EARTHBLOCKS IN THE SUDD: FINDING SOLUTIONS ON UNLIKELY TERRAIN
Chris Rollins, P.E.
Senior Engineer, AECOM International South Sudan
cebengineering@gmail.com
John Thon N’gor
Best Practices Engineer, AECOM International South Sudan
thonngor@gmail.com
Abstract
South Sudan is an extremely difficult location for construction due to ubiquitous expansive clay soil, extreme dry and wet
seasons, a very poor road system unusable for over half the year, and frequent tribal violence. Despite these obstacles, since
2010 USAID has funded the construction of remote government offices in an effort to promote governance and stability. The
South Sudan Transition and Conflict Mitigation program has now built over a dozen structures using stabilized soil block
technology in the seasonal swamp of the White Nile using the in situ Montmorillonite Clay ('black cotton soil') stabilized with
cement and blended with locally available fine sand.
In 2013, AECOM implemented a USAID funded grant to explore Best Practices to improve construction methods and costs,
while improving building utility and thermal performance:
•
•
•
California Bearing Ratio, compression testing, and rupture testing of blocks made with alternative stabilizers,
including lime, Claycrete™, ANSS™, and Earthzyme™, to optimize costs and durability
Refinement of building detailing to promote passive cooling and reduce load from fans on PV system
Piloting of Earthbags as an alternative to Stabilized Soil Blocks to achieve a lower cost and better durability
This paper documents lessons learned and data collected, while mapping the way forward as USAID expands its program of
remote construction toward better governance for the world's newest country.
Keywords
South Sudan, Sudd, Jonglei, Africa, compressed earth block, CEB, stabilized soil block, SSB, earth bag, earthbag, expansive clay,
black cotton soil, Montmorillonite, vertisol, stabilizer, stabilization, stabilisation, cement, lime, passive cooling, confined
masonry, Hydraform, Makiga, USAID, AECOM, OTCM, SSTCM.
Introduction
South Sudan suffers from a massive underinvestment in infrastructure and governance due to decades of civil war, a very rural
and uneducated population, and geographical isolation. In addition, the introduction of cheap and plentiful light arms has
made the traditional culture of cattle raiding more brutal and costly in terms of human life. The US Agency for International
Development (USAID) administers the South Sudan Transition and Conflict Mitigation (SSTCM) program through implementing
partner AECOM International South Sudan (AISS) in an effort to stabilize the main areas of conflict and facilitate a more
orderly national transition from civil war to independent and viable statehood.
A major part of this program is the construction of governmental offices and other municipal structures such as chambers of
commerce, traditional authority centers, and judicial court buildings in rural areas far from urban centers. These engineered
buildings include a reinforced concrete frame, rooftop rainwater harvesting to HDPE water storage tanks, lights and fans
coupled to photovoltaic power systems, and CODAN radios. In 2013, SSTCM greatly increased both the quantity and quality of
construction, and also conducted research to improve soil stabilization, to monitor passive cooling performance, to better size
and specify photovoltaic systems, and to explore the viability of alternative water storage tank materials. This grant and
lessons learned from the 2013 projects will drive 2014 construction, which aims to create a new standard by which other rural
projects will be measured, as well as provide guidance to other organizations doing remote infrastructure.
Figure 1 - Traditional Payam Headquarters in Wickol, Jonglei State.
Figure 2- New Payam Headquarters in Alor, Lakes State.
There are major constraints on this program. These include the difficulty of travel through the Sudd, a massive swamp formed
by the White Nile River, expansive Montmorillonite clay in this wetland, seasonal fighting over resources, and an absence of
skilled local labor for construction. Most importantly, the current program does not provide for extended operations and
maintenance of the built infrastructure; coupled with the lack of skill and resources on the part of the local beneficiaries, this
means that the building and its component systems have to be designed as robustly as possible to remain functional until
some future date when South Sudan government partners will be responsible for their care and maintenance. Ultimately, we
believe a building engineered with a holistic approach to materials, layout, energy, and water should cost less to build and
maintain, while also delivering a higher standard of comfort and utility.
Existing Design
Figure 3 - Payam design showing foundation, gradebeam, compressed earthblock layout, doors and windows, and furniture for scale.
