Search results for: embedment strength

Authors: Eun Mi Ryu, Ah Young An, Ji Yeon Kang, Yeong Soo Shin, Hee Sun Kim

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As the number of fire incidents has been increased, fire incidents significantly damage economy and human lives. Especially when high strength reinforced concrete is exposed to high temperature due to a fire, deterioration occurs such as loss in strength and elastic modulus, cracking, and spalling of the concrete. Therefore, it is important to understand risk of structural safety in building structures by studying structural behaviors and rehabilitation of fire damaged high strength concrete structures. This paper aims at investigating rehabilitation effect on fire damaged high strength concrete beams using experimental and analytical methods. In the experiments, flexural specimens with high strength concrete are exposed to high temperatures according to ISO 834 standard time temperature curve. After heated, the fire damaged reinforced concrete (RC) beams having different cover thicknesses and fire exposure time periods are rehabilitated by removing damaged part of cover thickness and filling polymeric mortar into the removed part. From four-point loading test, results show that maximum loads of the rehabilitated RC beams are 1.8~20.9% higher than those of the non-fire damaged RC beam. On the other hand, ductility ratios of the rehabilitated RC beams are decreased than that of the non-fire damaged RC beam. In addition, structural analyses are performed using ABAQUS 6.10-3 with same conditions as experiments to provide accurate predictions on structural and mechanical behaviors of rehabilitated RC beams. For the rehabilitated RC beam models, integrated temperature–structural analyses are performed in advance to obtain geometries of the fire damaged RC beams. After spalled and damaged parts are removed, rehabilitated part is added to the damaged model with material properties of polymeric mortar. Three dimensional continuum brick elements are used for both temperature and structural analyses. The same loading and boundary conditions as experiments are implemented to the rehabilitated beam models and nonlinear geometrical analyses are performed. Structural analytical results show good rehabilitation effects, when the result predicted from the rehabilitated models are compared to structural behaviors of the non-damaged RC beams. In this study, fire damaged high strength concrete beams are rehabilitated using polymeric mortar. From four point loading tests, it is found that such rehabilitation is able to make the structural performance of fire damaged beams similar to non-damaged RC beams. The predictions from the finite element models show good agreements with the experimental results and the modeling approaches can be used to investigate applicability of various rehabilitation methods for further study.

Keywords: fire, high strength concrete, rehabilitation, reinforced concrete beam

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Authors: Esma Gizem Daskiran, Mehmet Mustafa Daskiran, Mustafa Gencoglu

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Textile reinforced cementitious composite (TRCC) is a development of a composite material where textile and fine-grained concrete (matrix) materials are used in combination. These matrices offer high performance properties in many aspects. To achieve high performance, polymer modified fine-grained concretes were used as matrix material which have high flexural strength. In this study, ten latex polymers and ten powder polymers were added to fine-grained concrete mixtures. These latex and powder polymers were added to the mixtures at different rates related to binder weight. Mechanical properties such as compressive and flexural strength were studied. Results showed that latex polymer and redispersible polymer modified fine-grained concretes showed different mechanical performance. A wide range of both latex and redispersible powder polymers were studied. As the addition rate increased compressive strength decreased for all mixtures. Flexural strength increased as the addition rate increased but significant enhancement was not observed through all mixtures.

Keywords: textile reinforced composite, cement, fine grained concrete, latex, redispersible powder

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Authors: Frank Jaksoni Mweta, Nozomu Adachi, Yoshikazu Todaka, Hirokazu Sato, Yuta Sato, Hiromi Miura, Masakazu Kobayashi, Chihiro Watanabe, Yoshiteru Aoyagi

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Advances in the consumption of hydrogen fuel increase demands of high strength steel pipes and storage tanks. However, high strength steels are highly sensitive to hydrogen embrittlement. Because the introduction of hydrogen into steel during the fabrication process or from the environment is unavoidable, it is essential to improve hydrogen embrittlement resistance of high strength steels through microstructural control. In the present study, the heterogeneous nanostructure with a tensile strength of about 1.8 GPa and the homogeneous nanostructure with a tensile strength of about 2.0 GPa of 316LN steels were generated after 92% heavy cold rolling and high-pressure torsion straining, respectively. The heterogeneous nanostructure is composed of twin domains, shear bands, and lamellar grains. The homogeneous nanostructure is composed of uniformly distributed ultrafine nanograins. The influence of heterogeneous and homogenous nanostructures on the hydrogen embrittlement resistance was investigated. The specimen for each nanostructure was electrochemically charged with hydrogen for 3, 6, 12, and 24 hours, respectively. Under the same hydrogen charging time, both nanostructures show almost the same concentration of the diffusible hydrogen based on the thermal desorption analysis. The tensile properties of the homogenous nanostructure were severely affected by the diffusible hydrogen. However, the diffusible hydrogen shows less impact on the tensile properties of the heterogeneous nanostructure. The difference in embrittlement behavior between the heterogeneous and homogeneous nanostructures was elucidated based on the mechanism of the cracks' growth observed in the tensile fractography. The hydrogen embrittlement was suppressed in the heterogeneous nanostructure because the twin domain became an obstacle for crack growth. The homogeneous nanostructure was not consisting an obstacle such as a twin domain; thus, the crack growth resistance was low in this nanostructure.

