Study And Application Of Hydration Characteristics Of Layered Sodium Silicate-silica Fume-cement Slurry

In today’s world,where the geological environment has been destroyed due to overexploitation of geological resources and simultaneously geological disasters occur frequently,the natural environment is being threatened by large amounts of industrial waste.Thus it is significant to reduce damage towards the geological environment and prevent and control geological disasters.Disposal of industrial waste is also important for protecting the geological environment.Portland cement,which is cheap and has wide source,has often been used as base material for grouting materials in protecting and treating geological environment.But Portland cement tends to be unstable when used as slurry base material and additives or supplements have to be added to achieve availability of such cement-based grout.This essay aims to prepare the process of Portland cement additive layered sodium silicate by using recyclable biomass rice husk ash（RHA）instead of siliceous mine as silicon source and high water-cement ratio of layered sodium silicate and industrial by-product silica fume,investigating into the mechanism of layered sodium silicate as active activator towards cement slurry hydration and providing scientific and theoretical basis for developing green and environmentally friendly grout and reducing siliceous mine development and application of industrial by-products in grout.This essay investigates the effects of synthetic temperatures and time on products’composition and their capacity of calcium ion exchange in the process of synthesizing layered sodium silicate using RHA.Based on physicochemical properties of cement,cement-layered sodium silicate,cement-silica fume and layered sodium silicate-silica fume-cement systems with different hydration periods,modern analytical techniques,such as X-ray diffraction,infrared spectroscopy,scanning electron microscopy and differential thermal analysis have been adopted to characterize and study the morphology,phase change and pore distribution of the hydration products in slurry hydration process.The main research findings are as follows:（1）It is feasible to prepare layered sodium silicate by using recyclable biomass silicon source as an alternative to siliceous mine silicon source.δ-Na₂Si₂O₅ with high specific area and up to 90%of porosity can be prepared using a sintering process below720℃for 120 min,whose calcium and magnesium ion exchange capacity can reach430mg/g and 396mg/g.δ-Na₂Si₂O₅ has high ion exchange capacity and its crystal structure has a basic ring structure composed of silicon tetrahedron and a lamellar structure composed of a ring structure with larger pore size and more regular surface structure.There is a close relationship between spatial distribution of some sodium atoms in the cell on the surface of the unit cell.（2）The layered sodium silicate can effectively reduce the bleeding rate of the cement slurry and improve the stability of the slurry;it can accelerate the hydration speed of the cement particles in the initial hydrolysis period and the acceleration period,and reduce the hydration speed of the cement particles during the deceleration period.Reducing the initial fluidity of the slurry and shortening the initial setting time and working time of the slurry can increase the compressive strength of the slurry for one day,but greatly reduce the compressive strength of the slurry in the later stage.The layered sodium silicate will cause the morphology of the early type I hydration product C-S-H in the cement slurry to change from short fiber to type II three-dimensional grid structure.The content of silicate group with high polymerization degree in C-S-H in the late hydration stage decreases,while the content of lamellar C-S-H in the slurry will reduce or miss.This transformation results in a reduction in the slit type of about 20 nm in the slurry and an increase in the number of closed pores.Layered sodium silicate will lead to the growth of ettringite in the cement slurry in the a,b and c directions.The three-dimensional size of ettringite will increase significantly,the number of particles will decrease,and it is easy to have radial outward growth,focusing on some growth points.The change will have significant effects on the number,distribution and pore shape of the pores in the range of 0.1μm²-4μm² in the slurry,which can increase the compressive strength of hydration for one day and greatly reduce the strength of hydration for 28 days.In the initial stage of hydration,the layered sodium silicate exchanges with the calcium ions released by hydration in the slurry to form calcium silicate hydrate to reduce the content of calcium hydroxide in the slurry.The calcium hydroxide crystals tend to grow along the（100）direction,forming relatively large,thinner sheet-like morphology.The flaky particles in the late hydration will coalesce into a larger scale sheet polymer.（3）1.0 high water-cement ratio can be used to reduce the bleeding rate of the cement slurry and the initial fluidity of the slurry;it will greatly extend the initial setting time,final setting time and working time of the slurry;it will delay hydration rates during the pre-and post-acceleration cement induction.The response during the induction period does not tend to stagnate but slowly progress,which can increase the compressive strength of the slurry for one day,but will greatly reduce the compressive strength of the slurry in the later stage.Silica fume does not have significant effect on the morphology of C-S-H and ettringite in cement slurry.The reaction of siliceous ash with calcium hydroxide formed by hydration will be obvious after 14 days of hydration,which is beneficial to reducing the slurry’s calcium hydroxide content.（4）The layered sodium silicate will greatly reduce the bleeding rate and initial fluidity of the silica fume-cement system,and shorten the working time,initial setting time and final setting time of the slurry;it can improve the compressive strength of the slurry for one day and will increase the compressive strength of the slurry in the later stage relative to the layered sodium silicate-cement system and the silica fume-cement system slurry.The layered sodium silicate is added to the cement-silica fume slurry:the layered sodium silicate can effectively activate the activity of the silica fume,and the reaction with the calcium hydroxide formed by hydration is obvious after 7 days’hydration.To promote the consumption of calcium hydroxide in the slurry,the content of calcium hydroxide in the slurry under hydration for 28 days is 60%of that in the cement/silica body slurry,and about 43%of that in the net cement slurry.In the first day of hydration,the preference of calcium hydroxide will increase,and the preference for hydration for 14 days and 28 days will decrease.The layered sodium silicate is added to the cement-ilica fume slurry:the morphology of the early hydration product C-S-H changes from short fiber type I to type II three-dimensional grid shape;the growth of ettringite crystal particles is relatively limited along a and b-axis direction,while growth in the c-axis direction is enhanced.And it is easy to have radial outward growth around some growth points.The addition of layered sodium silicate to the cement/silica fume slurry contributes to reducing the pore size of the millimeter-scale pores in the slurry and increasing the number of pores with larger pore size in the micron-sized pore range.The total pore size of the nano-scale is similar.The open porosity of about 20 nm is greatly increased.（5）Based on the research results of the characteristics of solids-porosity-properties in the hydration process of layered sodium silicate-silica fume-cement slurry,a slurry with great advantages in compressive strength and early strength was designed.The design idea of slurry from micro and macro verification provides theoretical basis and technical guidance for the development,design and application of green high-performance slurry of this system or other systems.