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ISSUES ON SOIL-CEMENTCONSTRUCTIONHC UzoegboUniv of the Witwatersrand South Africa
The built environment is estimated to contribute
approximately 40% of total energy use and associated greenhouse gas (GHG) emissions globally
the biggest contributors to GHG are found to be
concrete and steel. Cement in concrete is main contributor to GHG.
Followed by transportation of materials.
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Greener Concrete
Reduce the amount of cement without
compromising quality.
Partial cement replacement (eg pozzolans)
Deposits of natural pozzolans in Rift Valley, E. Africa
Use soil of soil cement for low-rise housing
Reduce distance of material transportation
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Why soil-cement blocks
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CASE STUDY
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Basic Mix Design
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Sieve the soil after excavation, use the
soil from the construction site.
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Load the soil and cement into the mixer
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Mix the soil, cement and water
5% Cement
(by volume)4MPa block
8% Cement
(by volume)
7MPa block
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BLOCK PRODUCTION
M7 MOBILE BLOCK MACHINE
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Manual Block Machine
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After 2-3 minutes mixing move the mix
to the compression chamber
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Carry and stack the block, cure for 7
days
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Hydraform Blocks
Length- 240mm
Width - 220mm ( or 140mm)
Height - 115mm
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Hydraform Blocks
37 blocks / m2 of wall.
1m3 soil for 75 blocks.
1 bag of cement for 100 blocks. Minimal mortar between blocks, dry stacked
interlocking speeds up construction, 220mm
block.
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Cost Comparison
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COST COMPARISON
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Lessons from Ancient Dry-Stack
Construction
Great Zimbabwe Ruins
Capital 15th Century
Shona Kingdom
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FREE-STANDING WALLS
Need to tie top
courses to prevent
toppling
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BULGING OF RETAINING WALL PANELS
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SPLITTING IN WALL PANELS
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VERY LOW ARCHING MECHANISM
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Construction with Interlocking Blocks
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House in Johannesburg, SA
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House in Malawi
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Hydraform House in Malawi
f
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Hydraform House in Malawi
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Assessment of Block Unit Strength
A real challenge due to irregular shape
Test method must be developed for every
interlocking design
Three methods of testing for compression
strength of Hydraform blocks
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1. Centre Top Loading
Hydraform Block
Top machinesteel platen
Bottom machine
steel platen
P
Hard board
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Failure mode
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2. Shoulder Loading
Aditional Steelbearing platen
Hydraform Block
Top machinesteel platen
Bottom machinesteel platen
P
Hard board
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Failure Mode
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3. Cube Testing
Cube - 1
Cube - 3
Cube - 2
Cube - 4
Top Side(Low Density)
Bottom Side(High Density)
Hydraform Block
Top machine
steel platen
Bottom machinesteel platen
P
Hard board
Hard board
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Normalised strength factors
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Center Vs. Shoulder Testing
(15% cement content blocks)
0
3
6
9
12
15
18
Wet Specimens Dry Specimens
SpecimensStrength[MPa]
Centre
Loading
Shoulder
Loading
ll l
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Dry-Wall Panel Assessment
L t l L di W ll P l
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Lateral Loading on Wall Panel
Test Wall
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Test Wall3 June 2008 The Structural Engineer 25, C. Mundell
Dry Wall Prior to Failure
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Dry-Wall Prior to Failure3 June 2008 The Structural Engineer 25, C. Mundell
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E i l f l l l d
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Experimental set-up for lateral load test
LATERAL LOADING
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LATERAL LOADING
O S
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FAILURE MODE: MEDIUM SPAN
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FAILURE MODE: LONGSPAN
FAILURE MODE:PLASTERED DRY-STACK
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FAILURE MODE:PLASTERED DRY STACK
WALL
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FAILURE MODE:CONVENTIONAL WALL
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Load-Deflection Curves
Conventional MasonryLoad-deflection behavior for standard mansory brick wall
0.00
1.00
2.00
3.00
4.00
5.00
6.00
-20 0 20 40 60 80 100 120
Deflection (mm)
Load(Kn/m2)
gage1
gage2
gage3
gage4
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Load-Deflection CurvesCombination plot of middle point (gage1)
0
1
2
3
4
5
6
7
-20 0 20 40 60 80 100
Deflection (mm )
Loadcapacity(kPA)
5PB
5RBG
PW
2RBG(10mm)
2PB
RPW
2RBG(20mm)
SMW
Conclusions
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Conclusions
Cement stabilised soil block is cheaper than
conventional concrete block
Clay content of soil is necessary for early age
handling and stability
Approx. 40% loss in strength under sustained wet
conditions