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) CH 3 OH (CH 2 ) m (COOH) 2 + SiO 2, Na 2 O n SiO 2 + x H 2 O + (CH 2 ) m (COONa) 2 hydrolysis gel formation

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

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

INITIAL VISCOSITY

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

SETTING TIME

TEMPERATURE VS. SETTING TIME

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 = (V H * d H * 6200)/(V S * d S * N A ) * M H V S = silicate volume (l) d S = density of silicate (S.G) N A = weight % alkali (Na 2 O) in silicate M H = molecular weight of hardener V H = volume of hardener (l) d H = density of hardener (S.G.)

DEGREE OF NEUTRALIZATION

COMPRESSIVE STRENGTH

INITIAL VISCOSITY VS. COMPRESSIVE STRENGTH

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. Si O - H Si HO Si O H2OH2O

DEGREE OF SYNERESIS Main factors influencing degree of syneresis: Silicate ratio (ratio > = Syn <) Degree of neutralisation (neutralization > = Syn <) SiO 2 content of the grout formulation (SiO 2 content > = Syn >)

DEGREE OF SYNERESIS