Wyniki wyszukiwania - BazTech

1

Shear behavior of prestressed UHPC rectangular beams: experimental investigation and limit equilibrium state‑based prediction method

Sun Bin, Luo Rui, Quan Chenghao, Song Chaolin, Xiao Rucheng

Archives of Civil and Mechanical Engineering

|

2024

|

Vol. 24, no. 1

art. no. e31, 2024

EN

Ultra-high performance concrete (UHPC) is a durable and versatile construction material that enables the engineering of slender fabricated beams. Nonetheless, existing design methodologies exhibit certain discrepancies in predicting the ultimate shear capacity of UHPC beams. This study aimed to develop an improved predictive shear model based on design and mechanical properties. Eleven prestressed rectangular UHPC beams were subjected to shear tests, systematically investigating essential design parameters such as shear-span-to-depth ratio, stirrups ratio, longitudinal reinforcement ratio, prestressing force, and prestressing type. The results demonstrated that UHPC beams exhibit strain-hardening behavior after cracking, accompanied by the formation of dense diagonal cracks. Localized cracking eventually led to shear failure. The shear behavior was primarily influenced by the shear-span-to-depth ratio, showing an inverse relationship with shear strength. Increasing the longitudinal reinforcement ratio, stirrups ratio, and prestressing force marginally improved shear capacity. Furthermore, a limit equilibrium state-based method was proposed to develop a practical prediction formula that incorporates steel fibers and matrix interaction. The proposed method demonstrated superior accuracy compared to existing design models, displaying an average difference of 1.1% and a correlation coefficient of 0.96 with experimental results.

2

Synergistic effects of hybrid macro basalt fibers and micro fibers on the mechanical properties of UHPC

Chen Zhiyuan, Wang Xin, Ding Lining, Jiang Kaidi, Huang Huang, Liu Jianxun, Wu Zhishen

Archives of Civil and Mechanical Engineering

|

2023

|

Vol. 23, no. 4

art. e264, 1-20

EN

This study aims to optimize the mechanical properties of ultra-high performance concrete (UHPC) reinforced with macro basalt fibers (MBFs). Six types of fibers, containing micro fibers and macro fibers, were employed to reinforce UHPC by mono or hybrid method. The micro fibers contained micro basalt fiber, polypropylene fiber, and polyvinyl alcohol fiber corresponding to the modulus of 90, 3.5, and 41 GPa, respectively. The macro fibers contained MBF, macro polypropylene fiber, and polyvinyl alcohol fiber corresponding to the modulus of 43, 2.9, and 23 GPa, respectively. The flowability, and compressive and flexural behavior of UHPC were tested and analyzed. The micro fibers with high modulus effectively restricted microcracks owing to the dense fiber distribution and strong restraint, thereby significantly enhanced the mechanical properties of UHPC before cracking; thus, UHPC with 0.3% micro basalt fiber showed the highest compressive and flexural strength of 132.6 and 26.10 MPa. The macro fibers showed pullout failure and consumed energy during fiber pullout process, leading to a ductile failure and enhancement in mechanical properties of UHPC after cracking. UHPC with 3% MBFs had the highest compressive, flexural first-cracking and post-cracking strength of 151.8, 24.97, and 26.32 MPa, owing to the great energy consumption, low damage to fiber-matrix interface and strong macrocrack resistance supported by MBFs. For UHPC with hybrid fibers, UHPC with 3% MBFs and 0.3% micro fibers had the best comprehensive performance, corresponding to the flexural first-cracking and post-cracking strength of 27.95 and 28.01 MPa. It was because that MBF and micro basalt fibers with proper content, which had the highest modulus, synergistically limited microcracks and macrocracks before and after UHPC cracked. The principle, choosing the fiber combination with high modulus and proper content, applies to the improvement of mechanical properties of UHPC with different mixture in practice.

