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CONTENTS
Volume 11, Number 3, March 2021
 


Abstract
Due to economic and environmental benefits, increasing the substitution ratio of ordinary cement by industry byproducts like fly ash (FA) is one of the best approaches to reduce the impact of the concrete industry on the environment. However, as the substitution rate of FA increases, it will have an adverse impact on the performance of cement-based materials, so the actual substitution rate of FA is limited to around 10-30%. Therefore, in order to increase the early-age strength of high replacement (30-70%) low-calcium ultrafine FA blended cement paste, sodium sulfate and calcium sulfate dihydrate were used to improve the reactivity of FA. The results show that sodium sulfate has a significant enhancement effect on the strength of the composite pastes in the early and late ages, while calcium sulfate dihydrate has only a slight effect in the late ages. The addition of sodium sulfate in the cement-FA blended system can enhance the gain rate of non-evaporation water, and can decrease the Ca(OH)2 content. In addition, when the sulfate chemical activators are added, the ettringite content increases, and the surface of the FA is dissolved and hydrated.

Key Words
high volume fly ash; low-calcium ultrafine fly ash; sodium sulfate; calcium sulfate dihydrate; activation

Address
Baoju Liu, Jinxia Tan, Jinyan Shi: School of Civil Engineering, Central South University, Changsha 410075, China
Hui Liang: School of Civil Engineering, Central South University, Changsha 410075, China; China Light Industry Nanning Design Engineering CO.LTD., Guangxi Nanning 530031, China
Junyi Jiang, Yuanxia Yang: School of Civil Engineering, Central South University, Changsha 410075, China

Abstract
Extensive research has been conducted on the basic mechanical property and structural applications of engineered cementitious composites (ECC). Despite the high tensile ductility and high toughness of ECC, transverse steel reinforcement is still necessary to confine ECC for high performance. However, limited research has examined performance of ECC confined with practical amount of transverse reinforcement. This paper presents the results of axial compression tests on 14 square ECC columns and 4 conventional concrete columns (used as control specimens) with transverse reinforcement. The test variables were spacing, configuration (square ties or square and diamond shape ties), and yield strength of stirrups. The test showed that ECC columns confined with steel stirrup had good compressive ductility, and the stirrup spacing had the greatest effect on the compressive performance. The self-confinement effect of ECC results in a more uniform but slower expansion of the whole column compared with CC ones. The test results are then compared against the predictions from a number of existing models for conventional confined concrete. It is indicated that these models fail to predict the axial strains at peak axial stress and the trend of the stress-strain curve of steel stirrups-confined ECC with sufficient accuracy. Several new equations are then proposed for the compressive properties of steel-confined ECC based on test results and potential approaches for future studies are proposed.

Key Words
columns; compressive behavior; engineered cementitious composite (ECC); steel reinforcement; confinement; stress-strain model

Address
Pan-deng Zheng: School of Civil Engineering, Huaqiao University., Xiamen 361021, China
Zi-xiong Guo: School of Civil Engineering, Huaqiao University., Xiamen 361021, China; Key Laboratory for Structure Engineering and Disaster Prevention of Fujian Province, Xiamen 361021, China
Wei Hou: School of Civil Engineering, Huaqiao University., Xiamen 361021, China; Key Laboratory for Structure Engineering and Disaster Prevention of Fujian Province, Xiamen 361021, China; LETS Holding Group Co., Ltd, Xiamen 361004, China
Guan Lin: Department of Civil and Environmental Engineering, The Hong Kong Polytechnic University, Hong Kong, China

Abstract
This study relates to a production of Quaternary Cement Concrete (QCC) prepared by using Micro Silica (MS), Marble Dust (MD) and Rice Husk Ash (RHA), followed by an investigation towards fresh and hardened properties of blended concrete. A total of 39 mixes were cast by incorporating different percentages of MS (6%, 7% and 8%), MD (5%, 10% and 15%) and RHA (5%, 10%, 15% and 20%) as partial replacement of Ordinary Portland Cement. The workability of fresh concrete was maintained in the range of 100+-25 mm by adding 0.7% of Super Plasticizer in the mix. Optimum mechanical strength was observed at combination of 8% MS+5% MD+10% RHA. Marble dust replacement from 10 to 15% and Rice husk ash replacements from 15 to 20% depicted a substantial reduction in compressive strength at all ages. Durability parameter with respect to water absorption at 28 days shows an increasing trend as the percentage of blending increases.

