Effect of Carbonation and Drying-Wetting Cycles on Chloride Diffusion Behavior of Coral Aggregate Seawater Concrete

Based on seawater immersion,drying-wetting cycles,carbonation and drying-wetting cycles for coral aggregate sea-water concrete(CASC)with different strength grades,the effect of carbonation and drying-wetting cycles on chloride diffusion be-havior of CASC is studied.The results show that the free surface chloride concentration(Cs),free chloride diffusion coefficient(Df)and time-dependent index(m)of CASC in the drying-wetting cycles is obviously higher than that in seawater immersion.The Df and m of CASC of carbonation and drying-wetting cycles is higher than that in the drying-wetting cycles.Carbonation increases the Df and m of CASC,which is against CASC to resist chloride corrosion.The corrosion possibility of CASC structures in different ex-posed areas is as follows:splash zone(carbonation and drying-wetting cycles)>tidal zone(drying-wetting cycles)>underwater zone(seawater immersion).Besides,the chloride diffusion rate of C65-CASC is 17.8%-63.4%higher than that of C65-ordinary aggre-gate concrete(OAC)in seawater immersion(underwater zone).Therefore,anti-corrosion measures should be adopted to improve the service life of CASC structure in the oceanic environment.

Research on the Pitting Mechanism of Dispersion-Strengthened High-Strength Steel Under Wet-Dry Cycling in a Marine Environment

Due to the wet-dry cycling in the ocean tidal zone,the supply of dissolved oxygen and salt-containing particles were sufficient,so the corrosion was serious.Pitting corrosion was a common form of localized corrosion.This paper studied the pitting corrosion mechanism of dispersion-strengthened high-strength steel under different wet-dry ratio environments.Electrochemical Impedance Spectroscopy was used to study the changes of corrosion rate and electric double layer structure of the dispersionstrengthened high-strength steel.Scanning electron microscope,Raman spectroscopy,electron probe microanalysis and laser confocal scanning microscope were used to observe the corrosion product morphologies,analyze the corrosion product compositions,analyze the secondary distribution of alloy elements in the corrosion products and analyze the pitting information of the steel after the corrosion products were removed.The results showed that the degree of the steel corrosion was slight when the wetting time was longer,the size and depth of the corrosion pits on the surface were smaller.This was because the environment with longer wetting time made the corrosion products denser.In this environment,the conversion ofγ-FeOOH to Fe3O4 was promoted.In addition,it could also promote the alloying elements to be more concentrated in the rust layer.The above phenomena hindered the further corrosion of the matrix by dissolved oxygen and Cl−in the seawater.

Durability of concrete beams reinforced with CFRP sheet under wet-dry cycles and loading

The test results of eight concrete beams reinforced with carbon fiber reinforced polymer （CFRP） sheets subjected to an aggressive environment under a sustained load are presented. The beams are 1 700 mm long with a rectangular cross-section of 120- mm width and 200-mm depth. The beams are precracked with a four-point flexural load, bonded CFRP sheets, and placed into wet-dry saline water（ NaCl） either in an unstressed state or loaded to about 30% or 60% of the initial ultimate load. The individual and coupled effects of wet-dry saline water and sustained bending stresses on the long term behaviour of concrete beams reinforced with the CFRP are investigated. The test results show that the coupled action of wet-dry saline water and sustained bending stresses appears to significantly affect the load capacity and the failure mode of beam strengthened with CFRP, mainly due to the degradation of the bond between CFRP and concrete. However, the stiffness is not affected by the coupled action of wet-dry cycles and a sustained load.

Effect of salts on earthen materials deterioration after humidity cycling

Salt weathering leads to destruction of many valuable cultural heritage monuments and porous building material. The present study aims at providing more laboratory evidence for evaluating the effects of salt precipitation on the deterioration process. In view of this, the remoulded soil specimens were mixed with three kinds of salts(i.e., NaCl, Na_2SO_4 and their mixture) with different salt concentrations, and the specimens were kept in environment cabinet for undergoing different wet-dry cycles. After each cycle, the ultrasound velocity measurements were employed to monitor the deterioration process. For the specimens that have suffered three wet-dry cycles, the mechanical properties(i.e. shear strength and compression strength) were determined to evaluate the degree of deterioration. Furthermore, considering the realistic conservation environment of earthen sites, mechanical stability of these specimens against sediment-carrying wind erosion was conducted in a wind tunnel. These experiments results indicate that the overall average velocities of the specimens after the third cycle are significantly lower than those subjected to only one cycle. Ultrasound velocity, mechanical strength and wind erosion rate decrease when salt content increases. However, the internal friction angle increases firstly, and then decreases with the increase in salt content added to the specimens. Na_2SO_4 contributes most of the surface deterioration, while NaCl plays little role in the deterioration. The damage potential of the salt mixture is less obvious and largely dependent on the crystallisation location.

