مجله تحقیقات بتن ایران
سال شانزدهم شماره 4 (زمستان 1402)

Fiber-reinforced polymer (FRP) anchors are used to prevent or delay the debonding of FRP sheets in the strengthening of structures. There are various methods to prevent or delay the debonding of FRP sheets, among them is the use of FRP anchors. In this research, the behavior of the bond between the FRP sheet and the FRP anchor after the debonding of the reinforcement sheet from the concrete surface was evaluated. Therefore, the specimens were reinforced in such a way that there is no bond between the reinforcement sheet and the concrete surface. The simultaneous increase in the ratio of the cross-sectional area and the length of the fan leads to an increase in the bond strength; therefore, the specimens with a fan length of 90 mm experience an average increase of 50% in bond strength. In this case, the failure mode was anchor debonding from the sheet. Results showed that increasing the length of the fan improved the bond strength. Therefore, the specimens with a fan length of 150 mm reached the bond strength to almost the ultimate tensile strength of the FRP composite. The amount of slip, in this case, is on average 2.5 times the specimens with a 60 mm length of fan. According to the failure mode of the specimens, the embedment depth of 50 mm has the ability to fully transfer the stress to the concrete and the anchor has not been pulled out.

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,

Industrial activities, particularly in petrochemical and refinery sectors, have introduced a wide range of organic pollutants into the environment, leading to the pollution of aggregate materials with crude oil or petroleum products. This study investigates the influence of aggregate materials contaminated with crude oil and diesel on the cement hydration process and concrete properties. Around 90 concrete samples with polluted aggregates were evaluated over a 6-month period. Compressive strength tests and water absorption percentage tests were conducted at different ages. Microstructural analysis through SEM, structural analysis via EDX, and XRD analysis for hydration product characterization were performed. Results showed a significant reduction in compressive strength (47% and 31%) for samples contaminated with crude oil and diesel, respectively, compared to the control. Water absorption and permeability increased in polluted samples. SEM, and XRD, results indicated increased ettringite production, decreased nanostructure C-S-H, reduced strength and durability, and increased water absorption and permeability in the concrete. This study highlights the detrimental effects of organic contaminants on concrete properties, emphasizing the need for pollution management in aggregate materials for sustainable construction practices.

In this paper, activated carbon prepared from agricultural waste has been used as pollutants absorbent in porous concrete. This activated carbon is produced during two stages of carbonization (pyrolysis) and activation at high temperature. In order to reach the desired and optimal results, the response surface method (RSM) has been used. while evaluating the ability to remove pollutants from runoff water, it has been trying to improve the mechanical characteristics of this type of concrete by adding activated carbon, micro silica, water to cement ratio changes and the amount of fine grains. Design-Expert software was used to design the experiment using the Box-Behnken method. To use the Box-Behnken method, 4 input variables were defined including active carbon percentage (1% to 2.5%), water-cement ratio (0.3 to 0.4%), micro silica percentage (5% to 10%) and fine grain percentage (0 to 10%), which provided 27 mixing plans. Results showed that the presented models for estimating 28-day compressive strength are correlated with R² value of 0.97, 7-day compressive strength with R² value of 0.84, 42-day compressive strength with R² value of 0.95, COD with R² value of 0.94, TSS with R² value of 0.93 , TDS with R² value of 0.91 and copper heavy metal removal with R² value of 0.94, which indicate the significance of the test design as well as the improvement of the mechanical characteristics and removal of pollutants in porous concrete containing waste activated carbon.

