Search results for: Concrete damaged plasticity

Authors: S. M. Gupta, Vanita Aggarwal, Som Nath Sachdeva

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The work reported through this paper is an experimental work conducted on High Performance Concrete (HPC) with super plasticizer with the aim to develop some models suitable for prediction of compressive strength of HPC mixes. In this study, the effect of varying proportions of fly ash (0% to 50% @ 10% increment) on compressive strength of high performance concrete has been evaluated. The mix designs studied were M30, M40 and M50 to compare the effect of fly ash addition on the properties of these concrete mixes. In all eighteen concrete mixes that have been designed, three were conventional concretes for three grades under discussion and fifteen were HPC with fly ash with varying percentages of fly ash. The concrete mix designing has been done in accordance with Indian standard recommended guidelines. All the concrete mixes have been studied in terms of compressive strength at 7 days, 28 days, 90 days, and 365 days. All the materials used have been kept same throughout the study to get a perfect comparison of values of results. The models for compressive strength prediction have been developed using Linear Regression method (LR), Artificial Neural Network (ANN) and Leave-One-Out Validation (LOOV) methods.

Keywords: ANN, concrete mixes, compressive strength, fly ash, high performance concrete, linear regression, strength prediction models.

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Authors: Mantai Chen, Johnny Ching Ming Ho

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The stress-strain relationship of concrete under flexure is one of the essential parameters in assessing ultimate flexural strength capacity of RC beams. Currently, the concrete stress-strain curve in flexure is obtained by incorporating a constant scale-down factor of 0.85 in the uniaxial stress-strain curve. However, it was revealed that strain gradient would improve the maximum concrete stress under flexure and concrete stress-strain curve is strain gradient dependent. Based on the strain-gradient-dependent concrete stress-strain curve, the investigation of the combined effects of strain gradient and concrete strength on flexural strength of RC beams was extended to high strength concrete up to 100 MPa by theoretical analysis. As an extension and application of the authors’ previous study, a new flexural strength design method incorporating the combined effects of strain gradient and concrete strength is developed. A set of equivalent rectangular concrete stress block parameters is proposed and applied to produce a series of design charts showing that the flexural strength of RC beams are improved with strain gradient effect considered.

Keywords: Beams, Equivalent concrete stress block, Flexural strength, Strain gradient.

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Authors: Klara Krizova, Rudolf Hela

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The paper reflects current state of popularization of static elasticity modulus of concrete. This parameter is undoubtedly very important for designing of concrete structures, and very often neglected and rarely determined before designing concrete technology itself. The paper describes assessment and comparison of four mix designs with almost constant dosage of individual components. The only difference is area of origin of small size fraction of aggregate 0/4. Development of compressive strength and static elasticity modulus at the age of 7, 28 and 180 days were observed. As the experiment showed, designing of individual components and their quality are the basic factor influencing elasticity modulus of current concrete.

Keywords: Concrete, Aggregate, Strength, Elasticity Modulus, Quality

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Authors: M. Cortés, E. Vera, O. Rojas

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The research studies of the kinetics of the corrosion process that attacks concrete and occurs within sewerage systems agree on the amount of variables that interfere in the process. This study aims to check the impact of the pH levels of the corrosive environment and the concrete surface, the concentrations of chemical sulfuric acid, and in turn, measure the resistance of concrete to this attack under controlled laboratory conditions; it also aims to contribute to the development of further research related to the topic, in order to compare the impact of biogenic sulfuric acid and chemical sulfuric acid involvement on concrete structures, especially in scenarios such as sewerage systems.

Keywords: Acid Sulfuric, concrete, corrosion.

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Authors: A. Zaidi, F. Khelifi, R. Masmoudi, M. Bouhicha

