Search results for: high strength

Authors: Minsu Kim, Hae-Chang Cho, Jae Hoon Chung, Inwook Heo, Kang Su Kim

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For safe design of the UHPC flexural members, accurate estimations of their shear strengths are very important. However, since the shear strengths are significantly affected by various factors such as tensile strength of concrete, shear span to depth ratio, volume ratio of steel fiber, and steel fiber factor, the accurate estimations of their shear strengths are very challenging. In this study, therefore, the Adaptive Neuro-Fuzzy System (ANFIS), which has been widely used to solve many complex problems in engineering fields, was introduced to estimate the shear strengths of UHPC flexural members. A total of 32 experimental results has been collected from previous studies for training of the ANFIS algorithm, and the well-trained ANFIS algorithm provided good estimations on the shear strengths of the UHPC test specimens. Acknowledgement: This research was supported by Basic Science Research Program through the National Research Foundation of Korea(NRF) funded by the Ministry of Science, ICT & Future Planning(NRF-2016R1A2B2010277).

Keywords: ultra-high-performance concrete, ANFIS, shear strength, flexural member

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Authors: Elie Awwad, Bilal Hamad, Mounir Mabsout, Helmi Khatib

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The paper reports test results on the long-term behavior of sustainable hemp-concrete material prepared in research work conducted at the American University of Beirut. The tests results are in terms of compressive and splitting tensile tests conducted on standard 150x300 mm cylinders. A control mix without fibers, one polypropylene-concrete mix, and ten hemp-concrete mixes were prepared with different percentages of industrial hemp fibers and reduced coarse aggregate contents. The objective was to investigate the strength properties of hemp-reinforced concrete at 1.5 years age as compared with control mixes. The results indicated that both the compressive strength and the splitting tensile strength results of all tested cylinders increased as compared with the 28-days values. Also, the difference between the hemp-concrete samples and the control samples at 28 days was maintained at 1.5 years age indicating that hemp fibers did not exhibit any negative effect on the long-term strength properties of concrete.

Keywords: hemp-reinforced concrete, natural fibers, compressive strength, splitting tensile strength

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Authors: Mlk. Khouadjia, B. Mezghiche

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The environment protection has led to a growing interest in the use of crushed sand, which is not correctly exploited due to the high rate of fine particles that it contains and which affect concrete properties. This study will examine the variation of the compressive strength of concrete with several local areas of sand exposed to freeze-thaw cycles and chemical solutions. The experiments have been realized on crushed, river, and dune sands. We use software (MATLAB) to find the coefficient of particle shape. Finally, we have found a relationship between the reference concrete without modification and concrete modified with river and dune sands to predict the variations of resistance after curing in different environments. The results showed that the behavior of concrete is different according to the types of sand and the environment of exposition.

Keywords: crushed sand, compressive strength, freeze-thaw, MATLAB, dune sand, river sand

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Authors: Cesar Ferreira Amorim, Tamotsu Hirata, Runer Augusto Marson

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The purpose of this study was to determine the effect of strength ramp isometric contraction on changes in surface electromyography (sEMG) signal characteristics of the hamstrings muscles. All measurements were obtained from 20 healthy well trained healthy adults (age 19.5 ± 0.8 yrs, body mass 63.4 ± 1.5 kg, height: 1.65 ± 0.05 m). Subjects had to perform isometric ramp contractions in knee flexion with the force gradually increasing from 0 to 40% of the maximal voluntary contraction (MVC) in a 20s period. The root mean square (RMS) amplitude of sEMG signals obtained from the biceps femoris (caput longum) were calculated at four different strength levels (10, 20, 30, and 40% MVC) from the ramp isometric contractions (5s during the 20s task %MVC). The main results were a more pronounced increase non-linear in sEMG-RMS amplitude for the muscles. The protocol described here may provide a useful index for measuring of strength neuromuscular fatigue.

