Concrete Research
https://jcr.guilan.ac.ir/
Concrete Researchendaily1Thu, 22 Dec 2022 00:00:00 +0330Thu, 22 Dec 2022 00:00:00 +0330Numerical study of nonlinear behavior of deep concrete beams with rectangular opening in the web reinforced with FRP strip
https://jcr.guilan.ac.ir/article_6069.html
The great depth of the deep beams allows the opening in the web. Openings in deep beams are intended for the passage of pipes and installation ducts. The presence of openings in the web cuts the members of the tie and strut in the equivalent truss and reduces the load-bearing capacity and ductility of the beam, which can even cause rupture. One solution to this problem is to use FRP reinforcing strips. In this research, the effect of FRP reinforcement sheets on the bearing capacity of deep concrete beams with rectangular opening has been investigated. For this purpose, reference laboratory samples were modeled and validated by finite element method with Abaqus software, then a number of parameters that may affect the response of the deep beam, such as the number, dimensions and distances of openings, were selected and kept constant. Other parameters, the response of the beam to its changes were examined. The results showed that the samples with BOX shaped reinforcement sheet had less bearing capacity than U-shaped reinforcing sheet. Also, samples with U-shaped FRP sheet have 38% more load capacity than sample without sheet and 13% more than BOX sheet. By comparing the reinforced specimens in terms of ductility and coefficient of behavior, it was found that the U-shaped reinforcing sheet has better performance.Parametric study of the behavior of exterior post-tensioned slab column connections under lateral loading
https://jcr.guilan.ac.ir/article_6070.html
The use of post tensioned flat slabs is common in structures that require the construction of long span. The main advantages of using this type of slabs are increasing the span to thickness ratio, deflection control and reducing the thickness of the floor. Post tension slabs are usually designed to withstand gravitational loads in the building. However, slab column connections in these systems must be able to withstand the deformations created by lateral loads and have sufficient ductility. In this research, an exterior unbonded post tensioned slab column connection is validated in ABAQUS finite element software. After ensuring the accuracy of the numerical model results, the effect of concrete compressive strength, the amount of effective prestressing levels and the tendon bonding influence in the seismic behavior of post tension slab joints are investigated. The results showed that the compressive strength of concrete and the prestressing level of concrete have a significant effect on the load-bearing capacity and ductility of the joints, while the bonding condition does not have much effect on the behavior of the joints.The effects of FRP fiber's elongation angles on strength behavior of RC beam-columns
https://jcr.guilan.ac.ir/article_6071.html
Strengthening of RC columns using FRP composites is done with the aim of increasing bearing capacity and ductility. One common method in this case is to enclose the entire outer surface of the column with FRP. In this paper, it has been done to strengthen this columns under eccentricity axial load, with the FRP layers. The specimens used have a circular cross-section with a diameter of 125 mm and a height of 800 mm, which are loaded in two cases by eccentricity. First case, the eccentricity is twice the radius of the column (2R) and the second case the eccentricity is four times the radius of the column (4R). Due to the eccentricity of the load, parts of the column are subjected to bending tension. Ten numerical models in two groups (2R and 4R) were analyzed using Abaqus software. In order to verify the accuracy of the modeling, first two existing experimental specimens were simulated with software and then the results were evaluated. The results showed that by increasing the eccentricity of the load, the longitudinal composites are more effected than transverse composites on force bearing and displacements. Also, the fiber has been effected on ductility increasing more than force tolerance in the column. In the 2R group, specimens with transverse composite have been increased about 14% in forcing and 15% in displacement capacities than longitudinal. Conversely, in the 4R group, the above mentioned numbers in samples with longitudinal composite increased by about 7% and 332% relative to transverse.Experimental study on the effect of active confinement of AFRP fibers on the seismic performance of reinforcement concrete columns under axial and lateral loads
https://jcr.guilan.ac.ir/article_6072.html
Fiber Reinforced Polymers (FRP) are often used for structural repairs to improve the strength and ductility of the structures. Previous studies have shown that utilizing active confinement in concrete structures can improve the seismic behavior of concrete columns under pressure. In this study, the behavior of concrete columns actively confined by AFRP fibers was investigated under the combined effects of axial compressive and cyclic lateral loads. Two concrete columns were actively confined by AFRP strips. In addition, a non-confined column (SCR) was utilized as a control specimen. Then all specimens were tested under axial and lateral cyclic loading. Experimental results showed that the ultimate compressive strength and axial strain of specimens with active confinement are improved compared to the SCR specimen. Also, due to the increased number of small cracks in the specimen, a higher extent of energy was absorbed under the applied loading. The loading protocol caused no rupture in the AFRP strips, and no shear crack and brittle failure in the specimens were observed.Experimental study of durability of self compacting concrete containing micro-silica and slag in Persian Gulf tidal environment