Planning and design of a micro energy network for seawater desalination and regional energy interconnection

With the rapid developme nt of the economy, the continu ously in creasing populati on, and ongoing climate change, the shortage of freshwater resources has become an increasingly important global problem. Seawater desalination tech no logy can effectively alleviate the pressure on freshwater supplies and has bee n in vestigated in many countries. However, the majority of existing projects focus on the research and development of desalination equipment and the use of new tech no logies and pay less atte ntion to the operation optimizati on of the desalinati on process. The micro energy n etwork (MEN) designed in this study is an efficient distributed energy supply system that can be used to simultaneously supply electricity, cooling, heating, and freshwater as photovoltaic power, wind power, combined heat and power (CHP), electric cooling and heating, and a seawater desalinati on device are in teg rated into the MEN. In this study, a model for operati on optimization of a MEN for seawater desalination was developed and the influences of the electric cooling and heating ratios and the operation optimization of the seawater desalination device were studied with the aim of minimizing the life cycle cost. Based on the results of this study, MENs can reduce the operation cost of desalination devices and improve the efficiency of renewable energy sources.

Effect of carbonation-drying-wetting on durability of coral aggregate seawater concrete

Based on the drying-wetting cycles experiment and the carbonation-drying-wetting cycles experiment for coral aggregate seawater concrete(CASC)with different strength grades,the effects of carbonation-drying-wetting on the durability of CASC are studied with the surface state,mass loss rate,relative dynamic elastic modulus,ultrasonic wave velocity and cube compressive strength as indices.Results show that the mass loss rate of CASC increases gradually with the increase in cycle times in the drying-wetting and carbonation-drying-wetting cycles.The mass loss rate increases relatively slowly at the initial stage but it increases remarkably after 10 cycles.The relative dynamic elastic modulus and ultrasonic wave velocity decrease gradually with the increase in cycle times.After 6 cycles,the decrease rate of the relative dynamic elastic modulus and ultrasonic wave velocity of CASC tends to be flat and the surface is slightly damaged.Compared with the initial 28 d cube compressive strength,the cube compressive strength of CASC decreases by 8.8%to 11.0%.Drying-wetting cycles and carbonation can accelerate seawater erosion on CASC,and drying-wetting cycles result in salting-out and accelerate the destruction of concrete.Therefore,the carbonation-drying-wetting accelerates the destruction of CASC.

Effect of incubation temperature and wet-dry cycle on the availabilities of Cd,Pb and Zn in soil

The effect of incubation temperature and wet-dry cycle on the availabilities of Cd, Pb and Zn was studied. Three soils with pH ranging from 3.8 to 7.3, organic carbon （OC） from 0.7% to 2.4%, and clay from 12.3% to 35.6% were selected. Soils were spiked with reagent grade Cd（NO3）2, Pb（NO3）2, and Zn（NO3）2 at concentrations of 30 mg Cd/kg soil, 300 mg Zn/kg soil and 2000 mg Pb/kg soil. The soils were incubated at 35, 60, 105℃, respectively and went through four wet-dry cycles. Metal availability in soils was estimated by soil extraction with 0.1 mol/L Ca（NO3）2. According to this study, the effect of the spiking temperature on the metal availabilities was different among the metals, soils and wet-dry cycles. Mostly, 35 ~C was the first recommended spiking temperature for Cd and Pb while no spiking temperature was obviously better than others for Zn. Three wet-dry cycles was recommended regardless of the type of metals and incubation temperature.

