Long-Term Performance and Microstructural Characterization of Dam Concrete in the Three Gorges Project

This study investigates the long-term performance of laboratory dam concrete in different curing environments over ten years and the microstructure of 17-year-old laboratory concrete and actual concrete cores drilled from the Three Gorges Dam.The mechanical properties of the laboratory dam concrete,whether cured in natural or standard environments,continued to improve over time.Furthermore,the laboratory dam concrete exhibited good resistance to diffusion and a refined microstructure after 17 years.However,curing and long-term exposure to the local natural environment reduced the frost resistance.Microstructural analyses of the laboratory concrete samples demonstrated that moderate-heat cement and fine fly ash(FA)particles were almost fully hydrated to form compact micro structures consisting of large quantities of homogeneous calcium(alumino)silicate hydrate(C-(A)-S-H)gels and a few crystals.No obvious interfacial transition zones were observed in the microstructure owing to the longterm pozzolanic reaction.This dense and homogenous microstructure was the crucial reason for the excellent long-term performance of the dam concrete.A high FA volume also played a significant role in the microstructural densification and performance growth of dam concrete at a later age.The concrete drilled from the dam surface exhibited a loose microstructure with higher microporosity,indicating that concrete directly exposed to the actual service environment suffered degradation caused by water and wind attacks.In this study,both macro-performance and microstructural analyses revealed that the application of moderate-heat cement and FA resulted in a dense and homogenous microstructure,which ensured the excellent long-term performance of concrete from the Three Gorges Dam after 17 years.Long-term exposure to an actual service environment may lead to microstructural degradation of the concrete surface.Therefore,the retained long-term dam concrete samples need to be further researched to better understand its microstructural evolution and development of its properties.

Long-term performance of recycled asphalt mixtures containing high RAP and RAS

The application of reclaimed asphalt pavement(RAP)and reclaimed asphalt shingles(RAS)on asphalt pavement can reduce the asphalt paving cost,conserve energy and protect the environment.However,the use of high contents of RAP and RAS in asphalt pavement may lead to durability issues,especially the fatigue cracking and thermal cracking.It is necessary to conduct a series of analyses on asphalt mixtures containing high RAP and RAS,and seek methods to enhance their long-term performance.This paper provides a comprehensive over-view of the long-term performance of recycled asphalt mixtures containing high contents of RAP and RAS.The findings in this research show that rutting resistance of high recycled asphalt mixtures is not a concern,whereas their resistance to fatigue and thermal cracking is not conclusive.Recycling agents can be used to improve the thermal cracking resistance of high recycled asphalt mixtures.An optimum decision on recycling agents will improve the durability properties of high recycled asphalt mixtures.It is recommended that to use a balanced mixture design approach with testing of the blended asphalt binders will provide better understanding of long-term performance of recycled asphalt mixtures containing high RAP and RAS.

Experiment and simulation of creep performance of basalt fibre asphalt mortar under uniaxial compressive loadings

The creep performance of basalt fibre（BF）reinforced in asphalt mortar under uniaxial compressive loadings is investigated. The samples of basalt fibre asphalt mortar（BFAM） with different BF mass fractions（0. 1%,0. 2%, and 0. 5%） and without BF in asphalt mixture are prepared, and then submitted for the compressive strength test and corresponding creep test at a high in-service temperature.Besides, numerical simulations in finite element ABAQUS software were conducted to model the compressive creep test of mortar materials, where the internal structure of the fibre mortar was assumed to be a two-component composite material model such as fibre and mortar matrix. Finally, the influence factors of rheological behaviors of BFAM are further analyzed. Results indicate that compared to the control sample, the compressive strength of BFAM samples has a significant increase, and the creep and residual deformation are decreased. However, it also shows that the excessive fibre, i.e. with the BF content of 0. 5%, is unfavorable to the high-temperature stability of the mortar. Based on the analysis results, the prediction equations of parameters of the Burgers constitutive model for BFAM are proposed by considering the fibre factors.

