High Strength Concrete
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High Strength Concrete
High-strength concrete
Definitions The definition of high-performance concrete is more controversial. Mehta and Aitcin used the term, highperformance concrete (HPC) for concrete mixtures possessing high workability, high durability and high ultimate strength.
P.K. Mehta and P.J.M. Monteiro, Concrete: Microstructure, Properties, and Materials
High-strength concrete
Definitions ACI defined high-performance concrete as a
concrete meeting special combinations of performance and uniformity requirements that cannot always be achieved routinely using conventional constituents and normal mixing, placing, and curing practice.
P.K. Mehta and P.J.M. Monteiro, Concrete: Microstructure, Properties, and Materials
High-strength concrete
Typical Classification
Normal Strength
20-50 MPa
High Strength
50-100 MPa
Ultra High Strength
100-150 MPa
Especial
> 150 MPa
P.K. Mehta and P.J.M. Monteiro, Concrete: Microstructure, Properties, and Materials
High-strength concrete
Microstructure From the general principles behind the design of high-strength concrete mixtures, it is apparent that high strengths are made possible by reducing porosity, inhomogeneity, and microcracks in the hydrated cement paste and the transition zone.
P.K. Mehta and P.J.M. Monteiro, Concrete: Microstructure, Properties, and Materials
High-strength concrete
Microstructure The utilization of fine pozzolanic materials in high-strength concrete leads to a reduction of the size of the crystalline compounds, particularly, calcium hydroxide. Consequently, there is a reduction of the thickness of the interfacial transition zone in high-strength concrete. The densification of the interfacial transition zone allows for efficient load transfer between the cement mortar and the coarse aggregate, contributing to the strength of the concrete. For very high-strength concrete where the matrix is extremely dense, a weak aggregate may become the weak link in concrete strength. P.K. Mehta and P.J.M. Monteiro, Concrete: Microstructure, Properties, and Materials
High-strength concrete
Materials - Cement Almost any ASTM portland cement type can be used to obtain concrete with adequate rheology and with compressive strength up to 60 MPa. In order to obtain higher strength mixtures while maintaining good workability, it is necessary to study carefully the cement composition and finenesses and its compatibility with the chemical admixtures. Experience has shown that low-C3A cements generally produce concrete with improved rheology.
P.K. Mehta and P.J.M. Monteiro, Concrete: Microstructure, Properties, and Materials
High-strength concrete
Materials -- Aggregate In high-strength concrete, the aggregate plays an important role on the strength of concrete. The low-water to cement ratio used in high-strength concrete causes densification in both the matrix and interfacial transition zone, and the aggregate may become the weak link in the development of the mechanical strength. Extreme care is necessary, therefore, in the selection of aggregate to be used in very high-strength concrete.
P.K. Mehta and P.J.M. Monteiro, Concrete: Microstructure, Properties, and Materials
High-strength concrete
Materials -- Aggregate The particle size distribution of fine aggregate that meets the ASTM specifications is adequate for high-strength concrete mixtures. If possible, Aitcin recommends using fine aggregates with higher fineness modulus (around 3.0). His reasoning is as follows: – a) high-strength concrete mixtures already have large amounts of small particles of cement and pozzolan, therefore fine particles of aggregate will not improve the workability of the mix; – b) the use of coarser fine aggregates requires less water to obtain the same workability; and – c) during the mixing process, the coarser fine aggregates will generate higher shearing stresses that can help prevent flocculation of the cement paste. P.K. Mehta and P.J.M. Monteiro, Concrete: Microstructure, Properties, and Materials
High-strength concrete
Guidelines for the selection of materials The higher the targeted compressive strength, the smaller the maximum size of coarse aggregate.
Up to 70 MPa compressive strength can be produced with a good coarse aggregate of a maximum size ranging from 20 to 28 mm.
