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Influence of steel corrosion on axial and eccentric compression behavior of coral aggregate concrete

《结构与土木工程前沿（英文）》 2021年 第15卷 第6期   页码 1415-1425 doi: 10.1007/s11709-021-0786-9

摘要： To study the behavior of coral aggregate concrete (CAC) column under axial and eccentric compression, the compression behavior of CAC column with different types of steel and initial eccentricity (ei) were tested, and the deformation behavior and ultimate bearing capacity (Nu) were studied. The results showed that as the ei increases, the Nu of CAC column decreases nonlinearly. Besides, the steel corrosion in CAC column is severe, which reduces the steel section and steel strength, and decreases the Nu of CAC column. The durability of CAC structures can be improved by using new organic coated steel. Considering the influence of steel corrosion and interfacial bond deterioration, the calculation models of Nu under axial and eccentric compression were presented.

关键词： coral aggregate concrete column     axial compression     eccentric compression     steel corrosion     calculation model    

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Damage-constitutive model for seawater coral concrete using different stirrup confinements subjected

《结构与土木工程前沿（英文）》 2023年 第17卷 第3期   页码 429-447 doi: 10.1007/s11709-022-0913-2

摘要： Recently, the application of detrital coral as an alternative to natural aggregates in marine structures has attracted increased attention. In this study, research on the compressive performance of coral aggregate concrete (CAC) confined using steel stirrups with anti-rust treatment was experimentally conducted. A total of 45 specimens were cast, including 9 specimens without stirrups and under different strength grades (C20, C30, and C40) and 36 specimens under different strength grades (C20, C30, and C40). Moreover, three stirrup levels (rectangular, diamond-shaped compound, and spiral stirrups) and different stirrup spacings (40, 50, 60, and 70 mm) were used. Subsequently, the stress−strain curves of specimens subjected to axial loading were measured. The effects of the stirrup spacing and stirrup configurations on the stress and strain were investigated, respectively, and the lateral effective stress of the different stirrups was calculated based on the cohesive-elastic ring model and modified elastic beam theory. Moreover, a damage-constitutive model of CAC considering the lateral stress was set up based on damage mechanics theory. The results indicated an increase in the stress and strain with a decrease in the stirrup spacing, and the adopted stirrup ratio had a better strengthening effect than the different concrete grades, and the variation in the deformation was restricted by the performance of coral coarse aggregate (CA). However, an increment in the lateral strain was observed with an increase in the axial strain. The lateral stress model showed a good agreement with the experimental data, and the proposed damage-constitutive model had a good correlation with the measured stress−strain curves.

关键词： coral aggregate concrete     stress−strain curves     lateral effective stress     peak stress     axial−lateral curves     damage-constitutive model.    

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考虑垫片形状和尺寸效应的珊瑚混凝土劈裂抗拉性能的三维细观研究 Article

吴彰钰, 张锦华, 余红发, 方秦, 麻海燕, 陈力

《工程（英文）》 2022年 第17卷 第10期   页码 110-122 doi: 10.1016/j.eng.2021.02.024

摘要：

珊瑚混凝土（CAC）作为一种新型建筑材料，已经在岛礁工程结构建设领域引起了极大的关注。为了研究CAC的静态劈裂抗拉性能，本文提出了一种考虑骨料形状和空间分布随机性的三维（3D）随机混凝土细观模型，影响因素包括试件形状和支承垫片尺寸。我们建立了12 个不同的混凝土细观模型，按照试件形状可分为两种，即边长为150 mm的立方体和尺寸为ϕ150 mm×300 mm的圆柱体。其中，支承垫片宽度为6 mm、9 mm、12 mm、15 mm、18 mm和20 mm。本文系统分析和讨论了试件几何形状和垫片宽度对CAC劈裂抗拉性能的影响规律，研究内容包括混凝土开裂过程、最终破坏模式和劈裂抗拉强度（fst）。结果表明：本文所开发的细观模型具有很高的可靠性，并确定了适用于CAC劈裂抗拉性能模拟和预测的最优计算参数。CAC的fst值与试件形状和垫片宽度直接相关。其中，在垫片尺寸相同的情况下，立方体CAC试件的fst值要略高于圆柱体模型，表明可以采用断裂面积的差异来解释试件形状效应对CAC fst值的影响规律。此外，当垫片的相对宽度由0.04 增加到0.13 时，CAC的fst值会呈现逐渐增大的趋势。基于弹性力学理论，本文初步确定了不同垫片宽度条件下CAC fst的取值范围，这对于研究CAC的抗拉性能具有重要意义。

