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CONTENTS
Volume 20, Number 2, August 2025
 

Abstract
This study investigates the effects of heating temperature and water-to-binder ratio (W/B) on the interfacial transition zones (ITZ) in recycled concrete, with a focus on multiple interfaces, including the interface between old aggregate and new mortar (LG-XJ), the interface between old aggregate and old mortar (LG-LJ), and the interface between old mortar and new mortar (LJ-XJ). The results show that heating temperature significantly impacts the ITZ microstructure and mechanical properties. Lower temperatures (300°C and 500°C) promote dehydration of old mortar, leading to denser ITZ structures with increased interfacial hardness and reduced transition zone widths. Conversely, at 700°C, decomposition of hydration products increases porosity and microcracking, resulting in decreased interfacial hardness and wider transition zones. Similarly, higher W/B ratios lead to insufficient cement hydration, increased porosity, and looser ITZ microstructures, thereby reducing interfacial microhardness and widening the ITZ. SEM analysis further reveals distinct microstructural characteristics among the interfaces, with the LJ-XJ interface exhibiting better density and uniformity compared to the LG-XJ interface after heat treatment. These findings highlight the importance of optimizing heating temperature and W/B ratio to enhance the interfacial properties and overall performance of recycled concrete.

Key Words
heating temperature; interfacial transition zone; microstructural properties; recycled concrete

Address
(1) Xiaohui Yan, Ruihua Yang:
Shanghai Urban Construction Vocational College, Shanghai 200438, China;
(2) Xiaonan Zhang:
Xianyang Normal University, Xianyang 712000,China;
(3) JiaYuan Wang:
China Construction Seventh Engineering Division. Corp. LTD, Zhengzhou 450000, China.

Abstract
In order to accurately assess the response of a structure when subjected to impact or vibration loading, there is an urgent need to carry out studies on the dynamic mechanical properties of high-strength concrete. Impact tests on C80 concrete with different combinations of stress wavelengths and strain rates were conducted using a 75 mm SHPB test system and compared with dynamic impact tests on C35 plain concrete. The following conclusions can be obtained: Under the action of multiple impacts, the cumulative damage of C80 concrete and the number of impacts show the form of "rapid rise - smooth development-rapid rise." The dynamic strength of C80 concrete is positively correlated with the peak strain and strain rate, and the increase of stress wavelength and impact velocity raises the overall development trend of peak strain. As the impact velocity increases, the cumulative damage increases significantly while the number of repeated impacts gradually decreases. The established C80 concrete cumulative damage evolution model can calculate the physical significance of the model parameters and simultaneously reflect the impact velocity and impact number. Additionally, it confirms the model's logic and accuracy of the physical parameters, which might serve as a particular benchmark for related studies. Comparative analysis shows C35 exhibits greater deformability than C80 at equivalent strain rates (80 s-1). The growth in peak strain for C35 surpasses that of C80 as strain rates escalate from 50 s-1 to 80 s-1, with C35's strain-rate curve showing a steeper slope. Microstructural analysis attributes C80's restrained deformation to its denser matrix, which enhances strength retention but limits crack propagation. These findings provide critical insights for material selection in protective structures.

Key Words
C80 concrete; damage model; SHPB; strain rate effect; stress wave effect

Address
Department of Urban and Underground Space, School of Civil and Transportation Engineering, Henan University of Urban Construction, Pingdingshan 467000, China.

Abstract
This paper presents a detailed evaluation of the performance of Double Corrugated Steel Plate Shear Walls (DCSPs) through comprehensive numerical analysis. The study is conducted in three distinct phases. The target is to determine how DCSPs would perform if it was the main lateral bearing system of a predesigned dual system enhanced by moment frames and X-Braces. In the first phase, six numerical models were developed using Abaqus to assess the effectiveness of DCSPs compared to conventional industrial braced frames. The analysis focused on steel structures ranging from 10 to 30 stories, incorporating both DCSPs and traditional brace sections. To ensure a fair comparison, the capacities of the two systems were equalized at three different building heights. Push-over analysis revealed that DCSPs in shorter structures exhibit load-displacement capacities similar to those of braced frames, which aligns with the desired performance. However, as the building height increases, DCSPs demonstrate superior material efficiency, maintaining equivalent load-displacement capacities. In the second phase, the study examines the structural performance of DCSPs in high-rise buildings by determining the Response Modification Factor (R factor) for both systems using push-over curves. The results indicate that DCSPs achieve a higher R factor compared to braced frames despite both systems displaying nearly identical push-over curves with comparable capacities. This suggests that DCSPs offer enhanced structural performance under seismic conditions. The third phase involves a time-history analysis of two models: one with 10-story frames enhanced by braces and the other by DCSPs. Both systems were subjected to two different earthquake scenarios to evaluate base shear, drift, plastic behavior, and energy outputs. Although both systems were designed to have similar capacities, DCSPs demonstrated superior performance and greater capacity. The DCSPs are a practical option for structural enhancement compared to traditional braced frames, offering better overall efficiency and resilience in seismic events.

