This document presents research on using class F fly ash as a cement replacement material activated using alkali solutions. Fly ash particles were activated using either sodium hydroxide or sodium silicate solutions under different curing temperatures and conditions. Results showed that mortar mixtures cured with higher molar sodium hydroxide concentrations or lower silicate to sodium oxide ratios at higher temperatures under moist conditions achieved the highest compressive strengths. Statistical analysis indicated the silicate to sodium oxide ratio had the greatest effect on early strengths, while later strengths were most influenced by interactions between the sodium oxide ratio and curing condition.

1. Novel Cement Replacement Materials for Sustainable Infrastructure
Kingsten Banh1, Narayanan Neithalath2
Advanced Cementitious Materials and Systems Laboratory
School of Sustainable Engineering and the Built Environment, Arizona State University, Tempe, AZ
INTRODUCTION
 The production of Portland cement annually consumes 10-11
EJ of energy to produce 3 Gt and releases about 0.85 t of
carbon dioxide throughout all processing stages.
 Cement replacement materials utilizes industrial wastes as
the only binding material in making concrete.
 Alkali activating solutions used to activate the strength
development of the cement-free materials were sodium
hydroxide and liquid sodium silicates (waterglass).
 Dry and moist heat curing at different temperatures were
adopted to cure the activated samples.
BINDING MATERIAL
 Class F fly ash produced from
the combustion of coal powered
electricity generation.
 In compliance with ASTM C 618
 High silica and alumina contents,
but low calcium hydroxide
PROPERTIES OF CLASS F FLY ASH
 Fly ash consists of very fine, and glassy spherical particles.
 60% of particles are finer than 30 𝜇m.
Scanning electron micrograph of
typical class F fly ash particles
Particles size distribution of
class F fly ash
Component (wt.%) Class F (Bituminous) Fly Ash
Silicon Dioxide, SiO2 20-60
Aluminum Oxide, Al2O3 5-35
Iron Oxide, Fe2O3 10-40
Calcium Oxide, CaO 1-12
Magnesium Oxide, MgO 0-5
Sulfur Trioxide, SO3 0-4
Sodium Oxide, Na2O 0-4
Potassium Oxide, K2O 0-3
LOI 0-15
Chemical composition of class F fly ash
CURING CONDITIONS
 All alkali activated fly ash mortars were subjected to dry and moist
OF 40OC, 60oC, or 80oC within24 and 72 hours simultaneously.
0
5
10
15
20
25
30
35
40
45
50
4M - 40 4M - 60 4M - 80 8M - 40 8M - 60 8M - 80
CompressiveStress,MPa
NaOH Concentration - Curing Temperature
Dry Curing
24 Hours 72 Hours
0
5
10
15
20
25
30
35
40
45
50
4M - 40 4M - 60 4M - 80 8M - 40 8M - 60 8M - 80
CompressiveStress,MPa
NaOH Concentration - Curing Temperature
Moist Curing
24 Hours 72 Hours
SODIUM HYDROXIDE ACTIVATED BINDER
 4 M and 8 M concentrations of sodium hydroxide (NaOH)
solutions were used to activated fly ash with 0.4 activator
solution-binder ratio.
Compressive strength of sodium hydroxide activated fly ash mortars
under dry and moist curing
 Moist heat at high temperature cured of 8M NaOH concentration
activated mortars demonstrated higher compressive strength
despite the curing duration.
SODIUM SILICATES ACTIVATED BINDER
 n-ratio of 0.04 or 0.07 with Ms-ratio of 1.0 or 2.0 solutions were
used activated fly ash binder with liquid-to-powders ratio of 0.4
0
5
10
15
20
25
30
35
0.04 - 40 0.04 - 60 0.04 - 80 0.07 - 40 0.07 - 60 0.07 - 80
CompressiveStress,MPa
Na2O-to-Binder Ratio - Curing Temperature
Water Glass Solutions (Ms = 2.0)
24 Hours - Dry 24 Hours - Moist 72 Hours - Dry 72 Hours - Moist
0
5
10
15
20
25
30
35
0.04 - 40 0.04 - 60 0.04 - 80 0.07 - 40 0.07 - 60 0.07 - 80
CompressiveStress,MPa
Na2O-to-Binder Ratio - Curing Temperature
Water Glass Solutions (Ms = 1.0)
24 Hours - Dry 72 Hours - Dry 24 Hours - Moist 72 Hours - Moist
ALKALI ACTIVATOR PARAMTER
 Na2O-to-binder ratio is denoted as ‘n’
 SiO2-to-Na2O ratio is denoted as ‘Ms’
Compressive strength of sodium silicates activated fly ash mortars
under dry and moist curing
Normal probability plot of residuals for compressive stress models
for 1 and 3 days, respectively.
FACTORIAL STATISCALANALYSIS
 The 2k factorial experimental design consists of 2 levels of 4
different factor to evaluate the most influential factor that
contributes the most to the strength development.
 Remove 40oC curing temperature from the sodium silicates
activated binder to turn into a factorial experimental design.
Factor Description Low Level (-1) High Level (+1)
A SiO2-to-Na2O ratio Ms 2 1
B Na2O-to-binder ratio, n 0.04 0.07
C Curing Condition Dry Moist
D Temperature 60 80
Acknowledgements
1 – Barrett Honors Student, Arizona State University
2 – Associate Professor, Arizona State University
List of investigating factors
Compressive
Stress
Coefficient of Regression
A∙ 𝒙 𝟏 B∙ 𝒙 𝟐 C∙ 𝒙 𝟑 D∙ 𝒙 𝟒 BC∙ 𝒙 𝟐 𝒙 𝟑 R2 Adjusted R2
1 Day 4.06 2.22 1.42 1.98 0 0.94 0.92
3 Days 2.93 3.19 1.99 2.01 1.16 0.95 0.94
Coefficient of effective factors of regression model for compressive stress
 Activated fly ash mortars of lower Ms value with higher n value
under moist curing at same curing duration have higher strength
 Both regression models shown high correlation between all
investigating factors
 While all factor contributes to the strength development of
the sample, the Ms value has more effect on 1 day strength.
 For 3 days strength, the interactive effect between n-value
and curing condition also affects the strength.
0
10
20
30
40
50
60
70
80
90
100
-3 -2 -1 0 1 2 3
NormalProbability,%
Residuals
1 Day Residuals of Estimates
0
10
20
30
40
50
60
70
80
90
100
-3 -2 -1 0 1 2 3
NormalProbability,%
Residuals
3 Days Residuals of Estimates