Effects of creep feeding and supplemental glutamine or glutamine plus glutamate (Aminogut) on pre- and post-weaning growth performance and intestinal health of piglets

Background： Creep feeding is used to stimulate piglet post-weaning feed consumption.L-Glutamine（GLN） is an important source of fuel for intestinal epithelial cells.The objective of this study was to determine the impact of creep feeding and adding GLN or AminoGut（AG;containing glutamine ＋ glutamate） to pre-and post-weaning diets on pig performance and intestinal health.Litters（N = 120） were allotted to four treatments during 14–21 d of lactation： 1） No creep feed（NC,n = 45）;2） creep fed control diet（CFCD,n = 45）;3） creep fed 1% GLN（CFGLN,n = 15）;4） creep fed.88% AG（CFAG,n = 15）.After weaning,the NC and CFCD groups were sub-divided into three groups（n = 15 each）,receiving either a control nursery diet（NC-CD,CFCD-CD） or a diet supplemented with either GLN（NC-GLN,CFCD-GLN） or with AG（NC-AG,CFCD-AG）.Litters that were creep fed with diets containing GLN or AG also were supplemented with those amino acids in the nursery diets（CFGLN-GLN,CFAG-AG）.Glutamine was added at 1% in all three post-weaning diet phases and AG was added at.88% in phase 1 and 2 and at.66% in phase 3.Results： Feed conversion（feed/gain） showed means among treatment means close to significance（P = 0.056） and Tukey＇s test for pairwise mean comparisons showed that Pigs in the CFGLN-GLN group had the best feed conversion（feed/gain） in the first three-week period post-weaning,exceeding（P = 0.044） controls（CFCD-CD） by 34%.The NC-AG group had（P = 0.02） the greatest feed intake in the last three week of the study,exceeding controls（CFCD-CD） by 12%.CFGLN-GLN,CFCD-GLN and sow reared（SR） pigs had the greatest（P = 0.049） villi height exceeding the CFCD-AG group by 18%,20% and 19% respectively.The CFAG-AG group had the deepest（P = 0.001） crypts among all treatments.CFGLN-GLN,CFCD-GLN and SR groups had the greatest（P = 0.001） number of cells proliferating（PCNA） exceeding those in the NC-CD group by 43%,54% and 63% respectively.Sow reared pigs showed the greatest（P = 0.001） intestinal absorption capacity for xylose and mannitol.Conclusion： Supplementation of creep feed and nursery diets with GLN and/or AminoGut in the first three week improved feed conversion possibly due to improved intestinal health.

Creep aging behavior and performance of Al-Zn-Mg-Cu alloys under different parameters in retrogression aging treatment

A study was conducted to better understand how different parameters, namely, regression aging time and regression aging temperature, affect the creep aging properties, i.e., the creep deformation and performance of Al-Zn-MgCu alloy during regressive reaging. The corresponding creep strain and mechanical properties of samples were studied by conducting creep tests and uniaxial tensile tests. The electrical conductivity was measured using an eddy-current conductivity meter. The microstructures were observed by transmission electron microscopy(TEM). With the increase in regression aging time, the steady creep strain first increased and then decreased, and reached the maximum at 45 min.The steady creep strain increased with the increase in regression aging temperature, and reached the maximum at 200 ℃.The level of steady creep strain was determined by precipitation and dislocation recovery. Creep aging strengthens 7B50-RRA treated with regression aging time at 190 ℃ for 10 min, and the difference in the mechanical properties of alloy becomes smaller. The diffusion of solute atoms reduces the scattering of electrons, leading to a significant improvement in electrical conductivity and stress corrosion cracking(SCC) resistance after creep aging. The findings of this study could help in the application of creep aging forming(CAF) technology in Al-Zn-Mg-Cu alloy under RRA treatment.

