مجله تحقیقات بتن ایران
سال دوازدهم شماره 2 (تابستان 1398)

In this paper, the effect of adding fiber to lightweight (containing Light Expanded Lica Aggregate) self-compacting concrete under high-temperature conditions (25-100, 250-500, 700 ° C) was investigated in the form of compressive, tensile and flexural strength tests. In these experiments, 3 types of fibers, including steel fiber, and polypropylene and steel springs, were used for 0.4% volumetric rate of concrete. In general, the results indicate that the use of steel fiber and spring increases the compressive strength of concrete by up to 20%. Polypropylene fiber can be used to improve the tensile strength of concrete, because it increases up to 70% tensile strength after high temperature conditions. Also, at a temperature of 700 °, the flexural strength of all samples was negligible and were destroyed due to their own weight. Also, due to the severe drop in resistance after a temperature of 500 ° C, after this temperature, self-compacting concrete is not serviceable.

In this paper, the effect of three waterborne acrylic resins on physical, mechanical, stability, and permeability of concrete was investigated. For this purpose, concrete samples were prepared with a mass ratio of water to cement and solid-resin to cement equal to 0.445 and 0.05, respectively. Compressive stress tests of 7, 28, and 56 days, tensile strength, chlorine ion accelerated migration, capillary water absorption and initial and final water absorption on the test specimens were performed. It was observed that acrylic resin could act as a superplasticizer and reduce the amount of water needed to increase the fluidity of fresh concrete. Adding a resin with a minimum film formation temperature (MFFT) above the operating temperature reduces the chlorine ion penetration depth and coefficient by 14%. As a general result, it can be said that by accepting a reduction of 20-30%reduction in compressive strength of concrete structures, the fluidity of the fresh concrete, physical and penetration properties of the concrete mix can be increased by the use of the waterborne acrylic resin with MFFT higher than ambient temperature.

Hybrid Fiber Reinforced Concrete, a composite obtained by mixing at least 2 different types of fibers, is extensively explored by researchers due to its superior mechanical properties. The present study is aimed to investigate the effect of incorporation of steel, glass and polypropylene fibers as well as the air entraining admixture on the durability of concrete subjected to freezing and thawing cycles, compressive strength and split tensile strength. In order to evaluate the durability of concrete specimens after subjecting the specimens to freezing and thawing cycles, relative dynamic modulus of elasticity and the percentage of the weight loss were measured in 3 different stages (1) prior to staring the main test (2) after subjecting the specimens to 150 cycles of freezing and thawing (3) after subjecting the specimens to 300 cycles of freezing and thawing. Based on the results of the experimental program it appears that utilization of specific combination of fibers at specific volume fractions along with air entraining admixture results in significant improvement of durability of the concrete specimens. The best performance in freezing and thawing test belongs to the specimen containing 0.5% of PP fibers and 1% of steel fibers in which the relative dynamic modulus of elasticity measured after 300 cycles dropped 5%, while the modulus of elasticity for control specimens decreased 30% after these cycles. It is worth noting that the simultaneous monitoring of modulus of elasticity and the weight loss in a specimen can provide more detailed information on the durability of the specimen.

In this paper, the effect of using natural zeolite as a supplementary cementitious material and micro-nano bubble as a substitute for concrete mixture water has been evaluated on the mechanical properties and durability of concrete. The evaluated parameters for properties of modified concrete include: compressive strength, tensile strength, Bending strength, electrical resistivity and water absorption. The results indicate that the use of zeolite and micro-nano bubble in concrete increases the mechanical properties and the durability of concrete. The greatest improvement is related to the two-phase samples from the combination of 10% zeolite and 100% micro-nano bubble, which compressive strength, tensile strength, bending strength and electrical resistivity increase by 15, 14.88, 5.65 and 194.12% respectively, and water absorption decrease by 25.22%. In general, according to the results, it can be concluded that zeolite and micro-nano bubble, improve the mechanical properties and durability of concrete and their combination has the most positive effect on modified concrete.

This paper presents the results of axial pressure testing on reinforced concrete columns (RCC) loaded with confined normal concrete (NC) and high-strength concrete (HSC) using glass-fiber reinforced plastic pipes (GRP) casing as well as carbon fiber reinforced polymer (CFRP). This study aimed to evaluate the behavior and mechanical properties of columns confined with GRP and FRP under pressure loads. The major parameters in the experiments were the types of concrete, the effect of GRP and FRP wrapping, as well as the number of FRP layers. 12 cylindrical RCC (150*600 mm) were prepared and divided into two groups, NC and HSC, and each group was divided into two parts. In each part, one column was without FRP, a column was wrapped with one layer and another column with two layers. All columns were tested under concentrated compression load. The results showed that the utilization of FRP and GRP improved compression capacity and ductility of RCC. The addition of one and two layer-FRP wrapping increased compression capacity in the NC group to an average of 18.5% and 26.5% and in the HSC group to averagely 10.2% and 24.8%. Meanwhile, the utilization of GRP increased the compression capacity of the columns by 4 times in the NC group and 3.38 times in the HSC group. These results indicated that although both FRP and GRP result in confinement, the GRP resulted in increased compression capacity and ductility of the RCC due to higher confinement. Furthermore, the confinement effect was higher on the first group.

