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19 pages, 6134 KiB

Open AccessArticle

Feasibility of Recycled Aggregate Concrete in a Novel Anchoring Connection for Beam-to-Concrete-Filled Steel Tube Joints

by Jianhua Su, Qian Zhao, Li’ao Cai, Xiaohui Li, Hongyin Pu, Wei Dai, Jian Zhang, Deng Lu and Feng Liu

Buildings 2024, 14(4), 1178; https://doi.org/10.3390/buildings14041178 - 21 Apr 2024

Viewed by 423

Abstract

Owing to the substantial benefits in environmental protection and resource saving, recycled aggregate concrete (RAC) is increasingly used in civil engineering; among the different types, RAC-filled steel tubes are an efficient structural form utilizing the advantages of concrete and steel tubes. This paper [...] Read more.

Owing to the substantial benefits in environmental protection and resource saving, recycled aggregate concrete (RAC) is increasingly used in civil engineering; among the different types, RAC-filled steel tubes are an efficient structural form utilizing the advantages of concrete and steel tubes. This paper proposed a novel full-bolted beam-to-concrete-filled steel tube (CFST) joint and investigated the anchoring behavior of the steel plates embedded in RAC-filled steel tubes, which represents the behavior of the tensile zone in this joint, to demonstrate the feasibility of utilizing RAC in composite structures. The specimen consisted of a CFST and a connecting plate embedded in the CFST. In total, 18 specimens were tested to study the effects of concrete type (i.e., recycled aggregate concrete and natural aggregate concrete), anchoring type (i.e., plate with holes, notches, and rebars), and plate thickness on the pullout behavior, such as anchorage strength, load–displacement response, and ductility. Based on experimental results, the aggregate type of the concrete does not affect the pullout behavior obviously but the influence of anchoring type is significant. Among the three anchoring methods, the plate with rebars exhibits the best performance in terms of anchorage strength and ductility, and is recommended for the beam-to-CFST joint. In addition, plate thickness obviously affects the behavior of plates with holes and notches, the bearing area of which is proportional to the thickness, whereas the pullout behavior of the plates with rebars is independent of thickness. Finally, design formulas are proposed to estimate the anchorage strength of the connecting plates, and their reasonability is validated using the experimental results. Full article

(This article belongs to the Special Issue New Concrete Materials: Performance Analysis and Research)

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27 pages, 20905 KiB

Open AccessArticle

Bond–Slip Performance of Steel–Fiber-Reinforced Polymer Composite Bars (SFCBs) and Glass Fiber with Expansion-Agent-Reinforced Seawater Sea-Sand Concrete (GF-EA-SSSC) under Freezing–Thawing Environment

by Yufu Li, Jiayu Jian, Yuying Song, Wei Wei, Yilin Zhang, Gangliang Li, Huanyu Zhu, Jiawei Lin and Zhe Xiong

Buildings 2024, 14(4), 1121; https://doi.org/10.3390/buildings14041121 - 17 Apr 2024

Viewed by 303

Abstract

The combined application of steel–FRP composite bars (SFCBs) and seawater sea-sand concrete (SSSC) in marine engineering not only solves the problem of resource scarcity and reduces the construction cost but also avoids the problems of chloride corrosion of steel reinforcement in seawater sea-sand [...] Read more.

The combined application of steel–FRP composite bars (SFCBs) and seawater sea-sand concrete (SSSC) in marine engineering not only solves the problem of resource scarcity and reduces the construction cost but also avoids the problems of chloride corrosion of steel reinforcement in seawater sea-sand concrete and the lack of ductility of FRP bars. At the same time, the addition of glass fiber (GF) and expansion agent (EA) in appropriate amounts improves the crack resistance and seepage resistance of concrete. However, the durability of SFCB with GF- and EA-reinforced SSSC in freezing–thawing environment remains unclear, which limits its potential application in cryogenic marine engineering. This study investigates the bonding properties between SFCB and GF-EA-SSSC interfaces using eccentric pullout experiments under different thicknesses of concrete protective cover and a number of freezing–thawing cycles. The results showed that the compressive strength and dynamic elastic modulus of SSSC decrease, while the mass loss increases with an increasing number of freezing–thawing cycles. Additionally, the bond strength and stiffness between SFCB and SSSC decrease, leading to an increase in relative slip. However, the rate of bond strength and stiffness loss decreases with an increase in the thickness of the concrete protective cover. Furthermore, formulas for bond strength, relative slip, and bond stiffness are established to quantify the effects of the thickness of the concrete protective cover and the number of freezing–thawing cycles. The experimental values obtained verify the accuracy of these formulas, with a relative error of less than 5%. Moreover, a bond stress–slip constitutive model is developed for SFCB and GF-EA-SSSC, and the fitting results closely resemble the experimental values, demonstrating a high level of model fit. Full article

