Transcript Super-Classified Fly Ash Poster (PPT, 1181KB)

Engineering Properties and Durability of Super-Classified Fly Ash Concrete
Research Student: Bruce K.T. Kandie
Supervisor: Dr. Ewan A. Byars
Sponsored by: Kenya
Government
Research Programme
Introduction
Combustion of coal (Fig 1) in modern power plants (Fig 2) produces some bottom
ash, but most of the burnt minerals escape with the flue gases and is called fly ash
(PFA), Fig 3. This ash is subsequently removed from the gas by electrostatic
precipitation.
PHASE ONE
Fly Ash Characterization
•Fineness
•Loss on Ignition
•Pozzolanicity
BS3892: Part 1 PFAs
2
3
4
5
6
7
1
Results and Discussions
Fig 5a shows that SPFA has a high water reducing effect compared to other cementitious material,
due to it’s hydrophilic nature and spherical shape.
Fig 5b shows the strength development, for a range of concrete mixes designed for 28-day in
strength, it can be seen that 5% and 10% SPFA concrete has higher strength than control up to 10
days. This is in contrast to conventional BS3892 PFA, all of which lags behind the OPC control
up to design age, as indeed do the micro-silica concrete mixes. Fig 5c shows the strength
development curve for 125 N/mm2 strength at 28 days. This was made with a blend of SPFA and
MS at replacement of 15% each.
SPFA
Fly ash poses a major waste disposal problem in the world (Fig 4). However, when
used in blended cements it can reduce greenhouse gas emissions, the cost of
concrete and improve the strength, durability and other properties of concrete.
Other uses
0.5%
Cement raw material
3.2% Blended cement
2.8%
Stockpiled
6.9%
Concrete addition
8.0%
Aerated concrete
blocks
10.2%
Non-aerated blocks
0.9%
Lwt. Aggregate
2.3%
Bricks and ceramics
0.2%
Grouting
5.1%
Disposal
43.6%
Landfill, land
reclamation and
restoration
9.8%
In-fill
1.1%
Structural fill
3.2%
General fill
2.3%
PHASE THREE
Mechanical & Physical Properties
•Compressive Strength
•Tensile Strength
•Dry Shrinkage
Grade 120 Mix
OP C 40
SP 40/ 05
SP 40/ 10
SP / MS120/ 15/ 15
B S3892: P a r t 1 P FA
40
P FA5/ 30
13 0
MS40/ 05
MS40/ 10
Compressive Strength N/mm2
Figure 3. Comparison between
SPFA and various types of PFAs
Figure 2. Burning coal to produce
electricity and fly ash
Grade 40 Mixes
Water Demand
Compressive Strength N/mm2
Figure 1. Coal
PHASE TWO
Fresh Concrete Properties
•Water Requirement
•Setting Time
•Admixture Compatibility
% Water requirement of OPC
8 µm
34
28
12 0
110
10 0
Extra refinement of fly ash produces Super-Classified Fly Ash-(SPFA), an ultra fine
powder with average 8µm particle size. It is a very reactive pozzolan compared to
BS3892: Part 1[1] fly ashes and has high potential for use as an alternative to microsilica (MS) for high strength concrete and other applications[2].
Aim of this Research
The aim of this research is to develop specialist concrete mixes for high performance
applications using optimised mix proportions with SPFA and compare this on a
performance and economic basis with MS and BS3892: Part 1 fly ashes.
Objectives
To achieve the project aim, the following objectives have been identified:
i) To determine how the various replacement levels of SPFA for cement affects the
fresh, hardened and the durability properties of concrete. Water demand, early and
long term strength development, self-compacting concrete, creep, shrinkage,
carbonation resistance, chloride resistance and sulfate resistance will be studied.
ii) To measure the effect of SPFA on the microstructure of concrete.
iii) On the basis of (i) and (ii), perform economic analysis to determine the most
appropriate uses of SPFA in concrete.
0
PHASE FOUR
Permeability Properties
•Oxygen Diffusion
•Porosity
80
70
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Figure 4. Fly ash disposal and utilisation in the UK
90
7
14
21
28
0
7
14
21
Age-days
Age-days
Pozzolan replacement (%)
(b)
(a)
(c)
Figure 5. Shows (a) Water demand and (b and c) the compressive strength curves for the SPFA and BS3892: Part 1 fly ashes
Conclusion
The use of SPFA in concrete has achieved the following:
• A water deduction of 18% for 30% replacement of cement (Fig 5a).
PHASE FIVE
Durability
•Chloride Ingress
•Sulfate Resistance
•Carbonation
•Freezing/Thawing
PHASE SIX
Economic Analysis
• Concrete with a strength of 125 N/mm2 at 28 days (fig 5c) in water curing-for normally
compacted concrete, 150N/mm2 at 90-days.
• Self compacting concrete made with only 380 kg/m3 cementitious cement and minimal
plasticizer[3].
References
1. BRITISH STANDARDS INSTITUTION. Specification for pulverized-fuel ash for use as a
cementitious component in structural concrete. BS 3892 : Part 1. BSI, London, 1993.
2. Fossey, S. D., Byars, E.A. and Zhu, H.Y. 2003. Super-Classified PFA For Self-Compacting
Concrete. ICCC-2003. Durban, South Africa, (in press).
3. Tsartsari, A. and Byars, E. A. 2000. Ultra-High Strength Concrete Using Conventional
Casting. Concrete, Vol. 36 , No 1, pp 16-17.
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