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In order to eradicate the degradation of reinforced concrete structures due to the steel corrosion, professionals in constructions suggest using fiber reinforced polymers (FRP) for their excellent properties. Nevertheless, high temperatures may affect the bond between FRP bar and concrete, and consequently the serviceability of FRP-reinforced concrete structures. This paper presents a nonlinear numerical investigation using ADINA software to investigate the effect of the spacing between glass FRP (GFRP) bars embedded in concrete on circumferential thermal deformations and the distribution of radial thermal cracks in reinforced concrete beams submitted to high temperature variations up to 60 °C for asymmetrical problems. The thermal deformations predicted from nonlinear finite elements model, at the FRP bar/concrete interface and at the external surface of concrete cover, were established as a function of the ratio of concrete cover thickness to FRP bar diameter (c/d_b) and the ratio of spacing between FRP bars in concrete to FRP bar diameter (e/d_b). Numerical results show that the circumferential thermal deformations at the external surface of concrete cover are linear until cracking thermal load varied from 32 to 55 °C corresponding to the ratio of e/d_b varied from 1.3 to 2.3, respectively. However, for ratios e/d_b >2.3 and c/d_b >1.6, the thermal deformations at the external surface of concrete cover exhibit linear behavior without any cracks observed on the specified surface. The numerical results are compared to those obtained from analytical models validated by experimental tests.

Keywords: Concrete beam, FRP bars, spacing effect, thermal deformation.

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Authors: Jongho Park, Taekyun Kim, Jungbhin You, Sungnam Hong, Sun-Kyu Park

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Due to the aging of bridges, increasing of maintenance costs and decreasing of structural safety is occurred. The steel corrosion of reinforced concrete bridge is the most common problem and this phenomenon is accelerating due to abnormal weather and increasing CO₂ concentration due to climate change. To solve these problems, composite members using textile have been studied. A textile reinforced concrete can reduce carbon emissions by reduced concrete and without steel bars, so a lot of structural behavior studies are needed. Therefore, in this study, textile reinforced concrete beam was made and flexural test was performed. Also, the change of flexural strength according to the prestressing was conducted. As a result, flexural strength of TRC with prestressing was increased compared and flexural behavior was shown as reinforced concrete.

Keywords: AR-glass, flexural strength, prestressing, textile reinforced concrete.

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Authors: L. Wong, H. Asrah, M.E. Rahman, M.A. Mannan

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The storage of chemical fertilizers in concrete building often leads to durability problems due to chemical attack. The damage of concrete is mostly caused by certain ammonium salts. The main purpose of the research is to investigate the durability properties of concrete being exposed to ammonium nitrate solution. In this investigation, experiments are conducted on concrete type G50 and G60. The leaching process is achieved by the use of 20% concentration solution of ammonium nitrate. The durability properties investigated are water absorption, volume of permeable voids, and sorptivity. Compressive strength, pH value, and degradation depth are measured after a certain period of leaching. A decrease in compressive strength and an increase in porosity are found through the conducted experiments. Apart from that, the experimental data shows that pH value decreases with increased leaching time while the degradation depth of concrete increases with leaching time. By comparing concrete type G50 and G60, concrete type G60 is more resistant to ammonium nitrate attack.

Keywords: Normal weight concrete durability, Aggressive Ammonium Nitrate Solution, G50 & G60 concretes, Chemical attack.

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Authors: Pedro Gutemberg de Alcântara Segundinho, José Antonio Matthiesen, Marcelo Rodrigo Carreira

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Timber-concrete structures were recently introduced in Brazil as a viable option for bridge construction on side roads. Binding between timber and concrete is fundamentally important to assure the rigidity and performance of this structural system. The objective of this study was to assess the structural performance of a timber-concrete bridge prototype with width of 170cm and span of 400cm, whose binding among timber beams and concrete slabs was made with metal pins, obtained from CA 50 construction steel bars of 12.5mm diameter. It was possible to conclude, from the results obtained experimentally in laboratory, that the timber-concrete bridge prototype showed a good structural performance. This structural system provides an economical, rapid implementation solution, which may be used on side roads, favoring regional integration and agricultural production flow.

Keywords: Binding, bridge prototype, timber and concrete

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Authors: Ahmad B. Habieb, Gabriele Milani, Tavio Tavio, Federico Milani

