علی صدر ممتازی

In this article, the effect of using different weight percentages of materials with pozzolanic properties, such as feldspar and microsilica (as a partial substitute for cement) on the mechanical and durability characteristics of the specimens, has been investigated. Studying the effect of using steel fibers with a volume percentage of 1% on the mechanical properties of cement composite is one of the other goals of this research. In the current research, 19 mixing plans were made from cement composites containing microsilica, feldspar and steel fibers. Feldspar and microsilica with weight percentages of 5%, 10% and 15% individually and in combination were replaced with cement. The examined properties include: compressive strength, Bending strength, tensile strength by direct, electrical resistance, percentage of water absorption and (SEM). The results showed that in samples containing short metal fibers, an improvement in compressive strength was observed; So that all the fiber samples had increased resistance compared to the control sample. Among the samples without fibers, the lowest amount of compressive strength loss due to heat was assigned to the design sample with 15% feldspar replacement. All samples containing 1% steel fibers, regardless of the replacement percentage of feldspar and microsilica, resulted in higher bending strength. Examining the results of the direct tensile test shows the significant effect of steel fibers on increasing the tensile strength of cement composites containing microsilica and feldspar; In such a way that the use of 1% of short steel fibers causes the tensile strength to increase by 39% on average.

Considering the high consumption of concrete, especially in structures, and the increasing need for cement production, it seems necessary to pay attention to the harmful environmental effects of this material. In the construction industry, to solve this problem, alternative adhesives are used in concrete, and geopolymers are one of these alternatives. Making geopolymer concretes based on slag can be one of the ways to produce environmentally friendly materials that reduce the harmful effects of cement production. Also, using lightweight concrete has valuable advantages, such as reducing the structure's dead load, and combining geopolymer with lightweight concrete can be beneficial. In this research, two series of lightweight geopolymer concrete have been used. In the first series, by keeping geopolymer ratios constant (Al/Bi=0.65, SS/SH=1 and sodium hydroxide concentration 2 M), Geopolymer concretes with different percentages (50, 60, 70, 80, 90, and 100) of scoria were made instead of coarse aggregate. Then, the designs with structural conditions (compressive strength above 17 MPa and specific weight below 2000 Kg/m3) were selected by comparing the samples' specific weight and compressive strength. In the second series of making lightweight geopolymer concretes by adding steel fibers (0.5, 1, and 1.5%), polypropylene fibers (0.1%), and hybrid, the mechanical characteristics of the samples were evaluated. By examining the compressive strength test, as expected, the compressive strength of the light geopolymer samples increases with the increase in the percentage of steel fibers. Also, samples containing 0.1% of polypropylene fibers face decreased compressive strength. When combined with steel fibers with percentages (0.5, 1, and 1.5), this decrease in compressive strength will be increased. By checking the compressive strength and specific weight, the samples containing 70, 80, and 90% scoria has structural conditions.  By examining the tensile strength test, it can be concluded that adding steel and polypropylene fibers both increase the tensile strength can be seen. In the flexural strength test, flexural strength increases with an increase in the percentage of steel fibers.  It can also be seen that the effect of steel fibers is more significant than polypropylene fibers in increasing the bending strength. An ultrasonic pulse speed test determines the quality of manufactured concrete. According to the observed results, it can be concluded that with the increase in the percentage of fibers (steel and polypropylene), the speed of the ultrasonic pulse also increases. The samples of 70% scoria-containing steel fibers are of excellent quality; this indicates that this design has a better quality geopolymer paste than other samples. Also, the geopolymer concrete sample containing 90% scoria has the lowest value of ultrasonic pulse speed. This reduction can be attributed to many voids in the scoria aggregate. The modulus of elasticity test results showed that the samples containing steel fibers were far more than the other samples, and the most significant increase was seen in steel fibers with a percentage of 1.5. Finally, by examining the microstructure of fiber geopolymer lightweight concrete using scanning electron microscope (SEM) images, it can be seen that the geopolymer sample without fibers contains voids, which are filled to a large extent when steel and polypropylene fibers are added.

Ground Granulated Blast furnace slag (the GGBFS) is known as a potential by-product that can be used as a source of alumina-silicate in production of the geopolymers. The GGBFS based geopolymers possess disadvantages such as high shrinkage, low workability and short setting time. It has been proven that these defects can be reduced by partial replacement of the GGBFS by the other low calcium alumina-silicate materials. The bamboo leaf ash (BLA), which contains high content of SiO2 and low content of CaO, can be one of these materials. In this article, the effects of bamboo leaf ash on fresh, microstructural and mechanical properties of the GGBFS and the GGBFS/natural zeolite powder based geopolymer pastes have been investigated. Moreover, effect of the NaOH solution concentration( i.e. 8, 12 and 16 mole/liter) and the Al/Bi ratio (i.e. 0.5, 0.6 and 0.7) on properties of the geopolymer pastes have been evaluated. The results show that replacing 10% wt. of the base materials by the BLA in the studied geopolymer pastes leads to an increase in the workability and setting time. While, this substitution results a reduction in the amount of crystalline phases produced and consequently a decrease in the mechanical characteristics. Based on the results, as the NaOH solution concentration increases from 8 to 16 mole/liter, the workability, setting time and mechanical characteristics of the GGBFS/BLA based geopolymer paste have been reduced. Moreover,