, the effective parameters on the performance of reinforced concrete shear walls, such the amount of longitudinal and transverse rebars, openings, opening aspect ratio, Regular and irregularly aligned openings at the height of the wall and opening distance from the edge of the wall have been studied and the most appropriate parameters for the reinforced concrete shear wall have been provided. Reinforced concrete shear walls of 0.35×6.5×16.5m3 have been under cyclic loading. Non-linear finite element analysis using the ABAQUS code has been performed. Concrete damage plasticity model has been used. A wall with no openings and with minimum longitudinal and transverse reinforcement of has been considered as the control sample and other samples have been compared with it through measures such as load bearing capacity, dissipated energy, and cracking and crushing distributions and patterns. The results show that the presence of openings in concrete shear walls in the amount of 18.65% of the wall surface caused a reduction of 24% resistance and 43% of the initial hardness of the opening wall compared to the sample without opening, irregularly of the opening at the wall height increased by 8% Resistance and 12% hardness of the wall. Also, the strength and hardness of the opening specimens were the distance between the opening and the edge of the wall and the adjacent opening, so that the most suitable openings for the shear wall were a wall with openings up to 1.5 times its width from the edge of the wall.

Flexural behavior investigation of concrete materials is one of the most important issues in evaluating its mechanical behavior and is one of the main criteria for the design of concrete structures. The flexural behavior analysis of concrete specimens in a laboratory can simulate the behavior of concrete in a real scale with acceptable accuracy. Flexural strength, failure energy, bending coefficient and toughness are parameters that can be extracted from concrete bending results. Each of these parameters is important in the complex and sensitive design of high-rise or non-structural structures. In this research, two pozzolans of zeolite and silica ash, as well as two types of steel and glass fibers are used to improve the concrete specificationsThe effect of individual behavior of these materials and their effects simultaneously has been highlighted. The materials used in this project have a significant research background. However, in the combination of materials mentioned, little research has been done; and there are still more studying points. The results of pre-loading concrete fibers represented new aspects of concrete behavior in structural performance. It was observed that in the non-pozzolan specimens, increasing the amount of steel fibers increased flexural strength while increasing the amount of glass fibers did not have a significant effect on increasing flexural strength. Also, in the specimens with mixed pre-loading, with the decrease of the percentage of silica soot, the difference of results is reduced. This trend indicates that zeolite has a more important role in repairing cracks for shorter time intervals. Examination of fracture energy showed that specimens containing 1% steel fiber had the highest fracture energy due to fiber performance. After the specimens are damaged, this process is maintained and it seems that cracking in the fiber specimens does not necessarily lead to disruption of fracture energy changes.

Aim of this paper is studying the effect of mineral addictive and type of them, on the processing of cement produce and quality of it. For this purpose, preparation of samples of cement clinker with additives of pozzolan, perlite, pumice and also abrasive organic compounds have been investigated their grinding efficiency. Then, concrete blocks with dimensions of 10 × 10 cm were constructed, than tested compressive strength at different ages of 2, 3, 7 and 28 days. Based on the results, the use of mineral additives has led to an increase in the number of Blaine, in other words, additives have played the role of abrasive aid. The mixing plan of 85% of clinker and 15% of pozzolan resulted in the highest amount of blast cement (4546 m2/kg). The use of additives at the age of 2 and 3 days of concrete has reduced the compressive strength. At the age of 28 days, the presence of additives increases its compressive strength compared to the non-use of the additive. The combination of organic abrasives and mineral additives in all cases has led to an increase in concrete bulk and compressive strength. The combination of 15% by weight of pozzolan, 85% clinker, 4% gypsum and 3 g of abrasive organic compound, is the optimum combination of cement.

Utilization of Self-compacting concrete can reduce expenses of the construction and time, therefore the use of artificial intelligence methods to estimation of concrete properties seems necessery .The main purpose of the study presented in this paper was to investigate the feasibility of using multivariate adaptive regression spline (MARS) for the prediction of 28-day compressive strength of self-compacting concrete with an optimal mixing ratio. Total of 94 dataset collected from the published paper were used in this study. To compare the performance of the technique, prediction was also done using a multilayer perceptron neural network model. MARS model in the training phase model (RMSE=4/250) was better performance than Neural Network (RMSE=4/626). The results of error indices of the testing stage in MARS and Neural Network methods respectively (RMSE=3/007) and (RMSE=4/049) were performed accurately in compressive strength prediction The analysis indicated that the proposed MARS model can gain a high precision, which provides an alternative method for predicting the properties of SCC.

Concrete is a brittle material and the deficiencies of concrete such as low tensile strength, small ultimate strain and shrinkage are greatly limited the application of concrete. Fiber-reinforced concrete (FRC) is concrete containing fibrous material which increases its structural integrity. It contains short discrete fibers that are uniformly distributed and randomly oriented. Polyvinyl alcohol (PVA) fiber is as one of the most appropriate polymeric fibers to be used for fiber-reinforced concrete. This research demonstrates the effects of PVA fibers on the mechanical properties of concrete mixtures. This paper presents an experimental study on the properties of fresh and hardened concrete that was built with Polyvinyl alcohol fiber. For this purpose, five fiber fractions of PVA (0, 0.25, 0.5, 0.75 and 1%) were used in the mixtures. The tests include slump, density, compressive strength, splitting tensile strength, flexural strength, and modulus of elasticity. Test results showed that after the addition fibers, the workability Property of concrete was reduced. Also, it was seen that PVA fiber meaningfully increase the static properties of concrete as well as improving its post-peak response and ductile behavior.Moreover, high ratios of PVA fiber in the concrete mixture caused negative effects on the compressive strength of concrete. Finally, the optimum percentages of PVA fiber corresponding to the most significant increases in the mechanical properties were presented.