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Housings in developing countries have often inadequate seismic protection, particularly for masonry. People choose this type of structure since the cost and application are relatively cheap. Seismic protection of masonry remains an interesting issue among researchers. In this study, we develop a low-cost seismic isolation system for masonry using fiber reinforced elastomeric isolators. The elastomer proposed consists of few layers of rubber pads and fiber lamina, making it lower in cost comparing to the conventional isolators. We present a finite element (FE) analysis to predict the behavior of the low cost rubber isolators undergoing moderate deformations. The FE model of the elastomer involves a hyperelastic material property for the rubber pad. We adopt a Yeoh hyperelasticity model and estimate its coefficients through the available experimental data. Having the shear behavior of the elastomers, we apply that isolation system onto small masonry housing. To attach the isolators on the building, we model the shear behavior of the isolation system by means of a damped nonlinear spring model. By this attempt, the FE analysis becomes computationally inexpensive. Several ground motion data are applied to observe its sensitivity. Roof acceleration and tensile damage of walls become the parameters to evaluate the performance of the isolators. In this study, a concrete damage plasticity model is used to model masonry in the nonlinear range. This tool is available in the standard package of Abaqus FE software. Finally, the results show that the low-cost isolators proposed are capable of reducing roof acceleration and damage level of masonry housing. Through this study, we are also capable of monitoring the shear deformation of isolators during seismic motion. It is useful to determine whether the isolator is applicable. According to the results, the deformations of isolators on the benchmark one story building are relatively small.

Keywords: Masonry, low cost elastomeric isolator, finite element analysis, hyperelasticity, damped non-linear spring, concrete damage plasticity.

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Authors: V. Spaeth, A. Djerbi-Tegguer

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The recycling of concrete, bricks and masonry rubble as concrete aggregates is an important way to contribute to a sustainable material flow. However, there are still various uncertainties limiting the widespread use of Recycled Concrete Aggregates (RCA). The fluctuations in the composition of grade recycled aggregates and their influence on the properties of fresh and hardened concrete are of particular concern regarding the use of RCA. Most of problems occurring while using recycled concrete aggregates as aggregates are due to higher porosity and hence higher water absorption, lower mechanical strengths, residual impurities on the surface of the RCA forming weaker bond between cement paste and aggregate. So, the reuse of RCA is still limited. Efficient polymer based treatment is proposed in order to reuse RCA easier. The silicon-based polymer treatments of RCA were carried out and were compared. This kind of treatment can improve the properties of RCA such as the rate of water absorption on treated RCA is significantly reduced.

Keywords: Recycled concrete aggregates, water absorption, silicon-based agent and polymer.

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Authors: Y. Mohammadi, H. M. Ghasemzadeh, T. B. Talari, M. A. Ghorbani

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Concrete pavement has superior durability and longer structural life than asphalt pavement. Concrete pavement requires less maintenance compared to asphalt pavement which requires maintenance and major rehabilitation. Use of the concrete pavement has been grown over the past decade in developing countries. Fibre reinforced concrete (FRC) has been successfully used in design of concrete pavement in past decade. In this research, the effect of fibre volume fraction in modulus of rupture, load-deflection, equivalent flexural strength (fe,3) and the equivalent flexural strength ratio (Re,3) has been used in different fibre volume fraction. Crimped-type flat steel fibre of size 50 x 2.0 x 0.6 mm was used with 1.0%, 1.5% and 2.0% volume fraction. Beam specimens of size 500 x 100 x 100 mm were used for flexural as well as with JCI method for analysis flexural toughness, equivalent flexural strength. It was obtained as the 2% fibre volume fractions; reduce 45% of the concrete pavement thickness.

Keywords: Concrete pavement, Equivalent flexural strength, Fibre, Load-deflection curves.

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Authors: Chun-Yao Lee, Siang-Ren Wang

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This paper aims to discuss the influence of resistance characteristic on the high conductive concrete considering the changes of voltage and environment. The high conductive concrete with appropriate proportion is produced to the press-electrode method. The curve of resistivity with the changes of voltage and environment is plotted and the changes of resistivity are explored.

Keywords: conductive concrete, resistivity.

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Authors: S. S. Awanti, Aravindakumar B. Harwalkar

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Concrete construction in future has to be environmental friendly apart from being safe so that society at large is benefited by the huge investments made in the infrastructure projects. To achieve this, component materials of the concrete system have to be optimized with reference to sustainability. This paper presents a study on development of mix proportions of high volume fly ash concrete (HFC). A series of HFC mixtures with cement replacement levels varying between 50% and 65% were prepared with water/binder ratios of 0.3 and 0.35. Compressive strength values were obtained at different ages. From the experimental results, pozzolanic efficiency ratios and mix design curves for HFC were established.

Keywords: Age factor, compressive strength, high volume fly ash concrete, pozzolanic efficiency ratio.