Severe hydraulic gradients in open channels cause severe bed erosion and problems caused by sedimentation. Fabric concrete is a unique product with high execution speed that can replace traditional concrete surfaces. According to the mechanical resistance parameters of this product, in addition to its good durability against corrosive factors, one of the applications of fabric concrete is its use on the surface of canals and water course culverts. In this research, first, the flow of open channels in trapezoidal section is simulated under 9 scenarios, which include 3 common channel geometries in the state of a straight path, a path with bends and deviations, and finally, a channel path with a change in height at the bottom of the channel. In each of the states, 3 different flow regimes have been investigated along with flow turbulence modeling using flow-3d software.Different flow regimes have been investigated along with flow turbulence modeling using flow-3d software. Using ABAQUS software, fabric concrete components and their connection areas have been modeled, and by applying forces equated to the concrete surface and vulnerable connection areas, the amount of created stresses has been checked. The results show that the created stresses are very low compared to the tensile and compressive stress capacity of fabric concrete. In order to validate the hydraulic studies of flow and concrete, the relevant laboratory results have been used.

Seven mixing plans with, 20%, 30%, 40%, 50%, 60% and 70% of slag in powdered form replaced part of the cement and the specimens were made at the ages of 28, 56, 91 and 120 days. They were subjected to the necessary tests. Slump tests, specific weight of fresh concrete, compressive strength, tensile strength of halving, electrical resistance, volumetric water absorption and depth of water penetration of the specimens made from reference concrete and cement-slag were performed. The results showed that the slag powder had no significant effect on mechanical properties of the specimens until the age of 56 days, but with the passage of time, the compressive strength of the specimen containing 40% slag at the age of 120 days was 1% compared to the reference specimen. In terms of tensile strength, specimens containing 30% slag at the age of 120 days showed an increase of 4% compared to the reference specimen; although the increase of 1% seems insignificant, but it indicates that until the age of 120 days, the slag has a positive effect on compressive strength, it is worth mentioning. The percentage of water absorption at the age of 120 days in the specimen containing 40% slag showed an increase of 3.4% compared to the reference specimen. In addition, the electrical resistance of the specimen containing 40% slag at the age of 120 days decreased by 37% and the water penetration depth in the specimen containing 40% slag increased by 2.8 mm compared to the reference specimen.

The existence of waste materials from various physical and chemical processes is one of the important problems of industrialized and developing countries. For this reason, extensive research is being done on the methods of recycling or disposing of them in order to minimize the damage to the environment. In the present study, the effect of using recycled asphalt crumb (RAP) as a substitute for natural aggregate and steel slag as a substitute for cement in self-compacting concrete (SCC) mixtures for the construction of road pavements has been investigated. For this purpose, fresh concrete tests including slump flow, V funnel, L box, J ring and hardened concrete tests of compressive, tensile and bending strength were performed on the samples. The results showed the effect of using slag instead of cement and asphalt chips. Instead of coarse grain, it reduces the compressive, tensile and bending resistance of self-dense concrete. Also, by replacing up to 25% of stone materials with small asphalt materials and 30% of slag with cement, minimum acceptable standards were achieved according to the relevant standards. Also, for the design of double mixes, the design containing 30% asphalt crumb instead of stone materials with 25% slag instead of cement has shown more suitable results. The most optimal mode of using these materials is respectively using 30% slag instead of cement and 25% asphalt crumb instead of stone materials.

The performance of concrete structures is affected by the transfer of force between rebar and concrete, which depends on factors such as concrete strength, yield stress, rebar geometry, rebar diameter, concrete cover and splice length. Also, the use of reinforced polymer materials has become popular due to their successful application in structure. In this study, the effect of various factors on the bond strength of glass fiber-reinforced polymer bars, used in concrete beams, is evaluated and the accuracy of the equations proposed by different regulations and researchers is investigated. To investigate the effect of different factors on bond strength of glass fiber-reinforced polymer, the results of 43 tests conducted by different researchers have been used. Factors studied on the bond strength include the effect of the surface shape of the reinforcement, concrete strength, the amount of concrete cover on the bar, the splice length and transverse reinforcement. After examining the effect of various factors, the accuracy of the equations provided by regulations and researchers in determining the bond resistance for these laboratory results, the accuracy and standard deviation of each equation is evaluated. The results showed that increasing the compressive strength of concrete in samples without stirrup increases the bond strength, and in samples with stirrup, it has no effect on the bond strength. Also, the majority of existing equations estimate the amount of bond strength more than the values obtained from experiment results.