Carbon nanotube, a product of chemical exfoliation of graphite, is a suitable additive for use as nanoreinforcement in cement-based materials due to its high aspect ratio, good water dispersibility and excellent mechanical properties. In the present study, the effect of volume fraction, aspect ratio, distribution orientation and interaction between surfaces on the mechanical properties of cement matrix reinforced with carbon nanotubes using multi-scale modeling was investigated. To Model in the Abaqus software, with the conceptual understanding of the volume representative element, a developed MATLAB and Python scripts were applied. To observe the interphase behavior between the matrix and fillers, the cohesive surface theory was used. Also, the output results of molecular dynamics modeling was used to determine the cohesive surface parameters. Modeling was done in the states of full and limited bonding between two phases in nano-compsite with compressive axial loading. The cement models with 0, 0.5, 1, and 1.5 vol% with aspect ratios of 10 and 20 were evaluated and discussed. Furthermore, the distribution effect was studied by defining the nanotubes to be parallel, perpendicular and random regarding the force direction. The results showed that increasing the volume fraction of CNTs improves the yield strength and toughness of the samples. Increasing the CNT aspect ratio from 10 to 20 leads to an increase of elastic limit and an improvement of plastic behavior of the next matrix. Finally, the cohesive modeling of the interactions of matrix and CNT eventuated in 3 to 6% reductions per 0.5 and 1% CNT/cement composites.

Concrete may be loaded at an early age for a variety of reasons. This loading can have negative and sometimes destructive effects on the hardened properties of concrete. Therefore, in the present study, the mechanical properties of fiber-reinforced geopolymer concrete after loading at an early age have been investigated. In the present study, the effect of preload on compressive strength at the ages of 28 and 90 days for geopolymer concrete containing fibers has been investigated. For this purpose, the samples were loaded at ages of 1, 3, and 7 days, equivalent to 30 and 70% of their compressive strength at the same age. The samples were then treated again in a humid environment and subjected to compressive loading at 28 and 90 days of age. The effect of preload on flexural strength as well as energy absorption of geopolymer concrete containing fibers was also investigated. Steel fibers with volumetric percentages of 0.25, 0.5, 0.75, and 1 and polypropylene fibers with volumetric percentages of 0.25, 0.5, and 0.75 were used in fabricating laboratory samples. The results demonstrate the positive effect of fibers on reducing the destructive effects of preload on compressive and flexural strength. The effect of fibers on reducing the destructive effects of 1-day preload is higher at higher loading percentage (70% pre-loading), such that the samples containing fibers with preload of 30% at the age of one day experienced a 28.8% increase in 28-day compressive strength, while this increase was 33.2% for the samples with preload of 70%. Samples containing 0.75% polypropylene fibers at 28 and 90 days of age compared to those containing 0.25 and 0.5% polypropylene showed less energy absorption on average due to preloading. In general, the design containing 0.25 polypropylene fiber and 1% steel fiber had the best result of flexural strength among preloaded samples.

Selection, design and control of materials are very important for achievement of a compatible, durable and economical repair overlay. Suitable bonding of repair overlay to substrate and good resistance against fracture are basics for a durable overlay. Using Polymer Concretes (PC) and Polymer Modified Concretes (PMC) which present great performance and durability can be considered as a method of restoration in damaged structures. In this research, mechanical properties and strengths of bonding to substrate concrete of Polymer Concretes and Polymer Modified Concretes as repair overlays are investigated and compared. Strength of Bonding to substrate concrete was obtained by Pull-Off test method. Bonding strength to substrate concrete in Polymer Concretes mix designs samples was weaker than Polymer Modified Concretes mix designs samples in similar conditions. In comparison with conventional concrete repair overlays in Pull-Off test, the maximum increment of bonding strength to substrate concrete was observed in mix design containing %50 of water replacement with SBR-based polymer which was %30 of increment and after that in mix design containing %50 of water replacement with Acrylic-based polymer which was %28 of increment. In Polymer Modified Concretes, %5 replacement of cement with Silica Fume decreased the amount of shrinkage but in higher values of replacement the amounts of shrinkage were increased in samples.

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.

Self-compacting concrete or SCC can be considered as the concrete of the future. The most important feature of self-compacting concrete is flowing under its own weight to fill the mould or framework completely, and also to create a dense and sufficiently homogeneous mix between the bars, without any need for vibration. But the excessive Liquidity of this concrete increases the hydrostatic pressure on the frameworks. So, decrease in the weight of self-compacting concrete could be lead to reducing the pressure on frameworks. It is also clear that decreasing the density of concrete has a significant effect on the reduction of the structure’s weight and will lead to decrease in the size of structural elements. On the other hand, there are general concerns about the segregation of lightweight aggregates during transportation or placing. In this research, the ability of maintaining the homogeneity of the mixture and the mechanical properties of lightweight self-compacting concrete (LWSCC) made with common lightweight aggregates in the country including Scoria, Leca and Pumice, has been investigated on concrete columns, using the Semi-destructive and non-destructive methods. To do this, reinforced concrete columns made by self-compacting concrete were investigated using a semi-destructive core test to determine the compressive strength and impermeability. Non-destructive ultrasonic test at different heights of the columns was also conducted. The results showed that Scoria aggregate had generally better performance in self-compacting concrete compared to other lightweight aggregates.

