Reduction of Autogenous Shrinkage of Ultra-High-Strength Concrete Containing Silica Fume-Premix Cement

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1 Reduction of Autogenou Shrinkage of Ultra-High-Strength Concrete Containing Silica Fume-Premix Cement Yuji Mitani, Shinpei Maehori and Makoto Tanimura Reearch & Development Center, Taiheiyo Cement Corporation, Japan 2-4-2, Oaku, Sakura City, Chiba Prefecture, , Japan ABSTRACT Thi paper invetigate autogenou hrinkage behaviour of ultra-high-trength concrete containing ilica fume-premix cement with a water-to-binder-ratio of 3% to 2%. The concrete mix wa added with expanive additive (EX), hrinkage reducer (SR) or hrinkagereducing type uperplaticizer (SRSP) olely or in combination of EX and SR or EX and SRSP, and effect of thee admixture in reducing autogenou hrinkage were examined. The ultra-high-trength concrete pecimen ubjected to high temperature to imulate actual temperature condition in maive column exhibited ditinct difference from thoe cured at a contant temperature of 2 C in autogenou hrinkage train behaviour and reultant tre induced. Significant reduction in autogenou hrinkage wa noted in all pecimen, irrepective of the temperature condition. Further invetigation revealed that the effect of combined ue of EX and SR, or of EX and SRSP, wa equal to or greater than the um of their individual effect. Keyword. Ultra-high-trength concrete, Autogenou hrinkage, Silica fume-premix cement, Expanive additive, Shrinkage reducer INTRODUCTION High-trength concrete ha been widely tudied over the lat decade and ha been increaingly applied to enhance the tructural performance and durability of concrete tructure. Recently, ultra-high-trength concrete (UHSC) with deign trength of 5N/mm 2 ha been in practical ue. However, uch very low water-to-binder ratio () concrete are known to hrink ignificantly at early age, which i likely to be caued by autogenou (elfdeiccation) hrinkage, and poibly exhibit increaed enitivity to early-age cracking (Maruyama, 28). Since UHSC i expected to yield more durable tructural member, the etablihment of a technique for minimizing autogenou hrinkage i an important tak. Experimental invetigation on how to control autogenou hrinkage have been carried out comprehenively from a material point of view. Thee tudie revealed that inorganic expanive additive and/or organic hrinkage reducer are effective in reducing autogenou hrinkage (Tazawa, 992, Tanimura, 22). However, few tudie have been performed to

2 evaluate the applicability of aforementioned admixture on reducing autogenou hrinkage of UHSC with a lower of 2% or le. The preent tudy, therefore, focued on invetigating how much expanive additive and/or Shrinkage reducer contribute to reducing autogenou hrinkage in UHSC. EXPERIMENTAL PROGRAMS Table and Table 2 lit the contituent material and mixture proportion of concrete, repectively. The expanive additive with a higher finene (SSA: approximately 5cm 2 /g), compared to conventional one (SSA: approximately 33cm 2 /g), wa ued to reduce the rik of remarkable expanion at long-term age (Tanimura, 29). Targeted lump flow value and air content of concrete were 75±75mm for =3% and 6±5mm for =6.5-2%, and le than 2%, repectively. Table. Contituent material Material Symbol Type / Characteritic Cement C Silica fume-premix cement / denity: 3.7g/cm 3, SSA*: 66cm 2 /g Expanive additive EX Lime-baed / denity: 3.9g/cm 3, SSA*: 492cm 2 /g Fine aggregate S Pit and / denity**: 2.56g/cm 3 (erie,2), 2.58g/cm 3 (erie 3) aborption: 2.24%(erie,2),.9%(erie 3) Coare aggregate G Cruhed and tone / maximum ize: 2mm, denity**: 2.64g/cm 3, aborption:.5 %, olid content: 6% Shrinkage reducer SR Lower-alcohol alkylene oxide adduct Superplaticizer (SP) SP SP2 SP3 High-range water reducer / Polycarboxylic acid baed Air-entraining and high-range water reducer / Polycarboxylic acid baed High-range water reducer (hrinkage reducing type) / Polycarboxylic acid and glycolic baed * Specific urface area meaured by Braine Method ** Saturated urface-dry condition Serie 2 3 Table 2. Mixture proportion of concrete Symbol * /a Unit Content (kg/m 3 ) (%) (vol.%) W C EX S G** SR PL EX PL EX PL EX PL EX SR ES SP SP-EX SP-EX SP SP3-EX SP3-EX * B=C+EX ** Bulk volume of coare aggregate:.53 m 3 /m 3 Primatic pecimen of x x 8 mm for erie and x x 4 mm for erie 2 and 3 were prepared to meaure the autogenou hrinkage train of concrete. An embedded train gauge with a reference length of mm and low elatic modulu of 39 N/mm 2 to meaure the free deformation, and a thermocouple were placed at the center of the pecimen. The autogenou hrinkage train of concrete wa determined by ubtracting the thermal

