Liquefaction and post-liquefaction behaviors of sands affected by immersion-induced degradation of crushed mudstone

A series of undrained triaxial tests was conducted to investigate the effect of crushed mudstone with the immersion-induced degradation on the liquefaction and post-liquefaction properties,and the undrained shearing behavior without precedent cyclic-loading histories of sands containing crushed mudstone.The tested materials with a main particle diameter of 2-0.85 mm were prepared by mixing sands and crushed mudstone to reach the prescribed mudstone content defined by dry mass ranging from 0% to 50%.The mixtures were subjected to immersion under a certain stress level and were subsequently tested.In addition,one-dimensional compression tests were also supplementally performed to visually observe the immersion-induced degradation of crushed mudstone.The test results mainly showed that: (1) the liquefaction resistance,the post-liquefaction undrained strength,and the undrained strength without a precedent cyclic-loading history decreased significantly with increasing mudstone content,M c ,up to 20%;(2) even a small amount of crushed mudstone affected these strengths;(3) the above-mentioned large reductions in the strengths were attributed to the immersion-induced degradation of crushed mudstone;(4) at M_(c) >20%,the liquefaction resistance increased while the significant increase in the undrained static strengths with and without precedent cyclic-loading histories was not observed;and (5) the increase in the liquefaction resistance at M_(c) >20% may have been attributed to both the gradual increase in the plasticity and the formation of the soil aggregates among deteriorated crushed mudstone,while the increase in the specimen density did not play an important role in such behavior.

Investigation of Carbonation of Concrete Based on Crushed Sand and Admixtures

Carbonation is a natural aging process that occurs in all types of concrete. One of its primary implications is the acceleration of steel corrosion caused by the phenomena of depassivation. The goal of this research is to investigate the carbonation of quarry sand-based concrete. The concrete is made of 100% crushed sand 0/6.3, gravel 8/15, and 15/25 from the Arab Contractor quarry in Nomayos, Cameroon, with CEM II B-P 42.5 R from CIMENCAM (Cimenteries du Cameroun). The study employed two admixtures: one with a dual superplasticizing and reducing action (Sikamen) and another with a water-repellent effect (Sika liquid). Carbonation was performed on concrete samples at the following dates: 0, 7, 14, 28, 56, 90, 180 days, one year, and six months. Carbonated concrete (CC) and non-carbonated concrete (NCC) samples are compared in terms of their physical attributes and mineralogical characteristics. The results of this investigation reveal that after more than a year and six months of carbonation, porosity decreases and permeability increases. Despite the high fineness modulus of quarry sand, the compressive strength of quarry sand-based concrete is satisfactory. Carbonation depth is relatively high on some dates, exceeding the minimal cover value for concrete reinforcement. Sikament additive increases concrete compactness and durability while decreasing permeability. Sika water repellant mixes with the lime in cement to generate complimentary crystallizations that block the mortar’s capillaries, making it watertight.

Effect of Crushed Air-cooled Blast Furnace Slag on Mechanical Properties of Concrete

Morphology characteristics of mix aggregates with crushed air-cooled blast furnace slag（SCR） and crushed limestone（LCR） with 5-20 mm and 20-40 mm gradation were represented by numerical parameters including angularity number（AN） and index of aggregate particle shape and texture（IAPST）.The effect of mix aggregates containing SCR on compressive strength and splitting tensile strength of concrete was investigated.Fracture characteristics of concrete,interfacial structure between aggregates and matrix were analyzed.The experimental results show that porous and rough SCR increases contact area with matrix in concrete,concave holes and micro-pores on the surface of SCR are filled by mortar and hydrated cement paste,which may increase interlocking and mechanical bond between aggregate and matrix in concrete.SCR can be used to produce a high-strength concrete with better mechanical properties than corresponding concrete made with LCR.The increase of AN and IAPST of aggregate may enhance mechanical properties of concrete.