(This article belongs to the Special Issue New Concrete Materials: Performance Analysis and Research)

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16 pages, 4213 KiB

Open AccessArticle

Mechanical and Thermal Properties of an Energy-Efficient Cement Composite Incorporating Silica Aerogel

by Tatiana Aleksandrovna Koriakovtseva, Anna Evgenyevna Dontsova and Darya Viktorovna Nemova

Buildings 2024, 14(4), 1034; https://doi.org/10.3390/buildings14041034 - 08 Apr 2024

Viewed by 370

Abstract

The thermal performance of the building envelope is significant in energy-efficient construction. Because concrete is widely used in civil engineering, options to reduce its R-value should be considered. This study explores the thermal and structural properties of aerogel-enhanced concrete. Silica aerogel powder was [...] Read more.

The thermal performance of the building envelope is significant in energy-efficient construction. Because concrete is widely used in civil engineering, options to reduce its R-value should be considered. This study explores the thermal and structural properties of aerogel-enhanced concrete. Silica aerogel powder was mixed with fine-grained concrete at 15 vol.%. Two series of samples were prepared to identify the preferred technology. The first series of samples were mixed without isopropyl alcohol; for the second series, the alcohol was mixed with silica aerogel before mixing into the dry mix. The thermal conductivity, compressive strength, and bending resistance of the specimens were measured. The presence of silica aerogel admix resulted in a decrease in the compressive strength of the specimens by 30% compared with that of the reference samples and a reduction in the bending strength of the samples by 9% compared with that of the reference samples. For the first and second series of samples, the K-values of the aerogel-enhanced specimens varied in the range from 0.83 W/(m·K) to 1.13 W/(m·K), respectively. To further decrease the thermal conductivity, gypsum putty was then added to the specimens, resulting in the K-values further decreasing to 0.64 W/(m·K) and 0.84 W/(m·K), respectively. The calculation of heat losses through 1 m² of the aerogel-enhanced concrete wall was performed. It has been shown that energy expenses for heating can be lowered by 30%. The calculation of the greenhouse gas emissions from the combustion of fuel required for heating was also considered. The emissions decreased by 30.2% compared with the reference sample. Microscopic examination of the face and section surfaces of the sample revealed a significant number of pores compared with conventional fine-grain concrete. Full article

(This article belongs to the Special Issue New Concrete Materials: Performance Analysis and Research)

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20 pages, 8592 KiB

Open AccessArticle

Combined Effects of Steel and Glass Fibres on the Fracture Performance of Recycled Rubber Concrete

by Xiaohui Li, Zezhou Pan, Hao Zhen, Wenhua Luo, Zhuangwei Chen, Hongming Li, Zhichao Wu, Feng Liu and Lijuan Li

Buildings 2024, 14(4), 864; https://doi.org/10.3390/buildings14040864 - 22 Mar 2024

Viewed by 462

Abstract

As an environmentally friendly construction material, recycled rubber concrete (RRC) is commonly used as a road material owing to its excellent flexural strength and crack resistance. Previous studies have shown that the addition of fibres is an effective method for improving the crack [...] Read more.

As an environmentally friendly construction material, recycled rubber concrete (RRC) is commonly used as a road material owing to its excellent flexural strength and crack resistance. Previous studies have shown that the addition of fibres is an effective method for improving the crack resistance of concrete. The purpose of this study is to investigate the fracture performance of RRC reinforced with steel fibres (SFs) and glass fibres (GFs). A total of 28 RRC mixtures were prepared. The results of the fracture test showed that the addition of SFs and GFs significantly enhanced the RRC fracture performance. The maximum increases or decreases in flexural strength, brittleness coefficient, fracture energy, initial fracture toughness, and unstable fracture toughness were 64.9, −34.6, 775.6, 92.0, and 118.4%, respectively. The ideal GF content is usually in the range of 0.4–0.6% and decreases with increasing SF content. In addition, scanning electron microscope (SEM) tests were conducted to explore the mechanism of the effect of hybrid fibres on RRC at a microscopic level. The results show that SFs were always pulled out, while GFs were pulled apart at the initial defects. At the same time, excessive GFs caused more initial defects. These results are expected to provide theoretical direction and experimental support for the practical application of hybrid fibre-reinforced recycled rubber concrete (HFRRRC). Full article