Keywords: biosignal, surface electromyography, ramp contractions, strength

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Authors: Khaled Saad Eldin Mohamed Ragab

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This paper investigates analytically the torsion behavior of steel fibered high strength self compacting concrete beams reinforced by GFRP bars. Nonlinear finite element analysis on 12­ beams specimens was achieved by using ANSYS software. The nonlinear finite element analysis program ANSYS is utilized owing to its capabilities to predict either the response of reinforced concrete beams in the post elastic range or the ultimate strength of a reinforced concrete beams produced from steel fiber reinforced self compacting concrete (SFRSCC) and reinforced by GFRP bars. A general description of the finite element method, theoretical modeling of concrete and reinforcement are presented. In order to verify the analytical model used in this research using test results of the experimental data, the finite element analysis were performed. Then, a parametric study of the effect ratio of volume fraction of steel fibers in ordinary strength concrete, the effect ratio of volume fraction of steel fibers in high strength concrete, and the type of reinforcement of stirrups were investigated. A comparison between the experimental results and those predicted by the existing models are presented. Results and conclusions thyat may be useful for designers have been raised and represented.

Keywords: nonlinear analysis, torsionally loaded, self compacting concrete, steel fiber reinforced self compacting concrete (SFRSCC), GFRP bars and sheets

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Authors: Nursah Kutuk, Sevil Cetinkaya

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Geopolymers are becoming new concrete materials to use alongside cement, which are formed due to reaction between alumino-silicates and oxides with alkaline media. Silicates obtained from natural minerals or industrial wastes are used for geopolymer synthesis. Geopolymers have recently received wide attention because of their advantages over other cementitious material like Portland cement. Some of the advantages are high compressive strength, low environmental impact, chemical and fire resistance and thermal stability. In this study, geopolymers were prepared by using inorganic materials such as kaolinite and calcite. The experiments were carried out by varying the concentration of NaOH as 5, 10, 15 and 20 M, and at cure temperature of 22, 45 and 65 °C. Compressive strengths for each mixes at each cure temperature were measured. Results of the analyses indicated that the compressive strength of geopolymers did not increase steadily with increasing concentration of NaOH, but did increase steadily with increasing cure temperature. We examined the effect Na2SiO3/NaOH weight ratio on the properties of the geopolymers, too. It was seen that Na2SiO3/NaOH weight ratio was also important to prepare geopolymers that can be applied to construction industry.

Keywords: geopolymers, compressive strength, kaolinite, calcite

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Authors: A. Bara, D. Barkat

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The liquid-liquid extraction of copper (II) from aqueous solution by capric acid (HL) in chloroform at 25°C has been studied. The ionic strength effect of the aqueous phase shows that the extraction of copper(II) increases with the increase in ionic strength. with different ionic strengths 1, 0.5, 0.25, 0.125 and 0.1M in the aqueous phase. Cu (II) is extracted as the complex CuL2(ClO4).

Keywords: liquid-liquid extraction, ionic strength, copper (II), capric acid

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Authors: N. Tabatadze

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The research aim is to study the physical and mechanical characteristics of hydraulic concrete in the surface active environment. The specific goal is to obtain high strength and low deformable concrete based on nano additives, resistant to the aggressive environment. As result of research, the alkali-silica reaction was improved (relative elongation 0,122 % of admixture instead of 0,126 % of basic concrete after 14 days). The aggressive environment impact on the strength of heavy concrete, fabricated on the basis of the hydraulic admixture with the penetrating waterproof additives also was improved (strength on compression R28=47,5 mPa of admixture instead of R28=35,8 mPa). Moreover, water absorption (W=0,59 % of admixture instead of W=1,41 %), water tightness (R14=37,9 mPa instead R14=28,7 mPa) and water-resistance (B=18 instead B=12). The basic parameters of concrete with admixture was improved in comparison with basic concrete.

Keywords: hydraulic concrete, alkali-silica reaction, water absorption, water-resistance

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Authors: Amar Patnaik, Pankaj Agarwal

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This paper investigates the experimental study of hardness and compressive strength of hybrid glass/steel fiber reinforced polymer composites by varying the glass and steel fiber layer in the epoxy matrix. The hybrid composites with four stacking sequences HSG-1, HSG-2, HSG-3, and HSG-4 were fabricated by the VARTM process under the controlled environment. The experimentally evaluated results of Vicker’s hardness of the fabricated composites increases with an increase in the fiber layers sequence showing the high resistance. The improvement of micro-structure ability has been observed from the SEM study, which governs in the enhancement of compressive strength. The finite element model was developed on ANSYS to predict the above said properties and further compared with experimental results. The results predicted by the numerical simulation are in good agreement with the experimental results. The hybrid composites developed in this study was identified as the preferred materials due to their excellent mechanical properties to replace the conventional materialsused in the marine structures.

