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Volume 16, Number 1, July .2023

This study presents the experimental results performed to evaluate the effects of Polyvinyl Polyvinyl-alcohol (PVA) and Polypropylene (PP) fibers on the fresh and residual mechanical properties of the hybrid fiber reinforced SCC before and after the exposure of 250°C, 500°C and 750°C temperatures. The compressive and splitting tensile strength, modulus of rupture (MOR), ultrasonic pulse velocity (UPV) as well as toughness and weight loss were investigated at different temperatures. PVA and PP fibers were added into S CC mixtures having only macro steel fiber and also having binary hybridization of both macro and micro steel fiber. The results showed that the use of micro steel fiber replaced by macro steel fiber improved the fresh and hardened properties compared to th e use of only macro steel fiber. Moreover, it was emphasized that PVA or PP enhanced the residual flexural performance of SCC, generally, while it negatively influenced the workability, weight loss, UPV and the residual strengths with regards to the use of single steel fiber and binary steel fiber hybridization. Compared to the effect of synthetic fibers, PP had slightly more positive effect in the view of workability while PVA enhanced the residual mechanical properties more more.

Key Words
high temperature hybrid fiber reinforced self compacting concrete polypropylene fiber; polyvinyl alcohol fiber; residual strength and toughness

(1) Kazim Turk, Esma Balalan:
Inonu University, Engineering Faculty, Department of Civil Engineering, Malatya, Türkiye;
(2) Ceren Kina:
Malatya Turgut Ozal University, Faculty of Engineering and Natural Sciences, Department of Civil Engineering, Malatya, Türkiye.

This work presents a complete optimal model for trapezoidal combined footings that support a concentric load and moments around of the "X" and "Y" axes in each column to obtain the minimum area and the minimum cost. The model presented in this article considers a pressure diagram that has a linear variation (real pressure) and the equations are not limited to some cases. The classic model takes into account a concentric load and the moment around of the "X" axis (transverse axis) that is applied due to each column, i.e., the resultant force is located at the geometric center of the footing on the "Y" axis (longitudinal axis), and when the concentric load and moments around of the "X" and "Y" axes act on the footing is considered the uniform pressure applied on the contact surface of the footing, and it is the maximum pressure. Four numerical problems are presented to find the optimal design of a trapezoidal combined footing under a concentric load and moments around of the "X" and "Y" axes due to the columns: Case 1 not limited in the direction of the Y axis; Case 2 limited in the direction of the Y axis in column 1; Case 3 limited in the direction of the Y axis in column 2; Case 4 limited in the direction of the Y axis in columns 1 an 2. The complete optimal design in terms of cost optimization for the trapezoidal combined footings can be used for the rectangular combined footings considering the uniform width of the footing in the transversal direction, and also for different reinforced concrete design codes, simply by modifying the resisting capacity equations for moment, for bending shear, and for the punching shear, according to each of the codes.

Key Words
bending shear; minimum cost; moments; optimal design; punching shear; trapezoidal combined footings

Institute of Multidisciplinary Researches, Autonomous University of Coahuila, Blvd. Revolución No, 151 Ote, CP 27000, Torreón, Coahuila, México.

Majority of the plastic produced each year is being disposed in land after single-use, which becomes waste and takes up a lot of storage space. Therefore, there is an urgent need to find alternative solutions instead of disposal. Recycling and reusing the PET plastic waste as aggregate replacement and fiber in concrete production can be one of the eco- friendly methods as there is a great demand for concrete around the world, especially in developing countries by raising human awareness of the environment, the economy, and Carbon dioxide (CO2) emissions. Self-compacting concrete (SCC) is a key development in concrete technology that offers a number of attractive features over traditional concrete applications. Recently, in order to improve its durability and prevent such plastics from directly contacting the environment, various kinds of plastics have been added. This review article summarizes the latest evident on the performance of SCC containing recycled PET as eco-friendly aggregates and fiber. Moreover, it highlights the influence of substitution content, shape, length, and size on the fresh and properties of SCC incorporating PET plastic. Based on the findings of the articles that were reviewed for this study, it is observed that SCC made of PET plastic (PETSCC) can be employed in construction era owing to its acceptable mechanical and fresh properties. On the other hand, it is concluded that owing to the lightweight nature of plastic aggregate, Reusing PET waste in the construction application is an effective approach to reduces the earthquake risk of a building.

Key Words
PET aggregate; PET fiber; SCC containing PET plastic (PETSCC); Self-compacting concrete (SCC)

Civil Engineering Department, College of Engineering, University of Duhok (UoD), Zakho Street 38, 1006 AJ, Duhok 42001, Kurdistan Region, Iraq.

In the pumping process, concrete moves along the pipe and experiences both pressure and shear. This changes the workability and flow characteristics of the concrete. However, the effect of pressure and shear on the change in properties of concrete during the pumping process has not yet been accurately identified. This study analyzed the effects of pressure and shear on the properties of concrete during pumping. For quantitative tests, lab-scale test equipment capable of simulating the pressure and shear applied to concrete during pumping was used. For one coarse aggregate type, two paste types, three mortar types, and five concrete types, the effects of pressure, shear, and shear under pressure conditions were examined by varying the maximum pressure (0 to 200 bar) and the rotational speed of the vane for shear (0 to 180 rpm). Under the maximum pressure condition of 200 bar, the water absorption of coarse aggregate increased by 0.62% and that of fine aggregate also increased. When the concrete was under pressure, significant changes (a reduction in a slump and an increase in viscosity and yield stress) compared with the effect of the elapsed time occurred owing to an increase in the water absorption of the aggregates. When both pressure and shear were applied to concrete, both the slump and viscosity decreased. As the rotational speed of the vane increased, changes in properties became significant. Shearing in the absence of pressure maintained the properties of concrete. However, shearing under pressure conditions caused a reduction in slump and viscosity.

Key Words
concrete properties; pumping process; effect of pressure and shear; water absorption of aggregate; slump; viscosity

(1) Jung Soo Lee, Seung Hee Kwon:
Department of Civil and Environmental Engineering, Myongji University, 116 Myongji-ro, Cheoin-gu, Yongin-si, Gyeonggi-Do, 17058, Republic of Korea;
(2) Kyong Pil Jang:
Department of Building Research, Korea Institute of Civil Engineering and Building Technology, 283, Goyangdae-Ro, Ilsanseo-Gu, Goyang-Si, Gyeonggi-Do, 10223, Republic of Korea;
(3) Chan Kyu Park:
Institute of Construction Technology, Samsung C & T Corporation, 26, Sanil-ro 6-gil, Gangdong-gu, Seoul, 05288, Republic of Korea.

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