ancient ruins in Rome Colosseum (A.C80)

Transcription

1 LONG-TERM DURABILITY OF REINFORCED CONCRETE STRUCTURES USING SHIRASU CONCRETE IN ACTUAL MARINE ENVIRONMENT ancient ruins in Rome Pantheon ( B.C27 ) Koji Takewaka, Department of Ocean Civil Engineering, Graduate school of Science and Engineering Kagoshima University, JAPAN ancient ruins in Rome Colosseum (A.C8) Naples Somma Ruins Ercolano Ruins Vesuvio Vlcano Pompei Ruins Ancient Rome Somma Ruins Ancient Rome Somma Ruins The Ruin is being excavated from 24 by Aoyagi Project 1

2 Concrete used in Somma Ruins What is pyro-clastic flow ash? Pyro-clastic flow is a type of volcano eruption. Large amount of volcano ash runs down along mountain serface, like as photographs shown below; Pyroclastic flow Ancient Roman Concrete is assumed to be made of pyro-clastic flow ash Pyroclastic flow at Unzen, Nagasaki, Japan in 1991 Sapporo What is? is a local name of pyro-clastic flow deposit due to very big eruption of volcano around 2, years ago. The name means White sand in Japanese. In the southern part of Kyushu Island, Japan, enormous volume of pyro-clastic flow deposit called has been deposited Tokyo Pyroclastic flow Kagoshima Pyroclastic flow at Unzen, Nagasaki, Japan in 1991 What is? What is? deposit More than 6 billion m 3 of cover in Kagoshima prefecture 2

3 What is? The deposits seems to be rock because of strong binding effect between particles What is? The deposits seems to be rock because of strong binding effect between particles However, once the rock is scratched, changes to sandy condition However, once the rock is scratched, changes to sandy condition Before scratching After scratching What is? The deposits seems to be rock because of strong binding effect between particles However, once the rock is scratched, changes to sandy condition What is? concrete, which is made of cement used as binder and as fine aggregates. is very closed to Authors have been developed so-called concrete, in which is used as fine aggregate. Ancient Roman Concrete, which is estimated to be made of lime powder and volcano (pyroclastic flow) ash Before scratching After scratching What is? Physical Characteristics of used as fine aggregate in this research work Physical Characterristics Normal sand Density of surface-dry state (g/cm 3 ) ~2.7 Absorption capacity ratio (%) 7.9 1~3 Content ratio of the fine powder (%) 2.11 ~. Fineness modulus of aggregate (F.M.) ~3. Solid volume ratio (%).11 ~6 has about 8% of the density and nearly three times of the absorption capacity as compared with the usual sand What is? One of the characteristics of is to have pozzolanic reactivity Chemical composition of SHIRASU Chemical composition SiO 2 Al 2 O 3 Fe 2 O 3 CaO Na 2 O K 2 O content ratio (%) As a result It is assumed that concrete has high durability performance against chloride attack, sulfate attack, alkali silica reaction, etc. 3

4 What is? One of the characteristics of is to have pozzolanic reactivity The surface condition of concrete in 1% Na 2 SO 4 solution after 2. years of exposure (Cement: BFC) Objective of this research From previous researches about concrete using as a fine aggregate concrete seems to be durable in various environments However % % 1% 2% 7% content in fine aggregate The durability in actual marine environment has not been investigated yet Objective of this research To evaluate quantitatively the long-term durability of concrete using in marine environment Basic Experiments Two types of small specimen are used. 1 years-on-site exposure test in marine environment Basic experiments using small specimens Experiments using largerscale specimens modeling actual marine structures / Specimens without any crack / Specimens with crack Shape of specimen for basic experiments Shape of specimen for basic experiments Specimens without any crack (1 1 in size) Rebars (D1) with of Epoxy coating cover thickness Tension Bolt Specimens with crack (1 1 6cm in size) 1cm 1cm Rebars (D1) with of cover thickness.2mm of maximum crack width 4

