Search results for: crushing strength

Authors: Vijay Pal Singh, Yogesh Chandra Kotiyal

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Structures are a combination of various load carrying members which transfer the loads to the foundation from the superstructure safely. At the design stage, the loading of the structure is defined and appropriate material choices are made based upon their properties, mainly related to strength. The strength of materials kept on reducing with time because of many factors like environmental exposure and deformation caused by unpredictable external loads. Hence, to predict the strength of materials used in structures, various techniques are used. Among these techniques, Non-Destructive Techniques (NDT) are the one that can be used to predict the strength without damaging the structure. In the present study, the compressive strength of concrete has been predicted using Artificial Neural Network (ANN). The predicted strength was compared with the experimentally obtained actual compressive strength of concrete and equations were developed for different models. A good co-relation has been obtained between the predicted strength by these models and experimental values. Further, the co-relation has been developed using two NDT techniques for prediction of strength by regression analysis. It was found that the percentage error has been reduced between the predicted strength by using combined techniques in place of single techniques.

Keywords: rebound, ultra-sonic pulse, penetration, ANN, NDT, regression

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Authors: Jiaxu Huang

Abstract:

The melt carbonized blast furnace slag containing TiC was produced by carbothermal reduction of high titanium blast furnace slag. The treatment technology of melt carbonized blast furnace slag with TiC as raw material was studied, including the influence of different cooling methods, crushing atmosphere and sieving particle size on the target product TiC in the slag. The results show that air-cooling and water-cooling have little effect on TiC content of molten carbide blast furnace slag, and have great effect on crystal structure and grain size. TiC content in slag is different when carbide blast furnace slag is crushed in argon atmosphere and air atmosphere. After screening, the difference of TiC content of carbide blast furnace slag with different particle size distribution is obvious. The average TiC content of 100-400 mesh carbide blast furnace slag is 14%. And the average TiC content of carbide blast furnace slag with particle size less than 400 mesh is 10.5%.

Keywords: crushing atmosphere, cooling methods, sieving particle size, TiC

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Authors: J. Y. Lee, H. S. Lim, S. H. Yoon

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This paper presents an analysis of the diagonal crack widths of RC members with various types of materials by simulating a compatibility-aided truss model. The analytical results indicated that the diagonal crack width was influenced by not only the shear reinforcement ratio but also the yield strength of shear reinforcement and the compressive strength of concrete. The yield strength of shear reinforcement and the compressive strength of concrete decreased the diagonal shear crack width of RC members for the same shear force because of the change of shear failure modes. However, regarding the maximum shear crack width at shear failure, the shear crack width of the beam with high strength materials was greater than that of the beam with normal strength materials.

Keywords: diagonal crack width, high strength stirrups, high strength concrete, RC members, shear behavior

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Authors: J. P. Gorninski, J. M. L. Reis

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This present work was aimed to develop polymeric mortars having as binder two polyester resins namely isophtalic and orthophtalic polyester. The inorganic phase was composed by medium-size river sand and fly ash fíller, a by-product of the burning of coal in power plants. The compositions in this study are high performance mortars and were assessed by mechanical properties, through compressive strength and flexural strength, by durability strength when exposed to the cyclical variation of temperature from -400C to +300C and by the chemical aggression test. The composites displayed good performance when exposed to cyclical temperature variations and chemical solutions. The mechanical strength values reached the 100 MPa, the flexural strength yielded values of about twenty percent of mechanical strength.

Keywords: polymer mortar, mechanical strength, cyclical temperatures, chemical strength, sustainability

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Authors: I Lamri, L Arabet, M. Hidjeb

Abstract:

The direct shear test was used to determine the shear strength parameters C and Ø of a series of samples with different cement content. Samples stabilized with a certain percentage of cement showed a substantial gain in compressive strength and a significant increase in shear strength parameters. C and Ø. The laboratory equipment used in UCS tests consisted of a conventional 102mm diameter sample triaxial loading machine. Beyond 4% cement content a very important increase in shear strength was observed. It can be deduced from a comparative study of shear strength of soil samples with 4%, 7%, and 10% cement with sample containing 2 %, that the sample with a 4% cement content showed 90% increase in shear strength while those with 7% and 10% showed an increase of around 13 and 21 fold.