Use of common bers, in addition to increasing ductility, toughness, rst point cracking, and ultimate strain, plays a major role in preventing shrinkage and thermal cracks. The role of temperature in ber bridging and change of material structure has been investigated in previous studies. Use of waste materials in structural materials can decrease further pollution of ecosystem. On the other hand, increase in oil and polymer-based waste materials, caused some concern in the international community because of the adverse environmental impact of this material. For this reason, in this research, steel ber (0.4, 0.5 and 0.6), Polypropylene ber (0.03, 0.05 and 0.1), and recycled Polyethylene terephthalate (PET) ber (0.2, 0.3 and 0.4) percent of the concrete mixture volume were used. The results of the rheological (V-funnel, T50, Slump and L-Box), mechanical properties (e.g., compressive, exural, and splitting tensile strength) and Ultrasonic Pulse Velocity (UPV) Test of self-compacting concrete exposed to temperatures of 20, 200, 300, 400, and 600 showed that high contents of bers did not satisfy some rheological and mechanical aspects of self-compacting concrete. Steel bers increased the compressive, exural, and splitting tensile strengths of concrete with maximum amount of 9.8% and two other bers cause 15% decrease in strength of unheated specimens at most. Fiber reinforced specimens had an increase in resistance in the range of 8 to 21% by heating specimens to600 . The exural strength of steel ber reinforced specimens had an increase of maximum 30% for unheated ones. PET and P.P. ber reinforced specimens had 9 to 20% increase in exural strength. The presence of bers increases the mechanical strength, toughness, and ductility of concrete and prevents loss of strength and spalling phenomenon at high temperatures, as well as having a fundamental role in the reduction of heat, microcracks, and retaining fundamental structure of concrete.

The behavior of concrete subjected to impact load, is different compared to the behavior under static loading. A test program was carried out to determine static and dynamic properties of rubberized concrete. In this study, waste tire rubber particles were replaced with fine aggregate in concrete mixture in 3 sizes, 0-1, 1-3 and 3-5 mm and in volume ratio of 0%, 10%, 20%, 30%, 40% and 50%. Static and dynamic tests are done with hydraulic and drop hammer machines. Results of compressive and flexural strength, velocity of ultrasonic wave, Static and dynamic modulus of elasticity, strain and Static and absorption energy of rubberized concrete are determined. The results indicated that: larger rubber particles in replacement of sand have better results than smaller sizes. Also increased in rubber content, decreased the unit weight, compressive strength and static and dynamic modulus of elasticity of rubberized concrete. Using rubber particles in concrete significantly increased the ductility and strain capacity of concrete. In addition in this study equation of impact test with using mass-spring modelling, was determined.

When the concrete loses its moisture, shrinkage and volume reduction is happening and eventually cracks create and deformations in the concrete are increased. In this study, the effect of polypropylene, steel, glass, basalt and polymer fiber on compressive strength, flexural strength and shrinkage cracks (early ages) of high strength concrete mixtures were evaluated. The restrained shrinkage test was performed on concrete ring specimens with height of 150 mm, inner diameter of 30 mm and outer diameter of 40 mm according to ASTM C 1581 standard. The crack width and age of restrained shrinkage cracking were main parameters studied in this research. The results showed that, adding fiber, caused increases the compressive strength 16%, 20% and 3% at the age of 3, 7 and 28 days respectively, and also, increased flexural toughness index up to 7.7 times. steel and glass fiber provided good performance in flexural strength, but had relatively poor action in the velocity reduction and cracking time of restrained shrinkage. Also, crack in all of concrete ring specimens except polypropylene containing mixture, was developed to full depth crack. The mixture of polypropylene fiber containing showed reduction in crack width up to 62% and increasing age cracking up to 84%.

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.

The bond between aggregate and cement paste, called the interfacial transition zone (ITZ) is an important parameter that effect on the mechanical properties and durability of concrete. Transition zone microstructure and porosity (pores) of cement paste or concrete are affected by the type and properties of materials used which evaluated in this research. On the other hand, the use of efficient, low-cost and reliable method is particularly important for evaluating of concrete performance against the chloride ion penetration and its relationships with transition zone as a suitable index to assess the durability. So far, various methods to approach the electrical Indices are presented. In this research, the effect of pozzolanic materials fly ash (10%, 20% and 30%) and silica fume (5% and 10%) as substitute of cement by weight in binary and ternary mixtures on the fresh and hardened concrete properties were investigated. To determine mechanical properties, the compressive strength, splitting tensile strength and modulus of elasticity tests were performed. Also, water penetration depth, porosity, water sorptivity, specific electrical resistivity, rapid chloride penetration test (RCPT) and rapid chloride migration test (RCMT) tests were applied to evaluate concrete durability. To examine the border of aggregate and cement paste morphology of concrete specimens, scanning electron microscope images (SEM) was used. The fresh concrete results showed that the presence of silica fume in binary and ternary mixtures reduced workability and air content but fly ash increased them. Adding silica fume to mixtures of containing flay ash while increasing mechanical strength reduced the porosity and pores to 18%. The presence of pozzolanic materials in addition to increasing bond quality and uniformity of aggregate-cement matrix border a considerably positive effect on the transport properties of concrete.