Keywords: diffusible hydrogen, heterogeneous nanostructure, homogeneous nanostructure, hydrogen embrittlement

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Authors: Sirwan Kamal, Hsein Kew, Hamid Jahromi

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This paper reports results of a study conducted to investigate strength, sorptivity, and permeability under pressure of concrete specimens, cured using a water-based curing compound. The specimens are treated with waterproofing admixtures or surface treatments to enhance performance while exposed to water. Four types of concrete specimens were prepared in the laboratory, Portland cement (CEM I), Portland-fly ash (CEM II/A-V), Blast-furnace cement (CEM III) and Portland-silica fume (CEM II/A-D). Concrete cubes were de-molded three hours after casting, and sprayed with a curing compound. Admixtures were added to the mix during batching, whereas surface treatments were applied on concrete after 28 days. Compressive strength test was carried out to assess the efficiency of curing compound to develop required strength. In addition, sorptivity and permeability tests were conducted to evaluate the performance of treated specimens with respect to water ingress. Results show that strength development in specimens cured with curing compound achieved up to 96% and 90% at 7 and 28 days respectively, compared to cubes cured in water. Moreover, specimens treated with waterproofing admixtures or surface treatments materials characterized by hydrophobic impregnation considerably reduced water penetration compared to untreated control cubes. On the other hand, cubes treated with admixtures or surface treatments materials characterized by crystalline effect were ineffective in reducing water penetration.

Keywords: admixtures, concrete, curing compound, surface treatments

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Authors: Ali Jahanfar, Brajesh Dubey, Bahram Gharabaghi, Saber Bayat Movahed

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Ever increasing population growth of major urban centers and environmental challenges in siting new landfills have resulted in a growing trend in design of mega-landfills some with extraordinary heights and dangerously steep slopes. Landfill failure mobility risk analysis is one of the most uncertain types of dynamic rheology models due to very large inherent variabilities in the heterogeneous solid waste material shear strength properties. The waste flow of three historic dumpsite and two landfill failures were back-analyzed using run-out modeling with DAN-W model. The travel distances of the waste flow during landfill failures were calculated approach by taking into account variability in material shear strength properties. The probability distribution function for shear strength properties of the waste material were grouped into four major classed based on waste material compaction (landfills versus dumpsites) and composition (high versus low quantity) of high shear strength waste materials such as wood, metal, plastic, paper and cardboard in the waste. This paper presents a probabilistic method for estimation of the spatial extent of waste avalanches, after a potential landfill failure, to create maps of vulnerability scores to inform property owners and residents of the level of the risk.

Keywords: landfill failure, waste flow, Voellmy rheology, friction coefficient, waste compaction and type

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Authors: Joseph Mwiti Marangu, Joseph Karanja Thiong'o, Jackson Muthengia Wachira

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The mechanical performance of hydrated cements mortars mainly depends on its compressive strength and setting time. These properties are crucial in the construction industry. Pozzolana based cements are mostly characterized by low 28 day compressive strength and long setting times. These are some of the major impediments to their production and diverse uses despite numerous technological and environmental benefits associated with them. The study investigated the effects of potential chemical activators on calcined clay- Portland cement blends with an aim to achieve high early compressive strength and shorter setting times in cement mortar. In addition, standard consistency, soundness and insoluble residue of all cement categories was determined. The test cement was made by blending calcined clays with Ordinary Portland Cement (OPC) at replacement levels from 35 to 50 percent by mass of the OPC to make test cement labeled PCC for the purposes of this study. Mortar prisms measuring 40mmx40mmx160mm were prepared and cured in accordance with KS EAS 148-3:2000 standard. Solutions of Na2SO4, NaOH, Na2SiO3 and Na2CO3 containing 0.5- 2.5M were separately added during casting. Compressive strength was determined at 2rd, 7th, 28th and 90th day of curing. For comparison purposes, commercial Portland Pozzolana cement (PPC) and Ordinary Portland Cement (OPC) were also investigated without activators under similar conditions. X-Ray Florescence (XRF) was used for chemical analysis while X-Ray Diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR) were used for mineralogical analysis of the test samples. The results indicated that addition of activators significantly increased the 2nd and 7th day compressive strength but minimal increase on the 28th and 90th day compressive strength. A relatively linear relationship was observed between compressive strength and concentration of activator solutions up to 28th of curing. Addition of the said activators significantly reduced both initial and final setting time. Standard consistency and soundness varied with increased amount of clay in the test cement and concentration of activators. Amount of insoluble residues increased with increased replacement of OPC with calcined clays. Mineralogical studies showed that N-A-S-H is formed in addition to C-S-H. In conclusion, the concentration of 2 molar for all activator solutions produced the optimum compressive strength and greatly reduced the setting times for all cement mortars.