https://jcr.guilan.ac.ir/article_6073.html
Reinforced concrete structures on the shores of the Persian Gulf experience a severe corrosion environment, and in the case of the structures that are in tidal conditions or some of their members are submerged in the sea, such as piers and ports, this problem is more acute due to the penetration of chloride ions. To increase the efficient life of concrete structures in the Persian Gulf, the use of self-compacting concrete along with cement substitutes has been suggested by researchers. In this paper, two powdered materials, slag and micro-silica, have been selected to replace part of the cement content in concrete. The durability test in submerged and tidal conditions has been performed on the specimens. Based on the results of experiments on 216 concrete specimens, the use of the proposed concrete on average increases the compressive strength by 22%, electrical resistance by 50% and decreases the permeability of volumetric water absorption by 12% and capillary water absorption by 30% in tidal conditions.Design, fabrication and inspection of textile concrete based on polymer / composite paste casting coating technology
https://jcr.guilan.ac.ir/article_6074.html
One of the main challenges of conventional concrete canvas is the separation of the geo-membrane layer from the fabric concrete substrate, which has caused major problems in the discussion of the application of this product. In this work, the method of casting polymer paste based on acrylic resins was used to create a single-layer coating of sealing resin with the high overall mechanical strength of the product, and the properties of the product were investigated. In this method, polymer paste is formed in one step without the use of adhesive and geo-membrane layer on the three-dimensional substrate bed, and the overall productivity of concrete canvas is formed. The results showed that concrete canvas produced based on polymer paste casting method with suitable mechanical strength (30 (kN / mm2)), better sealing (up to 30 days without changing weight against water), non-layering, Suitable chemical resistance against hexane, toluene, benzene and octane and better temperature resistance (from -20 to 100 C) than conventional concrete canvas product.Studying the ability of sewage sludge ash in controlling alkali-silica reaction and it's synergic behavior with natural pozzolans
https://jcr.guilan.ac.ir/article_6075.html
Sewage sludge is one of the subsidiary products of sewage treatment that should be managed in an appropriate way due to its pollutant components and massive production. One of these methods is incineration. In recent decades, many studies have been done on sewage sludge ash (SSA) as a supplementary cementitious material (SCMs) in concrete. On the other hand, one phenomena leading to deterioration of concrete, is alkali-silica reaction (ASR). One way to control this reaction is through using SCMs that prevent the formation of alkali-silica gel and expansion by consuming alkalis available in cement paste. According to results obtained from SSA utilized as SCM in former studies, it is possible that it could prevent ASR in concrete by decreasing the alkali content. However, very few studies have been done on this issue. In this study, SSA was used as a replacement for cement at 10, 30 and 50% levels in order to assess its ability to control ASR. In addition, the effect of trass and pumice as natural pozzolans in improving its ability to control ASR was investigated. The results revealed that only at 50% replacement level, SSA was able to control the ASR expansion in mortars. However adding 5% trass or 10% pumice improved this ability to a considerable extent.Effect of High power ultrasonic-assisted in increasing compressive strength of concrete
https://jcr.guilan.ac.ir/article_6076.html
Today, staying in economic markets depends on maintaining the quality and cost of production due to the intense competition of producers. It has also led governments to take tougher approaches to improve the environmental situation of industries. Therefore, the use of new technologies that leads to maintaining or increasing product quality and reducing costs without harming the environment will be desirable. Today, the use of high-power ultrasonic waves, due to the lack of noise pollution, has been highly regarded by various industries to improve engineering processes. The effectiveness of these waves in the manufacturing and production industries, such as reducing machinery, increasing surface smoothness, grinding metals during freezing, etc., can also be the motivation for its use in the construction industry. Therefore, the widespread use of high-power ultrasonic waves in various fields of engineering and the identification of the positive effects of these waves on the properties of materials and materials is the reason for the present study. For this purpose, for the first time in this study, the use of high ultrasonic power waves with different powers, different times, and a frequency of 20 kHz in concrete compaction and its effect on concrete compressive strength has been investigated. The results of this study show that the use of ultrasonic high-power waves as a complementary process in the compaction of fresh concrete will increase the compressive strength of concrete by up to 10%.STUDY OF STRENGTH PROPERTIES OF CONCRETE BY USING MICRO SILICA AND NANO SILICA
