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SILICATES FOR GROUND CONSOLIDATION

SILICATES FOR GROUND CONSOLIDATION. Silicate based grouts usually contain three main components: Sodium silicate Hardener or reagent Water. CHEMICAL REACTION BETWEEN SILICATE AND HARDENER. (CH 2 ) m (COOCH 3 ) 2 + H 2 O (CH 2 ) m (COOH) 2 + 2 CH 3 OH

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SILICATES FOR GROUND CONSOLIDATION

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  1. SILICATES FOR GROUND CONSOLIDATION Silicate based grouts usually contain three main components: Sodium silicate Hardener or reagent Water

  2. CHEMICAL REACTION BETWEEN SILICATE AND HARDENER (CH2)m(COOCH3)2 + H2O (CH2)m(COOH)2 + 2 CH3OH (CH2)m(COOH)2 + SiO2, Na2O n SiO2 + x H2O + (CH2)m(COONa)2 hydrolysis gel formation

  3. FACTORS TO BE CONSIDERED • Initial grout viscosity and the viscosity profile during gelation • Setting time of the grout • Effect of temperature • Degree of neutralization of the gel • Nature of treatment required e.g. water proofing, short or long term consolidation • Nature of the grout to be treated

  4. GROUT VISCOSITY • For a given temperature, the initial viscosity of a silicate grout depends on: • Type of silicate used (ratio, % solids) • Ratio silicate/water • Amount of hardener

  5. INITIAL VISCOSITY

  6. INITIAL VISCOSITY

  7. SETTING TIME • The grout setting time depends on: • Nature of silicate; the higher the ratio the longer the setting time. The higher the solid content of the silicate the shorter the setting time, assuming a constant degree of neutralization • Concentration of the silicate; at constant volumetric dosages of hardener, the setting time increases with increasing silicate levels. • Type of hardener and concentration of hardener • Grout and soil temperature; the higher the temperature the shorter the setting time • Nature of the soil; acidity of the soil, calcium/magnesium content in the soil could influence the setting time

  8. SETTING TIME

  9. TEMPERATURE VS. SETTING TIME

  10. DEGREE OF NEUTRALIZATION In general the higher the degree of neutralization the higher the mechanical strength (compressive strength) the higher the durability. Degree of Neutralization = (VH * dH * 6200)/(VS * dS * NA) * MH VS = silicate volume (l) dS = density of silicate (S.G) NA = weight % alkali (Na2O) in silicate MH = molecular weight of hardener VH = volume of hardener (l) dH = density of hardener (S.G.)

  11. DEGREE OF NEUTRALIZATION

  12. COMPRESSIVE STRENGTH

  13. COMPRESSIVE STRENGTH

  14. INITIAL VISCOSITY VS. COMPRESSIVE STRENGTH

  15. SYNERESIS Syneresis is the phenomenon of the reaction of silanol groups whereby a siloxane bond will be formed and water will be released. This loss of water leads to shinkage and/or distortion of the silica gel structure. H2O O O - H HO Si Si Si Si

  16. DEGREE OF SYNERESIS • Main factors influencing degree of syneresis: • Silicate ratio (ratio > = Syn <) • Degree of neutralisation (neutralization > = Syn <) • SiO2 content of the grout formulation • (SiO2 content > = Syn >)

  17. DEGREE OF SYNERESIS

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