جستجوی مقالات مرتبط با کلیدواژه "بتن خودمتراکم" در نشریات گروه "عمران"

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.

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.

In many parts of Iran, especially in the southern regions of the country where concrete is exposed to seawater, sulfates are the main destructive factors of concrete. The main factors related to the durability of concrete are the type of materials, concrete structure, density, and curing. Inadequate compaction of concrete due to the lack of acceptable vibration in the limited parts between the formwork and rebars is one of the main factors of low structural reliability exposed to sulfates. Due to the lack of information related to the effect of aggregate strength on the performance of self-compacting concrete, in this paper, the effects of type and strength of aggregates on the durability of self-compacting concrete against sodium sulfate is presented. Granite, marble, andesite, rhyolite, travertine, lime, green tuff, crystalline green tuff, and basalt were used to make concrete. "Twist-off" and "Drilled core" tests were employed to measure the compressive strength of rocks. "Twist-off" test is an accurate method with a wide range of applications in determining the strength of materials both in the laboratory and on site and is considered as a fast, accurate and low-cost technique with minor failure in the field of semi-destructive testing. The attractiveness of this method is in accuracy, speed, simplicity, minor breakdown, and low cost of doing it, which makes it more comparable than other on-site tests. This test can be performed in horizontal, vertical, and generally on any smooth surface without the need for prior planning. The tools used in this test are very simple and accessible and performing the test does not require previous skills. The experiments were performed at ages 7, 14, and 28. The results show a direct relationship between the strength of the parent rock and the strength of self-compacting concrete made with of rock. At an early age, there is an increase in compressive strength of samples placed in sodium sulfate compared to samples treated in water. Also, a high correlation coefficient was obtained between the results of the "twist-off" test and the "Drilled core" test, which could be used to measure the compressive strength of rocks with the "twist-off" test with high confidence.

Self-compacting concrete is an innovation in the field of concrete that has resolved one of the main problems in the construction of concrete structures, namely the problem of concrete compaction. This type of concrete has caused a uniform composition in concrete with a new composition and the invention of superplasticizer. In the present study, the effect of introducing the additives of zeolite and micro silica and their replacement with a part of cement has been evaluated by testing the mechanical properties including compressive, tensile, flexural and ultrasonic waves tests on the control specimen of self-compacting concrete and expansive self-compacting concrete. Also, the short-term deformation due to shrinkage of self-compacting concrete caused by drying for a period of 210 days after the fabrication of specimens has been investigated. Experimental results have shown that micro silica and zeolite pozzolans improve the microstructure of the evaluated concrete, which improves the mechanical properties. In fact, the replacement of cement with pozzolans has made the parts of the transition zone of the specimens better and condensed. Shrinkage test results also show that zeolite and micro silica pozzolans lead to a significant reduction in drying shrinkage. Drying shrinkage of the concrete containing 15% zeolite and 7.5% micro silica decreased by 32% and 15% compared to the control concrete containing expansive materials at the age of 210 days, respectively.

concrete is one of the main materials in the construction industry. The tendency of the industry to use concrete materials has led to numerous researches in the field of repairing defects and repairing its cracks in order to prevent the destruction of concrete. One of the causes of cracks in buildings that is less considered by structural designers is torsion. Torsion in reinforced concrete structures is usually caused by the integrity and cohesion of the members. One of the available methods for concrete repair is the use of glass pipes containing polyurethane inside the concrete and making self-healing concrete, which many researchers have experimented with in this field. In this study, by making a torsion device, self-healing concrete beams containing glass pipes with a length of 10 and 100 cm were loaded and then the effect of pipe length on the performance of the restoration was compared and the restored concrete was compared with the control sample. In the end, it was concluded that the use of self-healing concrete containing glass pipes containing polyurethane is able to increase the remaining torsional capacity in cracked concrete, but the use of self-healing concrete containing glass pipes with a length of 100 cm due to lack of space. The gap between the pipe pieces that are placed in one direction and the fact that cracked glass from any place has the possibility of breaking the pipes has a greater advantage than using self-healing concrete containing 10 cm long glass pipes.

