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
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
Cd0·8Zn0·2S films were prepared by the spray pyrolysis technique on glass and conducting glass (fluorine doped tin oxide) substrates,
by spraying aqueous solutions of cadmium chloride, zinc chloride and thiourea. The spray rate was varied from 4 cc/min to
16 cc/min. It is found that film thickness increases with increase in spray rate. The electrical and optical properties of
the films namely dark conductivity, thermoelectric power and optical absorption were studied; conductivity and thermoelectric
power are higher for the films prepared at lower spray rate (4·3 cc/min). 相似文献