关键词： 珊瑚混凝土     三维细观模拟     劈拉试验     抗拉强度     试件形状     支承垫片    

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Chloride ingress and macro-cell corrosion of steel in concrete made with recycled brick aggregate

《结构与土木工程前沿（英文）》 2021年 第15卷 第6期   页码 1358-1371 doi: 10.1007/s11709-021-0769-x

摘要： An investigation on chloride ingress and macro-cell corrosion of steel bars in concrete made with recycled brick aggregate (RBA) was carried out. As control cases, virgin brick aggregate (BA) and stone aggregate (SA) were also investigated. Both cylindrical and cracked prism specimens were studied for 16 different cases. The prism specimens were made with a segmented steel bar providing electrical connection from outside of the specimens to measure macro-cell corrosion current continuously under seawater splash exposure for a period of 30 d using a data logger. Cylindrical specimens were submerged in 3% NaCl solution at a temperature of 40°C to investigate chloride ingress in concrete made with RBA, BA, and SA after 120 and 180 d. Half-cell potential, corrosion area, and depths of corrosion were also investigated. The chloride ingress as well as corrosion of steel bars in concrete made with the different types of aggregate is ordered as RBA > BA > SA.

关键词： brick aggregate     chloride ingress     macro-cell corrosion     recycled brick aggregate    

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Understanding the behavior of recycled aggregate concrete by using thermogravimetric analysis

Subhasis PRADHAN, Shailendra KUMAR, Sudhirkumar V. BARAI

《结构与土木工程前沿（英文）》 2020年 第14卷 第6期   页码 1561-1572 doi: 10.1007/s11709-020-0640-5

摘要： The physio-chemical changes in concrete mixes due to different coarse aggregate (natural coarse aggregate and recycled coarse aggregate (RCA)) and mix design methods (conventional method and Particle Packing Method (PPM)) are studied using thermogravimetric analysis of the hydrated cement paste. A method is proposed to estimate the degree of hydration ( ) from chemically bound water ( ). The PPM mix designed concrete mixes exhibit lower . Recycled aggregate concrete (RAC) mixes exhibit higher and after 7 d of curing, contrary to that after 28 and 90 d. The chemically bound water at infinite time ( ) of RAC mixes are lower than the respective conventional concrete mixes. The lower , Ca(OH) bound water, free Ca(OH) content and FT-IR analysis substantiate the use of pozzolanic cement in the parent concrete of RCA. The compressive strength of concrete and cannot be correlated for concrete mixes with different aggregate type and mix design method as the present study confirms that the degree of hydration is not the only parameter which governs the macro-mechanical properties of concrete. In this regard, further study on the influence of interfacial transition zone, voids content and aggregate quality on macro-mechanical properties of concrete is needed.

关键词： recycled aggregate concrete     Particle Packing Method     thermogravimetric analysis     chemically bound water     degree of hydration     Fourier transform infrared spectroscopy    

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Behaviors of recycled aggregate concrete-filled steel tubular columns under eccentric loadings

