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学者姓名：张青天
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Abstract ：
In this paper, the effects of river sand, sea-sand, recycled sand, and shell sand on the carbonation performance of recycled aggregate concrete (RAC) were studied. The results showed that the carbonation depth of RAC prepared from sea-sand was 89.8-96.8 %, 83.8-93.4 %, and 70.5-84.8 % of that prepared from recycled sand, shell sand, and river sand, respectively. The compressive strength of RAC made from sea-sand was the highest, followed by RAC made from river sand, shell sand, and recycled sand. The chloride ions in the sea-sand promoted the formation of Friedel's salt and C-S-H with a high Ca/Si ratio, increasing the density of the concrete, thereby blocking the CO2 diffusion channel and reducing the carbonation rate. On the other hand, the weak strength and bond of shell sand, and the weak interfacial transition zone of recycled sand resulted in weak concrete microstructure. In this paper, after 90 days of carbonation, the increment of CaCO3 for preparing RAC from sea-sand was 95.1 %, 67.7 %, and 37.7 % of that of river sand, shell sand, and recycled sand, respectively. The RAC made of shell sand or recycled sand had a porous microstructure, which provided sufficient growth space for CaCO3, and its total porosity was significantly reduced after carbonation. Finally, a prediction model of RAC's carbonation depth was proposed, which was highly consistent with the experimental results. The mean error of the model was close to 1.0 and the COV was 0.169.
Keyword ：
Carbonation depth Carbonation depth Carbonation properties Carbonation properties Fine aggregates Fine aggregates Prediction model Prediction model Recycled aggregate concrete (RAC) Recycled aggregate concrete (RAC)
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| GB/T 7714 | Zhang, Kaijian , Wang, Lin , Li, Ziying et al. Effects of different fine aggregates as sand replacements on the carbonation properties of recycled aggregate concrete [J]. | CONSTRUCTION AND BUILDING MATERIALS , 2025 , 468 . |
| MLA | Zhang, Kaijian et al. "Effects of different fine aggregates as sand replacements on the carbonation properties of recycled aggregate concrete" . | CONSTRUCTION AND BUILDING MATERIALS 468 (2025) . |
| APA | Zhang, Kaijian , Wang, Lin , Li, Ziying , Zhang, Qingtian . Effects of different fine aggregates as sand replacements on the carbonation properties of recycled aggregate concrete . | CONSTRUCTION AND BUILDING MATERIALS , 2025 , 468 . |
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The compressive strength data of 3D printed concrete (3DPC) in X (Print direction), Y (Adjacent stripes), and Z (Stacked stripes) were collected and analyzed to evaluate its anisotropic behavior and statistical parameters. Similar to conventional cast concrete, there is a linear relationship between the compressive strength of 3DPC and the binder-to-water ratio (B/W). For the normalized strength data, the average ratios of X/C, Y/C, and Z/C at 28 days are 0.87, 0.80, and 0.82 respectively, indicating a decrease in the compressive strength and anisotropy compared to cast concrete. Compared to the coefficient of variation (COV) of cast specimens mentioned in the specifications, there is an increase of 4.3–69 %. The weak interfaces and unique pore shapes in 3DPC interact to cause stress concentration and redistribution of internal stresses, resulting in decreased compressive strength, anisotropy, and variability. This investigation can provide material parameters for studying the structural performance of 3DPC components. © 2024
Keyword ：
3D printing 3D printing Anisotropy Anisotropy Compressive strength Compressive strength
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| GB/T 7714 | Zhang, Kaijian , Lin, Wenqiang , Zhang, Qingtian et al. Evaluation of anisotropy and statistical parameters of compressive strength for 3D printed concrete [J]. | Construction and Building Materials , 2024 , 440 . |
| MLA | Zhang, Kaijian et al. "Evaluation of anisotropy and statistical parameters of compressive strength for 3D printed concrete" . | Construction and Building Materials 440 (2024) . |
| APA | Zhang, Kaijian , Lin, Wenqiang , Zhang, Qingtian , Wang, Dehui , Luo, Surong . Evaluation of anisotropy and statistical parameters of compressive strength for 3D printed concrete . | Construction and Building Materials , 2024 , 440 . |