Keywords: cement, compression strength, shear stress, cohesion, angle of internal friction

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Authors: May Haggag, Ezzat Fahmy, Mohamed Abdel-Mooty, Sherif Safar

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Sandwich sections have a very complex nature due to variability of behavior of different materials within the section. Cracking, crushing and yielding capacity of constituent materials enforces high complexity of the section. Furthermore, slippage between the different layers adds to the section complex behavior. Conventional methods implemented in current industrial guidelines do not account for the above complexities. Thus, a throughout study is needed to understand the true behavior of the sandwich panels thus, increase the ability to use them effectively and efficiently. The purpose of this paper is to conduct numerical investigation using ANSYS software for the structural behavior of sandwich wall section under eccentric loading. Sandwich walls studied herein are composed of two RC faces, a foam core and linking shear connectors. Faces are modeled using solid elements and reinforcement together with connectors are modeled using link elements. The analysis conducted herein is nonlinear static analysis incorporating material nonlinearity, crashing and crushing of concrete and yielding of steel. The model is validated by comparing it to test results in literature. After validation, the model is used to establish extensive parametric analysis to investigate the effect of three key parameters on the axial force bending moment interaction diagram of the walls. These parameters are the concrete compressive strength, face thickness and number of shear connectors. Furthermore, the results of the parametric study are used to predict a coefficient that links the interaction diagram of a solid wall to that of a sandwich wall. The equation is predicted using the parametric study data and regression analysis. The predicted α was used to construct the interaction diagram of the investigated wall and the results were compared with ANSYS results and showed good agreement.

Keywords: sandwich walls, interaction diagrams, numerical modeling, eccentricity, reinforced concrete

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Authors: A. J. Shah, Neeraj Kumar Sahu

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Reactive powder concrete (RPC) is high performance and high strength concrete which composes of very fine powdered materials like cement, sand, silica fume and quartz powder. It also constitutes steel fibre (optional) and super-plasticizer. The present study investigates the performance of reactive powder concrete with fly ash as a replacement of cement under hot water and normal water curing conditions. The replacement of cement with fly ash is done at 10%, 20%, 30% and 40%. To compare the results of cement replaced RPC and traditional RPC, the performance of various mixes is evaluated by compressive strength, flexural strength, split tensile strength and durability. The results show that with increasing percentage of fly ash, improvement in durability is observed and a slight decrease in compressive strength and flexural strength is also observed. It is observed that specimen under hot water curing showed 15 to 20 % more strength than specimens under normal water curing.

Keywords: high strength concrete, the flexural strength of RPC, compressive strength of RPC, durability

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Authors: Shree Laxmi Prashant, Subhash C. Yaragal, K. S. Babu Narayan

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Concrete is found to undergo degradation when subjected to elevated temperatures and loose substantial amount of its strength. The loss of strength in concrete is mainly attributed to decomposition of C-S-H and release of physically and chemically bound water, which begins when the exposure temperature exceeds 100°C. When such a concrete comes in contact with moisture, the cement paste is found rehydrate and considerable amount of strength lost is found to recover. This paper presents results of an experimental program carried out to investigate the effect of recuring on strength gain of OPC concrete specimens subjected to elevated temperatures from 200°C to 800°C, which were subjected to retention time of two hours and four hours at the designated temperature. Strength recoveries for concrete subjected to 7 designated elevated temperatures are compared. It is found that the efficacy of recuring as a measure of strength recovery reduces with increase in exposure temperature.

