جستجوی مقالات مرتبط با کلیدواژه « چسبندگی » 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.

In most buildings, concrete and steel are used side by side, and according to the type of loads, various stresses are created at their interface. When the repair layer is in direct contact with the steel or reinforcement, the stresses caused by the shrinkage of the mortars as well as temperature changes have a negative effect on the adhesion between the repair mortar and the steel. According to the CEB-FIP MODEL CODE standard, the shear adhesion between mortar and simple reinforcement is equal to τ=0.3√(fc). But it has not provided conditions to consider the type of implementation. Considering that shrinkage causes shear stresses at the interface of mortar and steel, therefore, in this article, by using the in-situ twist-off test, the shear adhesion strength between mortar and plain steel has been evaluated under different processing conditions. The results of the twist-off test show that the above equation is used if the sample is under processing until the moment of the test, otherwise there will be a big drop in the amount of adhesion, which even reaches 50%. The results of the shear adhesion strength obtained from the twist-off test for the samples that were processed in water until the time of the test, at a young age are almost equal to the equation provided by the CEB-FIP Model Code standard. At older ages, the shear bond strength results from the twist-off test between mortar and steel are on average more than 10% higher than the equation provided by the CEB-FIP Model Code standard. For the samples that were processed for a week and then left in the open space, it is observed that there is a big difference between the shear adhesion strength obtained from the twist-off test and the equation provided by the CEB-FIP Model Code standard. For practical cases where processing is usually done for about seven days, it is suggested that the shear adhesion strength between steel and mortar is measured for samples that have been subjected to wet processing for at least one week and prepared and stored under appropriate conditions. According to the equation, τ=0.15√(fc) should be considered. The amount of 90-day shrinkage for mortar treated in water and left in open space is 0.1083 and 0.2679%, respectively. The amount of shrinkage for mortar processed in water is 59% less than the shrinkage of mortar left in the open space.

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.

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.

Given the damages to concrete structures caused by different factors, some materials should be used to repair and strengthen them. In general, cement-based mortars are used to repair concrete structures. The shrinkage and inappropriate compaction of repair mortars can reduce the bond strength between mortar and concrete substrate. the shrinkage is an important problem that has an adverse effect on the adhesion between repair mortar and concrete substrate. The shrinkage can create tensile stress inside mortars, leading to cracking due to their low tensile strength. The mortar-substrate interface is of great importance since the improper compaction can create fine pores and lower the bond strength.The suitable compaction of repair mortar while applying it on the concrete substrate is an effective factor in increasing the adhesion between the mortar and concrete. The mortar-substrate interface is of great importance since the improper compaction can create fine pores and lower the bond strength. Therefore, in this study, different prestresses were imposed on repair mortar to evaluate their effects on the shear and tensile bond strength between repair mortar and concrete substrate using friction-transfer and pull-off tests. The role of curing in reducing the shrinkage of mortars was also evaluated. The semi-destructive friction-transfer and pull-off tests were then used to assess the in-situ compressive strength of cement-based mortars. By calculating the correlation coefficient and plotting the calibration curves, relationships were provided to convert the measurements obtained from the semi-destructive tests to the compressive strength of the mortars. Eventually, the cracks and stresses that appeared in the specimens were presented using finite element ABAQUS software. The obtained results indicated the effect of prestress on increasing the shear and tensile bond strength between the concrete substrate and repair layers. Moreover, a high correlation coefficient was found between the measurements of the in-situ and laboratory tests. A good agreement was also observed between the finite element modeling and the experimental results. In some researches, friction transfer and pull-off tests have been used to compare the compressive strength of fiber-reinforced mortars and polymer-modified mortars with the results of the above tests, which has resulted in a very high correlation coefficient between the results.Imposing a prestress of 0.5 kg/cm2 resulted in an increase of 30.1% and 31.4%, respectively, in the shear and tensile bond strength between the repair mortar and the concrete substrate at the age of 90 days. Imposing a prestress of 0.1 kg/cm2 resulted in an increase by 7.5% and 5.8%, respectively, in the shear and tensile bond strength between the repair mortar and the concrete substrate at the age of 90 days. Keeping the specimen in the free space resulted in 64% more shrinkage compared to the one cured in water. The friction-transfer and pull-off test results had a correlation coefficient of more than 0.98 with the repair mortar's compressive strength. Therefore, these tests can be used to evaluate the in-situ compressive strength of mortars. The compressive strength of repair mortar can be calculated by substituting x for the friction-transfer and pull-off test results, respectively, in the equations y=10x-0.805 and y=17.32x+1.83.