To produce 100 MPa compressive strength aggregate with a maximum size of 10 to 20 mm should be used. To date, concretes with compressive strengths of over 125 MPa have been produced, with 10 to 14 mm maximum size coarse aggregate. P.K. Mehta and P.J.M. Monteiro, Concrete: Microstructure, Properties, and Materials
High-strength concrete
Guidelines for the selection of materials Using supplementary cementitious materials, such as blast-furnace slag, fly ash and natural pozzolans, not only reduces the production cost of concrete, but also addresses the slump loss problem. The optimum substitution level is often determined by the loss in 12- or 24-hour strength that is considered acceptable, given climatic conditions or the minimum strength required. While silica fume is usually not really necessary for compressive strengths under 70 MPa, most concrete mixtures contain it when higher strengths are specified.
P.K. Mehta and P.J.M. Monteiro, Concrete: Microstructure, Properties, and Materials
High-strength concrete
Usage of Superplasticizers Constant w/c: Increase in the workability
Constant workability: Lower w/c
same workability No admixture
MLS
SMF
SC
LOWER WATER CONTENT
Lower w/c
Courtesy from Prof. Gettu P.K. Mehta and P.J.M. Monteiro, Concrete: Microstructure, Properties, and Materials
High-strength concrete
Superplasticizer-Silica Fume Interaction
Without superplasticizer, the cement + water + silica fume system tends to coagulate, making the
use of a superplasticizer essential.
REPULSIVE FORCES Silica fume
COAGULATION
Silica fume
DISPERSION Courtesy from Prof. Gettu
P.K. Mehta and P.J.M. Monteiro, Concrete: Microstructure, Properties, and Materials
High-strength concrete
Selection of the Superplasticizer
Study of the compatibility
Optimum superplasticizer dosage
Cost-benefit considerations In several cases, this order is inverted, resulting in costly consequences
Courtesy from Prof. Gettu P.K. Mehta and P.J.M. Monteiro, Concrete: Microstructure, Properties, and Materials
High-strength concrete
Marsh Cone Test: Evaluation of the compatibility and dosage Comparison with yield shear stresses obtained with a viscometer
800-1000 ml 7.0
25
Cement I 52.5R w/c=0.33 Superplasticizer SD1
15.5 cm
20 6.5
Bingham yield stress (Pa)
6 cm
6.0
10
5.5 5
Diameter: 8 mm 5.0
200-500 ml
15
τ 0 (Pa)
29 cm
Flow time (s)
Marsh cone flow time (s)
0 0.5
1.0
1.5
2.0
2.5
% sp/c
3. 0
3.5
Courtesy from Prof. Gettu
P.K. Mehta and P.J.M. Monteiro, Concrete: Microstructure, Properties, and Materials
High-strength concrete
Practical Significance of the Saturation Point 210
Marsh cone flow time, s
w/c = 0.35 T = 22°C 170
60 min
Saturation Point
130
5 min
90
50 0.0
0.4
0.8
1.2
1.6
2.0
2.4
Superplasticizer dosage (% sp/c)
2.8 Courtesy from Prof. Gettu
P.K. Mehta and P.J.M. Monteiro, Concrete: Microstructure, Properties, and Materials
High-strength concrete
Cement/Superplasticizer Compatibility 200
Marsh cone flow time, s
180
w/c = 0.35 T = 23° C
60 min
160 140 120 60 min
Cement A
100
Cement B
80
5 min
5 min
60 0
0.4
0.8
1.2
1.6
2.0
2.4
Superplasticizer dosage (% sp/c) P.K. Mehta and P.J.M. Monteiro, Concrete: Microstructure, Properties, and Materials
2.8
High-strength concrete
Selection of Superplasticizer COST-BENEFIT RATIO
Time (s)
% sp/c CBR = × (cost/kg) × time (s) s.r.
CBR =
w/c = 0.33
CBR =
0.25 % sp/c × ( 3 euros/kg) × 5 s = 12.5 0.3 s.r.
1.5% sp/c ×( 1 euro/kg) ×7 s = 26.3 0.4 s.r.