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Authors: Hamed Ahmadi Moghadam, Omolbanin Arasteh Khoshbin

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Nowadays, the performance required for concrete structures is more complicated and diversified. Self-compacting concrete is a fluid mixture suitable for placing in structures with congested reinforcement without vibration. Self-compacting concrete development must ensure a good balance between deformability and stability. Also, compatibility is affected by the characteristics of materials and the mix proportions; it becomes necessary to evolve a procedure for mix design of SCC. This paper presents an experimental procedure for the design of self-compacting concrete mixes with different water-cement ratios (w/c) and other constant ratios by local materials. The test results for acceptance characteristics of self-compacting concrete such as slump flow, V-funnel and L-Box are presented. Further, compressive strength, tensile strength and modulus of elasticity of specimens were also determined and results are included here

Keywords: Self-Compacting Concrete, Mix Design, Compressive Strength, Tensile Strength, Modulus of Elasticity

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Authors: Rashad Al Araj, Adil K. Tamimi

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Concrete, despite being one of the most produced materials in the world, still has weaknesses and drawbacks. Significant concern of the cementitious materials in structural applications is their quasi-brittle behavior, which causes the material to crack and lose its durability. One of the very recently proposed mitigations for this problem is the implementation of nanotechnology in the concrete mix by adding carbon nanotubes (CNTs) to it. CNTs can enhance the critical mechanical properties of concrete as a structural material. Thus, this paper demonstrates a state-of-the-art review of reinforcing concrete with CNTs, emphasizing on the structural performance. It also goes over the properties of CNTs alone, the present methods and costs associated with producing them, the possible special applications of concretes reinforced with CNTs, the key challenges and drawbacks that this new technology still encounters, and the most reliable practices and methodologies to produce CNT-reinforced concrete in the lab. This work has shown that the addition of CNTs to the concrete mix in percentages as low as 0.25% weight of cement could increase the flexural strength and toughness of concrete by more than 45% and 25%, respectively, and enhance other durability-related properties, given that an effective dispersion of CNTs in the cementitious mix is achieved. Since nano reinforcement for cementitious materials is a new technology, many challenges have to be tackled before it becomes practiced at the mass level.

Keywords: Sustainability, carbon nanotube, microsilica, concrete.

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Authors: Som Nath Sachdeva, Vanita Aggarwal, S. M. Gupta

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Use of concrete paver blocks is becoming increasingly popular. They are used for paving of approaches, paths and parking areas including their application in pre-engineered buildings and pavements. This paper discusses the results of an experimental study conducted on Fly Ash Concrete with the aim to report its suitability for concrete paver blocks. In this study, the effect of varying proportions of fly ash, 20% to 40%, on compressive strength and flexural strength of concrete has been evaluated. The mix designs studied are M-30, M-35, M-40 and M-50. It is observed that all the fly ash based mixes are able to achieve the required compressive and flexural strengths. In comparison to control mixes, the compressive and flexural strengths of the fly ash based mixes are found to be slightly less at 7-days and 28 days and a little more at 90 days.

Keywords: Compressive strength, flexural strength, high volume fly ash concrete, paver blocks.

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Authors: Hasan Şahan Arel

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In this study, literature related to the replacement of cement with waste marble and the use of waste marble as an aggregate in concrete production was examined. Workability of the concrete decreased when marble powder was used as a substitute for fine aggregate. Marble powder contributed to the compressive strength of concrete because of the CaCO₃ and SiO₂ present in the chemical structure of the marble. Additionally, the use of marble pieces in place of coarse aggregate revealed that this contributed to the workability and mechanical properties of the concrete. When natural standard sand was replaced with marble dust at a ratio of 15% and 75%, the compressive strength and splitting tensile strength of the concrete increased by 20%-26% and 10%-15%, respectively. However, coarse marble aggregates exhibited the best performance at a 100% replacement ratio. Additionally, there was a greater improvement in the mechanical properties of concrete when waste marble was used in a coarse aggregate form when compared to that of when marble was used in a dust form. If the cement was replaced with marble powder in proportions of 20% or more, then adverse effects were observed on the compressive strength and workability of the concrete. This study indicated that marble dust at a cement-replacement ratio of 5%-10% affected the mechanical properties of concrete by decreasing the global annual CO₂ emissions by 12% and also lowering the costs from US$40/m³ to US$33/m³.

Keywords: Cement production, concrete, CO2 emission, marble, mechanical properties.

