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树盘干缩异向性引起应变的测算及分析

付宗营,赵景尧,蔡英春

《中国工程科学》 2014年 第16卷 第4期   页码 25-29

摘要：

研究探讨了干燥过程中树盘受抑制干缩应变、自由干缩应变、弹性应变、黏弹性蠕变应变以及机械吸附蠕变的图像解析测算法；运用该方法测算了白桦树盘常规缓慢干燥（含水率分布均匀）过程中干缩异向性引起的弦向各应变，分析了干燥过程中不同含水率阶段的应力状态及应力与各应变的关系。结果表明：应变的图像解析测算法可满足精度要求；树盘干燥至fiber saturation point( FSP)以下，弦向首先受拉伸应力作用，随着干燥的进行，拉伸应力转变为压缩应力；应力方向与各应变对应关系不同，与黏弹性蠕变应变无明显对应关系，与机械吸附蠕变基本对应。

关键词： 图像解析法     树盘     干缩异向性     干燥应力     弦向应变    

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Effect of natural pozzolan content on the properties of engineered cementitious composites as repair material

Said CHOUCHA, Amar BENYAHIA, Mohamed GHRICI, Mohamed Said MANSOUR

《结构与土木工程前沿（英文）》 2018年 第12卷 第3期   页码 261-269 doi: 10.1007/s11709-017-0394-x

摘要：

In order to determine the effect of Natural Pozzolan (NP) content on the mechanical properties and durability characteristics on Engineered Cementitious Composites (ECC) as repair material. This study focused on the evaluation of the most factors influencing compatibility between the repair material and the base concrete including mechanicals properties such as, compressive and flexural strengths, elastic modulus, capillary absorption and drying shrinkage. The experimental results showed that natural pozzolan reduces the compressive strength and the flexural strength of ECC at all ages. The elastic modulus of ECC was remarkably lower than that of normal-strength concrete. This lower Young’s modulus is desirable for repair concrete, because it prevents the stresses induced by restrained shrinkage. In addition, the incorporation of high-volume natural pozzolan decreases significantly the coefficient of capillary absorption at long term and increases the drying shrinkage. Generally, based on the results obtained in the present experimental investigation, ECC can be used effectively as an overlay material over existing parent concrete.

关键词： natural pozzolan     engineered cementitious composites     mechanical strengths     elastic modulus     capillary absorption     drying shrinkage    

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Fresh and hardened properties of high-strength concrete incorporating byproduct fine crushed aggregate as partial replacement of natural sand

Dammika P. K. WELLALA, Ashish Kumer SAHA, Prabir Kumar SARKER, Vinod RAJAYOGAN

《结构与土木工程前沿（英文）》 2021年 第15卷 第1期   页码 124-135 doi: 10.1007/s11709-020-0673-9

摘要： This paper presents the fresh and hardened properties of high-strength concrete comprising byproduct fine crushed aggregates (FCAs) sourced from the crushing of three different types of rocks, namely granophyre, basalt, and granite. The lowest void contents of the combined fine aggregates were observed when 40% to 60% of natural sand is replaced by the FCAs. By the replacement of 40% FCAs, the slump and bleeding of concrete with a water-to-cement ratio of 0.45 decreased by approximately 15% and 50%, respectively, owing to the relatively high fines content of the FCAs. The 28 d compressive strength of concrete was 50 MPa when 40% FCAs were used. The slight decrease in tensile strength from the FCAs is attributed to the flakiness of the particles. The correlations between the splitting tensile and compressive strengths of normal concrete provided in the AS 3600 and ACI 318 design standards are applicable for concrete using the FCAs as partial replacement of sand. The maximum 56 d drying shrinkage is 520 microstrains, which is significantly less than the recommended limit of 1000 microstrains by AS 3600 for concrete. Therefore, the use of these byproduct FCAs can be considered as a sustainable alternative option for the production of high-strength green concrete.