(This article belongs to the Special Issue New Concrete Materials: Performance Analysis and Research)

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19 pages, 9338 KiB

Open AccessArticle

Geopolymerization of Coal Gangue via Alkali-Activation: Dependence of Mechanical Properties on Alkali Activators

by Xiaoping Wang, Feng Liu, Zezhou Pan, Weizhi Chen, Faheem Muhammad, Baifa Zhang and Lijuan Li

Buildings 2024, 14(3), 787; https://doi.org/10.3390/buildings14030787 - 14 Mar 2024

Viewed by 527

Abstract

Coal gangue (CG) is a residual product from coal mining and washing processes. The reutilization of CG to produce geopolymers is a low-carbon disposal strategy for this material. In this study, the calcined CG (CG_700°C) was used as aluminosilicate precursors, and [...] Read more.

Coal gangue (CG) is a residual product from coal mining and washing processes. The reutilization of CG to produce geopolymers is a low-carbon disposal strategy for this material. In this study, the calcined CG (CG_700°C) was used as aluminosilicate precursors, and the effects of alkali activators (i.e., Na₂SiO₃/NaOH, NaOH concentration, and liquid–solid) on the mechanical characteristics and microstructure of CG_700°C-based geopolymers were investigated. The findings indicated that the specimens with a liquid–solid ratio of 0.50 (G_2.0-10-0.50) exhibited a compact microstructure and attained a compressive strength of 24.75 MPa. Moreover, increasing the Na₂SiO₃/NaOH mass ratio has shortened the setting times and facilitated geopolymer gel formation, resulting in a denser microstructure and improved compressive strength. The higher NaOH concentrations of alkali activators facilitated the dissolution of CG_700°C particles, and the geopolymerization process was more dependent on the condensation of SiO₄ and AlO₄ ions, which promoted the formation of geopolymer networks. Conversely, an increase in the liquid–solid ratio from 0.50 to 0.65 had a negative impact on compressive strength enhancement, impeding the polycondensation rate. Examination through scanning electron microscopy and mercury intrusion porosimetry revealed that employing a lower Na₂SiO₃/NaOH mass ratio (G_1.2-10-0.55), smaller NaOH concentrations (G_2.0-8-0.55), and a higher liquid–solid ratio (G_2.0-10-0.65) led to the presence of larger pores, resulting in decreased 28 days compressive strength values (15.87 MPa, 13.25 MPa, and 14.92 MPa, respectively), and a less compact structure. The results suggest that the performance of CG_700°C-based geopolymers is significantly influenced by alkali activators. Full article

(This article belongs to the Special Issue New Concrete Materials: Performance Analysis and Research)

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21 pages, 11990 KiB

Open AccessArticle

Experimental Study on the Effects of Straight and Ring-Type Steel Fibres on the Bond Behaviour of Steel Bars in Rubber-Recycled Aggregate Concrete

by Honglong Ma, Huawei Li, Jinhu Zheng, Wei Wei, Shaohua He, Xiaopeng Tian, Xiaohui Li and Feng Liu

Buildings 2024, 14(2), 504; https://doi.org/10.3390/buildings14020504 - 12 Feb 2024

Viewed by 593

Abstract

The application range of rubber-recycled aggregate concrete (RRAC), a new type of green building material, is currently limited due to performance defects, including low hardness, high water absorption, and poor adhesion. To expand its application in reinforced concrete structures, it is crucial to [...] Read more.