One major weakness of concrete is the brittle fracture behaviour in tension, with low tensile strength and ductility. This brittleness has been recognized as a bottleneck hindering structural performances in terms of safety, durability and sustainability. The lack of structural ductility is due to brittle nature of concrete in tension which may lead to loss of structural integrity. Many infrastructure deterioration problems and failures can be traced back to the cracking and brittle nature of concrete. Many attempts have been made in the recent years to overcome these problems. To effectively solve these severe problems, a new type of composite, called as Engineered Cementitious Composites (ECC), reducing the brittle behaviour of concrete has been developed in recent decades. ECC with its flexible processing has emerged from laboratory testing to field applications leading to speedy construction, reduced maintenance and a longer life span for the Structures. Micromechanical design allows optimization of ECC for high performance, resulting in extreme tensile strain capacity while minimizing the amount of reinforcing fibers, typically less than 2% by volume. Tensile strain capacity exceeding 5% has been demonstrated on ECC reinforced with polyethylene and polyvinyl alcohol (PVA) fibers. Unlike ordinary cement-based materials, ECC strain hardens after first cracking, similar to a ductile metal, and demonstrates a strain capacity 350 to 550 times greater than normal concrete. Even at large imposed deformation, crack widths of ECC remain small, less than 80 μm. With intrinsically tight crack width and high tensile ductility, ECC represents a new generation of high performance concrete (HPC) material that offers significant potential to naturally resolving the durability problem of reinforced concrete structures. In the past few decades, substitution of mineral admixtures, such as fly ash (FA) and Ground Blast-Furnace Slag (GBFS), has been of great interest and gradually applied to practical applications of ECC. It has been found that incorporating high amount of FA can reduce the matrix toughness and improve the robustness of ECC in terms of tensile ductility. Additionally, unhydrated FA particles with small particle size and smooth spherical shape serve as filler particles resulting in higher compactness of the fiber/matrix interface transition zone that leads to a higher frictional bonding. This aids in reducing the steady-state crack width beneficial for long-term durability of the structure. In this study, the workability, mechanical properties and durability of ECC different mixtures contains two mineral materials (slag / fly ash) as to replace part of the cement weight and two types aggregate (Silica/ River sand) were evaluated. The results showed that mixtures containing fly ash despite lower mechanical strength to compared with mixtures containing slag, significantly have higher performance in strain- hardening behavior at post- cracking portion. ECC mixtures performance against the durability testing (Rapid chloride penetration, Electrical Specific Resistivity, Drying Shrinkage and Accelerated Reinforcement Corrosion) were appropriate and quantitatively was to form of slag> fly ash. In this study, in order to calculate the direct tensile strength of ECC mixtures, a new model (different geometry) compared to other models (used by prior researchers) proposed and tested. The its results showed that the tensile strength measured by the new model compared to the previous models, was higher 10% to 17%.

The use of fiber reinforced polymer (FRP) composites is ever growing in the construction industry. High strength- weight ratio, corrosion resistance and suitable durability are the main criteria for FRP selection and design. However, in case of high temperature exposure, change in the material properties affects the overall structure performance. The aim of this study is to evaluation the effect of cement and epoxy adhesives on the thermal performance of concrete flexural specimens strengthened with basalt (BFRP) and glass (GFRP) fabrics. Therefore, 105 flexural specimens (100 × 100 × 500 mm) were made by a constant water-cement ratio; and were kept under the 50°, 100° and 200°, for a period of one and three hours, respectively. The results show that increasing the temperature led to decreased flexural strength of unreinforced specimens by 48%. Also, flexural strength of cement and epoxy adhesives impregnated specimens decreased up to 47% and 60% respectively. Results from the presented model shows at temperatures lower than 100 0C, flexural strength of cement adhesive impregnated specimens was lower than epoxy adhesive impregnated specimens; but at 200 0C, flexural strength of specimens strengthened with basalt and glass fabrics increases 1.3 and 1.15, respectively. Also, curve for flexural strength of specimens strengthened with basalt fabrics compared to glass fabrics had an ascending trend, while it had a descending trend for epoxy adhesive impregnated specimens.

Structures might be subjected to impulse loads such as impact ones in useful lifetime. Production of new materials that are shown less vulnerable to sudden shocks and vibrations, is the items that should be considered. Concrete is a brittle material and when is exposed to dynamic loads, in addition to its injury, it may be damage to the environment due to disintegration .In this study, waste rubber particles were replaced of fine aggregate in concrete mixture in 3 size 0-1, 1-3 and 3-5 mm and in volume ratio of 0%, 10%, 20%, 30%, 40% and 50%. First with compressive strength test, optimum sizes of rubber particles obtained, then silica fume and polypropylene fiber added to concrete mixture contained optimum size of rubber particles. In addition compressive strength, dry unit weight, velocity of ultrasonic wave, impact with drop hammer and gas gun device test were done. The results shown that, adding rubber particles to concrete mixture decreases compressive strength but increases ductility of it. Also silica fume because of pozzolanic properties increased adhesive in concrete matrix, so increased strength of concrete and polypropylene fiber increased ductility of concrete.

Application of nanoparticles in cement, regarding their synthesis and utilization procedure, provides various mechanical, electrical and thermal properties to cement based composites. The superior properties of carbon nanotubes (CNTs) have made them as one of the most beneficial nano-reinforcement material. On the other hand, metal particles have been known to be effective for enhancing electrical properties. Accordingly, it seems that the synergistic incorporation of CNTs and copper particles can introduce suitable piezoelectric properties to cement matrices. To this end, in the current investigation, in order to prepare the reinforcement material, copper coated CNTs were prepared using an efficient electroless deposition process. The synthesized samples were characterized using SEM, TEM, XRD, TGA, ICP and AAS. Our results revealed that the process covers most surfaces of the CNTs. Furthermore, the calculated bath efficiency showed to be more than 99%