Keywords: finite element method, interfacial strength, polymer composites, VARTM

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Authors: Seyed Mohammad Mahdi Zamani, Kamran Behdinan

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In this study, a multiscale framework is performed to model the strength of Nextel fibers in presence of an atomistic scale pre-crack at finite temperatures. The bridging cell method (BCM) is the multiscale technique applied in this study, which decomposes the system into the atomistic, bridging and continuum domains; solves the whole system in a finite element framework; and incorporates temperature dependent calculations. Since Nextel is known to be structurally stable and retain 70% of its initial strength up to 1100°C; simulations are conducted at both of the room temperatures, 25°C, and fire temperatures, 1200°C. Two cases are modeled for a pre-crack present in either phases of alumina or mullite of the Nextel structure. The materials’ response is studied with respect to deformation behavior and ultimate tensile strength. Results show different crack growth trends for the two cases, and as the temperature increases, the crack growth resistance and material’s strength decrease.

Keywords: Nextel fibers, multiscale modeling, pre-crack, ultimate tensile strength

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Authors: Fetta Ait Ahsene-Aissat, Messaoud Hachemi, Yacine Moussaoui, Yacine Kerchiche

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Our study focuses on two important aspects, environmental by using a sub industrial product (FAD), by economic incorporation as an addition to Portland cement, thus improving resistance to compression and bending with different proportions ADF % up to 40 additions. We studied the effect of different substitutions 0%, 10%, 20%, and 40% of additions to the mechanical effect of the mortar. We obtained a compressive strength of 61 MPa at 90 days for the cement mixture porthland FAD-40% against a resistance of 58MPa for porthland cement without addition. The flexural strength also showed a marked increase in the cement substitution. We also monitored the behavior of the mixed ash-cement by XRD analysis and scanning electron microscopy (SEM).

Keywords: FAD, porthland, flexural strength, compressive strength, DRX

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Authors: Oguz Ugurkan Akkaya, Alpaslan Sipahi, Ozgur Firat Pamukcu, Murat Yasar, Tolga Guler, Arif Ulu, Ferit Cakir

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With the increase in human population, expansion, and renovation of cities, infrastructure systems today need to be manufactured to be more durable and long-lasting. The most cost-effective and durable manufacturing of components is a general problem of all engineering disciplines. Therefore, it is important to determine the most optimal components. This study mainly focuses on the most optimal component design of the polymer concrete. For this purpose, the lower and upper limits of the three main components of the polymer concrete are determined. The effects of these three principal components on the compressive strength, tensile strength, and unit price of polymer concrete are estimated using the response surface method. Box-Behnken Design is used in designing the experiments. Compressive strength, tensile strength, and unit prices are successfully estimated with variance ratios (R²) of 0.82, 0.92, and 0.90, respectively, and the optimum mixture quantity is determined.

Keywords: Box-Behnken Design, compressive strength, mechanical tests, polymer concrete, tensile strength

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Authors: Humphrey Danso, Seth Adu

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The high cost of cement and its greenhouse effect on the environment have led to the use of alternative building materials in the production of block and bricks. This study seeks to investigate the properties of compressed earth blocks (CEBs) enhanced with clay pozzolana. CEBs of size 290 × 140 × 100 mm were prepared with 10, 20 and 30 % weight of clay pozzolana. The CEBs were compressed at a constant pressure of 5 MPa and cured for 28 days. The blocks, after 7, 14, 21 and 28 days of curing were tested for density, water absorption, compressive strength and erosion. It was found that amount of pozzolana content did not have much influence on blocks’ density. There was a decline in water absorption of the stabilised blocks ranged between 32.8% and 252.2% over the unstabilised blocks. The highest compressive strength (3.75MPa) of the stabilized blocks was achieved at 28th day of curing with 30% clay pozzolana content, which showed an improvement of 116.8% strength over the unstabilised blocks. Furthermore, there was a statistically significant difference in the erosion resistance between the stabilized blocks and the unstabilised blocks. The study concludes that the inclusion of the clay pozzolana increased the properties of the CEBs, and therefore recommended for use in the building of houses.

