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CONTENTS
Volume 28, Number 1, July 2021
 


Abstract
The stress-strain curve of concrete under a uniaxial compression can reflect much information about its mechanical properties. This paper performs an experimental study and modeling on the stress-strain curve of concrete subjected to external sulfate attack (ESA). To shorten the experimental period, cement mortar specimen (CMS) with a small size is selected as research objected, and is immersed into purified water, 2.5% and 5.0% Na2SO4 solution. First, an economic test equipment is designed by adding rigid elements to ordinary hydraulic testing machine. Second, the evolution of stress-strain curve and mechanical properties of sulfate-corroded CMS with immersion time is obtained. Based on least-square method, the expressions of two chemical damage parameters are determined to respectively characterize the time-varying elastic modulus and compression strength of CMS caused by ESA. Then, a coupling chemo-mechanical damage constitutive model for sulfatecorroded CMS is established by introducing the chemical damage parameters. Finally, the numerical solution of the model is presented, and is validated by the above experimental data of stress-strain curve of CMS.

Key Words
cement mortar; chemical damage; constitutive model; mechanical properties; stress-strain curve; sulfate attack

Address
Guang-Ji Yin: Department of Civil Engineering, School of Civil and Transportation Engineering, Ningbo University of Technology, Ningbo 315211, P.R. China
Xiao-Bao Zuo: Department of Civil Engineering, School of Science, Nanjing University of Science & Technology, Nanjing 210094, P.R. China
Xiao-Dong Wen: Department of Civil Engineering, School of Civil and Transportation Engineering, Ningbo University of Technology, Ningbo 315211, P.R. China
Yu-Juan Tang: Department of Building Materials, School of Civil Engineering, Yangzhou Ploytechnic College, Yangzhou 225009, P.R. China

Abstract
In this paper, Elasto-Damage model previously proposed by Khan and Zahra for natural aggregates concrete is reformulated to capture the behavior of recycle aggregate concrete (RAC) subjected to uniaxial compressive stress state. The compressive stress-strain relationship was investigated through existing published data for different recycled coarse aggregate (RCA) with replacement percentages of 0%, 30%, 50%, 70% and 100%. Use of recycled aggregate concrete has been advocated widely to be one of the solution for the global issue of depletion of natural resources while fulfilling the needs of material and structural performance required in reinforced-concrete structures. The adoption of RAC in construction industry requires development of appropriate constitutive models that can be implemented in software based on finite element method to predict the reliable results. The proposed model uses four parameters; a, b and r which helps to predict the different behavior of concrete in tension and compression while the fourth parameter critical energy release rate (Rc) controls the damage growth rate. These parameters are defined as a function of concrete compressive strength (fc') and its initial elastic modulus (Eo). The model is validated through existing test results for uniaxial compressive state of stress and it was concluded that it predicts better post cracking and post peak-behaviour of RAC as compared to the commercially available models for the conventional concrete.

Key Words
concrete; constitutive modelling; Elasto-damage; recycled aggregate concrete; uniaxial compression

Address
Fatima Khalid, Asad-ur-Rehman Khan and Shamsoon Fareed: Department of Civil Engineering, NED University of Engineering & Technology, Karachi - 75270, Pakistan

Abstract
Experimental and numerical methods were used to investigate the relationship between point load index and mode II fracture toughness of granite. A punch-through shear test was used to measure the mode II fracure toughness of granite. Point load test was performed to measured the point load index of jointed granite. Three granite samples with dimension of 20 mmx150 mmx40 mm consisting parallel non-persisent joint were prepared in the laboratory for punch test. Also six recangular specimen with echelon joint was prepared for point load test. Cuncurrent with experimental tests, numerical simulations have been done for punch test by PFC2D and poin load test by PFC3D. Numerical model for punch test has dimension of 100 mmx120 mm. similar to those for joints configuration systems in the experimental test, three models with different rock bridge lengths were prepared. Also, numerical model for point load test has dimension of 100 mmx100 mmx40 mm. six models consisting non-persistent joint were prepared. The punch testing results showed that the failure process was mostly governed by the rock bridge lengh. The shear strengths of the specimens were related to the fracture pattern and failure mechanism of the discontinuities. It was shown that the shear behaviour of discontinuities is related to the number of the induced tensile cracks which are increased by increasing the rock bridge length. The strength of samples decreases by increasing the joint length. The point load testing results showed that the tensile cracks initiate beneath the loading cone and propagates through the intact rock till coalescence with notch tips. The value of point load index has close relationship with mode II fracture toughness obtained by punch test. The failure pattern and failure load are similar in both methods i.e., the experimental testing and the numerical simulation methods.

