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21.
P. Hagelia R. G. Sibbick N. J. Crammond C. K. Larsen 《Cement and Concrete Composites》2003,25(8):1131-1140
Thaumasite formation (TF) and limited thaumasite form of sulfate attack (TSA) has recently been detected in several Norwegian sprayed concretes. TF and TSA is frequently associated with contemporaneous and late stage internal calcite formation by: (a) decalcification of calcium silicate hydrate (CSH): (b) decomposition of thaumasite associated with secondary liberation of SO42− and occasional formation of subordinate gypsum; (c) supersaturation of fluids in voids. Popcorn calcite and other textural forms were characteristic for these reactions. Also co-precipitation of popcorn calcite + thaumasite, as well as later stage dissolution of both minerals occurred. The entire process was represented by a drop in pore fluid pH from about 13 towards 5–7.
In this paper we study the TF–TSA–carbonation process in several environments: (1) three examples of 2–13 years old steel fibre reinforced sprayed concrete made with Sulfate Resisting Portland Cement (SRPC) and silica fume in contact with carbon-, calcite- and sulfide bearing Alum Shale: (2) two examples of ≈30 years old, and severely damaged, SRPC based sprayed concrete within the Alum Shale: (3) one 16 years old sprayed concrete made with Portland Cement (PC) and possibly fly ash in presence of sulfate bearing ground water and (4) one 10 years old steel fibre reinforced sprayed concrete in a sub-sea tunnel with inflow of somewhat modified seawater. This PC based concrete with silica fume had suffered localised crumbling and mush formation after less than 5 years. The critical factors for thaumasite formation are discussed together with consequences for further deterioration and timing of repair. 相似文献
22.
种法力 《特种铸造及有色合金》2012,32(6):508-510
利用等离子体喷涂技术在铜合金基体上制备1mm的钨涂层,并对大气和真空等离子体喷涂钨涂层性能进行比较。结果表明,真空喷涂钨涂层气孔率低、传热能力高、杂质含量低、结合强度高,热负荷性能好。与大气等离子体喷涂钨涂层相比,真空喷涂技术更适合应用到核聚变实验装置内壁上。 相似文献
23.
徐兆雄 《理化检验(物理分册)》2001,38(10):434-434,437
介绍了对专用一级公路上的桥梁钢管进行疲劳试验,用以检验桥梁钢管长期在特定的自然条件下的安全可靠性。 相似文献
24.
万家寨引黄工程总干线一、二线泵站防火喷涂项目，在施工过程中，承包商提出了索赔要求，本文介绍了该项目索赔的分析过程，包括索赔证据的确立及索赔费用计算等。 相似文献
25.
利用喷射成形技术制备高强度Zn-35Al-3.5Mn-2.2Cu-0.1Mg合金,对合金在不同温度和保温时间下进行固溶处理.用X射线衍射和扫描电镜等手段研究了合金的显微组织,并测定了合金的力学性能.结果表明,双级固溶和单级固溶处理制度相比,前者得到的组织较为理想,再结晶晶粒尺寸较小,同时回溶颗粒较多.采用双级固溶处理(360℃×3 h+390℃×1h和120℃×15 h时效处理)后,合金的抗拉强度和屈服强度分别达到526 MPa和471MPa,伸长率达到9.2%. 相似文献
26.
A sprayed waterproofing interlayer between primary and secondary tunnel linings has the potential to create composite structural interaction between them, mainly in circumferential flexure. This depends on the bond between sprayed surfaces and on the structural and chemical properties of the material. Data on bond is reviewed. Recent tests in tension, compression and shear to determine the structural properties of a particular elastomeric waterproofing material are presented, analysed and discussed. Values for Young’s modulus and the shear modulus G are proposed, for serviceability verifications that include limitation of crack width caused by excessive local flexure.It is concluded that where sufficient bond is present, composite action arising from transfer of circumferential shear between the linings can be relied upon to improve performance in service for short-term and accidental situations. This allows for reduction of stiffness during the first few years. There is no evidence from tests lasting up to 2.2 years that significant further reduction would occur, but prediction of 100-year performance remains difficult. 相似文献
27.
Sprayed concrete is a well established application method for concrete repairs and ground supports; its popularity ever increasing in the past decades. In this field, the development of new fundamental and practical knowledge relies heavily on understanding the placement process, which controls the amount of rebound loss and consequently the in-place material composition and properties. In this context, an important experimental study investigating placement mechanisms at the process scale (spray scale) was undertaken and key findings are presented here. Indeed, the spatial distribution of the in-place sprayed material, around the spray axis, offers a unique view of the placement mechanisms; the effect of the spraying process is highlighted through the evaluation of the in-place material composition and distribution. In light of this study, a new approach is provided to initiate a thorough discussion on how shotcreting parameters and equipment can affect rebound losses and the quality of the in-place material. 相似文献
28.
Fiber-reinforced spayed concrete has been used for several years in civil and tunneling operations.Research conducted to reduce cure times and increase compressive and flexural strengths resulted in the development of Tekcrete Fast~, a cementitious product capable of obtaining 41 MPa compressive strength and 8 MPa flexural strength in only 3 h and reaching 7 d strengths of 62 and 11.7 MPa, respectively.A single bag product that uses conventional shotcrete and gunite application systems makes it a natural crossover product for mining applications.The discovery of incredible adhesion properties and high resistance to chloride permeability helps ensure long-term stability and increases the ease of application.Project results from Disaster City~ in Texas and the application for rehabilitating a coal mine belt entry are presented.The case study illustrates the effectiveness of the product in stabilizing a coal mine beltway and adjacent cross-cuts that were subjected to progressive sloughage due to humidity and cyclical loading. 相似文献
29.
由于年久失修、施工质量、地震等级的改变等原因,使砌体承载力严重不足,为延长建筑物的使用年限,以发挥其最大的经济效益和社会效益,现实生活中很建筑都迫切需要加固。现从以下几个方面系统介绍“夹板墙”加固砌体的方法,供大家参考。 相似文献
30.
李振亮;贾国栋 《特种铸造及有色合金》2015,35(9):923-926
综述了镁合金中长周期堆垛有序结构（LPSO）相的最新研究进展,系统总结了镁合金中LPSO相的类型、形成机理及影响因素,重点对Mg-Nd-Zn型LPSO相的形成进行理论分析,最后指出了喷射沉积技术制备Ca/Nd复合高合金化镁合金中LPSO相的4个发展方向。 相似文献