Study On Alkali-activated Fly Ash-Slag Grouting Material In Road Engineering

Slag and fly ash were the main industrial by-products of steel and coal.The output of slag and fly ash were very high because of the large demand of steel and coal in China every year.In order to build a resource-saving and environment-friendly society,alkali-activated fly ash-slag grouting material suitable for road engineering was prepared by taking advantages of the superior mechanical properties and excellent permeability resistance of alkali-activated fly ash-slag.Preparation of grouting material by using slag and fly ash can not only solve the problem of large demand for grouting material in road engineering but also good for resource utilization.In this paper,the rheological properties and fluidity of alkali-activated fly ash-slag slurry were studied systematically.A kind of test method for evaluation of fluidity of slurry was proposed,which was simple and quick.In order to meet the requirement of grouting material for road engineering,the setting time of alkali-activated fly ash-slag slurry and the compressive strength of alkali-activated fly ash-slag concretion were studied.In the discussion of the influence of various factors on the cementitious behavior of alkali-activated fly ash-slag grouting material,the mixture ratio screening was carried out.Finally,to evaluate the effect of grouting of alkali-activated fly ash-slag grouting material,the diffusion distance formula was established by groutability test,and the compressive strength,permeability resistance and microstructure of the grouting specimens were investigated.The rheological properties and fluidity of alkali-activated fly ash-slag grouting material were investigated.The results showed that the Marsh cone with a 10mm inner diameter was the optimal choice for alkali-activated fly ash-slag grouting material fluidity tests.Alkali-activated fly ash-slag grouting material was a shear thicking slurry withing reological property index greater than 1.A time-dependent mutation relationship was existed between the yield stress and Marsh fluidity of the slurry.When fly ash and slag were ground to a D50which was less than 10μm,the time-dependent mutation relationship was diappeared.The correlations between Marsh fluidity of the slurry and the yield stress,Marsh fluidity of the slurry and plastic viscosity of the slurry were both greater than 0.8,indicating a desirable correlations.Moreover,the correlation of the relationship between rheological property with20 S^-1 shear rate and Marsh fluidity were optimal,which means the Marsh cone method could be implemented to measure the rheological properties.The investigations on the setting time and compressive strength of alkali-activated fly ash-slag grouting material indicated that all the slurry in the test met the requirements of road engineering with initial setting time greater than 30 min and final setting time less than 400min.Considering the working performance,mechanical performance of the grouting material,economic benefits and the ease of operation,alkali-activated fly ash-slag grouting material were prepared with water/binder ratio of 0.45,slag content of 10 wt%and sodium silicate with modulus of 2.0.The compressive strength of alkali-activated fly ash-slag grouting material was ranged from 8.8 MPa to 12.7 MPa,which can be controlled by regulating the concentration of activator from 12 wt%to 24 wt%.The compressive strength of alkali-activated fly ash-slag grouting material also met the needs of different roadbed reinforcement（greater than 4.2 MPa）.The compressive strength of alkali-activated fly ash-slag grouting material was 38.2 MPa if the slag content increased to 20 wt%and the concentration of activator was 24 wt%,meeting the requirements of the treatment of the bottom of cement concrete slab and the semi-rigid base layer（greater than 30 MPa）.The compressive strength of the concretion was not only related to the amount of reaction products and structural compactness,but also related to the degree of polymerization of the product.The investigations on the grouting of alkali-activated fly ash-slag grouting material in laboratory indicated that grouting pressure was the most important factor affecting the diffusion distance and grouting amount.The yield stress of the slurry was the second factor affecting the grouting amount,and the grouting amount was the second factor affecting the diffusion distance.The diffusion distance was mainly affected by the external factors of grouting pressure,grouting amount and the permeability coefficient of sand.The correlation formula between grouting amount（Q）and grouting pressure（P）,permeability coefficient of sand（k）,plastic viscosity of slurry（η）,and yield stress of slurry（τ₀）was as follows:Q（28）2095.946P^0.546k^0.314η^-0.053τ₀^-0.368 The correlation formula between diffusion distance（L）and grouting pressure（P）,permeability coefficient of sand（k）,plastic viscosity of slurry（η）,yield stress of slurry（τ₀）,and grouting amount（Q）was as follows:L（28）0.0792P^0.0682k^0.510η^-1.684τ₀^-0.177Q^0.429 The compressive strength of alkali-activated fly ash-slag grouting specimens after curing for28 days was ranged from 5.6 MPa to 28.6 MPa,and the order of magnitude of the permeability coefficient was ranged from 10^-99 m/s to 10^-1111 m/s.The permeability resistance of alkali-activated fly ash-slag slurrry with different proportions could reach the highest level（P15）,and the porosities of grouting specimens were lower than 20.81%,which means the grouting work was effective.