The application range of rubber-recycled aggregate concrete (RRAC), a new type of green building material, is currently limited due to performance defects, including low hardness, high water absorption, and poor adhesion. To expand its application in reinforced concrete structures, it is crucial to enhance the bonding performance between RRAC and steel bars. In this study, the effects of adding straight steel fibres (SSFs) and ring-type steel fibres (RSFs) to RRAC were investigated, in order to enhance the bonding performance. To investigate the impact of steel fibres (SFs) on the bonding properties of RRAC and steel bars, a total of 51 specimens were subjected to pull-out tests to systematically examine the impact of SSF and RSF dosages on the bonding performance. The results demonstrated that incorporating the optimal amount of SSFs and RSFs can significantly improve the bond strength and bond stiffness. Moreover, the combined use of SSFs and RSFs yielded even better enhancement effects. The RRAC exhibited remarkable performance, when the total content of SFs was 1.2% and the proportion of RSFs 75%. In this case, the bond strength and bond stiffness were enhanced by 3.7% and 53.88%, respectively. Finally, a bond–slip constitutive model for RRAC and steel bar was established. The combined use of SSFs and RSFs minimizes the limitations of poor mechanical properties in traditional RRAC and holds significant value for the widespread adoption and application of RRAC. Full article

(This article belongs to the Special Issue New Concrete Materials: Performance Analysis and Research)

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21 pages, 21456 KiB

Open AccessArticle

Study on the Dynamic Performance and Damage Evaluation of Rubber-Modified Non-Autoclaved Concrete Pipe Piles under Axial Drop Hammer Impact

by Sheng Lan, Feng Liu, Fei Yang, Wanhui Feng and Dawei Chen

Buildings 2024, 14(2), 489; https://doi.org/10.3390/buildings14020489 - 09 Feb 2024

Viewed by 400

Abstract

In order to improve the weak impact resistance of non-autoclaved concrete pipe piles, this study replaced sand in the concrete with rubber particles of different volume contents to obtain rubber-modified non-autoclaved concrete pipe piles (with volume contents of 0%, 5%, 10%, and 15%). [...] Read more.

In order to improve the weak impact resistance of non-autoclaved concrete pipe piles, this study replaced sand in the concrete with rubber particles of different volume contents to obtain rubber-modified non-autoclaved concrete pipe piles (with volume contents of 0%, 5%, 10%, and 15%). The dynamic impact response characteristics of rubber-modified non-autoclaved concrete pipe piles were obtained through large-scale axial hammer impact experiments. The results indicate the following. (1) Non-autoclaved concrete pipe piles without rubber additives were prone to expansion deformation instability under impact. When the rubber content was 10%, the expansion deformation of the piles was the weakest, and the state was the most stable. (2) When the impact energy exceeded 48 kJ, the deformation energies of piles with 5% and 10% rubber contents significantly increased. (3) The damage levels of the piles after hammer impact were classified into four grades: no damage, mild damage, moderate damage, and severe damage. When the impact energy was greater than or equal to 48 kJ, rubber-modified non-autoclaved concrete pipe piles exhibited damage. The zone with no damage for piles with 10% rubber content was the smallest, making it less prone to damage under impact loads. The rubber-modified non-autoclaved concrete pipe piles with 10% rubber content not only had excellent impact resistance but also utilized the advantages of being environmentally friendly and energy-saving. They filled a certain knowledge gap in green building materials. Full article

(This article belongs to the Special Issue New Concrete Materials: Performance Analysis and Research)

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22 pages, 8622 KiB

Open AccessArticle

Performance Evaluation of Thermal Insulation Rubberized Mortar Modified by Fly Ash and Glass Fiber

by Zezhou Pan, Feng Liu, Huawei Li, Xiaohui Li, Daochu Wang, Zao Ling, Huanyu Zhu and Yuhao Zhu

Buildings 2024, 14(1), 221; https://doi.org/10.3390/buildings14010221 - 14 Jan 2024

Cited by 4 | Viewed by 1088

Abstract

The utilization of waste rubber as a viable option for manufacturing building materials holds great significance for the sustainable development of the construction industry. This study explores the addition of two additives, fly ash (FA) and glass fiber (GF), to rubberized mortar in [...] Read more.

The utilization of waste rubber as a viable option for manufacturing building materials holds great significance for the sustainable development of the construction industry. This study explores the addition of two additives, fly ash (FA) and glass fiber (GF), to rubberized mortar in order to improve its performance. The impact of different waste rubber powder (RP) replacement rates and modified additive dosages on the performance of rubberized mortar, including fluidity, mechanical properties, drying shrinkage, impact resistance, and thermal insulation properties, was investigated. Furthermore, the analytic hierarchy process (AHP) was adopted to study the priorities of the rubberized mortar modified by FA and GF. The results indicate that the addition of RP leads to a decrease in mortar fluidity, mechanical properties, and drying shrinkage. However, it can enhance its impact resistance and thermal insulation properties. The additives, FA and GF, have a significant influence on the properties of rubberized mortar. By means of AHP method analysis, this study concludes that the optimal comprehensive properties of FA- and GF-modified rubberized mortar can be achieved by replacing 10% of sand with RP and using 10% FA and 0.4% GF. This study presents a configuration method for modified thermal insulation rubberized mortar, and it may lead to FA and GF being considered potential candidates for developing environmentally friendly building materials. Full article

