A PRACTICAL STUDY ON RELIABLE CONCRETE PRODUCTION SYSTEM USING IMMERSION BATCHING OF FINE AGGREGATE

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1 A PRACTICAL STUDY ON RELIABLE CONCRETE PRODUCTION SYSTEM USING IMMERSION BATCHING OF FINE AGGREGATE (Tranlati rom Proceeding o JSCE,No.697/V-4,February ) Ryuichi CHIKAMATSU Shigeyuki SOGO The ctrol o ccrete quality begin ith precie meaurement o the peciied quantitie o material beore producti begin. Hoever, there i no eay ay to preciely and quickly meaure the moiture o ine in mot producti ytem currently in operati. To olve thi problem, the author have devied an "immeri " method or ine, in hich i immered in ater beore being batched in a et cditi. Thi enable the precie quantitie o ater and ine to be calculated independent o luctuating level o moiture. Thi paper ummarize the reult o veriicati tet aimed at practical implementati o a ccrete producti ytem baed immeri o the ine. Batching ctrol o the ine immered in ater and peciicati o the equipment are alo decribed, and the reult o quality cirmati tet ccrete made uing thi method are reported. Keyord: ine, moiture, method immering and in ater,high reliability, ccrete producti ytem Ryuichi Chikamatu i a deputy chie civil engineer o Obayahi Corporati, Technical Reearch Intitute, Tokyo, Japan. He received hi Mater o Engineering Degree rom Univerity o Tukuba in Hi reearch activitie include the characteritic o lo-heat blended cement, development o Sel-Compacting Ccrete. He received JSCE Yohida Reearch Prize in He i a member o JSCE and JCI. Shigeyuki Sogo i a general manager o Obayahi Corporati, Technical Reearch Intitute, Tokyo, Japan. He received hi Mater and Doctor o Engineering Degree rom Univerity o Kyuhu Intitute o Technology in 1974 and 1991 repectively. He ha been occupied ith development o pecial ccreting method, uch a Underater Placing, Ma Ccrete, and impliying ith Sel-Compacting Ccrete. He i a member o JSCE and JCI.

2 1.INTRODUCTION The ctructi o more reliable ccrete tructure require that a ytem o auring adequate ccrete quality be ormulated. The ne method or ine decribed in thi paper i intended a part o uch a quality aurance ytem. Quality tability i an index or judging the reliability o ccrete. The ideal ccrete producti ytem i e in hich quality luctuati are minimized, regardle o the actual quality level, and in hich the reult o producti are adequately evaluated. Producti ytem currently in ue generally aume that i in a moit cditi and require meaurement o moiture to correct the ater ctent. Variou enor ytem have been propoed or making ctinuou meaurement o moiture, a needed to allo or correcti, including ytem baed microave, capacitance, and neutr. Yet, ctrol o moiture remain a problem at mot plant [1]. With thi a the background, the author have devied a method o aturated ine, obtained by immeri in ater, together ith the ater a a method o preciely ctrolling ine and ater independently o luctuating moiture level. Thi paper ummarize the reult o veriicati tet aimed at putting thi immeri method into practical ue. The method o ctrol and peciicati o the equipment are decribed, and the method o preparing immered ine i given. Finally, the quality o ccrete made ith ine prepared uing thi method i alo reported..overview OF IMMERSION BATCHING OF FINE AGGREGATE.1 Baic ccept The baic ccept o thi method i that ine i immered in ater and then the mae o ine and ater are calculated rom the total volume and ma baed the dierence denity beteen the to compent (See Fig.1). By thi method, the ine ctent, hich i normally expreed in term o eight in the aturated -dry cditi, i determined ithout adjuting the moiture. A a reult, ccrete o the required quality can be eiciently produced, ince no moiture ctrol o the ine i neceary []. Cement Water Fine Coare Level enor Water Load cell Water + Fine Mixer Fig.1 Ccept o immeri o ine

