PHYSICAL MATHEMATICS SEMINAR


TOPIC:		WHAT OSTEOPOROSIS AND CONCRETE EMPLOYED IN NUCLEAR WASTE
		STORAGE SYSTEM HAVE IN COMMON


SPEAKER:	FRANZ-JOSEF ULM
		Gilbert W. Winslow Associate Professor
		Department of Civil & Environmental Engineering
		Massachusetts Institute of Technology

ABSTRACT:

Osteoporosis is a skeletal disease characterized by low bone mass
density (BMD) and microarchitectural deterioration of bone tissue.  Recent
estimations by the National Osteoporosis Foundation indicate that in 1996
approximately 29 million people aged over 50 in the United States either
had osteoporosis or were at risk of developing the disease. This number is
expected to be 41 million by the year 2015. In undegraded bone, a finely
tuned cellular activity ensures a continuous remodeling of bone, repairing
damage and fracture in the microstructure.  This process is regulated by
two types of cells: Resorbing cells, called osteoclasts, dissolve bone
minerals (hydroxyapatite), and osteoblasts cells move into the space left
by the osteoclasts, regenerating the collagenous micromorphology and the
chemical boundary conditions for the re-mineralization of bone.  While the
biochemomechanical deterioration of bone that leads to osteoporosis is
still a matter of intensive research, it seems to result from a kinematic
imbalance between osteoclast and osteoblast activity.  With increasing
age, the overall resorption rate is higher than the overall refilling
rate, and this kinematic imbalance leads ultimately to an increased risk
of bone fracture during downfall.

At first glance, concrete durability problems are of a different kind:
they are conditioned by heat- and mass transport phenomena, amplified in
time and space by chemical reactions, which are coupled with deformation
and fracture of the material.  A typical example is Calcium leaching of
cementitious materials, which some years ago has been recognized as
critical for concrete employed in nuclear waste storage systems.  The
leaching is caused by water intruding the storage system having a lower
calcium concentration than some chemical equilibrium condition.  The
leaching of the Calcium from the matrix (Portlandite Crystals, C-S-H),
leads to a significant loss of strength and stiffness, and the material
becomes significantly pressure sensitive, which may ultimately impair the
structural integrity of the storage system.

On second sight, osteoporosis and Calcium leaching of concrete materials
have several things in common, starting from a `bony' microstructure of
Calcium leached cementitious materials, which shows strong similarity with
osteoporotic bones; and progress in one field may well improve health
monitoring capabilities in the other. Having this in mind, the talk
reviews some recent results of research on Calcium leached cement-based
material systems dealing with (1) deterioration kinetics; (2)  asymptotic
material behavior, and (3) monitoring by modeling the integrity of
concrete structures subjected to severe chemical softening.


DATE:		TUESDAY, APRIL 24, 2001

TIME:		2:30 PM

LOCATION:	Building 2, Room 338

Refreshments will be served at 3:30 PM in Room 2-349


Massachusetts Institute of Technology
Department of Mathematics
Cambridge, MA  02139