CARBONATING MAGNESIA FOR SOIL STABILIZATION

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RELEVANCE OF STABILISATION

To improve the engineering properties of soil

Bearing capacity of soil may be inadequate

Decrease permeability, compressibility

To obtain adequate strength

To control swelling and shrinkage

CHEMICAL STABILIZATION?

The chemicals undergo various reactions Increases the binding property between the soil particles changes surface molecular properties

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STABILIZING CHEMICALS

•Lime • Calcium and sodium chloride•Lignin•Water proofers like siliconates , amines•Natural and synthetic polymers•Dispersants and aggregants

An alternative solution for Stabilization by ordinary Portland cement

Reasons

Less energy consumption CO2 sequestration Higher compressive strength

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BASIC REACTIONS

MgO+H2O→Mg(OH) 2 (brucite)

Mg(OH) 2 +CO 2 +2H2O→ MgCO3.3H2O (Nesquehonite)

5 Mg(OH) 2 +4 CO 2 +H2O →(Mg) 5(CO3 ) 4(OH) 2 .5H2O (dypingite)

5 Mg(OH) 2 +4 CO 2 →(Mg) 5(CO3 ) 4(OH) 2 .4H2O (hydromagnesite)

•Expansive reactions (3.8 - 6.7)

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SCANNING ELECTRON MICROSCOPE STUDIES

Courtesy:Yaolin Yi, Martin Liska

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Slightly clayey silty sand (90% sharp sand , 5% kaolin clay, 5% silica flour )

organic clayey silt (82% silica flour ,15% kaolin clay , 3% peat )

Confining pressure 400 KPa

CO 2 Pressures 200 Kpa,100 KPa, 50 KPa

carbonation period 0.5-7 hours

LABORATORY SET -UP

Water content Vs Dry density

GRAPHS AND RESULTS

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Optimum water content for maximum dry density is more than that of OPC – Rapid hydration

Contd…

Water content Vs UCS

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optimum water content for maximum UCS is lesser than that of OPC – enough carbonation

Contd…

UCS Of MgO treated soil after a carbonation period of 3 Hours= UCS of PC stabilized soil at 28 days

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Lower the MgO content and Higher the carbonation period cracks will be more

o Lower MgO ,Higher water content

o MgO impurities like dead burnt MgO

COLUMN INSTALATION & CARBONATION

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Column installation Laboratory scale auger set up

MgO grout is pumped into grout inject

Three switch travel stop mechanism

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•Auger penetration and withdrawal-5.2 mm/sec at 50 rpm

• grout pumped at 7.2 g/sec

Column carbonation

Method 1

•Pumping gaseous CO 2 through the auger• Auger is connected to CO 2 canister

•Method 2

• perforated plastic pipe system• More homogeneous carbonation• Pipe Diameter 20 mm

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Real Life Applications

CARBONATION IS ACHIEVED THROUGH

Deep mixing carbonation method Injected reactive MgO powder is mixed with soil by an auger followed by carbonation(Through perforated pipe)

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DEEP MIXING CARBONATION

Auger with hollow drill

Mixing tool at the bottom

Grout is passed through the drill rod

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CONCLUSION Adequately carbonated MgO treated soil in few hours reach 28 day strength of PC stabilised soil

Reactive MgO – A promising stabilisation binder through the sequestration of CO 2

Magnesium oxide has less environmental impact compared with PC, in which the production process is conducted at a temperature far less than that of PC.

Compared to CaCO3 it is resistant to sulphate attack

More stable than CaCO3

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REFERENCES

1. "Physical properties, Electrical Resistivity and strength characteristics of Carbonated silty soil admixed with reactive Magnesia" - Devendra Narain Singh, Guang Hua Cai: Canadian geotechnical journal(April 2015)

2. "Carbonating magnesia for soil stabilization" - Yaolin Yi, Martin Liska, Cise Uniuer: Canadian geotechnical journal (June 2013) 3. "Soil stabilization using Lime: Advantages, Disadvantages and proposing a potential alternative" -Ibtehaj Taha Jawad, Mohd Raihan Taha, Zaid Hameed Majeed , Tanveer A .Khan: Research journal of applied sciences, Engineering and technology (May 10,2014) 4. "Strength and deformation characteristics of carbonated reactive magnesia treated silt soil" -CAI Guang-hua , LIU Song-Yu, DU Yan-jun, ZHANG Ding-wen, ZHENG Xu:Central south University press and Springer (2015) 5. "Preliminary Laboratory-scale model Auger installation and testing of carbonated soil-MgO columns" - Yaolin Yi, Martin Liska, Cise Uniuer: Geotechnical testing journal (March 2013) 

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