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.

One of the key factors that reduce the bond strength between repair mortars and concrete substrate is improper compaction of the repair layer when applied to concrete. Due to the fact that compacting has a direct effect on the adhesion of the interface of two layers, so the lack of proper compaction causes small cavities between the two layers and as a result causes a decrease in bond strength. Therefore, in this paper, by applying semi-destructive tests, by applying initial compression for 24 hours on the mortar applied to the concrete substrate, the effect of compression on bond between the repair layer and the concrete has been studied. The effect of one week of curing on the dry shrinkage of repair mortars is also presented. In the following, the compressive strength of repair mortars was evaluated using the "twist-off" and "pull-off" tests. In this regard, calibration diagrams were drawn between laboratory tests and semi-destructive tests and linear equations were presented to convert the original results from semi-destructive tests to the compressive strength of mortars. ABAQUS software was used to investigate cracks and stresses in mortars. The results show an increase in bond strength between the repair mortar and the concrete substrate by applying initial compression. Applying initial compression of 0.5 kg/cm2 on unhardened mortar increased the shear and tensile strength between the repair and concrete layers at the age of 90 days by 36.9% and 31.4%, respectively. Also, a linear relationship with high correlation was observed between the readings obtained from the above tests with the compressive strength of repair mortars.

In the concrete repair industry, the adhesion between the repair layer and the concrete plays a decisive role in the successful composite performance of the repair layers. Due to the shrinkage and its effect on adhesion loss, in this paper the effect of polypropylene fibers on the adhesion between mortar/concrete has been investigated. A new "twist-off" test has been used to perform the experiments. In all experiments, the results of the "twist-off" test were compared with the results of the "pull-off" test. X-ray diffraction pattern and scanning electron microscopy tests were used to further analyze the results. Also, the effect of fibers on shrinkage and mechanical properties of mortars and its relationship on adhesion between mortar and concrete were investigated. In this regard, the tests of "twist-off" and "pull-off" were used in the laboratory and compared with the outputs of computer modeling. Also, by examining the correlation coefficient between the results of in-situ tests and laboratory tests, calibration diagrams were presented to convert the readings obtained from the "twist-off" and "pull-off" tests into the compressive strength of mortars. The results indicate that for the fibrous sample, the peak intensity of Ca (OH)2 or calcium hydroxide is reduced, resulting in the production of more hydrated calcium silicate or C-S-H gel, which results in improved final properties of the mortar and increased adhesion. Also, on average, the shear and tensile bond strength of 90 days obtained from "twist-off" and "pull-off" tests with the addition of fibers increased by 49.5% and 43.1%, respectively.

