جستجوی مقالات مرتبط با کلیدواژه « cohesion » در نشریات گروه « عمران »

The present study has investigated the effect of vinyl acrylic polymer emulsion (VA) on the shear strength of aeolian sands in the Khuzestan plain. For this purpose, after sampling the aeolian sands of the mentioned area, a standard compaction test was performed and the optimum water content and maximum dry density of the aeolian sand were determined. Then, solutions with percentages of 10, 20 and 30% of polymer material were made and added to the aeolian sand in such a way that it reached the optimum water content. The prepared soil with maximum dry density was placed in square metal molds kept in the laboratory for 1, 7, 14 and 21 days and then subjected to direct shear test. The results of the direct shear test on the stabilized samples showed that by increasing the curing time and the concentration of the polymer solution, cohesion and the shear strength increase and the angle of internal friction decreases. So the polymer solution with a concentration of 30% has caused a 146% increase in shear strength aeolian sand. Electron microscope images (SEM) show the creation of bridges between sand grains in the stabilized samples, which is the reason for the increased cohesion and shear strength of the samples.

An efficient approach to road safety coupled with preventive maintenance of asphalt pavements is the application of colored slurry seal, as it improves the road visibility while enhancing the aesthetic aspects of the urban space. Around the globe, application of colored surface treatments on roads has witnessed a growth in recent years, especially in urban areas. This study aims at investigating the feasibility and effectiveness of using electric-arc furnace steel slag as an alternative to natural aggregates in the colored slurry seal mixture design followed by a performance assessment of the resultant mixture. For this purpose, first, characteristics of the aggregate and steel slag were investigated. Next, performance of the designed slurry seal mixture was assessed by testing five different mixtures containing the slag at 0, 10, 20, 30 and 40 wt.%. Evaluation and comparison of the asphalt specimens were performed by conducting 30- and 60-min wet cohesion tests, 60-min wet track abrasion test, loaded wheel-sand adhesion test, and loaded wheel-displacement test according to ASTM D3910. Based on the XRF results, the considered steel slag powder contained a significant amount of calcium oxide (~ 57% of natural aggregate). The high CaO/SiO2 ratio for the steel slag indicates its alkalinity, which suggests its improved adhesion to bitumen thanks to its rather acidic nature. According to FESEM results, the steel slag material was found to be composed of particles of angular geometry with a rougher surface and higher porosity than natural aggregates, further indicating better slag-bitumen adhesion. Performance assessments indicated superior performance of the steel slag-containing specimens of colored slurry seal. Among the studied mixtures, the one with 40 wt.% steel slag exhibited the best performance, as shown by 27.8 and 37.3% increase in the mixture cohesion upon 30- and 60-min wet cohesion tests, respectively, as compared to the control specimen. Furthermore, 47.7% lower moisture sensitivity and 50.8% and 40% smaller vertical and lateral displacements, respectively, were observed for the slag-containing mixture. The bleeding potential of the mixtures decreased with increasing the steel slag dosage from 0 to 40 wt.%, so that the mixture containing steel slag at 40 wt.% exhibited 23.7% lower bleeding potential. Trying to optimize the asphalt emulsion dosage, it was figured out that the optimal content of asphalt emulsion increases with the added content of steel slag to the mixture. Accordingly, the mixture containing steel slag at 40 wt.% required 1.9% more asphalt emulsion to achieve a given cohesion level within a certain time. Based on the results of this research, in order to improve performance characteristics of colored slurry seal mixtures while observing environmental obligations, it is recommended to use steel slag as an alternative to natural aggregates in this type of surface treatment. Therefore, according to the environmental issues and the limitations of natural resources, it is recommended that steel slag be replaced by natural aggregates up to 40% in the colored slurry mixture. By replacing steel slag, proper adhesion and cohesion between asphalt mixture materials is achieved and its resistance to moisture sensitivity, traffic loading and bleeding is improved.

