of the Pozzolanic reaction in Peat clays for stabilization by Calcium Carbide
Residues with fly ash
Supervisor(s): Dr. A.S. Ranathunga
of Civil Engineering
OF MORATUWA – SRI LANK
1. Introduction. 1
2. Statement of the problem.. 2
3. Significance of the research. 2
4. Scope and Limitations of the study. 3
5. Objectives of the research. 4
6. Proposed Methodology. 4
7. Time Schedule. 6
8. Estimated cost built up. 7
9. References. 8
In the present
most of geotechnical engineers and highway engineers who work under
construction of expressways through areas underlain by soft peaty clays face
major challenge which is the improvement of strength and stiffness
characteristics of such soil in-situ within relative short period of time.
Peaty clay has characteristics of high compressibility and
low stability. So this soil should be stabilized prior to the constructions.
Sri Lanka several remedies are taken such as: ground improvement techniques and
removal existing soil and filling back with granular soil etc. As ground
improvement techniques based on consolidation, pre-loading with vertical drains
has been used successfully in the present. But the problem is the long time
duration for these processes. Lots of researches are being implemented and some
of them have been already done under this scenario.
Soft peaty clay is commonly
encountered in recent construction projects in Sri Lanka. It had been improved
mainly by different techniques of Pre-Consolidation. If peat clay is mixed
in-situ with an appropriate binder material, significant rise in strength and
stiffness may be achieved within short time period. Cement was a suggested as a
binder material which was mixed in-situ with peaty clay. In laboratory
experiment studies, required cement content was high to be treated with peaty
clay. The percentage of cement added should be greater than 15% to achieve a
reasonable improvement. (W G S Munasinghe, 2001) When we
regard the weight of cement needed, it was about 150 – 250 kg per cubic meter
of treated soil. Thus
cost of this treatment would be very high. Therefore any alternative materials
are to be needed as binder material or any material is used to reduce the
required cement content. (S A S
studies are focused on using industrial byproducts to replace the cement usage.
Further, use of these byproducts reduces the higher costs associated with the
process and also are environmental friendly. Calcium Carbide Residues (CCR) is
one such byproduct from manufacturing of Acetylene gas. It is also used to
enhance stabilization process of peat clay by mixing. Fly ash (FA) is also a
byproduct of coal power plants and it is also used for such purpose. In this
research we mainly focus on adoption of CCR and FA from various proportions.
There several factories manufacturing acetylene gas in Sri Lanka such as Ceylon
Oxygen Limited in Colombo 15, Industrial Gases (Pvt) Ltd at Supugaskanda and
Ovin Gases (Pvt) Ltd at Nugegoda etc. We will get CCR from these factories
freely. Fly ash will be available from Norochcholi power plant. As both
materials are freely available in Sri Lanka, we have selected these materials
for this research.
Statement of the problem
In Sri Lanka, soft peat clay is most probably encountered during
Construction of highway embankment. When that soil is used for constructions
without doing any soil improvement techniques, life time of the road will be
less, can cause for construction failures and much time is taken for the
stabilization process. Therefore,
Engineers have to find solutions to overcome this problem. Up to now several
precautions have been taken by doing researches.
When we take remedies for this issue, we should think that it would be
cost effective, that process can be continued with less amount of drawbacks and
required materials are easily available.
Mixing cement with peat clay is used as a remedy today. It will enhance
the strength as well as the permeability characteristics of peat. But this
method is costly. That is the drawback of it.
Generally in Sri Lanka, FA are mainly generated from the Norochcholai
power plant and it is categorized under Class F. Calcium content is
significantly low in Class F fly ash. Hence when we use that type FA for the
improvement of peat clay, it could not provide required enhancement. Because
CaO content is 12.15% in FA and 70.78% in CCR. (Suksun Horpibulsuk, 2012)
of the research
The outcome of this research is very significant for Geotechnical
engineers and Highway engineers. This research is based on experimental study.
