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CONTENTS
Volume 9, Number 3, March 2020
 

Abstract
Raw perlite is a volcanic alumino-silicate and is used as aggregate in the construction industry. The high silica and alumina contained in the raw perlite allows the production of geopolymer mortar with the help of alkaline solutions. In this study, different geopolymer mortars are obtained by mixing ground perlite (GP), sodium hydroxide (NaOH), water and CEN standard sand and the strength and microstructure of these mortars are investigated. Mortar specimens are placed in the oven 24 hours after casting and kept at different temperatures and times, then the specimens are cured under laboratory conditions until the day of strength tests. After curing, unit weight, ultrasound pulse velocity, flexural and compressive strengths are determined. Experimental results indicate that the mechanical properties of the mortars enhance with increasing oven-curing period and temperatures as well as increasing NaOH molarity. In addition, SEM/EDS and XRD analyses are performed on the mortar specimens and the results are interpreted.

Key Words
geopolymer; ground perlite; oven curing; mortar; strength; microstructure

Address
Serhat Celikten: Department of Civil Engineering, Nevsehir Haci Bektas Veli University, Nevsehir, Turkey
Burak Isikdag: Porsuk Vocational School, Eskisehir Technical University, Eskisehir, Turkey

Abstract
Progressive collapse in a structure occurs when load bearing members are failed and the adjoining structural elements cannot resist the redistributed forces and fails subsequently, that leads to complete collapse of structure. Recently, construction using precast concrete technology is adopted increasingly because it offers many advantages like faster construction, less requirement of skilled labours at site, reduced formwork and scaffolding, massive production with reduced amount of construction waste, better quality and better surface finishing as compared to conventional reinforced concrete construction. Connections are the critical elements for any precast structure, because in past, major collapse of precast structure took place because of connection failure. In this study, behavior of four different precast wet connections with U shaped reinforcement bars provided at different locations is evaluated. Reduced 1/3rd scale precast beam column assemblies having two span beam and three columns with removed middle column are constructed and examined by performing experiments. The response of precast connections is compared with monolithic connection, under column removal scenario. The connection region of test specimens are filled by cast-in-place micro concrete with and without polypropylene fibers. Performance of specimen is evaluated on the basis of ultimate load carrying capacity, maximum deflection at the location of removed middle column, crack formation and failure propagation. Further, Finite element (FE) analysis is carried out for validation of experimental studies and understanding the performance of structural components. Monolithic and precast beam column assemblies are modeled using non-linear Finite Element (FE) analysis based software ABAQUS. Actual experimental conditions are simulated using appropriate boundary and loading conditions. Finite Element simulation results in terms of load versus deflection are compared with that of experimental study. The nonlinear FE analysis results shows good agreement with experimental results.

Key Words
precast concrete; wet connection; progressive collapse; U-shaped reinforcement; nonlinear finite element analysis; concrete damage plasticity

Address
Digesh D. Joshi, Paresh V. Patel, Husain M. Rangwala and Bhautik G. Patoliya: Civil Engineering Department, School of Engineering, Institute of Technology, Nirma University, Sarkhej-Gandhinagar Highway, Ahmedabad - 382481, Gujarat, India

Abstract
This paper aims at investigating the effect of crumb rubber size and content on compressive behaviors of concrete under axial compression. Concrete specimens are designed and produced by replacing natural aggregate with crumb rubber content of 0%, 5%, 10%, 15% and three different sized crumb rubbers (No. 20, No. 40, No. 80 crumb rubber). And the failure mode, compressive strength, elastic modulus, stress-strain curves, peak strain and ultimate strain are experimentally studied. Based on the test results, formulas have been presented to determine the compressive strength, elastic modulus, the relationship between prism compressive strength and cube compressive strength, stress-strain curves and peak strain of crumb rubber concrete (CRC). It is found that the proposed formulas agree well with the test result on the whole, which may be used to practical applications.

Key Words
crumb rubber; concrete; stress-strain; axial compression; compressive strength

Address
Rui Ren: School of Civil Engineering, Xi\'an University of Architecture & Technology, Xi\'an 710055, China; State Key Laboratory of Green Building in Western China, Xi\'an University of Architecture & Technology, Xi\'an 710055, China
Jiong-Feng Liang, Da-wei Liu, Jin-he Gao and Lin Chen: School of Civil & Architecture Engineering, East China University of Technology, Nanchang 330013, China

Abstract
Many failures of concrete structures are related to steel corrosion. For this reason, it is important to recognize how the carbonation can affect the durability of reinforced concrete structures. The repeatability of the carbonation depth measure in a specimen of concrete sprayed with a phenolphthalein solution is consistently low whereby it is necessary to have an impartial method to measure the carbonation depth. This study presents two automatic algorithms to detect the non-carbonated zone in concrete specimens. The first algorithm is based solely on digital processing image (DPI), mainly morphological and threshold techniques. The second algorithm is based on artificial intelligence, more specifically on an array of Kohonen networks, but also using some DPI techniques to refine the results. Moreover, another algorithm was developed with the purpose of measure the carbonation depth from the image obtained previously.

