Techno Press
Tp_Editing System.E (TES.E)
Login Search


acc
 
CONTENTS
Volume 11, Number 2, February 2021
 


Abstract
Investigations on the dynamic behavior of concrete members, incorporating steel fibers with different aspect ratios, are limited so far and do not covered comprehensively in prior studies. Present endeavor is devoted to examine the dynamic response of the steel fibrous concrete beams and slabs under the influence of impact loading. These members were reinforced with steel fibers in different length of 25 mm and 50 mm. Four concrete mixes were designed and used based on the proportion of long and short fibers. Twenty-four slabs and beams were fabricated with respect to the concrete mix and these specimens were tested in impact load experiment. Testing observations revealed that the maximum dynamic deflection or ductility of the member can be achieved with increasing the fiber length. Structural behavior of the tested structures was predicted using nonlinear finite element analysis with specific material constitutive relationships. Eight nodes plate elements have been considered in the present dynamic analysis. Dynamic fracture energy of the members was calculated and agreement ratio, of more than 70%, was noticed between the experimental and analysis outcomes.

Key Words
concrete beams; concrete slabs; steel fibrous concrete; impact loading; nonlinear dynamic analysis; fracture energy

Address
James H. Haido: Civil Engineering Department, College of Engineering, University of Duhok, Kurdiatn Region, Iraq
Ayad A. Abdul-Razzak: Department of Civil Engineering, College of Engineering, University of Mosul, Iraq
Mustafa M. Al-Tayeb: School College of Applied Engineering and Urban Planning, University of Palestine, Gaza, Palestine
B.H. Abu Bakar: School of Civil Engineering, University Sains Malaysia, Penang, Malaysia
Salim T. Yousif: Department of Civil Engineering, AL-Qalam University College, Iraq
Bassam A. Tayeh: Civil Engineering Department, The Islamic University of Gaza, Gaza, Palestine

Abstract
Slag blended concrete is widely used as a mineral admixture in the modern concrete industry. This study shows an optimization process that determines the optimal mixture of air-entrained slag blended concrete considering carbonation durability, frost durability, CO2 emission, and materials cost. First, the aim of optimization is set as total cost, which equals material cost plus CO2 emission cost. The constraints of optimization consist of strength, workability, carbonation durability with climate change, frost durability, range of components and component ratio, and absolute volume. A genetic algorithm is used to determine optimal mixtures considering aim function and various constraints. Second, mixture design examples are shown considering four different cases, namely, mixtures without considering carbonation (Case 1), mixtures considering carbonation (Case 2), mixtures considering carbonation coupled with climate change (Case 3), and mixtures of high strength concrete (Case 4). The results show that the carbonization is the controlling factor of the mixture design of the concrete with ordinary strength (the designed strength is 30MPa). To meet the challenge of climate change, stronger concrete must be used. For high-strength slag blended concrete (design strength is 55MPa), strength is the control factor of mixture design.

Key Words
slag; carbonation; frost; service life; durability; low-CO2 concrete; sustainability; optimal design

Address
Xiao-Yong Wang: Department of Architectural Engineering, Kangwon National University, Chuncheon-Si, Korea; Department of Integrated Energy and Infra System, Kangwon National University, Chuncheon-Si, Korea
Han-Seung Lee: Department of Architectural Engineering, Hanyang University, Ansan-Si, Korea

Abstract
Concrete cracking due to brittle tension strength significantly prevents fully utilization of the materials for "flexuralshear failure" type shear walls. Theoretical and experimental studies applying fiber reinforced concrete (FRC) have achieved fruitful results in improving the seismic performance of "flexural-shear failure" reinforced concrete shear walls. To come to an understanding of an optimal design strategy and find common performance prediction method for design methodology in terms to FRC shear walls, seismic performance on shear walls with PVA and steel FRC at edge columns and plastic region are compared in this study. The seismic behavior including damage mode, lateral bearing capacity, deformation capacity, and energy dissipation capacity are analyzed on different fiber reinforcing strategies. The experimental comparison realized that the lateral strength and deformation capacity are significantly improved for the shear walls with PVA and steel FRC in the plastic region and PVA FRC in the edge columns; PVA FRC improves both in tensile crack prevention and shear tolerance while steel FRC shows enhancement mainly in shear resistance. Moreover, the tensile strength of the FRC are suggested to be considered, and the steel bars in the tension edge reaches the ultimate strength for the confinement of the FRC in the yield and maximum lateral bearing capacity prediction comparing with the model specified in provisions.

