|
Potential Portland cement replacement levels
Replacement
with fly ash
Sample calculation
Replacement with slag cement
Example from a case study of replacement with
fly ash
Future process for optimization of replacement
with SCMs
Simply substituting SCM
for cement is not recommended; the mixture should be specifically
proportioned for its intended use. See suggested
specification clauses [pdf] for EcoSmart concrete for more guidance.
Potential
levels of Portland cement replacement with fly ash in various structural
elements
|
Element in structure |
% Portland cement
replacement with fly ash * |
|
Suspended slabs and
slab bands |
20
- 50% |
|
Slab on grade (interior
parking) |
20
- 40% |
|
Slab on grade (no
parking) |
20
- 50% |
|
Slab on grade (exterior)
** |
10
- 30% |
|
Footings |
35 - 50% |
|
Walls |
30
- 50% |
|
Columns |
30
- 50% |
Source: Based on specifications
for TEF III and Vento Housing case studies.
The intent of these percentages
is that by the addition of fly ash, the cement content (relative
to the total cementitious material of a corresponding conventional
mix) should be proportionally reduced.
* Percentages indicate replacement
for Portland cement by mass. Variations in material sources and
environmental conditions may require alternate substitution rates.
For example, 40% Portland cement replacement may be used for suspended
slabs when ambient temperature is more than 5°C, but may be
reduced by 5% (to 35%) when ambient temperature is less than 5°C.
Further, the design strength of a mix will also affect substitution
rates (e.g., a 40 MPa concrete may allow a higher cement replacement
level than a 25 MPa concrete, because a 40 MPa concrete has more
cement in the mix to start). Consult your fly ash supplier and/or
concrete supplier for additional assistance.
** For the exterior slab
on grade for these projects, the lower limit for % cement replacement
was used. Some jurisdictions require minimum cement content for
this structural element.
Sample
calculation
Actual SCM mix: Min. 45%
cement replacement with fly ash in suspended slabs
Base mix: 30 MPa at 28 days for suspended slabs, non-air-entrained
concrete
Portland cement content
of base mix (kg/m3) = Design strength values in MPa at
28 days x K
|
where |
K = 10
for non-air-entrained concrete, or |
|
|
K = 12.5
for air-entrained concrete. |
Portland cement content
of base mix = 30 MPa x 10 kg/m3 / MPa = 300 kg/m3
Calculation of reduction
in cement content in actual SCM mix:
45% x 300 kg/m3 = 135 kg/m3 reduction in cement
content from base mix
Cement content in actual
SCM mix:
300 kg/m3 - 135 kg/m3 = 165 kg/m3
cement content in actual SCM Mix
Potential
levels of Portland cement replacement with slag cement in various
concrete applications
|
Concrete application |
% Portland cement
replacement with slag cement |
|
Concrete paving |
25-50% |
|
Exterior flatwork
not exposed to deicer salts |
25-50% |
|
Exterior flatwork
exposed to deicer salts with w/cm < 0.45 |
25-50% |
|
Interior flatwork |
25-50% |
|
Basement floors |
25-50% |
|
Footings |
30-65% |
|
Walls & columns |
25-50% |
|
Tilt-up panels |
25-50% |
|
Pre-stressed concrete |
20-50% |
|
Pre-cast concrete |
20-50% |
|
Concrete blocks |
20-50% |
|
Concrete pavers |
20-50% |
|
High strength |
25-50% |
|
ASR mitigation |
25-70% |
|
Sulfate resistance |
|
|
Type II equivalence |
25-50% |
|
Type V equivalence |
50-65% |
|
Lower permeability |
25-65% |
|
Mass concrete |
50-80% |
Source: Slag Cement Association
Percentages indicate replacement
for Portland cement by mass. These replacement rates are suggested
for individual applications and are based on historical performance.
Variations in material sources and environmental conditions may
require alternate substitution rates. Further, the design strength
of a mix will also affect substitution rates (e.g., a 40 MPa concrete
may allow a higher cement replacement level than a 25 MPa concrete,
because a 40 MPa concrete has more cement in the mix to start).
Consult your slag cement supplier for additional assistance.
Example
of levels of Portland cement replacement with fly ash in various
structural elements in the Courtyard on Bear & Cave Avenue housing
case study
See page 7 of the report from March 31, 2004:
http://ecosmartconcrete.com/kbase/filedocs/csrbanff.pdf
Optimum
levels of Portland cement replacement with SCMs
See SOS
(SCM Optimization System) update - currently under development.
Until the SOS is developed and operational, optimization
of replacement levels with SCMs will need to be conducted by experienced
professionals and individual concrete producers, using the Potential
Levels of Replacement with Fly Ash or Slag Cement as a guide. |