Courtesy from Prof. Gettu P.K. Mehta and P.J.M. Monteiro, Concrete: Microstructure, Properties, and Materials
High-strength concrete
Factors that Affect the Saturation Point
• Type of cement • Water/cement ratio • Presence of mineral admixtures • Mixing sequence (better to separate the
incorporation of water and superplasticizer by at least 1 minute of mixing)
• Temperature Courtesy from Prof. Gettu P.K. Mehta and P.J.M. Monteiro, Concrete: Microstructure, Properties, and Materials
High-strength concrete
Effect of Temperature on the Loss of Fluidity
15
16
c = I 52.5 R sp = SN w/c = 0.33 sp/c = 1%
35ºC
5ºC
45ºC
10
15ºC 25ºC
5
0 5 15
30
45
60
75
90
Marsh Cone flow time (s)
Marsh Cone flow time (s)
20
12
c = I 52.5 R sp = SC w/c = 0.33 sp/c = 0.3% 35ºC 25ºC
8
15ºC 45ºC 5ºC
4
0 5 15
30
Time (min)
45
60
75
90
Time (min)
• Loss of fluidity in the paste is lower for polycarboxylate based superplasticizers.
• There is no clear trend with respect to temperature. Courtesy from Prof. Gettu P.K. Mehta and P.J.M. Monteiro, Concrete: Microstructure, Properties, and Materials
High-strength concrete
Effect of Temperature on the Water Demand of Cement
Water demand (w/c)
0.30
c = I 52.5 R sp = SN
0.28 0.26 0.24
45 ºC 35 ºC
0.22
25 ºC 0.20
15 ºC 5 ºC
0.18 0.0
1.0
2.0
% sp/c
3.0
4.0
• The water demand of cement increases with an increase in temperature.
• This demand decreases due to incorporation of superplasticizer until the saturation point.
P.K. Mehta and P.J.M. Monteiro, Concrete: Microstructure, Properties, and Materials
High-strength concrete
Differences Between NSC and HSC In normal strength concrete, the microcracks form when the compressive stress reaches ~ 40% of the strength. The cracks interconnect when the stress reaches 80-90% of the strength For HSC, Iravani and MacGregor reported linearity of the stress-strain diagram at 65 to 70, 75 to 80 and above 85% of the peak load for concrete with compressive strengths of 65, 95, and 105 MPa.
P.K. Mehta and P.J.M. Monteiro, Concrete: Microstructure, Properties, and Materials
High-strength concrete
Differences Between NSC and HSC (2) The fracture surface in NSC is rough. The fracture develops along the transition zone between the matrix and aggregates. Fewer aggregate particles are broken. The fracture surface in HSC is smooth. The cracks move without discontinuities between the matrix and aggregates.
P.K. Mehta and P.J.M. Monteiro, Concrete: Microstructure, Properties, and Materials
High-strength concrete
Mechanical Behavior Stress-strain curve is more linear The strain corresponding to the maximum stress increases with strength The post-peak domain gets steeper The ultimate deformation decreases with the increasing strength
P.K. Mehta and P.J.M. Monteiro, Concrete: Microstructure, Properties, and Materials
High-strength concrete
Strength Based on 289 observations of moist-cured highstrength concrete samples made with Type III cement, Mokhtarzadeh and French obtained the following relationship
fcm
t = fc28 0.89 + 0.97t
P.K. Mehta and P.J.M. Monteiro, Concrete: Microstructure, Properties, and Materials
High-strength concrete
Long-term strength Iravani and MacGregor suggested the following strength values for sustained loading: 70 to 75% (of the short-time loading strength) for 65 MPa concrete 75 to 80% for 95 MPa concrete, without silica fume 85 to 90% for 105 MPa concrete, with silica fume 85 to 90% for 120 MPa concrete, with silica fume P.K. Mehta and P.J.M. Monteiro, Concrete: Microstructure, Properties, and Materials
High-strength concrete
Elastic Modulus Great care should be taken if using well-established equations developed for normal-strength concrete to estimate the elastic modulus of high-strength concrete. Extrapolation beyond the validity of the equations often leads to overestimation of the elastic modulus.
P.K. Mehta and P.J.M. Monteiro, Concrete: Microstructure, Properties, and Materials
High-strength concrete
Elastic Modulus for normal weight concrete with 21 MPa < fc < 83 MPa where Ec is the elastic modulus of concrete, fc the compressive strength.