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Authors: Md. Jahidul Islam, A. K. M. Rakinul Islam, Md. Salamah Meherier

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This study investigates the suitability of using plastic, such as polyethylene terephthalate (PET), as a partial replacement of natural coarse and fine aggregates (for example, brick chips and natural sand) to produce lightweight concrete for load bearing structural members. The plastic coarse aggregate (PCA) and plastic fine aggregate (PFA) were produced from melted polyethylene terephthalate (PET) bottles. Tests were conducted using three different water–cement (w/c) ratios, such as 0.42, 0.48, and 0.57, where PCA and PFA were used as 50% replacement of coarse and fine aggregate respectively. Fresh and hardened properties of concrete have been compared for natural aggregate concrete (NAC), PCA concrete (PCC) and PFA concrete (PFC). The compressive strength of concrete at 28 days varied with the water–cement ratio for both the PCC and PFC. Between PCC and PFC, PFA concrete showed the highest compressive strength (23.7 MPa) at 0.42 w/c ratio and also the lowest compressive strength (13.7 MPa) at 0.57 w/c ratio. Significant reduction in concrete density was mostly observed for PCC samples, ranging between 1977–1924 kg/m³. With the increase in water–cement ratio PCC achieved higher workability compare to both NAC and PFC. It was found that both the PCA and PFA contained concrete achieved the required compressive strength to be used for structural purpose as partial replacement of the natural aggregate; but to obtain the desired lower density as lightweight concrete the PCA is most suited.

Keywords: Polyethylene terephthalate, plastic aggregate, concrete, fresh and hardened properties.

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Authors: B. Akturk, N. Yuzer, N. Kabay

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When concrete is exposed to high temperatures, some changes may occur in its physical and mechanical properties. Especially, high strength concrete (HSC), may exhibit damages such as cracks and spallings. To overcome this problem, incorporating polymer fibers such as polypropylene (PP) in concrete is a well-known method. In high temperatures, PP decomposes and releases harmful gases such as CO and CO2. This study researches the use of raw rice husk (RRH) as a sustainable material, instead of PP fibers considering its several favorable properties, and its usability in HSC. RRH and PP fibers were incorporated in concrete at 0.5-3% and 0.2-0.5% by weight of cement, respectively. Concrete specimens were exposed to 20 (control), 300, 600 and 900°C. Under these temperatures, residual compressive and splitting tensile strength was determined. During the high temperature effect, the amount of released harmful gases was measured by a gas detector.

Keywords: Gas analysis, high temperature, high strength concrete, polypropylene fibers, raw rice husk.

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Authors: T. D. Gunneswara Rao, Mudimby Andal

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Research on the utilization of fly ash will no longer refer the fly ash as a waste material of thermal power plants. Use of fly ash in concrete making, makes the concrete economical as well as durable. The fly ash is being added to the concrete in three ways namely, as partial replacement to cement, as partial replacement to fine aggregates and as admixture. Addition of fly ash to the concrete in any one of the form mentioned above, makes the concrete more workable and durable than the conventional concrete. Studies on fly ash as partial replacement to cement gained momentum as such replacement makes the concrete economical. In the present study, an attempt has been made to understand the effects of fly ash on the workability characteristics and strength aspects of fly ash concretes. In India major number of thermal power plants is producing low calcium fly ash. Hence in the present investigation low calcium fly ash has been used. Fly ash in concrete was considered for the partial replacement of cement. The percentage replacement of cement by fly ash varied from 0% to 40% at regular intervals of 10%. More over the fine aggregate to coarse aggregate ratio also has been varied as 1:1, 1:2 and 1:3. The workability tests revealed that up to 30% replacement of cement by fly ash in concrete mixes water demand for reduces, beyond 30% replacement of cement by fly ash demanded more water content for constant workability.

Keywords: Cementing Efficiency, Compressive Strength, Low Calcium Fly Ash, Workability.

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Authors: Carlos H. Cuadra

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The present report describes the characteristics of damages and behavior of reinforced concrete buildings during the tsunami action. The discussion is based on the field damage survey in selected cities located on the coast of the zone affected by the Great East Japan Earthquake on March 11, 2011. This earthquake is the most powerful know earthquake that has hit Japan with a magnitude 9.0 and with epicenter located at 129 km of Sendai city (off the coast). The earthquake triggered a destructive tsunami with run up height of up to 40 meters that mainly affect cities located on the Pacific Ocean coast of the Tohoku region (north-east region of Japan). Reinforced concrete buildings in general resist the tsunami without collapse however the non-structural elements like panels and ceilings were severely damaged. The analysis of damages has permitted to understand the behavior of RC buildings under tsunami attack, and has also permitted to establish recommendations for their use to take refuge from tsunami in places where natural topography makes impossible to reach hilltops or other safer places.