Vivian W. Y. TAM, Jianzhuang XIAO, Sheng LIU, Zixuan CHEN

《结构与土木工程前沿（英文）》 2019年 第13卷 第3期   页码 628-639 doi: 10.1007/s11709-018-0501-7

摘要： The paper investigates the behaviors of recycled aggregate concrete-filled steel tubular (RACFST) columns under eccentric loadings with the incorporation of expansive agents. A total of 16 RACFST columns were tested in this study. The main parameters varied in this study are recycled coarse aggregate replacement percentages (0%, 30%, 50%, 70%, and 100%), expansive agent dosages (0%, 8%, and 15%) and an eccentric distance of compressive load from the center of the column (0 and 40 mm). Experimental results showed that the ultimate stresses of RACFST columns decreased with increasing recycled coarse aggregate replacement percentages but appropriate expansive agent dosages can reduce the decrement; the incorporation of expansive agent decreased the ultimate stresses of RACFST columns but an appropriate dosage can increase the deformation ability. The recycled coarse aggregate replacement percentages have limited influence on the ultimate stresses of the RACFST columns and has more effect than that of the normal aggregate concrete-filled steel tubular columns.

关键词： concrete filled steel tubes     recycled aggregate concrete     columns     expansive agent     eccentric load    

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Punching shear behavior of recycled aggregate concrete slabs with and without steel fibres

Jianzhuang XIAO, Wan WANG, Zhengjiu ZHOU, Mathews M. TAWANA

《结构与土木工程前沿（英文）》 2019年 第13卷 第3期   页码 725-740 doi: 10.1007/s11709-018-0510-6

摘要： A study on the punching shear behavior of 8 slabs with recycled aggregate concrete (RAC) was carried out. The two main factors considered were the recycled coarse aggregate (RCA) replacement percentage and the steel fibre volumetric ratio. The failure pattern, load-displacement curves, energy consumption and the punching shear capacity of the slabs were intensively investigated. It was concluded that the punching shear capacity, ductility and energy consumption decreased with the increase of RCA replacement percentage. Research findings indicated that the incorporation of steel fibres could not only improve the energy dissipation capacity and the punching shear capacity of the slab, but also effectively improve the integrity of the slab tension surface and thereby changing the trend from typical punching failure pattern to bending-punching failure pattern. On the basis of the test, the punching shear capacity formula of RAC slabs with and without steel fibres was proposed and discussed.

关键词： recycled aggregate concrete     steel fibres     slab     punching shear     recycled coarse aggregates replacement percentage    

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Long term performance of recycled concrete beams with different water–cement ratio and recycled aggregate

Jingwei YING; Feiming SU; Shuangren CHEN

《结构与土木工程前沿（英文）》 2022年 第16卷 第3期   页码 302-315 doi: 10.1007/s11709-022-0803-7

摘要： The purpose of this study is to reveal the service performance of recycled aggregate concrete (RAC) components for different values of water−cement ratio and replacement rate of recycled coarse aggregate (RCA). Generally, the concrete strength decreases with the increase of the replacement rate of RCA, in order to meet the strength requirements when changing the replacement rate of RCA, it is necessary to change the water−cement ratio at the same time. Therefore, the axial compressive strengths of prism with 25 mix proportions, the short-term mechanical properties and long-term deformation properties of reinforced concrete beams were tested respectively by changing water−cement ratio and RCA replacement rate. The bearing capacity and the strain nephogram of samples under different loads were obtained using the Digital Image Correlation (DIC) method, and a self-made gravity loading experimental device was used for long-term deformation investigation. Results showed that the damage pattern of RAC was the same as that of natural aggregate concrete (NAC), but the brittleness was more pronounced. The brittleness of concrete before failure can be reduced more effectively by adjusting the replacement rate of RCA than by adjusting the water−cement ratio. The water−cement ratio has an evident influence on the axial compressive strength and early creep of concrete, while the replacement rate of RCA has a remarkable effect on the long-term deformation of the concrete beams.