E c = 3320 fc + 6900 MPa
P.K. Mehta and P.J.M. Monteiro, Concrete: Microstructure, Properties, and Materials
High-strength concrete
Data from Tomosawa and Noguchi
Elastic Modulus (MPa)
60000
40000
river gravel Crushed Graywack Crushed Quartz Crushed Limestone Crushed Andesite Blast furnace slag Calcined bauxite Crushed Cobble Crushed Basalt Lightweight CA Lightweight FA + CA Model
20000
0 0
50
100
150
200
Compressive Strength (MPa)
P.K. Mehta and P.J.M. Monteiro, Concrete: Microstructure, Properties, and Materials
High-strength concrete
Chemical and Autogeneous shrinkage During hydration of the cement paste in a closed system, the volume of the hydration products, , is less than the sum of the volume of water and the volume of cement that is hydrated. This leads to chemical shrinkage whose magnitude can be expressed by
ε ch
Vc ( =
+ Vw ) − Vh
Vci + Vwi
where and are the current and initial volume of cement, and and are the current and initial volume of water, respectively. P.K. Mehta and P.J.M. Monteiro, Concrete: Microstructure, Properties, and Materials
High-strength concrete
Early Volume Change
Before setting, the chemical shrinkage is not constrained and, therefore, it will induce shrinkage of the same magnitude in the cement paste. As a rigid network of hydration products starts to develop, the values of the chemical shrinkage and that of the measured shrinkage in the cement paste start to diverge, since the rigidity of the paste restrains the deformation.
P.K. Mehta and P.J.M. Monteiro, Concrete: Microstructure, Properties, and Materials
High-strength concrete
Definition of the autogenous shrinkage according to the Japanese Concrete Institute macroscopic volume reduction of cementitious materials
when cement hydrates after initial setting. Autogenous shrinkage does not include volume change due to loss or ingress of substances, temperature variation, and application of an external force and restraint.
P.K. Mehta and P.J.M. Monteiro, Concrete: Microstructure, Properties, and Materials
High-strength concrete
Definitions The definition of high-performance concrete is more controversial. Mehta and Aitcin used the term, highperformance concrete (HPC) for concrete mixtures possessing high workability, high durability and high ultimate strength.
P.K. Mehta and P.J.M. Monteiro, Concrete: Microstructure, Properties, and Materials
High-strength concrete
Definitions ACI defined high-performance concrete as a
concrete meeting special combinations of performance and uniformity requirements that cannot always be achieved routinely using conventional constituents and normal mixing, placing, and curing practice.
P.K. Mehta and P.J.M. Monteiro, Concrete: Microstructure, Properties, and Materials
High-strength concrete
Typical Classification
Normal Strength
20-50 MPa
High Strength
50-100 MPa
Ultra High Strength
100-150 MPa
Especial
> 150 MPa
P.K. Mehta and P.J.M. Monteiro, Concrete: Microstructure, Properties, and Materials
High-strength concrete
Microstructure From the general principles behind the design of high-strength concrete mixtures, it is apparent that high strengths are made possible by reducing porosity, inhomogeneity, and microcracks in the hydrated cement paste and the transition zone.
P.K. Mehta and P.J.M. Monteiro, Concrete: Microstructure, Properties, and Materials
High-strength concrete
Microstructure The utilization of fine pozzolanic materials in high-strength concrete leads to a reduction of the size of the crystalline compounds, particularly, calcium hydroxide. Consequently, there is a reduction of the thickness of the interfacial transition zone in high-strength concrete. The densification of the interfacial transition zone allows for efficient load transfer between the cement mortar and the coarse aggregate, contributing to the strength of the concrete. For very high-strength concrete where the matrix is extremely dense, a weak aggregate may become the weak link in concrete strength. P.K. Mehta and P.J.M. Monteiro, Concrete: Microstructure, Properties, and Materials
High-strength concrete
Materials - Cement Almost any ASTM portland cement type can be used to obtain concrete with adequate rheology and with compressive strength up to 60 MPa. In order to obtain higher strength mixtures while maintaining good workability, it is necessary to study carefully the cement composition and finenesses and its compatibility with the chemical admixtures. Experience has shown that low-C3A cements generally produce concrete with improved rheology.
