Moisture content in concrete

Transcription

1 Universal Moisture Transport Model in Concrete under Natural Environment Takumi Shimomura Nagaoka University of Technology Moisture content in concrete Shrinkage and creep of concrete Transport of aggressive agent in concrete Deterioration of concrete and reinforcement in concrete T RH Local hydrothermal condition Transport model in concrete time Modelling climatic action

2 Moisture transport model in concrete T RH Transport model in concrete time Outline of moisture transport model (992-) Structural concrete member Drying and wetting behaviour Concrete element Aggregate Cement paste Aggregate-paste composite model Thermodynamic behaviour of water 2(r+dr) dv(r)/dr dv(r) V(r)=V o {-exp(-br c )} 2r Gas phase Hydrate Liquid water pore size distribution function for cement paste in concrete r Thermodynamic equilibrium Mechanical equilibrium Vapor diffusion 2r s P G -P L J V J L Transport of liquid water

3 Micropore structure of concrete concrete 2(r+dr) dv(r) 2r pore size distribution measured by mercury injection method V(r)=V o {-exp(-br c )} Pore size distribution function dv(r)/dr r Thermodynamic equilibrium of liquid and gas in pores 2r s Gas phase p v Liquid phase Solid part Kelvin equation pv 2γM w ln p RTρ r vo Volume density (capillary condensation theory) l s Pore size distribution Liquid r s Gas Pore radius

4 Transport of vapour in pore structure Kv= Kv< J V Kv: tortuosity (material constant) J v K V v g D vo gradρ Diffusion in free space Vg: Volume fraction of gas phase (variable) v Volume density Liquid V l Gas V g Pore radius Transport of liquid water in (non-saturated) pore structure Laminar flow in cylindrical straight pore 2r v 2 r 8μ v(r) r grad p l J l J r s l 0 ρ l dv dr 2 r 2 Kl grad dr r 8μ s ( r) γ K l : tortuosity (material constant) Volume density V l r s 0 dv dr Liquid V l ( r) dr Gas V g Transportation of liquid water takesplacesinsaturatedpores. r s Pore radius

5 Capillary suction from concrete surface Velocity in each pore Capillary suction in a horizontal straight vessel dx dt ri ri 8t surface liquid water 液状水 concrete 供試体の厚さ d w w j- w j w j+ w m r cap r r i- r i = r a r ii+ J l r cap dv l dr r K lp r 8t cap dr K lp : tortuosity (material constant) Capillary suction water fills greater pores faster. Volume density x x j- r cap x j r cap x j+ dv ( r ) dr dr Capillary suction water Pore radius r n x m Cyclic drying and wetting drying process capillary condensed water gas phase (vapour) Diffusion of vapour and liquid water in non saturated concrete wetting process capillary condensed water capillary suction water Capillary suction from the surface drying process capillary condensed water transition Diffusion of vapour and liquid water in non saturated concrete

6 Modelling local hydrothermal condition T RH Modelling local hydrothermal condition time Local hydrothermal condition Influence of sunlight sunlight RH s p p v vos RH a p p vo vos RH a relative humidity RH s p vos p vo saturated vapour pressure partial pressure of vapour (p v ) concrete T s T a temperature surface Drying is accelerated by temperature rise on the surface

7 Local hydrothermal condition Influence of time-dependent change of atmospheric temperature Condensed water T RH s >.0.0 RH a relative humidity time p vo saturated vapour pressure partial pressure of vapour (p v ) concrete p vos T a temperature T s surface Wetting with condensed water on the surface Estimation of surface temperature of concrete by heat transfer analysis Heat transfer within concrete T c divgradt t Solar radiation sunlight Weather station (or public meteorological data) T s R n Atmospheric temperature T a temperature concrete Heat flux through the boundary surface T mt s Ta Rn n surface

8 Verification of moisture transport model and local hydrothermal condition model with field exposure test Specimens and exposure test exposed surface Exposure test Specimen Case A: subjected to temperature and humidity change insulator one-dimensional heat and moisture transfer Case B: subjected to temperature and humidity change, rainfall and sunlight

9 Experimental and analytical surface temperature Case A atmospheric experiment analysis Case B Temperature (deg) atmospheric temperature measured surface temperature calculated surface temperature Time (day) 6 June 203 Case A: subjected to temperature and humidity change 7 Temperature (deg) atmospheric temperature measured surface temperature calculated surface temperature Time (day) 6 June 203 Case B: subjected to temperature and humidity change, rainfall and sunlight 7 Experimental and analytical drying and wetting behaviour Case B Case B: subjected to temperature and humidity change, rainfall and sunlight Case A Case A: subjected to temperature and humidity change

10 Modelling climatic action T RH time Modelling climatic action Climatic actions affecting moisture transport in concrete Temperature Relative humidity Rainfall (precipitation, hours of rain) Sunlight (solar radiation, hours of sunlight) How to obtain previous climatic data at the location of the structure? How to estimate future climatic action to be used in long term simulation?

11 AMeDAS (Automated Meteorological Data Acquisition System) Provided by Japan Meteorological Agency 300 points in Japan (every 20km) Previous and present data Available through Internet Modelling of temperature, relative humidity, and global solar radiation based on AMeDAS data

12 Modelling of wetting action by rain based on AMeDAS data one month (744 hours) Original record summation of raining and not raining time divided by 24 Modelled drying wetting cycle (each raining time is set one hour) 5 hours hour 620 hours 24 hours 24 cycles not raining raining The length of one cycle by which the effect of rain is adequately represented was determined based on sensitivity analysis (204). Numerical simulation of long term drying and wetting behaviour of concrete under natural environment T RH time

13 Procedure of numerical simulation of long term drying and wetting behaviour r of concrete Location of the objective structure AMeDAS data near the objective structure during Niigata Tokyo T RH open-air roof time Creating annual hydrothermal condition model for the structure with and without roof 300mm Calculation of moisture transport within 300mm from the surface for 0 years Objective concrete structures Computational results of time-dependent change of average moisture content in concrete Tokyo roof

14 Computational results of time-dependent change of average moisture content in concrete open-air Tokyo Computational results of time-dependent change of average moisture content in concrete open-air Tokyo roof

15 Computational results of time-dependent change of average moisture content in concrete open-air Niigata Tokyo roof Conclusion The enhanced moisture transport model in concrete considers coupled transport of heat, vapour and liquid water in concrete pore structure, capillary suction from the surface, condensation of vapour on the surface and acceleration of evaporation by direct sunlight. Local hydrothermal condition of the objective structure, which directly affect drying and wetting of concrete, is evaluated in terms of temperature, humidity, rain fall, sunlight and their time-dependent changes. Climatic action on the structure at the service location is taken into account based on AMeDAS (Automated Meteorological Data Acquisition System), which is provided by JMA (Japan Meteorological Agency) through Internet. Nagaoka University of Technology

16 THANK YOU Nagaoka University of Technology