1. A Partnership in Research and Outreach David A. Lange, CEAT Director Department of Civil and Environmental Engineering Chang Joon Lee, Robert Rodden, Yi-Shi Liu, Zachary C. Grasley

2. Moisture curling project Basic driving force  Internal capillary stresses imposed under partial saturation Measurement of material properties  Creep  Elastic properties Material modeling  Hygrothermal forces, shrinkage, creep  Time dependence, inter-dependence Structural modeling Validation using lab tests & NAPTF slab tests

3. Two cases Highly restrained slab  Cracking Low restraint in slab  Curling + Wheel Load  Cracking

4. Shrinkage measurement Specimen sliced into the dimensions of 5”x1”x1/8”  uniform moisture condition throughout the cross section of the specimen under drying Linearly varying displacement transducer (LVDT)

5. Experimental results The shrinkage curves share similar characteristics under various relative humidity conditions The linear responses end after one day of drying, and tend to level off

6. Results (cont’d) Both matrices yielded lower drying shrinkage than plain cement matrix system Shrinkage of rice husk ash matrix is lower than that of fly ash matrix Larger amount of amorphous silica and surface area in rice husk ash

7. Mechanism of shrinkage Both autogenous and drying shrinkage dominated by capillary surface tension mechanism As water leaves pore system, curved menisci develop, creating reduction in RH and “vacuum” (underpressure) within the pore fluid Also plays a role in thermal dilation Hydratio n product

8. RH related to capillary pressure Kelvin-Laplace Equation relates RH directly to capillary pressure We can effectively calculate the internal stress by measuring RH As vapor pressure contributes little p” = vapor pressure  = pore fluid pressure R = universal gas constant T = temperature in kelvins v’ = molar volume of water

9. Measuring internal RH

10. UIUC field system UIUC field-ready system can sample RH and temperature at user prescribed interval and log to a nonvolatile external memory chip  Current system utilizes 55 channels (5 microprocessors)  Data can be collected with a laptop via a serial connection

11. Field-Ready RH/Temp Multiplexer In October 2005:  Cast 3 slabs (Plain, Cured, and SRA PCC) with a depth of 15” at ATREL Collected RH/Temp data at various locations above, at the surface, and through the depth of all slabs for three months continuously ALL above surface data showed little deviance from ambient

12. Novel Surface Sampling Technique A novel surface sampling technique was employed to measure the RH/temp at the surface An sensor was placed in a sleeve of Gore-Tex which was then troweled into the surface New technique yielded excellent repeatability

13. Preliminary Through Depth Data Internal RH measured from the surface of a 15” thick moist cured PCC slab

14. Preliminary Through Depth Data Drying occurs at the surface and base of the slab Daily cycling of RH and temp is evident RH and temp daily fluctuation is less as depth is greater

15. Determining creep properties

16. Computer Modeling

17. ABAQUSDIANAICON Gradient excitations YES Aging concrete properties NOYES Hygrothermal model for shrinkage NO YES Aging effect on creep NOSIMPLESOLIDIFYING NOTE: Assessments are based on the built-in functions of the codes Why is our modeling concept useful?

18. “Instantaneous” response - Static “Delayed” response - Creep Hygrothermal Model Concrete is an Aging Material Linear Elastic Continuum Solidification Theory [Bazant 1977] “Hygrothermal” response - Shrinkage & Thermal Expansion Material models

19. Uniaxial compressive test with axial & lateral strains Young’s modulus Lab Test: Stress-strain & Young’s modulus

20. Sealed testExposed to ambient Drying Sealed Basic creep Total deformation Lab test - creep

21. Lift-off displacement A VD-1 VD-4 CL-3 VD-5 CL-4 CL-2 Deformation comparison CL = Clip gauge VD = Vertical Displacement Transducer

22. Summary CEAT working to provide  a more complete understanding of mechanisms  new sensor technology  accurate, complete material models  useful software tool for analysis Results relate to material selection (e.g. high FA concrete) and pavement design