Microscopic Analysis of Cementitious Sand and Gravel Damming Materia

The mechanical properties of cementitious sand and gravel damming material have been experimentally determined by means of microscopic SEM(Scanning Electron Microscopy)image analysis.The results show that the combination of fly ash and water can fill the voids in cemented sand and gravel test blocks because of the presence of hydrated calcium silicate and other substances;thereby,the compactness and mechanical properties of these materials can be greatly improved.For every 10 kg/m^(3) increase in the amount of cementitious material,the density increases by about 2%,and the water content decreases by 0.2%.The amount of cementitious material used in the sand and gravel in these tests was 80-110 kg/m^(3),the water-binder ratio was 1-1.50.Moreover,the splitting tensile strength was 1/10 of the compressive strength,and the maximum strength was 7.42 MPa at 90 d.The optimal mix ratio has been found to be 50 kg of cement,60 kg of fly ash and 120 kg of water(C50F60W120).The related dry density was 2.6 g/cm^(3),the water content was 6%,and the water-binder ratio was 1.09.

A field experimental study of lignin sand stabilizing material(LSSM) extracted from spent-liquor of straw pulping paper mills

A new technique was introduced for sand stabilization and re-vegetation by use of lignin sand stabilizing material(LSSM). LSSM is a reconstructed organic compound with lignin as the most dominant component from the extracts of black-liquor issued by straw pulp paper mills. Unlike the polyvinyl acetate or foamed asphalt commonly used for dune stabilization, the new material is plant-friendly and can be used with virescence actions simultaneously. The field experimental study was conducted since 2001 in China's Northwest Ningxia Hui Autonomous Region and has been proved that LSSM is effective in stabilizing the fugitive dunes, making the arenaceous plants survive and the bare dune vegetative. The advisable solution concentration is 2% and the optimal field spraying quantity is 2 5 L/m^2 The soil nutrients of the stabilized and greened dune, such as organic matter, available phosphorous and total nitrogen are all increased compared with the control treatment, which is certainly helpful to the growth of arenaceous plants. The technique is worthwhile to be popularized because it is provided not only a new method for desertification control but also an outlet for cleaning contaminants issued from the straw paper mills.

Coating process of multi-material composite sand mold 3D printing

Sand mold 3 D printing technology is an advanced manufacturing technology which has great flexible manufacturing ability. A multi-material composite sand mold can control the temperature field of metallic parts during the pouring process, while the current sand mold 3 D printing technology can only fabricate a single material sand mold. The casting temperature field can not be adjusted by using single sand mold material with isotropous heat exchange ability during the pouring process. In this work, a kind of novel coating device was designed. Multi-material composite sand molds could be manufactured using the coating device according to the casting process demands of the final parts. The influences of curing agent content, coating velocity and scraper shape on compactness and surface roughness of the sand layer(silica sand and zircon sand) were studied. The shapes and sizes of transition intervals of two kinds of sand granules were also tested. The results show that, with the increase of the added volume of curing agent, the compactness of sand layer reduces and the surface roughness value rises. With the increase of the velocity of the coating device, the compactness of sand layer reduces and the surface roughness value rises similarly. In addition, the scraper with a dip angle of 72 degrees could increase the compactness value of the sand layer. The criteria of quality parmeters of the coating procedure are obtained. That is, the surface roughness(δ) of sand layer should be equal to or lesser than half of main size of the sand particles(Dm). The parameter H of the coating device which is the distance between the base of hopper and the surface of sand layer impacts the size of transition zone. The width of the transition zone is in direct proportion to the parameter H, qualitatively. Through the optimization of the coating device, high quality of multi-material sand layers can be obtained. This will provide a solution in manufacturing the multi-material composite sand mold.

Glass matrix composite material prepared with waste foundry sand

The technology of glass matrix of the composite material manufactured through a sintering process and using waste foundry sand and waste glass as the main raw materials was studied. The effects of technological factors on the performance of this material were studied. The results showed that this composite material is formed with glass as matrix, core particulate as strengthening material, it has the performance of glass and ceramics, and could be used to substitute for stone.