3 The calculati are a given belo: M + M = M (1) M ρ + M ρ = V () Tranorming Eq. (1) and (), M M ( M ρ V ) ( ρ ρ ) = ρ (3) ( ρ V M ) ( ρ ρ ) = ρ (4) here, M S ;ma o ine,ρ S ;aturated -dry denity o ine M ;ma o ater,ρ ;denity o ater M ;total ma o ine and ater V ;total volume o ine and ater. Equipment or immeri Table 1 ho a typical example o the equipment and ctrol method needed or immeri o ine. Equipment may be o the volume-meaurement or volume-ctrol type. Photo 1 ho an example o volume-meaurement type equipment. The peciicati o the equipment are decribed a ollo: a) Batching range or ine A a rule, thi method i ued or the total quantity o ine to be ued in the ccrete. Since it i baed the ame principle a in JIS A (Method o teting or moiture o ine ), the moiture can alo be calculated. In cae here it i impoible to immere the all o the ine required in the batch, a a reult o the lo ater ctent, can be carried out by immering ly part o the ine. In thi cae, the moiture ctent i calculated, and then the remaining amount o ine i adjuted to correct the batch. b) Method o ctrolling Though material may be ctrolled by either ma or volume, a in cvential, ma-baed ctrol may be more practical. With volume-meauring type equipment, the ma o immered ine i eighed under ctrol, and it volume i meaured. Even i the ma o immered ine i eighed a peciied, the meaured volume o immered ine may vary depending it moiture, changing the calculati in term o volume in a aturated dry cditi. On the other hand, volume-ctrolling type equipment imultaneouly ctrol the ma and volume o immered ine. The a-batched volume o immered ine i et beorehand, and ater i replaced ith ine hile maintaining the et volume. The eight meaurement increae according to the ma o ine added to the ater. When the ma o immered ine reache the et value, o ine and ater at the peciied quantitie i completed. Thi method permit quick and eicient producti o ccrete ith the target quality and quantity. There are ome variati o the method uing dierent combinati o meaurement. With Type B, hon in Table 1, the mae o ater and et ine are eighed and the immered ine i obtained by charging both into a ctainer o knon capacity.

4 Table 1 Typical example o equipment and ctrol method or immeri o ine Type o equipment Volume-meaurement Volume-ctrol A Volume-ctrol B Schematic outline Special eature Batching item Caluculati item Fine or immeri Ctrol method Adjuting o mix Water ith immered ine Ma o etted ine Ma o immered ine Volume o immered ine Water ith immered ine Fine in term o aturated cditi Total quantity *1 Ma ctrolling,volume meauring Required Total quantity *1 Ma and volume alo ctrolled Not required *1 * (Meauring) (Ctrolling) (Ctrolling) Surace moiture *1 *1 *1 In cae o meauring the moiture o and, poible to batch a part o ine c) Ctainer or meauring immered ine The capacity o the ctainer or immeri i imilar to that ued ith cvential method. There are no particular limitati the ctainer hape. Hoever, hen determining the volume o immered ine rom a diplacement meaurement, a tall ctainer ith a mall cro-ectial area i deired to enhance the accuracy o meaurement. The cro ecti hould be circular rather than rectangular, and the diameter hould be lightly greater (rather than maller) toard the bae to acilitate eay dicharge o the et ine. In ciderati o thee requirement, a batcher in the hape o a rutum o a ce and having a height 4 time the bae diameter a elected a the model. It capacity a 4 liter. More than e type o ine i normally blended to produce ready-mixed ccrete. In immeri, a ecd ine can be batched a in cvential method, though eparate increae accuracy. A rate comparable to cvential method can be achieved by adjuting the etting o inene or other material or by adopting volume-ctrolling equipment d) Meauring method and accuracy o ma and volume A ith cvential method, a load cell i ued. A comprei-type load cell, a ued in the model equipment, olve the problem o ctainer ocillati and allo precie detecti o liquid diplacement hen making volume meaurement. A variety o method are available or meauring volume, uch a loat diplacement gauge, mechanical diplacement gauge, and ctact-ree microave diplacement meter. Amg volume-ctrolling equipment, e type include a movable eir i itted to the ctainer o a to allo ater replaced by ine to overlo. Another type entail pumping exceive ater out through an adjutable hoe et at the peciied level. The peciicati or the model batcher include a load cell ith an accuracy o 1/ and an electrode level enor attached to a mechanical lider, hich i capable o meauring diplacement to an accuracy o.1 mm.