P.K. Mehta and P.J.M. Monteiro, Concrete: Microstructure, Properties, and Materials
High-strength concrete
Materials -- Aggregate In high-strength concrete, the aggregate plays an important role on the strength of concrete. The low-water to cement ratio used in high-strength concrete causes densification in both the matrix and interfacial transition zone, and the aggregate may become the weak link in the development of the mechanical strength. Extreme care is necessary, therefore, in the selection of aggregate to be used in very high-strength concrete.
P.K. Mehta and P.J.M. Monteiro, Concrete: Microstructure, Properties, and Materials
High-strength concrete
Materials -- Aggregate The particle size distribution of fine aggregate that meets the ASTM specifications is adequate for high-strength concrete mixtures. If possible, Aitcin recommends using fine aggregates with higher fineness modulus (around 3.0). His reasoning is as follows: – a) high-strength concrete mixtures already have large amounts of small particles of cement and pozzolan, therefore fine particles of aggregate will not improve the workability of the mix; – b) the use of coarser fine aggregates requires less water to obtain the same workability; and – c) during the mixing process, the coarser fine aggregates will generate higher shearing stresses that can help prevent flocculation of the cement paste. P.K. Mehta and P.J.M. Monteiro, Concrete: Microstructure, Properties, and Materials
High-strength concrete
Guidelines for the selection of materials The higher the targeted compressive strength, the smaller the maximum size of coarse aggregate.
Up to 70 MPa compressive strength can be produced with a good coarse aggregate of a maximum size ranging from 20 to 28 mm.
To produce 100 MPa compressive strength aggregate with a maximum size of 10 to 20 mm should be used. To date, concretes with compressive strengths of over 125 MPa have been produced, with 10 to 14 mm maximum size coarse aggregate. P.K. Mehta and P.J.M. Monteiro, Concrete: Microstructure, Properties, and Materials
High-strength concrete
Guidelines for the selection of materials Using supplementary cementitious materials, such as blast-furnace slag, fly ash and natural pozzolans, not only reduces the production cost of concrete, but also addresses the slump loss problem. The optimum substitution level is often determined by the loss in 12- or 24-hour strength that is considered acceptable, given climatic conditions or the minimum strength required. While silica fume is usually not really necessary for compressive strengths under 70 MPa, most concrete mixtures contain it when higher strengths are specified.
P.K. Mehta and P.J.M. Monteiro, Concrete: Microstructure, Properties, and Materials
High-strength concrete
Usage of Superplasticizers Constant w/c: Increase in the workability
Constant workability: Lower w/c
same workability No admixture
MLS
SMF
SC
LOWER WATER CONTENT
Lower w/c
Courtesy from Prof. Gettu P.K. Mehta and P.J.M. Monteiro, Concrete: Microstructure, Properties, and Materials
High-strength concrete
Superplasticizer-Silica Fume Interaction
Without superplasticizer, the cement + water + silica fume system tends to coagulate, making the
use of a superplasticizer essential.