Keywords: elevated temperature, recuring, strength recovery, compressive strength

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Authors: Kebaili Bachir

Abstract:

The reuse of concrete waste as a secondary aggregate could be an efficient solution for sustainable development and long-term environmental protection. The variable nature of waste concrete, with various compressive strengths, can have a negative effect on the final compressive strength of recycled concrete. Accordingly, an experimental test programme was developed to evaluate the effect of parent concrete qualities on the performance of recycled concrete. Three grades with different compressive strengths 10MPa, 20MPa, and 30MPa were considered in the study; moreover, an unknown compressive strength was introduced as well. The trial mixes used 40% secondary aggregates (both course and fine) and 60% of natural aggregates. The compressive strength of the test concrete decrease between 15 and 25% compared to normal concrete with no secondary aggregates. This work proves that the strength properties of the parent concrete have a limited effect on the compressive strength of recycled concrete. Low compressive strength parent concrete when crushed generate a high percentage of recycled coarse aggregates with the less attached mortar and give the same compressive strength as an excellent parent concrete. However, the decrease in compressive strength can be mitigated by increasing the cement content 4% by weight of recycled aggregates used.

Keywords: compressive, concrete, quality, recycled, strength

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Authors: D. K. Soni

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A study of engineering properties of stones, i.e. compressive strength, tensile strength, modulus of elasticity, density, hardness were carried out to explore the possibility of optimum utilization of stone. The laboratory test results on equally dimensioned discs of the stone show a considerable variation in computed split tensile strength with varied rates of deformation. Hence, the effect of strain rate on the tensile strength of a sand stone and lime stone under wet and dry conditions has been studied experimentally using the split tensile strength test technique. It has been observed that the tensile strength of these stone is very much dependent on the rate of deformation particularly in a dry state. On saturation the value of split tensile strength reduced considerably depending upon the structure of rock and amount of water absorption.

Keywords: sedimentary rocks, split tensile test, deformation rate, saturation rate, sand stone, lime stone

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Authors: Alaa I. Arafa, Hemdan O. A. Said. Marwa A. M. Ali

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This paper investigates and evaluates experimentally the structural behavior of high strength concrete (HSC) beams under fire and compares it with that of Normal strength concrete (NSC) beams. The main investigated parameters are: concrete compressive strength (300 or 600 kg/cm²); the concrete cover thickness (3 or 5 cm); the degree of temperature (room temperature or 600 ^oC); the type of cooling (air or water); and the fire exposure time (3 or 5 hours). Test results showed that the concrete compressive strength decreases significantly as the exposure time to fire increases.

Keywords: experimental, fire, high strength concrete beams, monotonic loading

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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 fiber 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; Fiber 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 fiber 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 fiber 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: S. Ritddech, P. Aroonjarattham, K. Aroonjarattham

Abstract:

The pullout strength had an effect on the stability of plate screw fixation when inserted in the cervical spine. Nine different titanium alloy bone screws were used to test the pullout strength through finite element analysis. The result showed that the Moss Miami I can bear the highest pullout force at 1,075 N, which causes the maximum von Mises stress at 858.87 MPa, a value over the yield strength of titanium. The bone screw should have large outer diameter, core diameter and proximal root radius to increase the pullout strength.

Keywords: pullout strength, screw parameter, cervical spine, finite element analysis

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Authors: H. B. Mahmud, Syamsul Bahri, Y. W. Yee, Y. T. Yeap

Abstract:

This paper reports the strength and durability properties of high strength high performance concrete incorporating rice husk ash (RHA) having high silica, low carbon content and appropriate fineness. In this study concrete containing 10%, 15% and 20% RHA as cement replacement and water to binder ratio of 0.25 were investigated. The results show that increasing amount of RHA increases the dosage of superplasticizer to maintain similar workability. Partial replacement of cement with RHA did not increase the early age compressive strength of concrete. However, concrete containing RHA showed higher compressive strength at later ages. The results showed that compressive strength of concrete in the 90-115 MPa range can be obtained at 28 curing days and the durability properties of RHA concrete performed better than that of control concrete. The water absorption of concrete incorporating 15% RHA exhibited the lowest value. The porosity of concrete is consistent with water absorption whereby higher replacement of RHA decreased the porosity of concrete. There is a positive correlation between reducing porosity and increasing compressive strength of high strength high performance concrete. The results also indicate that up to 20% of RHA incorporation could be advantageously blended with cement without adversely affecting the strength and durability properties of concrete.