Recent researches have shown that use fiber in concrete can increase the flexural, tensile, and abrasion resistance. On the other hand Self-Compacting Concrete is a high flowable homogenous concrete which can eliminate several common problems in normal concretes by means of its compaction under its own weight. The above properties of self compacting concrete facilitate the fabrication of concrete structural members with congested reinforcement.
On the other hand, in the past two decades application of nano-technology has significantly revolutionized human knowledge. Using nano silica particles as a product of pozolanic reaction, can strongly improve the permeability of concrete. Thus concrete having the properties of both self compacting concrete and fiber reinforced concrete with strengthened micro matrices can improve the fabrication of durable structures with high performance level. In this research, the combined effect of nano-silica particles and fibers type (steel, polypropylene and glass) on mechanical properties (compressive, tensile and flexural strength, modulus of elasticity), rheological behavior (L-box, slump flow and T50) and also the durability of Self-Compacting concrete were evaluated using water absorption and Rapid Chloride Penetration Test (RCPT). Furthermore, XRD test has been used.
For this purpose, forty mixtures in A, B, C and D series representing 0, 2, 4 and 6 percent of nano silica particles replacing cement content were cast. Each series involved three different fiber type and content. 0.2, 0.3 and 0.5% volume for steel fiber, 0.1, 0.15 and 0.2% of volume for polypropylene fiber and finally 0.15, 0.2 and 0.3% of volume for glass fiber. The results show that the combined usage of optimum percent of fiber and nano silica particles will improve the mechanical properties and durability of self-compacting concrete.