REPULSIVE FORCES Silica fume
COAGULATION
Silica fume
DISPERSION Courtesy from Prof. Gettu
P.K. Mehta and P.J.M. Monteiro, Concrete: Microstructure, Properties, and Materials
High-strength concrete
Selection of the Superplasticizer
Study of the compatibility
Optimum superplasticizer dosage
Cost-benefit considerations In several cases, this order is inverted, resulting in costly consequences
Courtesy from Prof. Gettu P.K. Mehta and P.J.M. Monteiro, Concrete: Microstructure, Properties, and Materials
High-strength concrete
Marsh Cone Test: Evaluation of the compatibility and dosage Comparison with yield shear stresses obtained with a viscometer
800-1000 ml 7.0
25
Cement I 52.5R w/c=0.33 Superplasticizer SD1
15.5 cm
20 6.5
Bingham yield stress (Pa)
6 cm
6.0
10
5.5 5
Diameter: 8 mm 5.0
200-500 ml
15
τ 0 (Pa)
29 cm
Flow time (s)
Marsh cone flow time (s)
0 0.5
1.0
1.5
2.0
2.5
% sp/c
3. 0
3.5
Courtesy from Prof. Gettu
P.K. Mehta and P.J.M. Monteiro, Concrete: Microstructure, Properties, and Materials
High-strength concrete
Practical Significance of the Saturation Point 210
Marsh cone flow time, s
w/c = 0.35 T = 22°C 170
60 min
Saturation Point
130
5 min
90
50 0.0
0.4
0.8
1.2
1.6
2.0
2.4
Superplasticizer dosage (% sp/c)
2.8 Courtesy from Prof. Gettu
P.K. Mehta and P.J.M. Monteiro, Concrete: Microstructure, Properties, and Materials
High-strength concrete
Cement/Superplasticizer Compatibility 200
Marsh cone flow time, s
180
w/c = 0.35 T = 23° C
60 min
160 140 120 60 min
Cement A
100
Cement B
80
5 min
5 min
60 0
0.4
0.8
1.2
1.6
2.0
2.4
Superplasticizer dosage (% sp/c) P.K. Mehta and P.J.M. Monteiro, Concrete: Microstructure, Properties, and Materials
2.8
High-strength concrete
Selection of Superplasticizer COST-BENEFIT RATIO
Time (s)
% sp/c CBR = × (cost/kg) × time (s) s.r.
CBR =
w/c = 0.33
CBR =
0.25 % sp/c × ( 3 euros/kg) × 5 s = 12.5 0.3 s.r.
1.5% sp/c ×( 1 euro/kg) ×7 s = 26.3 0.4 s.r.
Courtesy from Prof. Gettu P.K. Mehta and P.J.M. Monteiro, Concrete: Microstructure, Properties, and Materials
High-strength concrete
Factors that Affect the Saturation Point
• Type of cement • Water/cement ratio • Presence of mineral admixtures • Mixing sequence (better to separate the
incorporation of water and superplasticizer by at least 1 minute of mixing)
• Temperature Courtesy from Prof. Gettu P.K. Mehta and P.J.M. Monteiro, Concrete: Microstructure, Properties, and Materials
High-strength concrete
Effect of Temperature on the Loss of Fluidity
15
16
c = I 52.5 R sp = SN w/c = 0.33 sp/c = 1%
35ºC
5ºC
45ºC
10
15ºC 25ºC
5
0 5 15
30
45
60
75
90
Marsh Cone flow time (s)
Marsh Cone flow time (s)
20
12
c = I 52.5 R sp = SC w/c = 0.33 sp/c = 0.3% 35ºC 25ºC
8
15ºC 45ºC 5ºC
4
0 5 15
30
Time (min)
45
60
75
90
Time (min)
• Loss of fluidity in the paste is lower for polycarboxylate based superplasticizers.
• There is no clear trend with respect to temperature. Courtesy from Prof. Gettu P.K. Mehta and P.J.M. Monteiro, Concrete: Microstructure, Properties, and Materials
High-strength concrete
Effect of Temperature on the Water Demand of Cement
Water demand (w/c)
0.30
c = I 52.5 R sp = SN
0.28 0.26 0.24
45 ºC 35 ºC
0.22
25 ºC 0.20
15 ºC 5 ºC
0.18 0.0
1.0
2.0
% sp/c
3.0
4.0
• The water demand of cement increases with an increase in temperature.
• This demand decreases due to incorporation of superplasticizer until the saturation point.
P.K. Mehta and P.J.M. Monteiro, Concrete: Microstructure, Properties, and Materials
High-strength concrete
Differences Between NSC and HSC In normal strength concrete, the microcracks form when the compressive stress reaches ~ 40% of the strength. The cracks interconnect when the stress reaches 80-90% of the strength For HSC, Iravani and MacGregor reported linearity of the stress-strain diagram at 65 to 70, 75 to 80 and above 85% of the peak load for concrete with compressive strengths of 65, 95, and 105 MPa.