Keywords: tsunami, RC buildings, East Japan Earthquake, seismic damage

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Authors: Ross Jeffry, Muhammad N. S. Hadi

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High strength concrete (HSC) provides high strength but lower ductility than normal strength concrete. This low ductility limits the benefit of using HSC in building safe structures. On the other hand, when designing reinforced concrete beams, designers have to limit the amount of tensile reinforcement to prevent the brittle failure of concrete. Therefore the full potential of the use of steel reinforcement can not be achieved. This paper presents the idea of confining concrete in the compression zone so that the HSC will be in a state of triaxial compression, which leads to improvements in strength and ductility. Five beams made of HSC were cast and tested. The cross section of the beams was 200×300 mm, with a length of 4 m and a clear span of 3.6 m subjected to four-point loading, with emphasis placed on the midspan deflection. The first beam served as a reference beam. The remaining beams had different tensile reinforcement and the confinement shapes were changed to gauge their effectiveness in improving the strength and ductility of the beams. The compressive strength of the concrete was 85 MPa and the tensile strength of the steel was 500 MPa and for the stirrups and helixes was 250 MPa. Results of testing the five beams proved that placing helixes with different diameters as a variable parameter in the compression zone of reinforced concrete beams improve their strength and ductility.

Keywords: Confinement, ductility, high strength concrete, reinforced concrete beam.

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Authors: K. Krizova, R. Hela

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The paper is focused on monitoring of dependencies of different composition concretes on elastic modulus values. To obtain a summary of elastic modulus development in dependence of concrete composition design variability was the objective of the experiment. Essential part of this work was initiated as a reaction to building practice when questions of elastic moduli arose at the same time and which mostly did not obtain the required and expected values from concrete constructions.

Keywords: Concrete, Compressive strength, Modulus of elasticity, EuroCode 2.

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Authors: Ali A. Sayadi, Thomas R. Neitzert, G. Charles Clifton

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Lightweight concrete is being used in the construction industry as a building material in its own right. Ultra-lightweight concrete can be applied as a filler and support material for the manufacturing of composite building materials. This paper is about the development of a stable and reproducible ultra-lightweight concrete with the inclusion of poly-lactic acid (PLA) beads and assessing the feasibility of PLA as a lightweight aggregate that will deliver advantages such as a more eco-friendly concrete and a non-petroleum polymer aggregate. In total, sixty-three samples were prepared and the effectiveness of mineral admixture, curing conditions, water-cement ratio, PLA ratio, EPS ratio and perlite ratio on compressive strength of perlite concrete are studied. The results show that PLA particles are sensitive to alkali environment of cement paste and considerably shrank and lost their strength. A higher compressive strength and a lower density was observed when expanded polystyrene (EPS) particles replaced PLA beads. In addition, a set of equations is proposed to estimate the water-cement ratio, cement content and compressive strength of perlite concrete.

Keywords: Perlite concrete, poly-lactic acid, expanded polystyrene, concrete.

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Authors: M. Linek, P. Nita

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In the previous airfield construction industry, pavements made of reinforced concrete have been used very rarely; however, the necessity to use this type of pavements in an emergency situations justifies the need reference to this issue. The paper concerns the problem of airfield pavement dimensioning made of reinforced concrete and the evaluation of selected dimensioning methods of reinforced concrete slabs intended for airfield pavements. Analysis of slabs dimensioning, according to classical method of limit states has been performed and it has been compared to results obtained in case of methods complying with Eurocode 2 guidelines. Basis of an analysis was a concrete slab of class C35/45 with reinforcement, located in tension zone. Steel bars of 16.0 mm have been used as slab reinforcement. According to comparative analysis of obtained results, conclusions were reached regarding application legitimacy of the discussed methods and their design advantages.

Keywords: Reinforced concrete, cement concrete, airport pavements.