Key Words
quaternary cement concrete; workability; compressive strength; split tensile strength; flexural strength; water absorption

Address
Ashhad Imam, Shahzad Asghar Moeeni, Vikas Srivastava: Department of Civil Engineering, Vaugh Institute of Agriculture Engineering and Technology, SHUATS, Allahabad 211007, U.P, India
Keshav K Sharma: Department of Civil Engineering, Vaugh Institute of Agriculture Engineering and Technology, SHUATS, Allahabad 211007, U.P, India

Abstract
In recent years, geopolymer cements, have gained significant attention as an environmental-friendly type of cement. In this experimental research, effects of different alkaline activator solutions and variations of associated parameters, including time of addition, concentration, and weight ratio, on the mechanical strengths of Granulated Ground Blast Furnace Slag (GGBFS)-based Geopolymer Concrete (GPC) were investigated. Investigation of the effects of simultaneous usage of KOH and NaOH solutions on the tensile and flexural strengths of GGBFS-based GPC, and the influence of NaOH solution addition time delay on the mechanical strengths is among the novel aspects investigated in this research. four series of mix designs and corresponding specimen testing is conducted to study different parameters of the active alkali solutions on GPC mechanical strengths. The results showed that addition of NaOH to the mix after 3 min of mixing KOH and Na2SiO3 with dry components (1/3 of the total mixing duration) resulted in the highest compressive, tensile and flexural strengths amongst other cases. Moreover, increasing the KOH concentration up to 12 M resulted in the highest compressive strength, while weight ratio of 1.5 for Na2SiO3/KOH was the optimum value to achieve highest compressive strengths.

Key Words
geopolymer concrete; blast furnace slag; KOH; NaOH

Address
Alireza Esparham, Amir Bahador Moradikhou: Young Researchers and Elites Club, Science and Research Branch, Islamic Azad University, Tehran, Iran
Faeze Kazemi Andalib: Department of Inorganic Chemistry, Faculty of Chemistry, Kharazmi University, Tehran, Iran
Mohammad Jamshidi Avanaki: School of Civil Engineering, College of Engineering, University of Tehran, Tehran, Iran

Abstract
The present work aims at investigating the effects of using various fine mineral additions as partial replacement to Portland cement on the tribological properties of concrete. To achieve this goal, concrete mixtures were prepared with different percentages (10, 20 and 30%) of limestone fillers (LF) and natural pozzolana (NP), and (20, 40 and 60%) of blast furnace slag (BFS). The interface yield stress (t0) and viscous constants (n) that allow characterizing friction at the concrete-pipe wall interface were determined using a rotational tribometer. In addition, the compositions of the boundary layers that formed in the pumping pipes of the different concretes under study were also identified and analyzed. The experimental results obtained showed that the concretes studied have a linear tribological behavior that can be described by the Bingham model. Furthermore, the use of different mineral additions, especially limestone fillers and blast furnace slags, even at high rates, had a beneficial effect on the optimization of the volume of paste present in the boundary layer, which made it possible to significantly reduce the viscous constant of concrete. However, a maximum rate of 10% of natural pozzolana was recommended to achieve tribological properties that are favorable to the pumpability of concrete.

Key Words
ecological concrete; interface yield stress; viscous constant; pumpability; mineral additions; boundary layer

Address
Amina Belaidi, Mohammed Amine Boukli Hacene: Department of Civil Engineering, Laboratory EOLE, University of Tlemcen, BP 230-13000 Chetouane Tlemcen, Algeria
El-Hadj Kadri: Department of Civil Engineering, Laboratory L2MGC, University of Cergy-Pontoise, 33, Boulevard du Port, 95011 Cergy-Pontoise, Cedex, France
Omar Taleb: Department of Civil Engineering, Laboratory EOLE, University of Tlemcen, BP 230-13000 Chetouane Tlemcen, Algeria

Abstract
The behavior of concrete containing waste glass as a replacement of cement or aggregate was studied previously in the most of researches, but the present investigation focuses on the recycling of waste glass powder as a substitute for silica fume in high strength concrete (HSC). This endeavor deals with the efficiency of using waste glass powder, as an alternative for silica fume, in the flexural capacity of HSC beam. Thirteen members with dimensions of 0.3 m width, 0.15 m depth and 0.9 m span length were utilized in this work. A comparison study was performed considering HSC members and hybrid beams fabricated by HSC and conventional normal concrete (CC). In addition to the experiments on the influence of glass powder on flexural behavior, numerical analysis was implemented using nonlinear finite element approach to simulate the structural performance of the beams. Same constitutive relationships were selected to model the behavior of HSC with waste glass powder or silica fume to show the matching between the modeling outputs for beams made with these powders. The results showed that the loading capacity and ductility index of the HSC beams with waste glass powder demonstrated enhancing ultimate load and ductility compared with those of HSC specimens with silica fume. The study deduced that the recycled waste glass powder is a good alternative to the pozzolanic powder of silica fume.