Keywords: clay pozzolana, compressed earth blocks (CEBs), compressive strength, erosion test

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Authors: Kianoosh Samimi, Farhad Estakhr, Mahdi Mahdikhani, Faramaz Moodi

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Due to their fluidity and simplicity of use, self-compacting concretes (SCCs) have undeniable advantages. In recent years, the role of metakaolin as a one of pozzolanic materials in concrete has been considered by researchers. It can modify various properties of concrete, due to high pozzolanic reactions and also makes a denser microstructure. The objective of this paper is to examine the influence of three type of Portland cement and metakaolin on fresh state, compressive strength and sulfuric acid attacks in self- consolidating concrete at early age up to 90 days of curing in lime water. Six concrete mixtures were prepared with three types of different cement as Portland cement type II, Portland Slag Cement (PSC), Pozzolanic Portland Cement (PPC) and 15% substitution of metakaolin by every cement. The results show that the metakaolin admixture increases the viscosity and the demand amount of superplasticizer. According to the compressive strength results, the highest value of compressive strength was achieved for PSC and without any metakaolin at age of 90 days. Conversely, the lowest level of compressive strength at all ages of conservation was obtained for PPC and containing 15% metakaolin. According to this study, the total substitution of PSC and PPC by Portland cement type II is beneficial to the increasing in the chemical resistance of the SCC with respect to the sulfuric acid attack. On the other hand, this increase is more noticeable by the use of 15% of metakaolin. Therefore, it can be concluded that metakaolin has a positive effect on the chemical resistance of SCC containing of Portland cement type II, PSC, and PPC.

Keywords: SCC, metakaolin, cement type, durability, compressive strength, sulfuric acid attacks

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Authors: Min Sang Lee, Hee Jae Shin, In Pyo Cha, Sun Ho Ko, Hyun Kyung Yoon, Hong Gun Kim, Lee Ku Kwac

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The prepreg process among the CFRP (Carbon Fiber Reinforced Plastic) forming methods is the short term of ‘Pre-impregnation’, which is widely used for aerospace composites that require a high quality property such as a fiber-reinforced woven fabric, in which an epoxy hardening resin is impregnated. the reality is, however, that this process requires continuous researches and developments for its commercialization because the delamination characteristically develops between the layers when a great weight is loaded from outside. to supplement such demerit, three lamination methods among the prepreg lamination methods of CFRP were designed to minimize the delamination between the layers due to external impacts. Further, the newly designed methods and the existing lamination methods were analyzed through a mechanical characteristic test, Interlaminar Shear Strength test. The Interlaminar Shear Strength test result confirmed that the newly proposed three lamination methods, i.e. the Roll, Half and Zigzag laminations, presented more excellent strengths compared to the conventional Ply lamination. The interlaminar shear strength in the roll method with relatively dense fiber distribution was approximately 1.75% higher than that in the existing ply lamination method, and in the half method, it was approximately 0.78% higher.

Keywords: carbon fiber reinforced plastic(CFRP), pre-impregnation, laminating method, interlaminar shear strength (ILSS)

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Authors: Abdoullah Namdar, Fadzil Mat Yahaya

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Many synthetic additives have been using for improve cement mortar and concrete characteristics, but natural additive is a friendly environment option. The quantity of (2% and 4%) seashell powder has been replaced in cement mortar, and compared with plain cement mortar in early age of 7 days. The strain gauges have been installed on beams and cube, for monitoring fluctuation of flexural and compressive strength. Main objective of this paper is to study effect of linear static force on flexural and compressive strength of modified cement mortar. The results have been indicated that the replacement of appropriate proportion of seashell powder enhances cement mortar mechanical properties. The replacement of 2% seashell causes improvement of deflection, time to failure and maximum load to failure on concrete beam and cube, the same occurs for compressive modulus elasticity. Increase replacement of seashell to 4% reduces all flexural strength, compressive strength and strain of cement mortar.

Keywords: compressive strength, flexural strength, compressive modulus elasticity, time to failure, deflection

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Authors: Houssem Ayari

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Sheet molding compounds (SMC) are high strength thermoset moulding materials reinforced with glass treated with thermocompression. SMC composites combine fibreglass resins and polyester/phenolic/vinyl and unsaturated acrylic to produce a high strength moulding compound. These materials are usually formulated to meet the performance requirements of the moulding part. In addition, the vinyl ester resins used in the new advanced SMC systems (A-SMC) have many desirable features, including mechanical properties comparable to epoxy, excellent chemical resistance and tensile resistance, and cost competitiveness. In this paper, a proposed model is used to take into account the Young modulus evolutions of advanced SMC systems (A-SMC) composite under fatigue tests. The proposed model and the used approach are in good agreement with the experimental results.

