Megiddo 2010
Synchronizing clocks at Armageddon
Moira Wilson School of Mechanical, Aerospace and Civil Engineering,
The University of Manchester
Megiddo 2010
RHXSome scientific observations and issues
Team RHX: Moira Wilson Chris Hall
Margaret Carter Ceren Ince
Bill Hoff
One microbalance
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Basis of method is “moisture expansion”
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Moisture induced expansion is of concern to builders and civil engineers because it gives rise to strain.
Rule of thumb: bricks should not be used for about 2 weeks after firing.(i.e. when they have finished expanding (Ha!))
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• The lime mortar accommodated strain.
• Modern cement mortars do not, so expansion joints are specified in design codes.
Moisture expansion in structural masonry
•Old brick masonry (before ~ 1950) doesnot have expansion joints.
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How big are these effects?
EXPANSION: 1 km of wall will expand by ~ 1 m over 200 y
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FILM OF BRICK GAINING MASS
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• Moisture expansion was known to be REVERSIBLE (but no agreement on the temperature required to do this)
Of most interest
• The moisture expansion was accompanied by an increase in mass (but only 1 set of data in the literature from 1962). (No point in engineering)
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The Manchester and Edinburgh worktime¼ law
(2003)
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Discovery of the (time)1/4 law:
(2003)
Megiddo 2010 (2003)
Megiddo 2010 (2003)
Fresh brick
1900 year old brick
20 year old brick
120 year old brick
Discovery of the (time)1/4 law:
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Effect of environmental conditions (i)
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Effect of environmental conditions (ii)
SATURATED
DRY
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Discovery of the 2 stage process:
0
0.1
0.2
0 2 4 6Time1/4 (mins1/4)
103 S
trai
n, ε
1 day
Expansion versus t1/4
0
0.1
0.2
0.3
0 5 10Time1/4 (min1/4)
103 ∆
m/m
o
16 days
Mass gain versus t1/4
(2005)
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TIME 1/4
The t1/4 law means that equal amounts of expansion or mass gain occur in the time intervals 1, 16, 81, 256 etcseconds / minutes/ years after firing.
These correspond to 14, 24, 34, 44 etc seconds / minutes/ years.
If we plot mass gain or expansion against t1/4 we geta straight line.
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The older the brick, the bigger it is.
Could the new rate law be exploited to produce a dating method for fired clay ceramics??
It gets bigger and heavier at a precisely defined rate
EUREKA!
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Principle of the dating method
•1 Measure initial length (L) or mass (m)
2. Measure early time mass or expansion following reheating
3. Extrapolate stage II data
4. Age of sample
t1/4
Exp
ansi
on
L,mo
L,m
ta1/4
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Expansion in fresh/reheated brick
Linear fits to Stage 2 data:(F) ε = 0.93×10-5t1/4 + 2.77×10-5
(R1) ε = 0.45×10-5t1/4 + 3.67×10-5
(R2) ε = 0.33×10-5t1/4 + 2.45×10-5
Systematic reductionin Stage II gradienton repeated reheating
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0 1 2 3 4 5 6
Time1/4 (mins1/4)
10
3 Str
ain
, E
Fresh
Reheat 1
Reheat 2
1 day
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FORM of data sameas expansion data- scattery.
Same 2 stage process observed
0
0.1
0.2
0.3
0 5 10Time1/4 (min1/4)
103 ∆m
/mo
16 days
Why?
Started looking at mass gain again:
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Is the mass gain reversible?
y = 0.0039x + 0.0285
y = 0.0435x - 0.1174
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0 5 10 15 20 25 30
Time^0.25 /mins
Mass
gain
%
Freshly fired brick
y = 0.0039x + 0.0205
270 days y = 0.004x + 0.0248
y = 0.025x - 0.0395
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0 2 4 6 8 10 12
Time^0.25 /mins
Mas
s %
gai
ned
Same brick reheated
y = 0.004x + 0.0248
7 days
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Predicted ageof 49 weeks.
5 10 15 20 25
1279.6
1280.0
1280.2
1280.4
1280.6
1279.8
1281.0
1281.4
1280.8
1281.2
1281.6
Initial mass of 39 week old brick
Extrapolated Stage II data
Stage II data
Time1/4 (min1/4)
Ma
ss (
g)
14 days
The first “dating” experiment
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m = 0.0382t 1/4 + 128.9531
m = 0.0289t 1/4 + 129.02
128
129
130
131
132
133
134
135
0 50 100 150 200
Time1/4 (mins1/4)
Mas
s (g
)
A × 1.33 = B(mean over all trials)
1,957 Years
A B
The first dating trial
Calculated date too young
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Knownage
Ratio of predicted to known age
(in t1/4)
Predicted age with average
multiplier (1.33)
(a) 150 ±10 1.36 144
(a) 150 ±10 1.31 166
(a) 150 ±10 1.26 192
(b) 367±160 1.37 298
(b) 367±160 1.37 303
(c) 1932±75 1.34 1968
(d) 1957±50 1.30 2123
Mean= 1.33
The first dating trial
All dates came outwrong-
BY THE SAME AMOUNT
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m = 0.0382t 1/4 + 128.9531
m = 0.0289t 1/4 + 129.02
128
129
130
131
132
133
134
135
0 50 100 150 200
Time1/4 (mins1/4)
Mas
s (g
)
1,957 Years
A B
The DATA
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The microbalance:
The next step…
Allows us to weigh 5 gpieces of brick under tightly controlled conditions to 0.1µg. (1/10 of a millionth of a gram).
