earthblocks in the sudd: finding solutions on unlikely terrain chris rollins, p.e. senior engineer,...
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EARTHBLOCKS IN THE SUDD:FINDING SOLUTIONS ON UNLIKELY TERRAIN
Chris Rollins, P.E.Senior Engineer, AECOM International South Sudan
The SUDD
The PROBLEM
The SOIL
The CATTLE
The YOUTH
The ROADS
The AID
The GOVERNMENT
The SOLUTION?
10 similar projects in 2013, 20+ in 2014 +/-$150k each
Dablual - Galvanized roof
Manajoka - Concrete block
Jaac - Largest roof overhang
Alor - Average construction
How to achieve quality in this environment:• Modular 3m x 4m layout• Reinforced Concrete frame with CEB non-load bearing wall• All rebar sizing & detailing SAME throughout• Prefab steel doors and windows in city• QA/QC manual with photos• 1200W PV System, Rainwater Catchement, VIP Latrine
Energy considerations:• Building at +/- 10˚N Latitude – sun on S and N!• Passive Cooling principles – venting, shading, light colored roof, reduce reflected
radiation• Orient building on E-W axis for shade and max PV energy production
Blockmaking
Makiga Engineering (Nairobi) block press replicates size and shape of Hydraform block (Johannesburg).
Confined Masonry
Generally a good idea, but in area of extreme wet and dry cycles (and no seismic problems), this constraining can cause cracking in plaster between dry stack joints when blocks contract when dry.
Typical Construction
2013 Best Practices GrantWHAT
• Identify methods and materials to develop standards for rural South Sudano Theoretical AND practical o Pave way for future building code?
WHY• Current construction is very low quality• Keep pre-fabs (‘containers’) and air conditioning (‘split units’) out of the bush• Big Picture - Promote good ideas in a warming world
HOW• Energy study with temperature and humidity data analysis• Soil stabilization study with CBR and compression testing• Earthbag prototypeOther topics in Best Practices Grant:• PV system optimization, ferrocement and CEB water storage tanks• QA/QC manual, seminars, training, networking with government and industry
RAISE THE BAR SO THAT OTHERS MUST FOLLOW.
Temperature and Humidity Data Study
• How does the current design perform?• How can the design be improved?
Temperature and Humidity Data Study- Questions
Temperature and Humidity Study- Answers
• Buildings cooler than ambient by as much as 12°C• Galvanized roof has significantly lower temperatures.• Concrete Masonry Units underperform CEB buildings –
hotter day AND night.• 2-hour lag between the hottest ambient (2:30 p.m.) and
the hottest interior (4:30 p.m.) o Good for office building
• Nighttime interior temp 2-3°C higher than ambient o Poor for housing o May not find more efficiency without active cooling
7:30 a.m.
9:30 a.m.
11:30 a.m. 12:30 p.m. 2:30 p.m.
3:30 p.m. – hottest time of day
4:30 p.m.5:30 p.m.
0 10 20 30 40 500.0000
0.0020
0.0040
0.0060
0.0080
0.0100
0.0120
0.0140
0.0160
0.0180
0.0200
0.0220
Psychrometric Chart at 95.5 kPa
Dry Bulb Temperature (°C)
Hum
idity
Rati
o (k
gw/k
gda)
RH=100
%
ASHRAE Comfort Zone
RH=30%
Manajoka
Alor
Jaac
Dablual
• Cannot hit ASHRAE zone without reducing humidity!
Performance in afternoon sun
• Shade from water tank lowers building surface temp up to 10˚C• Should emphasize landscaping and/or curtain wall going forward.
Soil Stabilizer Study
Soil Stabilizer Study –Questions
• What compression strength are we achieving with current techniques and mixes?
(10-12% cement by volume)• What compression strength is possible?• Can we use CBR data to infer compression strength?• What alternative stabilizers might be stronger, more
durable, easier to use, and cheaper?
Soil Stabilizer Study –Answers
• Current compression strength is terrible: <1 MPa.• Lime has very good CBR results but poor
compression testing results(no correlation between CBR and compression methods)
• Liquid stabilizers (Earthzyme and Claycrete) appear to achieve 2Mpa strength at much lower cement %
• Weatherization study ongoing – which stabilizer will return best long term results in this wet/dry cycle?
Traditional Authority Center 2011
Oldest building in program, built in most unfavorable conditions.
Cohesion and Adhesion Failure
Is this due to salt build-up, use of cement bag wash, internal wet/dry cycles in block, or combination?
GRADATION TEST• South Sudan is a swamp - soils are very fine due to low energy• Inconsistent results on same sample from three different labs (See
Gudele samples)
California Bearing Ratio test
CBR test measures pressure required to penetrate a soil sample (soaked in water); divide by the pressure required for equal penetration
on a standard crushed rock material.
Compression Testing
Hydraform block press (Johannesburg) used to make blocks for more consistent ‘laboratory’ conditions.
Curing is typical
Hydraform block testing machine (Johannesburg) will be used solely for field testing in future, but a more accurate test device must be procured first.
Compression testing results are not consistent with CBR data, and also not rational – must repeat.
Blocks are currently curing for long term (90-day) compression testing, one sample of each removed from tarp for weatherization study.
4% cement
Claycrete + 4% cement4% lime
4% ANSS
Earthbag Prototype –Questions
• Are earthbags a suitable alternative to chemical stabilization?
• Is this cheaper (product + transport + labor)?• Can local people use this technology at home?• Could this create cottage industry making
bags?
Earthbag Prototype –Answers
• Very difficult getting outside expert to assist, therefore project was not managed.
• AECOM team and local community very enthusiastic about technology:
‘I am going to build my house like this!’• Problems filling bags in rainy weather,
resorted to 1:12 stabilized sand.• Will try again in dry season on larger project.
Bags from Eternally Solar in Capetown
What’s Next?
• Soils lab necessary for accurate engineering study!• Build 1-2 buildings with earthbags, using better management
and outside expert.• Build 1-2 buildings with different stabilizers: Claycrete, other.• Study stabilizer combinations (i.e. lime + cement)• Attempt some kind of active cooling system – undecided
o floor - earth temp may be higher than ambient at night!o evaporative – potential mold problems, legionnaires’ disease?
• Emphasize landscaping or low-cost curtain wall to reduce reflected and direct radiance.
• Try new ideas from US, Germany, Mexico, Brasil, Spain, etc.