Key Words
reinforced concrete beams; waste glass powder; high strength concrete; flexural strength of beam; silica fume; steel fibers

Address
James H. Haido, Marwa A. Zainalabdeen: Department of Civil Engineering, College of Engineering, University of Duhok, Duhok, Kurdistan Region, Iraq
Bassam A. Tayeh: Civil Engineering Department, Islamic University of Gaza, Gaza, Palestine

Abstract
Vibration of protein microtubules is investigated based upon Orthotropic Elastic Shell Model, considering the effect of thermal stresses. The complete analytical formulas of thermal vibration for microtubules are obtained. It is observed that the effects of thermal stresses on the vibrational frequency mode are more significant when the longitudinal and circumferential wave vectors are large enough. But when the length of wave vector reduces to 5 nm, these effects have no significant effects. The present results well agree with the lattice vibrations of microtubules. Moreover, the results show that the effects of thermal stresses due to small change in temperature are not so significant but with the increase in temperature its effects are obvious.

Key Words
microtubules; Hooks law; vibration; orthotropic; thermal stress

Address
Muhammad Taj: Department of Mathematics, University of Azad Jammu and Kashmir, Muzaffarabad, 1300, Azad Kashmir, Pakistan
Mohamed A. Khadimallah: Prince Sattam Bin Abdulaziz University, College of Engineering, Civil Engineering Department, Al-Kharj, 16273, Saudi Arabia; Laboratory of Systems and Applied Mechanics, Polytechnic School of Tunisia, University of Carthage, Tunis, Tunisia
Muzamal Hussain: Research Scholar, Department of Mathematics, Govt. College University Faisalabad, 38000, Faisalabad, Pakistan
Khurram Fareed: Department of Mathematics, University of Azad Jammu and Kashmir, Muzaffarabad, 1300, Azad Kashmir, Pakistan
Muhammad Safeer: Department of Mathematics, University of Azad Jammu and Kashmir, Muzaffarabad, 1300, Azad Kashmir, Pakistan
Khaled Mohamed Khedher: Department of Civil Engineering, College of Engineering, King Khalid University, Abha 61421, Saudi Arabia; Department of Civil Engineering, High Institute of Technological Studies, Mrezgua University Campus, Nabeul 8000, Tunisia
Manzoor Ahmad: Department of Mathematics, University of Azad Jammu and Kashmir, Muzaffarabad, 1300, Azad Kashmir, Pakistan
M. Nawaz Naeem: Research Scholar, Department of Mathematics, Govt. College University Faisalabad, 38000, Faisalabad, Pakistan
Amjad Qazaq: Prince Sattam Bin Abdulaziz University, College of Engineering, Civil Engineering Department, Al-Kharj, 16273, Saudi Arabia
Abdelaziz Al Qahtani: Prince Sattam Bin Abdulaziz University, College of Engineering, Civil Engineering Department, Al-Kharj, 16273, Saudi Arabia
S.R. Mahmoud: GRC Department, Faculty of Applied studies, King Abdulaziz University, Jeddah, Saudi Arabia
Afaf S. Alwabli: Department of Biological Sciences, Faculty of Science, King Abdulaziz University, Jeddah, Saudi Arabia
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

Abstract
In this study, a new understanding is presented on the microcracking behavior of high strength concrete (HSC) with steel fiber addition having prior compressive loading history. Microcracking behavior at critical stress (rcr) region, using seven fiber addition volume of 0.5, 0.75, 1.0, 1.25, 1.5, 1.75, and 2.0% was evaluated, at two aspect ratios (60 and 75). The specimens were loaded up to a specified compressive stress levels (0.70fc–0.96fc), and subsequently subjected to split tensile tests. This was followed by microscopic analyses afterwards. Four compressive stress levels as percentage of fc were selected according to the linearity end point based on stress–time (r-t) diagram under uniaxial compression. It was seen that pre-compression has an effect on the linearity end point as well as fiber addition where it lies within 85-91% of fc. Tensile strength gain was observed in some cases with respect to the 'maiden' tensile strength as oppose to tensile strength loss due to the fiber addition with teething effect. Aggregate cracking was the dominant failure mode instead of bond cracks due to improved matrix quality. The presence of the steel fiber improved the extensive failure pattern of cracks where it changes from 'macrocracks' to a branched network of microcracks especially at higher fiber dosages. The applied pre-compression resulted in hardening effect, but the cracking process is similar to that in concrete without fiber addition.

Key Words
high strength concrete; steel fiber reinforced concrete; loading history; microcracking behavior; uniaxial compression; critical stress

Address
Abdulhameed U. Abubakar: Department of Civil Engineering, Eastern Mediterranean University (EMU), Famagusta North Cyprus, Mersin 10, Turkey; Department of Civil Engineering, Modibbo Adama University of Technology, Yola, Adamawa, Nigeria
Tulin Akcaoglu: Department of Civil Engineering, Eastern Mediterranean University (EMU), Famagusta North Cyprus, Mersin 10, Turkey


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