5 ine ine ater ater lever enor enor Ctainer or meauring load cell or or meauring meauring ma ma Photo 1 immered ine electrode electrode ormeauring meauring or ater ater Overvie o model equipment or immeri (volume-meauring type) ３ INVESTIGATION OF IMMERSION BATCHING 3.1 Trial calculati o error o immered ine JIS A peciie the tolerance or and ater to be ± and ±1%, repectively. The maller tolerance or ater repreent it greater eect ccrete quality. It i thereore neceary to batch the ater a preciely a poible to enure the required unit ater ctent. The poible rea or error in immeri include entrapped air bubble in the ine and luctuati in ine denity, a ell a intrumentati error. The error o ater, ｗ, can be expreed uing the ma error, α, and the volume error, αv, a ollo: M + M = M (1 + α) (1 ) M ρ + M ρ = V (1 + αv ) ( ) = (M M) M = (αv kα) (1 k ) () here, ｋ = ｆ + (1 ｆ)ρ /ρ A an example, the error due to entrapped air i calculated by auming thatｆ=.6 and ρ (aturated -dry denity o ine ) =.6 g/cm3, hile alo making the aumpti that there i no intrumentati error. According to Eq. (), the volume error hould be limited to. or le, in order to limit the error o ater to not more than approximately 1.%. The error due to luctuati in and denity i expreed a ollo:

6 ( 1 ( + ρ) ) αv = 1 1 ρ (6) here, ρ;luctuati in aturated -dry denity o and Thi indicate that a luctuati in and denity o.1 lead to an error o around.% in volume. It hould be noted that the eect o luctuati in and moiture i expreed a ollo: ( ρ ) β α v = 1 (7) here, β;error in moiture etting In light o the calculati made uing Eq. (), the error in moiture etting hould be ctrolled to ithin ±. o a to limit the error or mixing ater, including moiture the ine, to 1% or le. 3. Eect o ine cditi error Immered ine a prepared uing ine ith dierent moiture ctent to examine the eect error o uch actor a the ratio o ine to ater, cumulative, timing or the additi o ine, and ine compacti. The immeri equipment hon in Photo 1 a ued or the experiment. The moiture o the ine to be ued a meaured in advance to determine the etting or ine and ater (primary ater + moiture) and compared ith the value determined rom the batched ma and volume o the immered ine. The dierence beteen the experimental etting and the actually batched value include uch error actor a the meaurement error o the load cell and o the diplacement gauge, error in etting the moiture o the ine, and error due to entrapped air. In reporting the tet reult, thee meaurement error are hon by being cverted to moiture value. Typical reult are hon in Fig. to Fig.7. The experiment a pre to greater error than hen uing actual equipment becaue the ample quantity a mall, ith a little a 3 liter o immered ine. With thi ize o batch, a dierence in diplacement o 1 mm lead to a volume dierence o around.%. Neverthele, error ere ound to be retricted to ±. in term o moiture o the ine regardle o it ater aborpti, the percentage o ine immered, and involvement o vibratory compacti. Thi ugget that ine meaurement i eaible by thi method ith practically uicient accuracy. meaurement error (%) (cverted to moiture) knocker Land and Solid volume ratio 6-68% meaurement error (%) (cverted to moiture) knocker Land and Solid volume ratio 6-68% Surace moiture -1% moiture o and (%) Fig. Inluence o moiture immeri error time o and (min) Fig. 3 Inluence o time o ine meaurement error

7 meaurement error (%) (cverted to moiture) immered ine type vibrator olid ratio land and cruhed 6 71% 9% and 69% meaurement error (%) (cverted to moiture) irt tep lat tep Solid volume ratio o immered and 6% No ith vibrator moiture o and (%) Land and Cruhed and mixed ratio (%) Fig. 4 Inluence o moiture Fig. Inluence o cumulative immeri error meaurement error meaurement error (%) (cverted to moiture) Land and Solid volume ratio o immered and 69% Surace moiturre -1% vibrator vibrator vibrator +4% meaurement error (%) (cverted to moiture) vibrator vibrator vibrator Cruhed and Solid volume ratio o immered and 64% Surace moiturre -1% +1% olid volume ratio (%) olid volume ratio (%) Fig. 6 Inluence o immered ine Fig. 7 Inluence o immered ine olid volume meaurement error (1) olid volume meaurement error () 3.3 Compacti o immered ine Immeri i premied le than the total amount o primary mixing ater ith the ine. Reducing the amount o ater batched ith the ine ould allo the amount o ecdary ater to be increaed, acilitating the additi o chemical admixture. To look into reducing the amount o ater ued or ith the ine, the eect o vibratory compacti o the ine in ater a examined uing an internal vibrator hile preparing immered ine. Photo ho the tate o the immered ine at each percentage o ine in the batch. Land and ith a olid volume percentage o 69% could not be immered ithout vibrati at a ine percentage o 6. When compacted uing a vibrator, the ine again became impoible to immere at a ine percentage o 71%. The eect o compacti depended the type o ine. A hon in Fig. 6 and Fig. 7, the eect improved a the olid volume percentage o the decreaed. Photo 3 ho the dicharge o immered ine rom the batcher. When prepared ithout vibratory compacti, the ine particle ere dicharged a a lo, herea under compacti they ormed into a dene ma. In both cae, a ater membrane i ormed beteen the ine and the batcher, permitting eay dicharge. The amount o ine remaining a reidue in the batcher i practically negligible, o thi poe no problem a regard quality

