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Toward a sustainable SCC through the
use of high volume Fly ash and Slag to
reduce cement in SCC and the effect on
its cracking potential
Salah Altoubat
University of Sharjah, UAE
Middle East Conference on
Sustainable Building Materials
February 23rd, 2011
• SCC Characteristics: – Does not need vibration– Excellent deformability
– High resistance to segregation
• Attractive choice in the construction industry
• SCC has gained wide recognition in the Gulf– its use is on the rise
– Research on local materials is demanded
Background
• Carbon footprint of concrete is contributed by the following: – Material production (cement, reinforcement, agg…etc)
– Concrete production
– Repair during service life
– Demolition and recycling
• Sustainable concrete demands reduction of cement use– One ton of cement produce around 0.9 ton of CO2
• Sustainable concrete demands durable concrete– Reduce Repair and increase service life
Sustainability Concern: Construction Industry contribute around 20 to 25% of CO2
• Durability is the other face of Sustainability
• Reduction of Cement
– Fly ash and GGBF Slag to replace cement
– High volume of replacement of cement
• Fly ash and GGBF slag are byproducts of steel
production and thermal power generation
– Reduce risk of environmental issues by using them in concrete
Sustainability Requirements:
• Significant Reduction of Cement
– use of supplementary cementitious materials
– High volume of slag and fly ash
• Keep eyes on durability issues
– Premature cracking
– Early age cracking
– Corrosion
– Quality control
• Early age shrinkage cracking is critical factor for
durability
– Shape the durability of concrete during service life
Scenarios to achieve sustainable concrete:
• Durability Issue:
– SCC exhibits high potential for shrinkage cracking.
– Results on drying shrinkage of SCC are conflicting
– Lack of local results in the Gulf
Motivation
SCC is typically characterized by:
SCC has high potential for shrinkage
• Low content of coarse aggregate
• Low water to cement ratio
• High content of binder
• High content of fine aggregate
Shrinkage cracking of SCC is a concern !!
Important Factors:
Shrinkage Cracking
• Shrinkage potential
• Tensile creep
• Curing conditions
• Restraint conditions
Restrained Shrinkage Test should be
performed !!
Material Parameters
External Parameters
Passive Restraint Test Active Restraint Test
Restrained Shrinkage Test: Linear Test
Restrained Shrinkage Test: Ring Test
Ring Test is a viable test to perform
Restrained Shrinkage
AASHTO STANDARD RINGSASTM STANDARD RINGS
Dimensions ASTM Standard Ring AASHTO Standard Ring
Steel Thickness 12 mm 12mm
Steel Height 150mm 150mm
Concrete Thickness 38mm 75mm
Concrete Height 150mm 150mm
Degree of Restraint Depends on type of Ring
ASTM ring: 60 to 70 % AASHTO ring: 40 to 50 %
• Studying the restrained shrinkage & cracking potential for SCC made from
local materials in UAE.
• Investigating the effect of following parameters on cracking potential of SCC– Type & proportion of supplementary cementitious materials( Fly ash, GGBS , Micro silica)
– Degree of Restraint
– Curing Regime
Objectives
• Perform restrained shrinkage ring
tests for SCC mixes with different
supplementary materials
• SCM includes:
– Fly Ash
– GGBS
– Micorsilica
– Control
Experimental program: Methodology
• External Parameters
– Degree of Restraint• High degree (ASTM ring) ~ 60 to 70 %
• Moderate degree (AASHTO ring) ~ 40 to 50 %
– Curing Conditions• Air drying
• Moist curing for 3 days
• Moist curing for 7 daya
• Materials parameters
– High strength SCC mix with w/c of 0.36
– Compressive strength = 60 MPa
– Proportion of fly ash (0, 20%, 35%, and 50%)
– Proportion of GGBS (35%, 50% and 70%)
– Proportion of micro silica (5, 7, and 10%)
– Combination of fly ash or GGBS with micro silica
Experimental program: Study Parameters
– Ring test
• Monitor steel strain
• Age at cracking
• Net time to cracking
– Compressive Strength
• At age of 3, 7, 14, 28, 56, 100 and 120 days
– Free shrinkage
• From demolding to age of 120 days
– Tensile strength
• At age of 3, 7, 14, and 28 days
Experimental program: Measurement
Mix
No.
Type
of
SCMs
Fly Ash
(SCMs)
(%)
Restrained Shrinkage Test (Ring Test)
ASTM Standard Test AASHTO Standard Test
Air
Drying
3Days
Moist
7Days
Moist
Air
Drying
3Days
Moist
7Days
Moist
1 Control - Х Х Х Х Х Х
2 Fly Ash 20 Х Х Х Х
3 Fly Ash 35 Х Х Х Х
4 Fly Ash 50 Х Х
7% micro silica was added to mixes 3 and 4 in addition
to fly ash and cured for 3 days
Experimental program: Test Matrix
Additional tests
Primary tests
Mix w/c Cementitious Materials
Kg/m3
Aggregate
Kg/m3
HRWRA
L/m3
VE
Kg/m3
Cement Fly Ash TotalCoarse
Agg.
Fine
Agg.
Fine Agg.
/Total Agg.
