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.

Stabilization of expansive soils using chemical additives: A review

Volume instability of expansive soils due to moisture fluctuations is often disastrous,causing severe damages and distortions in the supported structures.It is,therefore,necessary to adequately improve the performance of such soils that they can favorably fulfil the post-construction stability requirements.This can be achieved through chemical stabilization using additives such as lime,cement and fly ash.In this paper,suitability of such additives under various conditions and their mechanisms are reviewed in detail.It is observed that the stabilization process primarily involves hydration,cation exchange,flocculation and pozzolanic reactions.The degree of stabilization is controlled by several factors such as additive type,additive content,soil type,soil mineralogy,curing period,curing temperature,delay in compaction,pH of soil matrix,and molding water content,including presence of nano-silica,organic matter and sulfate compounds.Provision of nano-silica not only improves soil packing but also accelerates the pozzolanic reaction.However,presence of deleterious compounds such as sulfate or organic matter can turn the treated soils unfavorable at times even worser than the unstabilized ones.

A Review on Stabilization of Expansive Soil Using Industrial Solid Wastes

In developing countries like India, Industrialization is rising rapidly, and also?a great paucity of land is there, the demand for exploitation of industrial?wastes?which coming from industries is increasing. From geotechnical perspective,?fly ash, granite and quarry waste, cement kiln dust, silica fume, rice husk etc.?are the waste materials?which?have effectual features requisites by an excellent soil stabilization admixture. Stabilization using solid wastes is one of the different?methods of treatment, to improve the engineering properties and make it?suitable for construction. This paper briefs about the recent trends in stabilization of expansive soil using industrial waste (granite and quarry waste, cement kiln?dust, silica fume, rice husk) as stabilizers for decreasing the environmental?hazards.

一种岩土边坡深层水泥搅拌桩用聚合物材料制备及特性分析

解决传统的岩土边坡深层水泥搅拌桩对水泥材料的依赖性较高,工程建设成本长期居高不下的问题。深层水泥搅拌桩是提高岩土边坡尤其软土边坡地基力学性能的重要手段,研究以粉煤灰-矿渣聚合物岩土边坡深层水泥搅拌桩为例,尝试利用粉煤灰-矿渣等制备一种特殊聚合物水泥,对这种通过粉煤灰、矿渣等形成的聚合物原材料的综合性能进行分析。结果表明,当矿渣与粉煤灰的配合比为30∶70时,岩土边坡深层水泥搅拌桩的聚合物硬化时间最短,当碱浓度为2.5 mol/L时,能够获得最佳的材料压缩强度。

Freeze-thaw performance of chemically stabilized natural and recycled highway materials

This article provides an overview of several previous studies that investigated the stiffness and strength performance of chemically stabilized roadway materials under winter conditions （freeze-thaw cycling）. The objective of this research was to understand the behavior of different materials stabilized with different type of binders when they were subjected to freeze-thaw cycling. Nine different materials including natural soils （organic soil, clay, silt, sand, and road surface gravel）, reclaimed pavement material, and recycled asphalt pavement stabilized with nine different binders （five different fly ashes, lime, cement, lime kiln dust, cement kiln dust） were discussed. This article investigated how the volume, resilient modulus and unconfined compressive strength of soils/materials stabilized with different binders change in response to freeze-thaw cycling. Overall, the review results indicate that the stiffness and strength of all stabilized materials decrease somewhat with freeze-thaw cycling. However, the reduced strength and stiffness of stabilized materials after freeze-thaw cycling was still higher than that of unstabilized-unfrozen original soils and materials. In addition, materials stabilized with cement kiln dust provided the best performance against freeze-thaw cycling.

富里酸环境下粉煤灰水泥土的腐蚀性试验研究

研究水泥土在腐蚀环境中的耐久性问题对建筑结构的安全性具有重要意义,粉煤灰作为土木工程材料的重要外加剂,可降低水泥的使用量并可改善水泥土搅拌时的和易性,在实际工程中被广泛使用。为研究掺入粉煤灰的水泥土在泥炭(质)土环境中的腐蚀性问题,针对昆明地区泥炭(质)土环境,通过室内试验模拟其腐蚀环境,将纯水泥土和掺入粉煤灰的水泥土在富里酸环境中浸泡,通过浸泡过程中两组试样的表观变化、耗酸量和腐蚀软化深度的对比,研究纯水泥土与掺入粉煤灰的水泥土在富里酸环境中的腐蚀变化状况。分析结果得出掺入粉煤灰的水泥土在富里酸环境中劣化更为严重,考虑到建筑结构的长期安全性,在泥炭(质)土环境中的水泥土构筑物不宜掺入粉煤灰。

洞庭湖区掺粉煤灰水泥土性能试验研究

采用粉煤灰代替部分水泥作为胶凝材料的水泥土桩法,近年来逐渐在软弱地基的加固处理中得到应用。针对洞庭湖区湖泊相淤泥质软弱地基加固处理问题,结合该区域某分洪闸地基处理工程,在室内开展了不同粉煤灰掺量的水泥土试件的无侧限抗压强度、含水率以及中心部位土样溶液pH值的测定试验,然后探讨建立了不同粉煤灰掺量的水泥土无侧限抗压强度的组合指数式模型。研究结果表明:水泥土试件无侧限抗压强度在60 d龄期前随着粉煤灰掺量的增加而降低,但在90 d龄期时,不同粉煤灰掺量的4组试件强度值较为接近;水泥土试件含水率在28 d龄期之后随着粉煤灰掺量的增加而增加;水泥土试件中心部位土样溶液的pH值始终随着粉煤灰掺量的增加而降低;采用组合指数式强度模型能较好地描述粉煤灰掺量和龄期对水泥土无侧限抗压强度增长规律的影响;通过对不同粉煤灰掺量水泥土桩方案进行比选,建议洞庭湖区水泥土中粉煤灰掺量应在20%左右为宜。

沥青路面冷再生基层路用性能试验研究

以立志路改造工程为依托,对以水泥粉煤灰作为添加剂稳定石灰土加沥青表处的冷再生基层进行强度特性、干缩特性、温缩特性、疲劳特性、水稳定性、冰冻稳定性、劈裂强度等路用性能的分析,并结合试验路后期技术指标观测,论证石灰土加沥青表处结构冷再生作为农村低等级公路沥青路面基层的技术可行性和适用性,有很大的现实意义。