18 Shot Crete | Concrete

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  SECTION XVIIISHOTCRETE1801SCOPE This Section deals with the shotcrete to be used for permanent linings and fillings,where shown on the Drawings or required by NIA. 1802GENERAL Shotcrete shall be composed of an admixture of cement, sand, aggregates andaccelerating mixture.nless specifically modified by the following specifications or otherwise appro!ed,the shotcrete shall conform to and be applied in accordance with the recommendationscontained in the American oncrete Institute #$ecommended %ractice for Shotcreting#&A I '()))*.+here required, the shotcrete shall be reinforced with welded wire or chainlin- fabric. 1803 MATERIALS a. Cement ement shall comply with the pro!isions set forth in paragraph '(/, Section 01, oncrete. b. Sand and Aggregates The quality of sand and aggregates shall comply with the requirements set forth in paragraph '() for concrete wor-s. +hile the combined aggregate grading shall be asfollows2Sie!e Si3e Square 4esh%ercent %assing  by +eight#((/56#7(  ((/58#)'  7( No. 66'  9' No. 8/(  '' No. ):(  6( No. (((  (c. +ater TS01III  Shotcrete+ater shall comply with the requirements set forth in paragraph '(' for concretewor-s.d. Accelerating AdmixtureAccelerating admixture shall comply with the requirements set forth in paragraph'(6. 180PROPORTIONING AN! TESTING a. %roportioning The ontractor shall proportion the mixture for shotcrete so that the combinationof the ingredients de!elop the following minimum compressi!e strengths2  T meC#m$ress %e Strengt& '(g)*m2+C,ass AC,ass - At 8 hours/(At 9: hours6(At 9 days8(At :8 days/((/(( The tests shall be carried out at Site laboratory.  lass #A# shotcrete shall be used when a fast support or protection of the roc- isnecessary, especially in underground exca!ations.  lass #;# shotcrete shall be used in other cases and mainly for supports or  protections in outdoor exca!ation or slopes. The laboratory mixes shall be prepared considering '(()(( -g of cement, (.6(watercement ratio and accelerator in quantity necessary to obtain the requiredcompressi!e strengths, but in any case not exceeding )< by weight of the cement.The mixture shall be submitted for appro!al of NIA at least sixty &)(* days beforeshotcrete application. b. Pre.*#nstr/*t #n Tests Test cylinders shall be prepared by the ontractor before the wor- begins, in theamount requested by NIA, by shooting concrete !ertically downwards into molds of hardware fabric 7 mm &/56#* metal mesh to ma-e cylinders ' cm &)#* in diameter and/( cm &:#* high. =xcess material shall be trimmed off with a sharpedged trowel.TS01III:  Shotcrete ylinders shall not be mo!ed for at least eight hours after being shot, during which timethey shall be protected and treated in a manner satisfactory to NIA.These cylinders shall be manufactured so as to represent as closely as possible thequality of concrete to be placed in the wor-s. Test cylinders shall be shot with the sameequipment, air pressure, no33le tip, and water content as the concrete to be used in thewor-s.>ther preconstruction tests shall be carried out, shotcreting an inclined roc- surface and then obtaining core samples, as specified in subparagraph 8(6 c for fieldtests.>n the basis of the results obtained by the preconstruction tests, NIA will accept or refuse the mixtures prepared by the ontractor.naccepted mixtures cannot be utili3ed in permanent wor-s and shall besubstituted with new mix proportions.c.  e,d Tests ?ield tests shall normally be executed as described for preconstruction tests and inthe amount established by NIA. If the test results are unsatisfactory, NIA may refuse the payment of the defecti!eshotcrete.At the request of NIA and without extra payment, test specimens shall be obtained by core drilling from the lining. ore samples shall be 9.' cm &/#* in diameter and obtained by diamond core bit according to AST4 Designation 6: #4ethod of >btaining andTesting Drilled ores and Sawed ;eams of oncrete#.The compressi!e strength of an indi!idual class of shotcrete shall be consideredsatisfactory if both the following requirements are met2 The a!erage of three consecuti!e strength tests &tests composed of : cylinders*equals or exceeds the required compressi!e strength@ No indi!idual strength test falls below the required compressi!e strength bymore than '( -g5cm : . 180PREPARATION O SRACES The surfaces in contact with the shotcrete shall be cleaned before layingoperations, so as to free them from unstable material or materials on which the shotcretecannot stic- such as mud or shattered and rebound material. If necessary, the surface shall be thoroughly cleaned with water and compressed air@ remaining water shall be blownaway with compressed air.TS01III/  Shotcrete+here concentrated or scattered water inflows occur, the ontractor will trapand con!ey this water to drains by suitable means. nder no circumstances shall shotcrete be placed on a surface co!ered with standing or running water@ water shall be withheldfrom the fresh shotcrete until it has sufficiently set. 180E4IPMENT All equipment required to perform shotcreting operations shall be subect to theappro!al by NIA.The equipment used for measuring and batching concrete ingredients, for mixing,and for placing of the shotcrete shall be of a recogni3ed and pro!en type and of sufficientcapacity to perform the wor- in a wor-manli-e and efficient manner and to maintain the placing continuity. 1805-ATCHING AN! MIXING ;atching equipment shall be capable of performing accurate measurement to pro!ide uniformity of the concrete produced.;atching by weight shall be used unless otherwise appro!ed.The components of the shotcrete shall be thoroughly mixed in appro!ed mixers.4ixed concrete materials, excluding the admixture, which are not used within onehour of mixing, shall be wasted.The class of shotcrete shall be appro!ed by NIA according to the conditions of thewor- to be performed. 1808PLACING The shotcrete shall be placed in one or more layers to the thic-ness as directed by NIA so that at no time does sloughing of the placed concrete ta-e place. If the applicationof a succeeding layer has to be delayed such that the underlying layer has started to ta-eits initial set, the application of that succeeding layer shall be delayed until its applicationwill not disturb the initial setting process.The placing of the shotcrete shall be performed by experienced personnel in awor-manli-e and efficient manner, using proper air pressure, water pressure, and hoselength. In addition to the equipment operator and no33leman one or more men shall be present during the spraying operations to remo!e the rebounded material which under nocircumstances shall be used again as spray material.The thic-ness in place shall be in any point not less than the required !alues. 1806 CRING TS01III6
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