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CONTENTS
Volume 35, Number 5, May 2025
 

Abstract
Use of recycled concrete aggregates (RCA) in structural concrete necessitates the understanding of complete stress-strain response of recycled aggregate concrete (RAC). An experimental and numerical investigation, was therefore, carried out to study and simulate the complete, pre-and post-peak, stress-strain response of RAC under uniaxial compression and is presented in this paper. Concrete cylinders cast with natural aggregates and RCA were tested under uniaxial compression and splitting tension to determine the compressive and splitting tensile strength along with the elastic modulus and Poisson's ratio. Experimental stress-strain curves were also produced. Cylinders were cast with different replacement percentages of RCA i.e., 0%, 30%, 50%, 70% and 100% and water-to-cement ratios of 0.43, 0.5 and 0.6. An equation for the estimation of uniaxial compressive strength of RAC has been proposed. Predicted compressive strengths compare well with the experimentally observed strengths. Experimentally measured elastic modulus and Poisson's ratio along with estimated compressive strengths were used in the elasto-damage constitutive model, proposed previously by the authors, to compare the stress-strain curves predicted by the model with the experimental stress-strain curves for uniaxial state of stress. Overall comparison of predicted stress-strain curves was found to be in good agreement with the experimentally exhibited stress-strain curves.

Key Words
elastic modulus; Poisson's ratio; recycled aggregate concrete; stress-strain curve; uniaxial compression

Address
Department of the Civil Engineering, NED University of Engineering & Technology Karachi - 75270 Pakistan

Abstract
The present paper deals the time-dependent mixed convection Casson type MHD nanofluid flow with motile micro-organisms around a spinning body adopting laminar boundary layer theory. Dynamic flow dependent on time is taken into account. The guiding partial differential structure has been converted into ordinary differential structure via similarity transformations. The numerical results of ordinary differential equations have been acquired by using shooting technique via MATLAB software. Aspects of such physical parameters have been discussed and clarified in details using tables and graphs. The effect of different parameters such as acceleration parameter on primary velocity, secondary velocity, temperature function, non-dimensional nanoparticle concentration. Comparison with previous studies is also mentioned and it is noted that a good agreement with published literature.

Key Words
MATLAB software; micro-organisms; ordinary differential equations; shooting technique; similarity transformations

Address
Mohamed A. Khadimallah: 1) Department of Civil Engineering, College of Engineering in Al-Kharj, Prince Sattam Bin Abdulaziz University, Al-Kharj, 11942, Saudi Arabia, 2) Laboratory of Applied Mechanics and Engineering LR-MAI, University Tunis El Manar- -ENIT BP37- Le belvédère, 1002, Tunisia
Muzamal Hussain and Humaira Sharif: Department of Mathematics, Govt. College University Faisalabad, 38000, Faisalabad, Pakistan
Abdelouahed Tounsi: 1) YFL (Yonsei Frontier Lab), Yonsei University, Seoul, Korea, 2) Department of Civil and Environmental Engineering, King Fahd University of Petroleum and Minerals, 31261 Dhahran, Eastern Province, Saudi Arabia

Abstract
The use of fibers in concrete to prevent fractures and extend the joint seam space of concrete slabs is becoming more common in concrete pavements and bridge structures. However, their durability behavior against acid rain attacks and chloride ion penetration has been less studied. The current paper investigates how Fiber-Reinforced Concrete (FRC) containing 15% cementitious material (Metakaolin and Pumice) instead of Portland cement performs with respect to acid attack by using microstructure studies. In addition, the chloride penetration under marine environments was studied by simulating the tidal and immersion conditions. Durability findings demonstrate that Metakaolin and Pumice have a considerable impact on enhancing chloride penetration in marine environments. However, concrete with cementitious material shows a negative performance against acid attacks. From this research, Computed Tomography (CT) scan analysis and microstructure results show a porous structure in specimens containing admixture, and the Ca/Si ratio is decreased significantly due to decalcification.

