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.

Evaluation Method and Mitigation Strategies for Shrinkage Cracking of Modern Concrete

The complex compositions and large shrinkage of concrete,as well as the strong constraints of the structures,often lead to prominent shrinkage cracking problems in modem concrete structures.This paper first introduces a multi-field(hydro-thermo-hygro-constraint)coupling model with the hydration degree of cementitious materials as the basic state parameter to estimate the shrinkage cracking risk of hardening concrete under coupling effects.Second,three new key technologies are illustrated:temperature rise inhibition,full-stage shrinkage compensation,and shrinkage reduction technologies.These technologies can efficiently reduce the thermal,autogenous,and drying shrinkages of concrete.There after,a design process based on the theoretical model and key technologies is proposed to control thecracking risk index below the threshold value.Finally,two engineering application examples are provided that demonstrate that concrete shrinkage cracking can be significantly mitigated by adopting the proposed methods and technologies.

建筑碳中和的关键前沿基础科学问题

我国建筑全过程碳排放已占我国碳排放总量的50%以上,持续稳定的降低建筑碳排放将是我国实现碳中和目标的重要支撑。本文基于国家自然科学基金委员会第326期双清论坛总结了面向碳中和的建筑学科领域的研究现状、发展趋势及面对的挑战,凝练出未来5~10年建筑碳中和涉及的关键科学问题与技术前沿。

绿色建筑设计标准体系发展面临的问题与建议

全面推行绿色建筑是提升建筑宜居水平、实现建筑碳减排目标的最佳途径。本文基于国家自然科学基金委员会第326期双清论坛“建筑碳中和的关键前沿基础科学问题”的学术探讨,围绕“低碳建筑设计标准体系与方法”的论坛主题,梳理了我国绿色建筑设计标准体系发展过程面临的问题,提出了促进绿色建筑全面发展的建议:加强绿色建筑设计基础科学问题研究,全面提升我国绿色建筑设计标准体系,修订建筑学专业教材体系,解决我国绿色建筑推行过程中效果不理想的根源性问题。

Organization and evolution of climate responsive strategies,used in Turpan vernacular buildings in arid region of China

Under the global crisis of energy shortage and environmental pollution,the climate responsive strategies used in vernacular buildings have attracted much attention for their potential to reduce energy consumption and carbon emissions.However,the relationships between these traditional climatic strategies were not precisely perceived,which may cause the inapplicability of these strategies for contemporary rural houses.In this paper,taking the Turpan vernacular buildings in arid region of China,the climate responsive strategies of buildings in the most significant periods such as the Gaochang period(before 1318),the Khanate and Republican period(1318–1949),the Modern period(1949–2010),and the Contemporary period(2011–present)were summarized.In addition,two different types of climatic strategies organizations,namely multilayer spaces and integrated building envelopes,were identified based on the temperature difference measurement and comparative analysis.The assessment of thermal performance of the organizations was conducted by the methodology of software simulation.Furthermore,the applicability of the organizations in rural areas was discussed,and a new combined organization was proposed.Consequently,this study can contribute to provide the main approaches for climatically responsive rural houses.

Building climate zones of major marine islands in China defined using two-stage zoning method and clustering analysis

The current scheme of building climate zones in China generally assumes that building climate zones of island cities are identical to adjacent land stations.Consequently,building design strategies for island buildings usually refer to those developed for inland cities.This approach has to some extent hindered the energy-saving design and green development of island buildings in China.This research takes a first step on this issue by defining the building climate zones of 36 marine islands over China marine area using two-stage zoning methodology adopted by current building climate zoning standard(GB50178-1993).The meteorological data used for analysis was obtained from the National Climate Center of China over the 30-year period from 1985 to 2014.As comparison,40 coastal stations which are adjacent to the inves-tigated marine islands were also included in this study.Subsequently a more obiective techni-que-cluster analysis was operated as an effective supplement to discover the climate characteristics among different observations.The results of both methodologies consistentlyshow that among the 36 islands investigated,the majority of islands located in northern and eastern marine area belong to the same climate zones as their adjacent coastal cities.Howev-er,island cities in southern marine area cannot be assigned to any current climate zone,which was demonstrated by its distinctive climate features different from any other sites investi-gated through cluster analysis as well as different energy use patterns.Thus a new zone was defined to supplement the current building climate zoning scheme to cover marine area of China.