Key Words
PFC2D & PFC3D; point load test; punch-through shear test; rock bridge

Address
V. Sarfarazi: Department of Mining Engineering, Hamedan University of Technology, Hamedan, Iran
Kaveh Asgari: Department of Mining Engineering, Shahid Bahonar University of Kerman, Kerman, Iran
A.A. Naderi: Hamedan University of Technology, Hamedan, Iran

Abstract
In this paper, new analytical formulations, which can be easily applied to normal and high-strength concretes under monotonic compressive and direct tensile loads, are proposed. Moreover, plastic damage model for concrete under uniaxial cyclic loading is also employed by introducing a simple damage function. The majority of published material models focuses on a certain type of concrete based on their testing results, which can be hardly applied to other types of concrete such as normal or high strength concrete. This paper presents a novel approach that can be applied to different types of concrete and highlights that the differences among testing results may come from the variations of strain at the peak stress. The damage phenomenon of concrete is simplified by a non-linear degradation of elastic modulus function, which in turn creates a linear stress-strain relation under cyclic loading. The damage function can be easily and quickly used to calibrate concrete properties for plastic damage model, which is very useful for industrial applications. Finally, the accuracy and pre-eminence of the proposed damage model are verified through comparison with experimental data and analytical solutions.

Key Words
damage function; high-strength concrete; stress-strain relation; uni-axial cyclic compression and tension

Address
Trong Nghia-Nguyen, Thanh Cuong-Le: Faculty of Civil Engineering, Ho Chi Minh City Open University, Ho Chi Minh City, Vietnam
Samir Khatir: Department of Electrical energy, Metals, Mechanical constructions and systems, Faculty of Engineering and Architecture, Ghent University,9000 Gent, Belgium
Magd Abdel Wahab: CIRTech Institute, Ho Chi Minh City University of Technology (HUTECH), Ho Chi Minh City, Vietnam; Laboratory Soete, Ghent University, Belgium

Abstract
Engineered Geopolymer Composites has proved to be an excellent eco-friendly strain hardening composite materials, as well as, it exhibits high tensile strain capacity. An intelligent computing tool based predictive model to anticipate the compressive strength of ductile geopolymer composites would help various researchers to analyse the material type and its contents; the dosage of fibers; producing tailor-made materials; less time consumption; cost-saving etc., which could suit for various infrastructural applications. This paper attempts to develop a suitable ANN based machine learning model in predicting the compressive strength of strain hardening geopolymer composites with greater accuracy. A simple ANN network with a various number of hidden neurons have been trained, tested and validated. The results revealed that with seventeen inputs and one output parameters respectively for mix design & compressive strength and thirteen hidden neurons in its layer have provided the notable prediction with R2 as 96% with the RMSE of 2.64. It is concluded that a simple ANN model would have the perspective of estimating the compressive strength properties of engineered geopolymer composite to an accuracy level of more than 90%. The sensitivity analysis of ANN model with 13-hidden neurons, also confirms the accuracy of prediction of compressive strength.

Key Words
ANN; artificial intelligence; compressive strength; engineered geopolymer composites; machine learning; neural networks; prediction; strain-hardening

Address
K.K. Yaswanth, J. Revathy and P. Gajalakshmi: Department of Civil Engineering, School of Infrastructure, B.S. Abdur Rahman Crescent Institute of Science & Technology,
Chennai - 600048, India

Abstract
Protein structures, that form intermediate filaments (IFs) was first found by an experiment known as the computerized analysis of amino acid sequence of a human epidermal keratin derived from cloned cDNAs. This study is made by the application of Euler beam theory. The buckling of intermediate filaments is studied keeping the nonlocal effects under consideration. It is observed that the nonlocal parameter has a great impact on the dynamics of intermediate filaments. The buckling behavior of intermediate filaments is investigated with different four conditions like as simply supported, clamped, cantilever and propped cantilever beam. Also the effect of critical bucking force is seen for different strengths of nonlocal parameter as 1,2,3,4.

