Performance And Normal Temperature Of Chemical Activation Mechanism Research Of New Fly Ash Shotcrete Material

Fly ash is the largest single solid waste in China.A large amount of fly ash heaped up in the open air will cause serious harm to the environment,and its resource utilization is imminent.Using fly ash to replace sand in traditional cement mortar is an important direction of fly ash utilization,but too high addition amount of fly ash will have a negative impact on the performance of shotcrete material,and limit the use amount and effect of fly ash.In this paper,fly ash is used as the main raw material,by controlling the addition amount of fly ash,adjusting the type and amount of additives,to produce a new type a new type of fly ash shotcrete material.Considering the setting time,compressive strength,water absorption and microstructure tests of fly ash shotcrete materials in different curing ages,to study the performance variation rule of fly ash shotcrete materials and activation mechanism at room temperature.At the same time,exploring the best experimental conditions by the fluid mechanics simulation,to guide the field experiment.The main research conclusions are as follows:First of all,fly ash is used to replace sand in traditional cement mortar(cement:sand=1:3,mass ratio),and the change of setting time,compressive strength and water absorption of shotcrete materials with different fly ash addition amounts is studied.It is very feasible for fly ash to completely replace the sand in the traditional cement mortar shotcrete material,but it cannot meet the performance indexes of the shotcrete material without adding additives to stimulate the activity of fly ash.Secondly,alkali activator was used to modify the fly ash shotcrete material(cement:fly ash=1:3,mass ratio,the same below)to improve its compressive strength.Na₂SO₄,Na OH,Na₂Si O₃ were used respectively to three kinds of alkaline excitation agent on chemical activation temperature,one of the best excitation effect is Na₂SO₄,mainly by improving the cement hydration reaction and ash reaction speed and degree of reaction of fly ash to improve compressive strength of fly ash shotcrete material,adding amount of 3%(mass ratio of cement,the same below)at different curing age have a maximum compressive strength.Then,the water reducer was used to modify the fly ash shotcrete material to improve its setting time and reduce its water absorption.Polycarboxylic acid superplasticizer,naphthalene superplasticizer and aliphatic superplasticizer were used to chemically activate fly ash shotcrete material at room temperature,which stimulate the best effect of poly carboxylic acid water reducing agent,mainly through space steric effect release shotcrete materials flocculation in water,increase the hydration reaction rate and reaction degree,adding amount was 1%when the setting time for the 4 h,bibulous rate is low in different curing age.Finally,Na₂SO₄ and polycarboxylic acid water reducer were used to recombine fly ash shotcrete material to improve its comprehensive properties.When the Na₂SO₄content was 1.5%and the polycarboxylic acid water reducer content was 0.5%,the comprehensive performance reached the best.The early improvement of the compressive strength of the shotcrete material is mainly the result of the action of Na₂SO₄,while the long-term improvement of the compressive strength,the adjustment of setting time and the decrease of water absorption at different ages are the result of the synergistic action of Na₂SO₄ and polycarboxylic acid water reducer.The flow process of water phase and ash phase at the nozzle is simulated by ANSYS Fluent software,and the pressure field and velocity field are analyzed.It can be seen that when the flow rate of ash phase inlet is 12.5m/s and that of water phase inlet is 20m/s,the shotcrete material can be uniformly mixed.Using the results to guide the wall spraying experiment of workshop,a relatively smooth shotcrete layer can be obtained and long-term cracking can be guaranteed.Relevant performance tests at different curing ages can be carried out to determine that the formula and technological conditions can meet the actual needs.