https://jcr.guilan.ac.ir/article_5078.html
Concrete is the most widely used material in the world. At the same time, due to environmental and economic constraints and materials, the need to use materials that as an additive can help improve the performance of concrete while not reducing its main properties are of great importance.Due to different percentages of microsilica and nanosilica in the form of a new mixing plan as a laboratory study, the researcher investigated the different structural strengths of the concrete in the Iranian climate and a new type for the concrete with mixing microsilica and nanosilica and strength Over a 500 MPa and based on geographical area, economic and environmental requirements to overcome the limitations while maintaining standards. In the end, according to compliance with the upstream regulations, recommendations for implementation were presented as a suggestion.In the end, according to compliance with the upstream regulations, recommendations for implementation were presented as a suggestion.Investigation of the Pull-Off Strength of Geopolymer Concrete Containing GGBFS and Natural Zeolite Powder
https://jcr.guilan.ac.ir/article_6140.html
In this paper, effects of curing methods (i.e. curing at ambient temperature (A), in oven (O) and in boiling water (BW)), NaOH solution concentration (i.e. 8 and 12 moles/liter) and disc thickness (i.e. 1, 2 and 3 cm) on pull-off strength (POS) of the geopolymer concrete containing Ground Granulated Blast Furnace Slag (GGBFS) and Natural Zeolite Powder (NZP) have been investigated. The results show that the value of the POS obtained from the 3 cm thickness disc is on average 2.6% higher than that obtained from the 2 cm thickness disc. This implies that the discs with thicknesses of 2 and 3 cm have given approximately equal values of the POSs. Moreover, the value of the POS obtained from the 2 cm thickness disc is on average 28.4% higher than that obtained from the 1 cm thickness one. Based on the results obtained from the 2 cm thickness disc: a) the ratios of the POSs of the samples cured in boiling water and oven to that of the specimen cured at ambient temperature have been obtained on average equal to 1.383 and 1.089, respectively. b) as 20% wt. of the GGBFS is substituted by the NZP, the value of the POS reduces by an average of 16.29%. c) as the NaOH solution concentration increases from 8 to 12 mole/liter, the value of the POS increases by an average of 14.48%. From the results, there is a strong nonlinear relationship between the compressive and pull-off strengths of the geopolymer concrete.Determining the shear and normal stress in boundary between concrete and FRP sheet by the Element Free Galerkin method and comparing its results with the finite element software ABAQUS
https://jcr.guilan.ac.ir/article_6247.html
A model based on the Element Free Galerkin (EFG) method in the framework of linear elastic assumptions was developed to determine the distribution of interfacial stress in a concrete beam reinforced with FRP plates. In this model, the behavior of the adhesive layer between the surfaces is considered like a linear spring using its elastic properties, and MLS approximation functions are used to approximate the total displacement fields. In addition, the results were calculated and presented under the condition of complete adhesion between the surfaces. The results of the model were compared with the FEM model in Abaqus software for concrete beam and FRP panel. The results show that the EFG method has a good agreement with the outputs of the Abaqus model. To conclude this work, a parametric study was performed. It shows how the thickness of the adhesive layer and the FRP plate affect the shear and normal stress values of the adhesive.Experimental investigation of the effects of aggregate and fiber percentage on the behavior and cracking potential of Engineered Cementitious Composites
https://jcr.guilan.ac.ir/article_6285.html
The aim of this study is to determine the effect of replacing polyvinyl alcohol (PVA) fibers, fly ash (FA), and silica aggregate with polypropylene (PP) fibers, ground blast furnace slag (GBFS), iron furnace dust, limestone powder (LSP), natural sand, and microsilica to improve the mechanical properties and ductility of Engineered Cementitious Composites (ECC). Twelve different mixtures of ECC were designed and prepared. For each mixture, flexural and compression specimens were made and tested. The combination of microsilica and GBFS increases the strength and ductility of the composite, making it a viable alternative to fly ash. Replacement of silica sand with LSP that contains the appropriate composition can enhance ECC. The best results were achieved in ECC when the cementitious materials ratio was 1.25. By increasing the percentage of PP fibers from 1 to 1.5, the flexural strength increased by 65 percent, the middle span deflection of the flexural specimen increased by 21.7 percent, and the optimal amount of PP fibers to initiate hardening was 1.5 percent.Multiscale modeling of the mechanical properties of carbon nanotube reinforced cement composites.