Dimensionality regulation in tin halide perovskite solar cells: Toward high performance and stability

Tin halide perovskites(THPs)have received extensive attention due to their low toxicity and excellent optoelectronic properties,and are considered to be the most promising alternatives to develop efficient lead-free perovskite solar cells.However,due to the unique and inherent characteristics of Sn^(2+)being easily oxidized to Sn^(4+)and fast crystallization,tin perovskite solar cells(TPSCs)show relatively poor performance and stability,compared to the lead counterparts.Recently,the introduction of bulky organic spacers into three-dimensional(3D)THPs for dimensional regulation can not only prevent the intrusion of water and oxygen,but also inhibit the self-doping effect and ion migration.In this review,we will detail how dimensional regulation enables TPSCs with high performance and superior stability.First,we summarize the intrinsic properties of THPs and analyze the root causes of their poor performance and instability.Next,we discuss the specific structure and types of the dimensional regulation strategy.Then,the mechanism of dimensional regulation is discussed in detail,mainly from inhibiting the Sn^(2+)oxidation,optimizing crystallization,passivating defects,and improving energy level alignment.Finally,future challenges and prospects for dimensional regulation are elaborated to help researchers develop more efficient and stable TPSCs.

Energy and long-term hygrothermal performance of building enclosures based on dynamic environmental simulation test

Dynamic environmental testing is an effective means to study the energy and long-term hygrothermal performance of building enclosures. Southeast University is designing and building a large-scale dynamic environment simulation testing facility. It can simuhaneously and dynamically simulate temperature, relative humidity, infrared solar radiation, UV radiation, and precipitation. A transformation is needed to predict the energy and long-term hygrothermal performance of building enclosures under real service conditions using data obtained from accelerated tests.

Technical development and long-term performance observations of long-life asphalt pavement: A case study of Shandong Province

Based on the investigation of long-life asphalt pavement at home and abroad,the development of long-life asphalt pavement technology in Shandong Province,China is reviewed in this paper.The structural combination char-acteristics of typical long-life asphalt pavement in Shandong Province and their popularization and application are introduced.The application effect of combined base long-life asphalt pavement,which has been widely promoted,is evaluated.At the same time,taking the Binda perpetual pavement test road in Shandong Province as an example,the dynamic response and long-term performance evolution of long-life asphalt pavement are analyzed over a period of more than 17 years.Sections S1,S2,and S3 present information about full-depth asphalt pavement.Section S4 describes combined base asphalt pavement.The results show that the maximum strain of S1–S4 is within the endurance strain limit.S1,S2,S3 and S4 are all expected to be long-life asphalt pavements.In the current study,Sections S1–S4 were maintained in good condition during a service period of more than 17 years with no structural cracks and good deflection,rutting,and IRI indexes.The deflection index was stable without growth,and the IRI was also relatively stable following the opening to traffic.The rutting depth un-derwent a slight cumulative increase within 8 years of opening,and then stabilized.The average rutting depth over the 17-year period was less than 15 mm.Therefore,S1–S4 meet the design standards required for use as long-life pavements.From the perspectives of resource saving,energy saving,and emission reduction and service performance,full-depth asphalt pavement can be considered to represent a new generation of green and durable pavement structures with great future promotion potential.

Creep experimental test and analysis of high-performance concrete in bridge

Factors that have effect on concrete creep include mixture composition,curing conditions,ambient exposure conditions,and element geometry.Considering concrete mixtures influence and in order to improve the prediction of prestress loss in important structures,an experimental test under laboratory conditions was carried out to investigate compression creep of two high performance concrete mixtures used for prestressed members in one bridge.Based on the experimental results,a power exponent function of creep degree for structural numerical analysis was used to model the creep degree of two HPCs,and two series of parameters of this function for two HPCs were calculated with evolution program optimum method.The experimental data was compared with CEB-FIP 90 and ACI 209(92) models,and the two code models both overestimated creep degrees of the two HPCs.So it is recommended that the power exponent function should be used in this bridge structure analysis.

The Creep Feature Analysis of The High Performance Concrete

In order to seek the creep change rules of ased concrete with two different mix proportions, the test is carried out in the situation which is similar to that of the creation of concrete C60, and the creep test on the concrete of two different mix proportions is done under standard lab. Based on creep test of the high performance concrete, the creep degree and the creep coefficient are obtained. By comparing with the wide-adopted models of AC1209 （1997） and CEB- FIP MC90, it is found that the test result is good at its regularity and the research results offer reference to the calculating analysis of the on-the-spot experimental data.