5 Factor Types Types of concrete examined Fine aggregate Normal (Sea ) Cement Blast Furnace Cement (Type B) types of concrete are examined Measurement results of natural potentials of rebers in none-cracked concrete at tidal zone Natural potential (m mv vs CSE) %, Cover thickness: - - ASTM s threshold Exposure period (day) Measurement results of natural potentials of rebers in none-cracked concrete at tidal zone Natural potential (m mv vs CSE) %, Cover thickness: Exposure period (day) 腐食判定値 ASTM s threshold 1 12 Measurement results of natural potentials of rebers in none-cracked concrete at tidal zone Natural potential (m mv vs CSE) %, Cover thickness: Exposure period (day) - ASTM s threshold 1 12 ntent 量 Chloride 全塩化物イオン ion con (kg/m (kg/m 3 3 ) ) Measurement results of chloride contents in none-cracked concrete at tidal zone Setting position of rebar 6% Chloride 全塩化物イオン ion cont tent 量 (kg/m (kg/m 3 ) 3 ) Setting position of rebar Depth 表面からの深さ from surface (cm) (cm) Depth 表面からの深さ from surface (cm) (cm) Exposure period: 2 years Measurement results of Corrosion area on rebers in none-cracked concrete at tidal zone on rebar (%) Corrosion area Type of cement Cover thickness Normal Concrete Exposure period: 2 years 4% % 6% Only doted corrosion No corrosion

6 Measurement results of Corrosion area on rebers in none-cracked concrete at tidal zone on rebar (%) Corrosion area Type of cement Cover thickness Concrete 4% % 6% Estimation of corrosion initiation period based on chloride diffusion process into concrete ( when considering that C limit is assumed to be 1.2 kg/m 3 ) - - : 6%, Cover thickness :.31years.94 years Exposure period 年 (Year) Estimation of corrosion initiation period based on chloride diffusion process into concrete ( when considering that C limit is assumed to be 1.2 kg/m 3 ) : 6%, Cover thickness : Estimation of corrosion initiation period based on chloride diffusion process into concrete ( when considering that C limit is assumed to be 1.2 kg/m 3 ) : 6%, Cover thickness : years.39 years.94 years 1.2 years years years years Estimation of corrosion initiation period based on measurement results of natural potential of rebar (threshold value of the potential is -3mV vs. CSE or less) years 3. years Exposure period 年 (Year) Exposure period 年 (Year) Measurement results of natural potentials of rebers in cracked concrete at tidal zone otential CSE) Natural p (mv vs 6%, Cover thickness: ASTM Threshold h Exposure period (day) Chloride 全塩化物物イオン量 io on content (kg/ (kg/ /m /m 3 ) ) Measurement results of natural potentials of rebers in cracked concrete at tidal zone Setting position of rebar 全塩化物物イオン量 on content (kg g/m 3 ) ) Chloride io (kg/ Setting position of rebar Depth 表面からの深さ from surface (cm) (cm) Depth 表面からの深さ from surface (cm) (cm) Measured area for chloride content 6

7 Measurement results of Corrosion area on rebers in cracked concrete at tidal zone Measurement results of Corrosion area on rebers in cracked concrete at tidal zone The both corrosion areas are almost same. Corrosion weight loss :1.1g :.2g Corrosion speed is clearly different (%) bar (%) Corrosion 腐食面積率 area on re ( Cover thickness : 4% % 6% Corrosion condition is different - - rebar (%) (%) 腐食面積率 ( Corrosion area on r Cover thickness : % % 6% Experiments using specimens modeling actual marine structures Large-scale RC specimens are used Configuration of RC beam Cover thickness 2, 3, 4, cm Reference electrode Atmospheric zone 4 Large-scale specimens using different types of concrete were prepared and set on sea bed. 4.6m Tidal zone Under sea Sea bed Series (%) C Usual " Usual C Chemical admixture Mix proportion of Concrete s/a (%) W C Unit weight (kg/m 3 ) S % 4.6 concrete Usual concrete G Chemical admixture Air content % % % 4.9 (%) Super plasticizer Air entraining water reducing agent Slump (cm) Experimental Procedures 1) Every 3 months, monitoring half-cell potentials of rebars at the portion of each environmental zone Exposure period (day) 1 1 Splash zone Tidal zone Under sea CSE) Half- cell potential (mv vs C cm Monitoring result (Sea sand, Splash zone) 7