Moisture damage in asphalt mixtures generally occurs due to the separation of bitumen from the surface of stone materials and due to the presence of water. This type of failure causes stripping and premature failures. Investigating the effective factors in this type of damage can be useful in improving the process of designing and producing asphalt mixtures. In the past years, significant research and efforts have been made to reduce these types of failures. In this article, the effect of adding Polytec 505, as a new material with complex amines that reduce the acidic nature of bitumen, on the moisture damage of asphalt mixtures has been investigated. For this purpose, two types of granite and lime aggregate and 60-70 bitumen have been used. The modified Lottman test was used to check the moisture damage, and pull-off tests were used to evaluate the cohesion properties of bitumen and the adhesion of bitumen to aggregate. The results show that the use of this additive causes an increase in the indirect tensile strength ratio of samples with granite and limestone aggregate, and as a result, the performance of these samples against moisture damage improves. This improvement increases with the increasing of this additive. The results of the Pull-off test show that the use of this additive improves the adhesion and cohesion of pull-off pull off test.

The demand for using industrial waste has increased significantly due to their environmental impacts and limitation of natural resources. Copper waste (CW) is among those that are known to cause environmental problems. Categorized under waste materials, it causes various environmental problems, especially those related to waste disposal. The main purpose of the present study is to investigate the application of CW, as compared to mineral aggregate (MA), in surface treatment. For this purpose, various tests, including wet cohesion test, wet track abrasion test, loaded wheel – displacement test, and loaded wheel – sand adhesion test, were performed on five different mixtures designated as CW0+MA100, CW10+MA90, CW20+MA80, CW30+MA70, and CW40+MA60, with the designations defined based on total aggregate weight. Results showed that, thanks to its unique physical and chemical characteristics, the replaced CW could improve the treatment performance, especially in the CW30+MA70 sample, in terms of abrasion, wet cohesion, and vertical and lateral displacements by about 23, 22, 39, and 33%, respectively, at a residual asphalt of 8%. Also, regarding the analysis of variance, the copper slag is a more effective factor with respect to residual bitumen in increasing the cohesion and reducing the vertical and lateral deformations due to traffic loading

One of the most common damages in asphalt mixtures is due to the destructive effects of moisture on the cohesion of asphalt binder and adhesion of asphalt binder-aggregate which is called moisture damage (Xiao et al, 2010). Moisture damage can be divided into two mechanisms, adhesion and cohesion. They are related to the strength loss of asphalt mixtures (Tan and Guo, 2013). Water can penetrate between the surface of asphalt binders and the aggregates. It reduces adhesion between binders and aggregates. Also, water can be absorbed in the asphalt binder. It decreases the cohesion properties of asphalt binders. When the cohesion and adhesion properties of asphalt binder reduce, stiffness of asphalt mixtures reduces. There are several different approaches for improving adhesion and reducing moisture sensitivity in asphalt mixtures. One convenient approach is modifying the asphalt binder with a suitable agent. Most of road and transportation agencies have tried to use anti striping additives to increase adhesion at the aggregate-asphalt interface (Kakar et al, 2015). Liquid anti strip additives are chemical surfactants that decrease the aggregate’s surface tension and improve the surface coverage of aggregates. In contrast in this research, the potential of two types of metallic nano materials in two different percentages (nano AL2O3 and Fe2O3) were evaluated.

Moisture damage is one of the forms of asphalt pavement distress that occurs due to the presence of water and its effect on the mechanical properties of the asphalt mixture. Using nanomaterial as additives is one of the solutions that delays this event and increases the durability of the mixture. In this study, the effect of nanomaterial (nano-TiO2) on the moisture susceptibility of asphalt mixtures was investigated using surface free energy method, indirect tensile strength test (ITS) and resilient modulus (Mr). Asphalt samples were fabricated by neat bitumen with a penetration grade of 85/100 and Siliceous aggregate. The bitumen was modified with 3and 6% (weight of bitumen) of Nano-TiO2. The results of the bitumen section indicate that by modifying the bitumen with Nano-TiO2, the acidic component of surface free energy decreases and its basic component increases. On the other hand, as the non-polar component increases, the bitumen's free energy would be increased. The addition of nano-TiO2 to the asphalt mixture also increased the TSR. TSR reduction through the different freezing-thaw cycles for the modified mixtures was less compared to the control mixtures. The separation energy between bitumen-rock materials is also reduced by modifying the bitumen with this nanomaterial. Therefore, it improves the stripping resistance of the asphalt mixture. In addition, the results of resilient modulus indicate that bitumen modification with Nano-TiO2 increased the Mr values. Similar to changes in the TSR, the RMR value has been increased for the modified HMA and it increased the hot mix asphalt durability.