Hydraulic support crushed mechanism for the shallow seam mining face under the roadway pillars of room mining goaf

While the fully-mechanized longwall mining technology was employed in a shallow seam under a room mining goaf and overlained by thin bedrock and thick loose sands, the roadway pillars in the abandoned room mining goaf were in a stress-concentrated state, which may cause abnormal roof weighting, violent ground pressure behaviours, even roof fall and hydraulic support crushed(HSC) accidents. In this case,longwall mining safety and efficiency were seriously challenged. Based on the HSC accidents occurred during the longwall mining of 3-1-2 seam, which locates under the intersection zone of roadway pillars in the room mining goaf of 3-1-1 seam, this paper employed ground rock mechanics to analyse the overlying strata structure movement rules and presented the main influence factors and determination methods for the hydraulic support working resistance. The FLAC3 D software was used to simulate the overlying strata stress and plastic zone distribution characteristics. Field observation was implemented to contrastively analyse the hydraulic support working resistance distribution rules under the roadway pillars in strike direction, normal room mining goaf, roadway pillars in dip direction and intersection zone of roadway pillars. The results indicate that the key strata break along with rotations and reactions of the coal pillars deliver a larger concentrated load to the hydraulic support under intersection zone of roadway pillars than other conditions. The ‘‘overburden strata-key strata-roadway pillars-immediate roof" integrated load has exceeded the yield load that leads to HSC accidents. Findings in HSC mechanism provide a reasonable basis for shallow seam mining, and have important significance for the implementation of safe and efficient mining.

The creep compaction behavior of crushed mudstones under the step loading in underground mining

The crushed rocks are used as a filling material in mined丒out areas of underground mining. Compared with the man-made filling materials, the crushed rocks exhibit higher compressibility and lower stability, which may result in instability of surrounding rock and surface subsidence. To study the creep compaction behavior of crushed mudstones, a series of creep tests are conducted. The investigations show that the creep compaction behavior of crushed mudstones is highly dependent on the original grain composition and axial stress applied on the samples. The samples with more large particles are easier to deform at initial loading stage for more large voids existed in the samples, and exhibit greater stability than those with smaller particles when the axial stress less than the bearing capacity of uframework structure When the axial stress is higher than 20 MPa, the influences of grain composition on deformability of crushed mudstones are weakened after the samples experience repeated compression. At lower stress level, the creep behavior prefers to occur in the samples w.h smaller particles, which is mainly caused by particles flow without significant particle breakage. As the axial stress increases, the single-sized sample with smaller particle size and the well-graded sample with larger Talbol power exponent n present more unstable under the constant stress. In addition, the filling of the residual intergranular voids by small particles formed by crushing and splitting behavior is the main cause of creep deformation. Lastly, a creep equation of crushed mudstones is obtained in this paper, which can agree with the experimental results in good.

Porosity of crushed rock layer and its impact on thermal regime of Qinghai-Tibet Railway embankment

It has been proven that crushed rock layers used in roadbed construction in permafrost regions have a cooling effect. The main reason is the existence of large porosity of the rock layers. However, due to the strong winds, cold and high radiation conditions on the Qinghai-Tibet Plateau(QTP), both wind-blown sand and/or weathered rock debris blockage might reduce the porosity of the rock layers, resulting in weakening the cooling effect of the crushed rock layer(CRL) in the crushed rock embankment(CRE) of the Qinghai-Tibet Railway(QTR) in the permafrost regions. Such a process might warm the underlying permafrost, and further lead to potential threat to the QTR's integrity and stability. The different porosities corresponding to the different equivalent rock diameters were measured in the laboratory using water saturation method, and an empirical exponential equation between porosity and equivalent rock diameter was proposed based on the measured experimental data and an important finding is observed in our and other experiments that the larger size crushed rock tends to lead to the larger porosity when arbitrarily packing. Numerical tests were carried out to study impacts of porosity on permafrost degradation and differential thaw depths between the sunny and shady shoulders. The results show that the decrease in porosity due to wind-blown sand or weathered rock debris clogging can worsen the permafrost degradation and lead to the asymmetric thermal regime. In the traditional embankment(without the CRL within it), the largest differential thaw depth can reach up to 3.1 m. The optimized porosity appears in a range from 34% to 42% corresponding to equivalent rock diameter from 10 to 20.5 cm. The CRE with the optimized porosities can make underlying permafrost stable and 0 ℃ isotherms symmetric in the coming 50 years, even under the condition that the climate warming can lead to permafrost degradation under the CRE and the traditional embankment. Some practical implications were proposed to benefit the future design, construction and maintenance of CRE in permafrost regions.