Key Words
actin filaments; buckling of intermediate filaments; critical bucking force; propped cantilever beam; protein structures

Address
Muhammad Safeer: Department of Mathematics, University of Azad Jammu and Kashmir, Muzaffarabad, 1300, Azad Kashmir, Pakistan
Mohamed A. Khadimallah: Civil Engineering Department, College of Engineering, Prince Sattam Bin Abdulaziz University, Al-Kharj, 16273, Saudi Arabia; Laboratory of Systems and Applied Mechanics, Polytechnic School of Tunisia, University of Carthage, Tunis, Tunisia
Muhammad Taj: Department of Mathematics, University of Azad Jammu and Kashmir, Muzaffarabad, 1300, Azad Kashmir, Pakistan
Muzamal Hussain: Department of Mathematics, Govt. College University Faisalabad, 38000, Faisalabad, Pakistan
Elimame Elaloui: Laboratory of Materials Applications in Environment, Water and Energy LR21ES15, Faculty of Sciences, University of Gafsa, Tunisia
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
Corrosion of steel reinforcement due to hostile environments is regarded as one vital structural health concerns in concrete structures. Specifically, the development of corrosion affects the necessary bond strength of rebar in concrete contributing to the loss of resilience and possible structural failures. It is thus essential to understand the effects of corrosion on bond strength so that remedial measures can be done on existing and deteriorating RC structures. Hence, this study investigated through laboratory experiments and Artificial Neural Network (ANN) modeling the effects of corrosion on bond strength. Experimental results showed that at small amounts of corrosion less than 0.27%, the bond strength was observed to increase. At these levels, the amounts of corrosion products were sufficient enough to expand freely through the permeable structure of concrete and occupy the pore spaces. Beyond this level, however, the bond strength of concrete deteriorated significantly. There was an observed average decrease of 1.391 MPa in the bond strength values for every percent increase in the amount of corrosion. The expansive and progressive internal radial stress due to corrosion resulted to the development of internal and surface cracks in concrete. In the parametric investigation of the derived ANN model, the bond strength was also observed to decline continuously with the growth of corrosion derivatives as represented by the relative magnitudes of the ultrasonic pulse velocity (UPV). The prediction results of the model can be utilized as basis for design and select appropriate mitigating measures to prolong the service life of concrete structures.

Key Words
artificial neural network; bond strength; corrosion of rebar; ultrasonic pulse velocity

Address
Nolan C. Concha: Department of Civil Engineering, FEU-Institute of Technology, Sampaloc, Manila, Philippines
Andres Winston C. Oreta: Department of Civil Engineering, De La Salle University, Taft Avenue, Manila, Philippines

Abstract
An attempt has been made to study the influence of basalt fiber and latex on the behaviour of hypo sludge based concrete beams under cyclic loading. Two sets of four geometrically similar specimens were cast to study the deflection behaviour of beams. The analysis and study of parameters such as ultimate load carrying capacity, crack pattern, energy dissipation, stiffness degradation and ductility were conducted in this investigation. A preliminary investigation showed that the durability properties decreased when hypo sludge was added to concrete. To enhance the durability, SBR latex was added to one set of four specimens. Results indicate that the addition of basalt fibers and latex to the hypo sludge based concrete beams showed significant improvement in ultimate load carrying capacity, stiffness, energy dissipation and ductility compared to the control concrete beams. The specimen (LHSBFC) with 10% hypo sludge, 0.25% Basalt fiber and 10% SBR latex showed an increase of 1.82% load carrying capacity, 2.65% stiffness, 21.84% ductility, 16% energy dissipation when compared to the control concrete beam.

Key Words
basalt fiber; crack pattern; ductility; hyposludge; latex; stiffness

Address
S. Srividhya, R. Vidjeapriya: Department of Civil Engineering, College of Engineering Guindy, Anna University, Sardar Patel Road, Chennai 600025, Tamilnadu, India
M. Neelamegam: Department of Civil Engineering, Easwari Engineering College, Ramapuram, Chennai 600089, Tamil Nadu, India


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