3 train from the meaured train, auming the coefficient of thermal expanion of concrete to be x -6 / o C. RC beam pecimen of x x 8 mm with the embedded reinforcing bar wa prepared to evaluate the autogenou hrinkage tre of concrete. Reinforcement ratio wa 2.%, 3.8% and 8.% for erie and 3.5% for erie 2. Self-temperature compenated wire train gauge were attached to the upper and bottom ide of the reinforcement at mid-pan to meaure the reinforcement train. To minimize the friction between the mould and the concrete pecimen, a. mm thick Teflon heet wa placed at the bottom of the mould. Further, a 3 mm thick polytyrene board wa placed on both end of the mould. All the urface of the pecimen mould were covered with a. mm thick polyeter film. Cylindrical pecimen of x 2 mm were prepared to meaure the compreive trength at the age of 7 and 28 day in accordance with JIS A 8. Figure how curing condition of concrete pecimen. High temperature hyterei wa conidered to imulate actual temperature condition in maive column member contructed by UHSC. Temperature 温度 ( ) ( ) hyterei 履歴 ( (=3%) 履歴 養生 8 hyterei 履歴 (=6.5,2%) 材齢 7 日以降 after は2 7 養生 day 材齢 Age (day) ( 日 ) Figure. Curing condition Primatic pecimen of erie were demoulded at the age of 7day. Thoe of erie 2 and 3 were demoulded at the age of 24 hour for 2 o C curing and 7 day for temperature hyterei curing. After demoulding, all the primatic pecimen were promptly ealed with a. mm thick aluminium adheive tape to prevent water evaporation. Cylindrical pecimen for teting compreive trength were cured under ealed condition except for 2 o C water curing. RESULTS AND DISCUSSION Table 3 how the freh propertie of concrete and time of etting of ieved out mortar. The lump flow value ranged within the targeted value, from 74 to 85mm for =3% mixture and from 57 to 65mm for =6.5, 2% mixture. The doage of uperplaticizer of concrete with expanive additive wa omewhat larger than that of concrete without expanive additive regardle of addition or not of hrinkage reducer. Time of etting tended to be early in concrete with expanive additive, while be late in concrete with hrinkage reducer. However, the effect of containing expanive additive and/or hrinkage reducer on freh propertie of concrete i not ignificant from the viewpoint of practical ue.