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Authors: Salahaldein Alsadey, Issa Amaish

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Recycled aggregates (RA) have the potential to compromise concrete performance, contributing to issues such as reduced strength and increased susceptibility to cracking. This study investigates the impact of sisal fiber (SF) on the mechanical properties of concrete, with the objective of utilizing SFs as a reinforcing element in concrete compositions containing natural aggregate and varying percentages (25%, 50%, and 75%) of coarse RA replacement. The investigation aims to discern the positive and negative effects on compressive and flexural strength, thereby assessing the viability of SF-reinforced recycled concrete in comparison to conventional concrete composed of natural aggregate without SF. Test results revealed that concrete samples incorporating SF exhibited elevated compressive and flexural strength. Comparative analysis of these strength values was conducted with reference to samples devoid of SF.

Keywords: Sustainable construction, construction materials, recycled aggregate, sisal fibers, compressive strength, flexural strength, eco-friendly concrete, natural fiber composites, recycled materials, construction waste management.

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Authors: W. C. Bracken

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Given that concrete masonry walls are expected to experience shrinkage combined with thermal expansion and contraction, and in some cases even carbonation, throughout their service life, cracking is to be expected. However, after concrete masonry walls have been placed into service, originally anticipated and accounted for cracking is often misdiagnosed as a structural defect. Such misdiagnoses often result in or are used to support litigation. This paper begins by discussing the causes and types of anticipated cracking within concrete masonry walls followed by a discussion on the processes and analyses that exists for properly evaluating them and their significance. From here, the paper then presents a case of misdiagnosed concrete masonry cracking and the flawed logic employed to support litigation.

Keywords: Concrete masonry, masonry wall cracking, structural defect, structural damage, construction defect, forensic investigation.

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Authors: K. M. Aldossari, W. A. Elsaigh, M. J. Shannag

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An experimental study was conducted to investigate the effect of hooked-end steel fibers on the flexural behavior of normal and high strength concrete matrices. The fibers content appropriate for the concrete matrices investigated was also determined based on flexural tests on standard prisms. Parameters investigated include: matrix compressive strength ranging from 45 MPa to 70 MPa, corresponding to normal and high strength concrete matrices respectively; fibers volume fraction including 0, 0.5%, 0.76% and 1%, equivalent to 0, 40, 60, and 80 kg/m³ of hooked-end steel fibers respectively. Test results indicated that flexural strength and toughness of normal and high strength concrete matrices were significantly improved with the increase in the fibers content added; whereas a slight improvement in compressive strength was observed for the same matrices. Furthermore, the test results indicated that the effect of increasing the fibers content was more pronounced on increasing the flexural strength of high strength concrete than that of normal concrete.

Keywords: Concrete, flexural strength, toughness, steel fibers.

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Authors: M. Eckert, M. Oliveira

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The intensive use of natural aggregates, near cities and towns, associated to the increase of the global population, leads to its depletion and increases the transport distances. The uncontrolled deposition of construction and demolition waste in landfills and city outskirts, causes pollution and takes up space. The use of recycled aggregates in concrete preparation would contribute to mitigate the problem. However, it arises the problem that the high water absorption of recycled aggregate decreases the bleeding rate of concrete, and when this gets lower than the evaporation rate, plastic shrinkage cracking occurs. This phenomenon can be particularly problematic in hot and windy curing environments. Cracking facilitates the flow of liquid and gas into concrete which attacks the reinforcement and degrades the concrete. These factors reduce the durability of concrete structures and consequently the lifetime of buildings. A ring test was used, cured in a wind tunnel, to evaluate the plastic shrinkage cracking sensitivity of recycled aggregate concrete, in order to implement preventive means to control this phenomenon. The role of several aggregate properties on the concrete segregation and cracking mechanisms were also discussed.

Keywords: Recycled Aggregate, Plastic Shrinkage Cracking; Wind Tunnel, Durability.

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Authors: M. Nassereddine, J. Rizk, A. Hellany, M. Nagrial

Abstract:

The High Voltage (HV) transmission mains into the community necessitate earthing design to ensure safety compliance of the system. Concrete poles are widely used within HV transmission mains; which could have an impact on the earth grid impedance and input impedance of the system from the fault point of view. This paper provides information on concrete pole earthing to enhance the split factor of the system; further, it discusses the deployment of concrete structures in high soil resistivity area to reduce the earth grid system of the plant. This paper introduces the cut off soil resistivity SC ρ when replacing timber poles with concrete ones.

Keywords: Concrete Poles, Earth Grid, EPR, High Voltage, Soil Resistivity.

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