Keywords: composites SFRC, damage, fatigue, Mori-Tanaka

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Authors: Faramarz Ashenai Ghasemi, Ismail Ghasemi, Sajad Daneshpayeh

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In this study, tensile strength and elastic modulus of nanocomposites based on polypropylene/ linear low density polyethylene/ nano titanium dioxide (PP/LLDPE/TiO2) were studied. The samples were produced using a co-rotating twin screw extruder including 0, 2, 4 Wt .% of nano particles, and 20, 40, 60 Wt.% of LLDPE. The styrene-ethylene-butylene-styrene (SEBS) was used as comptabiliser. Tensile strength and elastic modulus were evaluated. The results showed that modulus was increased by 7% with addition of nano particles in comparison to PP/LLDPE. In addition, tensile strength was decreased.

Keywords: PP/LLDPE/TiO2, nanocomposites, elastic modulus, tensile strength

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Authors: Mostafa Osman, Ata El-Kareim Shoeib

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The main objective of this paper is study the influence of carbon nano-tubes fibers and nano silica fibers on the characteristic compressive strength and flexural strength on concrete and cement mortar. Twelve tested specimens were tested with square section its dimensions (40*40*160) mm, divided into four groups. The first and second group studied the effect of carbon nano-tubes (CNTs) fiber with different percentage equal to 0.0, 0.11 %, 0.22 %, and 0.33 % by weight of cement and effect of nano-silica (nS) fibers with different percentages equal to 0.0, 1.0 %, 2.0 %, and 3.0 % by weight of cement on the cement mortar. The third and fourth groups studied the effect of CNTs fiber with different percentage equal to 0.0 %, 0.11 %, and 0.22 % by weight of cement, and effect of nS fibers with different percentages were equal to 0.0 %, 1.0%, and 2.0 % by weight of cement on the concrete. The compressive strength and flexural strength at 7, 28, and 90 days is determined. From analysis of tested results concluded that the nano-fiber is more effective when used with cement mortar than that of used with concrete because of increasing the surface area, decreasing the pore and the collection of nano-fiber. And also by adding nano-fiber the improvement of flexural strength of concrete and cement mortar is more than improvement of compressive strength.

Keywords: carbon nano-tubes (CNTs) fibres, nano-silica (nS) fibres, compressive strength, flexural strength

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Authors: James Killian, Sarah Cox

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The use of stability criteria within geotechnical engineering is the way the results of analyses are conveyed, and sensitivities and risk assessments are performed. Historically, the primary stability criteria for slope design has been the Factor of Safety (FOS) coming from a limit calculation. Increasingly, the value derived from Strength Reduction Factor (SRF) analysis is being used as the criteria for stability analysis. The purpose of this work was to study in detail the relationship between SRF values produced from a numerical modeling technique and the traditional FOS values produced from Limit Equilibrium (LEM) analyses. This study utilized a model of a 3000-foot-high slope with a 45-degree slope angle, assuming a perfectly plastic mohr-coulomb constitutive model with high cohesion and friction angle values typical of a large hard rock mine slope. A number of variables affecting the values of the SRF in a numerical analysis were tested, including zone size, in-situ stress, tensile strength, and dilation angle. This paper demonstrates that in most cases, SRF values are lower than the corresponding LEM FOS values. Modeled zone size has the greatest effect on the estimated SRF value, which can vary as much as 15% to the downside compared to FOS. For consistency when using SRF as a stability criteria, the authors suggest that numerical model zone sizes should not be constructed to be smaller than about 1% of the overall problem slope height and shouldn’t be greater than 2%. Future work could include investigations of the effect of anisotropic strength assumptions or advanced constitutive models.

Keywords: FOS, SRF, LEM, comparison

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Authors: Mulubrhan Berihu, Supratic Gupta, Zena Gebriel