关键词： fine crushed aggregates     quarry dust     compressive strength     splitting tensile strength     drying shrinkage    

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Hydration, microstructure and autogenous shrinkage behaviors of cement mortars by addition of superabsorbent

Beibei SUN, Hao WU, Weimin SONG, Zhe LI, Jia YU

《结构与土木工程前沿（英文）》 2020年 第14卷 第5期   页码 1274-1284 doi: 10.1007/s11709-020-0656-x

摘要： Superabsorbent Polymer (SAP) has emerged as a topic of considerable interest in recent years. The present study systematically and quantitively investigated the effect of SAP on hydration, autogenous shrinkage, mechanical properties, and microstructure of cement mortars. Influences of SAP on hydration heat and autogenous shrinkage were studied by utilizing TAM AIR technology and a non-contact autogenous shrinkage test method. Scanning Electron Microscope (SEM) was employed to assess the microstructure evolution. Although SAP decreased the peak rate of hydration heat and retarded the hydration, it significantly increased the cumulative heat, indicating SAP helps promote the hydration. Hydration promotion caused by SAP mainly occurred in the deceleration period and attenuation period. SAP can significantly mitigate the autogenous shrinkage when the content ranged from 0 to 0.5%. Microstructure characteristics showed that pores and gaps were introduced when SAP was added. The microstructure difference caused by SAP contributed to the inferior mechanical behaviors of cement mortars treated by SAP.

关键词： Superabsorbent Polymer     mechanical properties     hydration heat     autogenous shrinkage     microstructure    

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Energy absorption potential of concrete floors containing secondary (shrinkage and temperature) reinforcements

K. S. SIVAKUMARAN,R. M. KOROL,Xiao FAN

《结构与土木工程前沿（英文）》 2014年 第8卷 第3期   页码 282-291 doi: 10.1007/s11709-014-0269-3

摘要： This paper experimentally investigates the energy absorption potential of two types of concrete floors, namely, normal density concrete and structural low-density concrete, containing secondary (shrinkage and temperature) reinforcements. The test program considered the following secondary reinforcements: 1) traditional welded-wire steel mesh, 2) steel fiber and 3) poly composite fiber. To estimate the extent to which crushing of floor slab materials would help absorb energy, a series of concrete penetration tests employing patch loading was undertaken on scaled down model slabs. Each concrete-secondary reinforcement combination considered slabs of 50 mm in depth with square plan dimensions ranging from 50 to 500 mm, resulting in a total of 30 test specimens. The first part of the paper discusses the test specimens, the test setup, and the test procedure. The second part of the paper presents the experimental results and establishes the energy absorption of different concrete- secondary reinforcement combinations. Sieve analysis results of the crushed specimens were used to derive a “work index” value that relates the pulverized particle size distributions to energy inputs. The work index values of concrete-secondary reinforcement systems can be used to assess the energy dissipation potential associated with such floor slabs in buildings undergoing progressive collapse. The results indicate that floors with secondary reinforcements could play an important role in helping arrest global progressive collapse.

关键词： concrete floors     structural low-density concrete     shrinkage and temperature reinforcements     energy absorption     penetration tests     sieve analysis    

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Effect of concrete creep and shrinkage on tall hybrid-structures and its countermeasures

Pusheng SHEN, Hui FANG, Xinhong XIA

《结构与土木工程前沿（英文）》 2009年 第3卷 第2期   页码 234-239 doi: 10.1007/s11709-009-0020-7

摘要： This paper aims to study the different vertical displacements in tall hybrid-structures and the corresponding engineering measures. First, the method to calculate the different vertical displacements in tall hybrid-structures is presented. This method takes into account the effects of construction process by applying loads sequentially story by story. Based on the concrete creep and shrinkage calculation formula in American Concrete Institute (ACI) code, with the assumption that loads are increased linearly in members, the creep and shrinkage effects of members are analyzed by adopting two parameters named average load-aged coefficient and average age-last coefficient. The effects of steel ratio on members creep are analyzed by age-adjusted module method (AEMM). The effects that core-tube were constructed in advance to outer steel frame were also considered. Then, based on the sample calculation, the measures to effectively reduce the different vertical displacements in hybrid-structures are proposed. This method is simple and practical in the calculation of different vertical displacements in tall and super-tall hybrid-structures.