Keywords: compressive strength, durability, high performance concrete, rice husk ash

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

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The deterioration of the reinforced concrete is continuously accelerated due to aging of the reinforced concrete, enlargement of the structure, increase if the self-weight due to the manhattanization and cracking due to external force. Also, due to the abnormal climate phenomenon, cracking of reinforced concrete structures is accelerated. Therefore, research on the Textile Reinforced Concrete (TRC) which replaced reinforcement with textile is under study. However, in previous studies, adhesion performance to single yarn was examined without parameters, which does not reflect the effect of fiber twisting and concrete strength. In the present paper, the effect of concrete strength and embedded length on 2400tex (gram per 1000 meters) and 640tex textile were investigated. The result confirm that the increasing compressive strength of the concrete did not affect the pullout strength. However, as the embedded length increased, the pullout strength tended to increase gradually, especially at 2400tex with more twists.

Keywords: textile, TRC, pullout, strength, embedded length, concrete

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Authors: Butchi Kameswara Rao Chittem, Rooban Kumar

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Cement concrete is a complex mixture of different materials. Concrete is believed to have a good fire resistance. Behaviour of concrete depends on its mix proportions and its constituent materials when it is subjected to elevated temperatures. Loss in compressive strength, loss in weight or mass, change in colour and spall of concrete are reported in literature as effects of elevated temperature on concrete. In this paper results are reported on the behaviour of normal strength concrete and high strength concrete subjected to temperatures 200°C, 400°C, 600°C, and 800°C and different cooling regimes viz. air cooling, water quenching. Rebound hammer test was also conducted to study the changes in surface hardness of concrete specimens subjected to elevated temperatures.

Keywords: normal strength concrete, high-strength concrete, temperature, NDT

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Authors: Mehrzad Mohabbi Yadollahi, Ramazan Demirboğa, Majid Atashafrazeh

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Geopolymers are highly complex materials which involve many variables which makes modeling its properties very difficult. There is no systematic approach in mix design for Geopolymers. Since the amounts of silica modulus, Na2O content, w/b ratios and curing time have a great influence on the compressive strength an ANFIS (Adaptive neuro fuzzy inference system) method has been established for predicting compressive strength of ground pumice based Geopolymers and the possibilities of ANFIS for predicting the compressive strength has been studied. Consequently, ANFIS can be used for geopolymer compressive strength prediction with acceptable accuracy.

Keywords: geopolymer, ANFIS, compressive strength, mix design

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Authors: Sayed Hessam Bahmani, Rolsndo P. Orense

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From an engineering point of view, pumice particles are problematic because of their crushability and compressibility due to their vesicular nature. Currently, information on the geotechnical characteristics of pumice sands is limited. While extensive empirical and laboratory tests can be implemented to characterize their behavior, these are generally time-consuming and expensive. These drawbacks have motivated attempts to study the effects of particle breakage of pumice sand through the Discrete Element Method (DEM). This method provides insights into the behavior of crushable granular material at both the micro and macro-level. In this paper, the results of single-particle crushing tests conducted in the laboratory are simulated using DEM through the open-source code YADE. This is done to better understand the parameters necessary to represent the pumice microstructure that governs its crushing features, and to examine how the resulting microstructure evolution affects a particle’s properties. The DEM particle model is then used to simulate the behavior of pumice sand during consolidated drained triaxial tests. The results indicate the importance of incorporating particle porosity and unique surface textures in the material characterization and show that interlocking between the crushed particles significantly influences the drained behavior of the pumice specimen.