The bonding of steel bars to concrete in a various environments is one of the most significant problems in the durability of concrete structures. There are several different factors such as concrete ages and properties, steel rebars characteristics and environmental condition which affect the bond strength between concrete and embedded steel rebars. Accordingly, in the present study, the bond strength between embedded steel rebars and self-compacting concrete which contain different values of granite and limestone powder as a filer is investigated under accelerated corrosion condition. Besides, the specimens were also preloaded up to 50% of concrete compressive strength to investigate the effect of induced cracks caused by external loading on the chloride ions penetration and corrosion process. According to obtained results from the experiments, the utilization of 15% granite powder has increased the bond strength and decreased corrosion level of concrete specimens. Also, the loading of the specimens has exacerbated corrosion and reduced bond strength considerably.

Self-compacting concrete is one kind of concrete under its weight flows and simultaneous with maintaining homogeneity, without need to vibrator can be filled mold and takes the shape of the container. This concrete due to high performance in construction doesn’t have any risk in aggregates separation. Also, self- compacting concrete has high strength and relatively durability. On the other hand, the existence of huge tile waste and sepulture of these waste by ceramic and tile factories indicates the importance of using this secondary product in the other industries, including the construction industry. Also, with apply of waste material environment can be healthy and safe. In present experimental study, firstly the self-compacting concrete mixing scheme was determined. Then, according to the obtained mixing scheme with replacing recycled aggregates with natural particles, samples with 0, 25, 50 and 100 percentages (by volume) have been made. It should be noted water to cement ratio and percentage of high plasticizer are constant. The amount of limestone and silica fume in all of the mixtures have been fixed. In prepared specimen’s slump test to determine efficiency and compression and water-absorbing tests in 3, 7, 14 and 28 days curing have been performed. Results of the present study show generally with increasing waste tile efficiency and compression strength decrease. Although, durability goes up. Also, especially, with replacing 100% of recycled material with exist particles major changes have been observed but up to 75% have not been seen.

This paper presents an experimental study on the properties of self-compacting concrete (SCC) using natural polymer (SCC). Fifteen series of mixed proportions were used, which were cured in two environments of magnesium sulphate and by water curing. The polymer used is alginate, which is used a lot in the dentistry industry. It is used extensively as an impression making material in dentistry, prosthetics, life casting and occasionally for creating positives for small scale casting. In addition, alginate is used in the food industry, engineering and construction. This polymer is made in a variety of percentages: 0.5, 1, 1.5 and 2, with dierent percentages: 1, 1.5 and 2, of resin. The values of w/c in all samples are 0.36. The objective of this study is to investigate the in uence of alginate on the fresh, hardened and sulphate resistance properties of SCC. The performance of alginate is established in SCC using fresh concrete tests, such as slump ow, T500 time, J ring and L-box ratio, and by hardened concrete tests, such as compressive strength, exural strength, water absorption and density in magnesium sulphate solutions. The compressive strength and density of each mix design, over 7, 28, 56, and 90 days, are determined. In addition, prismatic specimens are made to determine the exural strength at 28 days of curing. Two cubic specimens are made to determine water absorption at 28 days of curing. The results of the fresh concrete show that increasing alginate content negatively aected the blocking ratio, because of viscosity decrease. This reduction is because of diatomaceous earth. The use of alginate increases the strength of the sulphate solutions. The highest exural strength value is seen in the R1.5A1 sample in the sulphate environment. The R1A1 has the least density compared with other samples. The R2A1.5 sample has a higher compressive strength, over 56 and 90 days, in the sulphate environment rather than the water environment. Results show compressive and exural strength in upper ages. The R2A2 has the least water absorption compared to the other samples.