Keywords: activators, admixture, cement, clay, pozzolana

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Authors: Sujit Kumar Sinha, Madan Lal Regar

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Sewing thread plays an important role in the transformation of a two-dimensional fabric into a three-dimensional garment. The interaction of the sewing thread with the fabric at the seam not only influences the appearance of a garment but also its performance. Careful selection of sewing thread and associated parameters can only help in improvement. Over the years, ring spinning has been dominating the yarn market. In the pursuit of improvement to challenge its dominance alternative technology has also been developed. But no real challenge has been posed by the any of the developed spinning systems. Eli-Twist spinning system can be a new method of yarn manufacture to provide a product with improved mechanical and physical properties with respect to the conventional ring spun yarn. The system, patented by Suessen has gained considerable attention in the recent times. The process of produces a two-ply compact yarn with improved fiber utilization. It produces a novel structure combining all advantages of condensing and doubling. In the present study, sewing threads of three different counts each from cotton, polyester and polyester/cotton (50/50) blend were produced on a ring and Eli-Twist systems. A twist multiplier of 4.2 was used to produce all the yarns. A comparison of hairiness, tensile strength and coefficient of friction with conventional ring yarn was made. Eli-Twist yarn has shown better frictional characteristics, better tensile strength and less hairiness. The performance of the Eli-Twist sewing thread has also been found to be better than the conventional 2-ply sewing thread. The performance was estimated through seam strength, seam elongation and seam efficiency of sewn fabric. Eli-Twist sewing thread has shown less friction, less hairiness, and higher tensile strength. Eli-Twist sewing thread resulted in better seam characteristics in comparison to conventional 2-ply sewing thread.

Keywords: ring spun yarn, Eli-Twist yarn, sewing thread, seam strength, seam elongation, seam efficiency

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Authors: Z. Abdollahnejad, M. Kheradmand, F. Pacheco-Torgal

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The use of bio-based admixtures on construction materials is a recent trend that is gaining momentum. However, to our knowledge, no studies have been reported concerning the use of biopolymers on hybrid cement based mortars. This paper reports experimental results regarding the study of the influence of mix design of 43 hybrid cement mortars containing two different biopolymers on its mechanical performance. The results show that the use of the biopolymer carrageenan is much more effective than the biopolymer xanthan concerning the increase in compressive strength. An optimum biopolymer content was found.

Keywords: waste reuse, fly ash, waste glass, hybrid cement, biopolymers, mechanical strength

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Authors: Justin Zhengjie Tan, Yang Zhao

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Adiabatic Rapid Passage, a popular method of achieving population inversion, is studied in a Rabi dimer model in the presence of noise which acts as a dissipative environment. The integration of the multi-Davydov D2 Ansatz into the time-dependent variational framework enables us to model the intricate quantum system accurately. By influencing the system with a driving field strength resonant with the energy spacing, the probability of adiabatic rapid passage, which is modelled after the Landau Zener model, can be derived along with several other observables, such as the photon population. The effects of a dissipative environment can be reproduced by coupling the system to a common phonon mode. By manipulating the strength and frequency of the driving field, along with the coupling strength of the phonon mode to the qubits, we are able to control the qubits and photon dynamics and subsequently increase the probability of Adiabatic Rapid Passage happening.

Keywords: quantum electrodynamics, adiabatic rapid passage, Landau-Zener transitions, dissipative environment

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Authors: M. Shannag, A. Charif, S. Naser, F. Faisal, A. Karim

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Structural lightweight concrete is used primarily to reduce the dead-load weight in concrete members such as floors in high-rise buildings and bridge decks. With given materials, it is generally desired to have the highest possible strength/unit weight ratio with the lowest cost of concrete. The work presented herein is part of an ongoing research project that investigates the properties of concrete mixes containing locally available Scoria lightweight aggregates and mineral admixtures. Properties considered included: workability, unit weight, compressive strength, and splitting tensile strength. Test results indicated that developing structural lightweight concretes (SLWC) using locally available Scoria lightweight aggregates and specific blends of silica fume and fly ash seems to be feasible. The stress-strain diagrams plotted for the structural LWC mixes developed in this investigation were comparable to a typical stress-strain diagram for normal weight concrete with relatively larger strain capacity at failure in case of LWC.

Keywords: lightweight concrete, scoria, stress, strain, silica fume, fly ash

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Authors: Yuling Xu, Haibo Wang, Dong Xie

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A photopolymerizable dimethacrylamide was synthesized and copolymerized with the selected (meth)acrylates. The polymerization rate, degree of conversion, gel time, and compressive strength of the formed neat resins were investigated. The results show that in situ photo-polymerization of the synthesized dimethacrylamide with comonomers having an electron-withdrawing and/or acrylate group dramatically increased the polymerization rate, degree of conversion, and compressive strength. On the other hand, an electron-donating group on either carbon-carbon double bond or the ester linkage slowed down the polymerization. In contrast, the triethylene glycol dimethacrylate-based system did not show a clear pattern. Both strong hydrogen-bonding between (meth)acrylamide and organic acid groups may be responsible for higher compressive strengths. Within the limitation of this study, the photo-polymerization of dimethacrylamide can be greatly accelerated by copolymerization with monomers having electron-withdrawing and/or acrylate groups. The monomers with methacrylate group can significantly reduce the polymerization rate and degree of conversion.