The interface area between substrate concrete and repair mortars is of great importance. Shrinkage and incorrect compaction of the mortar causes fine cavities, and consequently, the bond strength decreases at the interface area. Therefore, in this paper, the influence of different precompressions on the shear and tensile bond strength between polypropylene fiber-reinforced mortar and substrate concrete has been investigated. Friction-transfer and pull-off tests were applied to measure shear and tensile bond strength, respectively. Furthermore, the effect of polypropylene fibers on shrinkage and bond strength is presented. Subsequently, using photography and analysis by Scanning Electron Microscopy (SEM) and X-Ray Diffraction (XRD) pattern, the effect of polypropylene fibers and precompression on the bond strength between fiber-reinforced mortars and the concrete substrate has been studied. Moreover, the compressive strength of fiber-reinforced mortars was evaluated by using semi-destructive in-situ tests. In addition to determining the correlation coefficient between in-situ tests and laboratory tests, calibration diagrams, and transformation equations of records obtained from semi-destructive tests to the mortar compressive strength, are presented. Finite element software ABAQUS has also been used to model the tests mentioned above and compare the outputs with laboratory results. The gained results reveal a positive effect of precompression on the bond strength between concrete and the repair layer. Polypropylene fibers also reduce the shrinkage of mortars and hence increase adhesion. In the XRD test, it was observed that adding polypropylene fibers to the mortar diminishes calcium hydroxide and thus increases calcium silicate hydrate, which has a positive effect on the properties of the mortar. Besides, the SEM photos reveal that the process of hydration and formation of calcium silicate hydrate (C-S-H) gel in the fibers' vicinity is carried out well and has made a better uniformity to the mortar composition. The results of numerical modeling are highly consistent with laboratory results. Due to the high correlation coefficient between in-situ and laboratory tests, it is possible to evaluate fiber-reinforced mortars' compressive strength by using friction-transfer and pull-off tests.

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.

The adhesion between the mortar and the substrate concrete depends on a number of factors including shrinkage, curing and use of modifying polymers. The methods of "Friction-transfer" and "Pull-off" are used to determine the mortar/concrete bond strength. The mortars used contained 10%, 15% and 20% styrene butadiene polymer, (related to cement weight). The results are compared with mortar with no added polymer. Three types of curing were employed. Mortars shrinkage was also investigated. The results tend to show the high impact of the polymer on the adhesion and shrinkage of the mortar. It was also seen that, a high correlation coefficient existed between the corresponding "Friction-transfer" and "Pull-off" results.

Considering using self-compacting concrete – because of no need to vibration and flow ability of this kind of concrete under its weight – under challenging situation for consolidation, it would be a very suitable option for using as repair layer in repairing and retrofitting of concrete structures. In this issue, quality of bonding between the repair layer and concrete substrate is one of the most important factors in durability and suitable performance of repairing works. On this base, in this research, some effective factors on bonding between two layers i.e. volume paste, water to cementitious materials and fiber dosages and their effects on rheological properties of repair self-compacting concrete firstly, on mechanical properties of it including compressive strength, tensile strength, modulus of elasticity and shrinkage secondly and on bonding quality between the self-compacting repair layer and concrete substrate finally have been assessed. For assessment of bonding between two concrete layers, three methods including pull-off, push-out and splitting prism have been used. The results show that because of highly effects of shrinkage on bonding, the factors that reduce shrinkage, i.e. volume paste, water to cementitious materials and fiber dosages will increase the bonding of the two concrete layers. In this issue, the exact effect of each of these parameters on bonding between the two concrete layers and the optimum value of them have been assessed. Also, the correlation between all three methods of assessment of bonding between self-compacting concrete as a repair layer and concrete substrate and preciseness of the methods have been found.

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%.

