Sang Yeon Seo Rock Mechanics Lab

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Nov 25, 2013 (3 years and 6 months ago)

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Sang
Yeon

Seo

Rock Mechanics Lab


Korean Geotechnical Seminar

Feb 18
th

2009

1

Lab Introduction


Rock Mechanics Lab (ECJ B.220)


Supervisor : Dr.
Fulvio

Tonon


Established in September 2005


Main Researches:


-

Rock Testing


-

International Tunneling Consortium


Funding


Study period


2

Concrete


Strong in compression


(Normal strength concrete ≈ 50MPa (7000psi)


Weak in tension and bending


Very
brittle

behavior (elastic
-
brittle)


Need to be reinforced!!!


3

Concrete Lining


Precast


Concrete


Shotcrete


-

Wet mix & Dry mix


4

Reinforcements


Reinforced Concrete


-

Steel reinforcement bars (
rebars
), Mesh


-

Reinforcing fibers


5

Reinforcing bar & Mesh


Steel
rebars


-

ACI standard (size) & ASTM 615 grade


Mesh


-

Wire mesh


-

Textile mesh (woven & knitted)




6

Fibers


Steel fibers


Synthetic (plastic) fibers


Glass fibers


Hybrid fibers

7

Fibers
-

effects


Provide ductility & load bearing capacity


Crack control


Durability through whole medium


Easy application


Cost performance


Uniform distribution (reinforcing effect)


Various applications

8

Steel fibers


Most commonly used so far


Length 40


60mm, Diameter 0.5


1.0 mm


Tensile strength 1,100
MPa


Elastic modulus 200
GPa


Specific gravity 7.2


Various shapes/sizes & different
performance levels





9

Synthetic (plastic) fibers
-

micro


Not commonly used yet in tunnel lining


Usually made with polypropylene


Control shrinkage crack, abrasion resistance,
plastic settlement, bleeding


Length 10


20mm, Diameter 10


30
μ
m


Tensile strength 350
MPa


Elastic modulus 3.5
GPa


Specific gravity 0.91 (polypropylene),






1.14 (nylon)



10

Synthetic (plastic) fibers
-

macro


Synthetic fibers with longer length and
larger diameter for structural purposes


Similar effect with steel fiber, but something
different!


Length 30


50mm, Diameter 0.5


1.0mm


Tensile strength 600MPa


Elastic modulus 9.5GPa


Specific gravity 0.92


11

Glass fibers


Main component : Silica (SiO
2
)


-

Alkali
-
Silica Reaction


-

AR (Alkali Resistant) glass fibers


Similar effect with steel/macro
-
synthetic
fibers, but something different!


Length 10


20 mm, Diameter 10


20
μ
m


Tensile strength 1,700MPa


Elastic Modulus 72Gpa


Specific gravity 2.68




12

Hybrid fibers


Steel fiber + Synthetic fiber


-

Combination differs & No application yet


Synergy effect


-

Different fibers work at different age of concrete


-

Improves mechanical properties better than one single type of fibers


13

Comparative evaluations


Mechanical properties considered in
concrete tunnel lining :


-

Flexural strength


-

Toughness (Energy absorption capacity)


-

Crack control (peak / post
-
peak)


-

Impact resistance


-

Ductility


-

Abrasion / Erosion resistance


-

Water tightness

14

Comparative evaluations


Other properties considered in concrete
tunnel lining :


-

Workability


-

Constructability


-

Fiber rebound (for
shotcrete
)


-

Economy (cost)

15

Mechanical properties


Flexural strength :


Not much difference between fibers


Mesh (rebar) / Steel fiber / Glass fiber



> macro
-
synthetic





16

Mechanical properties


Toughness (Energy absorption capacity)


Mesh > Steel fiber > Glass fiber > Synthetic
fiber
(Synthetic/Glass > Steel)


17

Mechanical properties


Ductility


Increases with length of fiber ↑ dosage ↑


18

Mechanical properties


Crack control


Failure mode in panel test


Mesh vs. Fibers


19

Mechanical properties


Peak Crack / Post
-
peak crack


Crack does not propagate after the first
peak crack



20

Other properties


Workability / Constructability


-

Mesh :
difficult installation, time consuming, difficult to
reinforce whole layer


-

Steel fiber :
bad workability (but better than mesh),
rebound, vulnerable at file loading


-

Synthetic fiber :
safer than steel fiber, no corrosion, easy
to handle


-

Glass fiber :
similar specific gravity, similar mechanical
properties to steel fiber / similar workability to synthetic fiber,
expensive / not commonly used yet

21

Further researches


Substitute synthetic / glass fiber for mesh /
steel fiber


-

Mechanical properties + economic issues


Application of hybrid fibers


New proportions (synergy effect)


-

Strain hardening & early crack control (steel fiber)


+ shrinkage crack control & post peak crack control & ductility
(synthetic fiber)


+ similar specific gravity with concrete (glass fiber)


22

Q & A

23