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Due to the design versatility, availability, and cost efficiency, concrete is continuing to be the most used construction material on earth. However, the production of Portland cement, the primary component of concrete mix is causing to have a serious effect on environmental and economic impacts. This shows there is a need to study using of supplementary cementitious materials (SCMs). The most commonly used supplementary cementitious materials are wastes and the use of these industrial waste products has technical, economical and environmental benefits besides the reduction of CO2 emission from cement production. The study aims to document the effect on strength property of concrete due to use of low cement by maximizing supplementary cementitious materials like fly ash or marble powder. Based on the different mix proportion of pozzolana and marble powder a range of mix design was formulated. The first part of the project is to study the strength of low cement concrete using fly ash replacement experimentally. The test results showed that using up to 85 kg/m3 of cement is possible for plain concrete works like hollow block concrete to achieve 9.8 Mpa and the experimental results indicates that strength is a function of w/b. In the second part a new set of mix design has been carried out with fly ash and marble powder to study the strength of both binary and ternary mixes. In this experimental study, three groups of mix design (c+FA, c+FA+m and c+m), four sets of mixes for each group were taken up. Experimental results show that c+FA has maintained the best strength and impermeability whereas c+m obtained less compressive strength, poorer permeability and split tensile strength. c+FA shows a big difference in gaining of compressive strength from 7 days to 28 days compression strength compared to others and this obviously shows the slow rate of hydration of fly ash concrete. As the w/b ratio increases the strength decreases significantly. At the same time higher permeability has been seen in the specimens which were tested for three hours than one hour.

Keywords: efficiency factor, cement content, compressive strength, mix proportion, w/c ratio, water permeability, SCMs

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Authors: Tomofumi Kubota, Mitsuhiro Okayasu

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In recent years, environmental problems and energy problems typified by global warming are intensifying, and transportation devices are required to reduce the weight of structural materials from the viewpoint of strengthening fuel efficiency regulations and energy saving. Carbon fiber reinforced plastic (CFRP) used in this research is attracting attention as a structural material to replace metallic materials. Among them, thermoplastic CFRP is expected to expand its application range in terms of recyclability and cost. High formability and weldability of the unidirectional CFRP sheets conducted by a proposed hot stamping process were proposed, in which the carbon fiber reinforced plastic sheets are heated by a designed technique. In this case, the CFRP sheets are heated by the high electric voltage applied through carbon fibers. In addition, the electric voltage was controlled by the area ratio of exposed carbon fiber on the sample surfaces. The lower exposed carbon fiber on the sample surface makes high electric resistance leading to the high sample temperature. In this case, the CFRP sheets can be heated to more than 150 °C. With the sample heating, the stamping and welding technologies can be carried out. By changing the sample temperature, the suitable stamping condition can be detected. Moreover, the proper welding connection of the CFRP sheets was proposed. In this study, we propose a fusion bonding technique using thermoplasticity, high current flow, and heating caused by electrical resistance. This technology uses the principle of resistance spot welding. In particular, the relationship between the carbon fiber exposure rate and the electrical resistance value that affect the bonding strength is investigated. In this approach, the mechanical connection using rivet is also conducted to make a comparison of the severity of welding. The change of connecting strength is reflected by the fracture mechanism. The low and high connecting strength are obtained for the separation of two CFRP sheets and fractured inside the CFRP sheet, respectively. In addition to the two fracture modes, micro-cracks in CFRP are also detected. This approach also includes mechanical connections using rivets to compare the severity of the welds. The change in bond strength is reflected by the destruction mechanism. Low and high bond strengths were obtained to separate the two CFRP sheets, each broken inside the CFRP sheets. In addition to the two failure modes, micro cracks in CFRP are also detected. In this research, from the relationship between the surface carbon fiber ratio and the electrical resistance value, it was found that different carbon fiber ratios had similar electrical resistance values. Therefore, we investigated which of carbon fiber and resin is more influential to bonding strength. As a result, the lower the carbon fiber ratio, the higher the bonding strength. And this is 50% better than the conventional average strength. This can be evaluated by observing whether the fracture mode is interface fracture or internal fracture.

Keywords: CFRP, hot stamping, weliding, deforamtion, mechanical property

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Authors: Heba Fouad, Tarek M. Madkour, Safwan A. Khedr

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This paper investigates multiple factors that impact the formation of geopolymers and their compressive strength to be utilized in construction as an environmentally-friendly material. Bentonite and Kaolinite were thermally calcinated at 750 °C to obtain Metabentonite and Metakaolinite with higher reactivity. Both source materials were activated using a solution of sodium hydroxide (NaOH). Thereafter, samples were cured at different temperatures. The samples were analyzed chemically using a host of spectroscopic techniques. The bulk density and compressive strength of the produced Geopolymer pastes were studied. Findings indicate that the ratio of NaOH solution to source material affects the compressive strength, being optimal at 0.54. Moreover, controlled heat curing was proven effective to improve compressive strength. The existence of characteristic Fourier Transform Infrared Spectroscopy (FTIR) peaks at approximately 1020 cm-1 and 460 cm-1 which corresponds to the asymmetric stretching vibration of Si-O-T and bending vibration of Si-O-Si, hence, confirming the formation of the target geopolymer.