Despite the fact that self-compacting concrete has been used for many years, until now, no-one has carried out any research on the strengthening eect of the weight of concrete at any level. For this reason, employing concrete columns made out of dierent mixes of selfcompacting concrete, a research is conducted. In order to measure the concrete strength at any level, the in-situ friction-transfer method was used. Having examined over 50 mix designs, nine mixes were proved to be self-compacting concrete and, therefore, were used for this investigation. In order to see the eect of the weight of the concrete above the level considered, concrete columns were cast using self-compacting concrete without giving any form of compaction. At specied ages, the hardened concrete columns were cut at 150 mm height intervals. Using the Friction-transfer method, the strengths of concrete at dierent levels were obtained. In the friction-transfer method, a 50 mm diameter partial core is made using a diamond tipped coring drill. A metallic gripping device is xed on top of this partial core by fastening its side bolts, and torsional moment is applied to the partial core via this gripping device by hand. The applied torsional moment is gradually increased until the partial core is failed, and the maximum (failure) torsional moment is recorded. Using the existing calibration graphs, the ultimate (failure) torsion is converted to the compressive strength of the concrete tested. The results show that the weight of the concrete situated above any level has a positive eect on the strength of the concrete at that level. In addition to the comparison of the obtained results with the respective results of ordinary concrete, the eect of changes in the llers, segregation and aggregate grading, on the strength of self-compacting concrete, is also studied.

Self-consolidating concrete (SCC) has been used increasingly over the last two decades, especially in the pre-cast concrete industry because of its ability to consolidate without vibration even in congested areas. The development of SCC mixture design has been driven mostly by private companies who desired to utilize advantages of SCC. Consequently, there exists limited public information regarding the performance of SCC mixtures. In addition, SCC can be characterized as flowing concrete without segregation and bleeding, capable of filling spaces and dense reinforcement. Further it should be able to flow through, and completely fill the form without vibration. Due to the technical and economic advantages that can be accrued by the use of pozzolans, they play an important role when added to Portland cement by usually increasing the mechanical strength and durability of concrete structures.This paper present, an experimental study on the properties of different self-consolidating concrete mixes containing three types of pozzolanic materials in comparison with SCC mixtures without any pozzolanic materials and conventionally vibrated concrete mixtures. Silica fume, pumice powder and rice husk ash were used for both cement and filler replacements. Various experiments such as slump-flow, J-ring, L-box, V-funnel and sieve segregation resistance were investigated for fresh concrete. Further, compressive strength,water and chloride-ion permeability and capillary water absorption at various days were carried out to determine the properties of self-consolidating concretes. The test results indicated that pozzolanic materials such as RHA and VP can be used to produce SCCs. Regarding the strength properties, the test results showed that the 270-day compressive strength of ordinary SCC is about 70 MPa, while SCC mixtures containing SF, RHA and VP have strengths more than 90, 77 and 76 MPa, respectively. In addition, the results proved that artificial and natural pozzolans enhanced the durability of SCC and reduced the penetration, significantly. For instance, adding 15% pumice and 7% silica fume in the SCC specimen reduced the water depth at 90 days by 19% and 54%, respectively.