The influence of moisture on the permeability of crushed shale samples

Shale cuttings and cores recovered from the subsurface and stored for hours to decades tend to dry out and lose moisture and hydrocarbons,leading to an increase in the effective matrix permeability.Moisture loss in shale samples is a fundamental sample preservation problem which can be solved by applying a standard moisture equilibration procedure to restore lost moisture.Our aim was to investigate the relationship between permeability and variable moisture as-received,as-received moisture-equilibrated and saturated moisture-equilibrated samples.Samples were crushed to a series of particle sizes(0.6-2.0)mm and moisture equilibrated at 97% relative humidity.Results show that moisture equilibration in the samples was achieved after 72 h.The permeability of the saturated moisture-equilibrated and as-received moisture-equilibrated samples decreased exponentially with increase in moisture content.The high correlation coefficient between permeability and particle size(r = 0.96 and 0.97)for moisture-equilibrated samples compared to 0.76 for as-received samples indicates that moisture equilibration improves permeability measurements in crushed shale samples.Furthermore,permeability measurements are repeatable for moisture-equilibrated samples compared to samples that were not equilibrated(as-received).We conclude that moisture content affects permeability and moisture equilibration normalizes and improves the repeatability of permeability measurements in crushed shale.

Microstructure and Properties of Silty Siliceous Crushed Stone-lime Aerated Concrete

The clayish crushed stone was used for making aerated concrete. Through studying hydro-thermal synthesis reaction, mix ratio, gas-forming and performance analysis, Grade-B05 and Grade-B06 aerated concrete were prepared successfully. The proper mix ratio and key processing parameters were achieved. The microstructure of aerated concrete with crush stone was analyzed by means of XRD and SEM. The experimental results indicate that the hydration products are poorly crystalline C- S- H （ B ）, tobermorite and hydrogarnet. No componeat of clay was found. Unreacted SiO2 cart be in existence, and the structure system of aerated concrete is homogencous and dense.

The cooling effect of crushed rock structures on permafrost under an embankment

Based on the analysis and comparison of soil temperature, thermal regime and permafrost table under the experimental embankment of crushed rock structures in Beiluhe, results show that crushed rock structures provide an extensive cooling effect, which produces a rising permafrost table and decreasing soil temperatures. The rise of the permafrost table under the embankment ranges from an increase of 1.08 m to 1.67 m, with an average of 1.27 m from 2004 to 2007. Mean annual soil temperatures under the crushed rock layer embankment decreased significantly from 2005 to 2007, with average decreases of ?1.03 °C at the depth of 0.5 m, ?1.14 °C at the depth of 1.5 m, and ?0.5 °C at the depth of 5 m. During this period, mean annual soil temperatures under the crushed rock cover embankment showed a slight decrease at shallow depths, with an average decrease of ?0.2 °C at the depth of 0.5 m and 1.5 m, but a slight rise at the depth of 5 m. After the crushed rock structures were closed or crammed with sand, the cooling effect of the crushed rock layer embankment was greatly reduced and that of the crushed rock cover embankment was just slightly reduced.

Crushed Gold Shell Nanoparticles Labeled with Radioactive Iodine as a Theranostic Nanoplatform for Macrophage-Mediated Photothermal Therapy

Plasmonic nanostructure-mediated photothermal therapy(PTT) has proven to be a promising approach for cancer treatment,and new approaches for its effective delivery to tumor lesions are currently being developed.This study aimed to assess macrophage-mediated delivery of PTT using radioiodine-124-labeled gold nanoparticles with crushed gold shells(124I-Au@AuCBs) as a theranostic nanoplatform.124I-Au@AuCBs exhibited effective photothermal conversion effects both in vitro and in vivo and were efficiently taken up by macrophages without cytotoxicity.After the administration of 124I-Au@AuCB-labeled macrophages to colon tumors,intensive signals were observed at tumor lesions,and subsequent in vivo PTT with laser irradiation yielded potent antitumor effects.The results indicate the considerable potential of 124I-Au@AuCBs as novel theranostic nanomaterials and the prominent advantages of macrophage-mediated cellular therapies in treating cancer and other diseases.