Performance of Concrete Subjected to Severe Multiple Actions of Composite Salts Solution under Wet-Dry Cycles and Flexural Loading in Lab

Several action regimes were employed, namely, those exposed to solutions containing single and/or composite chloride and sulfate salts, and under wet-dry cycles and/or flexural loading. The variations in dynamic modulus of elasticity（Erd values） were monitored, as well as the key factor impacting on the chloride ingress when concrete subjected to multiple action regimes was identified by the method of Grey Relation Analysis（GRA）. The changes in micro-structures and mineral products of interior concrete after different action regimes were investigated by means of X-ray diffraction（XRD）, mercury intrusion technique（MIP）, and scanning electron microscopy（SEM）. The test results showed that the cyclic wet-dry accelerated the deterioration of OPC concrete more than the action of 35% flexural loading based on the results of Erd values and the GEA. The analyses from micro-structures could give certain explanations to the change in Erd values under different action regimes.

Degradation of Pore Structure and Microstructures in Hardened Cement Paste Subjected to Flexural Loading and Wet-dry Cycles in Sea Water

Hardened cement paste was subjected to the flexural loading and wet-dry cycles in sea water. The degradation of microstructures was obtained using scanning electron microscope （SEM）, and the energy dispersive spectrum （EDS） analysis was carried to analyze the local composition. Mercury intrusion porosimetry （Poremaster GT-60） was used to analyze the degradation of pore structures. The experimental results show that the synergistic action of the flexural loading, wet-dry cycles and sea water leads to significant deterioration of hardened cement paste. The degradation of microstructures in the tensile region is more serious than that in the compressive region. The flexural loading and wet-dry cycles accelerate the chemical attack of sea water.

海水干湿循环作用下UHTCC动态压缩性能试验研究

为研究应变率和海水干湿循环周期对超高韧性水泥基复合材料(UHTCC)动态压缩性能的影响,采用直径75 mm的分离式霍普金森压杆系统对0~120 d海水干湿循环作用后的UHTCC试件开展动态压缩试验.通过改进ZWT非线性黏弹性本构模型,提出了一种考虑海水干湿循环作用的UHTCC试件的动态本构模型.结果表明,UHTCC试件的动态抗压强度增强因子随着干湿循环周期的增加逐渐减小.在同一冲击气压下,随着干湿循环周期的增加,UHTCC试件的峰值应力和耗能先增大后减小,并分别在60和90 d时达到峰值.在相同干湿循环周期下,UHTCC试件的峰值应力、动态抗压强度增强因子和耗能均随应变率的增大而增大,表现出明显的应变率效应.改进的动态本构模型能够较好地描述海水干湿循环作用下UHTCC试件的动态压缩应力-应变关系.

水泥加固淤泥土力学与抗海水腐蚀性能研究

为了分析水泥掺量和海水腐蚀对水泥加固淤泥土力学性能的影响规律,制备了水泥掺量为4%、8%、12%、16%和20%水泥加固淤泥土试件,分别经历了0、2、5、8、12、18次海水腐蚀干湿循环后,测试试件的单轴抗压强度、内聚力和内摩擦角,分析水泥掺量和海水腐蚀对水泥加固淤泥土力学性能的影响规律。研究结果表明,(1)随着水泥掺量的增大,水泥加固淤泥土的单轴抗压强度和内聚力呈线性增大,而内摩擦角呈指数衰减;(2)随着海水干湿循环次数的增加,水泥加固淤泥土的抗压强度、内聚力和内摩擦角均呈现不断变小的变化规律;(3)水泥掺量的增大能够有效提高加固淤泥土的抗海水腐蚀能力。