Loose Sand Cemented by Microbial Cementitious Material:Composition,Microstructure and Mechanical Properties

Through the influence of the dosage of culture solution and calcium source on hardness and compressive strength of samples,the formulation of microbial cementitious materials was optimized and defined.The influence of temperature on composition,microstructure and mechanical properties of loose sand cemented by microbial cementitious material was compared and analyzed systematically.With the increase of temperature,the performance of loose sand was improved remarkably.Calcite with cementitious properties could be induced at higher temperatures,but not at lower temperatures.When the temperature was 30℃,loose sand cemented by microbial cementitious material had more calcite and more dense structure.Moreover,hardness and compressive strength were also superior.The wind tunnel test showed that the wind erosion resistance was improved obviously and the mass loss was lower at high temperature.Engineering properties of loose sand cemented by microbial cementitious material was measured integrally.Through comparative analysis,engineering properties of loose sand were basically unchanged,and there was no negative effect on the later period use of sand.

Biodegradable materials as binders for IVth generation moulding sands

This paper focuses on the possibility of using the biodegradable materials as binders(or parts of binders' compositions) for foundry moulding and core sands. Results showed that there is a great possibility of using available biodegradable materials as foundry moulding sand binders. Using biodegradable materials as partial content of new binders, or additives to moulding sands may not only decrease the toxicity and increase reclamation ability of tested moulding sands, but also accelerate the biodegradation rate of used binders, and the new biodegradable additive(PCL) did not decrease the strength and thermal properties. In addition, using polycaprolactone(PCL) as a biodegradable material may improve the flexibility of moulding sands with polymeric binder and reduce toxicity.

Development of Sensible Heat Storage Materials Using Sand, Clay and Coal Bottom Ash

In this paper, the mechanical and thermal properties of a sand-clay ceramic with additives coal bottom ash (CBA) waste from incinerator coal power plant are investigated to develop an alternative material for thermal energy storage (TES). Ceramic balls are developed at 1000°C and 1060°C using sintering or firing method. The obtained ceramics were compressed with a compression machine and thermally analyse using Decagon devise KD2 Pro thermal analyser. A muffle furnace was also used for thermal cycling at 610°C. It was found that the CBA increased the porosity, which resulted in the increase of the axial tensile strength reaching 3.5 MPa for sand-clay and ash ceramic. The ceramic balls with the required tensile strength for TES were selected. Their volumetric heat capacity, and thermal conductivity range respectively from 2.4075 MJ·m-3·°C-1 to 3.426 MJ·m-3·°C-1 and their thermal conductivity from 0.331 Wm-1·K-1, to 1.014 Wm-1·K-1 depending on sand origin, size and firing temperature. The selected formulas have good thermal stability because the most fragile specimens after 60 thermal cycles did not present any cracks. These properties allow envisioning the use of the ceramic balls developed as filler material for thermocline thermal energy storage (structured beds) in Concentrating Solar Power plants. And for other applications like solar cooker and solar dryer.

The Cemented Material Dam： A New, Environmentally Friendly Type of Dam

The first author proposed the concept of the cemented material dam （CMD） in 2009. This concept was aimed at building an environmentally friendly dam in a safer and more economical way for both the dam and the area downstream. The concept covers the cemented sand, gravel, and rock dam （CSGRD）, the rockfill concrete （RFC） dam （or the cemented rockfill dam, CRD）, and the cemented soil dam （CSD）. This paper summarizes the concept and principles of the CMD based on studies and practices in projects around the world. It also introduces new developments in the CSGRD, CRD, and CSD.

Effects of temperature and age on physico-mechanical properties of cemented gravel sand backfills

Cemented backfill used in deep mines would inevitably be exposed to the ambient temperature of 20−60℃in the next few decades.In this paper,two types of cemented gravel sand backfills,cemented rod-mill sand backfill(CRB)and cemented gobi sand backfill(CGB),were prepared and cured at various temperatures(20,40,60℃)and ages(3,7,28 d),and the effects of temperature and age on the physico-mechanical properties of CRB and CGB were investigated based on laboratory tests.Results show that:1)the effects of temperature and age on the physico-mechanical properties of backfills mainly depend on the amount of hydration products and the refinement of cementation structures.The temperature has a more significant effect on thermal expansibility and ultrasonic performance at early ages.2)The facilitating effect of temperature and age on the compressive strength of CGB is higher than that on CRB.With the increase of temperature,the compressive failure modes changed from X-conjugate shear failure to tensile failure,and the integrity of specimens was significantly improved.3)Similarly,the shear performance of CGB is generally better than that of CRB.The temperature has a weaker effect on shear strength than age,but the shear deformation and shear plane morphology are closely related to temperature.