Keywords: photopolymerization, dimethacrylamide, the degree of conversion, compressive strength

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Authors: S. A. Naeini, M. Hamidzadeh

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Today, with the daily advancement of geotechnical engineering on soil improvement and modification of the physical properties and shear strength of soil, it is now possible to construct structures with high-volume and high service load on loose sandy soils. One of such methods is using micropiles, which are mostly used to control asymmetrical subsidence, increase bearing capacity, and prevent soil liquefaction. This study examined the improvement of Anzali's saturated loose silty sand using 192 micropiles with a length of 8 meters and diameter of 75 mm. Bandar-e Anzali is one of Iran's coastal populated cities which are located in a high-seismicity region. The effects of the insertion of micropiles on prevention of liquefaction and improvement of subsidence were examined through comparison of the results of Standard Penetration Test (SPT) and Plate Load Test (PLT) before and after implementation of the micropiles. The results show that the SPT values and the ultimate bearing capacity of silty sand increased after the implementation of the micropiles. Therefore, the installation of micropiles increases the strength of silty sand improving the resistance of soil against liquefaction.

Keywords: soil improvement, silty sand, micropiles, SPT, PLT, strength

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Authors: Mbugua R. N., Salim R. W., Ndambuki J. M.

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Natural admixtures provide concrete with enhanced properties but their processing end up making them very expensive resulting in increase to cost of concrete. In this study the effect of Gum from Acacia Karroo (GAK) as set-retarding admixture in cement pastes was studied. The possibility of using GAK as water reducing admixture both in cement mortar concrete was also investigated. Cement pastes with different dosages of GAK were prepared to measure the setting time using different dosages. Compressive strength of cement mortars with 0.7, 0.8 and 0.9% weight of cement and w/c ratio of 0.5 were compared to those with water cement (w/c) ratio of 0.44 but same dosage of GAK. Concrete samples were prepared using higher dosages of GAK (1, 2 and 3\% wt of cement) and a water bidder (w/b) of 0.61 were compared to those with the same GAK dosage but with reduced w/b ratio. There was increase in compressive strength of 9.3% at 28 days for cement mortar samples with 0.9% dosage of GAK and reduced w/c ratio.

Keywords: compressive strength, Gum Acacia Karroo, retarding admixture, setting time, water-reducing admixture

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Authors: Khandaker Fariha Ahmed, Md. Noman Munshi, Tarin Sultana, Md. Zoynul Abedin

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Suitability number (SN) is perhaps one of the most important parameters of coarse-grained soil in assessing its appropriateness to use as a backfill in retaining structures, sand compaction pile, Vibro compaction, and other similar foundation and ground improvement works. Though determined in an empirical manner, it is imperative to study SN to understand its relation with other aggregate properties like fineness modulus (FM), and strength and density properties of sandy soil. The present paper reports the findings of the study on the examination of the properties of sandy soil, as mentioned. Random numbers were generated to obtain the percent fineness on various sieve sizes, and fineness modulus and suitability numbers were predicted. Sand samples were collected from the field, and test samples were prepared to determine maximum density, minimum density and shear strength parameter φ against particular fineness modulus and corresponding suitability number Five samples of SN value of excellent (0-10) and three samples of SN value fair (20-30) were taken and relevant tests were done. The data obtained from the laboratory tests were statistically analyzed. Results show that with the increase of SN, the value of FM decreases. Within the SN value rated as excellent (0-10), there is a decreasing trend of φ for a higher value of SN. It is found that SN is dependent on various combinations of grain size properties like D10, D30, and D20, D50. Strong linear relationships were obtained between SN and FM (R²=.0.93) and between SN value and φ (R²=.94). Correlation equations are proposed to define relationships among SN, φ, and FM.

Keywords: density, fineness modulus, shear strength parameter, suitability number

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Authors: Przemyslaw Brzyski, Stanislaw Fic

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Hydrated lime, because of the life cycle (return to its natural form as a result of the setting and hardening) has a positive environmental impact. The lime binder is used in mortars. Lime is a slow setting binder with low mechanical properties. The aim of the study was to evaluate the possibility of improving the properties of the lime binder by using different pozzolanic materials as partial replacement of hydrated lime binder. Pozzolan materials are the natural or industrial waste, so do not affect the environmental impact of the lime binder. The following laboratory tests were performed: the analysis of the physical characteristics of the tested samples of lime mortars (bulk density, porosity), flexural and compressive strength, water absorption and the capillary rise of samples and consistency of fresh mortars. As a partial replacement of hydrated lime (in the amount of 10%, 20%, 30% by weight of lime) a metakaolin, silica fume, and zeolite were used. The shortest setting and hardening time showed mortars with the addition of metakaolin. All additives noticeably improved strength characteristic of lime mortars. With the increase in the amount of additive, the increase in strength was also observed. The highest flexural strength was obtained by using the addition of metakaolin in an amount of 20% by weight of lime (2.08 MPa). The highest compressive strength was obtained by using also the addition of metakaolin but in an amount of 30% by weight of lime (9.43 MPa). The addition of pozzolan caused an increase in the mortar tightness which contributed to the limitation of absorbability. Due to the different surface area, pozzolanic additives affected the consistency of fresh mortars. Initial consistency was assumed as plastic. Only the addition of silica fume an amount of 20 and 30% by weight of lime changed the consistency to the thick-plastic. The conducted study demonstrated the possibility of applying lime mortar with satisfactory properties. The features of lime mortars do not differ significantly from cement-based mortar properties and show a lower environmental impact due to CO₂ absorption during lime hardening. Taking into consideration the setting time, strength and consistency, the best results can be obtained with metakaolin addition to the lime mortar.