Most of the times, flow passing above, through or below hydraulic structures is in the form of jets, which can cause downstream soil material erosion. When the amount of clay in soil materials is more than 10%, they can be considered as cohesive soils. If the results of cohesionless sediment research are generalized to cohesive sediments, the scour values obtained will be more or less than the actual values. On the other hand, there are no specific conversion ratios to estimate the characteristics and temporal changes of the scouring of cohesive sediments from cohesionless sediments. The duration of reaching maximum scour depth in cohesive sediments has shown to be longer than that of cohesionless ones.Previous works on cohesive sediments are often performed on flumes or by using a submerged vertical jet device. However, the jets formed below the hydraulic structures are mostly horizontal or oblique which are examined in this paper.Based on dimensional analysis, it was determined that the parameters of nozzle diameter, jet drop height, jet angle, jet velocity, tailwater depth, fluid density, dynamic fluid viscosity, critical shear stress and gravity acceleration affect the scour of cohesive sediments caused by the jet which is studied here.

Experiments were carried out at the Hydraulic Lab of Tarbiat Modares University in a rectangular flume 0.6 m wide and 0.6 m high. A 0.2 m deep hole is created on the floor to place cohesive sediments. The laboratory channel is equipped with a 2m3 inlet tank, from which water is pumped into the jet tube. Froude numbers 3, 5, 7, and 9 are established based on common hydraulic structures and previous works.The experiments were performed using horizontal, oblique and vertical jets using tubes with nozzle diameters of 10, 15, 20 and 25 mm and with 3 tailwater depths of 5, 10 and 15 cm and 3 jet drop heights of 20, 50 and 60 cm. The cohesive sediments used were produced from a combination of fine sand with clay (including kaolin and bentonite at a ratio of 3 to 1). The amount of clay was considered to be 20% by weight of the total soil based on natural soils and previous works.Prior to the start of tests, tailwater was established on the sediment layer in order to allow it to saturate. After reaching equilibrium in the experiments, water was completely drained from the channel and the scouring hole and bed profiles were extracted by a laser distance meter device.

Erosion of cohesive sediments has the greatest scouring potential in the initial stage and in the later stages, the sediment bed becomes rougher and its resistance to scouring increases until equilibrium establishes.A sedimentary ridge is formed at the end of the scouring hole by horizontal and oblique jets and around the scouring hole by vertical jets. In horizontal and oblique jets, the maximum scour depth does not necessarily form on the centerline. The growth of the length and width of scouring hole stops almost simultaneously, but deepening of it continues after that. This is in accordance with findings of Mazurek et al. (2001), Ansari et al. (2002), and Mazurek et al. (2003).As the jet height rises, the time it takes to reach equilibrium increases and leads to maximum scouring occur at a greater distance from the jet nozzle. In horizontal jets, the location of the maximum scouring depth shifts in the early stages of scouring but stabilizes after approximately 2 hours. Increased shear stress due to jet flow increases the scouring rate.Increasing the ratio of tailwater depth to jet drop height (Yt / H) has a dual effect on the maximum relative scour depth. So that the maximum relative scour depth first increases with increasing Yt / H to about 0.3 for horizontal jets and about 0.35 for vertical jets, then the trend reversed and with increasing Yt / H ratio the scour rate relatively reduced. Increasing the Froude number increases the amount of scouring. Also, the amount of scouring at two angles of 0 and 30 degrees relative to the horizon, are very close to each other. At larger angles, except for the 90 degree angle, the scour depth increases as the jet angle increases. The 45 degree angle jet creates the maximum scouring depth.