Triaxial shear behavior of a cement-treated sand——gravel mixture

A number of parameters,e.g.cement content,cement type,relative density,and grain size distribution,can influence the mechanical behaviors of cemented soils.In the present study,a series of conventional triaxial compression tests were conducted on a cemented poorly graded sandegravel mixture containing 30% gravel and 70% sand in both consolidated drained and undrained conditions.Portland cement used as the cementing agent was added to the soil at 0%,1%,2%,and 3%(dry weight) of sandegravel mixture.Samples were prepared at 70% relative density and tested at confining pressures of 50 kPa,100 kPa,and150 kPa.Comparison of the results with other studies on well graded gravely sands indicated more dilation or negative pore pressure in poorly graded samples.Undrained failure envelopes determined using zero Skempton’s pore pressure coefficient (= 0) criterion were consistent with the drained ones.Energy absorption potential was higher in drained condition than undrained condition,suggesting that more energy was required to induce deformation in cemented soil under drained state.Energy absorption increased with increase in cement content under both drained and undrained conditions.

Effects of fluid flow rate and viscosity on gravel-pack plugging and the optimization of sand-control wells production

Series of experiments were performed to simulate the invasion of formation sand into and the plugging process of gravel-pack at different viscosities and flowing rates of fluid.Two types of formation sands with the medium size of 0.10 mm and 0.16 mm and the quartz sand and ceramsite of 0.6-1.2 mm were used in the experiments.A new viscosity-velocity index(the product of fluid viscosity and velocity)was put forward to characterize the influencing mechanism and law of physical property and flow condition of formation fluid on gravel-pack plugging,and a new method to optimize the production rate of wells controlling sand production with gravel-packing was proposed.The results show that the permeability of formation sand invaded zone and final permeability of plugged gravel-pack have negative correlations with viscosity and flow velocity of fluid,the higher the flow velocity and viscosity,the lower the permeability of formation sand invaded zone and final permeability of plugged gravel-pack will be.The flow velocity and viscosity of fluid are key factors affecting plugging degree of the gravel zone.The viscosity-velocity index(v-v index)can reflect the flow characteristics of fluid very well and make it easier to analyze the plugging mechanism of gravel zone.For different combinations of fluid viscosity and flow velocity,if the v-v index is the same or close,their impact on the final gravel permeability would be the same or close.With the increase of the v-v index,the permeability of plugged gravel zone decreases first,then the reduction rate slows down till the permeability stabilizes.By optimizing production and increasing production step by step,the optimal working scheme for sand-control well can reduce the damage to gravel-pack zone permeability caused by sand-carrying fluid effectively,and increase well productivity and extend the sand control life.

Effects of Different Gravel Mulched Years on Soil Microbial Flora and Physical and Chemical Properties in Gravelsand Mulched Fields

Soil microbial flora and influencing factors of soil microbes in soil and gravel-sand mixed layer（ SGSML）,roots denseness layer（ RDL）,eluviate layer（ EL） and calcium accumulation layer（ CAL） in gravel-sand mulched fields（ GSMFs） with different gravel mulched years（ 1,6,12,19 and 25 years） were studied. The results showed that in the composition of soil microbes in the GSMFs,the quantity of bacteria was the largest,followed by actinomycetes,while the number of fungi was the smallest. The total quantity of soil microorganisms in the GSMFs dropped rapidly with the increase of soil depth,which was related to the sudden decrease in the quantity of bacteria. The number of microbes in the RDL was larger than that in the SGSML with few roots due to the effects of root distribution. The number of bacteria and actinomycete in the growing season was larger than that in the non-growing season,while the quantity of fungi in the growing season was smaller than that in the non-growing season. The quantity of bacteria and fungi was the largest in the GSMFs which had been mulched with gravel for 6-12 years. With the increase of mulching time,the GSMFs aged gradually,so their quantity reduced gradually. The quantity of actinomycetes was the smallest in the GSMFs which had been mulched with gravel for 6-12 years and increased with the increase of mulching time. The number of soil microbes in the GSMFs had a good correlation with soil moisture content,p H and mulching time. Soil total carbon content was an important factor restricting the quantity of soil microbes in the GSMFs.