Keywords: pumice sand, triaxial compression, simulation, particle breakage

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Authors: Chinedu F. Anochie

Abstract:

The presence of gangue particles in recovered metal concentrates has been a serious challenge to ore dressing engineers. Middlings lower the quality of concentrates, and in most cases, drastically affect the smelter terms, owing to exorbitant amounts paid by Mineral Processing industries as treatment charge. Models which encourage optimization of liberation operations have been utilized in most ore beneficiation industries to reduce the presence of locked particles in valuable concentrates. Moreover, methods such as incorporation of regrind mills, scavenger, rougher and cleaner cells, to the milling and flotation plants has been widely employed to tackle these concerns, and to optimize the grade–recovery relationship of metal concentrates. This work compared the crushing and grinding method of liberation, to the mine to mill route, by evaluating the proportion of middlings present in selectively processed complex Pb-Zn ore samples. To establish the effect of size reduction operations on the percentage of locked particles present in recovered concentrates, two similar samples of complex Pb- Zn ores were processed. Following blasting operation, the first ore sample was ground directly in a ball mill (Mine to Mill Route of Comminution), while the other sample was manually crushed, and subsequently ground in the ball mill (Crushing and Grinding Route of Comminution). The two samples were separately sieved in a mesh to obtain the desired representative particle sizes. An equal amount of each sample that would be processed in the flotation circuit was then obtained with the aid of a weighing balance. These weighed fine particles were simultaneously processed in the flotation circuit using the selective flotation technique. Sodium cyanide, Methyl isobutyl carbinol, Sodium ethyl xanthate, Copper sulphate, Sodium hydroxide, Lime and Isopropyl xanthate, were the reagents used to effect differential flotation of the two ore samples. Analysis and calculations showed that the degree of liberation obtained for the ore sample which went through the conventional crushing and grinding route of comminution, was higher than that of the directly milled run off mine (ROM) ore. Similarly, the proportion of middlings obtained from the separated galena (PbS) and sphalerite (ZnS) concentrates, were lower for the crushed and ground ore sample. A concise data which proved that the mine to mill method of size reduction is not the most ideal technique for the recovery of quality metal concentrates has been established.

Keywords: comminution, degree of liberation, middlings, mine to mill

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Authors: Sujeet Kumar, Arun Prasad

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The present work investigates the effect of multiple parameters on the unconfined compressive strength of the bauxite residue-lime mix. A number of unconfined compressive strength tests considering various curing time, lime content, dry density and moisture content were carried out. The results show that an empirical correlation may be successfully developed using volumetric lime content, porosity, moisture content, curing time unconfined compressive strength for the range of the bauxite residue-lime mix studied. The proposed empirical correlations efficiently predict the strength of bauxite residue-lime mix, and it can be used as a generalized empirical equation to estimate unconfined compressive strength.

Keywords: bauxite residue, curing time, porosity/volumetric lime ratio, unconfined compressive strength

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Authors: Rahimullah Habibzai

Abstract:

To achieve a sustainable concrete industry, reduce exploitation of the natural aggregate resources, and mitigate waste concrete environmental burden, one way is to use recycled concrete aggregate. The utilization of low-quality fine aggregate inclusively recycled concrete sand that is produced from crushing waste concrete recently has become a popular and challenging topic among researchers nowadays. This study provides a scientific base for promoting the application of concrete waste as fine aggregate in producing concrete by conducting a comprehensive laboratory program. The mechanical properties of mortar made from recycled concrete fine aggregate (RCFA), that is produced by pulse power crushing concrete waste are satisfactory and capable of being utilized in the construction industry. A better treatment of RCFA particles and enhancing its quality will make it possible to be utilized in producing structural concrete. Pulse power discharge technology is proposed in this research to produce RCFA, which is a more effective and promising technique compared to other recycling methods to generate medium to high-quality recycled concrete fine aggregate with a reduced amount of powder, mitigate the environmental burden, and save more space.

Keywords: construction and demolition waste, concrete waste recycle fine aggregate, pulse power discharge

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Authors: Mohamed A. Shanan, Ashraf H. El-Zanaty, Kamal G. Metwally

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This paper presents the effect of concrete compressive strength and rectangularity ratio on strength and ductility of normal and high strength reinforced concrete columns confined with transverse steel under axial compressive loading. Nineteen normal strength concrete rectangular columns with different variables tested in this research were used to study the effect of concrete compressive strength and rectangularity ratio on strength and ductility of columns. The paper also presents a nonlinear finite element analysis for these specimens and another twenty high strength concrete square columns tested by other researchers using ANSYS 15 finite element software. The results indicate that the axial force – axial strain relationship obtained from the analytical model using ANSYS are in good agreement with the experimental data. The comparison shows that the ANSYS is capable of modeling and predicting the actual nonlinear behavior of confined normal and high-strength concrete columns under concentric loading. The maximum applied load and the maximum strain have also been confirmed to be satisfactory. Depending on this agreement between the experimental and analytical results, a parametric numerical study was conducted by ANSYS 15 to clarify and evaluate the effect of each variable on strength and ductility of the columns.