Key Words
carbonation; concrete; phenolphthalein; Kohonen network; artificial intelligence; image processing

Address
Christian C. Ruiz, Jose L. Caballero, Juan H. Martinez and Willian A. Aperador: Department of Mechatronic Engineering, Universidad Militar Nueva Granada, Carrera 11 #101-80, Colombia

Abstract
This paper reports on the result of an experimental investigation carried out to study the compressive strength and sorptivity properties of blended cement concrete exposed to 5% and 10% MgSO4 solution using fly ash (FA) and silpozz. Usually in sulphate environment the minimum grade of concrete is M30 and the mix design is done for target mean strength of 39 MPa. Silpozz is manufactured by burning of agro-waste rice husk in designed furnace in between 600o to 700oC which is one of the main agricultural residues obtained from the outer covering of rice grains during the milling process. There are four mix series taken with control mix. The control mix made 0% replacement of FA and silpozz with Ordinary Portland Cement (OPC). The first mix series made 0% FA and 10-30% replacement of silpozz with OPC. The second mix series made with 10% FA and 10-40% replacement of silpozz with OPC. The third mix series made 20% FA and 10-30% replacement of silpozz with OPC and the fourth mix series made 30% FA and 10-20% silpozz replaced with OPC. The samples (cubes) are prepared and cured in normal water and 5% and 10% MgSO4 solution for 7, 28 and 90 days. The studied parameters are compressive strength and strength deterioration factor (SDF) for 7, 28 and 90 days. The water absorption and sorptivity tests have been done after 28 days of normal water and magnesium sulphate solution curing. The investigation reflects that the blended cement concrete incorporating FA and silpozz showing better resistance against MgSO4 solution when compared to normal water curing (NWC) samples.

Key Words
blended cement concrete; compressive strength; SDF; sorptivity; water absorption

Address
Trilochan Jena: Department of Civil Engineering, ITER, S

Abstract
This paper focuses on the engineering properties of Bentonite-Cement-Sodium silicate (BCS) grout, which was prepared by partially replacing the ordinary Portland cement in Cement-Sodium silicate grout with lithium bentonite (Li-bent) and sodium bentonite (Na-bent), respectively. The effect of different Water-to-Solid ratio (W/S) and various replacement percentages of bentonite on the apparent viscosity, bleeding, setting time, and early compressive strength of BCS grout were investigated. The XRD method was used to detect its hydration products. The results showed that both bentonites played a positive role in the stability of BCS grout, increased its apparent viscosity. Na-bent prolonged the setting time of BCS, while 5% of Li-bent shortened the setting time of BCS. The XRD analysis indicated that the hydration products between the mixture containing Na-bent and Li-bent did not differ much. Using bentonite as supplementary cementitious material (SCM) to replace partial cement is a promising way to cut down on carbon dioxide emissions and to produce low-cost, eco-friendly, non-toxic, and water-resistant grout. In addition, Li-bent was superior to Na-bent in improving the strength and the thickening of BCS grouts.

Key Words
cement-sodium silicate grout; bentonite; supplementary cementitious materials; global warming; engineering behavior

Address
Yao Zhou, Gui H. Wang and Yong H. Chang: School of Engineering and Technology, China University of Geosciences (Beijing), 29 Xueyuan Road, Haidian District, Beijing 100083, China

Abstract
To investigate the long-term behavior of eccentrically loaded RC columns, which are more realistic in practice than concentrically loaded RC columns, long-term eccentric loading tests were conducted for 10 RC columns. Test parameters included concrete compressive strength, reinforcement ratio, bar yield strength, eccentricity ratio, slenderness ratio, and loading pattern. Test results showed that the strain and curvature of the columns increased with time, and concrete forces were gradually transferred to longitudinal bars due to the creep and shrinkage of concrete. The long-term behavior of the columns varied with the test parameters, and long-term effects were more pronounced in the case of using the lower strength concrete, lower strength steel, lower bar ratio, fewer loading-step, higher eccentricity ratio, and higher slenderness ratio. However, in all the columns, no longitudinal bars were yielded under service loads at the final measuring day. Meanwhile, the numerical analysis modeling using the ultimate creep coefficient and ultimate shrinkage strain measured from cylinder tests gave quite good predictions for the behavior of the columns.