Key Words
acid attack; marine environment; microstructure; polyolefin; polypropylene

Address
Faculty of Civil, Water, and Environmental Engineering, Shahid Beheshti University, Tehran, Iran

Abstract
This work examines the dynamic response of nanoplates by including the flexomagnetic effect based on the novel shear deformation theory. The plate's equilibrium equation is shown by using the concept of virtual work to solve the equation. The novelty of this work is to show the influence of the flexomagnetic effect on the displacement, velocity, and acceleration responses of nanoplates when subjected to time-varying loads. This study employs the finite element approach, using four nodal elements, each having six degrees of freedom. The finite element model in this study has been validated for dependability by comparison with previously reported findings. This research uses numerical calculations to demonstrate how geometric dimensions, material properties, and frequency of external pressures affect the dynamic response of nanostructures. This study is valuable for designers seeking to optimize the creation of nanoplates for practical use.

Key Words
finite element method; flexomagnetic; forced vibration; nanoplates; novel shear deformation theory

Address
Le Truong Son, Do Van Thom and Phung Van Minh: Faculty of Mechanical Engineering, Le Quy Don Technical University, 236 Hoang Quoc Viet Street, Hanoi, 100000, Vietnam
Nguyen Chi Tho: Institute of Techniques for Special Engineering, Le Quy Don Technical University, 236 Hoang Quoc Viet Street, Hanoi, 100000, Vietnam
Van Minh Chinh: 1) Graduate University of Science and Technology, Vietnam Academy of Science and Technology, 18 Hoang Quoc Viet, Cau Giay, Hanoi, 100000, Vietnam, 2) Air Force-Air Defence Technical Institute, Hanoi, 100000, Vietnam
Abdelouahed Tounsi: 1) Department of Civil and Environmental Engineering, King Fahd University of Petroleum & Minerals, 31261 Dhahran, Eastern Province, Saudi Arabia, 2) Department of Civil and Environmental Engineering, Lebanese American University, 309 Bassil Building, Byblos, Lebanon

Abstract
This study focuses on to predict the ultimate shear strength of steel fiber reinforced concrete (SFRC) slender and deep beams without stirrups using the gene expression programming (GEP). For this purpose, a large database containing 437 shear strength tests of SFRC beams that failed in shear mode were divided into two different groups according to their span-depth ratios and two different models were developed for slender and deep beams. The effective depth of beam (d), longitudinal reinforcement ratio (p), shear span to effective depth ratio (a/d), compressive strength of concrete (fc'), fiber volume percentage (Vf) and fiber factor (F) were considered as input parameters in GEP models. The results of the proposed models were compared to those of the existing models in the literature. It was concluded that the proposed models provide the best performance and accuracy for the shear strength of both slender and deep beams. Furthermore, sensitivity and parametric analysis were performed separately to evaluate the influence of input parameters on the shear strengths of both slender and deep SFRC beams.

Key Words
deep beam; gene expression programming; reinforced concrete; sensitivity analysis; shear strength; slender beam; steel fiber

Address
Department of Civil Engineering, Yildiz Technical University, 34220, Istanbul, Turkey

Abstract
This article draws support from time-displacement curve and phase trajectory to illustrate the transient responses of functionally graded carbon nanotube reinforced composite (FG-CNTRC) cylindrical shell subjected to uniform blast load in hygro-thermal environment, the elastic foundation and geometrical imperfection are also considered. Subsequently, the transient response problem of the FG-CNTRC cylindrical shell is solved using the Runge-Kutta method, and the response of three degree of freedom system under blast load is tracked by time-displacement curves and phase trajectory. Finally, the effects of CNT distribution type, CNT volume fraction, elastic foundation, geometrical parameters of the cylindrical shell, prestress, geometrical imperfection, axial velocity, damping, load types, and other factors on the transient response of the FG-CNTRC cylindrical shell are discussed in numerical analysis, and the conclusions suggest that increasing the content of CNT and adjusting the geometrical parameters of the structure reasonably have a positive impact.