3

The flexural behaviors and mechanism of wollastonite microfiber modified ultra-high performance concrete with steel fiber from micro to macro scale

Zeng Deming, Cao Mingli

Archives of Civil and Mechanical Engineering

|

2022

|

Vol. 22, no. 1

art. no. e32, 2022

EN

Wollastonite microfiber (WF) is a naturally occurring calcium silicate (CaSiO3) produced in fibrous form and often used in ceramic industry as a cheap and valuable mineral. It is tried to be applied in ultra-high performance concrete (UHPC) in this study with expectation to improve the flexural performance and compensate for the deficiencies of steel fiber in enhancing UHPC from micro scale. The effects of WF on the flexural behaviors of UHPC with or without steel fibers were explored. The bonding behaviors of steel fiber in WF-modified ultra-high performance concrete (WFMUHPC) under different curing conditions were researched combined with single fiber pull-out tests. The results showed that WFs could significantly resist and delay the formation of microcracks in UHPC. When WFs were added to UHPC with steel fiber, the flexural properties of concrete were significantly improved from micro to macro scale. Accelerated curing contributed to the flexural strengths but deteriorate the toughness of WFMUHPC with steel fiber. The presented load–deflection curves proved that WFs had a significant improvement of first crack load and there were post-peak curve gaps because of the reinforcing effect of WFs on the frictional sliding behavior of steel fiber. The results of X-ray diffraction and scanning electron microscope showed that WFs had the bridging and filling effect and improved the interfacial transition zone between WFs and matrix. Meanwhile, the combined effect between WFs and high temperature that WFs provided sites for hydration products from cement particles and active minerals including silica fume and fly ash further improved the flexural behaviors. Moreover, a flexural strength model established could accurately describe the reinforcing effect of WFs on this particular UHPC and was expected to provide guidance for practical engineering applications.

4

Effect of polymer fibers on pore pressure development and explosive spalling of ultra-high performance concrete at elevated temperature

Zhang Dong, Chen Baochun, Wu Xiangguo, Weng Yiwei, Li Ye

Archives of Civil and Mechanical Engineering

|

2022

|

Vol. 22, no. 4

art. no. e187, 2022

EN

This paper investigated pore pressure development of ultra-high performance concrete (UHPC) included various polymer fibers, i.e., linear low-density polyethylene (LLDPE), ultra-high molecular weight polyethylene (UHMWPE), polypropylene (PP), polyester (PET), and polyamide (PA) fibers. Temperature and pore pressure were measured simultaneously at different depths of UHPC specimens subjected to one-dimensional heating. It was found that the PP and PA fibers prevented spalling of UHPC by enhancing moisture migration, which resulted in the development of pore pressure in the deeper region of the specimens. The moisture migration in UHPC with LLDPE fibers caused spalling of a layer of concrete in a deep region of specimen. UHMWPE fibers did not affect pore pressure development and spalling resistance of UHPC significantly, while with PET fibers, the pore pressure of UHPC raised sharply due to inadequate moisture migration, leading to spalling of a whole layer. Instead of melting polymer fibers and empty channels left, microcracks created by the fibers were responsible for releasing vapor pressure and spalling prevention. Fibers with high thermal expansion between 100 and 200 °C are recommended for spalling prevention of UHPC.

5

Nowoczesne kierunki rozwoju technologii betonu

Kostrzanowska-Siedlarz A.

Magazyn Autostrady

|

2017

|

Nr 4

60--65

PL

W artykule przedstawiono aktualne osiągnięcia w dziedzinie technologii betonu oraz podjęto próbę analizy rozwoju kierunków technologii betonu. Czy w przyszłości będzie można wyobrazić sobie drogi bez konieczności napraw? Mosty, które przez cały okres użytkowania wyglądają jak nowo wybudowane i ostrzegają o niebezpieczeństwach oraz permanentnie monitorują ruch? A budowa będzie przebiegała w wydruku 3D z ograniczeniem całego tradycyjnego zaplecza budowy? Faktem jest, że jednoznaczne odpowiedzi na powyższe pytania są trudne, z uwagi na postęp badań nad różnymi technologiami betonu, ale mam nadzieję, że przedstawione w artykule informacje pozwolą na przybliżenie technologii i problemów badawczych podejmowanych na świecie.

EN

The article presents the latest achievements in the field of concrete technology and attempts to analyze the directions of the concrete technology development. Will it be possible to imagine a road with no need to repair in the future? Bridges that look like newly built for their entire lifetime, that warn about dangers and permanently monitor traffic? A construction using 3D printing without the whole traditional construction site facilities? The fact is that unambiguous answers to these questions are difficult due to the progress of the research on different concrete technologies, but I hope the information presented in this paper will allow to approach these technologies and research problems undertaken in the world.