The document discusses the influence of quicklime reactivity and origin on the production of autoclaved aerated concrete (AAC). It details the objective, methods, and findings, notably that highly reactive quicklimes can lead to overheating and impact compressive strength, while the reactivity affects expansion rates differently based on limestone origin. A lab-scale methodology was developed to monitor these effects, emphasizing the complex relationship between quicklime characteristics and AAC properties.

1. Impact of
quicklime reactivity and origin
on Autoclaved Aerated Concrete production
D. Lesueur (didier.lesueur@lhoist.com), F. Mücke,
H. Oeinck, U. Peter, C. Pust and F. Verhelst
Lhoist R&D / Rheinkalk / Lhoist

2. Outline
• Objective
• Materials
• Methods
• Results
• Conclusions
2

3. Outline
• Objective
• Materials
• Methods
• Results
• Conclusions
3

4. Objective
• Specifications on quicklime for AAC production are
essentially based on reactivity (EN 459-2)
90
80
Temperature (°C)
70
60
max
min
Quicklime
50
40
30
20
10
0
0
10
20
30
40
50
time (min)
• Is this enough?
4

5. Outline
• Objective
• Materials
• Methods
• Results
• Conclusions
5

6. Quicklimes
with various origin and reactivity
Calcination
LA1
LA2
LA3
IA1
IA2
IB
IC
Laboratory
Laboratory
Laboratory
Industrial
Industrial
Industrial
Industrial
Limestone
Origin
A
A
A
A
A
B
C
CaO
t60
wt.%
95.5
95.6
96.2
93.5
94.0
95.8
93.8
min
4.1
5.2
7.6
1.9
3.1
8.2
5.2
6

7. Quicklimes
with various origin and reactivity
80
temperature (°C)
70
LA1 4.1min
LA2 5.2min
LA3 7.6min
IA1 1.9min
IA2 3.1min
IB 8.2min
IC 5.2min
60
50
40
30
20
0
5
10
15
time (min)
20
25
30
7

8. 3 recipes covering
P2-0.35, P2 – 0.4 and P4 – 0.55 (EN 771-4)
Target density
Target compressive strength
Return Slurry
Quartz Sand
Cement
Lime
Anhydrite
Aluminium Paste
Water/Solid wt. ratio
Units
kg/m3
MPa
wt.%
wt.%
wt.%
wt.%
wt.%
wt.%
-
P2 – 0.35
300-350
>2
20
50
28
17
5
0.22
0.68
P2 – 0.4
350-400
>2
20
55
25
15
5
0.16
0.65
P4 – 0.55
500-550
>4
20
59
18
19
4
0.08
0.65
8

9. Outline
• Objective
• Materials
• Methods
• Results
• Conclusions
9

10. AAC production
and monitoring at laboratory scale
• Mix ingredients
¬
¬
¬
¬
Return slurry
Hot water (70°C)
Powders
Aluminium paste
900 Rpm Dissolver
Mixture
30L
Bucket
• Monitor green cake
expansion
¬ Height and temperature
¬ Final hardness
Datalogger
Ultrasound
sensor
Thermocouple
Green cake
10

11. AAC production
and monitoring at laboratory scale
• Autoclaving
¬ 225 l autoclave
¬ 2 hrs linear increase
¬ 6 hrs 11 bars / 190°C
• AAC testing
¬ density and
compressive strength
11

12. Outline
• Objective
• Materials
• Methods
• Results
• Conclusions
12

13. Quicklimes
with same origin and different reactivity
• Expansion monitoring P2 – 0.35
1.2
height / final height (-)
1.1
1.0
0.9
LA1 4.1min
LA2 5.2min
IA1 1.9min
IA2 3.1min
0.8
0.7
0.6
0.5
0.4
0
5
10
15
20
25
30
35
time (min)
40
45
50
55
60
13

14. Quicklimes
with same origin and different reactivity
• Expansion monitoring P2 – 0.35
height / final height (-)
1.10
1.05
1.00
LA1 4.1min
LA2 5.2min
IA1 1.9min
IA2 3.1min
0.95
0.90
10
15
20
time (min)
25
30
14

15. Quicklimes
with same origin and different reactivity
• Temperature P2 – 0.35
75
temperature (°C)
70
65
60
LA1 4.1min
LA2 5.2min
IA1 1.9min
IA2 3.1min
55
50
45
40
0
10
20
30
40
50
60
70
80
90
100
110
120
time (min)
15

16. Quicklimes
with same origin and different reactivity
• Expansion monitoring P2 – 0.35
1.2
height / final height (-)
1.1
1.0
0.9
LA2 5.2min
IA1 1.9min
IB 8.2min
IC 5.2min
0.8
0.7
0.6
0.5
0.4
0
5
10
15
20
25
30
35
40
45
50
55
60
time (min)
16

17. Quicklimes
with same origin and different reactivity
• Expansion monitoring P2 – 0.35
height / final height (-)
1.10
1.05
1.00
LA2 5.2min
IA1 1.9min
IB 8.2min
IC 5.2min
0.95
0.90
10
15
20
25
30
time (min)
17

18. Quicklimes
with different origin and reactivity
• Temperature P2 – 0.35
75
temperature (°C)
70
65
LA2 5.2min
IA1 1.9min
IB 8.2min
IC 5.2min
60
55
50
45
40
0
10
20
30
40
50
60
70
80
90
100
110
120
time (min)
18

19. Green cake:
Summary of findings
•
Thermal monitoring always matches expansion kinetics
•
With the studied recipes and methods, risk of overheating
was observed for P2 – 0.35 and highly reactive quicklimes
(expansion overshoot)
•
With the same limestone origin, the higher the reactivity, the
faster the green cake expansion
BUT with varying limestone origin, similar reactivities can lead
to different expansion kinetics
•
•
At the lab scale, green cake hardness essentially not affected
by quicklime properties
19

20. Quicklimes
with same origin and different reactivity
• Final AAC properties
compressive strength (MPa)
6
5
4
LA
IA
mean
3
2
1
250
300
350
400
450
500
550
density (kg/m3)
20

21. Quicklimes
with same origin and different reactivity
• Final AAC properties
compressive strength (MPa)
6
5
LA
IA
IB
IC
mean
4
3
2
1
250
300
350
400
450
500
550
density (kg/m3)
21

22. Final AAC:
Summary of findings
•
Final AAC properties were little affected by quicklime origin
•
Highly reactive quicklimes (expansion overshoot) gave low
compressive strength for the P2-0.35 recipe
•
IB quicklime seem to give consistently higher compressive
strength for a given density
¬ Tobermorite crystal size?
22

23. Outline
• Objective
• Materials
• Methods
• Results
• Conclusions
23

24. Conclusions
•
We developped a methodology to study quicklime effect on
AAC at the lab scale through
¬ Green cake monitoring
¬ AAC final properties
•
With the studied recipes and methods, risk of overheating
was observed for P2 – 0.35 and highly reactive quicklimes
(expansion overshoot) leading to low compressive strength
•
With the same limestone origin, the higher the reactivity, the
faster the green cake expansion
BUT varying limestone origin, similar reactivities can lead to
different expansion kinetics
•
24

25. Thank you for your attention