Rural houses with appropriate strategies in northwest China:a practice of ecological houses in Ningxia Province

The severe problem of rural vernacular houses in northwest china is low thermal comfortableness with high consumption of energy in winter.Under such circumstance,the appropriate technologies that create comfortable living environment under the inclement local weather by low cost should be encouraged.In Ningxia Province,Jianfuqiao village,the ecological technologies are presented.By comparing with traditional buildings,the testing and thermal environment analysis verified the effectiveness of the passive used solar technologies.

The comparative study of dwelling houses in the southwest multi-ethnic region,taking Fugong county for example

A number of ethnic minorities are being distributed in southwest China.Yunnan Province is an area inhabited by multi-ethnic groups.For a long time,the ethnic groups have been interacted by others in the cultural aspect,while retaining their own ethnic traditions.The performances of ethnic groups’dwelling houses are similar as determined by natural and cultural elements of the same area.This paper mainly analyzes decisive factors behind similar appearances by the way of field research on two minorities,Nu ethnic group and Li-su ethnic group,in the Fugong county,Nujiang Li-su autonomous prefecture.Moreover,the paper tries to summarize the commonality and individuality of the minorities in order to provide useful theoretical reference for the minorities building of new socialist countryside in the future.

Green building research from design to operation in the past 20 years: A perspective

dented levels during the past centuries.Along with the rapid urbanization crossing the world,serious environmental and energy issues have become global challenges.To address these challenges,the promotion of green building is critical because the construction industry consumes about 40%of the total energy and accounts for 30%of the total greenhouse gas emissions.The goals of green buildings is twofold:1)enhancing indoor environmental quality(IEQ),promoting human health and productivity;2)conserving energy,limiting pollutants and carbon dioxide emissions.

Benefit-based cost allocation for residentially distributed photovoltaic systems in China:A cooperative game theory approach

Distributed photovoltaic(PV)systems have constantly been the key to achieve a low-carbon economy in China.However,the development of Chinese distributed PV systems has failed to meet expectations because of their irrational profit and cost allocations.In this study,the methodology for calculating the levelized cost of energy(LCOE)for PV is thoroughly discussed to address this issue.A mixed-integer linear programming model is built to determine the optimal system operation strategy with a benefit analysis.An externality-corrected mathematical model based on Shapley value is established to allocate the cost of distributed PV systems in 15 Chinese cities between the government,utility grid and residents.Results show that(i)an inverse relationship exists between the LCOEs and solar radiation levels;(ii)the government and residents gain extra benefits from the utility grid through net metering policies,and the utility grid should be the highly subsidized participant;(iii)the percentage of cost assigned to the utility grid and government should increase with the expansion of battery bank to weaken the impact of demand response on increasing theoretical subsidies;and(iv)apart from the LCOE,the local residential electricity prices remarkably impact the subsidy calculation results.

Degradation of limestone calcined clay cement(LC^(3))mortars under sulfate attack

Limestone Calcined Clay Cement(LC^(3)) is a newly proposed low-carbon cement,which can effectively reduce energy consumption and carbon emissions of the traditional cement industry without changing the basic mechanical properties of cement-based materials.In this study,the degradation process of mortar samples of limestone and calcined clay cementitious material under sulfate attack is studied by both macroscopic and microscopic analysis.The results show that compared with pure Portland cement,the addition of calcined clay and limestone can significantly reduce the expansion rate,loss of dynamic modulus and mass loss of mortar specimens under sulfate attack.The addition of calcined clay and limestone will refine the pore size distribution of mortar specimens,then inhibiting the diffusion of sulfate and formation of corrosive products,therefore leading to a significant improvement of the sulfate resistance.