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Polypropylene fibers possess high strength and excellent abrasion resistance, and have been used to enhance concrete materials. This study investigated the influence of polypropylene fibers on the dynamic compressive properties of seawater sea-sand recycled aggregate concrete (SSRAC) under three strain rates (10- 5 , 10-4, and 10-3/s). 90 specimens were prepared, with fiber lengths of 9, 13.5, and 18 mm (the corresponding aspect ratio of 357, 536, and 714, respectively), and fiber contents of 0.6, 0.9, and 1.2 kg/m3. The test results indicate that the polypropylene fiber reinforced SSRAC specimens are more sensitive to strain rate in terms of peak stress and peak strain, and the incorporation of fibers generally increases the peak stress. Furthermore, the microscopic morphology and nanoindentation analysis are conducted on the interfacial transition zone (ITZ) of the polypropylene fiber reinforced SSRAC. The addition of polypropylene fibers increases the local porosity of the ITZ, and reduces the bonding area between mortar and aggregates, resulting in a decrease in the elastic modulus of the ITZ. This reduction effect varies with different lengths and contents of fibers, which has a significant impact on the peak stress, peak strain, and elastic modulus of specimens, leading to some degree of dispersion in the corresponding strain effect. Finally, a dynamic prediction model for fiber-reinforced SSRAC is derived, which provides a theoretical basis for the study of the dynamic mechanical properties of fiber reinforced SSRAC.
Keyword ：
Interfacial transition zone (ITZ) Interfacial transition zone (ITZ) Polypropylene fibers Polypropylene fibers Seawater sea-sand recycled aggregate concrete Seawater sea-sand recycled aggregate concrete (SSRAC) (SSRAC) Stress-strain curve Stress-strain curve Uniaxial compression Uniaxial compression
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| GB/T 7714 | Zhang, Kaijian , Lin, Wenqiang , Lan, Qibin et al. Compressive properties of polypropylene fiber reinforced seawater sea-sand recycled aggregate concrete under different strain rate loading [J]. | CONSTRUCTION AND BUILDING MATERIALS , 2024 , 452 . |
| MLA | Zhang, Kaijian et al. "Compressive properties of polypropylene fiber reinforced seawater sea-sand recycled aggregate concrete under different strain rate loading" . | CONSTRUCTION AND BUILDING MATERIALS 452 (2024) . |
| APA | Zhang, Kaijian , Lin, Wenqiang , Lan, Qibin , Zhang, Qingtian . Compressive properties of polypropylene fiber reinforced seawater sea-sand recycled aggregate concrete under different strain rate loading . | CONSTRUCTION AND BUILDING MATERIALS , 2024 , 452 . |
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Abstract ：
In the past 20 years, recycled aggregate concrete (RAC), as a type of low-carbon concrete, has become a worldwide focus of research. However, the design methodology for RAC structural components remains a challenge. Consequently, demands for a unified design of natural aggregate concrete (NAC) and RAC components have been presented. Accordingly, this study analyses the necessity of a unified design theory and provides an in-depth demonstration of the strength determination, compressive constitutive relationship, and design method of concrete components. The coefficient of variation of RAC strength is found to be generally higher than that of NAC strength. The compressive and tensile strengths of RAC can be defined and determined using the same method as that used for NAC. The uniaxial compressive constitutive relationship between NAC and RAC has a unified mathematical expression. However, the elastic modulus of RAC decreases, and its brittleness exhibits an increasing trend compared with that of NAC. Finally, to unify the design formulae of RAC and NAC components for bearing capacity, modification factors for RAC components are proposed considering safety and reliability. Additionally, the feasibility of the proposed unified time-dependent design theory is demonstrated in terms of conceptual design and structural measures considering the effects of strength degradation and reinforcement corrosion. It is believed that this study enriches and develops the basic theory of concrete structures. (c) 2023 THE AUTHORS. Published by Elsevier LTD on behalf of Chinese Academy of Engineering and Higher Education Press Limited Company. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
Keyword ：