Long-term Performance of Moderate Heat Portland Cement with Double-expansive Sources

The long-term performance of moderate heat Portland cement with double-expansive sources （DE cement） in the system of high MgO clinker and gypsum was studied by XRD, SEM/EDAX and test methods for strength and expansion of cement. Results indicate that the periclase particle, whose size was 5-7.5μm in DE cement clinker containing 4.8 % MgO, existed individually. The periclase hydration in hardened DE cement paste started at about 60 days and completed up to 2 000 days, and ettringite in the paste was stable from 3 days to 2 000 days. Under the conditions of 4.5%-5.0 % MgO in clinker and 2.8%-3.4 %SO3 in cement, ettringite expansion and brucite expansion in DE cement paste had a continuity, entirety and stability. At the ages of 90, 365,730 and 2 000 days the expansion of the paste reached 0.07%-0.11%, 0.16%-0.21%, 0.21%-0.27 %, and 0.29%-0.38%, respectively. The results suggest that by using this cement in mass concrete it may compensate its temperature shrinkage and autogenous shrinkage to some extent.

Curling of New Concrete Pavement and Long-Term Performance

Curling results from the temperature differential across the concrete slab thickness and may induce undue stresses in newly placed slab. This study deals with the finite element （FE） analysis of curling, curling stresses, field measurement of curling on a newly built jointed plain concrete pavement, and comparison of its long-term performance using both Mechanistic-Empirical Pavement Design Guide （MEPDG） and HIPERPAVII software. The FE analysis was performed with a software program, ANSYS. The test section was modeled as a three-layer system with 300 mm concrete slab, 100 mm treated drainable base, and 150 mm lime-treated subgrade. All layers were assumed to be linear elastic. Temperature data was collected at five different depth locations across the concrete slab with digital data loggers. Curling was measured on five different days with a simple setup. The effect of temperature nonlinearities across the slab thickness was also examined. The results show that both upward and downward curling increase as the temperature differential increases. The maximum stress resulting from the combined effect of curling and traffic loading due to positive temperature differential is higher than that due to the negative temperature differential of the same magnitude. Since temperature differential has a significant influence on curling, both curling and curling stresses can be mitigated at an early age with temperature control, namely via enhanced curing. Both MEPDG and HIPERPAVII showed approximately the same performance for the PCC thickness ranging from 215 mm to 300 mm for this project. Performance prediction from HIPERPAVII is very sensitive to the change in PCC thickness less than 230 mm whereas MEPDG prediction is not as sensitive to the thickness change as with HIPERPAV 1I.

Long-Term Bending Behaviour of Prestressed Glulam Bamboo-Wood Beam Based on Creep Effect

Creep is an important characteristic of bamboo and wood materials under long-term loading.This paper aims to study the long-term bending beha-viour of prestressed glulam bamboo-wood beam(GBWB).For this,14 pre-stressed GBWBs were selected and subjected to a long-term loading test for 60 days.Then,a comparative analysis was performed for the effects of pre-tension values,the number of pre-stressed wires,and long-term load on the stress variation of the steel wire and the long-term deflection of the beam midspan.The test results showed that with the number of prestressed wires increasing,the total stress of the steel wire in the beam midspan and the ratio of the long-term deflec-tion to the total deflection decreases decreased,but when the number of steel wires exceeded 4,the total stress and long-term deflection was less infuenced;with the pre-tension value increasing,the ratio of the total stress of the steel wire in the beam midspan and the ratio of the long-temm deflection to the total deflec-tion also decreased,but when the prestress force was greater than 3.975 kN,the:total stress and long-term deflection were less affected;with the other parameters unchanged,when the value of the long-term load increased,the total stress of the steel wire decreased,and the long-temm deflection of the beam midspan increased,which shall be more significant with the long-term load greater than 30%of the standard ultimate bearing capacity.After the test,the experimental data were fitted,and the creep coefficient was given.Finally,the long-term stiffness calcula-tion fommula of the pre-stressed GBWB based on creep effect was proposed.The research findings have certain theoretical significance and engineering value.