S‌e‌l‌f-c‌o‌m‌p‌a‌c‌t‌i‌n‌g c‌o‌n‌c‌r‌e‌t‌e (S‌C‌C) i‌s a n‌e‌w c‌l‌a‌s‌s o‌f h‌i‌g‌h p‌e‌r‌f‌o‌r‌m‌a‌n‌c‌e c‌o‌n‌c‌r‌e‌t‌e t‌h‌a‌t c‌a‌n s‌p‌r‌e‌a‌d r‌e‌a‌d‌i‌l‌y i‌n‌t‌o p‌l‌a‌c‌e u‌n‌d‌e‌r i‌t‌s o‌w‌n w‌e‌i‌g‌h‌t a‌n‌d f‌i‌l‌l r‌e‌s‌t‌r‌i‌c‌t‌e‌d s‌e‌c‌t‌i‌o‌n‌s, a‌s w‌e‌l‌l a‌s c‌o‌n‌g‌e‌s‌t‌e‌d r‌e‌i‌n‌f‌o‌r‌c‌e‌m‌e‌n‌t s‌t‌r‌u‌c‌t‌u‌r‌e‌s, w‌i‌t‌h‌o‌u‌t t‌h‌e n‌e‌e‌d f‌o‌r m‌e‌c‌h‌a‌n‌i‌c‌a‌l c‌o‌n‌s‌o‌l‌i‌d‌a‌t‌i‌o‌n a‌n‌d w‌i‌t‌h‌o‌u‌t u‌n‌d‌e‌r‌g‌o‌i‌n‌g a‌n‌y s‌i‌g‌n‌i‌f‌i‌c‌a‌n‌t s‌e‌p‌a‌r‌a‌t‌i‌o‌n o‌f m‌a‌t‌e‌r‌i‌a‌l c‌o‌n‌s‌t‌i‌t‌u‌e‌n‌t‌s. T‌h‌e u‌s‌e o‌f S‌C‌C c‌a‌n i‌m‌p‌r‌o‌v‌e p‌r‌o‌d‌u‌c‌t‌i‌v‌i‌t‌y i‌n s‌t‌r‌u‌c‌t‌u‌r‌a‌l a‌p‌p‌l‌i‌c‌a‌t‌i‌o‌n‌s s‌u‌c‌h a‌s r‌e‌p‌a‌i‌r‌s, a‌n‌d f‌a‌c‌i‌l‌i‌t‌a‌t‌e t‌h‌e f‌i‌l‌l‌i‌n‌g o‌f r‌e‌s‌t‌r‌i‌c‌t‌e‌d s‌e‌c‌t‌i‌o‌n‌s. S‌u‌c‌h c‌o‌n‌c‌r‌e‌t‌e h‌a‌s b‌e‌e‌n w‌i‌d‌e‌l‌y u‌s‌e‌d t‌o f‌a‌c‌i‌l‌i‌t‌a‌t‌e c‌o‌n‌s‌t‌r‌u‌c‌t‌i‌o‌n o‌p‌e‌r‌a‌t‌i‌o‌n‌s, e‌s‌p‌e‌c‌i‌a‌l‌l‌y i‌n s‌e‌c‌t‌i‌o‌n‌s p‌r‌e‌s‌e‌n‌t‌i‌n‌g p‌a‌r‌t‌i‌c‌u‌l‌a‌r d‌i‌f‌f‌i‌c‌u‌l‌t‌i‌e‌s i‌n c‌a‌s‌t‌i‌n‌g a‌n‌d v‌i‌b‌r‌a‌t‌i‌o‌n, s‌u‌c‌h a‌s t‌h‌e b‌o‌t‌t‌o‌m s‌i‌d‌e‌s o‌f b‌e‌a‌m‌s, g‌i‌r‌d‌e‌r‌s, a‌n‌d s‌l‌a‌b‌s. W‌o‌r‌k‌a‌b‌i‌l‌i‌t‌y r‌e‌q‌u‌i‌r‌e‌m‌e‌n‌t‌s f‌o‌r s‌u‌c‌c‌e‌s‌s‌f‌u‌l c‌a‌s‌t‌i‌n‌g o‌f S‌C‌C i‌n‌c‌l‌u‌d‌e h‌i‌g‌h d‌e‌f‌o‌r‌m‌a‌b‌i‌l‌i‌t‌y, p‌a‌s‌s‌i‌n‌g a‌b‌i‌l‌i‌t‌y, a‌n‌d p‌r‌o‌p‌e‌r r‌e‌s‌i‌s‌t‌a‌n‌c‌e t‌o s‌e‌g‌r‌e‌g‌a‌t‌i‌o‌n. D‌e‌f‌o‌r‌m‌a‌b‌i‌l‌i‌t‌y r‌e‌f‌e‌r‌s t‌o t‌h‌e a‌b‌i‌l‌i‌t‌y o‌f S‌C‌C t‌o f‌l‌o‌w i‌n‌t‌o a‌n‌d c‌o‌m‌p‌l‌e‌t‌e‌l‌y f‌i‌l‌l a‌l‌l s‌p‌a‌c‌e‌s w‌i‌t‌h‌i‌n t‌h‌e f‌o‌r‌m‌w‌o‌r‌k, u‌n‌d‌e‌r i‌t‌s o‌w‌n w‌e‌i‌g‌h‌t. D‌e‌f‌o‌r‌m‌a‌b‌i‌l‌i‌t‌y i‌s t‌h‌e p‌r‌o‌p‌e‌r‌t‌y m‌o‌s‌t c‌o‌m‌m‌o‌n‌l‌y a‌s‌s‌o‌c‌i‌a‌t‌e‌d w‌i‌t‌h S‌C‌C a‌n‌d p‌r‌o‌v‌i‌d‌e‌s j‌u‌s‌t‌i‌f‌i‌c‌a‌t‌i‌o‌n f‌o‌r a‌c‌c‌e‌p‌t‌a‌n‌c‌e o‌f t‌h‌e t‌e‌c‌h‌n‌o‌l‌o‌g‌y. I‌n r‌e‌c‌e‌n‌t y‌e‌a‌r‌s, p‌r‌o‌g‌r‌e‌s‌s i‌n c‌o‌n‌c‌r‌e‌t‌e t‌e‌c‌h‌n‌o‌l‌o‌g‌y h‌a‌s m‌a‌d‌e i‌t p‌o‌s‌s‌i‌b‌l‌e t‌o p‌r‌o‌d‌u‌c‌e S‌C‌C, w‌h‌i‌c‌h i‌s o‌f m‌o‌r‌e w‌o‌r‌k‌a‌b‌i‌l‌i‌t‌y a‌n‌d d‌u‌r‌a‌b‌i‌l‌i‌t‌y t‌h‌a‌n n‌o‌r‌m‌a‌l v‌i‌b‌r‌a‌t‌e‌d c‌o‌n‌c‌r‌e‌t‌e (N‌V‌C). A r‌e‌m‌a‌r‌k‌a‌b‌l‌e p‌r‌o‌b‌l‌e‌m i‌n c‌o‌n‌c‌r‌e‌t‌e e‌l‌e‌m‌e‌n‌t‌s i‌s i‌t‌s l‌o‌w e‌n‌e‌r‌g‌y d‌i‌s‌s‌i‌p‌a‌t‌i‌o‌n a‌n‌d, t‌h‌u‌s, i‌t‌s h‌i‌g‌h b‌r‌i‌t‌t‌l‌e‌n‌e‌s‌s. A‌l‌t‌h‌o‌u‌g‌h S‌C‌C h‌a‌s h‌i‌g‌h‌e‌r s‌t‌r‌e‌n‌g‌t‌h t‌h‌a‌n (N‌V‌C), o‌b‌s‌e‌r‌v‌i‌n‌g i‌t‌s s‌t‌r‌e‌s‌s-s‌t‌r‌a‌i‌n c‌u‌r‌v‌e r‌e‌v‌e‌a‌l‌s t‌h‌a‌t t‌h‌e d‌e‌c‌l‌i‌n‌i‌n‌g s‌e‌g‌m‌e‌n‌t o‌f t‌h‌e c‌u‌r‌v‌e i‌s a‌l‌m‌o‌s‌t v‌e‌r‌t‌i‌c‌a‌l a‌n‌d n‌o c‌o‌n‌s‌i‌d‌e‌r‌a‌b‌l‌e s‌t‌r‌a‌i‌n s‌o‌f‌t‌e‌n‌i‌n‌g i‌s d‌e‌t‌e‌c‌t‌e‌d, w‌h‌i‌c‌h c‌a‌u‌s‌e‌s s‌u‌d‌d‌e‌n b‌r‌i‌t‌t‌l‌e f‌r‌a‌c‌t‌u‌r‌e i‌n t‌h‌e s‌t‌r‌u‌c‌t‌u‌r‌e. S‌t‌u‌d‌i‌e‌s s‌h‌o‌w t‌h‌a‌t a‌d‌d‌i‌t‌i‌o‌n o‌f d‌i‌f‌f‌e‌r‌e‌n‌t f‌i‌b‌e‌r‌s d‌o‌e‌s n‌o‌t f‌u‌n‌d‌a‌m‌e‌n‌t‌a‌l‌l‌y c‌h‌a‌n‌g‌e t‌h‌e b‌e‌h‌a‌v‌i‌o‌r o‌f t‌h‌e c‌o‌n‌c‌r‌e‌t‌e p‌r‌i‌o‌r t‌o i‌t‌s m‌a‌x‌i‌m‌u‌m s‌t‌r‌e‌s‌s, w‌h‌i‌l‌e i‌t g‌r‌e‌a‌t‌l‌y i‌m‌p‌r‌o‌v‌e‌s t‌h‌e c‌o‌n‌c‌r‌e‌t‌e p‌o‌s‌t-c‌r‌a‌c‌k‌i‌n‌g b‌e‌h‌a‌v‌i‌o‌r. T‌h‌i‌s m‌e‌t‌h‌o‌d p‌o‌s‌i‌t‌i‌v‌e‌l‌y i‌n‌f‌l‌u‌e‌n‌c‌e‌s o‌t‌h‌e‌r p‌r‌o‌p‌e‌r‌t‌i‌e‌s o‌f t‌h‌e c‌o‌n‌c‌r‌e‌t‌e i‌n‌c‌l‌u‌d‌i‌n‌g t‌o‌u‌g‌h‌n‌e‌s‌s, f‌r‌a‌c‌t‌u‌r‌e e‌n‌e‌r‌g‌y a‌n‌d f‌l‌e‌x‌u‌r‌a‌l s‌t‌r‌e‌n‌g‌t‌h. O‌n t‌h‌e o‌t‌h‌e‌r h‌a‌n‌d, i‌n t‌h‌e p‌a‌s‌t t‌w‌o d‌e‌c‌a‌d‌e‌s, a‌p‌p‌l‌i‌c‌a‌t‌i‌o‌n o‌f n‌a‌n‌o-t‌e‌c‌h‌n‌o‌l‌o‌g‌y h‌a‌s s‌i‌g‌n‌i‌f‌i‌c‌a‌n‌t‌l‌y r‌e‌v‌o‌l‌u‌t‌i‌o‌n‌i‌z‌e‌d h‌u‌m‌a‌n k‌n‌o‌w‌l‌e‌d‌g‌e. U‌s‌i‌n‌g n‌a‌n‌o-s‌i‌l‌i‌c‌a p‌a‌r‌t‌i‌c‌l‌e‌s a‌s a p‌r‌o‌d‌u‌c‌t o‌f p‌o‌z‌o‌l‌a‌n‌i‌c r‌e‌a‌c‌t‌i‌o‌n c‌a‌n s‌t‌r‌o‌n‌g‌l‌y i‌m‌p‌r‌o‌v‌e t‌h‌e p‌e‌r‌m‌e‌a‌b‌i‌l‌i‌t‌y o‌f c‌o‌n‌c‌r‌e‌t‌e b‌y i‌n‌c‌r‌e‌a‌s‌i‌n‌g t‌h‌e t‌r‌a‌n‌s‌i‌t‌i‌o‌n l‌a‌y‌e‌r o‌f f‌i‌b‌e‌r a‌n‌d c‌e‌m‌e‌n‌t m‌a‌t‌r‌i‌x. T‌h‌u‌s, c‌o‌n‌c‌r‌e‌t‌e, h‌a‌v‌i‌n‌g t‌h‌e p‌r‌o‌p‌e‌r‌t‌i‌e‌s o‌f b‌o‌t‌h s‌e‌l‌f c‌o‌m‌p‌a‌c‌t‌i‌n‌g c‌o‌n‌c‌r‌e‌t‌e a‌n‌d f‌i‌b‌e‌r r‌e‌i‌n‌f‌o‌r‌c‌e‌d c‌o‌n‌c‌r‌e‌t‌e w‌i‌t‌h s‌t‌r‌e‌n‌g‌t‌h‌e‌n‌e‌d m‌i‌c‌r‌o m‌a‌t‌r‌i‌c‌e‌s, c‌a‌n i‌m‌p‌r‌o‌v‌e t‌h‌e f‌a‌b‌r‌i‌c‌a‌t‌i‌o‌n o‌f d‌u‌r‌a‌b‌l‌e s‌t‌r‌u‌c‌t‌u‌r‌e‌s a‌t a h‌i‌g‌h p‌e‌r‌f‌o‌r‌m‌a‌n‌c‌e l‌e‌v‌e‌l. I‌n t‌h‌i‌s r‌e‌s‌e‌a‌r‌c‌h, t‌h‌e c‌o‌m‌b‌i‌n‌e‌d e‌f‌f‌e‌c‌t‌s o‌f n‌a‌n‌o-s‌i‌l‌i‌c‌a p‌a‌r‌t‌i‌c‌l‌e‌s a‌n‌d f‌i‌b‌e‌r t‌y‌p‌e (s‌t‌e‌e‌l, p‌o‌l‌y‌p‌r‌o‌p‌y‌l‌e‌n‌e a‌n‌d g‌l‌a‌s‌s) o‌n t‌o‌u‌g‌h‌n‌e‌s‌s, f‌r‌a‌c‌t‌u‌r‌e e‌n‌e‌r‌g‌y, f‌l‌e‌x‌u‌r‌a‌l s‌t‌r‌e‌n‌g‌t‌h, a‌n‌d r‌h‌e‌o‌l‌o‌g‌i‌c‌a‌l b‌e‌h‌a‌v‌i‌o‌r (L-b‌o‌x, s‌l‌u‌m‌p f‌l‌o‌w a‌n‌d T50) o‌f s‌e‌l‌f-c‌o‌m‌p‌a‌c‌t‌i‌n‌g c‌o‌n‌c‌r‌e‌t‌e w‌e‌r‌e e‌v‌a‌l‌u‌a‌t‌e‌d.F‌o‌r t‌h‌i‌s p‌u‌r‌p‌o‌s‌e, f‌o‌r‌t‌y m‌i‌x‌t‌u‌r‌e‌s i‌n a‌n A, B, C a‌n‌d D s‌e‌r‌i‌e‌s, r‌e‌p‌r‌e‌s‌e‌n‌t‌i‌n‌g 0, 2, 4 a‌n‌d 6 p‌e‌r‌c‌e‌n‌t o‌f n‌a‌n‌o-s‌i‌l‌i‌c‌a p‌a‌r‌t‌i‌c‌l‌e‌s, r‌e‌p‌l‌a‌c‌i‌n‌g c‌e‌m‌e‌n‌t c‌o‌n‌t‌e‌n‌t, w‌e‌r‌e c‌a‌s‌t. E‌a‌c‌h s‌e‌r‌i‌e‌s i‌n‌v‌o‌l‌v‌e‌d t‌h‌r‌e‌e d‌i‌f‌f‌e‌r‌e‌n‌t f‌i‌b‌e‌r t‌y‌p‌e‌s a‌n‌d c‌o‌n‌t‌e‌n‌t; 0.2, 0.3 a‌n‌d 0.5\% v‌o‌l‌u‌m‌e f‌o‌r s‌t‌e‌e‌l f‌i‌b‌e‌r, 0.1, 0.15 a‌n‌d 0.2\% v‌o‌l‌u‌m‌e f‌o‌r p‌o‌l‌y‌p‌r‌o‌p‌y‌l‌e‌n‌e f‌i‌b‌e‌r a‌n‌d, f‌i‌n‌a‌l‌l‌y, 0.15, 0.2 a‌n‌d 0.3\% v‌o‌l‌u‌m‌e f‌o‌r g‌l‌a‌s‌s f‌i‌b‌e‌r. T‌h‌e r‌e‌s‌u‌l‌t‌s s‌h‌o‌w t‌h‌a‌t t‌h‌e c‌o‌m‌b‌i‌n‌e‌d u‌s‌a‌g‌e o‌f t‌h‌e o‌p‌t‌i‌m‌u‌m p‌e‌r‌c‌e‌n‌t o‌f f‌i‌b‌e‌r a‌n‌d n‌a‌n‌o-s‌i‌l‌i‌c‌a p‌a‌r‌t‌i‌c‌l‌e‌s w‌i‌l‌l i‌m‌p‌r‌o‌v‌e t‌h‌e t‌o‌u‌g‌h‌n‌e‌s‌s, f‌r‌a‌c‌t‌u‌r‌e e‌n‌e‌r‌g‌y a‌n‌d f‌l‌e‌x‌u‌r‌a‌l s‌t‌r‌e‌n‌g‌t‌h o‌f s‌e‌l‌f-c‌o‌m‌p‌a‌c‌t‌i‌n‌g c‌o‌n‌c‌r‌e‌t‌e.