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0
0.5
1
1.5
2
2.5
3
0 5 10Time1/4 (mins1/4)
103
∆m/m
0
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0 2 4 6 8 10 12
Time1/4 (mins1/4)
10
3 Δm
/m0
10 days
The data
• Vastly improved quality of data.
• Speed of data acquisition.
• Absolute confirmation of the t1/4 law
NO SCATTER!!!!!!
(WHY?)
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Putting the microbalancethrough its paces
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This shows that we have a chemical reaction going on ……… and that it’s TEMPERATURE DEPENDENT!
Arrhenius plot
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EUREKA! (again)• Scattery data due to temperature fluctuationsover course of measurement period
• First dating experiment worked because the brick had been sitting in the lab for 39 weeks – and the mass gain measurements following heating were carried out at the same temp (~ 25 OC)
AND
All samples in 1st dating trial were measured at ~25 OC!
→ Stage II gradients were too steep (temp too high),
→ Extrapolated Stage II data intersected line of initial mass too soon
→ Age of sample too young (2008)
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Second dating trial
3941
3942
3943
3944
3945
3946
3947
3948
3949
0.0 0.3 0.6 0.9 1.2 1.5 1.8 2.1 2.4
Time1/4 (hours1/4)
Mass
(m
g)
m /t 1/4 = -0.00006x + 0.79350
0
5
10
15
0 1000 2000 3000 4000 5000
Data points
Gra
die
nt (m
/t1/
4 )
Gradient = 0.2 min-1/4
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Started to get some REALLY good results
AND THEN …
yippee!
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We dated a Roman brick to March 2008!
(i.e. 8 months old)
AND THEN …
EEK!
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We dated a MEDIEVAL brick to 1942!
(i.e. 66 years old)
AND THEN …
– the “Canterbury Tale”…
NOW WHAT?
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Eventually…the “line of knowns”
50 person-years of effort for 6 data points!
REPLICATE VALUES (yrs)
330
321
333
308
307
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3941
3942
3943
3944
3945
3946
3947
3948
3949
0.0 0.3 0.6 0.9 1.2 1.5 1.8 2.1 2.4
Time1/4 (hours1/4)
Mass
(m
g)
m /t 1/4 = -0.00006x + 0.79350
0
5
10
15
0 1000 2000 3000 4000 5000
Data points
Gra
die
nt (m
/t1/
4 )
Improved methodology
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0.0 0.5 1.0 1.50.000
0.001
0.002
0.003
0.004
Mas
s ch
ang
e (m-m0)/m
0
Time1/4 ((hours)1/4)
Solid line: freshly-fired at 800ºC; □: following reheating at 500ºC.
1.0 1.5 2.0 2.5 3.0 3.5
0.0000
0.0005
0.0010
0.0015
0.0020(b)
Mas
s ch
ange
(m-m(2) 0)/m(2) 0
Time1/4 ((hours)1/4)
reheated
freshly-fired
(a)
Some other nice microbalance results
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NEW RESULTS:
1. Samian ware
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Samian ware Mass gain measured at 11 deg C and 30% RHfollowing reheating at 500 deg C
AGE = 1950 years
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Samian warePlot of gradient segments:
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25ºC
20ºC
15ºC
Samian wareMass gain at different temperatures:
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Samian ware
25ºC
20ºC
15ºC
11ºC
ln r = 1.6383
r = 0.1943 mg/hr1/4
Sample dates to 1943 years
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11ºC and 50 % RH
11ºC and 30 % RH
BOTH DATE TO
~ 1950 years old
Samian ware
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2. Saxon loom-weightMass gain measured at 11 deg C and 30% RH.Gradient stabilised after 7 days
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RHX age: 1159 years (= 850AD)
Assigned age:5th century8th century OR 9th century
RESULTS
Conclude 9th century
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1 2
2. Megiddo: RHX4 S7 Mass gain measured at 19 deg C and 30% RH.
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1 2
1 21
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3. Megiddo Plot of gradients vs number of data points:
The “Piasetzky Effect”
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Now have 2 sets of anomalous results:
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BET specific surface area results: SAMPLE SURFACE AREA
mm^2/g
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Thank you!
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Acknowledgements
• The Leverhulme Trust
• EPSRC
• The Museum of London Specialist Services
• Centre for Materials Science and Engineering, The University of Edinburgh
• A very patient husband (Master?)!
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Tel Aviv (hot and dry?): 32.2 OC (90 OF) and 46% RH (i.e. 46% of a large amount of water vapour)
Manchester (cold and wet) 12.8 OC (55 OF) and 67% RH (i.e. 67% of a much smaller amount of water vapour).
From these data, the water vapour pressure in Tel Aviv is 2.24 kPa compared with 1.00 kPa in Manchester
The air in Tel Aviv therefore contains much more water vapour than in Manchester