The Consequence of Particle Crushing in Engineering Properties of Granular Materials

This paper presents experimental investigation for particles breakage for natural sand. The particle breakage was induced by subjecting the sample to one dimensional compression. Grain size analyses were performed before and after induced breakage. Thereafter, the sand shear strength parameters were assessed using direct shear box tests and the coefficient of permeability was assessed using constant head permeameter. Examining the obtained results revealed that the amount of breakage due to one dimensional compression was of order higher than the amount occurring during direct shear test. Peak shear strength parameters decreased with the particles breakage increasing. Moreover, dilation angle of shear strength pronouncedly decreases with the amount of particles breakage increasing. Crushing has obvious effect on the evaluated coefficient of permeability.

Long-term effects of gravel-sand mulch thickness on soil microbes and enzyme activities in semi-arid Loess Plateau,Northwest China

In semi-arid areas of China,gravel and sand mulch is a farming technique with a long history.In this study,a sample survey was conducted on long term gravel sand mulch observational fields in the Northwest Loess Plateau to determine the effects of long term mulch on soil microbial and soil enzyme activities.We found that after long term gravel-sand mulch,compared with bare ground,soil organic matter,alkali nitrogen,conductivity decreased,while pH and soil moisture increased.Urease,saccharase and catalase decreased with increased mulch thickness,while alkaline phosphatase was reversed.The results of Illumina MiSeq sequencing shows that after gravel-sand mulch,the bacterial and fungal community structure was different from bare land,and the diversity was reduced.Compared with bare land,the bacteria Proteobacteria and Acidobacteria abundance increased with increased thickness,and Actinobacteria was opposite.Also,at the fungal genus level,Fusarium abundance was significantly reduced,and Remersonia was significantly increased,compared with bare land.Redundancy analysis(RDA)revealed that soil environmental factors were important drivers of bacterial community changes.Overall,this study revealed some of the reasons for soil degradation after long term gravel-sand mulch.Therefore,it is recommended that the addition of exogenous soil nutrients after long term gravel-sand can help improve soil quality.

Equal Volumes of Sand and Gravel Concrete Mix Ratios in Cameroon and Its Effect on Concrete Compressive Strength

In recent years, the rationalization of concrete mix ratios which batches equal volumes of sand and gravel in building projects has been gaining grounds in the Cameroon construction industry. The main objective of this study is therefore to investigate if the concrete produced with rationalized mix ratio can be adopted as conventional mix ratio in terms of minimum required compression strength of concrete for buildings. Specifically this work compared the conventional mix ratio of 350 kg of cement: 400 liters of sand: 800 liters of gravel for a cubic meter and the rationalized batch of 350 kg of cement: 600 liters of sand: 600 liters of 5/15 gravel, 15/25 gravel and a combination of 5/15 + 15/25 gravel. Average compressive tests’results for both the conventional and the rationalized mix ratios were found to meet the minimum compressive strength of 65% at 7 days, 90% at 14 days and 99% at 28 days for gravel size combination 5/15 + 15/25. Single size gravel of 5/15 and 15/25 did not meet the minimum required compressive strength of 20 N/mm2 for the rationalized mix ratio at 28 days curing based on the minimum compressive strength required, this study arrives at the conclusion that the equal volumes of sand and gravel mix ratio of 350 kg/m3 of cement: 600 liters of sand: 600 liters of gravel mix ratio can be adopted as a conventional concrete mix ratio for gravel size 5/15 + 15/25.

Sieving Error from Dry-Separating Silt-Sand-Gravel Soils

The dry-separation method is an alternative to the wet-preparation in the current European Standard for the determination of particle size distributions by the sieving of soils. Due to the risk of error, dry-separation is cautioned against in the standard;however, there is no additional guidance as to when it is unsuitable nor for the magnitude of error that it may introduce. This study investigates the dry-separation method as an alternative by comparing with the conventional method of Wet-preparation in terms of particle-size distributions of eight cohesionless sand-gravel soils with varying amounts of nonplastic fines. The findings indicate a gradually increasing sieving error for fractions at minus 0.5 mm with the amount of fines in the soil, and depending on the fines content of the soil, dry-separation introduced errors upwards of 45% in silt-sand-gravel soils. An empirical best-fit formula is proposed for the estimation of the error using the dry-preparation method on this type of soil. Furthermore, to avoid sieving errors, the results suggest that the dry-separation method should not be used for silt-sand-gravel soils exceeding 2% silt size fractions.