关键词： creep     shrinkage     construction process     hybrid-structure    

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Soybean drying characteristics in microwave rotary dryer with forced convection

Ruifang WANG, Zhanyong LI, Yanhua LI, Jingsheng YE

《化学科学与工程前沿（英文）》 2009年 第3卷 第3期   页码 289-292 doi: 10.1007/s11705-009-0022-y

摘要： A new hybrid drying technique by combining microwave and forced convection drying within a rotary drum, i.e., microwave rotary drying, was developed with the purpose to improve the uniformity of microwave drying. In a laboratory microwave rotary dryer, rewetted soybean was utilized as experimental material to study the effects of drum rotating speed, ventilation flow rate, and specific microwave power on the drying kinetics and cracking ratio of soybean. It was found that, with rotation, the cracking ratio can be lowered but without distinct improvement in the drying rate. Increasing ventilation flow rate and specific microwave power can improve the drying rate, but the cracking ratio also increases as a negative result. The cracking ratio lower than 10% can be attained for ventilation flow rate lower than 2.0 m ·h or specific microwave energy lower than 0.4 kW·kg in the present experiments.

关键词： cracking     microwave     rotary drying     soybean    

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Effects of microfine aggregate in manufactured sand on bleeding and plastic shrinkage cracking of concrete

Branavan ARULMOLY; Chaminda KONTHESINGHA; Anura NANAYAKKARA

《结构与土木工程前沿（英文）》 2022年 第16卷 第11期   页码 1453-1473 doi: 10.1007/s11709-022-0877-2

摘要： Construction industries have started to utilize manufactured sand (MS) as an effective alternative for river sand in concrete. High-grade parent rocks are crushed to obtain MS, which also produces a considerable amount of microfine aggregate (MFA). The higher percentage of MFA could lead to both positive and negative effects on the performance of cement-based mixes. This research was done to examine the influence of varying MFA levels, specifically 0%, 3%, 6%, 9%, and 12% (by weight) as the partial replacements of MS on bleeding and plastic shrinkage cracking of concrete. In addition to the varying MFA levels, some concrete mixes also included fly ash (FA) and superplasticizer to investigate the effect of free-water content in the mixes. The bleeding test data were taken as on-site measurements, while the cracks from the plastic shrinkage cracking test were evaluated using an image processing technique. The results concluded that the MFA replacements and the effective water-to-cement ratio have a significant effect on the selected concrete properties. With the increasing replacement levels, cumulative bleeding and crack initiation life gradually decreased, while a progressive increase was observed for crack width, crack length, and crack area.

关键词： manufactured sand     fresh concrete     microfines     admixtures     shrinkage     cracking    

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A comparative study of the mechanical properties, fracture behavior, creep, and shrinkage of chemically

Mahdi AREZOUMANDI, Mark EZZELL, Jeffery S VOLZ

《结构与土木工程前沿（英文）》 2014年 第8卷 第1期   页码 36-45 doi: 10.1007/s11709-014-0243-0

摘要： This study presents the results of an experimental investigation that compares the mechanical properties, fracture behavior, creep, and shrinkage of a chemically-based self-consolidating concrete (SCC) mix with that of a corresponding conventional concrete (CC) mix. The CC and SCC mix designs followed conventional proportioning in terms of aggregate type and content, cement content, air content, water-cementitiuos materials ( / ) ratio, and workability. Then, using only chemical admixtures, the authors converted the CC mix to an SCC mix with all of the necessary passing, filling, flowability, and stability requirements typically found in SCC. The high fluidity was achieved with a polycarboxylate-based high-range water-reducing admixture, while the enhanced stability was accomplished with an organic, polymer-based viscosity-modifying admixture. The comparison indicated that the SCC and CC mixes had virtually identical tensile splitting strengths, flexural strengths, creep, and shrinkage. However, the SCC mix showed higher compressive strengths and fracture energies than the corresponding CC mix.