As the jet height rises, the time it takes for the scouring to reach equilibrium increases. It also leads to maximum scouring to occur at a greater distance from the jet nozzle. Increasing shear stress by jet flow, increases the scouring rate.At lower values of Yt/H, with increasing this ratio, the maximum scour depth increases until it reaches the maximum value and then. the trend reverses.By increasing Froude number, scour rate increases. By steepening jet angle, the scour depth almost increases but when the jet becomes vertical, lower scour depths are observed.

Nowadays, construction on problematic soils is inevitable owing to the growing scarcity of land worldwide. Problematic soils are commonly characterized by low strength and high compressibility. Thus, the mechanical properties of these soils should be improved. In recent years the researchers have attempted to present approaches based on environmental measurements. One of the methods recently considered in the improvement of sandy soils, is Microbial-Induced Calcite Precipitation (MICP). In order to accelerate the MICP process, it is possible to improve the soil structure cementation and soil engineering properties by creating Urea microorganism. In order to do this, a solution containing bacterial cell and cementation is required which includes urea and one of the Calcium ion sources such as CaSO4.2H2O, CaCl2. 2H2O, CaCl2. In this paper, in order to accelerate the calcite precipitation, a Bacillus bacterium called Bacillus Pasteurii is used as catalyzer of this chemical reaction. In order to investigate the effectiveness of time factor on improving cohesion of silty sand from Firouzkooh city, Iran, an experimental study consisting of 5 direct shear tests were performed. The time taken for the experiments was 3, 7, 14, 21 and 28 days from MICP. The results of this research demonstrated that, over time, cohesion of improved silty sandy soils increased by bio-microbial method. This indicates the role of the growth of bacterial cells and accelerates the progress of the MICP process and the precipitation of calcite crystals in the pores. The results from scanning electron microscope (SEM) confirmed this finding. SEM images indicated that the rate of calcite precipitation increases with time. However, the rate of growth of bacteria depends on their amount of optimal growth or volume of residual pores of the soil that can be decreasing or increasing.

Nowadays, soil stabilization has a vital importance due to the population growth, the necessity of construction and unsuitable natural soil for structure construction. The use of additives such as lime and cement is one of the ways that can be applied for soil stabilization. Among new additives for soil stabilization, it can be pointed out that Nano-Material is a more efficient and most cost-effective method with respect to traditional additives. One of this Nano-Material is Nano-Lime that can be used for soil improvement. Therefore, in this study, the effect of Nano-Lime on soil resistance parameters was investigated. For this purpose, unconsolidated undrained triaxial test is performed on the soil specimens containing 0.5, 1 and 2% by weight of soil at 7, 14, and 28 days curing. According to the results, the values of maximum deviator stress are increased by adding Nano-Lime to the soil specimens, and this trend grows with an increasing percentage of Nano-Lime in the soil as well as curing days. That said, the 28-days maximum deviator stress of clean soil is increased by 21.3 to 38.3%, 27 to 59.3% and 29.6 to 70.8% with including 0.5%, 1% and 2% nano-lime for cell pressure 100, 200 and 300 kPa, respectively. Moreover, it can be seen that stiffness of specimens containing Nano-Lime rather than clean soil specimen is increased. Also, the obtained results show that the cohesion of soil increased due to effect of Nano-Lime on soil samples, which this trend increased with curing time.