Constitutive relation Constitutive relation Natural aggregate concrete (NAC) Natural aggregate concrete (NAC) Recycled aggregate concrete (RAC) Recycled aggregate concrete (RAC) Reliability Reliability Strength determination Strength determination Unified design theory Unified design theory
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| GB/T 7714 | Xiao, Jianzhuang , Zhang, Kaijian , Ding, Tao et al. Fundamental Issues Towards Unified Design Theory of Recycled and Natural Aggregate Concrete Components [J]. | ENGINEERING , 2024 , 29 : 188-197 . |
| MLA | Xiao, Jianzhuang et al. "Fundamental Issues Towards Unified Design Theory of Recycled and Natural Aggregate Concrete Components" . | ENGINEERING 29 (2024) : 188-197 . |
| APA | Xiao, Jianzhuang , Zhang, Kaijian , Ding, Tao , Zhang, Qingtian , Xiao, Xuwen . Fundamental Issues Towards Unified Design Theory of Recycled and Natural Aggregate Concrete Components . | ENGINEERING , 2024 , 29 , 188-197 . |
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To solve the problem of the lack of structural design basis of fiber reinforced recycled aggregate concrete (FRAC), and promote its realistic application, in this investigation, the replacement ratio of recycled coarse aggregate (RCA), fiber type, fiber content, and fiber blending forms are taken as experimental variables. With the size of Phi 100 mmx300 mm, 21 groups of cylindrical specimens are designed to study the influence of the above variables on the complete stress-strain curve of fiber RAC when bearing uniaxial tension. The results show that the tensile characteristic values decrease as the replacement ratio of RCA increases. When single doping of fibers was considered, the tensile characteristic values increased as fiber content increased. When the steel (SF) was mixed with polyvinyl alcohol fiber (PVAF) and polypropylene fiber (PPF), the tensile characteristic values were improved. Proper blending of PVAF and PPF can improve the characteristic values of tensile ductility. Through the results of the uniaxial tensile experiment, constitutive equations of the uniaxial tensile stress-strain curve of FRAC under different test variables were established, which can provide fundamental material parameters to design FRAC structures.
Keyword ：
Constitutive relationship Constitutive relationship Fiber Fiber Recycled aggregate concrete (RAC) Recycled aggregate concrete (RAC) Uniaxial tensile stress-strain curve Uniaxial tensile stress-strain curve
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| GB/T 7714 | Luo, Surong , Zhou, Wentao , Yu, Minming et al. Stress-strain relationship of fiber reinforced recycled aggregate concrete under uniaxial tension [J]. | CONSTRUCTION AND BUILDING MATERIALS , 2024 , 422 . |
| MLA | Luo, Surong et al. "Stress-strain relationship of fiber reinforced recycled aggregate concrete under uniaxial tension" . | CONSTRUCTION AND BUILDING MATERIALS 422 (2024) . |
| APA | Luo, Surong , Zhou, Wentao , Yu, Minming , Zhang, Kaijian , Zhang, Qingtian . Stress-strain relationship of fiber reinforced recycled aggregate concrete under uniaxial tension . | CONSTRUCTION AND BUILDING MATERIALS , 2024 , 422 . |
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Abstract ：
This paper presents a review of the research on seawater sea -sand recycled coarse aggregate concrete (SSRAC), which offers a solution to the scarcity of river sand and freshwater while also promoting the reuse of waste concrete. The study reveals that the conventional mix proportion design method underestimates the compressive strength of SSRAC at 28 days. The incorporation of seawater and sea -sand reduces the negative effects of recycled coarse aggregate (RCA) on compressive properties, compensating for the decreased mechanical properties of components made with RCA. Additionally, it enhances the bond strength between concrete and epoxy -coated bars while it has a lesser effect on that between concrete and fiber reinforced polymer (FRP) bars. Nevertheless, it appears to have adverse effects on workability and tensile properties. The primary factors influencing the stress -strain curves of SSRAC are RCA, shell content, and chloride ion concentration. The effective confinement of FRP and the stiffness of FRP bars are crucial considerations in the design of SSRAC components. Furthermore, the combination of SSRAC with other types of concrete offers an alternative design approach. Finally, this paper identifies research needs for SSRAC, with a focus on durability and time -dependent properties.
