual average temperature. The findings solved the scientific evaluation issue of cold energy storage capacity of CRL, and provided constructive engineering implications for its efficient application.

Arsenic Release from Various Sizes of Excavated Crushed Rock Mixed with Soil at Various Ratios under Three Mass Water Contents for Cropland.

The purpose of this experiment was to investigate the feasibility of treating arsenopyrite-containing excavated crushed rock (ECR) in cropland by examining the amounts of arsenic released from various sizes of ECR mixed with soils at different ratios under three water levels using a batch incubation experiment. A total of 4 particle sizes of ECR were mixed with soil from 0% to 100% in 25% increments under three mass water contents such as 15%, 27%, and saturation. The results showed that the amount of As released from ECR mixed with soil was in the order of 27% saturation and 15% for 180 days regardless of the ECR:soil ratios, and the increase in the amount of As released before 90 days was slightly greater than that after 90 days. The maximum and minimum contents of released As were observed at 350.3 mg·kg-1 (ECR:Soil = 100:0, ECR size = 0.0-0.053 mm, and Ɵm = 32.2%), indicating that the smaller the ECR particle size resulted in a higher extractable As concentration. The amount of As released was higher than the relevant standard (25 mg·kg-1), except for ECR with a mixing ratio (25:75) and particle size (4.75-10.0 mm). In conclusion, we assumed that the amount of As released from ECR was influenced by the higher surface area of smaller ECR particle sizes and mass water content, which determine the porosity of the soil. However, further studies are needed on the transport and adsorption of released As depending on the physical and hydrological properties of the soil to determine the size and incorporation rate of ECR into the soil in view of the government standard.

The Use of Wastes from Gas Purification Facilities of Alumina Production in Road-Building Technologies

The environmental problems of alumina production, caused by the formation of waste gas treatment plants are considered. The phase and chemical composition and microstructure of dust from gas treatment facilities of thermal power plants has been studied. It has been suggested to use gas-cleaning plant wastes as active mineral additives in road mixtures. The possibility of using electrofilter dust as a mineral powder for asphalt concrete has been experimentally verified. It has been established that the properties of asphalt concrete using the dust from gas cleaning facilities of heat-power equipment of alumina production are practically the same as those of asphalt concrete prepared on the crushed limestone rock of Mazul limestone mine.

Innovative Air Convection Embankment for Cold/Arctic Region Low-Volume Roads

Roadbed thaw settlement is a unique challenge for the durability of low-volume roads (LVRs) in permafrost regions. Air convection embankment (ACE) is an effective technique that acts as a semi-heat-transfer system to control temperature variation and reduce the thaw depth of subsoil. However, limited by the shortage of the necessary crushed rocks within a short distance, building an ACE in Alaska, U.S., is prohibitively expensive. Previous studies identified the feasibility of using cellular concrete for ACE and determined the optimized thickness of the cellular concrete aggregate interlayer for ACE. However, the economic efficiency and thermal and mechanical performance of the optimized, innovative cellular concrete aggregate ACE need further investigation. Therefore, two innovative cellular concrete ACEs with reasonable heights for cold/Arctic region LVRs were evaluated in this study. A thermal-mechanical coupling model was created using ANSYS Fluent and ANSYS Mechanical to evaluate the thermal and mechanical stability of the two optimized innovative cellular concrete aggregate ACEs by comparing them with a typical Alaskan flexible pavement, a silty sand/gravel embankment, and a conventional crushed-rock ACE. The fatigue damage was predicted using the elastic-based Alaska Flexible Pavement Design (AKFPD) program. A life-cycle cost analysis was conducted using AKFPD to evaluate the overall long-term economic efficiency of the cellular concrete ACEs. The results showed that cellular concrete ACE could achieve better thermal and mechanical performance with much lower embankment height than crushed-rock ACE. The cost analysis showed that the proposed cellular concrete ACEs had a significant cost advantage over the conventional crushed-rock ACE.

