JOURNAL OF CONCRETE RESEARCH
Year:2014 | Volume:7 | Issue:1|Papers Count:9

In recent years developments in technology have made it possible to make high strength concrete with higher workability and strength compared with conventional concrete. Now a day, in order to reduce current costs and reduce or eliminate the environmental problems the use of recycled materials and natural Pozzolan have become one of the topics of interest to many researchers. In this study, the use of zeolite as natural pozzolan and recycled aggregate concrete as recycled material in self-compacting concrete was investigated. For this purpose recycled self-compacting concrete mix design was optimized and different percentages of cement was replaced with zeolite (0%, 10%, 15%, 20%, 25% and 30%). In this study, after studying the compressive strength, tensile strength and modulus of elasticity in self-compacting concrete containing recycled aggregates and zeolite, empirical relations between compressive strength, tensile strength and modulus of elasticity have been established.

In this paper, three types of concrete slabs against impact loading caused by drop weight were examined and compared. Type I, slabs without fibers, Type II slabs with uniform percentage of fibers (Steel, poly propylene and hybrid) through thickness and type III slabs with variable percentage of fibers through thickness. Results showed that usage of fibers, significantly increased impact resistance of type II and III slabs compared to type I slabs. This study indicated that the efficacy of the tested slabs influenced by three factors including fiber type, fiber percentage and the position of the layers. Functionally graded arrangement of layers such that outer layers had more percentage of fibers than inner layers, considerably increased energy absorption of type III slabs compared to Type II slabs while total amount of fibers used were the same. Also the results of the experiments showed that ultrasonic pulse velocity decreases with increasing fiber percentage and pulse velocity in functionally graded slabs is variable through the thickness due to different amount of fibers in layers.

This paper studies seismic evaluation of unsymmetric-plan tall reinforced concrete (RC) buildings with a dual wall-frame system, in which the effect of higher modes in plan and height is important. In this paper, one unsymmetric-plane reinforced concrete building of 18-story height was studied. Shear walls were replaced with an equivalent beam-column and their nonlinear behavior was considered with the interaction point hinges (PMM) and fiber elements. The seismic responses of the buildings were computed by nonlinear response history analysis (NL-RHA), advanced pushover analyses including the modal pushover analysis (MPA), the consecutive modal pushover (CMP), the upper bound pushover analysis (UB) and the extended N2 method (EN2) and a conventional pushover analysis with fundamental mode force distribution considering the two nonlinear behavior for the shear walls mentioned above. The results show that floor displacements are slightly influenced by the shear wall nonlinear model in comparison with the story drifts and plastic hinge rotations. Errors resulting from interaction point hinge (PMM) are almost larger than those from the fiber element. Also, the results indicate that the advanced pushover analyses can evaluate the seismic demands accurately in unsymmetric-plane tall buildings; The EN2 method gives a larger error compared with the other advanced methods, especially in estimating plastic hinge rotations.

In this research, we observe the effect of high strength SCC concrete on shear behavior, cracking moment & condition. The main testing parameters are concrete type, stirrups distance and concrete strength variation. Therefore nine samples were casted which three of them are normal concrete with 400 MPa strength and the others were SCC with high strength of 60 and 80 MPa. Stirrup distances of 80, 100 and 133 millimeters used for each groups. The testing beams were loaded with simple supports under two concentrate loads. The results have appeared that stiffness and ultimate shear strength increased with using SCC concrete whereas the displacement decreased. Modes of cracking and patterns of normal and high strength SCC concrete were the same in ultimate load and ductility and ultimate load is increases by stirrups distance reduction in each beams.