关键词： recycled concrete     beam     the replacement rate of recycled coarse aggregate     water–cement ratio     digital image correlation    

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Destructive and non-destructive evaluation of concrete for optimum sand to aggregate volume ratio

《结构与土木工程前沿（英文）》 2021年 第15卷 第6期   页码 1400-1414 doi: 10.1007/s11709-021-0779-8

摘要： Aggregates are the biggest contributor to concrete volume and are a crucial parameter in dictating its mechanical properties. As such, a detailed experimental investigation was carried out to evaluate the effect of sand-to-aggregate volume ratio (s/a) on the mechanical properties of concrete utilizing both destructive and non-destructive testing (employing UPV (ultrasonic pulse velocity) measurements). For investigation, standard cylindrical concrete samples were made with different s/a (0.36, 0.40, 0.44, 0.48, 0.52, and 0.56), cement content (340 and 450 kg/m3), water-to-cement ratio (0.45 and 0.50), and maximum aggregate size (12 and 19 mm). The effect of these design parameters on the 7, 14, and 28 d compressive strength, tensile strength, elastic modulus, and UPV of concrete were assessed. The careful analysis demonstrates that aggregate proportions and size need to be optimized for formulating mix designs; optimum ratios of s/a were found to be 0.40 and 0.44 for the maximum aggregate size of 12 and 19 mm, respectively, irrespective of the W/C (water-to-cement) and cement content.

关键词： aggregates     non-destructive testing     sand-to-aggregate volume ratio (s/a)     maximum aggregate size (MAS)    

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Experimental study on behavior of mortar-aggregate interface after elevated temperatures

Wan WANG, Jianzhuang XIAO, Shiying XU, Chunhui WANG

《结构与土木工程前沿（英文）》 2017年 第11卷 第2期   页码 158-168 doi: 10.1007/s11709-016-0374-6

摘要： A push-out test program was designed and conducted to study the meso-scale behavior of mortar-aggregate interface for concrete after elevated temperatures ranging from 20°C to 600°C with the concept of modeled concrete (MC) and modeled recycled aggregate concrete (MRAC). The MCs and MRACs were designed with different strength grade of mortar and were exposed to different elevated temperatures. Following that the specimens were cooled to room temperature and push-out tests were conducted. Failure process and mechanical behaviors were analyzed based on failure modes, residual load-displacement curves, residual peak loads and peak displacements. It is found that failure modes significantly depended on specimen type, the elevated temperature and the strength grade of mortar. For MC, major cracks started to propagate along the initial cracks caused by elevated temperatures at about 80% of residual peak load. For MRAC, the cracks appeared at a lower level of load with the increasing elevated temperatures. The cracks connected with each other, formed a failure face and the specimens were split into several parts suddenly when reaching the residual peak load. Residual load-displacement curves of different specimens had similarities in shape. Besides, effect of temperatures and strength grade of mortar on residual peak load and peak displacement were analyzed. For MC and MRAC with higher strength of new hardened mortar, the residual peak load kept constant when the temperature is lower than 400°C and dropped by 43.5% on average at 600°C. For MRAC with lower strength of new hardened mortar, the residual peak load began to reduce when the temperatures exceeded 200°C and reduced by 27.4% and 60.8% respectively at 400°C and 600°C. The properties of recycled aggregate concrete (RAC) may be more sensitive to elevated temperatures than those of natural aggregate concrete (NAC) due to the fact that the interfacial properties of RAC are lower than those of NAC, and are deteriorated at lower temperatures.

关键词： mortar-aggregate interface     push-out test     elevated temperatures     modeled concrete (MC)     modeled recycled aggregate concrete (MRAC)    

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Comments on “Prediction on CO uptake of recycled aggregate concrete”, Frontiers of Structural and Civil

《结构与土木工程前沿（英文）》 2021年 第15卷 第6期   页码 1504-1506 doi: 10.1007/s11709-021-0782-0

摘要： A methodology to compute the CO2 uptake of recycled aggregate concrete is proposed in the commented paper. Besides some typos in several formulas, it is found that the approach to estimate the specific surface area of the recycled aggregates is not correct. This issue has some impact in the conclusions of the commented paper. Therefore, aiming to improve the understanding, accuracy and findings of the commented paper, an alternative approach to estimate the specific surface area of the recycled aggregates, as well as an erratum of the formulas and revised conclusions are suggested.
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Investigation into viability of using two-stage (pre-placed aggregate) concrete in Irish setting