Keywords: lime, binder, mortar, pozzolan, properties

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Authors: Yasir Ali, Zain Ul Abdin, Muhammad Wisal Khattak

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Nowadays various advanced techniques are used to enhance the performance of materials in the field of construction engineering. Structures exposed to an aggressive, humid and hostile environment are experiencing severe negative impacts which lead to premature failure. Polyester resin is one of the advanced material used for improving performance of structural materials especially for repair/ refurbish purpose of structures and protection from contaminated environmental effect/ hazards. This study investigated the aptness of the polyester resin as coating agent on the mortar and assessed its performance in an ambient environment of Pakistan. Cubical specimens of mortar were fabricated. These specimens were tested for water absorption and compressive strength after one day and sixty days. These tests were performed under different exposure conditions (ambient environment and submerged in water). The specimens were coated with one, two and three layers and results were compared to control (no/ zero resin layer) specimens. Test results indicated that there is a significant decrease in water absorption of mortar coated with resin when compared to controlled specimens. The compressive strength test results revealed that resin coated specimen had higher strength when compared to controlled specimens. The results suggested that resin is a promising material and can be used effectively in structures which are exposed to high temperatures. The study would be helpful in improving performance of the structural material in a hazardous environment.

Keywords: ambient environment, coating, mortar, polyester resin

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Authors: Mustafa Kaya

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In this study, the effect of pre-stressed strand diameters, providing the beam-to-column connections, was investigated from both experimental, and analytical aspects. In the experimental studies, the strength, stiffness, and energy dissipation capacities of the precast specimens comprising two pre-stressed strand samples of 12.70 mm, and 15.24 mm diameters, were compared with the reference specimen. The precast specimen with strands of 15.24 mm reached 96% of the maximum strength of the reference specimen; the amount of energy dissipated by this specimen until end of the test reached 48% of the amount of energy dissipated by the reference sample, and the stiffness of the same specimen at a 1.5% drift of reached 77% of the stiffness of the reference specimen at this drift. Parallel results were obtained during the analytical studies from the aspects of strength, and behavior, but the initial stiffness of the analytical models was lower than that of the test specimen.

Keywords: precast beam to column connection, moment resisting connection, post tensioned connections, finite element method

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Authors: M. Murmu, Govardhan, J. Satya Eswari

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Concrete is the most common and widely used building material. Concrete is basically made of aggregates, both fine and coarse, glued by a cement paste which is made of cement and water. Each one of these constituents of concrete has a negative environmental impact and gives rise to different sustainability issues. The current concrete construction practice is unsustainable because, not only it consumes enormous quantities of stones, sand, and drinking water, but also one billion tons a year of cement, which is not an environment friendly material. Preventing the reduction of natural resources and enhancing the usage of waste materials has become a challenge to the scientist and engineers. A number of studies have been conducted concerning the protection of natural resources, prevention of environmental pollution and contribution to the economy by using this waste material. This paper outlines the influence of Ground Granulated Blast furnace Slag (GGBS) as partial replacement of fine aggregate on mechanical properties of concrete. The strength of concrete is determined having OPC binder, replaced the fine aggregate with15%, 30%, 45% respectively. For this purpose, characteristics concrete mix of M25 with partial replacement of cement with GGBS is used and the strength of concrete cubes and cylinder have determined. The strength of concrete specimens has been compared with the reference specimen. Also X-ray diffraction (XRD) and scanning electron microscope (SEM) tests have been performed to examine the hydration products and the microstructure of the tested specimens. A correlation has been established between the developmental strength concrete with and without GGBS through analysis of hydration products and the microstructure.

Keywords: GGBS, sand, concrete, workability

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Authors: Ayad Salih Sabbar, Amin Chegenizadeh, Hamid Nikraz

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Utilizing waste materials in civil engineering applications has a positive influence on the environment by reducing carbon dioxide emissions and issues associated with waste disposal. Granulated blast furnace slag (GBFS) is a by-product of the iron and steel industry, with millions of tons of slag being annually produced worldwide. Slag has been widely used in structural engineering and for stabilizing clay soils; however, studies on the effect of slag on sandy soils are scarce. This article investigates the effect of slag content on shear strength parameters through direct shear tests and unconsolidated undrained triaxial tests on mixtures of Perth sand and slag. For this purpose, sand-slag mixtures, with slag contents of 2%, 4%, and 6% by weight of samples, were tested with direct shear tests under three normal stress values, namely 100 kPa, 150 kPa, and 200 kPa. Unconsolidated undrained triaxial tests were performed under a single confining pressure of 100 kPa and relative density of 80%. The internal friction angles and shear stresses of the mixtures were determined via the direct shear tests, demonstrating that shear stresses increased with increasing normal stress and the internal friction angles and cohesion increased with increasing slag. There were no significant differences in shear stresses parameters when slag content rose from 4% to 6%. The unconsolidated undrained triaxial tests demonstrated that shear strength increased with increasing slag content.