P.K. Mehta and P.J.M. Monteiro, Concrete: Microstructure, Properties, and Materials
High-strength concrete
Differences Between NSC and HSC (2) The fracture surface in NSC is rough. The fracture develops along the transition zone between the matrix and aggregates. Fewer aggregate particles are broken. The fracture surface in HSC is smooth. The cracks move without discontinuities between the matrix and aggregates.
P.K. Mehta and P.J.M. Monteiro, Concrete: Microstructure, Properties, and Materials
High-strength concrete
Mechanical Behavior Stress-strain curve is more linear The strain corresponding to the maximum stress increases with strength The post-peak domain gets steeper The ultimate deformation decreases with the increasing strength
P.K. Mehta and P.J.M. Monteiro, Concrete: Microstructure, Properties, and Materials
High-strength concrete
Strength Based on 289 observations of moist-cured highstrength concrete samples made with Type III cement, Mokhtarzadeh and French obtained the following relationship
fcm
t = fc28 0.89 + 0.97t
P.K. Mehta and P.J.M. Monteiro, Concrete: Microstructure, Properties, and Materials
High-strength concrete
Long-term strength Iravani and MacGregor suggested the following strength values for sustained loading: 70 to 75% (of the short-time loading strength) for 65 MPa concrete 75 to 80% for 95 MPa concrete, without silica fume 85 to 90% for 105 MPa concrete, with silica fume 85 to 90% for 120 MPa concrete, with silica fume P.K. Mehta and P.J.M. Monteiro, Concrete: Microstructure, Properties, and Materials
High-strength concrete
Elastic Modulus Great care should be taken if using well-established equations developed for normal-strength concrete to estimate the elastic modulus of high-strength concrete. Extrapolation beyond the validity of the equations often leads to overestimation of the elastic modulus.
P.K. Mehta and P.J.M. Monteiro, Concrete: Microstructure, Properties, and Materials
High-strength concrete
Elastic Modulus for normal weight concrete with 21 MPa < fc < 83 MPa where Ec is the elastic modulus of concrete, fc the compressive strength.
E c = 3320 fc + 6900 MPa
P.K. Mehta and P.J.M. Monteiro, Concrete: Microstructure, Properties, and Materials
High-strength concrete
Data from Tomosawa and Noguchi
Elastic Modulus (MPa)
60000
40000
river gravel Crushed Graywack Crushed Quartz Crushed Limestone Crushed Andesite Blast furnace slag Calcined bauxite Crushed Cobble Crushed Basalt Lightweight CA Lightweight FA + CA Model
20000
0 0
50
100
150
200
Compressive Strength (MPa)
P.K. Mehta and P.J.M. Monteiro, Concrete: Microstructure, Properties, and Materials
High-strength concrete
Chemical and Autogeneous shrinkage During hydration of the cement paste in a closed system, the volume of the hydration products, , is less than the sum of the volume of water and the volume of cement that is hydrated. This leads to chemical shrinkage whose magnitude can be expressed by
ε ch
Vc ( =
+ Vw ) − Vh
Vci + Vwi
where and are the current and initial volume of cement, and and are the current and initial volume of water, respectively. P.K. Mehta and P.J.M. Monteiro, Concrete: Microstructure, Properties, and Materials
High-strength concrete
Early Volume Change
Before setting, the chemical shrinkage is not constrained and, therefore, it will induce shrinkage of the same magnitude in the cement paste. As a rigid network of hydration products starts to develop, the values of the chemical shrinkage and that of the measured shrinkage in the cement paste start to diverge, since the rigidity of the paste restrains the deformation.
P.K. Mehta and P.J.M. Monteiro, Concrete: Microstructure, Properties, and Materials
High-strength concrete
Definition of the autogenous shrinkage according to the Japanese Concrete Institute macroscopic volume reduction of cementitious materials
when cement hydrates after initial setting. Autogenous shrinkage does not include volume change due to loss or ingress of substances, temperature variation, and application of an external force and restraint.
P.K. Mehta and P.J.M. Monteiro, Concrete: Microstructure, Properties, and Materials
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