(This article belongs to the Special Issue New Concrete Materials: Performance Analysis and Research)

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21 pages, 6180 KiB

Open AccessArticle

Effect of Expansion Agent and Glass Fiber on the Dynamic Splitting Tensile Properties of Seawater–Sea-Sand Concrete

by Huanyu Zhu, Zhe Xiong, Yuying Song, Keting Zhou and Yue Su

Buildings 2024, 14(1), 217; https://doi.org/10.3390/buildings14010217 - 13 Jan 2024

Cited by 6 | Viewed by 637

Abstract

In marine structural engineering, the impact resistance of concrete holds high significance. The determination of whether the combined use of expansion agent (EA) and glass fiber (GF) has a synergistic effect on the impact resistance of seawater–sea-sand concrete (SSC) and plays a role [...] Read more.

In marine structural engineering, the impact resistance of concrete holds high significance. The determination of whether the combined use of expansion agent (EA) and glass fiber (GF) has a synergistic effect on the impact resistance of seawater–sea-sand concrete (SSC) and plays a role in its performance and application. In this study, the dynamic Brazilian disc test at various strain rates was carried out with an SHPB device to investigate the effect of mixing 0% and 6% EA with 0% and 1% GF on the dynamic splitting tensile properties of SSC. The results show that strain rate effect on EA and GF-reinforced SSC during dynamic splitting tensile tests at higher strain rates, indicating strong strain rate sensitivity. The synergistic reinforcement of EA and GF consumed more energy under impact loading, thus maintaining the morphological integrity of concrete. However, the dynamic splitting tensile strength obtained in the Brazilian disc test had a significant overload effect which cannot be ignored. EA doped at 6% and GF doped at 1% showed a synergistic enhancement of SSC’s dynamic splitting tensile properties. Full article

(This article belongs to the Special Issue New Concrete Materials: Performance Analysis and Research)

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16 pages, 14453 KiB

Open AccessArticle

Bond Performance between Fiber-Wrapped Ribbed Basalt Fiber-Reinforced Polymer Bars and Seawater Sea-Sand Concrete

by Min Lin, Chenyue Weng, Hesheng Xiao, Dong Zeng, Baifa Zhang, Xiaopan Chen, Shaohua He and Lijuan Li

Buildings 2024, 14(1), 38; https://doi.org/10.3390/buildings14010038 - 22 Dec 2023

Viewed by 594

Abstract

The high corrosion resistance of fiber-reinforced polymers (FRPs) and related concrete structures means that they are suitable for application in the marine environment. Therefore, the replacement of steel bars with fiber-reinforced polymer (FRP) bars enhances corrosion resistance in seawater sea-sand concrete (SSC) structures. [...] Read more.

The high corrosion resistance of fiber-reinforced polymers (FRPs) and related concrete structures means that they are suitable for application in the marine environment. Therefore, the replacement of steel bars with fiber-reinforced polymer (FRP) bars enhances corrosion resistance in seawater sea-sand concrete (SSC) structures. Geometric parameters significantly influence the performance of the bond between ribbed FRP bars and SSC, thereby affecting the mechanical properties of the concrete structures. In this study, the performance of the bond between ribbed (i.e., with fiber wrapping) basalt-fiber-reinforced polymer (BFRP) bars and SSC was investigated through pull-out tests that considered rib geometry and SSC strength. The results demonstrated that an increase in rib and dent widths reduced the bond stiffness, while an increase in rib height and SSC strength gradually increased the bond stiffness and strength. Additionally, the bond stiffness and bond strength were relatively low because the surface fiber bundles buffered the mechanical interlocking force between the BFRP ribs and the concrete, resulting in plastic bond failure during the loading process. Furthermore, the adhesion of the fiber bundles to the surface of the BFRP bars also influenced bond performance, with higher adhesion leading to greater bond stiffness and strength. Full article

(This article belongs to the Special Issue New Concrete Materials: Performance Analysis and Research)

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