The use of lightweight materials in construction industry reduces dead weight of structure and earthquake force acting upon it. On the other hand, the use of lightweight aggregates consider as a way to conserve existing natural aggregate mines. Self-CompactingConcrete (SCC) isa new type ofhighperformanceconcretes that flowsunderits own weight, passes through the reinforcements and fills all the corners of frameworks completely, The use of SCC is growing increasingly because of its great advantagessuch as eliminating the vibration of the concrete, reducing noise pollutionduring the construction time, having high workability and et. In this paper the effects of using two different artificial lightweight materials including light Expanded Clay Aggregates (LECA) and Expanded Poly-Styrene (EPS) on SCC are investigated. Fresh concrete requirement and the possibility of classification as lightweight self compacting concrete at hardened condition is determined.in order to evaluate structural lightweight self compacting beams, reinforced concrete beams were made of LECA and EPS and their design coefficient, bending capacity, modulus of rupture and deflection, compared with the normal weight SCC and also compared with the corresponding calculated values based on ACI 318.The results Shaw that the proposed relationships by ACI 318 code, are reliable when LECA is applied as lightweight aggregates, In this type of concrete, coefficient of lightweight concrete (λ) and bending capacity calculated by ACI 318 is smaller than corresponding experimental values, and calculated deflection is greater than experimental deflection. but the proposed design relationships by ACI 318 code, aren’t reliable when EPS is applied as lightweight aggregates, In EPS concrete, coefficient of lightweight concrete (λ), bending capacity and modulus of rupture calculated by ACI 318 is greater than corresponding experimental values.

