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CONTENTS
Volume 12, Number 2, August 2021
 


Abstract
Self-compacting concrete used in reinforced concrete structures with high reinforcement ratios such as ports, tall buildings and bridges can bring benefits to the structures. However, the quality of self-compacting concrete is affected by climate conditions and curing methods. Climate conditions are dry and rainy seasons. Curing methods include external and internal curing. External curing by covering the surface of specimens with nylon sheet for zero hour, 4h, 6h and 24h was investigated in this study. Different amounts of lightweight sand to be able to hold water for internal curing were also examined. Results showed that with the combination of internal curing by using 20% lightweight sand to replace traditional sand and external curing by covering with nylon sheet for 24 hours, the compressive strength of self-compacting concrete in the dry season condition is higher than that of self-compacting concrete without lightweight sand ideally cured by soaking under water at laboratory condition.

Key Words
compressive strength; external curing; internal curing; self-compacting concrete

Address
Hung Dinh Nguyen: Department of Civil Engineering, International University-Vietnam National University Ho Chi Minh City, Quarter 6, Linh Trung Ward, Thu Duc District, Ho Chi Minh City, Vietnam
Luu Mai: Department of Civil Engineering, University of Transportation Ho Chi Minh City, No. 2, Vo Oanh Street, Ward 25, Binh Thanh District, Ho Chi Minh City, Vietnam
Hung Thanh Nguyen: Department of Civil Engineering, University of Technology and Education Ho Chi Minh City, No 1 Vo Van Ngan Street, Linh Chieu Ward, Thu Duc District, Ho Chi Minh City, Vietnam

Abstract
This paper introduces the experimental results of the influence of sea sand replacement rate and mixing water on the basic mechanical properties of sea sand concrete. A total of thirty test blocks were designed for uniaxial compression test. In this test two parameters were considered: (a) sea sand replacement ratio (i.e., 0%,25%, 50%,75%, 100%); (b) water for mixing (i.e., freshwater, seawater). The entire stress-strain curve of sea sand concrete under uniaxial compression was obtained. Based on the test results, the influence of sea sand replacement rate and mixing water on the peak stress, peak strain, and deformation performance of sea sand concrete were analyzed. Test results showed that the stress-strain curves of seawater sea sand concrete were steeper than that of ordinary concrete, which indicated that seawater sea sand concrete was slightly more brittle. On the whole, the sea sand replacement rate had no significant effect on the axial compressive properties of sea sand concrete. Under the same sea sand replacement rate, the deformation performance of freshwater sea sand concrete (FSC) was slightly greater than that of seawater sea sand concrete (SSC). Seawater had an enhanced effect on the early strength development of sea sand concrete.

Key Words
entire stress-strain curve; mixing water; sea sand concrete; sea sand replacement ratio; uniaxial compression

Address
Zongping Chen: College of Civil Engineering and Architecture, Guangxi University, Nanning, 530004, China; Key Laboratory of Disaster Prevention and Structure Safety of the Ministry of Education, Guangxi University, Nanning, 530004, China
Linlin Mo, Chunmei Song, Yaqi Zhang: College of Civil Engineering and Architecture, Guangxi University, Nanning, 530004, China

Abstract
In this paper, the effects of angle of Z shape non-persistent joint on the compressive behaviour of joint's bridge area under uniaxial compression load have been investigated. Furtheremore experimental test and Particle flow code in two dimension (PFC2D) have been used. concrete samples with dimension of 50 mmx50 mmx100 mm were prepared. Tensile strength of model material was 1 MPa. Within the specimen, three Z shape non-persistent notches were provided. The notch length was 1.5 cm. when two upper and lower notch have horizontal direction, the middle joint angle were 45o, 90o and 135o. When dips of two upper and lower notch was 90o, the middle joint angle were 45o, 90o and 135o degree. When dips of two upper and lower notch was 135 degree, the middle joint angle were 45o, 90o and 135o. Totally, 9 different configuration systems were prepared for Z shape non-persistent joints. Also, 37 models with different Z shape non-persistent notch angle were prepared in numerical model. The axial load with rate of 0.005 mm/s was applied to the model. Results indicated that the failure process was mostly governed by the Z shape non-persistent joint angle. The compressive strengths of the specimens were related to the fracture pattern and failure mechanism of the discontinuities. In addition it was shown that the compresssive behaviour of discontinuities is depend on the number of the induced tensile cracks which are increased by increasing the middle joint angle. The middle joint has significant effect on the failure pattern. In fixed upper and lower joints angles, when the middle joint angle is 90o the failure stress has maximum value. On the other hand, it has minimum value when the middle joint angle was 135o. In fixed middle joint angle, the samples have minimum value when the upper and lower joints angles are 135o. At the end, the failure pattern and strength results of the experiential tests and the numerical simulations were similar.

