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A MACRO-MODEL FOR SELF-DESICCATION IN HIGH PERFORMANCE CONCRETE

A MACRO-MODEL FOR SELF-DESICCATION IN HIGH PERFORMANCE CONCRETE. Lars-Olof Nilsson Div. of Building Materials Lund Institute of Technology Lund University. Kristina Mjörnell Dept. of Building Physics Swedish National Testing and Research Institute, Borås. Outline. 1. Introduction

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A MACRO-MODEL FOR SELF-DESICCATION IN HIGH PERFORMANCE CONCRETE

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  1. A MACRO-MODEL FOR SELF-DESICCATION IN HIGH PERFORMANCE CONCRETE Lars-Olof Nilsson Div. of Building Materials Lund Institute of Technology Lund University Kristina Mjörnell Dept. of Building Physics Swedish National Testing and Research Institute, Borås A MACRO-MODEL FOR SELF-DESICCATION IN HPC

  2. Outline 1. Introduction 2. The model for self-desiccation 3. Physical binding of water 4. Chemical binding of water 5. Internal curing 6. Predictions with the model 7. Conclusion A MACRO-MODEL FOR SELF-DESICCATION IN HPC

  3. HPC in Sweden • A few important marine concrete structures where a service-life of some 100 years is required in harsh marine environments (a SRPC/silica fume HPC) • 1000’s of concrete floor slabs where a moisture sensitive flooring is to be used (OPC HPC; w/C  0.40: Main reason for using HPC is the controlled and rapid drying by self-desiccation. A MACRO-MODEL FOR SELF-DESICCATION IN HPC

  4. Drying of HPC HPC NC A MACRO-MODEL FOR SELF-DESICCATION IN HPC

  5. Really true? Dominating mix parameters for self-desiccation cement type and w/c A MACRO-MODEL FOR SELF-DESICCATION IN HPC

  6. Self-desiccation in the sorption isotherm A MACRO-MODEL FOR SELF-DESICCATION IN HPC

  7. where The model for self-desiccation A MACRO-MODEL FOR SELF-DESICCATION IN HPC

  8. Alkali effect Physical binding of water we Scap we/C A MACRO-MODEL FOR SELF-DESICCATION IN HPC

  9. Desorption isotherms for HPCf(w/B, Si) A MACRO-MODEL FOR SELF-DESICCATION IN HPC

  10.  the desorption isotherm at different ages The model for self-desiccation A MACRO-MODEL FOR SELF-DESICCATION IN HPC

  11. Desorption isotherms for HPCat early ages (room temperature) A MACRO-MODEL FOR SELF-DESICCATION IN HPC

  12. where = chemical binding of water at different T & RH(t) The model for self-desiccation A MACRO-MODEL FOR SELF-DESICCATION IN HPC

  13. Chemical binding of water A MACRO-MODEL FOR SELF-DESICCATION IN HPC

  14. Chemical binding of waterlack of space bw/c ac A MACRO-MODEL FOR SELF-DESICCATION IN HPC

  15. carbonation? Chemical binding of watermoisture effects wn/C(RH, t1) bRH A MACRO-MODEL FOR SELF-DESICCATION IN HPC

  16. TGA-studies on reactivity at shortage of water Norling-Mjörnell (1997) SRPC, w/C=0.3, 5% Si-fume A MACRO-MODEL FOR SELF-DESICCATION IN HPC

  17. OPC Mjörnell (1997) Chemical binding of watermoisture effects wn/C(RH, t1) bRH A MACRO-MODEL FOR SELF-DESICCATION IN HPC

  18. OPC Si-fume Mjörnell (1997) Chemical binding of watermoisture effects wn(RH, t1) bRH A MACRO-MODEL FOR SELF-DESICCATION IN HPC

  19. Chemical binding of watermoisture effects wn(RH, t1) bRH alkali effect? f(a) A MACRO-MODEL FOR SELF-DESICCATION IN HPC

  20. cf. Snyder & Bentz(2004) Chemical binding of watermoisture effects bf,w ac A MACRO-MODEL FOR SELF-DESICCATION IN HPC

  21. Chemical binding of watertemperature effects A MACRO-MODEL FOR SELF-DESICCATION IN HPC

  22. Predictions with the model- cement hydration ac w/c 0.4 OPC A MACRO-MODEL FOR SELF-DESICCATION IN HPC

  23. Predictions with the model- self-desiccation, room temperature A MACRO-MODEL FOR SELF-DESICCATION IN HPC

  24. Predictions with the model- cement hydration, curing effects ac SRPC with w/c 0.4 A MACRO-MODEL FOR SELF-DESICCATION IN HPC

  25. Predictions with the model- self-desiccation, low temperature But later findings indicate quite another low-temperature curing effect! cf. Persson (2005) SRPC with w/c 0.4 A MACRO-MODEL FOR SELF-DESICCATION IN HPC

  26. Conclusions • The model for self-desiccation seems very promising and potentially useful for many applications of HPC • The model is especially designed for concrete floor slabs, where self-desiccation is beneficial. • Could very well be applied to concrete structures of HPC were the main concern of self-desiccation is shrinkage and early age cracking, and including internal curing. • The model can easily be integrated into a model that includes moisture transport (has been done!) • The most uncertain part of the model is the moisture effect on rate of reaction, where more research is needed, especially at very early ages. • The effect of early curing at low temperature may require special attention! A MACRO-MODEL FOR SELF-DESICCATION IN HPC

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