https://jcr.guilan.ac.ir/article_6286.html
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.Effect of geopolymer alkaline activators on mechanical properties and durability of pozzolanic concretes
https://jcr.guilan.ac.ir/article_6287.html
Simultaneous use of pozzolans and geopolymers to improve the properties of concrete is one of the relatively new areas of concrete technology. In this study, slag and zeolite pozzolans were used as a substitute for different percentages of cement weight in concrete. Alkaline activator was also used to reduce the negative effects of high percentages of pozzolan replacement and to investigate their interactions. Based on the results of the defined tests, it was found that the addition of activator to the concrete containing pozzolan had a significant role in recovering part of the loss of properties due to high consumption of pozzolan. By adding activator to the design containing 60% slag, an increase of 52.1% in compressive strength and 44.7% in electrical resistivity for 28 days was observed. Also, the mix design containing 60% zeolite, which had the highest decrease in compressive strength by 59.3%, led to the improvement of thermal insulation properties of concrete up to 14.3% compared to the control mix design.Evaluation of compressive strength of concrete using ultrasonic pulse velocity and electrical resistivity methods
https://jcr.guilan.ac.ir/article_6288.html
Compressive strength of concrete is considered as one of its most important properties and usually gives an overview of the quality of concrete, because the strength depends directly on the microstructure of the cement paste. Evaluation of compressive strength of concrete is done by destructive and non-destructive methods. Non-destructive methods, with a much fewer number of tests, can provide a good estimate of the compressive strength of concrete. In this research, non-destructive ultrasonic pulse velocity and electrical resistivity methods were used to estimate the compressive strength of normal concrete tests with three different water-to-cement ratios, and mathematical models were proposed to estimate the compressive strength were compared. SPSS statistical software was used to analyze the test data. Different linear and nonlinear mathematical models related the relationship between the parameters of electrical resistivity, ultrasonic pulse velocity and compressive strength for each of the water-to-cement ratios as well as 28-day age were extracted by software to estimate the compressive strength. The results showed that the combination of ultrasonic pulse velocity and electrical resistivity methods for estimating compressive strength has a higher accuracy compared to one method alone. For this purpose, the modified form of the exponential function with a coefficient range of 0.63-0.83 and the mean absolute value of relative error 2.3-6.5% and the polynomial function with the range 0.63-0.89 and the mean absolute value of relative error is 3.2-7% had better performance.Examining the Effects of Using Nano-silica on the Mechanical Properties of Sand-cement Mortar Under the Effects of Heat, Considering Cementitious Nanostructure Changes
https://jcr.guilan.ac.ir/article_6289.html
The present research investigates the effects of nano-silica on strength parameters of sand-cement mortar at high temperatures. For this, sand cement mortar replacing 5, 10 and 15 wt% of cement with nano-silica was prepared. The mortar, having been processed at 3, 28 and 90-day ages, was subjected to 25, 100, 200, 400, 600 and 800 &ordm;C, respectively. Effects of high-temperature rates on the physical and mechanical properties of the sand-cement mortar were examined by macrostructural experiments of compressive strength, weight loss and water uptake, as well as microstructural experiments using XRD and SEM. The research found that the macrostructural behavior of sand-cement mortar was highly dependent on microstructures and nanostructure cementitious changes when subjected to heat. At 600 &ordm;C, the initial portlandite was fully degraded, which caused the CaO to form as water exited. At 800 &ordm;C, in addition to alite (C3S) and Belite (C2S), &beta;- Wollastonite was formed from the degradation of the C-S-H nanostructure. The addition of nano-silica improved the strength properties of the sand cement mortar against heat, with the compressive strength of the 28-day samples without nano-silica experiencing a 57% weight loss as the temperature rose to 800 &ordm;C, decreasing from 31.1 MPa to 13.3 MPa. On the other hand, the compressive strength of the sand cement mortar samples containing 15% nano-silica experienced lesser strength loss (52%) at 800 &ordm;C, decreasing from 40.2 MPa to 19.2 MPa.Study on the mechanical properties of porous concrete with high permeability using aluminum slag