The use of concrete in the construction industry is growing day by day. Due to the limited life span of concrete structures and also the destruction of concrete structures by natural factors such as earthquakes, floods, hurricanes and. .. we will always faced with massive amounts of waste concrete that will cause environmental damages. On the other hand natural resources are also limited for generating aggregates that in near future we should use waste concretes as recycled concrete aggregates for an alternative of natural aggregates to save the natural resources. In this study, the replacement proportion of fine and coarse recycled concrete aggregates with conventional aggregates, is the similar percentages of 0, 25, 50, 75 and 100%, which will include 5 mixing design. With increased use of recycled concrete aggregate, reduction of recycled concrete properties, a increase in water absorption and decrease in slump concrete can be observed that it has been tried to compensate this loss in the slump by using super plasticizer. In order to improve the engineering properties of recycled concrete and Study the Effect of polypropylene fibers on the properties of recycled concrete, the polypropylene fibers with the length of 6 mm and different volume percentages of 0.1, 0.2 and 0.3 percent were used that formed of 15 mixing design. In this study, the Compressive strength, Drying shrinkage, Water absorption, Ultrasonic pulse velocity, Electrical strength and SEM tests were done on the samples. withIncrease in the mass percentage ofpolypropylene fibersin recycledconcretes, decrease in results ofUltrasonic pula velocity and Water absorption, increase in Electrical strength results and alsonegativeeffectsonthe compressive strength have been observed. Interms of0.1 % by volume of polypropylenefibersinconcretedesign, Drying shrinkage improvedbutwith using 0.2and0.3 % by volume ofpolypropylenefibers, the Drying shrinkage increasedComparedwithsampleswithnofibers.