Low-cost crushed-rock heat storage with oil or salt heat transfer

The demand for variable electricity and heat is met by fossil-fuel power plants because the power plant capital costs and the cost of storing fossil fuels are low. A low-carbon economy requires replacement of the storage function of fossil fuels to provide variable heat and electricity as needed. The Crushed Rock Ultra-large Stored Heat (CRUSH) system is a new technology with the goal to provide heat storage at an incremental capital cost of $2–4/kWh at scales of 10 s to 100 s of GWhs that enables economic daily to multi-week storage. CRUSH can be coupled to nuclear power plants, concentrated solar power (CSP) plants and thermal energy batteries to provide variable electricity and heat on demand. Sensible heat is stored in crushed rock—the lowest-cost heat-storage material. Heat is transferred to and from the crushed rock using nitrate salt or heat-transfer oils but these fluids do not store heat. Heat from a nuclear reactor, CSP plant or conversion of low-price electricity into heat is used to heat the salt or oil. The hot fluid is poured over the crushed rock, trickles downward by gravity through the rock, heats the rock and is collected by the drain pans under the crushed rock. To recover heat cold salt or oil is poured over hot crushed rock, trickles down by gravity while being heated and is collected by the drain pans under the crushed rock. The system design and engineering trade-offs are described. The technology is in the early stages of development.

Experimental Study and Mathematical Description of Gradation Effect on the Mechanical Characteristics of Crushed Waste Rocks

Crushed waste rocks, generated from mining operations, have been widely used for mining infrastructure constructions such as haul roads because of their low cost, high strength, and availability. Crushed waste rock gradation can, however, vary greatly, depending on blasting, mineralogy, and crushing process, but it is a key factor influencing the mechanical properties of crushed waste rocks (including resilient modulus, permanent deformation, and shear strength). Gradation should therefore be optimized to enhance their performance in the field. A series of repeated load and monotonic triaxial tests were carried out on crushed waste rocks with different gravel-to-sand (GS) ratios and fines contents (FC). Results showed that the optimum GS ratio was between 1 and 1.5 and contributed to provide higher resilient modulus and shear strength, and lower permanent strain. An increase in FC could, to the contrary, result in the decrease of resilient modulus and permanent strain and also a significant increase in shear strength. The structure state of crushed waste rocks was quantified using the cm model, and the mechanical properties of crushed waste rocks were dominated by sand and fines when the content of sand and fines was higher than 80%, while it was dominated by gravel particles as the content of sand and fines was lower than 60%. Here, the MR − θ model and the Rahman and Erlingsson model (extended using time-hardening approach) were well adapted to describe resilient modulus and accumulated permanent strain, respectively. Prediction models were also developed based on correlation analyses to predict the resilient modulus and permanent strain of crushed waste rocks based on gradation parameters.

Selecting rock types for very-low-cost crushed rock heat storage systems with nitrate salt heat transfer

Today the demand for variable electricity is met by fossil-fuel power plants because the capital costs and the cost of storing fossil fuels are very low. A low-carbon grid requires replacements for stored fossil fuels to provide variable heat and electricity as needed. The thermal energy replacement option is to send heat from nuclear and concentrated solar power (CSP) plants operating at full capacity to heat storage with variable heat output to the power block to provide variable electricity to the grid. Very low-priced electricity from wind and solar can also be converted into stored heat. Today the lowest-cost commercial heat storage systems are in CSP plants and use nitrate salt stored in hot and cold storage tanks. Advanced heat storage systems use nitrate salt for heat transfer but replace some or all the nitrate salt with lower cost crushed rock for heat storage. These systems may lower the capital cost of heat storage by a factor of five or more to several dollars per kWh of stored heat. Locally acquired crushed rock is the lowest-cost heat-storage material but not all rock is compatible with heat storage requirements including chemical compatibility, mechanical properties, and durability under thermal cycling. Rocks have been sorted into categories likely, possibly, and unsuitable and the basis for these conclusions has been documented. Potentially suitable rock types include basalt, peridotite, taconite, quartzite, quartzitic sandstone and serpentinite. Except for taconite, sedimentary rocks are unlikely to be suitable for service.

Assessment of the enhanced weathering potential of different silicate minerals to improve soil quality and sequester CO2

Enhanced weathering is a negative emission technology that involves the spread of crushed silicate minerals and rocks on land and water. When applied to agricultural soils, the resulting increase in soil pH and release of nutrients may co-benefit plant productivity. Silicate minerals and rocks differ in their enhanced weathering potential, i.e., their potential for both carbon dioxide (CO2) sequestration and soil quality improvements. However, studies comparing silicate minerals and rocks for this dual potential are lacking. Therefore, we compared the enhanced weathering potential of olivine (Mg2SiO4), basalt, wollastonite (CaSiO3), and two minerals that are novel in this context, anorthite (CaAl2Si2O8) and albite (NaAlSi3O8). A down-flow soil column experiment was designed allowing for measurements on soils and leachate, and calculations of organic and inorganic carbon budgets. Our results showed comparatively high CO2 capture by enhanced wollastonite and olivine weathering. Furthermore, CO2 capture per m2 specific surface area indicated potential for enhanced anorthite and albite weathering. Calculated carbon budgets showed that most treatments produced net CO2 emissions from soils, likely related to the short duration of this experiment. All silicates generally improved soil quality, with soil nickel contents remaining below contamination limits. However, nickel concentrations in leachates from olivine-amended soils exceeded the groundwater threshold value, stressing the importance of monitoring nickel leaching. We found a relatively high enhanced weathering potential for wollastonite, while the potential for olivine may be constrained by nickel leaching. The promising results for anorthite and albite indicate the need to further quantify their enhanced weathering potential.