The current Payam Headquarters building design, which is the standard for the other structures built by SSTCM, is a 6m x 16m
reinforced concrete frame on pad foundations, with 250mm x 250mm grade beam, non-structural compressed earth block
walls stabilized with 8-12% cement, steel doors and windows, a 200mm x 200mm ring beam, and a wooden trussed hip roof
with steel sheathing. In 2013, this structure was designed on a 3m x 4m ‘module’ to make detailing throughout the building
uniform: concrete and reinforcement specification for the 4m beams was also used in the 3m beams, and stirrup spacing is
regular throughout the grade beams, ring beams, and columns respectively. Although there are two distinct soil types in the
country (the far western and northern areas of Bahr el Ghazal have less expansive lateritic soils, locally called red murram),
the foundation for each project is specified at an assumed worst case scenario on clay soil. This uniformity of the design
greatly enhanced the management of the fourteen new buildings constructed, as the small team of four inspectors would
expect the same dimensioning on each structure, and plan reading by less skilled construction personnel was eased with
uniform rebar spacing throughout the structure. However, this also reduced structural efficiency and increased material
costs.
Figure 4 - Dablual Payam Headquarters, Unity State.
Figure 5 - Manajoka Payam Headquarters, Unity State (CMU construction).
Figure 6 - Jaac Payam Headquarters, Northern Bahr el Ghazal State.
Figure 7 - Alor Payam Headquarters, Lakes State.
Passive Cooling
A significant new feature in the 2013 design is passive cooling. Three methods that contribute to human comfort in the built
environment were identified as viable for the Payam projects:



Ventilation: increase size of window openings and install vents above doors and windows.
Reduce heat gain: increase the overhang of the soffit to 1350mm to achieve full shading of the south wall on 21
December1 to reduce radiant heat gain, and orient the building East-West to ensure that this overhang is most
effective (lower sun angle in morning and evening is on smallest facades, not largest)
Shed heat: introduce soffit and ridge venting to evacuate heated air in the attic through convection
Due to lack of skill on the part of inspectors and construction personnel, as well as the difficulty to regularly travel to some
sites due to weather and conflict, some features of the passive cooling design were not achieved: soffit venting on some
projects was diminished by the inclusion of wooden blocking above the roof truss plate, some overhangs were as small as
80cm, and some buildings are not oriented exactly east west, meaning they receive oblique sunlight at a time when other
buildings would be fully shaded. Luckily, this irregularity also resulted in the Dablual structure being built with galvanized iron
sheathing, which returned remarkable results compared to the other buildings with blue and green roofs.
Figure 8 – Blocking in soffit at roof truss plate,
Majok Yith Thiou Payam.
Figure 9 – Building orientation allowing oblique
sunlight on the north wall, Dablual.
Figure 10 – Mesh and soffit at Jaac Payam.
The goal of passive cooling in these buildings is to solve several different issues: local staff may be more willing to come to
work and stay if the building is cooler than any local structure (or even sitting under a tree, as many afternoons are spent in
the villages); it will reduce the load on the photovoltaic system from fans; and ultimately, it may eliminate the assumption
1
When the angle of the sun is the closest to the horizon at noon.
that modern buildings in South Sudan require air conditioning to be habitable. The buildings performed much better than
expected, based on the results of the temperature and humidity data study (see next section), and further lowering of interior
temperatures, beyond what could be achieved with proper venting, overhang, and the galvanized roof sheathing, may require
active measures such as fans, evaporative cooling, or foundation ventilation.
Temperature and Humidity Data Study
Through the Best Practices grant, 30 Logtag™ HAXO-8 temperature and humidity data loggers were purchased and distributed
to the various job sites for accurate measurement of building parameters at 15 minute intervals. Three of these devices were
placed in each structure: one in the attic at the center of the building 50cm above the ceiling; one in a central room on the
middle wall 200cm from the floor; and one on the back of the building at the center column, 50cm below the ring beam.
Although a significantly lower indoor air temperature was achieved by all buildings during the day (see Figure 12 and Figure
13), several significant findings were identified:





All structures were significantly cooler during the day than the ambient temperature, by as much as 12°C.
All structures enjoy a lag between the hottest time of the day (approximately 2:30 p.m.) and the hottest time in the
interior (4:30 p.m.), which is beneficial in an office facility where the building is not occupied in the evening.
Nighttime interior temperatures are 2-3°C higher than ambient, suggesting that the design should be improved for use as
an inhabited structure. This would also achieve a lower temperature at 7 a.m. when the building begins it heat gain cycle,
which could possibly result in lower afternoon temperatures as well.