Effect of long-term thermal exposure on microstructure and creep properties of DD5 single crystal superalloy

The effect of thermal exposure on the microstructure and creep properties of the Ni-based single crystal superalloy in different test conditions was studied.Long-term exposure was performed at 1,000 ℃ and 1,100 ℃ for 500 h prior to the creep tests.The creep lifetime is found to be improved after the long-term exposure at 1,000 ℃ for 500 h as a result of the formation of secondary M_(23)C_(6) in the interdendritic region.The coarsening of γ’ precipitates accompanied by the formation of TCP phase lead to the degradation of alloy,which is responsible for the reduction of the creep lifetime of Ni-base single crystal superalloy after long-term exposure at 1,100 ℃ for 500 h.The creep lifetime of 1,000 oC thermally exposed sample under the conditions of 1,093 ℃/137 MPa is lower than that of heat-treated state.Thermal exposure at 1,100 ℃ for 500 h causes the creep lifetime to drop drastically.

Comprehensive Analysis of High Temperature Performance of SBS-modified Asphalt Mixture

Evaluation of high temperature performance of SBS-modified asphalt mixture was presented.Both wheel loaded method and creep method were adopted for two different mixtures and two kinds of specimens with different height,and corresponding indicators were measured.Meanwhile,the correlation between these indicators was thoroughly analyzed and two kinds of mixtures were compared.The experimental results show that there is a good linear relationship between LWT indicators and CT indicators for M-13,while a relatively poor relationship for M-25,especially that between dynamic stiffness and static stiffness and that between dynamic stability and static creep stiffness.Besides,logarithmic relationship between DS and RD has a higher determination coefficient than that for linear relationship.Thus,multi-index evaluation should be taken for synthetically assessing high temperature performance of asphalt mixture.

Full-scale multi-functional test platform for investigating mechanical performance of track–subgrade systems of high-speed railways

Motivated by the huge practical engineering demand for the fundamental understanding of mechanical characteristics of high-speed railway infrastructure,a fullscale multi-functional test platform for high-speed railway track–subgrade system is developed in this paper,and its main functions for investigating the mechanical performance of track–subgrade systems are elaborated with three typical experimental examples.Comprising the full-scale subgrade structure and all the five types of track structures adopted in Chinese high-speed railways,namely the CRTS I,the CRTS II and the CRTS III ballastless tracks,the double-block ballastless track and the ballasted track,the test platform is established strictly according to the construction standard of Chinese high-speed railways.Three kinds of effective loading methods are employed,including the real bogie loading,multi-point loading and the impact loading.Various types of sensors are adopted in different components of the five types of track–subgrade systems to measure the displacement,acceleration,pressure,structural strain and deformation,etc.Utilizing this test platform,both dynamic characteristics and long-term performance evolution of high-speed railway track–subgrade systems can be investigated,being able to satisfy the actual demand for large-scale operation of Chinese high-speed railways.As examples,three typical experimental studies are presented to elucidate the comprehensive functionalities of the full-scale multi-functional test platform for exploring the dynamic performance and its long-term evolution of ballastless track systems and for studying the long-term accumulative settlement of the ballasted track–subgrade system in high-speed railways.Some interesting phenomena and meaningful results are captured by the developed test platform,which provide a useful guidance for the scientific operation and maintenance of high-speed railway infrastructure.

Mechanisms by which fibroblast growth factor 20 improves motor performance in a mouse model of Parkinson’s disease

