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Early Age Deformation, its Resultant Stress and Creep Properties of Concrete with and without Internal Curing Subjected to High Temperature History at an Early Age Yuko Ogawa, Ryoichi Sato and Kenji Kawai Institute of Engineering, Hiroshima


  1. Early Age Deformation, its Resultant Stress and Creep Properties of Concrete with and without Internal Curing Subjected to High Temperature History at an Early Age Yuko Ogawa, Ryoichi Sato and Kenji Kawai Institute of Engineering, Hiroshima University, Japan �������������������������������������������������������������������� � 1

  2. CONTENTS � 1. Introduction 2.Experimental programs 3. Results and discussion -Compressive strength and modulus of elasticity -Free strain in concrete -Shrinkage and temperature changed-induced strain in reinforcement -Effective modulus of elasticity -Evaluation of creep coefficient 4. Conclusions �������������������������������������������������������������������� � 2

  3. Introduction � JCI Guidelines for Control of Cracking of Mass Concrete 2016 (JCI Guidelines) � Main Target: newly placed members E e ( t e ) = Φ ( t e ) × E c ( t e ) Φ =0.65 Temperature such as wall-type structures restrained linear interpolation predominantly EXTERNALLY by Φ =0.42 existing members Inner part Tension Surface σ c Compression Schematic diagram of stress in concrete �������������������������������������������������������������������� � 3

  4. Introduction � A surface layer of newly placed members such as cap beams supported by piles is predominantly restrained due to nonlinear distribution of temperature in sections. Temperature Tension In this case, tensile stress develops Inner part up to a time at the peak temperature and thereafter compressive stress σ c develops. � Surface Compression Schematic diagram of stress in concrete �������������������������������������������������������������������� � 4

  5. Introduction-Objective � JCI Guidelines � Cracks due to internal restraint are not addressed in the verification because the cracks can be prevented in construction stages by using appropriate curing methods. � HOWEVER, structures could not always be cured sufficiently due to requirement of shorter construction period and so on. In that case, it is important to verify the superficial cracks beforehand. Objective � to investigate creep behavior of concrete, in which tensile stress develops up to a time at the peak temperature and thereafter the tensile stress decreases, by measuring concrete deformation, rebar strain in a reinforced concrete prism subjected to high temperature history with a maximum of 70 o C at an early age. �������������������������������������������������������������������� � 5

  6. Experimental Programs �������������������������������������������������������������������� � 6

  7. Materials and Mix proportions � Name � BB � BB-PCFA � W/C � 0.40 � 0.40 � C(cement): s/a � 0.45 � 0.45 � Portland blast furnace slag cement-type B � W � 165 � 165 � C � 413 � 413 � Unit content � S � 766 � 651 � (kg/m 3 � � PCFA � 0 � 100 � G � 952 � 952 � Porous ceramic fine aggregate Slump derived from roof tile waste � 13.5 � 10.0 � Target: 12±2.5 (cm) � Air content 4.0 � 4.5 � Target: 4.5±1.0 (%) � �������������������������������������������������������������������� � 7

  8. Item of Investigation � � Mechanical properties -Compressive strength and modulus of elasticity under compression -at the age of 1, 3, 7, 28 and 91 days -with a diameter of 100 mm and a height of 200 mm � Length change of concrete under temperature change -with an embedded gauge including thermocouple -at the center of a prism with a size of 100x100x400mm 100 400 100 Embedded gauge with thermocouple � Elastic strain in reinforcement induced by shrinkage and temperature change �������������������������������������������������������������������� � 8

  9. Item of Investigation � � Elastic strain in reinforcement induced by shrinkage and temperature change 100 1200 100 -a D19-bar located at the center of the D19-bar cross section of prismatic specimen 600 -two self-temperature-compensation 5mm-gauge gauges 40 Strain in bare reinforcement (x10/ o C) � T e m p -Strain of each gage in bare rebar was . 20 r i s e � measured in a temperature-controlled 0 room ranging from 10 o C to 70 o C automatically and repeatedly until -20 relationship between temperature rise and the measured strain overlapped that -40 between temperature drop and the ��������� ��������� ��������� measured strain. -60 ��������� ��������� ��������� -Elastic strain in reinforcement was -80 obtained by subtracting the strain in bare 10 20 30 40 50 60 70 rebar from measured strain in reinforced Temperature ( o C) � concrete prism. �������������������������������������������������������������������� � 9

  10. Curing Conditions � The top surface of all specimens were sealed after casting >Stored in a temperature-controlled room >High temperature history with the maximum temperature of 70 o C >Remolded at the age of 7 days, and sealed, and then stored at 20 o C 70 BB � 60 BB-PCFA � Temperature ( o C) � 50 Temperature inside of both concrete 40 specimens were almost the same as 30 that in the temperature-controlled room. Room 20 temperature � 10 Remolded, sealed and stored in a room at 20 o C � 0 0 2 4 6 8 10 12 14 Age (day) � �������������������������������������������������������������������� � 10

  11. Results and Discussion �������������������������������������������������������������������� � 11

  12. Compressive Strength and Modulus of Elasticity � JCI Guidelines � Temperature-adjusted concrete age, t e ⎡ ⎤ n where, Δ t i is the period of constant 4000 ∑ t e = Δ t i ⋅ exp 13.65 − ⎢ ⎥ temperature continuing in concrete (day); 273 + T ( Δ t i ) / T 0 ⎣ ⎦ j = 1 T ( Δ t i ) is concrete temperature for Δ t i ( o C); T 0 is 1 o C. Compressive strength strength, f’ c (t e ) t e − S f f ' c ( t e ) = a + b ( t e − S f ) f ' c ( t n ) where, t n is the strength control age of concrete cured under water at 20 o C (day); a and b are experimental constants; S f is the temperature adjusted concrete age corresponding to initiation of hardening (day); f’ c (t n ) is the compressive strength of concrete at t n (N/mm 2 ). Modulus of elasticity, E c (t e ) E c ( t e ) = C 3 × f ' c ( t e ) C 4 where, C 3 and C 4 are constants. �������������������������������������������������������������������� � 12

  13. Compressive Strength and � odulus of Elasticity � 60.0 40000 Modulus of elasticity (N/mm 2 ) � JCI Guidelines(BB W/C=0.4) � JCI Guidelines (BB W/C=0.4) � Compressive strength (N/mm 2 ) � 35000 100 S f : Initiation 50.0 BB40 50 30000 ε s,e BB BB40PCFA 0 40.0 BB-PCFA 25000 -50 -100 20000 30.0 15000 20.0 10000 10.0 5000 0 0.0 0.1 1 10 100 0.1 1 10 100 Temperature adjusted age (day) � Temperature adjusted age (day) � f’ c and E c with BB-PCFA were almost the same as those of BB They were higher during ages of 1 day to 10 days, and lower after the age of 10 days compared with those recommended by the JCI Guidelines. � �������������������������������������������������������������������� � 13

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