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Silica Fume in Shotcrete Tremely Low, Being in the "Excellent" *Morgan

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Silica Fume in Shotcrete Tremely Low, Being in the Silica ume in Shotcrete by John Wolsiefer, Sr., and Dudley R. Morgan 28 Shotcrete • Winter 2003 Table 3 - Plastic properties of wet-mix shotcrete Table 1 - Wet-mix shotcrete mix Mix A B c D designs, kgfm3 Mix type PC USF CLDSF CHDSF Ambient temperature, C 9 10 13 14 Mix A B D c Shotcrete temperature, C 14 12 15 13 Mix type PC USF CLDSF CHDSF Slump, mm Portland cement, Type I 401 350 353 359 Base shotcrete 40 50 45 100 Silica fume - 47 48 46 After SF & superplasticizer - 50 35 20 Coarse aggregate, 10 mm, 462 485 475 467 Air content, percent SSD Base shotcrete 8.5 7.2 8.0 7A Concrete sand, SSD 1258 1213 1239 1263 After SF & superplasticizer - 6A 5.8 5.8 Water 171 177 177 176 As-shot 4.8 3.9 3.2 2.6 Water-reducing 887 1952 1952 1922 admixture, ml Thickness to bond break Superplasticizer, m1 - 1597 1597 1360 Overhead application, mm 95 130 280 180 Air-entraining admixture, 118 296 296 296 Vertical application, mm 305 330 380 405 ml Overhead rebound, percent - 12.9 12.3 10.4 Total 2294 2297 2296 2314 Vertical rebound. nercent 3.4 2.7 3.7 3.9 Table- 2 Dry-mix shotcrete mix Table 4 - Plastic properties of dry-mix designs, kg/m3 shotcrete Mix E , F G H Mix E F .G H Mix type PC USF CLDSF CHDSF Mix type PC USF CLDSF CHDSF Portland cement, Type I 425 373 373 373 Ambient temperature, C 6 6 8 7 Silica fume - 49 49 49 Shotcrete temperature, C 14 16 14 13 Coarse aggregate, 10 mm, 495 491 491 491 Thickness to bond bread SSD Overhead application, mm 65 380 280 230 Concrete sand, SSD 1216 1204 1204 1204 Vertical application, mm 205 460 560 460 Water (estimated) 163 165 165 165 Overhead rebound, percent 42.7 20.4 25.2 18.6 Total 2300 2281 2281 2281 Vertical rebound percent 45.4 21.1 22.9 24.6 Shotcrete test program Mix designs and supply water reacting with the cement and sil­ ica fume is too short for effective A study was undertaken to evaluate the The wet- and dry-mix shotcrete mix water reduction before the mix is actu­ performance characteristics of three designs used are shown in Tables 1 ally consolidated in place on the shot­ different silica fume product forms in and 2. These mix designs are typical of crete surface. both wet-mix and dry-mix shotcrete: those used in rock slope stabilization The wet-mix shotcrete was brought and tunnelling projects in the United • as-produced uncompacted silica to the field test site by transit truck, States and Canada. The cement was a fume (USF) with the silica fume and superplasti­ portland Type I, with aggregates meet­ • compacted low-density silica fume cizer added on-site. A shotcrete piston ing the requirements of the ACI Stand­ (CLDSF) pump was used to apply the wet-mix ard Specification for Materials, • compacted high-density silica fume shotcrete. The dry-mix shotcrete was Proportioning, and Application of (CHDSF) weight-hatched in premixed super Shotcrete, ACI 506.2, Gradation No. 2. The performance characteristics sacks with cement, aggregate, and sil­ The control mixes are labelled A (Wet) ica fume all premixed. The dry-mix evaluated included rebound loss, thick­ and E (Dry). The silica fume mix de­ ness to bond breaking (sloughing) on was premoisturized to a moisture con­ signs, prepared with USF, CLDSF, and tent of 3 to 4 percent prior to discharge overhead and vertical surfaces, com­ CHDSF are designated, respectively, pressive strength, flexural strength, in a rotating barrel feed shotcrete gun. B, C, and D for the wet-mix and F, G, drying shrinkage at 50 percent relative and H for the dry-mix shotcretes. humidity, chloride permeability, elec­ The silica fume dosage averaged 13 Thickness to bond break and trical resistivity, boiled absorption, and percent (by mass of cement) for all sil­ rebound loss volume of permeable voids. These pa­ ica fume shotcrete mix designs. A Silica fume addition to shotcrete in­ rameters were compared to the per­ naphthalene sulphonate-based super­ creases adhesion to the bonding sur­ formance of a shotcrete control mix plasticizer was used to control the face and cohesion within the shotcrete; prepared with plain portland cement water-cement ratio in the wet shotcrete consequently, the thickness of shot­ mix. Superplasticizer is not required crete build-up attainable on overhead for dry-mix shotcrete, since most of and vertical surfaces is substantially *Morgan, D. R., "Recent Developments in Shotcrete Technology," Materials Engineering Perspective pre­ the water in the mix is added at the improved. There is no standard ASTM sented at the World of Concrete 1988, Las Vegas. shotcrete nozzle; contact time for the or ACI test to measure attainable Shotcrete • Winter 2003 29 84 84 77 77 70 70 "'- 63 63 1§. ~ ;: 56 ;: 56 "' 49 "'~ 49 ....