4 Serie 2 3 Table 3. Freh propertie of concrete and etting time Symbol Setting*** SP Slump Air 5mm-flow flow* (mm) time () content** (h-m) type B ma% (%) Initial Final PL3 SP EX3 SP PL6.5 SP EX6.5 SP PL2 SP EX2 SP PL SP EX SP SR SP ES SP SP SP SP-EX2 SP SP-EX3 SP SP3 SP SP3-EX2 SP SP3-EX3 SP * JIS A 5 ** JIS A 28 *** JIS A 47 Table 4 how the reult of compreive trength of the invetigated mixture. The compreive trength tended to be omewhat low in concrete with hrinkage reducer, while be negligible in concrete with expanive additive. Table 4. Experimental reult of compreive trength Serie 2 3 Symbol Age 2 o C 45 o C 8 o C 9 o C (day) curing hyterei hyterei hyterei PL EX PL EX PL EX PL EX SR ES SP SP-EX SP-EX SP SP3-EX SP3-EX Figure 2 how the meaurement reult of autogenou hrinkage train of erie concrete pecimen. The data are plotted a a function of temperature adjuted age (CEB-FIP, 99),

5 after initial et. Autogenou hrinkage train rapidly developed when ubjected to high temperature hyterei. Autogenou hrinkage/expanion train( -6 ) =3% PL3-9 PL3-45 PL3-2 EX3-9 EX3-45 EX Temperature adjuted age (day) =6.5% PL6.5-8 PL PL6.5-2 EX6.5-8 EX EX Temperature adjuted age (day) =2% PL2-8 PL2-45 PL2-2 EX2-8 EX2-45 EX Temperature adjuted age (day) Figure 2. Autogenou hrinkage/expanion train behaviour (erie ) Figure 3 how the rate of reduction in autogenou hrinkage train at temperature adjuted age of 4 day, correponding to the age of 7 day for 9 o C hyterei and of 6 day for 8 o C hyterei. The rate of reduction under temperature hyterei curing of =3%, 6.5% and 2% concrete wa approximately 2%, 7% and 7%, repectively, regardle of maximum temperature. On the other hand, that under 2 o C curing wa approximately 35%, 98% and 98%, repectively; therefore, the rate of reduction under temperature hyterei curing wa maller than that under 2 o C curing. Rate of reduction in autogenou hrinkage train (%) hyterei 8 hyterei 8 hyterei 3% 6.5% 2% Figure 3. Rate of reduction in autogenou hrinkage train (erie ) Figure 4 how the rate of reduction in autogenou hrinkage tre at temperature adjuted age of 4 day. The retrained tree are calculated baed on the following equation,

6 derived from the equilibrium of the force among concrete and reinforcement, in which the tre i poitive in tenion and negative in compreion. P c, Ac P E A () where, c : retrained tre of concrete, P : axial force in reinforcement, E : Young modulu of reinforcement, : meaured train in reinforcement, A : cro-ectional area of reinforcement, A c : cro-ectional area of concrete. The rate of reduction in autogenou hrinkage tre under temperature hyterei curing of =3%, 6.5% and 2% concrete wa approximately 3-45%, 55-7% and 5-75%, repectively. Rate of reduction in autogenou hrinkage tre (%) hyterei 8 hyterei 8 hyterei 9 hyterei 8 hyterei 8 hyterei 9 hyterei 8 hyterei 8 hyterei 3% 6.5% 2% 3% 6.5% 2% 3% 6.5% 2% Reinforcement ratio 2% Reinforcement ratio 3.8% Reinforcement ratio 8% Figure 4. Rate of reduction in autogenou hrinkage tre (erie ) Figure 5 how the comparion between the rate of reduction in autogenou hrinkage tre and train, in order to invetigate the influence of retraint or not. The cae of =6.5% and 2% revealed the -2% higher rate of reduction in autogenou hrinkage train, however, that of =3% revealed -3% higher rate of reduction in autogenou hrinkage tre, therefore rate of reduction differ between train and tre. The invetigation reult uggeted that the effectivene of material countermeaure againt autogenou hrinkage at early age hould be evaluated baed on not only train behaviour but alo tre behaviour.