Evaluation of red soil-bentonite mixtures for compacted clay liners

Compacted clay liners are an integral part of the waste landfills,which are provided to contain the leachate within the landfills and protect the surrounding environment.Generally,locally available natural soils are used for the construction of compacted clay liners if they satisfy the design criteria.However,not all soils in their natural state satisfy all the design criteria for the liner materials.Thus,there is a definite need to modify the locally available natural soils by blending with bentonite to meet the required design criteria for the liners.In view of this,the present study evaluates the suitability of an Indian red soil enhanced with bentonite as a liner material.To achieve this,a series of experiments were carried out using locally available red soil and bentonite.First,the suitability of the red soil was evaluated as a liner material.The experimental results showed that the red soil met all the selection criteria stipulated by the Environmental Protection Agencies(EPAs)for the liners except the hydraulic conductivity criterion.Therefore,the red soil was mixed with bentonite contents of 10%,20%and 30%,and the red soil-bentonite mixtures were evaluated for their suitability for liners in their compacted state.Further,as the liners in the arid and semi-arid regions are subjected to moisture variations due to seasonal moisture fluctuations and other factors,the red soil-bentonite mixtures were subjected to wetdry cycles,and their suitability was evaluated after wet-dry cycles.The experimental results revealed that all the red soil-bentonite mixtures met the stipulated EPA criteria for the liners in the as-compacted state.However,the red soil-bentonite mixtures with 20%and 30%bentonite contents only satisfied the hydraulic conductivity requirement even after wet-dry cycles.The experimental findings were supplemented with the microstructural insights captured through digital camera images,scanning electron microscopy(SEM),and mercury intrusion porosimetry(MIP)studies.

海洋环境条件海水海砂混凝土加速试验力学损伤评估

伴随着海洋开发与岛礁建设的进行,海砂、海水作为建筑材料具有巨大的潜在市场。海水海砂混凝土在海洋环境中的应用通常采用部分浸没温湿循环加速试验模型进行研究。文章建立海水海砂混凝土力学损伤理论计算模型,并根据动弹性模量预测加速试验后海水海砂混凝土的劣化时间。这项研究对部分浸没温湿循环加速试验模型的应用具有重要的科学意义。

渔船船体用HDPE材料的耐久性能

通过调整光辐照强度、海水温度、浸泡时间及冻融循环等因素,研究了其对渔船船体用HDPE力学性能的影响。结果表明,光辐照强度越高,HDPE性能劣化越严重,当强度为1600 W/m^(2)时的辐照1920 h后,HDPE的拉伸强度和弯曲强度分别降低了25.3%和23.7%;热氧作用对HDPE力学性能的整体影响较小,在温度为80℃条件下老化1920 h后,HDPE的拉伸强度和弯曲强度分别下降了8.5%和5.7%,而在常温条件下,HDPE的力学性能基本无影响;海水浸泡作用使HDPE发生轻微的吸湿现象,最大吸湿率仅为0.7%,随着海水浸泡时间的延长,材料的力学性能出现明显降低,拉伸强度和弯曲强度的最大降低幅度均达到了15%,而海水的盐度对HDPE的吸湿率及力学性能影响均较小;海水冻融循环作用使HDPE的力学性能出现小幅度增大,材料的耐冻融能力较强。

基于随机森林算法的海水循环冷却系统钙离子浓度预测模型

海水循环冷却系统中钙离子的检测问题已成为阻碍系统精细化管理的重要限制因素。文章将随机森林算法与海水循环水中钙离子浓度预测结合,充分总结运行经验,采用易实现在线检测的电导率值、pH值和系统日期作为模型特征,结合随机森林算法,实现海水循环水中钙离子浓度预测。利用随机森林算法和宁海电厂5#海水循环冷却系统2014年与2015年海水循环水水质监测数据,建立海水循环水中钙离子浓度预测模型。通过五数概括法进行数据清洗,将样本划分为训练集和测试集,采用五折交叉验证和网格搜索法优化模型参数。训练集和测试集上模型的验证和评价效果良好,该模型可用于预测海水循环水中钙离子浓度。

荧光示踪剂在监测二级水浓缩倍数中的应用

文章针对反渗透海水淡化二级产品水作为循环冷却系统补充水时,水中离子含量低、药剂干扰大,导致浓缩倍数计算结果偏差大的问题,采用添加荧光化合物的方法监测系统浓缩倍数,并探讨了荧光示踪剂1,3,6,8-芘四磺酸钠在去离子水中的荧光特性,考察了杀菌剂、阻垢缓蚀剂对荧光特性的影响;采用静态阻垢性能试验方法,模拟冷却系统条件,综合评价了浓缩条件变化对其荧光特性的影响。结果表明,1,3,6,8-芘四磺酸钠荧光信号稳定,能够有效监测循环冷却系统浓缩倍数变化。

Damage characteristics and new constitutive model of sandstone under wet–dry cycles