Key Words
joint angle; PFC2D; Z shape non-persistent joint

Address
Vahab Sarfarazi: Department of Mining Engineering, Hamedan University of Technology, Hamedan, Iran
Kaveh Asgari: Department of Mining Engineering, Shahid Bahonar University of Kerman, Kerman, Iran
Ali Reza Mahshoori: Department of Mining Engineering, Hamedan University of Technology, Hamedan, Iran

Abstract
In this study, it was aimed to contribute to a more environmentally friendly concrete production by using alternative binders, which are waste or by-products that can be used instead of cement. For this purpose, alkali-activated materials were used, a cleaner production process was supported by reducing the amount of activator, a different production method was preferred to prevent the workability problem caused by dry consistency, and roller compacted concrete was produced. Ground granulated blast furnace slag (GGBFS) and fly ash were used as precursors, and an activator solution prepared by mixing 10 M sodium hydroxide (NaOH) and sodium silicate (Na2SiO3), which has a Na2SiO3/NaOH ratio of 2.5, was used in production of alkali-activated roller compacted concretes. Also, Portland cement roller compacted concrete was produced with the same dosage for comparison purposes. Unit weight, total water absorption, ultrasonic pulse velocity (UPV), modulus of elasticity, abrasion resistance, 7 and 28-d compressive strength values of the alkali-activated RCCs were determined. While the roller compacted concretes produced with fly ash were weaker than Portland cement RCCs in terms of compressive strength, the specimens produced using blast furnace slag have been found to be superior.

Key Words
alkali-activation; blast furnace slag; fly ash; mechanical properties; roller compacted concrete

Address
Ismail Kilic and Saadet Gokce Gok: Department of Civil Engineering, Kirklareli University, Kirklareli, Turkey

Abstract
The Crumb rubber concrete is becoming a new interesting environmental material in the last two decades, which requires research studies on the recovery of local materials using industrial waste. The present paper is devoted to investigate the behavior of concrete made only with dunes sand and an ordinary concrete modified with various weight contents of crumb rubber. The mechanical and physical proporties such us the density, the compressive strength, the relative copmaction and the tension by bending strength of a dune sand concrete and an ordinary concrete modified with differents weight percentage of rubber crumb, 1%, 2%, 3%, 4% and 5% are investigated. The obtained results show that the optimal percentage of the crumb rubber is 3%. In addition, the results indicate that concrete made only with dunes sand has weaker elasticity modulus -54% approximately, and reduced compressive strength -63% compared to the modified ordinary concrete. Consequently, the ordinary concrete mix with crumb rubber and admixture incorporation has proven acceptable performances for the eventual use in the structural elements, however, the dunes sand only aggregate concrete modified by crumb rubber may limit its use in certain structural applications such us pavements borders. Finally, modified ordinary concrete and modified dunes sand are modeled by the finite element method and compared with the experimental results.

Key Words
elasticity modulus; finite elements; materials mechanical behavior; modified concrete; rubber crumb

Address
Amar Mezidi, Ratiba Mitiche Kettab: Department of Civil Engineering, National Polytechnic School of Algiers, Algeria
Hamid Hamli Benzahar: Department of Technology, Faculty of Sciences and Technology, University of Khemis Miliana, Algeria
Mahfoud Touhari: Acoustic and Civil Engineering Laboratory LAGC, Faculty of Sciences and Technology, University of Khemis Miliana, Algeria

Abstract
In this paper, a finite element (FE) simulation has been provided for investigation on thermal post-buckling of geometrically imperfect beams reinforced with graphene oxide powders (GOPs). To this end, a higher-order refined beam theory has been utilized to model the reinforced beam with uniform and non-uniform GOP content. Thus, the employed FE simulation contains a refined beam element in which shear deformations have been considered. Therefore, the degrees of freedom due to both bending and shear displacements have been included. It is also considered that the beam is in thermal environment leading to the thermal buckling at elevated temperatures. The first buckling mode shape of the beam has been considered as the geometrically imperfect configuration. The calculated post-buckling loads of a GOP-reinforced beam are shown to be dependent on several factors including graphene oxide volume, graphene oxide distribution, geometry imperfectness and also center deflection.