关键词： admixture     conventional concrete (CC)     creep     fracture mechanic     mechanical Properties     self-consolidating concrete (SCC)     shrinkage    

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Contribution of CNTs/CNFs morphology to reduction of autogenous shrinkage of Portland cement paste

Feneuil BLANDINE, Karin HABERMEHI-CWIRZEN, Andrzej CWIRZEN

《结构与土木工程前沿（英文）》 2017年 第11卷 第2期   页码 255-255 doi: 10.1007/s11709-017-0395-9

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Influence of recycled polyethylene terephthalate fibres on plastic shrinkage and mechanical properties

Necat ÖZAŞIK; Özgür EREN

《结构与土木工程前沿（英文）》 2022年 第16卷 第6期   页码 792-802 doi: 10.1007/s11709-022-0849-6

摘要： Polyethylene terephthalate bottles production has drastically increased year after year due to high versatility of polyethylene terephthalate plastics and considerable consumption of beverages. In tandem with that increase, the major concern of society has been the improper disposal of this non-biodegradable material to the environment. To deal with this concern, recycled polyethylene terephthalate bottles were incorporated in concrete as fibre reinforcements in this study. The objective of this research is to evaluate the mechanical properties of recycled polyethylene terephthalate fibre reinforced concrete (RPFRC) in comparison with control concrete without fibres. polyethylene terephthalate fibres with three different diameters (0.45, 0.65, and 1.0 mm) and two lengths (20 and 30 mm) were added at various proportions (0.5%, 1.0%, 1.5% and 2.0%) by volume of concrete in order to determine the effect of fibres initially on compressive, flexural and splitting tensile strengths of concrete. The results revealed that none of the fibres have detrimental effects up to 1% volume fraction, however further addition caused slight reductions on mechanical properties in some conditions. Plastic shrinkage resistance and impact resistance tests were also performed according to related standards. Polyethylene terephthalate fibres were observed to have marked improvements on those properties. Such a good performance could be attributed primarily to the bridging effect of fibres.

关键词： recycled PET     fibre-reinforced concrete     mechanical properties     plastic shrinkage     impact energy    

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A solar assisted heat pump drying system for grain in-store drying

Haifeng LI, Yanjun DAI, Jianguo DAI, Xibo WANG, Lei WEI,

《能源前沿（英文）》 2010年 第4卷 第3期   页码 386-391 doi: 10.1007/s11708-010-0003-3

摘要： For grain in-store drying, a solar assisted drying process has been developed, which consists of a set including a solar-assisted heat pump, a ventilation system, a grain stirrer, etc. In this way, low power consumption, short cycle time and water content uniformity can be achieved in comparison with the conventional method. A solar-assisted heat pump drying system has been designed and manufactured for a practical granary, and the energy consumption performance of the unit is analyzed. The analysis result shows that the solar fraction of the unit is higher than 20%, the coefficient of performance about system (COP) is 5.19, and the specific moisture extraction rate (SMER) can reach 3.05 kg/kWh.

关键词： solar energy     heat pump     airflow     in-store drying    

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现代混凝土收缩开裂的评估方法与控制关键技术 Article

刘加平, 田倩, 王育江, 李华, 徐文

《工程（英文）》 2021年 第7卷 第3期   页码 348-357 doi: 10.1016/j.eng.2021.01.006

摘要：

现代混凝土组成日趋复杂、收缩加大、结构约束增强，导致收缩开裂问题突出，严重影响构筑物的服役性能和使用寿命。本文以胶凝材料体系水化程度作为材料与环境温湿度交互作用的基本状态变量，提出了复杂胶凝材料体系水化反应活化能的计算方法，建立了水化-温度-湿度-约束耦合作用模型，实现了多种收缩的耦合计算和开裂风险的量化评估；介绍了水化温升抑制、全过程补偿收缩和化学减缩三项关键技术的作用机理及效果，这些技术能够有针对性地降低混凝土的温降收缩、自收缩和干燥收缩；在此基础上，提出了高抗裂混凝土的设计方法，采用该方法后，全过程控制开裂风险系数小于阈值；最后介绍了典型的工程应用案例，结果表明，采用所提出的方法和技术能够显著抑制甚至避免实际工程中收缩裂缝的产生。

关键词： 现代混凝土     收缩     水化程度     抑制技术     开裂风险    

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Modeling temperature and moisture dependent emissions of carbon dioxide and methane from drying dairy