Industrial Application of prefabricated reinforced concrete structures and the benefits it has been noted in recent years. Important advantage of precast industry is the production of precast segments in little time, low money and high quality. Due to some problems, the precast industry has not reached to its whole potential yet. The main problem is due to precast reinforced concrete connections.The behavior factor is an important parameter in linear analysis that indicates inelastic behaviors of structure such as over strength and ductility. In seismic codes, this factor is just written with a constant value. Considering the effect of precast concrete connection on the seismic performance of precast structure and factor such as period and ductility, behavior factor of these structures are different from cast in place one. So determining of this factor is necessary for these structures.In this research, the different types of semi precast moment resisting frames in different number of stories and bays with a Beam - Column Connection (connection used in Iran fram eco Company) were investigated. In this research, nonlinear static analysis was used. The results indicate moment resisting frames with low stories (4 story) have behavior factor equally withcast in situ structures but for many more stories (8 story to up), behavior coefficient is more than equivalent cast in situ structure.

Improvements on the performance and durability aspects of airfield concrete pavements are very crucial issue for operational and safety. In this regard, self-consolidating concrete (SCC) mixtures proposed for this means and their engineering properties were assessed. The effects of (1) w/c ratio, (2) cement content, (3) and air-entrancement agent are designated to be assessed from the aspects of rheological, mechanical and durability properties. The results confirmed the effectiveness of air-entrained SCC mixtures for freeze-and-thaw actions. Moreover it was found that the w/c ratio and cement content could be useful in this regard.

In this research the engineering features of HPSCC were investigated with the substitution of some parts of cement with pozzolans such as rice hush ash, silica fume and nano-SiO2. In HPSCC and implementing compressive strength, splitting tensile strength (Brazilian test), flexural strength, ultrasonic pulse velocity and water absorption. The tests of fresh HPSCC are also done including slump flow tests, V-funnel and L-box in addition to hardened concrete features. This research contains seven mixtures that the used pozzolans percentage in these mixtures are as bellow:The results show that combining cement with mentioned pozzolans causes promotion of engineering features of self-compacting concrete including compressive strength after 90 days. The substitution of rice husk ash for some parts of cement of course causes strength reduction at early ages in comparison to sample of control.

Bonding of fiber reinforced polymers (FRP) with epoxy layer has considered as a new structural strengthening technology in response to need for repair and strengthening of reinforced concrete structures and propagated in the last decade. Although epoxy bonding of FRP has many advantages, there is a common problem; before receiving the expected flexural capacity, most of the failure modes of these beams occur in a brittle manner, without any serious indication. The most commonly reported failure modes include ripping of the concrete cover and interfacial debonding. In the most researches who have studied the behavior of retrofitted structures, the effect of the interfacial behavior has been ignored. Proper prediction of flexural capacity of FRP strengthened of concrete beams in debonding modes is led to economical benefits in projects.In this article, the results have been verified with 6 beams in laboratory that have been loaded in two symmetric points load and divided to groups A and B. The beams had the same section, length and number of CFRP layer in each group, but thickness of CFRP was different. A nonlinear modeling with Finite Element (FE) method with the help of Abaqus is done, for investigation of real behavior of CFRP strengthened concrete beams and interfacial shear stresses concentration at CFRP cut off region, with presenting the failure theory and criterion and a method for cohesive layer simulation. Moreover the FE results are verified with an accurate experimental test results. The FEM results agreed well with the experiments, when using the cohesive model regarding failure modes, load capacity, force-displacement curves results and CFRP strains.

Many attempts have been done to increase the service life of the concrete structures. In this regard, the concrete properties should be evaluated by non destructive testing methods (NDT) periodically to estimate how the structures may behave in the future. It is so important to select a proper and simple method to examine the concrete properties during the service life. In the present paper, try has been done to evaluate the water cement ratio of the hardened concrete via non destructive measurement of the electrical resistance the concrete during one freeze thaw cycle. Five mix proportions were prepared. The electrical resistance of the cured specimens within one slow freeze thaw cycle was monitored within 24 hours at 1 minute interval. The results declared that as the temperature dropped to zero or minus 15oC, the electrical resistance variation of concrete is highly affected by water- cement ratio. The characteristics of the curve such as slope, upper and lower limits of electrical resistance curve are dependent on the water-cement ratio of the mixture. The results of the present work can relieve engineers´ anxiety about the proper water-cement ratio which was used in the concrete mixture.