8 Experimental Procedures Appearance Observation Every 1. years, all specimens are lifted up on the ground, and inspected in detail on the followings; Detail inspection Appearance observation This presentation explains about the results of detailed inspections up to 3 years of exposure Half cell potential of rebar Polarization Resistance Chloride ion contents in concrete Remove the marine organisms from surface of specimen Wet weight of marine organisms on concrete Measurement of half-cell potential ne organisms concrete Wet weight of mari adhered on c (kg) 1 1 Usual The half-cell potential of rebar was measured at 1cm of intervals on the specimen s surface. V Potential meter Reference electrode Appearance observation Appearance observation Atmospheric zone Micro surface cracks caused by drying shrinkage - Maximum width of corrosion crack 1. years exposure:.4mm 3 years exposure: 1.2mm 8

9 Measurement results of half-cell potential Appearance observation and half-cell potential years exposure 1 1 ASTM 2 Threshold 2 1. years 3 exposure 3 surface(cm) Distance from the top 4 4 Cover thickness: Maximum width of corrosion crack 1. years exposure:.4mm 3 years exposure: 1.2mm Atmospheric zone Micro surface cracks caused by drying shrinkage - Appearance observation Measurement results of half-cell potential Maximum width of corrosion crack 1. years exposure: Not any crack 3 years exposure:.2mm surface(cm) Distance from the top years 2 exposure years exposure ASTM Threshold Cover thickness: Maximum width of corrosion crack 1. years exposure: Not any crack 3 years exposure:.2mm Half-cell potential (3 years exposure) - rface(cm) Distance from the top sur cm 1 1 cm ASTM Threshold cm cm rface(cm) Distance from the top sur 4 Appearance observation - Atmospheric zone Micro surface cracks caused by dry shrinkage Maximum width of corrosion crack at 3 years exposure:.3mm - Maximum width of corrosion crack at 3 years exposure:. mm 9

10 Half-cell potential (3 years exposure) Polarization Resistance face(cm) Distance from the top surf cm ASTM Threshold Distance from the top surfa ace(cm) cm 4.6m ce n ce Poralization resistanc Resistan (kω (kω cm 2 ) Portion where corrosion cracks has arisen - Polarization Resistance (cover thickness:) - C- C- Usual Crack portion 4.6m Polarization Resistance nce Portion of corrosion crack No corrosion crack portion Polarization Polarization Resistance Resistance (cover (cover thickness:) thickness:) 1 1 nce Polarization Poralization Resistan resistan Poralization (kω (kω cm resistan Resista 2 ) 2 ) (kω (kω cm 2 ) Crack Crack portion portion portion Atmospheric Splash zone zone Tidal zone Under sea Chloride ion content profile in concrete Portion for checking chloride content Concrete powder m samples were take by drilling every 1cm in depth and measured the chloride ions concentration. Chloride ion contentsprofile in concrete Diffusion coefficient of chloride ion n content m 3 ) Chloride ion (kg/m Under sea (3 years exposure) C Shrasu 1.2 Shrasu Depth from concrete surface (cm) Depth from concrete surface (cm) Apparent diffu usion coefficient of chlo oride ion (cm 2 /year r) years exposure Splash Atmospheric zone Tidal zone Under sea Usual - - Usual Value specified in the JSCE Standard Specifications - C 1

11 Diffusion coefficient of chloride ion Conclusions iffusion hloride ion ear) Apparent di coefficient of c (cm 2 /ye years of exposure 3 years 3 years exposure of exposure - Tidal zone - - From results of this research, the conclusions are obtained as follows 1. concrete has high resistance against penetration of chloride ion inside 2. concrete can be expected improvement of its own quality due to Pozzolanic reactions concrete has high durability against chloride atteck including rebar corrosion in actual marine environment Thank you very much for your attention 11