Keyword ：
Mechanical properties Mechanical properties Recycled aggregate concrete (RAC) Recycled aggregate concrete (RAC) Seawater and sea-sand Seawater and sea-sand Stress-strain relationships Stress-strain relationships Structural behaviors Structural behaviors
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| GB/T 7714 | Zhang, Kaijian , Zhang, Qingtian , Lin, Wenqiang et al. Material and structural properties of recycled coarse aggregate concrete made with seawater and sea-sand: A review [J]. | JOURNAL OF BUILDING ENGINEERING , 2024 , 87 . |
| MLA | Zhang, Kaijian et al. "Material and structural properties of recycled coarse aggregate concrete made with seawater and sea-sand: A review" . | JOURNAL OF BUILDING ENGINEERING 87 (2024) . |
| APA | Zhang, Kaijian , Zhang, Qingtian , Lin, Wenqiang , Ou, Junrui . Material and structural properties of recycled coarse aggregate concrete made with seawater and sea-sand: A review . | JOURNAL OF BUILDING ENGINEERING , 2024 , 87 . |
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To explore the flexural fatigue performance of steel fibers reinforced recycled aggregate concrete (SF-RAC), the flexural fatigue test and residual strength test with different stress levels were conducted. Besides, the fatigue cracks propagation under cyclic loading were observed and analyzed by digital image correlation (DIC) technology. The results show that the flexural fatigue life of SF-RAC increases when the content of steel fibers increases, and it is proved to be well in accordance with the three-parameter Weibull distribution. The flexural fatigue life equation with different stress level and reliability (S-N-P equation) is obtained based on it, which shows that when the fiber volume content is 1.5%, the fatigue strength of SF-RAC is about 37.2% higher than that of RAC without fibers. Then, a fatigue strain-based damage evolution model is established, and the derived residual strength model can well predict the damage degree and residual life of SF-RAC. Moreover, the steel fibers can improve the critical crack propagation length and loading cycles of RAC. The crack propagation rate can be decreased by 97.63% when the fiber volume content is 1.5%, and it is increased with the development of stress level. Finally, the influence mechanism of steel fibers on flexural fatigue performance of RAC were explained through microstructure tests.
Keyword ：
Crack propagation rate Crack propagation rate Digital image correlation (DIC) Digital image correlation (DIC) Flexural fatigue performance Flexural fatigue performance Recycled aggregate concrete (RAC) Recycled aggregate concrete (RAC) Steel fibers Steel fibers Three -parameter Weibull distribution Three -parameter Weibull distribution
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| GB/T 7714 | Luo, Surong , Su, Yongqing , Zhang, Qingtian et al. Effects of steel fibers on the flexural fatigue performance of recycled aggregate concrete [J]. | CONSTRUCTION AND BUILDING MATERIALS , 2024 , 412 . |
| MLA | Luo, Surong et al. "Effects of steel fibers on the flexural fatigue performance of recycled aggregate concrete" . | CONSTRUCTION AND BUILDING MATERIALS 412 (2024) . |
| APA | Luo, Surong , Su, Yongqing , Zhang, Qingtian , Zhang, Kaijian . Effects of steel fibers on the flexural fatigue performance of recycled aggregate concrete . | CONSTRUCTION AND BUILDING MATERIALS , 2024 , 412 . |
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Abstract ：
考虑贝壳含量、龄期等因素,对不同加载应变率下的海水海砂再生混凝土(SSRAC)试件开展了单轴受压应力-应变曲线试验.结果表明:600 d时,与普通混凝土(NAC)相比,SSRAC峰值应力和峰值应变分别提高了10.4%、23.2%,弹性模量降低了29.1%;当掺入贝壳颗粒后,SSRAC应变率敏感性增加;结合试验以及文献数据,基于GB50010模型,考虑不同应变率下特征参数的动态增大系数,提出了适用于中低应变率(10-5～10-1 s-1)下SSRAC受压动力本构模型,并对其曲线特征进行了机理解释.