Key Words
blast load; carbon nanotube; hygro-thermal field; transient response

Address
College of Mechanical and Vehicle Engineering, Chongqing University, Chongqing 400044, China

Abstract
With the sharp reduction of natural resources and the surge of construction and demolition waste, recycled concrete aggregate (RCA), which uses waste concrete as the source of aggregate, has emerged. It aims to replace natural aggregate (NA) for the production of recycled aggregate concrete (RAC). However, compared to NA, the performance of RCA is relatively poor. These differences are mainly due to the adhered mortar (AM) on the RCA surface. RCA modification methods can be roughly divided into two categories: removal of attached mortar and strengthening attached mortar. However, these two modification methods still have shortcomings. In contrast, microbiologically induced calcium carbonate precipitation (MICP) has naturally become a hot spot in research on the modification of regenerated aggregate (RA). Because of its environmentally friendly characteristics. To ensure the high quality of RAC, appropriate modifications must be made for RCA. This study applied MICP technology to improve the properties of recycled concrete aggregate (RCA). We analyzed the physical properties and microscopic characteristics of three types of RCA before and after modification to ensure that these RCAs' basic properties meet the requirements of engineering applications. The test results showed that the originally loose interfacial transition zones (ITZ) of RCA became quite dense due to the intensive filling of the products produced by MICP, thus improving its physical and mechanical properties. The 24-hour water absorption rates of the three RCAs were significantly reduced after modification. The one with the best effect was reduced by 27.8%. In addition, the best results for dry specific gravity increased by 26.7%, and the best results for dry rodded unit weight increased by 5.2%. Moreover, compared with recycled aggregate concrete (RAC) using unmodified RCA, the compressive strength and splitting strength of RAC using MICP-modified RCA increased by 7.0% and 6.9%, respectively. This result indicated that applying MICP technology to strengthen the properties of RCA could ensure the mechanical properties of RAC.

Key Words
biomineralization; compressive strength; recycled aggregate concrete; recycled concrete aggregate

Address
Chao-Wei Tang: 1) Department of Civil Engineering and Geomatics, Cheng Shiu University, No. 840, Chengching Rd., Niaosong District, Kaohsiung 83347, Taiwan (R.O.C.), 2) Center for Environmental Toxin and Emerging-Contaminant Research, Cheng Shiu University, No. 840, Chengching Rd., Niaosong District, Kaohsiung 83347, Taiwan (R.O.C.), 3) Super Micro Mass Research and Technology Center, Cheng Shiu University, No. 840, Chengching Rd., Niaosong District, Kaohsiung 83347, Taiwan (R.O.C.)
How-Ji Chen and Yun-Chih Lu: Department of Civil Engineering, National Chung Hsing University, 145 Xingda Rd., South District, Taichung City 40227, Taiwan (R.O.C.)

Abstract
Determination of the mechanical properties of mortar at elevated temperatures is of great importance for fire safety and long-term durability of structures in civil engineering. In this study, experiments were conducted to determine the properties of mortar using four different chemical admixtures. The aim was to predict the mechanical property changes induced by chemical admixtures on mortar at very high temperature. In order to reach the most realistic predictions, the data was analyzed by testing well-known machine learning methods. The Multilayer Perceptron (MLP) method showed the best performance and was compared with Ordinary Least Squares (OLS) regression, known as the benchmark for prediction. The results showed that MLP is a very suitable predictor. At 300 oC the tensile strength decreased to 1 MPa and at 600 oC all admixture ratios resulted in compressive strengths below 5 MPa, indicating severe degradation. The innovative aspect of this study is the successful prediction of the mechanical properties of mortar in fire scenarios, through applying machine learning methods that use the results of experiments up to 600 oC, and allowing the use of data obtained from experimentation that is not costly, time consuming and conducted at high temperatures. To produce data, the specimens were prepared in the laboratory using four specially selected types of chemicals in various proportions. This careful selection and varied ratio application represent another supportive innovation of the study. This study provides important and instructive results for both future research and practical applications in the field of building safety.

Key Words
machine learning; mortar; multilayer perceptron; temperature; prediction

Address
Ilker Bekir Topcu and Aytac Unverdi: Department of Civil Engineering, Eskisehir Osmangazi University, Eskişehir, Turkey
Vural Yildirim: Institute of Earth and Space Sciences, Eskisehir Technical University, Eskişehir, Turkey

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