Key Words
reinforced concrete column; long-term behavior; eccentric loading test; creep and shrinkage; minimum reinforcement

Address
Chang-Soo Kim: School of Architecture, Seoul National University of Science and Technology, 232 Gongreung-ro, Nowon-gu, Seoul 01811, Republic of Korea
Yu Gong, Xin Zhang: School of Civil Engineering, Shandong Jianzhu University, Shandong Provincial Key Laboratory of Appraisal and Retrofitting in Building Structures, Fengming Road, Lingang Development Zone, Jinan, Shandong, 250101, P.R. China
Hyeon-Jong Hwang: School of Architecture, Konkuk University, 120 Neungdong-ro, Seoul 05029, Republic of Korea

Abstract
This research deals with the study of the orthotropic vibrational features of single-walled carbon nanotubes according to Kelvin\'s model and to check the accuracy of the models, the results have been compared with earlier modeling/simulations. Obtaining rough approximations of the natural frequencies of CNTs using continuum equations are still a common procedure, even at high harmonics. The effects of different physical and material parameters on the fundamental frequencies are investigated for zigzag and chiral single-walled carbon nanotubes invoking Kelvin\'s theory. By using nonlocal Kelvin\'s model, the fundamental natural frequency spectra for two forms of single-walled carbon nanotubes (SWCNTs) have been calculated. The influence of frequencies with nonlocal parameters and bending rigidity are investigated in detail for these tubes. Computer software MATLAB is utilized for the frequencies of SWCNTs and current results shows a good stability with comparison of other studies.

Key Words
SWCNTs; wave propagation approach; Kelvin Model; bending rigidity

Address
Muzamal Hussain, Muhammad N. Naeem: Department of Mathematics, Govt. College University Faisalabad, 38000, Faisalabad, Pakistan
Abdelouahed Tounsi: Materials and Hydrology Laboratory, Algeria Faculty of Technology Civil Engineering Department, University of Sidi Bel Abbes, Algeria; Department of Civil and Environmental Engineering, King Fahd University of Petroleum & Minerals, 31261 Dhahran, Eastern Province, Saudi Arabia

Abstract
Glass fiber-reinforced polymer (GFRP) bars have been introduced as an effective alternative for the conventional steel reinforcement in concrete structures to mitigate the costly consequences of steel corrosion. However, despite the superior performance of these composite materials in terms of corrosion, the effect of replacing steel reinforcement with GFRP on the seismic performance of concrete structures is not fully covered yet. To address some of the key parameters in the seismic behavior of GFRP-reinforced concrete (RC) structures, two full-scale beam-column joints reinforced with GFRP bars and stirrups were constructed and tested under two phases of loading, each simulating a severe ground motion. The objective was to investigate the effect of damage due to earthquakes on the service and ultimate behavior of GFRP-RC moment-resisting frames. The main parameters under investigation were geometrical configuration (interior or exterior beam-column joint) and joint shear stress. The performance of the specimens was measured in terms of lateral load-drift response, energy dissipation, mode of failure and stress distribution. Moreover, the effect of concrete damage due to earthquake loading on the performance of beamcolumn joints under service loading was investigated and a modified damage index was proposed to quantify the magnitude of damage in GFRP-RC beam-column joints under dynamic loading. Test results indicated that the geometrical configuration significantly affects the level of concrete damage and energy dissipation. Moreover, the level of residual damage in GFRP-RC beam-column joints after undergoing lateral displacements was related to reinforcement ratio of the main beams.

Key Words
GFRP-RC; seismic performance; cyclic loading; beam-column joints; reinforcement ratio; latera load-drift response; interior beam-column joints; exterior beam-columns; damage index

Address
Shervin K. Ghomi and Ehab El-Salakawy: Department of Civil Engineering, University of Manitoba, Winnipeg, Canada

Abstract
Concrete pipes are considered important structures playing integral role in spread of cities besides transportation of gas as well as oil for far distances. Further, concrete structures under seismic load, show behaviors which require to be investigated and improved. Therefore, present research concerns dynamic stress and strain alongside deflection assessment of a concrete pipe carrying water-based nanofluid subjected to seismic loads. This pipe placed in soil is modeled through spring as well as damper. Navier-Stokes equation is utilized in order to gain force created via fluid and, moreover, mixture rule is applied to regard the influences related to nanoparticles. So as to model the structure mathematically, higher order refined shear deformation theory is exercised and with respect to energy method, the motion equations are obtained eventually. The obtained motion equations will be solved with Galerkin and Newmark procedures and consequently, the concrete pipe\'s dynamic stress, strain as well as deflection can be evaluated. Further, various parameters containing volume percent of nanoparticles, internal fluid, soil foundation, damping and length to diameter proportion of the pipe and their influences upon dynamic stress and strain besides displacement will be analyzed. According to conclusions, increase in volume percent of nanoparticles leads to decrease in dynamic stress, strain as well as displacement of structure.

Key Words
dynamic response; soil medium; fluid; damping; nanoparticles

Address
Behrooz Keshtegar: Division of Computational Mathematics and Engineering, Institute for Computational Science, Ton Duc Thang University, Ho Chi Minh City, Viet Nam; Faculty of Civil Engineering, Ton Duc Thang University, Ho Chi Minh City, Viet Nam
Javad Tabatabaei: Department of petroleum engineering and geology, Meymeh branch, Islamic Azad University, Meymeh, Iran
Reza Kolahchi: Institute of Research and Development, Duy Tan University, Da Nang 550000, Viet Nam
Nguyen-Thoi Trung: Division of Computational Mathematics and Engineering, Institute for Computational Science, Ton Duc Thang University, Ho Chi Minh City, Viet Nam; Faculty of Civil Engineering, Ton Duc Thang University, Ho Chi Minh City, Viet Nam


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