https://jcr.guilan.ac.ir/article_6290.html
Principal recycling and reuse of industrial waste is one of the most important human challenges to protect the environment. In recent years, due to the unique properties of pervious concrete, the use of pervious concrete pavement as a good alternative to asphalt procedures has been considered. In this study, in order to assess a new method for the manufacture of high -environmentally friendly concrete pavements with aluminum slag replacement with 0, 5, 10, 15 and 30 % cement weight, the concrete samples were made and the tests including compressive strength, bending strength, water absorption percentage, permeability and porosity done. The results showed that aluminum slag replacement with 5 % of cement weight, compressive strength, bending resistance and water absorption percentage compared to the control sample did not change significantly. But using the replacement of aluminum slag with 10, 15 and 30 percent of the cement weight, compressive strength and bending strength comparing to the control sample were decreased by 16, 24 and 50% and by 6, 15 and 24 %, respectively. By replacing aluminum slag with 10 and 15% by weight of cement, the permeability comparing to the control sample was increased by 61 and 97%, respectively. It was also observed that due to the high porosity of the samples containing aluminum slag replacement with 30 % of the weight of the cement, water passed immediately and quickly.Prediction of the interlayer shear strength of SCS panels with corrugated-
strip shear connectors using gene expression programming algorithm
https://jcr.guilan.ac.ir/article_6291.html
Today, construction of large structures is growing quickly. For this reason, it is necessary to find the material with a rather low weight and high strength. For this purpose, Steel-Concrete-Steel (SCS) sandwich structures were proposed. SCS structures are composed of two steel layers and one concrete layer. Due to their low weight and high strength and flexibility, they have become popular among engineers. In the present research, first, three specimens of push-out test of strip shear connector were modeled and validated using ABAQUS finite elements software. Then, since the present equations to predict the shear strength of the shear connectors are complicated and are not so precise, the authors proposed an equation taking the effects of different geometrical parameters and the concrete&#039;s compressive strength in to account. For this purpose, using the experimental design, 17 specimens were designed and modeled. Then, an equation was proposed using the Genetic Expression Programming Algorithm (GEP) to predict the system&#039;s shear strength. Finally, the performance of the proposed equation was evaluated using the error parameters.Using Wavy Steel Fibers to Study the Rheological Properties, Mechanical and Fracture Parameters of Self-Compacting Concretes with Different Coarse Aggregate Volumes
https://jcr.guilan.ac.ir/article_6292.html
Considering the low concrete resistance to cracking and high volume of aggregate used in it, this study has addressed the effects of increasing the volume of wavy steel fibers (0.15, 0.3 and 0.45%) and volume of coarse aggregates (30, 40, 50 and 60%) in relation to the total volume of aggregates on the properties of fresh, hardened self-compacting concrete as well as on the fracture mechanics. To this end, different tests were performed on: 1) fresh concrete (slump-flow, T-50, J-Ring, Sieve analysis and L-BOX tests), 2) hardened concrete (compressive strength, tensile strength and modulus of elasticity tests) and 3) fracture mechanics (Mode I fracture toughness test on ENDB specimens) using 108 cylindrical specimens. Results showed that increasing the coarse aggregate volume improves the rheological properties and increasing the wavy steel fiber volume reduces the efficiency and flowability of the self-compacting concrete, but improves the compressive strength in concretes containing 50 and 60% coarse aggregate volume. Increasing this volume, will slightly reduce the tensile strength of only the fiber reinforced self-compacting concretes containing 60% coarse aggregates. Increasing the coarse aggregate volume by 30 to 60% improves the modulus of elasticity of specimens containing a fixed fiber percent and increasing the volume of wavy steel fibers, at 30 and 40% coarse aggregate volumes, increases the fracture toughness (Mode I) of the self-compacting concrete specimens containing wavy steel fibers.