Keywords: direct shear, shear strength, slag, UU test

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Authors: Dhara Shah, Chandrakant Shah

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Construction industry utilizes plenty of water in the name of curing. Looking at the present scenario, the days are not so far when all construction industries will have to switch over to an alternative-self curing system, not only to save water for sustainable development of the environment but also to promote indoor and outdoor construction activities even in water scarce areas. At the same time, curing is essential for the development of proper strength and durability. IS 456-2000 recommends a curing period of 7 days for ordinary Portland cement concrete, and 10 to 14 days for concrete prepared using mineral admixtures or blended cements. But, being the last act in the concreting operations, it is often neglected or not fully done. Consequently, the quality of hardened concrete suffers, more so, if the freshly laid concrete gets exposed to the environmental conditions of low humidity, high wind velocity and high ambient temperature. To avoid the adverse effects of neglected or insufficient curing, which is considered a universal phenomenon, concrete technologist and research scientists have come up with curing compounds. Concrete is said to be self-cured, if it is able to retain its water content to perform chemical reaction for the development of its strength. Curing compounds are liquids which are either incorporated in concrete or sprayed directly onto concrete surfaces and which then dry to form a relatively impermeable membrane that retards the loss of moisture from the concrete. They are an efficient and cost-effective means of curing concrete and may be applied to freshly placed concrete or that which has been partially cured by some other means. However, they may affect the bond between concrete and subsequent surface treatments. Special care in the choice of a suitable compound needs to be exercised in such circumstances. Curing compounds are generally formulated from wax emulsions, chlorinated rubbers, synthetic and natural resins, and from PVA emulsions. Their effectiveness varies quite widely, depending on the material and strength of the emulsion.

Keywords: curing methods, self-curing compound, compressive strength, modulus of elasticity, durability

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Authors: Zhuomin Zou, Thijs Van Landeghem, Elke Gruyaert

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Using supplementary cementitious materials, such as blast-furnace slag and limestone, to replace cement clinker is a promising method to reduce the carbon emissions from cement production. To efficiently use slag and limestone, it is necessary to carefully select the particle size distribution (PSD) of the binders. This study investigated the effects of the PSD of binders on the performance of slag-limestone ternary cement. The Portland cement (PC) was prepared by grinding 95% clinker + 5% gypsum. Based on the PSD parameters of the binders, three types of ternary cements with a similar overall PSD were designed, i.e., NO.1 fine slag, medium PC, and coarse limestone; NO.2 fine limestone, medium PC, and coarse slag; NO.3. fine PC, medium slag, and coarse limestone. The binder contents in the ternary cements were (a) 50 % PC, 40 % slag, and 10 % limestone (called high cement group) or (b) 35 % PC, 55 % slag, and 10 % limestone (called low cement group). The pure PC and binary cement with 50% slag and 50% PC prepared with the same binders as the ternary cement were considered as reference cements. All these cements were used to investigate the mortar performance in terms of workability, strength at 2, 7, 28, and 90 days, carbonation resistance, and non-steady state chloride migration resistance at 28 and 56 days. Results show that blending medium PC with fine slag could exhibit comparable performance to blending fine PC with medium/coarse slag in binary cement. For the three ternary cements in the high cement group, ternary cement with fine limestone (NO.2) shows the lowest strength, carbonation, and chloride migration performance. Ternary cements with fine slag (NO.1) and with fine PC (NO.3) show the highest flexural strength at early and late ages, respectively. In addition, compared with ternary cement with fine PC (NO.3), ternary cement with fine slag (NO.1) has a similar carbonation resistance and a better chloride migration resistance. For the low cement group, three ternary cements have a similar flexural and compressive strength before 7 days. After 28 days, ternary cement with fine limestone (NO.2) shows the highest flexural strength while fine PC (NO.3) has the highest compressive strength. In addition, ternary cement with fine slag (NO.1) shows a better chloride migration resistance but a lower carbonation resistance compared with the other two ternary cements. Moreover, the durability performance of ternary cement with fine PC (NO.3) is better than that of fine limestone (NO.2).

Keywords: limestone, particle size distribution, slag, ternary cement

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Authors: H. I. Beloufa, M. Tarfaoui

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For many applications, adhesively bonded assemblies have gained an increasing interest in the industry due to several advantages over welding, riveting and bolting, such as reduction of stress concentrations, lightness, low cost and easy manufacturing. This work is largely concerned to show the effects of the loading rate of the adhesively bonded joints under different speed rates. The tensile tests were conducted at four different rates; static (5mm/min, 50mm/min) and dynamic tests (1m/s, and 10m/s). An attempt was made to determine the damage kinetic and a comparison between the use of aluminium and composite laminate substrates is introduced. Aluminum T6082 and glass/vinylester laminated composite Substrates were used to construct aluminum/aluminum and laminate/laminate specimens. The adhesive used in this study was Araldite 2015. The results showed the effects of the loading rate évolution on the double joint strength. The comparison of the results of static and dynamic tests showed a raise of the strength of the specimens while the load velocity is elevated. In the case of composite substrates double joint lap, the stiffness increased by more than 60% between static and dynamic tests. However, in the case of aluminum substrates, the rigidity improved about 28% from static to moderately high velocity loading. For both aluminum and composite double joint lap, the strength increased by approximately 25% when the tensile velocity is increased from 5 mm/min to 50 mm/min (static tests). Nevertheless, the tensile velocity is extended to 1m/s the strength increased by 13% and 25% respectively for composite and aluminum substrates.