The Dablual Payam has significantly lower interior temperatures than the other structures, and it also has a lower attic
temperature throughout the day. This is apparently due to galvanized roof sheathing; all other structures have anodized
blue or green colors.
The Manajoka Payam is made with Concrete Masonry Units (CMUs). These have a significantly lower thermal mass, which
may explain why interior temperatures are relatively high during the day; however the lag is similar to the CEB walls (one
would assume that a lower thermal mass would have a lower lag time as heating and cooling would be relatively faster),
and the interior temps are also very high at night, when it is assumed the lower mass walls would cool faster and to a
lower temperature (see Figure 13). This is probably due to radiation from the walls toward the interior while the building
cools. Presumably, a higher thermal mass, achieved by packing the voids with soil for example, would reduce interior
temperatures.
The following table details temperature and humidity averages in various buildings:
Payam
Dablual
Manajoka
Jaac
Alor
Paweng2
Rumaker
Average
Ambient
Max Temp
(˚C)
40.5
35.5
38.5
36.2
39.1
40.4
Average
Internal
Max Temp
(˚C)
31.1
30.6
31.6
31.2
32.1
32.5
Max
Differential
(not average)
(˚C)
-12.2
-8.9
-9.6
-8.2
-15.0
-10.4
Average
Ambient
Min Temp
(˚C)
27.0
24.0
27.5
26.1
26.3
27.3
Average
Internal
Min Temp
(˚C)
29.6
28.3
29.5
28.5
29.6
30.0
Average
Nighttime
Differential
(˚C)
+2.6
+4.3
+2.0
+2.4
+3.3
+2.7
Average Ambient
Min Relative
Humidity
(%)
31
46
32
39
32
28
Table 1 - Temperature and Humidity data for selected buildings.
These nighttime differentials suggest that significant additional cooling may not be achieved with passive measures, as the
differences between the minimum ambient temperature and the minimum internal temperature are very low, 2-4°C, and this
small ΔT may not allow for additional heat shedding3. One avenue for exploration is the application of active cooling
techniques, such as evaporative cooling during the day, when the relative humidity is the lowest, for example by trickling
water down the interior of a hollow CMU or SSB wall. This design is currently under development, but considering the lack of
maintenance to be expected by the occupants, and the possibility for mold growth within the wall due to the moist
environment, it is not expected that this is a viable long term solution; however, it will be explored for research purposes and
the data gathered as proof of concept as an alternative to air conditioning in rural areas, which would require both
maintenance and significantly more electrical energy from the PV system.
2
Orientation is N-S, not E-W, meaning that structure receives full sun in morning and evening, resulting in higher ambient
temperatures on the face where ambient was measured.
3
Note that actual ambient temperatures may be lower than the results given by data loggers affixed to the external surface of the
building, however it was agreed that this location would minimize the chance of theft over the period of construction.
Another option is the use of ventilation through tubes under the floor slab, where incoming air to the building could be cooled
by the earth. This approach would require fans to push the cooler, denser air into the building, and this air may not be
sufficient to achieve perceptible improvements in indoor comfort. This technique must be further researched and modeled to
determine its viability in remote construction.
Psychrometric Chart at 95.5 kPa
0.0220
0.0200
Manajoka
0.0180
Dablual
0.0160
Jaac
0.0140
0.0120
0.0100
0.0080
Humidity Ratio (kgw/kgda)
Alor
0.0060
0.0040
ASHRAE Comfort Zone
0.0020
0.0000
0
10
20
30
40
50
Dry Bulb Temperature ( C)
Figure 11 – Psychrometric chart at 95.5kPa showing building averaged temperature and humidity ranges.
Figure 11 illustrates the temperature and humidity averages of the four different structures included in this study. Although
the ASHRAE Comfort Zone, which is based on polling of North Americans on perceptions of indoor comfort, is arguably not
applicable in a region where people are unaccustomed to modern comfort and have lived in much hotter conditions for
generations, the chart illustrates the indoor conditions as a factor of humidity and temperature, and it also shows that to
achieve a western level of comfort in this region, both temperature and humidity ratio must be reduced. Of the two,
temperature is the easier to manipulate, but significant reductions (i.e. greater than 2-3˚C) will not be possible without some
kind of active system, whether it is a fan, an evaporative cooling system, or some other mechanism to move air or water
through the building.