Collapse soils have a stable loose honeycomb-type structure in a low degree of saturation which is susceptible to a large reduction in total volume or collapse upon wetting. The aim of this study is to evaluate the collapse potential and shear strength parameters due to saturation of soil caused by the infiltration of contaminants including leachate wastewater and chemicals into the soil. Since the separation of leachate components is difficult, especially with change of ingredients and pH in long time, the two factors sulfuric acid and sodium hydroxide were used as representatives of the leachate in the pH of 1 to 14. Furthermore, collapse tests and direct shear tests were performed on soil samples which were saturated by leachate. Experimental results show that leachate with a low pH or acidic solutions increase the soil collapse potential; on the other hand, leachate with a high pH or alkaline solutions cause less soil collapse. Variation range of soil collapse in acidic solution was much more than alkaline solution. Direct shear test results demonstrate that acidic leachate increase the soil cohesion and reduce the internal friction angle of soils; however, alkaline leachate reduce the soil cohesion and increase the friction angle of soils.

Desirable physical and behavioral characteristics of clay soils have resulted in their wide usage in engineering landfills. Clay soils are able to interact with the materials in contaminants thanks to their special mineral structure and adsorb part or all of the hazardous materials present in the leachate leaked in them. Previous studies have shown that changes in the physical and chemical characteristics of pore fluid in soil, given the type of minerals clay soils and the soil structure, significantly influence the properties of soil engineering including shear parameters, the extent of swell, and water adsorption percentage. The aim of this research is to study the effect of heavy metal contaminants on some strength and geotechnical parameters of sandy clays. For this purpose, following preparation of the samples, adsorption and direct shear experiments along with determination of the liquid limit were performed on the samples which had been exposed to the heavy metal contaminants of Pb and Zn. The results indicated that across the three studied clay types (the mixed sand kaolinite samples with different sand percentages), with the increase in the concentration of both contaminants, soil cohesion diminishes, while the internal friction angle of the samples was not affected by presence of heavy metal contaminants. When concentration of Zn increases to 25 cmmol, cohesion of samples with 90% and 60% of kaolinite decreased 20% and 23% respectively. While in the presence of Pb decrease in cohesion is 42% and 51%.

Fatigue cracking is one of the main and dominant distresses of hot mix asphalt (HMA) at moderate temperatures. This distress happens mainly because of two reasons: 1) Cohesive fracture in the asphalt binder or mastic phase, and 2) Adhesive fracture at the interface of asphalt binder and aggregate. Therefore, one of the main features of the materials used in asphalt mixtures, which affects their fracture type, is the surface free energy (SFE) of asphalt binder and aggregates. In this study, SFE components of aggregates and asphalt binders were respectively determined by universal sorption device (USD) and sessile drop (SD) tests. Also, to evaluate the effects of adhesive and cohesive parameters on the
fatigue life of asphalt mixtures, the samples prepared with different combinations of asphalt binder and aggregate were examined by indirect tensile fatigue test. Results showed that the asphalt mixtures with limestone aggregates and asphalt binder 85-100 had the highest fatigue life compared to the mixtures produced by other aggregates. This feature can be caused by three parameters: 1) Limestone due to the high specifc surface area has the highest adhesion with asphalt binder. 2) By using the asphalt binder 85-100, greater adhesion energy was created between the asphalt binder and aggregate, which increased the energy required for separating the asphalt binder from the aggregate surface and the occurrence of adhesion rapture distress. 3) By using asphalt binder 60-70 caused less signifcant free energy of cohesion in the asphalt binder which resulted in the increased possibility of distress in mastic