8 Solid volume ratio 71% (compacti) Solid volume ratio 6 (no compacti) Photo State o top o immered ine Dicharge o immered ine Photo 3 Solid volume ratio 7 (compacti) Immered ine produced ithout compacti Immered ine produced ith compacti Dicharge o immered ine rom the batcher ４ QUALITY VERIFICATION OF CONCRETE PRODUCED BYIMMERSION BATCHING 4.1 Eect o immeri parameter ccrete qualitie The quality o ccrete produced by the immeri proce a compared ith that o ccrete according to cvential practice. The olloing parameter ere experimentally examined or their eect: moiture o ine, ine percentage in the batch, and ue o an internal vibrator. The cement a ued ordinary portland cement, the ine a land and ith a aturated dry denity o.6 g/cm3, a inene modulu o.7, and a olid volume percentage o 69%, and cruhed and ith a aturated dry denity o.66 g/cm3, a inene modulu o., and a olid volume percentage o 64%, the coare a cruhed te ith a aturated dry denity o.66 g/cm3 and a inene modulu o 6.7. An air-entraining and ater-reducing admixture and air-entraining and high-range ater-reducing admixture ere ued. All thee material ere charged imultaneouly into a biaxial orced-acti mixer ith a capacity o 1 liter and mixed or 1 ecd. immered immered compreive trength (N/mm ) air (%) lump (cm) Fig. 8 compare quality o the ccrete produced by immeri and cvential. Both method ere ound to produce ccrete o equivalent quality over a range o dierent mix proporti or dierent ater-cement ratio and lump level cvential Fig lump (cm) cvential air (%) W/C lump (% ) (cm) immered ine Land and Cruhed and Land and Land and Age 8day cvential 4 6 compreive trength (N/mm ) Dierence in ccrete qualitie produced by immeri and cvential method - 9 -

9 Table Mix proporti o ccrete Type W/C /a Unit eight (kg/m 3 ) (%) (%) Water Cement Sand Gravel A1 A Normal SCC A1:Water reduing air-entraining agent, A:High-range ater reducing air-entraining agent Table 3 Tet cae or immered o ine lump (cm) Bleeding ratio (%) air (%) Compreive trength (N/mm ) Fig. 9 Fine Immered ine olid volume ratio Cvential Type moiuture 6% 6 6% 6 method - NC SCC - - In cae o uing compacti in producti o immered ine : Normal Ccrete () (6.4%) (6) (6%) Solid volume ratio o immered and (6.4%) (6) moiture (6) Solid volume ratio o immered and (6) (6.4%) Cvential 1 1 Solid volume ratio o immered and (6) (6) (6%) 1 1 moiture (6%) () moiture Cvential Cvential 1 1 Age 8day Cvential () (6.4%) (6) (6) (6%) Solid volume ratio o immered and moiture 1 1 Secd ater/total ater (%) lump-lo (mm) O-unnel elux time () air (%) Compreive trength (N/mm ) Sel Compacting Ccrete Solid volume ratio o immered and 1 1 Qualitie o variou ccrete produced by immeri o ine (6) (6) 1 (6%) () moiture (6%) () Solid volume ratio o immered and Cvential moiture Cvential (6) 1 Solid volume ratio Cvential o immered and () (6%) (6) (6) 1 moiture (6) (6) (6%) Solid volume ratio () o immered and Age 8day moiture Cvential ecd ater/total ater (%)