Keyword ：
再生混凝土 再生混凝土 动态增大系数 动态增大系数 单轴受压应力-应变曲线 单轴受压应力-应变曲线 应变率 应变率 海水海砂 海水海砂
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| GB/T 7714 | 张青天 , 张凯建 . 海水海砂再生混凝土受压动力本构模型 [J]. | 建筑材料学报 , 2024 , 27 (7) : 580-588,610 . |
| MLA | 张青天 et al. "海水海砂再生混凝土受压动力本构模型" . | 建筑材料学报 27 . 7 (2024) : 580-588,610 . |
| APA | 张青天 , 张凯建 . 海水海砂再生混凝土受压动力本构模型 . | 建筑材料学报 , 2024 , 27 (7) , 580-588,610 . |
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This study utilizes recycled sand and shell sand to replace sea-sand in seawater sea-sand recycled aggregate concrete (SSRAC) and explores their dynamic compressive properties. A total of 28 sets of specimens were designed, and their stress-strain curves under different strain rates were analyzed. The findings indicated that the dynamic increasing factor (DIF) of peak stress in SSRAC reached its peak at a 50% replacement ratio of recycled sand, exhibiting a 3.9% to 7.7% increase compared to a 0% replacement ratio. Conversely, there was an overall decreasing trend in the DIF when the replacement ratio of shell sand increased. Using recycled sand resulted in an average reduction of approximately 45% in the elastic modulus of the interfacial transition zone (ITZ), while the introduction of shell sand slightly increased that of it. Finally, considering strain rate effects, a dynamic compressive prediction model for SSRAC with different types of fine aggregates was established.
Keyword ：
dynamic compressive properties dynamic compressive properties recycled sand recycled sand Seawater sea-sand recycled aggregate concrete (SSRAC) Seawater sea-sand recycled aggregate concrete (SSRAC) shell sand shell sand strain rates strain rates
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| GB/T 7714 | Zhang, Qingtian , Ou, Junrui , Lan, Qibin et al. Effects of recycled sand and shell sand as sand replacement on the dynamic properties of seawater sea-sand recycled aggregate concrete [J]. | JOURNAL OF SUSTAINABLE CEMENT-BASED MATERIALS , 2024 , 13 (11) : 1707-1723 . |
| MLA | Zhang, Qingtian et al. "Effects of recycled sand and shell sand as sand replacement on the dynamic properties of seawater sea-sand recycled aggregate concrete" . | JOURNAL OF SUSTAINABLE CEMENT-BASED MATERIALS 13 . 11 (2024) : 1707-1723 . |
| APA | Zhang, Qingtian , Ou, Junrui , Lan, Qibin , Zhang, Kaijian . Effects of recycled sand and shell sand as sand replacement on the dynamic properties of seawater sea-sand recycled aggregate concrete . | JOURNAL OF SUSTAINABLE CEMENT-BASED MATERIALS , 2024 , 13 (11) , 1707-1723 . |
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The compressive strength data of 3D printed concrete (3DPC) in X (Print direction), Y (Adjacent stripes), and Z (Stacked stripes) were collected and analyzed to evaluate its anisotropic behavior and statistical parameters. Similar to conventional cast concrete, there is a linear relationship between the compressive strength of 3DPC and the binder-to-water ratio (B/W). For the normalized strength data, the average ratios of X/C, Y/C, and Z/C at 28 days are 0.87, 0.80, and 0.82 respectively, indicating a decrease in the compressive strength and anisotropy compared to cast concrete. Compared to the coefficient of variation (COV) of cast specimens mentioned in the specifications, there is an increase of 4.3-69 %. The weak interfaces and unique pore shapes in 3DPC interact to cause stress concentration and redistribution of internal stresses, resulting in decreased compressive strength, anisotropy, and variability. This investigation can provide material parameters for studying the structural performance of 3DPC components.
Keyword ：
3DPC 3DPC Anisotropy Anisotropy Distribution of compressive strength Distribution of compressive strength Microstructures Microstructures Variability Variability
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| GB/T 7714 | Zhang, Kaijian , Lin, Wenqiang , Zhang, Qingtian et al. Evaluation of anisotropy and statistical parameters of compressive strength for 3D printed concrete [J]. | CONSTRUCTION AND BUILDING MATERIALS , 2024 , 440 . |
| MLA | Zhang, Kaijian et al. "Evaluation of anisotropy and statistical parameters of compressive strength for 3D printed concrete" . | CONSTRUCTION AND BUILDING MATERIALS 440 (2024) . |
| APA | Zhang, Kaijian , Lin, Wenqiang , Zhang, Qingtian , Wang, Dehui , Luo, Surong . Evaluation of anisotropy and statistical parameters of compressive strength for 3D printed concrete . | CONSTRUCTION AND BUILDING MATERIALS , 2024 , 440 . |
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