Keywords: ANSYS, concrete compressive strength effect, ductility, rectangularity ratio, strength

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Authors: Aliakbar Golshani, Armin Ramezanzad

Abstract:

Tensile strength which is an important parameter of the rock for engineering applications is difficult to measure directly through physical experiment (i.e. uniaxial tensile test). Therefore, indirect experimental methods such as Brazilian test have been taken into consideration and some relations have been proposed in order to obtain the tensile strength for rocks indirectly. In this research, to calculate numerically the tensile strength for granitic rocks, Particle Flow Code in three-dimension (PFC3D) software were used. First, uniaxial compression tests were simulated and the tensile strength was determined for Inada granite (from a quarry in Kasama, Ibaraki, Japan). Then, by simulating Brazilian test condition for Inada granite, the tensile strength was indirectly calculated again. Results show that the tensile strength calculated numerically agrees well with the experimental results obtained from uniaxial tensile tests on Inada granite samples.

Keywords: numerical simulation, particle flow code, PFC, tensile strength, Brazilian Test

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Authors: Reza Ziaie Moayed, Seyed Abdolhassan Naeini, Peyman Nouri, Hamed Yekehdehghan

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The shear strength of soils is a significant parameter in the design of clay structures, depots, clay gables, and freeways. Most research has addressed the shear strength of saturated soils. However, soils can become partially saturated with changes in weather, changes in groundwater levels, and the absorption of water by plant roots. Hence, it is necessary to study the strength behavior of partially saturated soils. The shear vane test is an experiment that determines the undrained shear strength of clay soils. This test may be performed in the laboratory or at the site. The present research investigates the effect of liquidity index (LI), plasticity index (PI), and saturation degree of the soil on its undrained shear strength obtained from the shear vane test. According to the results, an increase in the LI and a decrease in the PL of the soil decrease its undrained shear strength. Furthermore, studies show that a rise in the degree of saturation decreases the shear strength obtained from the shear vane test.

Keywords: liquidity index, plasticity index, shear strength, unsaturated soil

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Authors: Soner Guler, Demet Yavuz, Fuat Korkut

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Synthetic fibers are commonly used in many civil engineering applications because of its some superior characteristics such as non-corrosive and cheapness. This study presents the results of experimental study on compressive strength of synthetic fiber reinforced concretes. Two types of polyamide (PA) synthetic fiber with the length of 12 and 54 mm are used for this study. The fiber volume ratio is kept as 0.25%, 0.75%, and 0.75% in all mixes. The plain concrete compressive strength is 36.2 MPa. The test results clearly show that the increase in compressive strength for synthetic fiber reinforced concretes is significant. The greatest increase in compressive strength is 23% for PA synthetic fiber reinforced concretes with 0.75% fiber volume.

Keywords: synthetic fibers, polyamide fibers, fiber volume, compressive strength

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Authors: Mohammad Jan-Nataj Zeinab, Kahrizi Sedighe, Bayat Noshin, Giti Torkaman

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According to the importance of the back extensor muscle strength in postmenopausal women, this study aimed to determine the relationship between strength and changes in the thickness of back extensor muscles during isometric contraction in healthy and osteoporotic postmenopausal women. Strength and thickness of the muscles of 42 postmenopausal women were measured respectively, using a handheld dynamometer and ultrasonography. Also, the Pearson correlation coefficient was used to analyze the relationship between the strength and thickness. The results indicated a high reproducibility dynamometer test and ultrasonography. The decrease of strength in people with osteoporosis, occurred more through changes in muscle structure such as reducing the number and size of muscle fibers than changes in the nervous system part.