Keywords: adhesive, double lap joints, static and dynamic behavior, tensile tests

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Authors: Rama Shanker, Anil Kumar Sachan

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Basic ingredients of concrete are cement, fine aggregate, coarse aggregate and water. To produce a concrete of certain specific properties, optimum proportion of these ingredients are mixed. The important factors which govern the mix design are grade of concrete, type of cement and size, shape and grading of aggregates. Concrete mix design method is based on experimentally evolved empirical relationship between the factors in the choice of mix design. Basic draw backs of this method are that it does not produce desired strength, calculations are cumbersome and a number of tables are to be referred for arriving at trial mix proportion moreover, the variation in attainment of desired strength is uncertain below the target strength and may even fail. To solve this problem, a lot of cubes of standard grades were prepared and attained 28 days strength determined for different combination of cement, fine aggregate, coarse aggregate and water. An artificial neural network (ANN) was prepared using these data. The input of ANN were grade of concrete, type of cement, size, shape and grading of aggregates and output were proportions of various ingredients. With the help of these inputs and outputs, ANN was trained using feed forward back proportion model. Finally trained ANN was validated, it was seen that it gave the result with/ error of maximum 4 to 5%. Hence, specific type of concrete can be prepared from given material properties and proportions of these materials can be quickly evaluated using the proposed ANN.

Keywords: aggregate proportions, artificial neural network, concrete grade, concrete mix design

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Authors: Malik Shoeb Ahmad

Abstract:

The aim of the present study is to carry out investigations on Class F fly ash obtained from NTPC thermal power plant, Dadri, U.P. (India) and electroplating waste sludge from Aligarh, U.P. (India) along with geofibre for its subsequent utilization in various geotechnical and highway engineering applications. The experimental studies such as California bearing ratio (CBR) tests were carried out to evaluate the strength of plain fly ash as well as fly ash-waste sludge mix reinforced with geofibre, as the CBR value is the vital parameters used in the design of flexible and rigid pavements. Results of the study show that the strength of the mix is highly dependent on the curing period and the sludge and geofibre content. The CBR values were determined for mix containing fly ash (83.5-93.5%), waste sludge (5-15%) and 1-2% geofibre. However, out of the various combinations of mixes the CBR value of the mix 88.5%FA+10%S+1.5%GF at 28 days of curing was found to be 53.52% when compared with the strength of plain fly ash. It has been observed that the fibre inclusion increases the strength of the plain fly ash and fly ash-waste sludge specimens by changing their brittle to ductile behavior. The TCLP leaching test was also conducted to determine the heavy metal concentration in the optimized mix. The results of TCLP test show that the heavy metal concentration in the mix 88.5%FA+10%S+1.5%G at 28 days of curing reduced substantially from 24 to 98% when compared with the concentration of heavy metals in the waste sludge collected from source. It has also been observed that the pH of the leachate of this mix is between 9-11, which ensures the proper stabilization of the heavy metals present in the mix. Hence, this study will certainly help in mass scale utilization of two industrial wastes viz., electroplating waste and fly ash, which are causing pollution to the environment to a great extent.

Keywords: Dadri fly ash, geofibre, electroplating waste sludge, CBR, TCLP

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

Abstract:

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, pozolanic efficiency ratio

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Authors: Erma Desmaliana, Saptahari Sugiri

Abstract:

Limited availability of solid timber in large dimensions becomes a problem. The demands of timbers in Indonesia is more increasing compared to its supply from natural forest. It is associated with the issues of global warming and environmental preservation. The uses of timbers from HTI (Industrial Planting Forest) and HTR (Society Planting Forest), such as Jabon, is an alternative source that required to solve these problems. Having shorter lifespan is the benefit of HTI/HTR timbers, although they are relatively smaller in dimension and lower in strength. Engineering Wood Product (EWP) such as glulam (glue-laminated) timber, is required to overcome their losses. Glulam is fabricated by gluing the wooden planks that having a thickness of 20 to 45 mm with an adhesive material and a certain pressure. Glulam can be made a curved beam, is one of the advantages, thus making it strength is greater than a straight beam. This paper is aimed to know the material behavior of curved glue-laminated beam of Jabon timber. Preliminary methods was to gain physical and mechanical properties, and glue spread strength of Jabon timber, which following the ASTM D-143 standard test method. Dimension of beams were 50 mm wide, 760 mm span, 50 mm thick, and 50 mm rise. Each layer of Jabon has a thickness of 5 mm and is glued with polyurethane. Cold press will be applied to beam laminated specimens for more than 5 hours. The curved glue-laminated beams specimens will be tested about the bending behavior. This experiments aims to obtain the increasing of load carrying capacity and stiffness of curved glulam beam.