The mechanical properties of rock deteriorate under repeated wet-dry(WD)cycles,causing the deformation and failure of the rock mass.A reasonable damage constitutive model can truly reflect the whole process of rock deformation and failure.Therefore,it is of great significance to study the damage characteristics and constitutive behaviour of rock subjected to numerous WD cycles.First,sandstone from Tingliang tunnel was sampled for the WD cycle experiment,and uniaxial and triaxial tests were carried out on the rock samples after various numbers of WD cycles to analyze their macroscale damage characteristics.Then,the damage mechanisms of the rock samples under the action of WD cycling were identified by X-ray diffraction(XRD)and scanning electron microscopy(SEM).Finally,based on the test data,the WD cycle-induced damage variable,Weibull distribution function,damage threshold,Drucker-Prager(D-P)yield criterion and residual strength correction coefficient were introduced,a wet-dry loading(WDL)constitutive damage model that considers the cracking stress of rock masses was established,and the expressions of the corresponding parameters were given.The results show that an increasing number of WD cycles induces considerable variations in the macroscopic physical and mechanical parameters(such as the rock sample mass,saturated water content,longitudinal-wave velocity,compressive strength and elastic modulus),and the rate of change presents two stages,the inflection point of their rate of change is the 15th WD cycle.Microscopically,the rock sample structure changes from intact and dense to fragmented and unconsolidated;additionally,the surface roughness increases,and the mineral composition changes.The established constitutive damage model exhibited good agreement with the experimental data;thus,this model can reflect the deformation and failure of rocks under WDL conditions,and the physical meaning of each parameter is clear.

过冷法海水冰浆制备系统能耗特性分析

海水制冰浆技术可应用于海岛及海上风电的负荷转移和削峰以及冷冻保存海产品等,具有广阔应用前景。此外,海水制冰的原料近乎免费,并且利用海水作为冷却介质可以降低冷凝温度,进而提高系统能效,具有明显优势。通过建立双回路单级压缩循环制冰系统模型,分析利用过冷法制取海水冰浆的经济性和可行性,为海水制冰浆技术的实际应用提供理论指导。结果显示,该系统在计算条件下冬季循环性能系数平均值为4.76,夏季平均值为3.61,在蒸发器内较宽的海水流速范围内可维持较长时间正常运行。系统采用板式水冷冷凝器,并与空气源机组进行定量对比,结果表明循环机组采用水冷冷凝器在各指定工况点下的效益均高于采用空冷器,在设计工况下水冷机组单位投资蓄冷量为2.85kW·h/元,对应的空冷机组仅为1.37kW·h/元。

太阳能驱动的制冷循环海水淡化系统性能分析

建立太阳能驱动的制冷循环海水淡化系统数学模型,通过改变驱动热水流量、驱动热水供回水温差、集热器面积和所在城市这4个变量,进行系统性能分析,利用Matlab语言编制程序进行求解。结果表明:提高驱动热水流量和增大驱动热水供回水温差,均有利于提高淡水产量,但所需辅助热源热量增加,太阳能供能比例下降;增大集热器面积,有利于降低辅助热源热量,增大太阳能供能比例,但淡水产量微降;选择大连、北京和深圳3个城市,在相同的条件下,深圳地区太阳能供能比例最高,北京次之,大连最低。

渔船柴油机余热利用系统设计与热力学分析

为充分利用渔船柴油机余热,提出一种以CO_(2)为工质的新型余热利用技术,通过能源梯级利用,实现发电、制冷、制淡水的三联供系统。建立船舶余热驱动的CO_(2)超临界发电、跨临界制冷及蒸馏制淡水循环系统的热力学稳态模型,并以排气温度293℃、排气热量1668 kW的Wärtsilä6L45B型船舶柴油机为例,模拟分析关键热力参数对系统性能、余热利用的影响。研究结果表明,该余热利用系统可为渔船提供6.7~284.0 kW的净发电量,同时可为船上-40℃的速冻库和4℃的食品保鲜库分别提供22~150 kW和194~1311 kW的冷量用于速冻、保鲜或舱内空调,并提供5.25~12.75 t/d的淡水;通过控制膨胀机入口压力和海水淡化温度,灵活控制系统输出的净发电量、中低温冷量和淡水量以满足渔船在航行、捕捞等工作阶段对不同能量的需求。通过柴油机余热利用技术提供的电能、制冷量以及淡水,可减少渔船对柴油的消耗,具有明显的节能效果,为远洋作业渔船的余热利用提供参考。