Key Words
finite element method; graphene oxide powders; post-buckling; refined beam theory; thermal load

Address
Qingying Liu and Jiangping Ma: School of Architecture and Artistic Design, Xi'an Peihua University, Xi'an 710125, Shaanxi, China

Abstract
In this study, different types of metabentonite (MB) and slag (S)-based geopolymer were produced based on origin, polyvinyl alcohol (PVA) and basalt (B) fiber at different percentages of 0.2%, 0.4%, and 0.6%. A total of 7 series were produced. Two steps of curing method were applied for the samples, the first step was at room temperature from day 1-7, and the second step freezing-thawing from 8-28 days. Thus, the applicability of a curing method that used less energy instead of heat curing was investigated. Due to the freezing-thawing curing, the continuation of geopolymerization reactions was ensured and a compact structure was created. The produced samples were subjected to 10% sulfuric acid effect for 3 months after the 28th day. Compressive strength, flexural strength, ultrasonic pulse velocity (UPV), and weight losses due to acid effects were found. Despite the decrease in mechanical properties after the acid effect, the geopolymer products didn't experience easy dispersal because they had strong aluminosilicate bonds, crystalline phase formation, morphology, and lower calcium content that provided high stability. Also, SEM, XRD, FT-IR, and TGA-DTA analyzes and visual inspection resulting from the acid effect were examined.

Key Words
basalt fiber; freezing-thawing; geopolymer; metabentonite; PVA fiber; slag; sulfuric acid

Address
Yurdakul Aygörmez: Civil Engineering Department, Yildiz Technical University, Davutpasa Campus, Istanbul, Turkey

Abstract
A new model with the combination of the Galerkin's technique have been developed for functionally graded cylindrical shell. For the vibrations of rotating cylindrical shells, three volume fraction laws i.e., polynomial, trigonometric and exponential are combined mathematically. The obtained results show that by increasing length-to-radius and height-to-radius ratios, the backward and forward frequency value decreases and increases, respectively. Moreover, on increasing the rotating speed, the backward frequencies increases and forward frequencies decreases. The results generated furnish the evidence regarding applicability of present model with clamped-clamped boundary conditions and also verified by earlier published literature.

Key Words
clamped-clamped; frequency response; rotating speed; volume fraction laws

Address
Mohamed Amine Khadimallah: Department of Mathematics, Govt. College University Faisalabad, 38040, Faisalabad, Pakistan;
Laboratory of Systems and Applied Mechanics, Polytechnic School of Tunisia, University of Carthage, Tunis, Tunisia
Muzamal Hussain: Department of Mathematics, Govt. College University Faisalabad, 38040, Faisalabad, Pakistan
Faisal Al-Thobiani: Marine Engineering Department, Faculty of Maritime Studies, King Abdulaziz University, Jeddah, Saudi Arabia
Mohamed Elbahar: Prince Sattam Bin Abdulaziz University, College of Engineering, Civil Engineering Department, BP 655, Al-Kharj, 16273, Saudi Arabia
Abdullah F. Al Naim: Department of Physics, College of Science, King Faisal University, P.O. Box 400,Al-Ahsa 31982, Saudi Arabia
Elaloui Elimame: Laboratory of Materials Applications in Environment, Water and Energy LR21ES15, Faculty of Sciences, University of Gafsa, Tunisia
Imene Harbaoui: Laboratory of Applied Mechanics and Engineering LR-MAI, University Tunis EI Manar-ENIT BP37- Le belvedere, 1002, Tunis
Abdelouahed Tounsi: YFL (Yonsei Frontier Lab), Yonsei University, Seoul, Korea; Department of Civil and Environmental Engineering, King Fahd University of Petroleum & Minerals, 31261 Dhahran, Eastern Province, Saudi Arabia


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