Keywords: calcination of metakaolinite, compressive strength, FTIR analysis, geopolymer, green cement

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Authors: Youssouf Benmeriem

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Shear strength of sandy soils has been considered as the important parameter to study the stability of different civil engineering structures when subjected to monotonic, cyclic and earthquake loading conditions. The proposed research investigated the effect of grading characteristics on the shear strength and mechanical behavior of granular classes of sands mixed with silt in loose and dense states (Dr = 15% and 90%). The laboratory investigation aimed at understanding the extent or degree at which shear strength of sand-silt mixture soil is affected by its gradation under static loading conditions. For the purpose of clarifying and evaluating the shear strength characteristics of sandy soils, a series of Casagrande shear box tests were carried out on different reconstituted samples of sand-silt mixtures with various gradations. The soil samples were tested under different normal stresses (100, 200 and 300 kPa). The results from this laboratory investigation were used to develop insight into the shear strength response of sand and sand-silt mixtures under monotonic loading conditions. The analysis of the obtained data revealed that the grading characteristics (D10, D50, Cu, ESR, and MGSR) have significant influence on the shear strength response. It was found that shear strength can be correlated to the grading characteristics for the sand-silt mixture. The effective size ratio (ESR) and mean grain size ratio (MGSR) appear as pertinent parameters to predict the shear strength response of the sand-silt mixtures for soil gradation under study.

Keywords: grading characteristics, granular classes of sands, mechanical behavior, sand-silt, shear strength

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Authors: Perminder JitKaur, Santosh Satya, K. K. Pant, S. N. Naik

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Bamboo is extensively used in construction industry. Low durability of bamboo due to fungus infestation and termites attack under storage puts certain constrains for it usage as modern structural material. Looking at many chemical formulations for bamboo treatment leading to severe harmful environment effects, research on eco-friendly preservatives for bamboo treatment has been initiated world-over. In the present studies, eco-friendly preservative for bamboo treatment has been developed. To validate its application for structural purposes, investigation of effect of treatment on compressive strength has been investigated. Neem oil(25%) integrated with copper naphthenate (0.3%) on dilution with kerosene oil impregnated into bamboo culm at 2 bar pressure, has shown weight loss of only 3.15% in soil block analysis method. The results of compressive strength analysis using The results from compressive strength analysis using HEICO Automatic Compression Testing Machine, reveal that preservative treatment has not altered the structural properties of bamboo culms. Compressive strength of control (11.72 N/mm2) and above treated samples (11.71 N/mm2) was found to be comparable.

Keywords: D. strictus, bamboo, neem oil, presure treatment, compressive strength

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Authors: Demet Yavuz

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Freeze-thaw cycles are one of the greatest threats to concrete durability. Lately, protection against this threat excites scientists’ attention. Air-entraining admixtures have been widely used to produce freeze-thaw resistant at concretes. The use of air-entraining agents (AEAs) enhances not only freeze-thaw endurance but also the properties of fresh concrete such as segregation, bleeding and flow ability. This paper examines the effects of air-entraining on compressive strength of concrete. Air-entraining is used between 0.05% and 0.4% by weight of cement. One control and four fiber reinforced concrete mixes are prepared and three specimens are tested for each mix. It is concluded from the test results that when air entraining is increased the compressive strength of concrete reduces for all mixes with AEAs.

Keywords: concrete, air-entraining, compressive strength, mechanical properties

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Authors: Philipp Burger, Jonas Sommer, Haneen Daoud, Franz Hilmer, Uwe Glatzel

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Press-hardened structural components made of coated high-strength steel are an essential part of the automotive industry when it comes to weight reduction, safety, and durability. Alternative heat treatment processes, such as contact heating, have been developed to improve the efficiency of this process. However, contact heating of the steel sheets often results in cracking within the Al-Si-coated layer. Therefore, this paper will address the development of alternative coating compositions based on Al-Si-X, suitable for contact heating. For this purpose, robot-assisted thermal arc spray was applied to coat the high-strength steel sheets. This ensured high reproducibility as well as effectiveness. The influence of the coating parameters and the variation of the nozzle geometry on the microstructure of the developed coatings will be discussed. Finally, the surface and mechanical properties after contact heating and press hardening will be presented.

