مجله تحقیقات بتن ایران
سال نهم شماره 2 (پاییز و زمستان 1395)

The present study is an exploratory research that appraise and compare the performance of four rapid tests for assessing the chloride penetration of concrete; RCPT, RCMT, SR and MRCPT. Due to the concern raised by some scholars about the effect that the conductivity of the pore solution impinges upon the results on some of these rapid tests, Silica fume was used as Supplementary cementitious material in portions of 7.5% and 15%. All four methods exhibited substantial decrease in the chloride permeability of the concrete samples with silica fume as compared to control samples, at the age of 28 days. The increase in performance caused by Silica fume usage was significant for RCPT and SR methods, moderate for RCMT and marginal for MRCPT. The results show that the variation in the conductivity of the pore solution significantly alters the results of SR and RCPT tests, and marginally alters those of MRCPT.

Because of the many advantages, using of self competing concrete (SCC) in structures is increasing. Construction of precast-prefabricated components, with the use of concrete has also recently been considered. Concrete properties have significant role in precast-prefabricated girders behavior. Exact prediction of these properties is the base of members analysis and design. Determine the optimum composition is the mean to obtain the best set of useful concrete properties. In this paper, SCC mix design optimization method is presented based on multi-criteria optimization using particle swarm algorithm (PSO). The results show the Successful application of Pareto optimization method in the optimization of scc mix design used in bridge girders.

High Performance Fiber Reinforced Cementitious composites (HPFRCCs) are basically integrated with two main components including fiber and mortar. These two ingredients are interactively affected due to interfacial bonding which develop a strong composite. HPFRCCs are specific kinds of Fiber Reinforced cementitious composites which can undergo strain hardening behavior after initial cracks. In the present study, it is aimed to understand the strain hardening behavior of HPFRCCs under uniaxial compression, four-point flexural loads and pure shear. The types of fibers and loading path are the effective parameters in this study. Three types of fibers including Hooked end steel fibers, wavy steel fibers and Poly propylene fibers have been solely used or compounded 1.5% by volume of fibers in mortar mixtures. Different mix ratios have been evaluated to achieve the acceptable strain hardening behavior and the best mix ratio has been introduced. Uniaxial compression, four-point flexural loads and pure shear have been chosen as loading paths. The four-point flexural tests on splitless prisms and direct shear tests on split specimens (to decrease the non-optional failure cross section) have been applied. The test results have been more evaluated to assess the effects of types of fibers on shear and flexural toughness and ductility under compression. It is revealed that the mechanical properties of HPFRCCs have been considerably enhanced rather than normal concretes. HPFRCCs can be applied as an appropriate technique to restrain the reinforcement congestion, decrease the high value of transverse reinforcements at beam-column joints and also improve the shear capacity and ductility of the members.

With respect of a lot of resources of coal waste and its destructive impacts on environment & nature, presentation of engineering solutions for apply of this waste in concrete construction can have great impact on use of these coal wastes & subsequently, the decrease of environmental risks due to coal waste depot in nature. In this article from jig and flotation coal waste that is obtained around of the central Alborz markazi coal washing Factory in Zirab city of Mazandaran province, it use in concrete as substitution a part of cement and fine aggregate with two different resistance (20&31 MPa). Afterwards, the impact on various percentages of this substitution is reviewed on compressive strength properties of concrete. Base on gained compressive strength results, the best substitution percentage of used sand with fine aggregate of jig coal waste is 10% & the best substitution percentage of used cement with the powder of jig and flotation coal waste is 5% for the sample with 28 days age.

Light weight concrete, because of its practical benefits, is known as one of the most important structural materials in recent years. However, due to the high porosity of aggregates in the concrete, permeability models, specifications for durability and compressive strength of light weight concrete is different with ordinary concrete. In this article the effects of silica fume on the properties and durability of light weight concrete against chloride ion permeability is investigated. For this purpose, the basic parameters such as the ratio of water to cement in the concrete mix design and percentage of silica fume as the main parameters were analyzed And its effect on compressive strength, durability and permeability of chloride ion in lightweight concrete was studied. According to the chloride ion concentrations at various depths in concrete, the chloride penetration coefficient for concrete was determined according to the Fick's second law. Finally, a neural network based model for determining chloride penetration in concrete is presented.

The prestressed concrete was first introduced to predominance the concrete tension weakness and use the concrete compressive capacity to improve the serviceability state of such members. In these members the need of utilization of concrete with higher strength due to their lower prestressed losses have been recognized. There are very little investigations on prestressed members consisting of ultra high strngthed concrete, UHSC (concret with a compressive strength higher than 80MPa). This has led to concrete constructions with posttensioned ultra-high strength self-consolidating concrete, UHSSCC, which is relatively new category of concrete. Over the last two decades, numerous studies (experimentally and theoretically) have been conducted on the behavior of simply-supported and continuous reinforced concrete (RC) beams, that were strengthened with fiber reinforced polymer (FRP) composites. This paper investigates the finite element methods for modeling the unbounded posttensioned concrete beams. This objective is achieved by conducting flexural testing of unbonded post-tensioned UHSSCC continuous (full scale) I-beam strengthened by carbon fiber reinforced polymer, CFRP sheets in sagging and hogging regions. The numerical results was compared with experimental results in terms of crack pattern and different ductility indexes (which are significant is seismic zones) and the following results were drawn: Considering the optimized mesh density and the sensitivity analysis to dilation angle, a dilation angle of 36 yielded the best results comparing the numerical and experimental results. Despite the the application of unbounded tendon along the two span of the beam, the numerical and experimental crack pattern at different load steps were reasonably matched.