Key Words
shear wall; fiber; seismic performance; cyclical test; seismic behavior; edge column

Address
Hongmei Zhang and Zhiyuan Chen: College of Civil Engineering and Architecture, Zhejiang University, Hangzhou, 310058, China

Abstract
In this study, twenty-five geopolymer (GP) mixes were prepared by varying the alkaline solids to Metakaolin (MK) and sodium silicate to NaOH ratios from 0.1 to 0.5 and 0.2 to 1.0, respectively, thus giving a wide range of molar ratios of silica to alumina, sodium oxide to alumina and water to sodium oxide. The compressive strength of these GP mixes was determined for four curing schemes involving oven curing at 100oC for 24 h and three ambient curing with the curing ages of 3, 14, and 28 days. The test results revealed that for the manufacture of GP binder for structural applications of strength up to 90 MPa, the molar ratio of silica to alumina should be greater than 2.3, sodium oxide to alumina should be between 0.6 to 1.2, and water to sodium oxide should not exceed 12. The compressive strength of ambient cured GP mortar gets stabilized at 28 days of ambient curing. Experimental findings were also corroborated by GP microstructure analysis. The embodied energy of MK-based GP mortars, especially of high strength, is significantly less than the cement mortar of equivalent strength.

Key Words
metakaolin; geopolymer; compressive strength; microstructure; molar ratios; embodied energy

Address
Aref A. Abadel, Abdulrahman S. Albidah, Ali H. Altheeb, Fahed A. Alrshoudi, Husain Abbas and Yousef A. Al-Salloum: Chair of Research and Studies in Strengthening and Rehabilitation of Structures, Dept. of Civil Engineering, College of Engineering, King Saud University, P.O. Box 800, Riyadh 11421, Saudi Arabia

Abstract
This study is a basic research for evaluating the buildability of cementitious materials for three-dimensional (3D) printing. In the cement paste step, the thixotropy behavior according to the resting time, which represents the time interval between each layer, was analyzed. In addition, the relationship between the thixotropy behavior and 3D concrete printing buildability was derived by proposing a measurement method that simulates the 3D concrete printing buildup process. The analysis of the tendency of the thixotropy behavior according to the resting time revealed that the area of the hysteresis loop (AHyst) showed a tendency to increase and then converge as the resting time increased, which means hysteresis loop approach critical resting time for sufficient buildability. In the thixotropy behavior analysis that simulates the 3D concrete printing buildup process, the buildup ratio, which is the recovery rate of the shear stress, showed a tendency to increase and then converge as the resting time increased, which are similar results like hysteresis loop. It was concluded that AHyst and the buildup ratio can be used as parameters for determining the resting time, and they have close relationships with 3D concrete printing buildability.

Key Words
3D printing; buildability; thixotropy; resting time; cementitious material; rheology

Address
Keon-Woo Lee: Institute of Gas Safety R&D, Korea Gas Safety Corporation, Chungbuk Jinchun, Republic of Korea
Myoung Sung Choi: Department of Civil and Environmental Engineering, Dankook University, Gyeonggido Jukjeon-ro 152, Republic of Korea

Abstract
The major shortcoming of concrete in most of the applications is its high self-weight and thermal conductivity. The emerging trend to overcome these shortcomings is the use of foam-concrete, which is a lightweight concrete consisting of cement, filler, water and a foaming agent. This study aims at the development of a cost-effective high-volume fly-ash foamconcrete insulation wall cladding for existing buildings using natural fiber like rice straw in different proportions. The paper reports the results of systematic studies on various mechanical, acoustic, thermal and durability properties of foam-concrete with and without replacement of cement by fly-ash. Fly-ash replaces 60 percent by weight of cement in foam-concrete. The watersolid ratio of 0.3, the filler ratio of 1:1 by weight, and the density of 1100 kg/m3 (approx.) are fixed for all the mixes. Rice straw at 1%, 3% and 5% by weight of cement was added to improve the thermal and acoustic efficiency. From the investigations, it was inferred that the strength properties were increased with fly-ash replacement up to 1% rice straw addition. In furtherance, addition of rice straw and fly-ash resulted in improved acoustic and thermal properties.