Enzhu HU, Pakorn SUTITARNNONTR, Markus TULLER, Scott B. JONES

《农业科学与工程前沿（英文）》 2018年 第5卷 第2期   页码 280-286 doi: 10.15302/J-FASE-2018215

摘要： Greenhouse gas emissions due to biological degradation processes of animal wastes are significant sources of air pollution from agricultural areas. The major environmental controls on these microbe-induced gas fluxes are temperature and moisture content. The objective of this study was to model the effects of temperature and moisture content on emissions of CO and CH during the ambient drying process of dairy manure under controlled conditions. Gas emissions were continuously recorded over 15 d with paired fully automated closed dynamic chambers coupled with a Fourier Transformed Infrared gas analyzer. Water content and temperature were measured and monitored with capacitance sensors. In addition, on days 0, 3, 6, 9, 12 and 15, pH, moisture content, dissolved organic carbon and total carbon (TC) were determined. An empirical model derived from the Arrhenius equation confirmed high dependency of carbon emissions on temperature and moisture content. Results indicate that for the investigated dairy manure, 6.83% of TC was lost in the form of CO and 0.047% of TC was emitted as CH . Neglecting the effect of temperature, the moisture contents associated with maximum gas emissions were estimated as 0.75 and 0.79 g·g for CO and CH , respectively.

关键词： carbon dioxide     dairy manure     methane     moisture     temperature    

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Effects of previous drying of sediment on root functional traits and rhizoperformance of emerged macrophytes

《环境科学与工程前沿（英文）》 2021年 第15卷 第6期 doi: 10.1007/s11783-021-1427-1

摘要：

• Sediment desiccation alters morphological characteristics of aquatic sediment.

关键词： Fibrous-root macrophytes     Thick-root macrophytes     Nutrients removal     Wet sediment     Dried-rewetted sediment    

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标题 作者 时间 类型 操作

树盘干缩异向性引起应变的测算及分析

付宗营,赵景尧,蔡英春

期刊论文

Effect of natural pozzolan content on the properties of engineered cementitious composites as repair material

Said CHOUCHA, Amar BENYAHIA, Mohamed GHRICI, Mohamed Said MANSOUR

期刊论文

Fresh and hardened properties of high-strength concrete incorporating byproduct fine crushed aggregate as partial replacement of natural sand

Dammika P. K. WELLALA, Ashish Kumer SAHA, Prabir Kumar SARKER, Vinod RAJAYOGAN

期刊论文

Hydration, microstructure and autogenous shrinkage behaviors of cement mortars by addition of superabsorbent

Beibei SUN, Hao WU, Weimin SONG, Zhe LI, Jia YU

期刊论文

Energy absorption potential of concrete floors containing secondary (shrinkage and temperature) reinforcements

K. S. SIVAKUMARAN,R. M. KOROL,Xiao FAN

期刊论文

Effect of concrete creep and shrinkage on tall hybrid-structures and its countermeasures

Pusheng SHEN, Hui FANG, Xinhong XIA

期刊论文

Soybean drying characteristics in microwave rotary dryer with forced convection

Ruifang WANG, Zhanyong LI, Yanhua LI, Jingsheng YE

期刊论文

Effects of microfine aggregate in manufactured sand on bleeding and plastic shrinkage cracking of concrete

Branavan ARULMOLY; Chaminda KONTHESINGHA; Anura NANAYAKKARA

期刊论文

A comparative study of the mechanical properties, fracture behavior, creep, and shrinkage of chemically

Mahdi AREZOUMANDI, Mark EZZELL, Jeffery S VOLZ

期刊论文

Contribution of CNTs/CNFs morphology to reduction of autogenous shrinkage of Portland cement paste

Feneuil BLANDINE, Karin HABERMEHI-CWIRZEN, Andrzej CWIRZEN

期刊论文

Influence of recycled polyethylene terephthalate fibres on plastic shrinkage and mechanical properties

Necat ÖZAŞIK; Özgür EREN

期刊论文

A solar assisted heat pump drying system for grain in-store drying

Haifeng LI, Yanjun DAI, Jianguo DAI, Xibo WANG, Lei WEI,

期刊论文

现代混凝土收缩开裂的评估方法与控制关键技术

刘加平, 田倩, 王育江, 李华, 徐文

期刊论文

Modeling temperature and moisture dependent emissions of carbon dioxide and methane from drying dairy

Enzhu HU, Pakorn SUTITARNNONTR, Markus TULLER, Scott B. JONES

期刊论文

Effects of previous drying of sediment on root functional traits and rhizoperformance of emerged macrophytes

期刊论文