Although several researches were carried out under this statement of the
problem, more effective and useful remedy could not be achieved yet. That is
why this research is going to be done while supervising previous results of
Improvement of soft soil characteristics is vital in road embankment.
Peat clay is the most common soil type which is encountered in the site
underlying with thick layers. In the extension of Southern expressway project,
the heaviest soil type is the peat clay. So this soil must be stabilized prior
to construction. If cement is used for stabilization process, high amount
cement will be needed then it will be more expensive.
Both FA and CCR are easily available in Sri Lankan industry. Thus both of
them are useful for the improvement of soft clay characteristics. Since they
are available with high amount, adoption of them is very useful for the
extension of Southern Expressway project.
and Limitations of the study.
This research is not focused on a single parameter. When soil is
stabilized by using any method, we want to know how strength behavior, flow
behavior, what consolidation characteristics there and what microstructural
characteristics in that soil. This research will be going under consolidation
characteristics of peat clay which directly represented field behavior of the
treated soil. Here calcium carbide is the key component to be used to enhance
the pozzolanic reaction in peat clay. Combination of FA and CCR are going to be
added and then we can select best percentage and proportion of them by carrying
out the experiments.
We should regard specially for secondary consolidation settlements in
peat clay. It typically shows large amount of secondary consolidation
settlements. So here the effect on the parameters corresponding to primary and
secondary consolidation are going to be analyzed.
Considering time durations for the current project, several combinations
will be adopted. The samples for the research are collected from Southern
Expressway extension project and will be used as remoulded specimens to avoid
the higher heterogeneity of the samples.
of the research
Many Geotechnical researchers have used various materials
and techniques in an attempt to improve engineering characteristics of peaty
clay underlying in road embankment constructions. Early study for improvement
of peaty clay presented various methods of stabilization in practice at the
time. In the present, required time for stabilization process of peaty clay can
have been minimized in road embankment construction. The main aim of this
the suitability of using CCR as a high calcium additive to improve the
pozzolanic reactions of FA
This will be achieved using the following sub-objectives:
optimum mix proportion of CCR and FA to obtain the best consolidation
characteristics suitable for the filed application.
the micro-structural variation of the soil due to the addition of CCR and FA.
Peat will be brought from the
Extension of Southern Expressway project. At the very first, all debris and
other incidental particles should be removed. When the peat sample keep in the
laboratory, buckets of sample should be filled with water as the top surface of
peat must be fully submerged. Materials for mixing especially flay ash and
calcium carbide will be brought from places mentioned above. Then preparation
of sample for selected mixing proportions will be commenced as next stage. Then all samples should be cured well. Curing
should be done separately to the sample for 28 days and 90 days. First of all
basic properties of peat will be determined by doing tests as follows:
After 28 days
all tests will be started to carry out for different mix proportions. In this
research, laboratory consolidation test (Oedometer test) will be carried to the
prepared peat samples as following mix proportions.
No of tests for
One test by one
will have to be done and take results. If the results are more deviated than
what we are expecting, that particular samples must be tested again. Finally
all results are going to be analyzed. When the curing time for 90 day will
accomplish, tests of them will be carried out. Those results also should be
analyzed then we can come to a conclusion about this research.
of material and equipment
of the research proposal
of the literature review
of the different mixes in selected proportions
property testings for peat
out tests for 28 days cured samples
time for 90 day Testing
out tests for 90 days cured samples
Estimated cost built up
No of Units
Price/ unit (Rs)
10mm Steel Bar
· S A S Kulathilaka, D. R. (n.d.). Enhancement of
Engineering Characteristics of Peaty Clay due to Mixing With Cement.
· Suksun Horpibulsuk, C. P. (2012). Strength
development in silty clay stabilized with calcium carbide residue. Nakhon
· W G S Munasinghe. (2001). Methods for Improvement
of Engineering properties of Peat. Moratuwa.