Key Words
braced frames; earthquake engineering; lateral enhancement; numerical simulations; push-over analysis; response modification factor; steel plate shear walls; structural engineering; time history analysis

Address
Department of Civil Engineering, Faculty of Civil Engineering and Architecture, Shahid Chamran University of Ahvaz, Ahvaz, Iran.


Abstract
This study proposed a modular arch system that allows lean construction, considering the load-resistant features of the underground arch. In this proposed arch system, H-shaped steel frames and precast concrete panels are combined in a noncomposite state, giving them respective resistance roles to bending moment and compression force. Experimental and numerical approaches were conducted to investigate its load-resistant response and load transfer mechanism, focusing on strain, stress distribution, and deformation under load. The laboratory test revealed that the flexural strain of the concrete panel was negligible, and the strain distributions of the two members at the same cross-section were different, demonstrating the feasibility of this non-composite arch. Finite element analysis under various load conditions, including the arch's operation stage, revealed that even under high moments, the arch maintained its intended non-composite behavior with minimal stress and strain, indicating a high level of safety. Therefore, these results confirm that this arch enables efficient cross-sectional design by combining materials strong in bending and compression and assigning them independent roles. Additionally, based on the noncomposite behavior of this arch system, a theoretical design approach and a simplified analysis model for safety evaluation are proposed, along with guidelines for its practical design and analysis.

Key Words
FE analysis; loading test; load-resistance characteristics; non-composite modular arch system; precast concrete panel; steel beam

Address
(1) Jiwoon Yi:
Steel Structure Research Group, POSCO, Incheon 21985, Korea;
(2) Tae-Yun Kwon, Jin-Hee Ahn:
Department of Civil and Infrastructure Engineering, Gyeongsang National University, Jinju 52725, Korea.

Abstract
In order to improve the utilization rate of construction waste and iron tailings, the effect of modified materials formed under the joint action of basalt fiber and iron tailings on the performance of recycled concrete was studied by orthogonal test. The influence of different factors on the mechanical properties of recycled concrete is analyzed, and the effectiveness of the experiment is simulated by ABAQUS software. The results show that the replacement of natural river sand by iron tailings and the replacement of natural coarse aggregate by recycled coarse aggregate can not only reduce the use of natural aggregates, but also improve the mechanical properties of recycled concrete. The appropriate amount of basalt fiber and iron tailings can increase the peak strain of the specimen under bending, and the stress-strain curve calculated by the finite element software is consistent with the experimental results. Combined with the requirements of working performance and economic benefits, the comprehensive mechanical properties of basalt fiber iron tailings recycled concrete were the best when the basalt fiber volume content was 0.1%, the iron tailings sand substitution rate was 30%, the recycled coarse aggregate substitution rate was 50%, the recycled brick-concrete aggregate mix ratio was 1:2 and the water-glue ratio was 0.38.

Key Words
basalt fiber; iron tailings ore; numerical simulation; recycled brick aggregate; recycled concrete; recycled concrete aggregate

Address
School of Materials Science and Engineering, School of Architecture and Civil Engineering, Shenyang University of Technology, No.111, Shenliao West Street, Shenyang Economic and Technological Development Zone, Shenyang 110870, Liaoning Province, the People's Republic of China.

Abstract
This paper presents a machine-learning pipeline that predicts the rheological properties of fresh-state concrete based on concrete mixing components using various machine-learning algorithms. The well-known idea of a correlation between rheological parameters and conventional fluidity values, several tries at matching rheological parameters with flow values have been suggested. Even though some successful studies were able to match two related values, each research showed a different relationship depending on the case. However, in this study, a reliable and sustainable rheology parameter prediction model is suggested. The prediction was based on the mixing components of concrete by building a pipeline that sequentially integrates models that predict the physical properties of specific concrete types using various machine learning algorithms. A pipeline was built to sequentially connect the two models evaluated as having a desirable prediction performance, and the rheology parameter was predicted by inputting the mixing component. To validate the developed model, the experimental data was compared with the predictions generated by the model. As a result, the flow prediction error rate was 4.96%, and the yield stress prediction error rate was 6.59%, which is a favorable prediction performance of a constructed pipeline. This study presents a new method that can accurately predict the physical properties of fresh state concrete based on concrete mixing factors. This method will increase efficiency and ensure quality control of fresh state concrete.

Key Words
flow; fresh state concrete; machine learning; rheology; yield stress

Address
(1) Yujeong Lee, Jiuk Shin, Dongyeop Han:
Department of Architectural Engineering, Gyeongsang National University, 501, Jinju-daero, Jinju 52828, Republic of Korea;
(2) Taewook Kang:
Mirae Structural Engineering, 127, Beobwon-ro, Songpa-gu, Seoul, 05836, Republic of Korea.

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