~ ....a: 42 42 ~ "'~ "'> :> ;;; 35 ;;; 35 ~ ~ a: "'- 28 :'!: 28 :E :E ...,0 21 o A - Control Mix. Portland Cement ...,0 21 o E - Control Mix. Portland Cement + F - Uncompacted Silica Fume + B - Uncompacted S~ica Fume 14 o C - Compacted Low Density Silica F ...e 14 0 G - Compacted Low Density Siliea Fume • D - Compacted High Density Silica Fume 0 H - Compacted Hi9h Denaity Silieo Fume 7 0+-----.----.-----r----~----.-----.---~ 0+----.-----.-----r----.----.----------~ 0 20 40 60 0 20 40 60 AGE !DAYS) AGE (DAYS) Fig. 1 -Compressive strength of wet-mix shotcrete. Fig. 2 - Compressive strength of dry-mix shotcrete. Table- 5 Hardened properties of Table 6- Hardened properties of wet-mix shotcrete dry-mix shotcrete Mix ASTM A B c D Mix ASTM A B c D Mix type test PC USF CLDSF CHDSF Mix type I···· test PC USF ... · CLDSF CHDSF procedure procedure Compressive strength, c 39 Compressive strength, C39 MPa MPa ·-· 24 hours 14.5 21.7 16.8 17.3 24 hours - - 24.7 23.7 7days - 44.4 38.6 35.1 29 hours· 31.1 33.8 - - 28 days 43.8 63.5 55.9 57.4 7 days 44.2 49.2 45.2 44.4 63 days 44.0 69.7 64.0 64.9 28 days 53.8 59.9 58.7 54.9 Flexural strength, MPa C78 63 days 61.8 67.2 66.3 62.4 7 days - 4.9 3.8 4.1 Flexural strength, MPa C 78 28 days 5.3 6.7 6.0 6.5 28 days 7.4 8.4 6.6 7.5 Boiled absorption, I C642 5.9 6.6 6.9 6.3 Boiled absorption, C642 4.9 2.7 3.6 4.0 percent, 28 days percent, 28 days Vo!lll1le of permeallie 12.9 14.3 14.9 13.9 Volume of permeable 11.2 6.3 8.3 9.2 voids, percent, 28 days voids, percent, 28 days Bulk specific gravity 2.296 2.304 2.307 2.341 Bulk specific gravity 2.380 2.398 2.371 2.370 after immersion and after immersion and boiling boiling thickness build-up, so thickness to vertical rebound was reduced from Compressive and flexural bond break (sloughing) and rebound 45.5 percent in the plain control mix to strength loss were measured in a specially con­ 22.8 percent, on average, for the three Compressive strength was measured at structed rebound chamber. These pa­ silica fume product forms. The wet­ 24 hours, and 7, 28, and 63 days by rameters are shown in Tables 3 and 4. mix shotcrete rebound percentages testing cores extracted from shotcrete In the wet-mix shotcrete study, the were low in all mixtures. test panels. The panels were cured in overhead thickness at bond-break was the field for the first 24 hours, then 3.5 in. (90 mm) for the plain portland In summary, the wet-mix data vari­ transferred (in the wooden forms) to a cement Mix A, and reached a maxi­ ance for the three silica fume product laboratory, where the shotcrete was mum of 11 in. (280 mm) in Mix C forms shows no significant difference moist-cured. The strength data shown (CLDSF). The overhead thickness at in rebound loss, but some differences in Table 5 and Fig. I show that using bond break was typically greater for in thickness to bond break. For the silica fume generated significant in­ the dry-mix shotcrete, reaching a dry-mix shotcrete, there is a greater creases in the wet-mix shotcrete com­ pressive strength. The control mix maximum of 15 in. (380 mm) in Mix F thickness of 15 in. (380 mm) for USF compressive strength was 6390 psi (44 compared to 11 and 9 in. (280 and (USF), compared to 2.5 in. (65 mm) MPa) at 63 days compared to an aver­ for the plain Mix E. The dry-mix shot­ 230 mm) for the CLDSF and CHDSF age of 9590 psi (66.1 MPa) for the sil­ crete overhead rebound was decreased mixes, respectively. However, note ica fume shotcretes, about a 50 percent from 42.7 perclent for the plain control that these thicknesses were attained in increase. to an average of 21.4 percent for the a controlled test environment, and may The dry-mix silica fume shotcrete three silica fume product forms. The not be achievable in field applications. compressive strengths also were 30 Shotcrete • Winter 2003 7000 (/) ~ 3000 6000 3 2578 u 2500 5000 >- t: 2000 E - Control Mi•. Portland Cement 4000 A - Confrol Mi>c. Portland Cement F - Uncompacted s•co Fume B - Uncompacted Sica Fume ~ G - Compacted Low Density Silica Fume C - Compacted Low Density Silica Fume H - Compacted High Denoity Silica Fume D - Compacted Hi~ Oenaity Silica Fume 1500 3000 i 1000 2000 ~ ~ 1000 Q 500 ~ a: MIX DESIGN TYPE MIX DESIGN TYPE Fig.
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