Self-compacting concrete as a type of concrete that has no need to vibration can use for complicated frameworks and in conditions that compaction is hard. So this concrete is an excellent choice for repair and retrofitting of many kinds of concrete structures such as marine structures, bridges and so on. These concrete structures may be under aggressive environmental conditions and harmful agents. One of the most important damages of concrete structures is because of freezing and thawing cycles especially in exposed ones, like bridge’s decks. So, study of effect of different parameters on quality of self-compacting repair layer, its bonding to substrate and its durability under chemical and physical attacks is very important. In this study, effect of paste volume, water to cementitious materials and polypropylene fiber dosages in mix design on rheological, hardened properties and bonding of repair fiber-reinforced self-compacting concrete (FRSCC) to concrete substrate and its durability for freezing and thawing cycles has been assessed. Bonding between FRSCC as a repair layer and concrete substrate had been evaluate using pull-off test. The tests that failed exactly from the bond surface considered as a successful ones, and all tests that failure had been occurred in repair layer or concrete substrate is eliminated from the results. Freezing and thawing test was conducted according to ASTM C666. Both freezing and thawing processes were made in water. To assessment of bonding of FRSCC as a repair layer to concrete substrate, we made 15 cm cubes of substrate layer with compressive strength more than 50 MPa to ensure that the failure doesn’t occur in this layer while pull-off test. After six months (to have concrete substrate without shrinkage),we saw the cubes divided them to 3 pieces. With analyzing of effects of fiber dosages on rheological properties of the mix designs, we found that an increase in fiber percentage that leads to smaller diameter in slump flow test, higher flow time in T50 test, higher time in V-Funnel test, and lower ratio in L-Box test. Also, while compressive strength had no significant changes, tensile strength and modulus of elasticity experienced a big increase through adding polypropylene fibers. Shrinkage of repair layer had a great decrease after adding polypropylene fibers. The optimum dosage of polypropylene fibers for hardened properties of the mix designs was found 0.1% by volume. We can see that because of the positive effect of fibers on decreasing of shrinkage and increasing of tensile strength of repair layers, bonding between the repair layer and concrete substrate increased greatly especially by adding 0.1% polypropylene fibers (by volume). Also, increase of paste volume and water to cementitious materials (summation of cement and micro silica) had negative effect on bonding of repair layer to substrate. That is because of increase of shrinkage of repair layer. Although, adding polypropylene fibers improved bonding of repair layer and substrate in freezing and thawing cycles, we see smaller results for bonding. We defined debonding index (DI) that presents the rate of debonding during freezing and thawing cycles. Higher DI, higher rate of debonding. As we can see, for mixes that containing polypropylene fibers, DI is bigger in comparison with the ones without them.

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 use of Carbon Fiber Reinforced Polymer (CFRP) laminate systems, for strengthening of structures has gained popularity in recent years.Previous researches indicate that one of the difficulties facing this system is its behavior under high and freezing temperatures. this study investigates the behavior of concrete beams strengthened by CFRP fabrics and laminates, under high and freezing temperatures. in this studies, 24 non-reinforcement concrete beams of 30 x 100 x 100 mm sizes were cast using three different concrete strength. After curing, these beams were strengthened using both flexible and hard CFRP sheets. After setting and hardening of the glue used to adhere the CFRP sheets on to the concrete beams, they were exposed to -20°C, °C and °C temperatures, before undergoing the four point flexural test. Results of study indicate that while the failure of the CFRP sheets at room temperature seems to be due to the flexural cracking, the mode of failures at very low and high temperatures is due to the shear stresses. It may be said that, in addition to the effect of low and high temperatures on the adhesion between the CFRP sheet and substrate concrete, the materials properties involved in this systems are also seriously affected by the extreme temperatures. Examination of the ultimate strength of the strengthened beams also indicates that as the temperature reaches the glass transition temperature of the glue, the reduction in the ultimate strength becomes noticeable. Comparison of the experimental results with the related results of the analytical method, is also presented in this paper.

Among the systems used for Retrofitting and Strengthening of structures، FRP systems seem to be more popular. When using FRP، the surface strength of concrete plays major role in producing sufficient adhesion between FRP laminates and concrete. Therefore، this paper is devoted to the findings of research on five different concrete strength that were used in manufacturing concrete beams for Retrofitting. In total twenty beams were prepared for studying the changes in adhesion between concrete and CFRP layers. While half of the beams were wrapped with CFRP''s، the other half were left as they were for comparative studies. The adhesion of CFRP layers on concrete beams were measured by new Twist-off method and the results were compared with those obtained from standard flexural testing of the beams. Finally، the effect of concrete surface strength and the bond strength of the CFRP on the ultimate strength of the strengthened beams have been assessed.