Study Of Mixed Alkali-activated Fly Ash Geopolymer Grouting Materials

With the deepening of ecological civilization construction and the rising requirements of environmental protection,turning solid waste into resources and burdens into wealth has gradually become an urgent need for the construction of ecological civilization in China,and the concept of green development has been gaining popularity.In the past decades,alkaliactivated materials,including geopolymers,have been gradually accepted by academia and industry as effective and promising alternatives to Portland cement-based materials.The raw materials for geopolymers are simple and readily available.Most natural minerals,industrial wastes and tailings rich in silica-alumina fractions can be used as potential raw materials.Based on this,this paper investigates the effect of alkali activator on the pore structure and polymerization degree of fly ash geopolymer by using fly ash as raw material,and explores the reaction mechanism of organic alkali activated fly ash through the mixture of organic and inorganic alkali.The changes of fly ash reactivity after modification of fly ash by silane coupling agent were also studied to meet the process performance requirements of grouting materials,and the main findings are as follows:(1)Fly ash geopolymer was successfully prepared by mixing inorganic alkali sodium hydroxide,organic alkali sodium tert-butoxide and sodium acetate,respectively,with sodium silicate as the activator,and the effect of the type of alkali activator on the activation effect of fly ash was studied.The results showed that the alkalinity(p H)of the alkali activator had an essential effect on the fly ash geopolymer,and the 28 d compressive strength of the fly ash geopolymer reached 30.1 MPa when a mixture of sodium tert-butanol and sodium silicate was used as the activator,and the higher the alkalinity of the activator,the more obvious the effect on the reduction of silica-oxygen tetrahedral polymerization in fly ash.The weak alkali sodium acetate had almost no effect on the reduction of polymerization of silica-oxygen tetrahedra in fly ash.In addition,when the ratio of silicon to aluminum in the silica-aluminate network structure of fly ash geopolymer is closer to 2:1,the more stable the structure is,and the strong alkali exciter can reduce the polymerization degree of silica-oxygen tetrahedra in fly ash,which provides theoretical support for the subsequent development of organic strong alkali-activated fly ash preparation of geopolymers.(2)Fly ash geopolymer grouting materials with better mechanical properties were prepared using a new mixed alkali activator.The effects of activator content and type on the mechanical properties of fly ash geopolymer grouting materials were investigated using sodium tert-butanol,sodium silicate and sodium tert-butanol/sodium silicate hybrid excitants.The microstructures of fly ash geopolymer grouting materials were characterized by FTIR,SEM,EDS,XRD and BET physical adsorption methods.The results showed that the densities of the fly ash geopolymer prepared from a new mixed alkali activator of 5 wt% sodium tert-butoxide and 10wt% sodium silicate were better.Thus,the mechanical properties of this fly ash geopolymer were improved.The results show that the C-OH bond generated by the hydrolysis of sodium tert-butoxide reacts with Si-OH in the geopolymer to form a C-O-Si bond,which constitutes a complex three-dimensional network structure and improves the mechanical properties of the grouting material.(3)Based on the above experimental results,in order to improve the reaction degree of fly ash in alkaline environment,the surface of fly ash was modified by silane coupling agent KH550 to produce more active sites on the surface of fly ash and increase the specific surface area of fly ash.The results showed that the mechanical properties of the modified fly ash geopolymer were improved compared with the unmodified fly ash geopolymer,and the 28 d compressive strength of the fly ash geopolymer reached 30.8 MPa when a mixed alkali activator was used and the amount of KH550 was 2 wt%.on this basis,10 wt% of silica fume was added to the system,and the inorganic mixed alkali was used as the activator,and the amount of KH550 was 2wt%,the 28 d compressive strength of silica fume/fly ash geopolymer reached up to 32.5MPa.Figure [27] Table [19] Reference [98]...