10 Table and Table 3 give the trial mix proporti and combinati o parameter, repectively. Fig. 9 ho the quality o ccrete produced uing ine ith dierent moiture characteritic and ith varying proporti o ine in immeri. When implementing immeri, the amount o ater batched ith the ine depend moiture cditi and ine percentage. The deicit rom the peciied quantity o mixing ater i added eparately a ecdary ater, and chemical admixture are added to thi ecd batch o ater. For thi rea, Fig. 9 i arranged according to the ratio o additial (ecdary) ater to total mixing ater. In immeri, change in the ratio o ecdary ater to total ater caue variati in the ccentrati o diluted chemical admixture. It a cidered poible that thi might aect el- ccrete, in particular, becaue it ctain a high doage o an air-entraining and high-range ater reducing admixture. Hoever, the ccentrati o the diluted admixture carcely aected the quality o the reulting ccrete, regardle o the mix proporti. Variou compacti cditi during immeri alo had no appreciable inluence the quality o the ccrete, depite the dierence in the appearance o the dicharged ccrete mentied above. 4. Veriicati o quality tability o ccrete produced by immeri Experiment ere cducted to veriy that ccrete could be produced to a peciied quality by ue o immeri ; that i, ithout meauring the moiture o the ine. The mix proporti or the experiment are given in Table 4. The ine a ued ith no prior adjutment o the moiture. The moiture meaured ater the experiment or reerence purpoe ranged beteen 3.% and 8.%. Table give the reult o immeri and the quality o the ccrete produced uing the immered ine. Through thi proce o the ine in an immered tate and adjuting the job mixture baed the reult, ctant rheological propertie ere achieved: a lump-lo ranging beteen 6 and 6 mm and an O-unnel elux time ranging beteen 8 and 9 ecd. The trength propertie o the hardened ccrete ere alo ound to be ctant and independent o the original moiture ctent o the ine. Thee reult demtrate that the immeri method i capable o producing ccrete o ctant quality. The trength tet reult or each batch are hon in Fig.1. The batch-to-batch variance in trength rom the average i le than the deviati beteen pecimen taken rom the ame batch. Thee reult prove that material are accurately batched by the immeri method. At the ame time, eliminati o the need to meaure the moiture o the ine make thi a orthy tep orard. Table 4 Mix proporti o ccrete W/C /a Unit eight (kg/m 3 ) Type Limete (%) (%) Water Cement Sand Gravel A1 poder SCC A1:High-range ater reducing air-entraining agent Table Tet reult o immeri o ine and ccrete Meaured value Calculated value compreive Mixed volume Slump-lo O-unnel time Air No. Ma Volume Water Sand trength (kg) (L) W 1 (kg) S (kg) (L) (mm) () (%) (N/mm )

11 Compreive trength (N/mm ) Age 8day SCC W/C Tet No. Fig.1 Fluctuati in compreive trength beteen tet batche.conclusions The practical utility o a ccrete producti ytem involving immeri, hereby the ine and ater can be preciely batched independently o the moiture, ha been veriied through variou experiment. Within thee experiment, the olloing cclui ere reached: (1)Material can be ctrolled by either ma or volume. I uing volume-meauring equipment, each batch need to be adjuted depending the variable level o moiture, even i the ma o immered ine i batched according to the peciicati. On the other hand, volume-ctrolling equipment enable the operator to batch the peciied amount o both ine and ater at the point hen the combined ma reache a et value, ince the ine i immered and the total volume o ine and ater i ixed. ()In order to limit the ater error to not more than 1% during immeri, it i neceary to ctrol the volume error to ithin approximately.. Tet to veriy error by immeri under variou cditi indicated that the luctuati remained ithin ±. in term o moiture o ine, regardle o the original moiture ctent o the ine, the percentage o ine in the immeri, and hether vibratory compacti o the immeri a carried out. Immeri a thereby hon to be eaible ith accuracy uicient or practical ue. (3)When the ine by immeri, vibratory compacti can increae the denity o the immeri, particularly hen the olid percentage o the ine i lo. (4)Ccrete o nearly ctant quality can be produced regardle o uch cditi a the tate o immeri o the ine and the ccentrati o chemical admixture in the ecdary ater during immeri. ()Immeri o ine make available to the purchaer precie material reult. For thi rea, immeri i expected to orm part o an eective and reliable producti ytem that alo er quality aurance. The author intend to apply immeri at ccrete plant to produce ccrete or actual project, thereby accumulating urther data quality luctuati. Reerence 1) Japan Ccrete Intitute; Reearch Report Ccrete Producti Sytem, pp.1-1, 199. (in Japanee) ) Chikamatu, R., and Sogo, S.; Study High-Reliability Ccrete Producti Sytem ith Ne Batching Method by Immering Sand in Water, Journal o Material, Ccrete Structure and Pavement, No.676/V-1, pp.19-6, 1. (in Japanee)