John O’MALLEY, Hakim S. ABDELGADER,

《结构与土木工程前沿（英文）》 2010年 第4卷 第1期   页码 127-132 doi: 10.1007/s11709-010-0007-4

摘要： Two-stage (pre-placed aggregate) concrete (TSC) consists of coarse aggregate, which is first deposited into the formwork, and grout, which is later pumped into the formwork from the bottom up to bind the stone together into a monolith. During the course of this study the formation of grout for two stage concrete was investigated using readily available 5 mm sand mixed in a slow speed paddle mixer.  Silica fume and a superplasticizer were used in the mix to see if the necessary stability and fluidity could be achieved without the use of a specialized plant, essentially to see if TSC could be produced on a small scale using native Irish aggregates. A much higher degree of sedimentation was recorded during testing than was expected. As a result, the use of 5 mm sand and a slow speed mixer in combination were found to be not conducive to the successful production of TSC grout, without further research and testing.

关键词： grout     pre-placed     concrete     two-stage concrete (TSC)    

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Effects of coarse and fine aggregates on long-term mechanical properties of sea sand recycled aggregateconcrete

《结构与土木工程前沿（英文）》 2021年 第15卷 第3期   页码 754-772 doi: 10.1007/s11709-021-0711-2

摘要： Typical effects of coarse and fine aggregates on the long-term properties of sea sand recycled aggregate concrete (SSRAC) are analyzed by a series of axial compression tests. Two different types of fine (coarse) aggregates are considered: sea sand and river sand (natural and recycled coarse aggregates). Variations in SSRAC properties at different ages are investigated. A novel test system is developed via axial compression experiments and the digital image correlation method to obtain the deformation field and crack development of concrete. Supportive results show that the compressive strength of SSRAC increase with decreasing recycled coarse aggregate replacement percentage and increasing sea sand chloride ion content. The elastic modulus of SSRAC increases with age. However, the Poisson’s ratio reduces after 2 years. Typical axial stress–strain curves of SSRAC vary with age. Generally, the effect of coarse aggregates on the axial deformation of SSRAC is clear; however, the deformation differences between coarse aggregate and cement mortar reduce by adopting sea sand. The aggregate type changes the crack characteristics and propagation of SSRAC. Finally, an analytical expression is suggested to construct the long-term stress–strain curve of SSRAC.

关键词： sea sand recycled aggregate concrete     recycled coarse aggregate replacement percentage     sea sand chloride ion content     long-term mechanical properties     stress–strain curve    

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再生与原生混凝土结构构件统一设计理论的基础问题 Article

肖建庄, 张凯建, 丁陶, 张青天, 肖绪文

《工程（英文）》 2023年 第29卷 第10期   页码 188-197 doi: 10.1016/j.eng.2023.03.017

摘要：

再生混凝土作为一种低碳混凝土，成为近20年来国内外的研究热点，但是目前再生混凝土结构的设计仍是一个挑战。本文从原生与再生混凝土结构构件统一设计的新需求出发，剖析了两者统一设计的必要性，并从强度取值、受压本构关系以及结构构件设计方法等方面进行了深入论证。分析发现，再生混凝土的强度变异系数总体上高于原生混凝土，再生混凝土的抗压强度及抗拉强度代表值的定义和取值方法与原生混凝土一致；原生与再生混凝土的单轴受压本构关系具有统一的数学表达形式，但与原生混凝土相比，再生混凝土弹性模量降低、脆性增加。最后，提出了再生混凝土构件安全可靠度调整系数，实现了再生与原生混凝土构件承载力设计公式的统一，并从概念设计和构造措施上，论证了考虑时变强度与钢筋锈蚀等影响的时变可靠度统一的可行性。本文的工作，丰富和发展了混凝土结构基本理论。

关键词： 再生混凝土     原生混凝土     强度取值     本构关系     可靠度     统一设计方法    

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A new systematic firefly algorithm for forecasting the durability of reinforced recycled aggregate concrete

