Base course material

1. Pavement Research Group 18 SEAGC - Singapore - 2013
Improving Characteristics of Soil Cement in
Pavement by Nano-Silica

2. Soil Cement
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ACI 116 R (Cement and Concrete Terminology)
Mixture of soil and measured amounts of Portland cement and water
compacted to a highly density.
ACI 230.1 R (State-of-the-Art Report on Soil Cement)
Densely mixture of Portland cement, soil/aggregate , water used
primarily as a base material for pavement.
NOTE: Unlike concrete, it has lower cement and is so more porous that
individual particles is not completely coated with cement paste

3. Soil Cement Classification
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Cement-Modified Soil (CMS)
In this case, there is not standard design procedure and the cement is used to improve the performance
attributes of paving materials, particularly those which include silty or clayey soils in the sub-grade or
base layer. In CMS , it is reduced plasticity and water susceptibility or water content. Typically, a cement
content of 1% - 5% is used for this purpose.
Cement-Treated Base (CTB)
CTB uses more cement than CMS to develop the required tension strength in terms of flexural
resistance ,durability and modulus. The range of cement content in CTB varies from 2% - 10% as a
function of Unconfined Compressive Strength (UCS) in 7 or 28 days.
Full-Depth Reclamation (FDR)
The base aggregate is pulverised and recycled from old asphalt or wearing course material and base
material. FDR generally uses 3% - 6% cement content and can be designed as a modified or treated
layer.

4. Design Criteria
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Durability
Determination of cement content based on wet-dry cycles or freeze –thaw cycles ( ASTM D559, ASTM
560). Cement content about 3-5 % by wt for A-1-a ( PCA,1992)
In some countries such as Australia, priority has been given to other mechanical benchmarks due to
environmental conditions.
Fatigue
To achieve load repetition requirement
Flexural Strength (Modulus of Rupture)
Flexural –beam tests (or indirect-tension test) to estimate material
strength and corresponding modulus

5. Different Cement Requirements
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Although higher cement content is desirable according to durability
aspect but it can cause fatigue(modified case) and shrinkage issues.
[

6. Shrinkage
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Shrinkage Cracking
Cracking due to drying or environmental temperature change. Drying
because of moisture loss during hydration)
K.P. George ,PCA (2002)
Soil Type UCS7days
(KPa )
Max shrinkage
*10E-6
Crack
limit(mm)
Fine Grain <2070 525 1.5
Coarse Grain <3100 310 2.5
Shrinkage cracks can lead to deterioration and premature failure. As a
general rule, parameters such as cement content, moisture content,
density, compaction, curing, and the amount and type of fine particles
have a remarkable effect on the shrinkage cracking of soil cement

7. Shrinkage Effect Parameters
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2 (3CaO.SiO2) + 6H2O 3 CaO.2SiO2.3H2O + 3 Ca(OH)2
2 (2CaO2.SiO2) +4H2O 3 CaO.2SiO2.3H2O + Ca(OH)2
Hydration reactions rate.
The initial strength (first 7 days) relates to tricalcium silicate (C3S) and
later strength development is dependent on dicalcium silicate (C2S),
which reacts more slowly
Water:
Czernin (1962) stated that hydration reactions need a low amount of
water: cement ratio of around 1:4

8. Cement Paste Pores:
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Based on the International Union of Pure and Applied Chemistry
(IUPAC) classification, the pore structure is classified as:
Micropores: less than 25 nm
Mesopores: between 25 and 500 nm
Macropores: between 500 nm and 50 μm
Tristar II 3020 for
nitrogen adsorptionSuction pressure Versus Pore sizes (Chakrabarti et al,2007)

9. Pore Size Distribution
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Cumulative pore-size distribution curve (nm) for cement
paste at varying degrees of hydration, Bentur (1980).
From mercury porosimetry tests:
It is clear that the threshold diameter is reduced from 1000 nm down to 100 nm and up
to the point of 60% hydration with Portland cement paste. Beyond 60% hydration, the
more hydration, the greater the decrease in pore volume which goes from 80 nm down
to 30 nm in diameter. There is also a small reduction in mesopore volume, in contrast to
its continuous increase with hydration

10. Micro to Meso pores effect:
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Shrinkage is caused by pores within the range of micropores and
mesopores sizes, i.e. pore sizes between 2.5 nm and 30 nm, Bentur (1980)

11. Pozzolanic Additives
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Pozzolanic additives react with free lime or calcium hydrate Ca(OH)2 and
they produce similar products to those of hydration reactions. The
pozzolanic reaction of silica oxides has not been studied in as much depth
as has the hydration of cement.
3Ca (OH) 2 + 2SiO2 → 3 CaO.2SiO2.3H2O
• Ground Granulated Blast furnace Slag
• Fly ash
• Silica Fume
• Cement Kiln Dust

12. Other Benefits of Pozzolans
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Hence, it seems that the pozzolanic additives
are able to cover cement product deficiencies
in pore structure and create a balance between
shrinkage and soil-cement durability or strength
• Filling properties of pozzolanic material at the micro-level may be more significant
than the pozzolanic chemical effect.(Goldman and Bentur, 1994)
• Improve packing state, and decreases the amount of filling water (Zhang Chengzhi,
1996)

13. Nano Silica
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BSI, PAS71:
Nano-scale are particles that has one or more dimensions less than 100 nm
Nano-modified construction materials
are known for their higher strength,
greater durability, increased speed of
construction.
Nano silica (nS) has more than 98 % SiO2
with particle sizes in the range of 10 nm-
30 nm
These particles are able to make changes at the molecular level to modify material
characteristics at the macro-level.
Particle morphologies:Silca fume(Left),Nano-
silica(Right) , Byung-Wan Jo (2007)

14. Conclusion
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 Although it has done lots of research on soil cement by
different additive or pozzolanic material, but there isn't a way to
make balance between different design object.
 Nano-Silica is suggested for further research to achieve
opposite cement contents required.

15. Thank you