The biaxial compression mechanical properties of crushed rock

Crushed rock subgrade, as one of the roadbed-cooling methods, has been widely used in the Qinghai-Tibet Railway. Much attention has been paid on the cooling effect of crushed rock; however, the mechanical properties of crushed rock are somehow neglected. Based on the discrete element method, biaxial compression test condition for crushed rock is com- piled in FISH language in PFC2D, and the natural shape of crushed rock is simulated with super particle ＂cluster＂. The ef- fect of particle size, crushed rock strength and confining pressure level on overall mechanical properties of the crushed rock aggregate are respectively analyzed. Results show that crushed rock of large particle size plays an essential frame- work role, which is mainly responsible for the deformation of crushed rock aggregate. The strength of gravel has a great influence on overall mechanical properties which means that strength attenuation caused by the freeze thaw cycles cannot be ignored. The stress-strain curves can be divided into two stages including shear contraction and shear expansion at different confining pressures.

Analysis of the Cooling Mechanism of a Crushed Rock Embankment in Warm and Lower Temperature Permafrost Regions along the Qinghai-Tibet Railway

Based on data monitored in situ and theoretical analysis,the characteristics of the temperature field and mechanism of thermal conduction of a crushed rock embankment were studied along the Qinghai-Tibet Railway.The results of experi-ments in the field revealed that the cooling effect of a crushed rock embankment is influenced mainly by the natural con-vection in winter and shield effect in summer,the ventilation of crushed rocks,and the ground temperature regime be-neath the embankment.Consequently,these three factors should be taken into account in numerical simulations,but it is as a result of natural convection only.

Impregnation of Crushed Stone with Bitumenous Compounds Using Propane/Butane Impregnation Process Carried out in Supercritical Fluid Conditions

An efficient technology of impregnation of carbonate crushed stone by oil-product based on SCF-impregnation process usage with propane/butane solvent was developed. Regular impregnation throughout the volume of crushed stone sample is achieved. As a result of the appliance of proposed technology, the humidity of the treated crushed stone samples decreased down to 0.54%.

Thermal Characteristics of the Embankment with Crushed Rock Side Slope to Mitigate Thaw Settlement Hazards of the Qinghai-Tibet Railway

Permafrost （perennially frozen ground） appears widely in the Golmud-Lhasa section of the Qinghai-Tibet railway and is characterized by high ground temperature （≥1℃） and massive ground ice. Under the scenarios of global warming and human activity, the permafrost under the railway will gradually thaw and the massive ground ice will slowly melt, resulting in some thaw settlement hazards, which mainly include longitudinal and lateral cracks, and slope failure. The crushed rock layer has a thermal semiconductor effect under the periodic fluctuation of natural air. It can be used to lower the temperature of the underlying permafrost along the Qinghai-Tibet railway, and mitigate the thaw settlement hazards of the subgrade. In the present paper, the daily and annual changes in the thermal characteristics of the embankment with crushed rock side slope （ECRSS） were quantitatively simulated using the numerical method to study the cooling effect of the crushed rock layer and its mitigative ability. The results showed that the ECRSS absorbed some heat in the daytime in summer, but part of it was released at night, which accounted for approximately 20% of that absorbed. Within a year, it removed more heat from the railway subgrade in winter than that absorbed in summer. It can store approximately 20% of the ＂cold＂ energy in subgrade. Therefore, ECRSS is a better measure to mitigate thaw settlement hazards to the railway.

Numerical Analysis of the Settlement of Composite Foundation Reinforced with Crushed Stone Grouting Pile and Rigid Bearing Plate

This paper deals with a new type of crushed stone grouting pile with a rigid bearing plate. The load transfer characteristics were analyzed, and a settlement model of the composite foundation reinforced with crushed stone grouting pile and rigid bearing plate was built by FEM program. The effects of replacement ratio of capping plate, replacement ratio of pile, replacement ratio of grout diffusion zone, pile-soil modulus ratio, and serous-soil modulus ratio, on the composite foundation settlement were discussed. It is concluded that the proposed crushed stone grouting pile with a rigid bearing plate is effective in decreasing the settlement of composite foundation.

Physical Properties of Crushed Air-cooled Blast Furnace Slag and Numerical Representation of Its Morphology Characteristics

Physical properties and geometrical morphologies of crushed air-cooled blast furnace slag （SCR） and crushed limestone （LCR） were comparatively investigated. The shape, angularity, surface texture and internal pore structure of aggregate particles for different size and gradation were numerically represented by sphericity （ψ） and shape index （SI）, angularity number （AN）, index of aggregate particle shape and texture （IAPST）, porosity and pore size, respectively. The results show that SCR is a porous and rough aggregate. Apparent density, void, water absorption and smashing index of SCR are obviously higher than those of LCR with the same gradation, respectively. However, bulk density of SCR is lower than that of LCR with the same gradation. SI, AN, IAPST and porosity of SCR are obviously higher than those of LCR with the same gradation, respectively. The smaller particle size of SCR, the larger of its AN, IAPST and porosity.