7 Rate of reduction in autogenou hrinkage tre (%) Reinforcement ratio2%-8 9 hyterii Reinforcement ratio3.8%-8 9 hyterii Reinforcement ratio8%-8 9 hyterii Reinforcement ratio2%-45 hyterii Reinforcement ratio3.8%-45 hyterii Reinforcement ratio8%-45 hyterii =3% =6.5, 2% Rate of reduction in autogenou hrinkage train (%) Figure 5. Comparion with the rate of reduction in autogenou hrinkage tre and train Figure 6 and Figure 7 how the amount of reduction in autogenou hrinkage train and autogenou hrinkage tre of erie 2 concrete pecimen, repectively. A ynergitic effect of uing both expanive additive and hrinkage reducer wa oberved for autogenou hrinkage train regardle of curing condition; i.e., the reduction amount of ES wa greater than the um of thoe of EX and SR, hown in Figure a the calculated value. On the other hand, the reduction amount in autogenou hrinkage tre of ES wa almot ame a the um of their individual effect. Reduction of autogenou hrinkage train ( -6 ) EX SR ES EX+SR EX SR ES EX+SR calculated value 2 9 calculated value Figure 6. Amount of reduction in autogenou hrinkage train (erie 2)

8 Reduction of autogenou hrinkage tre (N/mm 2 ) EX SR ES EX+SR EX SR ES EX+SR calculated value 2 9 calculated value Figure 7. Amount of reduction in autogenou hrinkage tre (erie 2) Figure 8 how the rate of reduction in autogenou hrinkage train of erie 3 to evaluate the effectivene of hrinkage reducing type uperplaticizer (SP3), compared to the effect of hrinkage reducer (SR) of erie 2. The reult revealed that work of SP3 wa comparable to that of SR. Rate of reduction in autogenou hrinkage train(%) curing 9 hyterei SP3 SR SP3-EX3 ES Expanive admixture kg/m3 3 Expanive admixture 3kg/m3 3 Figure 8. Rate of reduction in autogenou hrinkage train (erie 3) Thu, ignificant reduction in autogenou hrinkage train/tre wa noted in all pecimen, irrepective of the temperature condition, demontrated that expanive additive (EX), hrinkage reducer (SR) or hrinkage-reducing type uperplaticizer (SRSP) olely or in combination of EX and SR or EX and SRSP were obviouly effective in reducing autogenou hrinkage train/tre. CONCLUSIONS The following concluion can be drawn from the preent tudy.

9 () The expanive additive (EX), hrinkage reducer (SR) or hrinkage-reducing type uperplaticizer (SRSP) olely or in combination of EX and SR or EX and SRSP were obviouly effective in reducing autogenou hrinkage not only train but alo tre induced. (2) Aforementioned effectivene wa diplayed even when ubjected to high temperature hyterei, imulating the actual temperature condition in maive column member. (3) The effect of combined ue of EX and SR, or of EX and SRSP, wa equal to or greater than the um of their individual effect. REFERENCES CEB-FIP MODEL CODE, 99, Thoma Telford, Maruyama, I., Suzuki, M., Nakae, H. and Sato, R. (28). "Self-induced tre and reultant crack in reinforced ultra high-trength concrete column - part experimental tudy on the effect of temperature hitory -." Journal of tructural and contruction engineering, tranaction of AIJ, Vol.73, No.629, (in Japanee) Tazawa, E. and Miyazawa, S. (992). "Autogenou Shrinkage Caued by Self Deiccation in Cementitiou Material," 9th International Congre on the Chemitry of Cement, Vol. 4, New Delhi, India, Tanimura, M., Hyodo, H., Nakamura, H. and Sato, R. (22). "Effectivene of Expanive Additive on Reduction of Autogenou Shrinkage Stre in High-Strength Concrete." Proceeding of the Third International Reearch Seminar on Self-Deiccation and It Importance in Concrete Technology, Lund, Sweden, Tanimura, M., Kwak, D., Fujita, H., Mitani, Y. and Hyodo, H. (29). "Applicability of Expanive Additive on Reducing Shrinkage in Ultra-High-Strength Concrete." 4th International Conference on Contruction Material: Performance, Innovation and Structural Implication, Nagoya, Japan,