2. 2
04.09.2022/GRI
Concrete and Aggregates Div. Cement Applications Course
Learning Objectives
Provide a basic understanding of the fundamental
concepts of concrete in the fresh and hardened state
3. 3
04.09.2022/GRI
Concrete and Aggregates Div. Cement Applications Course
Table of Content
1. What is Concrete?
2. What is Fresh Concrete?
3. What is Hardened Concrete?
4. Pore structure of Hydrated Cement Paste
Its effect on:
Strength
Permeability/Durability
Drying Shrinkage
4. 4
04.09.2022/GRI
Concrete and Aggregates Div. Cement Applications Course
What is Concrete?
Cement
Aggregates
An Artificial Rock,
mainly made of:
Admixtures
Water
5. 5
04.09.2022/GRI
Concrete and Aggregates Div. Cement Applications Course
Materials (kg) to prepare 1 m3 of Concrete
300
180
1900
Cement
Water
Aggregates
One cubic meter of normal concrete weighs ca. 2’400 kg
6. 6
04.09.2022/GRI
Concrete and Aggregates Div. Cement Applications Course
What is Fresh Concrete?
Fresh concrete is a concentrated suspension of solids in
water
Solids range widely in size
Size Range Designation Role in Fresh
Concrete
1 µm – 100 µm „Fines“
(Binders+Dust)
Specific Surface/
Cohesion
100 µm – 5 mm „Sand“ Specific Surface/
Cohesion + Filler
> 5 mm (usually
up to ca.30 mm)
„Gravel“ Filler
7. 7
04.09.2022/GRI
Concrete and Aggregates Div. Cement Applications Course
What is Fresh Concrete?
The sand and gravel particles are not in contact with
each other, but separated by a layer of „cement paste“
Cement paste is composed of water, the „fines“ (binders
+ dust) and air (entrapped or entrained)
8. 8
04.09.2022/GRI
Concrete and Aggregates Div. Cement Applications Course
What is Fresh Concrete?
The ability to flow of the fresh concrete depends,
basically, on the thickness and the viscosity of the
cement paste layer that separates the sand and gravel
particles
The easier the relative motion between the aggregate
particles, the more flowable the concrete becomes,
which happens:
The thicker the layer (i.e. the higher the content of the
cement paste in the mix and the coarser the aggregate
grading)
The less viscous the layer (i.e. higher water/fines ratio, use
of chemical admixtures )
10. 10
04.09.2022/GRI
Concrete and Aggregates Div. Cement Applications Course
Can withstand heavy loads in the fresh state
(RCC: Roller Compacted Concrete)
Some concretes……
14. 14
04.09.2022/GRI
Concrete and Aggregates Div. Cement Applications Course
Can flow freely down along chutes
Can flow like liquids without segregation (SCC)
Some concretes……
15. 15
04.09.2022/GRI
Concrete and Aggregates Div. Cement Applications Course
Can be demoulded immediately after compaction
Withstand heavy loads in the fresh state (RCC)
Can be raised with conveyor belts
Can be pumped at long distances and heights
Can be pneumatically sprayed
Can flow freely down along chutes
Flow like liquids without segregation (SCC)
Conclusions
Varying the rheological characteristics of fresh concrete
it is possible to produce concretes that:
17. 17
04.09.2022/GRI
Concrete and Aggregates Div. Cement Applications Course
What is Hardened Concrete?
Hardened concrete is a composite material, with a
discrete phase (the aggregate) dispersed in a
continuous phase (the cement paste matrix)
18. 18
04.09.2022/GRI
Concrete and Aggregates Div. Cement Applications Course
What is Hardened Concrete?
The discrete aggregate particles are glued („cemented“)
together into a monolithic material by the hardening
cement paste matrix
19. 19
04.09.2022/GRI
Concrete and Aggregates Div. Cement Applications Course
Unhydrated cement
Advanced hydration
Sketch of the growth of hydration products
Initial hydration
SEM at 1 hour
25. 25
04.09.2022/GRI
Concrete and Aggregates Div. Cement Applications Course
Microstructure of hardened cement paste
Remaining
Unhydrated
Cement
Consumption of unhydrated cement
26. 26
04.09.2022/GRI
Concrete and Aggregates Div. Cement Applications Course
Microstructure of hardened cement paste
Gel pore (≈ 2 nm)
C-S-H crystal
Model of microstructure of hydrated cement paste
Capillary pore
(10nm – 5 μm)
27. 27
04.09.2022/GRI
Concrete and Aggregates Div. Cement Applications Course
Microstructure of hardened cement paste
Adsorbed water
Gel water
Water strongly bound to C-S-H crystals,
leading to shrinkage when removed by drying
H2O (≈ 0.25 nm)
Water in small
capillary pores
(< 50 nm)
28. 28
04.09.2022/GRI
Concrete and Aggregates Div. Cement Applications Course
Water strongly bound in gel and small pores
Water in small pores (< 50 nm) is in a
“quasi-solid” state, due to the strong
interaction with the walls of the pores
(C-S-H- crystals), putting them under
stress
29. 29
04.09.2022/GRI
Concrete and Aggregates Div. Cement Applications Course
Removal of strongly bound water leads to shrinkage
The removal of water molecules due to
evaporation alters the stress equilibrium,
leading to a reduction of the space
between C-S-H- crystal layers and, thus,
to drying shrinkage.