Keywords: curved glulam beam, HTR&HTI, load carrying, strength

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Authors: Erdoğan Özbay, Hakan T. Türker, Müzeyyen Balçıkanlı, Mohamed Lachemi

Abstract:

In this paper, the effects of fiber types and elevated temperatures on compressive strength, modulus of rapture and the bond characteristics of fiber reinforced concretes (FRC) are presented. By using the three different types of fibers (steel fiber-SF, polypropylene-PPF and polyvinyl alcohol-PVA), FRC specimens were produced and exposed to elevated temperatures up to 800 ºC for 1.5 hours. In addition, a plain concrete (without fiber) was produced and used as a control. Test results obtained showed that the steel fiber reinforced concrete (SFRC) had the highest compressive strength, modulus of rapture and bond stress values at room temperatures, the residual bond, flexural and compressive strengths of both FRC and plain concrete dropped sharply after exposure to high temperatures. The results also indicated that the reduction of bond, flexural and compressive strengths with increasing the exposed temperature was relatively less for SFRC than for plain, and FRC with PPF and PVA.

Keywords: bond stress, compressive strength, elevated temperatures, fiber reinforced concrete, modulus of rapture

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Authors: Daniel Y. Abebe, Jaehyouk Choi

Abstract:

There are several types of metal-based devices conceived as dampers for the seismic energy absorber whereby damages to the major structural components could be minimized for both new and existing structures. This paper aimed to develop and evaluate structural performance of slit circular shear panel damper for passive seismic energy protection by inelastic deformation. Structural evaluation was done using commercially available nonlinear FE simulation program. The main parameters considered are: diameter-to-thickness (D/t) ratio and slit length-to-width ratio (l/w). Depending on these parameters three different buckling modes and hysteretic behaviors were found: yielding prior to buckling without strength degradation, yielding prior to buckling with strength degradation, and yielding with buckling and strength degradation which forms pinching at initial displacement. The susceptible location at which the possible crack is initiated is also identified for selected specimens using rupture index.

Keywords: slit circular shear panel damper, hysteresis characteristics, slip length-to-width ratio, D/t ratio, FE analysis

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Authors: Yared Assefa Demessie

Abstract:

This study may help to establish the appropriateness of ceramic waste aggregate for concrete production since it is obviously understood that the rising from continuous urbanization and industrialization development leads depletion of natural construction resource and the disposal of waste material. It can be used as base to conduct a study on the alternative readily available materials like ceramic industrial waste aggregates can lead to environmental concrete. The study assessed the fresh and hardened properties of the concrete produced by replacing part of the natural fine aggregate with an aggregate produced from ceramic industrial waste. In the study, experimental investigation was employed which involved two major tasks: material specifications and experimental evaluation of concrete were done in the laboratory. Experimental investigations such that workability, unit weight, compressive strength test, tensile strength test and flexural strength test for C-25 concrete mixes with different percentages of ceramic industrial waste aggregate after a curing period of 7 and 28 days has done and interpreted the result statically using mean, standard deviation and coefficient of variance.

Keywords: ceramic industrial waste, fresh concrete, hardened concrete, fine aggregate

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Authors: Joseph Shanks, Matthew Taylor, Foong Kiew Ooi, Chee Keong Chen

Abstract:

Introduction: Evidences of relationship between bone, muscle and standard of competition among young British population is limited in literature. The current literature recognises the independent and synergistic effects of fat free and fat mass as the stimulus for osteogenesis. This study assessed the extent to which physical activity (PA) and standard of competition (CS) influences quantitative ultrasound (QUS) measurements of bone on a cross-sectional basis accounting for muscular strength and anthropometrics in British young males. Methods: Pre-screening grouped 66 males aged 18-25 years into controls (n=33) and district level athletes (DLAs) (n=33) as well as low (n=21), moderate (n=23) and high (n=22) physical activity categories (PACs). All participants underwent QUS measurements of bone (4 sites, i.e. dominant distal radius (DR), dominant mid-shaft tibia (DT), non-dominant distal radius (NR) and non-dominant mid-shaft tibia (NT)), isokinetic strength tests (dominant and non-dominant knee flexion and extension) and anthropometric measurements. Results: There were no significant differences between any of the groups with respect to QUS measurements of bone at all sites with regards to PACs or CS. Significant higher isokinetic strength values were observed in DLAs than controls (p < 0.05), and higher than low PACs (p < 0.05) at 60o.s-1 of concentric and eccentric measurements. No differences in subcutaneous fat thickness were found between all the groups (CS or PACs). Percentages of body fat were significantly higher (p < .05) in low than high PACs and CS groups. There were significant positive relationships between non dominant radial speed of sound and fat free mass at both DR (r=0.383, p=0.001) and NR (r=0.319, p=0.009) sites in all participants. Conclusion: The present study findings indicated that muscular strength and body fat are closely related to physical activity level and standard of competition. However, bone health status reflected by quantitative ultrasound (QUS) measurements of bone is not related to physical activity level and standard of competition in British young males.

Keywords: bone, muscular strength, physical activity, standard of competition

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