The increasing demand for engineered cut and fill slopes on construction goals has increased the need of understanding of analytical methods, investigation tools and the most important stabilization methods to solve slope stability problems. The first step to maintain the stability of an earth slope is performing excavation in the slope crest or/and filling in the slope toe. This is the cheapest way (model) for stabilization of earth slopes. If the model cannot provide the required factor of safety, it is necessary to use other stabilization methods. Numerical and laboratory methods are useful for modeling earth slopes stabilization. Modeling the stability of earth slopes using numerical methods is a common practice in geotechnical engineering. Moreover , stabilization of earth slopes using piles has been practiced by many researchers by using numerical and analytical methods. Application of numerical and analytical methods to stabilization of earth slopes using piles is an issue commonly discussed by various researchers. Although , numerical and analytical methods have special capabilities, laboratory modeling is more reliable. Stability slope analysis has attract lots of researchers attention all across the world and it shows the significance of this matter. When we are suspicious about stability of earth slopes, immediate actions and preventative steps should be used for suppression of instability occurrence. Many projects intersect in valleys and rides , which can be prone to slope stability problems. Natural slopes that have been stable for many years may suddenly fail because of many reasons, therefore finding useful techniques for these matters now days are a great concern for geotechnical engineers. In all earth slopes the primary way for stabilization is the excavation in slope crest and/or filling slope toes , if this action would not increase safety factor enough , other procedures should be applied. Three common styles of stabilization methods are ; vertical reinforcement (such as stone columns and piles) , horizontal reinforcement (like Geo - grids) , oblique reinforcement (such as nailing). Stability of natural slopes is one of important issues in Geotechnical engineering. using easy and economical methods for improving stability of slopes are one of the greatest challenges that face engineers. One of the common methods that is use for increasing the safety factor of slopes is stone columns. All of the experimental tests were modeled and compared using the limit equilibrium (LE) and finite element (FE) methods, which are compliant with each other. Understanding of soil property is crucial for analysis of earth slopes, in this study effect of cohesion in embankment is considered, and based on exact understanding of this property and performing laboratory modeling and by using finite element method software (PLAXIS2D) and finite difference method software (FLAC3D), results are achieved. The sand slope is saturated through precipitation and failure after loading by installing the stone column at the middle of slope. Experimental studies in this article have the potential to give valuable information about effects of embankment cohesion and penetration depth of stone column into the stiffer layer, in stability of stone column reinforced earth slopes.

The effect of matric suction on shear strength of soil، because of its dominant role in geotechnical modelling، has received the attention of researchers in this filed. This research is focused in investigating the effect of matric suction on shear strength of a fine soil. The physical properties of the soil are determined. All samples are passed through No. 200 sieve. The soil is a high plasticity soil which is classified CH according to the unified classification system. The filter paper method is performed to extract the soil water characteristic curve. In addition to its simplicity، one of the major advantages of this method is the vast range of suctions can be measured by it. Specimens were compacted at identical void ratio with different water contents. Suctions are inferred from empirical relations that relate the suction to the measured moisture content of filter paper which has been in contact with soil sample. Air entry suction is determined 140 kPa from SWCC curve. In order to examine moisture content effects on shear strength parameters (cohesion and friction angle) of the clay، soil samples are prepared with different moisture content and consequently different matric suctions with respect to soil water characteristic curve. The specimens with different initial moisture contents are statically compacted at dry density of 1. 3 gr/cm3into direct shear test mould. The moisture contents of samples are in the range of 10 to 28 precent. Hence، according to soil water characteristic curve the initial matric suctions are between 42 to 25238 kPa. Direct shear tests are conducted in unsaturated state. After applying vertical stress the samples are left at least for 48 hours to allow the equalization of internal stresses. Based on experimental data the shear stress is plotted against horizontal displacement in different vertical stresses and moisture contents and the results and analysed and discussed. The effective stress equation proposed by Bishop (1959) is used to interpret the results. The effective stress parameter χ in each moisture content is calculated bythe equation suggested by Khalili & Khabbaz (1998) using the air entry suction extracted from SWCC curve. The results reveal that strength parameters do not substantially change at different moisture contents. The negligible changes in strength parameters may be attributed to slight changes in pore water pressure during shearing experiment. Such changes in pore pressure during shearing would be eliminated in constant suction consolidated drained experiments. The results of this paper support the validity of effective stress concept in unsaturated soils. In other words، with a proper estimate of effective stress، the saturated parameters are valid in unsaturated state and it is not necessary to measure strength parameters in unsaturated state. The unsaturated geotechnical experiments are time consuming and expensive and need special equipment and skills. The method proposed in this paper has a good degree of accuracy. Therefore it can decrease the costs of geotechnical investigation projects in arid lands.