W i t h t h e i n c r e a s e i n u s i n g c o n g e s t e d r e i n f o r c e m e n t s i n m o m e n t-r e s i s t i n g r e i n f o r c e d c o n c r e t e s t r u c t u r e s, t h e r e i s a g r o w i n g i n t e r e s t i n s p e c i f y i n g h i g h w o r k a b i l i t y c o n c r e t e. S e l f-c o n s o l i d a t i n g c o n c r e t e (S C C) i n t h e f r e s h s t a t e i s k n o w n f o r i t s e x c e l l e n t d e f o r m a b i l i t y, h i g h r e s i s t a n c e t o s e g r e g a t i o n, a n d i t s u s e, w i t h o u t a p p l y i n g v i b r a t i o n, i n c o n g e s t e d r e i n f o r c e d c o n c r e t e s t r u c t u r e s c h a r a c t e r i z e d b y d i f f i c u l t c a s t i n g c o n d i t i o n s. T h e r e u s e o f a g g r e g a t e s f r o m d e m o l i s h e d c o n c r e t e s t r u c t u r e s w a s i n t r o d u c e d i n t o p r a c t i c e m a n y y e a r s a g o a n d, f r o m t h e b e g i n n i n g, w a s m a i n l y c o n s i d e r e d f o r t w o e n v i r o n m e n t a l a s p e c t s: s o l v i n g t h e i n c r e a s i n g w a s t e s t o r a g e p r o b l e m a n d t h e p r o t e c t i o n o f l i m i t e d n a t u r a l s o u r c e s o f a g g r e g a t e. A t p r e s e n t, p l e n t y o f d e m o l i s h e d r e i n f o r c e d c o n c r e t e o r p r e s t r e s s e d-c o n c r e t e s t r u c t u r e s, o r i g i n a l l y e r e c t e d f r o m c o n c r e t e o f m o d e r a t e o r h i g h s t r e n g t h, c r e a t e a s i g n i f i c a n t s o u r c e o f r u b b l e a g g r e g a t e o f r e l a t i v e l y g o o d q u a l i t y.T h i s p a p e r p r e s e n t s t h e r e s u l t s o f a n i n v e s t i g a t i o n d e a l i n g w i t h t h e b o n d s t r e n g t h b e t w e e n s t e e l r e i n f o r c i n g b a r s a n d s e l f-c o n s o l i d a t i n g c o n c r e t e (S C C) m a d e w i t h r e c y c l e d a g g r e g a t e s. E i g h t c o n c r e t e m i x t u r e s, i n t w o g r o u p s o f S C C a n d n o r m a l c o n c r e t e (N C), w e r e c o n s i d e r e d. E a c h g r o u p c o m p r i s e d f o u r c o n c r e t e m i x t u r e s w i t h d i f f e r e n t p e r c e n t a g e s o f r e c y c l e d a g g r e g a t e s (0%, 30%, 50% a n d 100%). S i x t e e n c o n c r e t e s p e c i m e n s, g r o u p e d i n t w o s e r i e s, m a d e o f N C a n d S C C,w e r e a n u f a c t u r e d a n d t e s t e d. I n e a c h s p e c i m e n, f o u r s t e e l b a r s w e r e e m b e d d e d i n t h e c o n c r e t e a t t h e b o t t o m a n d t o p o f t h e s p e c i m e n. T h e e f f e c t o f b a r p o s i t i o n i n c o n c r e t e h a s b e e n s t u d i e d b y c o m p a r i n g t h e b o n d s t r e n g t h o f t o p a n d b o t t o m b a r s. T h e b o n d s t r e n g t h a n d s l i p o f e a c h r e i n f o r c i n g b a r w e r e m e a s u r e d i n a p u l l-o u t t e s t s e t u p. T h e t e s t s e t u p c o m p r i s e d a h y d r a u l i c j a c k, a l o a d s e l l, a L V D T a n d a c o m p u t e r a i d e d d a t a a c q u i s i t i o n s y s t e m. T h e L V D T m e a s u r e d t h e s l i p o f t h e r e i n f o r c i n g b a r i n t h e c o n c r e t e s p e c i m e n. I n e a c h t e s t, l o a d w a s i n c r e a s e d s l o w l y w i t h a n a p p r o x i m a t e r a t e o f 25 k N/m i n, u n t i l t h e b o n d f a i l u r e o f t h e r e i n f o r c i n g b a r f r o m t h e c o n c r e t e. T h e t y p e o f b o n d f a i l u r e w a s b y s p l i t t i n g f o r a l l s p e c i m e n s. T e s t r e s u l t s s h o w e d t h a t t h e u s e o f r e c y c l e d a g g r e g a t e s m a y n o t r e d u c e t h e b o n d s t r e n g t h i n S C C. H o w e v e r, f o r t h e c a s e o f N C, t h e r e c y c l e d a g g r e g a t e s d e c r e a s e d t h e b o n d s t r e n g t h. A l s o, t h e e f f e c t o f t o p b a r i n S C C i s s m a l l e r t h a n t h a t i n N C.