Presentation on the "Improvement of the geotechnical properties of lateritic soil using gypsum" at the" 17th African Regional Conference on Soil Mechanics and Geotechnical Engineering" from "7th - 9th October 2019"

1. Improvement of the geotechnical
properties of lateritic soil using
gypsum
Daniel Adeleke & Denis Kalumba
University of Cape Town, Department of Civil Engineering, South Africa
Sylvester Osuji
University of Benin, Department of Civil Engineering, Nigeria

2. Outline
• Introduction
• Materials and methodology
• Results
• Discussion and conclusions
2 Laterites as subgrade without stabilization, an illusion.

3. Introduction
• Not every soil is suitable for construction purposes.
3
Dam failure in Zambia triggered by
continuous erosion (FAO, 2010)
Slope failure in Laos initiated by exc
rainfall (SEACAP, 2009)

4. • Lateritic soil are important weathered
engineering material available in most tropical
countries.
• They are affected by climatic conditions and
parent material, hence, they vary in
characteristics as identified in various part of
the tropics.
• In Nigeria, laterites occur in large deposit over
cretaceous and tertiary sediment/bedrock, and
are used for building, road and dam
construction.
• Most often they are not suitable for major
engineering applications due to the presence of
clay and silt, hence the need for improvement.
4
What are laterites?

5. • Soil stabilization, aimed at improving the
engineering property of the laterite can be
achieved mechanically or chemically or
combination of both.
• For instance, an investigation by Degirmenci et al
(2007) revealed an improvement on lateritic soil
by using phosphogypsum, cement and fly ash as
chemical stabilizers.
• Studies examining the use of gypsum as the sole
stabilizer in improving laterite has not been fully
explored.
• Natural resources, reveals that 1 billion tons of
gypsum is deposited across Nigeria, therefore, it
can act as an economic substitute for cement and
other stabilizers.
5
What is laterites stabilization?

6. Materials and methodology
• The objective of this study was to investigate
the obtainable improvement of gypsum-
stabilized laterite.
• To achieve this, the index properties (IP) of
the laterite without gypsum (CaSO4.2H20)
were acquired, see next slide.
• Test such as sieve analysis, specific gravity,
Atterberg limits, Proctor, and California
bearing ratio (CBR), were carried out to
obtain IP according to BS 1377: 1990 No 2
&4.
• Having obtain the IP of the laterite, varying
percentages of gypsum (3%, 5%, 7%, 9%
and 11%) were added to the soil, and tests
repeated.
6

7. 7
Characteristics Data
Natural moisture content (%) 16,90
% passing BS No 200 sieve 1,5
Liquid limit (%) 37,10
Plastic limit (%) 16,62
Plasticity index (%) 20,48
AASHTO classification A-2-6
USCS classification SC
Maximum dry density MDD (kg/m3) 1430
Optimum moisture content OMC %) 15,8
Specific gravity (SG) 2,65
Colour of air-dried sample Brown
Material Constituent Percentage
(%)
Gypsum
CaO 32,6
SO3 46,5
H2O 20,9
Chemical composition of gypsum.
Properties of natural laterite.
Materials

8. 8
Results
Testing
(BS
1377)
Sample
preparat
ion
Methodology Experimental procedure
Testing
(Atterberg,
Proctor and CBR)
Experiment on
laterite only
0% gypsum
Experiment on
laterite stabilized
with gypsum
3%, 5%, 7%, 9% &
11% gypsum

9. Results
Behavior of materials before and after adding gypsum
9

10. Results
Effects of gypsum on laterite’s Atterberg limits
10
10
15
20
25
30
35
40
-1 1 3 5 7 9 11
Moisturecontent(%)
Gypsum %
Liquid limit Plastic limit

11. Results
Effects of gypsum on laterite’s maximum dry densities
11
1.55
1.6
1.65
1.7
1.75
1.8
-1 1 3 5 7 9 11 13
Maximumdrydensity,(kg/m3)
Gypsum %
Maximum Dry Density

12. Results
Effects of gypsum on laterite’s optimum moisture content densities
12
14.5
15
15.5
16
16.5
17
-1 1 3 5 7 9 11
Optimummositurecontent(%)
Gypsum %
Optimum Moisture Content

13. Effects of gypsum on laterite’s CBR value
13
0
5
10
15
20
25
30
35
-1 1 3 5 7 9 11
CBR(%)
Gypsum %
CBR
Results

14. Discussion and conclusion
• Stabilizing laterite with gypsum generally reduces the liquid limit, increases the
plastic limit and reduces plasticity index, which is a positive indicator of the ind
ex property.
• Increase in gypsum content resulted in an increase in density while the inverse
was recorded for moisture content. It would be more suitable in scenarios with
water scarcity.
• Gypsum stabilization generally increases the CBR of laterites, with the CBR val
ue of 30.0% obtainable at 11% gypsum content, which makes laterite applicabl
e for highway subgrade and embankment construction.
14
Subgrade without gypsum stabilization Subgrade with gypsum stabilization

15. Thank you for listening
15

16. 16