Control 0.36 450 - 450 736 1101 0.60 6.5 0.6
Fly Ash-20% 0.36 360 90 450 735 1090 0.60 6.5 0.6
Fly Ash-35% 0.36 292 185 450 723 1056 0.59 5.5 0.6
Fly Ash-50% 0.36 225 225 450 723 1032 0.59 5.5 0.6
Experimental program: Concrete Mix Proportion
with Fly Ash
Maximum aggregate size was 10 mm
Wash sand, crushed sand and dune sand as fine aggregate
Class F fly ash
Experimental program: Concrete Mix Proportion
with Slag
Maximum aggregate size was 10 mm
Wash sand, crushed sand and dune sand as fine aggregate
Class F fly ash
Mix w/c Cementitious Materials
Kg/m3
Aggregate
Kg/m3
HRWRA
L/m3
VE
Kg/m3
Cement GGBS Total Coarse Agg. Fine Agg.Fine Agg.
/Total Agg.
GGBS-35% 0.36 292 158 450 747 1096 0.59 5.5 -
GGBS-50% 0.36 225 225 450 748 1094 0.59 6.0 0.5
GGBS-70% 0.36 135 315 450 738 1083 0.59 5.5 0.6
Mix Fresh Properties
Slump Flow
(mm)
Flow Rate
(s)
L-Box
Ratio
Control 620 10 0.70
20%FA 720 5 0.85
35%FA 600 6 0.80
50%FA 680 5 0.95
L- Box Test≥0.7
Slum p Flow
(600-750mm)
Flow Rate
(3 – 10 sec)
Experimental program: Targeted Fresh Properties
Binder Materials
Type Specific Gravity Source
Cement 3.15 Union Cement Factory (UAE)
Class F Fly Ash 2.3 Available in UAE Market. It is originally from a
India.
Aggregates
Type Specific Gravity Absorption Source
10 mm Agg. 2.96 0.9 Siji
Crushed Sand 2.78 1.5 Ras Al Kaimah
Washed Sand 2.74 1.4 Siji
Dune Sand 2.63 0.8 Al Ain
Admixtures
CHRYSO® Fluid Optima 230 Poly Carboxelated based High range water reducing admixture
Feyplast SUB-AQUA Viscosity Enhancer Admixture in powder form
Materials Properties
Experimental program: Ring test set up and instrumentation
Data acquisition system
Experimental program: Curing and Strain Monitoring
Age of first cracking is sensitive to fly ash proportion and
curing condition
Test results: ASTM Steel Ring Strain Evolution
Test results: AASHTO Steel Ring Strain Evolution
Cracking sensitivity to fly ash proportion and curing
condition is more pronounced in AASHTO ring test
Curing is
effective
Test results: Summary of Net Time to Cracking
35% of fly ash perform well under high degree of
restraint, provided moist curing is adopted for 3 days
Test results: Summary of Net Time to Cracking
Addition of 7% SF combined with fly ash significantly
improved the crack resistance of the mix under high
degree of restraint.
Test results: Summary of Net Time to Cracking
50% of fly ash perform well under low degree of restraint,
provided moist curing is adopted for 7 days
Age of first cracking is sensitive to GGBS proportion and
curing condition
Test results (GGBS): ASTM Steel Ring Strain Evolution
Test results (GGBS): AASHTO Steel Ring Strain Evolution
Cracking sensitivity to GGBS proportion and curing
condition is more pronounced in AASHTO ring test
Test results: Summary of Net Time to Cracking
50% of GGBS perform well under high degree of
restraint, provided moist curing is adopted for 3 days
Test results: Summary of Net Time to Cracking
70% of GGBS perform well under low degree of restraint,
provided moist curing is adopted for 7 days
Air Drying 3Days Moist 7Days Moist
Test results: Crack Resistance Under High Degree
of Restraint
35% fly ash and 50% slag increase the
crack resistance relative to control
provided moist curing is adopted
Significant
improvement with
7% SF and fly ash.
Test results: Crack Resistance Under Low Degree
of Restraint
Fly ash and Slag increase the
crack resistance relative to control
provided moist curing is adopted
Fly Ash can be added by
up to 50% and Slag by
up to 70 % in low degree
of restraint application .
1. Tensile Strength
2. Shrinkage Potential
3. Induced Tensile Stress
4. Degree of Relaxation
Analysis: Key Parameters affecting cracking
Analysis: Free Shrinkage
Fly ash did not affect long term drying shrinkage
Early shrinkage potential decreased as the fly ash proportion increased
Analysis: Early Age Free Shrinkage
Analysis: Degree of Relaxation
Fly ash improves early age stress relaxation
Analysis: Degree of Relaxation
Slag improves early age stress relaxation
• Highlighted critical parameters to achieve sustainable SCC– % of Fly Ash
– % of GGBF Slag
– Curing Condition
– Degree of Restraint
• Fly ash and slag can be used to reduce cement in SCC– Fly ash can replace cement by up to 50%
– GGBF slag can replace cement by up to 70 %
• Fly Ash and GGBF typically IMPROVES crack resistance of SCC provided that moist curing is adopted
Summary and Conclusions
• Durability consideration:
– Fly ash can be added by up to 35% in HIGH DEGREE of restraint structure provided that moist curing for at least 3days is adopted.Beyond this proportion 7% micro silica should be added.
– For LOW DEGREE of restraint structure, fly ash can be added by up to 50% provided that moist curing for at least 3days is adopted, preferably 7days.
– GGBF Slag can be added by up to 50% in HIGH DEGREE of restraint structure provided that moist curing for at least 3days is adopted.
– For LOW DEGREE of restraint structure, Slag can be added by up to 70% provided that moist curing for at least 3days is adopted, preferably 7days.
Summary and Conclusions