40C
Dablual Ambient
38C
Dablual Attic
Dablual Interior
36C
Average Temperature
Average of all buildings shown in black.
Manajoka Ambient
34C
Manajoka Attic
Manajoka Interior
32C
Jaac Ambient
30C
Jaac Attic
Jaac Interior
28C
Alor Ambient
26C
Alor Attic
Alor Interior
24C
0:00
3:00
6:00
9:00
12:00
15:00
18:00
21:00
0:00
Time of Day
Figure 12 – Average temperatures in selected buildings.
160
125%
Dablual Ambient
Percentage = Interior Index / Ambient Index
120%
150
Manajoka, with CMU walls,
is worst performer
110%
105%
130
Jaac, with best venting,
cools more at night
than other buildings
100%
120
95%
90%
110
85%
100
Dablual (galvanized roof) has
lowest relative daytime
temperatures
6:30 - 7:00 a.m. typically the
coolest time of day,
Index = 100
80%
90
75%
3:00
6:00
Figure 13 – Indexed temperatures in same buildings.
9:00
12:00
Time of Day
15:00
18:00
21:00
0:00
Percentage = Interior Index / Ambient Index
Indexed Temperatures
140
0:00
Dablual Interior
115%
Manajoka Ambient
Manajoka Interior
Jaac Interior
Jaac Ambient
Alor Ambient
Alor Interior
Stabilizers
The vast interior of South Sudan is comprised of a seasonal flood plain of the White Nile River, which over the millennia has
deposited a deep layer of Montmorillonite clay, a decomposed basalt mineral from the volcanoes and mountains of the Rift
Valley to the south. In some locations, fine sand can also be found, but neither of these materials is suitable for high quality
construction4. However, due to the incredibly high cost of transport and the long distances to better materials, in many of the
SSTCM construction locations there is no suitable alternative to using the in situ soil.
This problem is also a huge impediment to road construction in the country, and to solve these two linked difficulties, SSTCM
embarked on a study of soil stabilizer performance to potentially value engineer a cheaper and more durable stabilized soil
matrix. Using a local black cotton soil source in Juba, California Bearing Ratio testing was first conducted, followed by a similar
series of tests using compressed earth blocks made from a hydraulically powered Hydraform machine5. This testing is to be
followed by a long term weatherization study and rupture testing over the current rainy season.
Figure 14 – Main north-south highway in South
Sudan at onset of rainy season. Road is murram
base on black cotton soil subbase, resulting in base
breakthrough under traffic from overloaded trucks
in saturated conditions.
Figure 15 – Making stabilized soil blocks from 12%
cement and black cotton soil blended with fine
sand, in Jonglei State.
Figure 16 – Alor Payam wall construction with
confined masonry technique. Reinforced concrete
column is cast after wall masonry is in place to
better lock walls in position.
Figure 17 – Lekuangole Payam construction at ring
beam level.
Figure 18 – Traditional Authorities Center in Pibor
(built in 2011) showing signs of surface
deterioration on black cotton soil earth blocks.
Figure 19 – Compression testing of stabilized soil
block using Hydraform testing machine.
Interesting results were found from this dual study of stabilizers:
•
•
•
A particular stabilizer, such as lime, may work very well as a subgrade material (according to CBR results), but it does not
necessary produce a viable stabilized soil block.
Enzymes appear to work well in combination with lime and cement. However, they can require very precise application in
the field, and this may not be possible with local labor and minimal management oversight.
Black cotton soil achieves 2 MPa when cured at 28 days, however this strength will change dramatically in the presence of
moisture. This may have influenced the results from the other stabilized samples, so further testing should be performed
to determine compression strength when soaked after stabilization.
Unfortunately, some of the samples were not covered well during the curing process and were exposed to precipitation; this
resulted in some samples showing a lower compression strength than they may have with a controlled, indoor stabilization.
Further testing in 2014 will expand and confirm these preliminary results.
4
Extensive engineering literature can be found on both soil stabilization and black cotton soil in East Africa, Texas, and India, so the
details of this concept and the basalt mineral will not be described here.
5
Unfortunately, due to access issues at the borrow site for the material used in the CBR site, a new site was identified, and the soil
characteristics are slightly different between the CBR and the compression testing data sets.