Study on the Elasticity-Plasticity-Stickiness of the Railway Crushed Stone Ballast

This paper is mainly aimed at the mechanics characteristic elas of ticity-plasticitystickiness existed in the CWR (continuously welded rails) track plane of the railway crushed stone ballast. As an important mechanics parameter of the CWR track plane, the ballast resistance is mainly influenced by this mechanics characteristic. Through the systematic experimental research and the theoretical analysis, this mechanics characteristic of the ballast resistance is revealed and a reasonable theoretical model is built for it. This study set a sound foundation for further studying the CWR track deformation property. It will be beneficial to the development of high-speed railway in China.

Theoretical Calculation of ITZ Volume Fraction and Morphological Characterization of Crushed Stone in Concrete

According to the morphological characteristics of crushed stone,the sphericity was introduced to establish the theoretical calculation model of volume fraction of interfacial transition zone(ITZ)around crushed stone.The sphericity of crushed stone was obtained by image processing technology and numerical statistics.The experimental results show that when the maximum particle size of coarse aggregate is less than 31.5 mm,the practical sphericity is generally around 0.75,while the sphericity of sand is generally above 0.85.And the closer to 1 the practical sphericity is,the smaller the ITZ volume fraction(V_(ITZ))is,that is,the closer to spherical shape the aggregate is,the lower the ITZ content in concrete is.The V_(ITZ) and ITZ thickness in concrete and mortar have a linear relationship,and the ITZ content in concrete is lower than that in mortar at the same aggregate volume fraction.

Elaboration of a Road Material Based on Clayey Soil and Crushed Sand

To contribute to the enhancement of unconventional local materials used for road construction,this study characterizes a crushed sand 0/5,a clayey soil and the litho-stabilized material without and with hydraulic binder and determines their use in accordance with some reference specifications(CEBTP 1984).It is shown that the different components are not usable alone in pavement base.Indeed,the plasticity index obtained for the clayey soil is 21%,a value higher than the imposed standards.In addition,the grading of the 0/5 crushed sand does not fit into the range proposed by CEBTP.A combination of these two(02)components is therefore considered to obtain a suitable material usable for the sub-base.This new material does not enter any class of the CEBTP lateritic soils.In order to be used in base layer,a treatment with hydraulic binder is carried out with the intention to improve its mechanical performances.The optimal dosage of hydraulic binder to achieve the desired mechanical performance is obtained by studying the evolution of the mechanical characteristics of the mixture.After this treatment,the Bearing Ratio index of the mix increases from 37 to 223 for the optimal dosage and the dry compaction density decreases from 2.11 to 2.06 g/cm3 while the optimal water content increases from 9%to 10.1%.

Density and Strength of Mortar Made with the Mixture of Wood Ash, Crushed Gneiss and River Sand as Fine Aggregate

The main purpose of this paper is to study the feasibility of using wood bottom ash to partially replace natural fine aggregate or crushed gneiss sand in the manufacturing of mortars. The experiment uses wood ash as fine aggregates, which passes through 5 mm sieve, in proportions of 5%, 10%, 15%, 20% and 25% by weight to replace partially river sand and crushed gneiss, and the both sand of the same size as the aggregate respectively. Experimental results show that density of mortar and the compressive strength of mortar decrease globally with the increase in wood ash content. At 56 days, and for all replacements with wood ash, compressive strengths values of mortar obtained with the mixture of wood ash and river sand is greater than 20 MPa, which is not the case for mortar made with crushed gneiss and wood ash. Moreover, for 5% of replacement with wood ash, compressive strengths of mortar obtained with the mixture of wood ash and river sand and the mixture of wood ash and crushed gneiss are respectively 37 MPa and 32 MPa at 56 days. These values satisfied the strength requirements. Hence, 5% replacement of crushed gneiss with wood ash is suggested and could be benefit for mortar. In addition, the replacement of sand by wood ash is preferable with river sand which contains fewer fines than crushed gneiss. The compressive strength of mortar with 25% wood ash + river sand could be suitable.