CALCINED SHALE AS A LOW COST
SUPPLEMENTARY CEMENTITIOUS
MATERIAL
Maria Juenger
Saamiya Seraj, Rachel Cano, & Raissa Ferron
The University of Texas at Austin, USA
Should we test this SCM?
SCM Viability
Production and
Cost Feasible?
(Task 1)
Yes
No
Stop
Testing
No
Yes
No
Can material be
treated/modified,
dose changed or
blended?
(Task 5)
Fail
Full ASTM C 618 Testing
(Task 2)
Fail
Can ATSM C 618
be modified?
Pass
Yes
Advanced Characterization Testing
Fail
(Task 2)
Pass
Paste and Mortar Testing
(Task 3)
Fail
Pass
Fail
Concrete Testing
(Task 4)
Pass
Recommendations
(Task 6)
Texas Department of Transportation Project 0-6717
SCM cost and production
Material
Cost
Use/Availability
Fly ash
40 USD/ton
130,000 tons/year*
Metakaolin (not highly reactive)
325 USD/ton
30,000 tons/year
Pumice
116 USD/ton
200,000 tons/year
Vitric Ash
130 USD/ton
300,000 tons/year
Expanded (Calcined) Clay Shale
50 USD/ton
500,000 tons/year
*approximate amount of fly ash used by the Texas DOT for structural concrete.
Expanded Clay Shale
• Clay shale (referred to as shale) is a fine grained
sedimentary rock formed from the compaction of clay
minerals and other particulate debris
• Produced in a rotary kiln
• Used as lightweight aggregate
• The crushing process results in waste
fines that can be used as SCMs
www.architectureweek.com
Materials
Oxide
Metakaolin Shale Fly Ash
SiO2 (%)
51.66
65.43
52.1
Al2O3 (%)
35.23
14.55
23.1
Fe2O3 (%)
1.98
5.72
4.0
CaO (%)
0.57
2.44
11.6
MgO (%)
0.45
2.30
2.1
SO3 (%)
0.06
0.39
0.5
Na2O (%)
0.10
1.14
0.4
K2O (%)
1.42
2.88
0.7
Rheology (Workability)
100
Control
90
20% Metakaolin-D
Shear Stress (Pa)
80
20% Shale-T
70
20% Fly Ash
60
50
40
30
20
10
Y-intercept =
yield stress 0
0
10
20
30
40
Shear Rate (1/s)
50
60
Rate of Cement Hydration
Portlandite Consumption
Amount of Ca(OH)2 (g) per gram of cement
0.35
0.30
Control
20% Metakaolin-D
20% Shale-T
20% Fly Ash
0.25
0.20
0.15
0.10
0.05
0.00
7 day
28 day
90 day
Mortar Compressive Strength (w/c=0.5)
60
Control
Compressive Strength, MPa
50
20% Metakaolin-D
20% Shale-T
40
20% Fly Ash
30
20
10
0
1 day
3 day
7 day
28 day
90 day
365 day
Alkali Silica Reaction: ASTM C1567
0.50
Control
15% Metakaolin-D
25% Shale-T
20% Fly Ash
0.45
0.40
0.35
Expansion (%)
0.30
0.25
0.20
0.15
0.10
0.05
0.00
0
5
10
Number of Days in NaOH solution
15
Sulfate Attack (ASTM C1012)
0.40
Control (w/cm = 0.485)
25% Metakaolin-D (w/cm = 0.51)
25% Shale-T (w/cm = 0.51)
25% Fly Ash (w/cm = 0.46)
0.35
% Expansion
0.30
0.25
0.20
0.15
ACI 201 limits
0.10
Class 1
0.05
Class 2
Class 3
0.00
0
100
200
300
400
500
Number of Days Submerged in Na2SO4 solution
Conclusions
• Calcined shale from the lightweight aggregate industry is
a pozzolanic SCM that can compete with metakaolin and
fly ash
• Shale has a lower cost than metakaolin
• Metakaolin outperforms shale in long-term compressive
strength and control of ASR
• However, given the cost, the performance of shale is
adequate and it can be considered a feasible replacement
for fly ash
http://library.ctr.utexas.edu/ctr-publications/0-6717-1.pdf