CBR Testing Results
98
100
88
90
88
Black Cotton Soil (BCS)
79
80
2% Cement + BCS
6% Cement + BCS
70
66
10% Cement + BCS
66
2% Lime + BCS
60
6% Lime + BCS
51
10% Lime + BCS
50
2% ANSS + BCS
43
6% ANSS + BCS
38
40
10% ANSS + BCS
Claycrete + BCS
30
26
Claycrete + 1% cement + BCS
Claycrete + 2% cement + BCS
20
15
10
10
8.5
11
Claycrete + 5% cement + BCS
EarthZyme + BCS
3
0
Figure 20 - Graph of California Bearing Ratio test results from various stabilizers and combinations with Black Cotton Soil from Juba.
3
2.5
28 days
2
14 days
MPa
7 days
1.5
1
0.5
0
Figure 21 - Compression testing results from various stabilizers in Black Cotton Soil, compressed with Hydraform testing machine. The low results from lime
stabilization suggest that results from CBR testing cannot be correlated with masonry compression testing.
Earthbags
Earthbag construction is perceived as a viable alternative to SSB methods for several reasons: earthbags could partially or
fully eliminate need for more costly cement stabilization; shipment of earthbags would be significantly cheaper than cement;
bag fabrication could be fostered as a local job generation scheme; earth bag walls may exhibit better long term weather
performance than stabilized blocks; and earthbag construction may prove affordable for local efforts at construction of nontraditional 'modern' structures. A pilot project is currently underway in Northern Bahr el Ghazal to explore the viability and
costs of this method, and it is anticipated that in 2014 at least two additional Payam sized structures will be built with
earthbags.
Figure 22 – Earth bag house under construction in
Rwanda.
Figure 23 – Earth bag corner detail (mockup) using
materials from Eternally Solar in Capetown.
Figure 24 – Earth bag filling tools.
In addition, it is hoped that temperature and humidity data logging in the earth bag buildings may yield better results than the
existing performance from the best CEB structures. The earth bag wall is 340mm wide nominally, whereas the current CEB
wall is 230mm, and the CMU wall 150mm (all dimensions without plastering). As the CEB wall clearly outperforms the CMU
wall in interior temperature levels, it may be assumed that a wider wall structure, with a higher thermal mass, may return
better interior temperatures than the CEB wall. This will be modeled during the 2014 energy study and also validated by data
logger study after the buildings are completed in mid-2014.
Conclusions
Several significant conclusions were derived from three years of construction and data from the Best Practices grant:
•
•
•
•
•
Better laboratory conditions must be found to achieve reliable data, however decent facilities and equipment for testing
do not exist in Juba.
Unstabilized black cotton soil as well as most stabilizers achieve 2 MPa in compression testing at 28 days. As 2 Mpa is the
target, according to the IBC, this suggests that compression testing may not be the best method to evaluate stabilizer
efficiency.
When stabilized with very high amounts of cement and blended with significant quantities of local sand, black cotton soil
has proven a viable construction material in South Sudan. However the long term stability of this material is questioned,
evidenced by deterioration on some early structures, and further research should be conducted on weatherization and
material performance when subjected to wet-dry cycles.
Implementation of passive cooling techniques results in significant reduction in indoor air temperature throughout the
day. Further research should be conducted on active evaporative cooling or ground ventilation to reduce temperatures
further and to make the design more viable for house construction with 24 hour occupancy.
Earthbag construction may be a superior building method in areas where soil stabilization is costly and increased thermal
mass is desirable, but this must be validated by constructability, value engineering, energy modeling, and temperature
and data logging in built structures.
Avenues for further study and effort are the following:
•
•
•
•
•
•
Experimentation with different stabilizers in field conditions, to determine whether similar results can be achieved with
mechanically operated block machines and local labor (January 2014).
Weatherization study of stabilized blocks made for compression testing to determine durability characteristics (AugustJanuary 2013).
Construction of a hollow CMU and/or CEB mockup wall for evaporative cooling (November 2013), implementation in a
Payam project (January-June 2014), and temperature and humidity data logging of this design (June 2014).
Research and design on floor ventilation to reduce interior temperatures by using the earth as a heat sink (August-January
2013).
Use of galvanized sheeting on all projects and better quality control with venting details to achieve more consistent and
favorable cooling results on 2014 projects (January-June 2014).
Reduction in PV system sizing through elimination of fans in some rooms in structure.