The Hydrochemical Characteristics of a Stressed Sand-Gravel Aquifer: Kazan Plain, Ankara, Turkey

Over-exploitation and sand-gravel mining affect groundwater resources in terms of both quantity and quality. Groundwater level and well yields in and around the sand-gravel pits significantly decrease. Sand-gravel mining also changes the turbidity levels and temperature of groundwater. Reduction and destruction of valuable aquifers are significant issues. In this case, the natural state of the aquifer disappears. The Kazan Plain in central Turkey is a dramatic example of these kinds of results. The productive sand-gravel aquifer in the Kazan plain has been substantially damaged due to intensive sand-gravel mining since the 1980s. Additionally, over-exploitation has caused notable declines in groundwater levels, particularly in the 2000s. This study focuses on the hydrogeochemical situation of the Kazan Plain alluvium aquifer after intensive sand-gravel mining and over-exploitation. Groundwater samples were collected seasonally in 2015, five years after the over-exploitation and heavy sand-gravel mining. The decline reached 20 m (about half of the saturated thickness of the sand-gravel aquifer) in the region where the intensive groundwater abstraction lasted until 2010. Some quarries continued to operate until 2010, but after that mining activity continued only at a minimum level. Today, groundwater quality has been significantly degraded due to the over-exploitation of sand-gravel mining and also the cessation of recharge from fresh river water.

洛阳盾构隧道地表沉降Peck公式参数修正

为准确预测洛阳粉质黏土与砂卵石复合地层中的盾构隧道地表沉降量,采用线性回归拟合方法,对洛阳地铁某区间隧道盾构掘进时的地表沉降监测数据进行拟合,引入地表最大沉降修正系数α和沉降槽宽度修正系数β对单线Peck公式进行修正。结果表明:针对单线隧道,采用线性回归方法拟合隧道横断面地表沉降得到的曲线与实际监测数据吻合度高,当修正系数α为0.4~0.9、β为0.5~0.7时得到的修正Peck公式精度最高;针对双线隧道,该地层下的地表沉降基本呈双峰“W”形,双线隧道的土体损失率η和沉降槽宽度系数K的分布区间分别为0.2%~0.8%和0.2~0.5,平均值分别为0.45%和0.37,且先行线的土体损失率均值、沉降槽宽度系数均值分别为后行线的1.4倍、1.3倍。研究成果可为洛阳典型粉质黏土与砂卵石复合地层中盾构隧道后续施工提供数据支撑。

Experiment Study of the Evolution of Coral Sand Particle Clouds in Water

The motion of particle clouds(i.e.,sediment clouds)usually can be found in engineering applications such as wastewater discharge,land reclamation,and marine bed capping.In this paper,a series of laboratory tests are conducted on coral sand to investigate the shape feature of the single particle and the mixing processes of the coral sand particle clouds.The shape of coral sand particle is measured and quantified.The experimental results demonstrate that the shape of coral sand particles tends to be spherical as the particle size decreases,and empirical equations were established to explain the variation of D50 and fS,50 of coral sand.Compared with the silica sand,the evolution of the coral sand particle cloud still experiences three stages,but the threshold for the Reynolds number of particle clouds entering the next stage changes.Further,the normalized axial distance of the coral sand particle clouds is 58%smaller.The frontal velocity exhibits similar varying tendency for the coral sand particle cloud.Considering the difference in shape between coral sand particles and silica sand particles,a semi-empirical formula was proposed based on the original silica sand prediction formula by adding the shape factor and the experimental data of 122μm≤D_(50)≤842μm.It can predict the frontal velocity of the coral sand particle clouds.

Effects of gravel mulch on aeolian transport:a field wind tunnel simulation

The shape,size and coverage of gravels have significant impacts on aeolian sand transport.This study provided an understanding of aeolian transport over the gravel mulching surfaces at different wind velocities by means of a mobile wind tunnel simulation.The tested gravel coverage increased from 5% to 80%,with a progressive increment of 5%.The gravels used in the experiments have three sizes in diameter.Wind velocities were measured using 10 sand-proof pitot-static probes,and mean velocity fields were obtained and discussed.The results showed that mean velocity fields obtained over different gravel mulches were similar.The analysis of wind speed patterns revealed an inherent link between gravel mulches and mean airflow characteristics on the gravel surfaces.The optimal gravel coverage is considered to be the critical level above or below which aeolian transport characteristics differ strongly.According to the present study,the optimal gravel coverage was found to be around 30% or 40%.Threshold velocity linearly increased with gravel coverage.Sand transport rate first increased with height above the wind tunnel floor（Hf）,reaching a peak at some midpoint,and then decreased.