Keywords: back extensor muscles, strength, thickness, osteoporosis

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Authors: Ahmed A.D. Sarhan, Chong Feng Duan, Mum Wai Yip, M. Sayuti

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Rapid Prototyping (RP) technologies enable physical parts to be produced from various materials without depending on the conventional tooling. Fused Deposition Modeling (FDM) is one of the famous RP processes used at present. Tensile strength and compressive strength resistance will be identified for different sample structures and different layer orientations of ABS rapid prototype solid models. The samples will be fabricated by a FDM rapid prototyping machine in different layer orientations with variations in internal geometrical structure. The 0° orientation where layers were deposited along the length of the samples displayed superior strength and impact resistance over all the other orientations. The anisotropic properties were probably caused by weak interlayer bonding and interlayer porosity.

Keywords: building orientation, compression strength, rapid prototyping, tensile strength

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Authors: E. Mello, C. Ribellato, E. Mohamedelhassan

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This study investigated the improvement in concrete properties with addition of cellulose, steel, carbon and PET fibers. Each fiber was added at four percentages to the fresh concrete, which was moist-cured for 28-days and then tested for compressive, flexural and tensile strengths. Changes in strength and increases in cost were analyzed. Results showed that addition of cellulose caused a decrease between 9.8% and 16.4% in compressive strength. This range may be acceptable as cellulose fibers can significantly increase the concrete resistance to fire, and freezing and thawing cycles. Addition of steel fibers to concrete increased the compressive strength by up to 20%. Increases 121.5% and 80.7% were reported in tensile and flexural strengths respectively. Carbon fibers increased flexural and tensile strengths by up to 11% and 45%, respectively. Concrete strength properties decreased after the addition of PET fibers. Results showed that improvement in strength after addition of steel and carbon fibers may justify the extra cost of fibers.

Keywords: concrete, compressive strength, fibers, flexural strength, tensile strength

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Authors: Ghada Diaa, Enas A. Khattab

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Ultra High Strength Concrete (UHSC) is a new advanced concrete that is being transferred from laboratory researches to practicable applications. In addition to its excellent durability properties, UHSC has high compressive and tensile strengths, and high modulus of elasticity. Despite of this low degree of hydration, ultra high strength values can be achieved by controlling the mixture proportions. In this research, an experimental program was carried out to investigate the shear behavior of ultra high strength concrete beams. A total of nine beams were tested to determine the effect of different parameters on the shear behavior of UHSC beams. The parameters include concrete strength, steel fiber volume, shear span to depth ratio, and web reinforcement ratio. The results demonstrated that nominal shear stress at cracking load and at ultimate load increased with the increase of concrete strength or the decrease in shear span-depth ratio. Using steel fibers or shear reinforcement increases the ultimate shear strength and makes the shear behavior more ductile. In this study, a simplified analytical model to calculate the shear strength of UHSC beams is introduced. Shear strength estimated according to the proposed method in this research is in good agreement with the experimental results.

Keywords: ultra high strength, shear strength, diagonal, cracking, steel fibers

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Authors: H. Ahmad Raji, R. Ziaie Moayed, M. A. Nozari

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Xanthan gum (XG) an eco-friendly biopolymer has been recently explicitly investigated for ground improvement approaches. Rheological behavior of this additive strongly depends on electrochemical condition such as pH, ionic strength and also its content in aqueous solution. So, the effects of these factors have been studied in this paper considering various XG contents as 0.25, 0.5, 1, and 2% of water. Moreover, adjusting pH values such as 3, 5, 7 and 9 in addition to increasing ionic strength to 0.1 and 0.2 in the molar scale has covered a practical range of electrochemical condition. The viscosity of grouts shows an apparent upward trend with an increase in ionic strength and XG content. Also, pH affects the polymerization as much as other parameters. As a result, XG behavior is severely influenced by electrochemical settings

Keywords: electrochemical condition, ionic strength, viscosity, xhanthan gum

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