STUDY OF DEFORMATION PROPERTIES OF PROTECTIVE STRUCTURES OF PREPARATORY MINING WORKS

Purpose. To study the stability of the security structures of the preparatory mine roadways of steep seams while unloading the coal-rock massif to prevent the collapse of side rocks in the excavation areas of the coal mine and create safe working conditions for miners. Method. In order to achieve the aim of the research, the study of the stability of security structures was carried out at the laboratory of mountain pressure by using experimental samples in the form of whole coal and structures consisted of crushed rock, which were subjected to uniaxial compression. Results. Under the conditions of uniaxial compression of whole coal or constructions consisted of crushed rock, with the ratio of length to width a/b= (1-2) and an increase in the cross-sectional area S (m2) of the experimental samples, a relative change of their volume δV was observed. For whole coal, the steady state is ensured by the relative volume change δV ≤ 0,1. Beyond the set value of δV, the whole coals lose their stability and collapse, which results in the collapse of the side rocks. For the crushed rock structures, with an increase in the cross-sectional area of the compressible specimens, the relative volume change decreases from δV = 0,2 to δV = 0,35. At the same time, the crushed rock is compacted in the whole volume of the used material, the bearing capacity of protective structures is increased, which enables limiting the movement of lateral rocks and ensures their integrity. Scientific novelty Within the limits of the deformation resource of protective structures consisting of crushed rock of different granulometric composition, with their uniaxial compression, a type of functional dependence was established, which enables us to estimate the relative change in the volume of flexible supports from stiffness, which is necessary for assessing their bearing capacity. Practical significance. In order to create safe working conditions for miners in the excavation areas of a deep coal mine and prevent the collapse of side rocks in the coal massif, it is advisable to use flexible protective structures for the protection of preparatory coal mine roadways, when the ratio of their linear dimensions corresponds to the ratio of length to width of a/b>(1-2).

ЗІСТАВЛЕННЯ ДЕФОРМАЦІЙНИХ ВЛАСТИВОСТЕЙ ОХОРОННИХ СПОРУД ПІДГОТОВЧИХ ГІРНИЧИХ ВИРОБОК

Purpose. Investigate and compare the deformation properties of protective structures in the form of coal pillars and structures made of crushed rock for a justified choice of the protection method, which can make it possible to ensure the stability of side rocks in the coal massif and preparatory works in the mining areas in the coal mine. Methodology. To achieve the goal, laboratory studies were performed on experimental samples subjected to uniaxial compression. For pillars, their thickness was changed, whereas for structures made of crushed rock the thickness of the rock layer was changed at a constant cross-sectional area. Results. As a result of the conducted research, the deformation properties of protective structures that were subjected to uniaxial compression have been determined. A 15% reduction in their stiffness was recorded for pillars, when their thickness h0 was two times changed, and for the external static load, which varied according to a linear dependence. Within the limits of the safe deformation resource, when the relative deformation is in the range of values 0.18≤λ≤0.23, the stability of the pillars and their bearing capacity is ensured. At the same time, the relative change in their volume should not exceed 7-9%. It has been established that exceeding the limit level of the specific potential energy of deformation by an average of 12-14% causes the destruction of coal pillars. For protective structures made of crushed rock with a relative volume change of 0.35≤δV≤0.28, the value of the compaction coefficient of the original material decreases from kcons = 1.5 to kcons = 1.42 with a simultaneous increase in the work of compression and an increase of more than 20% in the specific potential energy of deformation, thanks to which the rigidity of the embedded material and the bearing capacity of protective structures made of crushed rock are ensured. Scientific novelty. The regularities of formation of deformation properties of protective structures under conditions of uniaxial compression, taking into account the change in the specific potential energy of deformation and the relative change in their volume, have been established. Practical significance. In order to ensure the stability of side rocks in the coal massif and preparatory workings at excavation sites in the coal mine, the feasibility of using partial or complete paving of the produced space from crushed rock, which limits the movement of side rocks in the produced space, has been substantiated.