In this study, the seismic performance of reinforced concrete (RC) frames equipped with two different kinds of braces, i.e. special concentric braces (SCB) and buckling restrained braces (BRB), was investigated. Eight frames with various numbers of stories (four-, eight-, 12- and 16-story for each dual system) were designed on the basis of a code-design method for a high risk seismic zone. Nonlinear static and dynamic analyses of the frames have been performed using OpenSees software. To consider different ground motion characteristics, an array of time-series from ordinary far-fault records to near-fault motions with forward-directivity and fling-step effects was employed. Results from the analytical study indicate that the utilized design method for both dual systems was reasonable and the mean maximum drift of the frames under all ground motion sets were in acceptable range. Near-fault motions, especially records with forward-directivity effects, imposed higher demands than far-faults. For low-rise frames structural system of RC-SCBshowed better performance than RC-BRB, while better performance of the other frames were shown for RC-BRB system.

Integral bridges are jointless bridges that typically are constructed with flexible foundations which include one row of steel H piles. Because the main criterion limiting the length of integral bridges is the lateral displacement capacity of their supporting piles, longer integral bridges can be built by increasing that capacity. Detailing and the embedded length of pile inside the abutment of the bridges have a key role to provide shear and flexural resistance of pile - abutment connections. In this paper, first, a theoretical method was developed by authors to calculate the required embedded length of the pile, based on the plastic moment of the steel pile. Then, to evaluate the efficiency of proposed theoretical method, two specimens of pile-abutment connections were constructed with different embedded lengths of pile inside the abutment. The results of the experiment in conjunction with numerical and analytical studies showed that by increasing the embedded length less than the proposed method to the value of more than the proposed method increased the flexural capacity of the joint up to 100%.

Steel fibers have high elasticity modulus and failure strain. According to their deformability and high tensile strength, these products are considered as one of the most suitable and economic types of fibers. Additionally, seeping the fluid materials into the hardened concrete has an unfavorable effect on the concrete endurance. The amount of seepage depends on the permeability rate of hardened concrete. Essentially, in construction of the concrete tanks and dams, compression strength and permeability parameters of concrete against water is very important and it is so common to use the special concretes in these types of projects. Therefore, in the present study it has been tried to investigate the behavior of steel fibers concrete against permeability and its compression strength with a change in percentages of steel fibers. The effects of maximum coarse aggregate size on the compression strength and concrete permeability have also been studies. To achieve this goal, 4 mixing plans were designed based on the compression strength 40 MPa, water to cement ratio (W/C) equal to 0.42, the maximum coarse aggregate were respectively 19, 12.5, 9.5, 4.75 and then a suggested percentage of micro-silica and super-plasticizer was added in order to enhance the concrete properties. Each mixing design also includes steel fibers with volumetric percentages 0, 0.3, 0.6, 0.9 and 1.2 of the concrete. In the next step, compression strength of fiber cubic samples in considered ages of 7 and 28 days were determined and registered by the concrete- compression test apparatus. Meanwhile, the fiber cylindrical specimens in age of 28 days were also tested by the permeability tests apparatus. Results of these experiments showed that applying the metal fibers in low percentages (0.3 and 0.6), does not have considerable effect on the compression strength of samples, but in high percentages of metal fibers (0.9 and 1.2), compression strength of samples also increases. Additionally, in all cases, the concrete permeability of metal fibers is less than the ordinary concrete, so that in most designs, as steel fiber percentage increases and size of gravel aggregate decreases, the permeability coefficient tends to reduce. Finally, based on the experimental results, steel fiber concrete with the maximum gravel aggregate (9.5 mm) and the percentage fiber equal to 1.2 was introduced as the best mixing design

Disposal of effluent from wastewater treatment and reuse it is, one of the important issues in the collection and wastewater treatment industry. In this study, white cement has been produced by wastewater after treatment. For this purpose, wastewater has been gathered from first settling; second settling tank, sandy filter and final wastewater effluent. Actually, 116*40*40 mm rhomb models have been made. The wastewater has been used as mixing water. Bending strength compression 3, 7 and 28 days has been measured. In all experiments except quality of mixing water, other conditions were constant and the same. Therefore using wastewater on bending strength of 3 day has not effect. Actually, effect of impurities in the waste water and resistance to bending and compression 7 and 28 days were more tangible than 3 days bend in resistance. Actually, using industrial treatment wastewater to prepare white cement can be recommended.