Keywords: press hardening, hot stamping, thermal spraying, arc spraying, coating compositions

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Authors: Cise Unluer

Abstract:

Reactive MgO hydrates to form brucite (Mg(OH)2, magnesium hydroxide), which can then react with CO2 and additional water to form a range of strength providing hydrated magnesium carbonates (HMCs) within cement-based formulations. The presented work focuses on the use of reactive MgO in a range of concrete mixes, where it carbonates by absorbing CO2 and gains strength accordingly. The main goal involves maximizing the amount of CO2 absorbed within construction products, thereby reducing the overall environmental impact of the designed formulations. Microstructural analyses including scanning electron microscopy (SEM), X-ray diffraction (XRD) and thermogravimetry/differential thermal analysis (TG/DTA) are used in addition to porosity, permeability and unconfined compressive strength (UCS) testing to understand the performance mechanisms. XRD Reference Intensity Ratio (RIR), acid digestion and TG/DTA are utilized to quantify the amount of CO2 sequestered, with the goal of achieving 100% carbonation through careful mix design, leading to a range of carbon neutral products with high strengths. As a result, samples stronger than those containing Portland cement (PC) were produced, revealing the link between the mechanical performance and microstructural development of the developed formulations with the amount of CO2 sequestered.

Keywords: carbonation, compressive strength, reactive MgO cement, sustainability

Procedia PDF Downloads 180

Authors: Mizam Dogan, Hande Gökdemir

Abstract:

In reinforced concrete elements, reinforcement steel bars are placed in concrete both longitudinal and lateral directions. The lateral reinforcement (called as confinement) which is used for confining circular RC elements is in a spiral shape. If the cross section of RC element is rectangular, stirrups should be rectangular too. At very high compressive stresses concrete will reach its limit strain value and therefore concrete outside the lateral reinforcement, which is not confined, will crush and start to spell. At this stage, concrete core of the RC element tries to expand laterally as a reason of high Poisson’s ratio value of concrete. Such a deformation is prevented by the lateral reinforcement which applies lateral passive pressure on concrete. At very high compressive stresses, the strength of reinforced column member rises to four times σ 2. This increase in strength of member is related to the properties of rectangular stirrups. In this paper, effect of stirrup step spacing to column behavior is calculated and presented confined concrete model is proved by numerical solutions.

Keywords: confined concrete, concrete column, stress-strain, stirrup, solid, frame

Procedia PDF Downloads 451

Authors: Hee Yong Kang, Hyeon Ho Shin, Jung Cheol Yoo, Il Taek Lee, Sung Mo Yang

Abstract:

Lightweight technology using composites is being developed for vehicle seat structures, and its design must meet the safety requirements. According to the Federal Motor Vehicle Safety Standard (FMVSS) 207 seating systems test procedure, the back moment load is applied to the seat back frame structure for the safety evaluation of the vehicle seat. The seat back frame using the composites is divided into three parts: upper part frame, and left- and right-side frame parts following the manufacturing process. When a rear moment load is applied to the seat back frame, the side frame receives the bending load and the torsional load at the same time. This results in the largest loaded strength. Therefore, strength test of the component unit is required. In this study, a component test method based on the FMVSS 207 seating systems test procedure was proposed for the strength analysis of bending load and torsional load of the automotive Bulk Molding Compound (BMC) Seat Back Side Frame. Moreover, strength evaluation according to the carbon band reinforcement was performed. The back-side frame parts of the seat that are applied to the test were manufactured through BMC that is composed of vinyl ester Matrix and short carbon fiber. Then, two kinds of reinforced and non-reinforced parts of carbon band were formed through a high-temperature compression molding process. In addition, the structure that is applied to the component test was constructed by referring to the FMVSS 207. Then, the bending load and the torsional load were applied through the displacement control to perform the strength test for four load conditions. The results of each test are shown through the load-displacement curves of the specimen. The failure strength of the parts caused by the reinforcement of the carbon band was analyzed. Additionally, the fracture characteristics of the parts for four strength tests were evaluated, and the weakness structure of the back-side frame of the seat structure was confirmed according to the test conditions. Through the bending and torsional strength test methods, we confirmed the strength and fracture characteristics of BMC Seat Back Side Frame according to the carbon band reinforcement. And we proposed a method of testing the part strength of a seat back frame for vehicles that can meet the FMVSS 207.

Keywords: seat back frame, bending and torsional strength, BMC (Bulk Molding Compound), FMVSS 207 seating systems

Procedia PDF Downloads 210