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CONTENTS
Volume 19, Number 6, June 2025
 

Abstract
This paper presents the optimal surface for corner combined footings assuming that the contact area with the soil works partially in compression (one part of the contact surface of the footing is subjected to compression and the other part is not subjected to compression or tension). The methodology is developed by integration to obtain the resultant force and resultant moments on the X and Y axes acting on the footing due to soil pressure. The three types that can occur depending on the location of the maximum pressure are: 1) Corner of the footing; 2) At one end and on the outer side of the footing; 3) At one end and on the inner side of the footing. In this work, the simplified equations are shown when the maximum pressure is located in corner of the footing. Some engineers obtain the contact area of the footing by the trial and error method. Other authors present the minimum area for a corner combined footing taking into account that the contact area with the soil works completely in compression. Numerical examples are shown to obtain the minimum area of the footings and the results are compared with the current model. The new model shows a smaller soil contact area in some cases than the current model.

Key Words
contact area works partially to compression; corner combined footings; linear pressure distribution of the soil; optimal surface; resultant force; resultant moments

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


Abstract
This work presents the optimal surface for corner combined footings considering that the contact area with the soil works partially in compression (a part of the contact surface of the footing is subject to compression and the other there is no pressure and neither tensile). The methodology is developed by integration to obtain the resultant force and resultant moments in the X and Y axes that act on the footing due to the soil pressure. The three types that can occur depending on the location of the maximum pressure are: 1) Corner of the footing; 2) At one end and on the outer side of the footing; 3) At one end and on the inner side of the footing. In this work, the simplified equations are shown when the maximum pressure is located at one end and on the outer and inner side of the footing. Some engineers obtain the contact area of the footing by the trial and error method. Other authors present the minimum area for a corner combined footing taking into account that the contact area with the soil works completely in compression. Numerical examples are shown to obtain the minimum area of the footings and the results are compared with the current model. The new model shows a smaller soil contact area in some cases than the current model.

Key Words
contact area works partially to compression; corner combined footings; linear pressure distribution of the soil; optimal surface; resultant force; resultant moments

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


Abstract
This work investigates the effect of replacing cement with biochar on the mechanical properties and freeze-thaw resistance of concrete. Biochar, produced from wood pellets through thermal carbonization, was used as a partial substitute for cement at replacement ratios of 5%, 10%, and 15%. The fresh concrete properties, including slump and air content, were evaluated, followed by water curing for 14 and 28 days. The mechanical properties, including compressive strength, splitting tensile strength, and flexural strength, were measured under both standard curing and freeze-thaw conditions. Freeze-thaw durability was assessed based on the relative dynamic modulus of elasticity and mass-loss rates after 150 and 300 cycles. Scanning electron microscopy (SEM) was employed to analyze the bonding of biochar within the cement matrix and its interaction with hydration products. The results revealed that biochar replacement ratios within 10% improved both compressive and flexural strength while maintaining satisfactory freeze-thaw resistance. However, at 15% replacement, significant reductions in mechanical performance and durability were observed, with severe deterioration under freeze-thaw cycles.

Key Words
biochar; cement replacement; concrete durability; freezing and thawing; mechanical property

Address
(1) Sangwoo Kim, Jihyeong Lee, Yeji Hong, Jinsup Kim:
Department of Civil Engineering, Gyeongsang National University 501 Jinju Daero, Jinju-si, Gyeongsangnam-do 52828, Republic of Korea;
(2) Wonchang Choi:
Department of Architectural Engineering, Gachon University, 1342, Seongnam-daero, Sujeong-gu, Seongnam-si, Gyeonggi-do 13120, Republic of Korea.

Abstract
Frequently used in mechanical testing of concrete, cubic and cylindrical shapes are the subject of a number of studies questioning their influence on the material's strength. The aim of this study was to introduce a modified geometry to reduce the volume of test specimens and guarantee improved performance in strength tests, by investigating the effect of shape. Experimental results showed that the compressive strength of the modified shape was superior to that of standard shapes. However, due to its configuration, tensile strength was slightly improved. A regression analysis was carried out based on Bazant's formula for the effect of size. The results obtained indicate that this formula can be used to explain the proposed shape effect. In this respect, an empirical formula was proposed relating the compressive strength of the proposed specimens to the strength of standard specimens. A verification of the specimen damage model was also carried out in accordance with standards. Finally, a comparative analysis of the proposed geometry with existing literature was carried out.

Key Words
compressive strength; concrete; shape effect; size effect; tensile strength

Address
(1) Sadeq Hajar, Nasser Abdelkader, Kerkour El Miad Abdelhamid:
Mohammed First University Oujda, Faculty of Science Oujda, Laboratory of Materials, Wave, Energy and Environment (LaMOn2E), MEGCE team ESTO, Oujda, Morocco;
(2) Amar Najib: LABNORVIDA laboratory, Oujda, Morocco.

Abstract
This study investigates the effectiveness of thin jacketing with polypropylene fiber-reinforced concrete for strengthening reinforced concrete (RC) columns. Full-scale specimens were retrofitted using thin jackets of polypropylene fiberreinforced concrete, steel fiber-reinforced concrete, and plain concrete, then subjected to a constant vertical load combined with cyclic horizontal loading to simulate seismic conditions. Key performance metrics, including load-bearing capacity, ductility, energy dissipation, damage index, and crack propagation, were assessed and compared. The findings highlight the effectiveness of fiber-reinforced concrete thin jacketing in enhancing the seismic performance of RC columns. Notably, this method significantly improves load-bearing capacity, ductility, and energy dissipation while delaying crack formation and enhancing overall seismic resilience.

Key Words
cyclic loading; damage index; polypropylene fibers; RC columns; reinforcement; steel fibers

Address
(1) Rachid Labdaoui, Abdennour Toukal:
Materials-Processes and Environment Research Unit, University of Boumerdes, 35000, Algeria;
(2) Mohammed Kadri:
Civil Engineering Department, University of Boumerdes, 35000, Algeria.

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