Genome-wide studies have reported that Parkinson’s disease is associated with abnormal expression of various growth factors. In this study, male C57 BL/6 mice aged 10 weeks were used to establish Parkinson’s disease models using an intraperitoneal injection of 60 mg/kg 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine. 28 days later, 10 or 100 ng fibroblast growth factor 20 was injected intracerebroventricularly. The electrophysiological changes in the mouse hippocampus were recorded using a full-cell patch clamp. Expression of Kv4.2 in the substantia nigra was analyzed using a western blot assay. Serum malondialdehyde levels were analyzed by enzyme-linked immunosorbent assay. The motor coordination of mice was evaluated using the rotarod test. The results showed that fibroblast growth factor 20 decreased A-type potassium current in neurons of the substantia nigra, increased long-term potentiation amplitude in the hippocampus, and downregulated Kv4.2 expression. A high dose of fibroblast growth factor 20 reduced serum malondialdehyde levels and enhanced the motor coordination of mice. These findings confirm that fibroblast growth factor 20 has a therapeutic effect on the toxicity induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, and its mechanism of action is associated with the inhibition of A-type K+ currents and Kv4.2 expression. All animal procedures were approved by the Animal Care and Use Committee of Qilu Hospital of Shandong University, China in 2017(approval No. KYLL-2017-0012).

Supporting structure failure caused by the squeezing tunnel creep and its reinforcement measure

Tunnels deeply buried have high crustal stress and are prone to large deformation disasters when encountering soft rock.The large deformation phenomenon during the construction process of the Maoxian Tunnel on the Chengdu-Lanzhou Railway is particularly evident.This article focuses on the large deformation problem of the No.1 inclined shaft of the Maoxian Tunnel,and uses on-site monitoring methods to explore the reasons for tunnel structure failure,and analyzes the mechanical behavior of the tunnel structure.By using numerical simulation methods,the effectiveness of the second-layer support in resisting creep loads in tunnels was studied,and the influence of the construction time of the secondlayer support on the mechanical properties of the tunnel was discussed.The results indicate that the first-layer support in the tunnel is a structural failure caused by asymmetric deformation caused by creep,while the second-layer support has a good effect on resisting creep loads.The research results can provide a technical reference for deformation control of squeezing tunnels.

A numerical case study on the long-term seismic assessment of reinforced concrete tunnels in corrosive environments

The paper investigates the long-term seismic behaviour of an underground reinforced concrete(RC)metro tunnel in Santiago,Chile,considering the combined effects of chloride-induced corrosion and cumulative,low-amplitude seismic shaking on the structure’s performance.The soil-tunnel response is evaluated with the aid of transient,nonlinear finite element analysis using a two-dimensional(2D)plane strain numerical model that adopts advanced nonlinear models for the simulation of soil and concrete plasticity and the dynamic stiffness behaviour.The effects of corrosion deterioration are demonstrated in terms of time-dependent loss of rebar area and cover concrete stiffness and strength.The study illustrates the influence of ageing and repeated seismic shaking on lining deformation,crack development,and the modal characteristics of the intact and degrading systems.The results indicate that multiple lowamplitude events drive the non-degrading RC tunnel beyond its elastic regime without significant structural response consequences.A noticeable impact of corrosion deterioration on the structure’s seismic performance is revealed,increasing with the number and intensity of earthquake events.Two different tunnel embedment depths are comparatively assessed.The analyses demonstrate larger coseismic section convergence in the case of the deeper tunnel,yet a less pronounced effect of ageing and successive seismic loading compared to the shallow section,which is evident in the RC lining cracks at the end of shaking.

不同温度下聚酰亚胺薄膜的蠕变性能

为研究聚酰亚胺薄膜的蠕变黏弹性本构关系模型,选用厚度25μm的聚酰亚胺膜材料,初始应力选取极限抗拉强度的50%,在23、 50、 80、 110、 140、 170℃下进行单轴蠕变拉伸实验,分析不同温度下膜材料蠕变的变化规律.用经典Kelvin、经典Maxwell、 Burgers、三参数广义Kelvin、五参数广义Kelvin蠕变本构模型对数据进行拟合,分析拟合效果.结果表明,聚酰亚胺膜材料具有明显的黏弹性,初始应力对聚酰亚胺膜材料的蠕变性能影响显著,初始应力越大,黏弹性越明显.五参数广义Kelvin模型能够较好地预测聚酰亚胺膜材料的蠕变性能,可决系数均超过0.98,Burgers模型次之,其余3种模型的拟合可决系数为0.708~0.958,拟合结果满足实际工程需要.