Wafaa Mohamed SHABAN; Khalid ELBAZ; Mohamed AMIN; Ayat gamal ASHOUR

《结构与土木工程前沿（英文）》 2022年 第16卷 第3期   页码 329-346 doi: 10.1007/s11709-022-0801-9

摘要： This study presents a new systematic algorithm to optimize the durability of reinforced recycled aggregate concrete. The proposed algorithm integrates machine learning with a new version of the firefly algorithm called chaotic based firefly algorithm (CFA) to evolve a rational and efficient predictive model. The CFA optimizer is augmented with chaotic maps and Lévy flight to improve the firefly performance in forecasting the chloride penetrability of strengthened recycled aggregate concrete (RAC). A comprehensive and credible database of distinctive chloride migration coefficient results is used to establish the developed algorithm. A dataset composite of nine effective parameters, including concrete components and fundamental characteristics of recycled aggregate (RA), is used as input to predict the migration coefficient of strengthened RAC as output. k-fold cross validation algorithm is utilized to validate the hybrid algorithm. Three numerical benchmark analyses are applied to prove the superiority and applicability of the CFA algorithm in predicting chloride penetrability. Results show that the developed CFA approach significantly outperforms the firefly algorithm on almost tested functions and demonstrates powerful prediction. In addition, the proposed strategy can be an active tool to recognize the contradictions in the experimental results and can be especially beneficial for assessing the chloride resistance of RAC.

关键词： chloride penetrability     recycled aggregate concrete     machine learning     concrete components     durability    

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标题 作者 时间 类型 操作

Influence of steel corrosion on axial and eccentric compression behavior of coral aggregate concrete

期刊论文

Damage-constitutive model for seawater coral concrete using different stirrup confinements subjected

期刊论文

考虑垫片形状和尺寸效应的珊瑚混凝土劈裂抗拉性能的三维细观研究

吴彰钰, 张锦华, 余红发, 方秦, 麻海燕, 陈力

期刊论文

Chloride ingress and macro-cell corrosion of steel in concrete made with recycled brick aggregate

期刊论文

Understanding the behavior of recycled aggregate concrete by using thermogravimetric analysis

Subhasis PRADHAN, Shailendra KUMAR, Sudhirkumar V. BARAI

期刊论文

Behaviors of recycled aggregate concrete-filled steel tubular columns under eccentric loadings

Vivian W. Y. TAM, Jianzhuang XIAO, Sheng LIU, Zixuan CHEN

期刊论文

Punching shear behavior of recycled aggregate concrete slabs with and without steel fibres

Jianzhuang XIAO, Wan WANG, Zhengjiu ZHOU, Mathews M. TAWANA

期刊论文

Long term performance of recycled concrete beams with different water–cement ratio and recycled aggregate

Jingwei YING; Feiming SU; Shuangren CHEN

期刊论文

Destructive and non-destructive evaluation of concrete for optimum sand to aggregate volume ratio

期刊论文

Experimental study on behavior of mortar-aggregate interface after elevated temperatures

Wan WANG, Jianzhuang XIAO, Shiying XU, Chunhui WANG

期刊论文

Comments on “Prediction on CO uptake of recycled aggregate concrete”, Frontiers of Structural and Civil

期刊论文

Investigation into viability of using two-stage (pre-placed aggregate) concrete in Irish setting

John O’MALLEY, Hakim S. ABDELGADER,

期刊论文

Effects of coarse and fine aggregates on long-term mechanical properties of sea sand recycled aggregateconcrete

期刊论文

再生与原生混凝土结构构件统一设计理论的基础问题

肖建庄, 张凯建, 丁陶, 张青天, 肖绪文

期刊论文

A new systematic firefly algorithm for forecasting the durability of reinforced recycled aggregate concrete

Wafaa Mohamed SHABAN; Khalid ELBAZ; Mohamed AMIN; Ayat gamal ASHOUR

期刊论文