Key Words
foam-concrete; wall cladding; strength properties; thermal properties; acoustic properties; durability

Address
Amritha Raj, Dhanya Sathyan and K.M. Mini: Department of Civil Engineering, Amrita School of Engineering, Coimbatore, Amrita Vishwa Vidyapeetham, India

Abstract
This paper studies the effect of using multi-scale reinforcement additives on mechanical strengths, damage performance, microstructure, and water absorption of cementitious composites. Small dosages of carbon nanotubes (CNTs) or polypropylene (PP) microfibers; 0.05%, 0.1%, and 0.2% by weight of cement; were added either separately or simultaneously into cement mortar. The experimental results show the ability of these additives to enhance the mechanical behavior of the mortar. The best improvement in compressive and flexural strengths of cement mortar reaches 28% in the case of adding a combination of 0.1% CNTs and 0.2% PP fibers for compression, and a combination of 0.2% CNTs and 0.2% PP fibers for flexure. Adding CNTs does not change the brittle mode of failure of plain mortar whereas the presence of PP fibers changes it into ductile failure and clearly enhances the fracture energy of the specimens. Scanning electron microscopic (SEM) images of the fracture surfaces highlights the role of CNTs in improving the adhesion between the PP fibers and the hydration products and thus enhance the ability of the fibers to mitigate cracks propagation and to enhance the mechanical performance of the mortar.

Key Words
carbon nanotubes; polypropylene fibers; cement mortar; strength; damage

Address
Mohammad R. Irshidat, Nasser Al-Nuaimi and Mohamed Rabie: Center for Advanced Materials (CAM), Qatar University, P.O. Box 2713, Doha, Qatar

Abstract
The main objective of this work is to contribute to the valorization of plastic and glass waste in the improvement of concrete properties. Waste glass after grinding was used as a partial replacement of the cement with a percentage of 15%. The plastic waste was cut and introduced as fibers with 1% by the total volume of the mixture. Mechanical and durability tests were conducted for various mixtures of concrete as compressive and flexural strengths, water absorption, ultrasonic pulse velocity, and acid attack. Also, other in-depth analyses were performed on samples of each variant such as X-ray diffraction (XRD), thermogravimetric analysis (DSC-TGA), and scanning electron microscope (SEM). The results show that the addition of glass powder or plastic fibers or a combination of both in concrete improved in the compression and flexural strengths in the long term. The highest compressive strength was obtained in the mix which combines the two wastes about 26.72% of increase compared to the control concrete. The flexural strength increased in the mixture containing the glass powder. Therefore, the mixture with two wastes exhibits better resistance to aggressive sulfuric acid attack, and incorporating glass powder improves the ultrasonic pulse velocity.

Key Words
mechanical; durability; concrete; waste glass; plastic waste

Address
Houssam Eddine Abdelli: Research Unit of Emergent Materials, University Ferhat Abbas Setif 1, 19000 Algeria
Larbi Mokrani: Department of Civil Engineering, University Ferhat Abbas Setif 1, 19000 Algeria
Salim Kennouche: Department of Civil Engineering, University of Bouira, 10001 Algeria
J.L. Barroso de Aguiar: University of Minho, C-TAC Research Centre, Guimaraes 4800-058, Portugal


Techno-Press: Publishers of international journals and conference proceedings.       Copyright © 2021 Techno-Press
P.O. Box 33, Yuseong, Daejeon 34186 Korea, Tel: +82-2-736-6800 (SCS, EAS, WAS, ANR) +82-42-828-7995 (GAE, SEM, SSS, CAC) Fax : +82-2-736-6801, Email: info@techno-press.com