Preparation And Properties Of Alkali-activated Cementitious Materials

Ordinary Portland cement has been widely used as a cementing material in the construction industry for a long time,but because it consumes a lot of resources and energy in the production process and has huge carbon emissions,it is contrary to today's social concepts of green environmental protection and sustainable development.Industrial solid wastes such as fly ash and slag have been used as concrete admixtures,intended to reduce the amount of cement used and save costs,while suppressing the heat release of cement.Some scholars have suggested that if a certain material is added to fly ash and slag,its potential activity can be stimulated,and it can be used as a cementing material separately from ordinary portland cement.Alkali-activated gelling material is a new type of gelling material produced by the reaction of potentially active gelling materials such as slag,fly ash,steel slag,and phosphorous slag with liquid and solid activators.Under alkali environment conditions,the silica-alumina mineral raw material has high activity,hydration speed is faster than cement,it can produce gelling substance in a short time,and the reaction speed is faster in materials with high calcium content.Compared with ordinary Portland cement,alkali-activated cementitious materials have higher strength,lower heat of hydration,and better properties of fast hardening,corrosion resistance,frost resistance,and reinforcement,etc.Moreover,the production process is simple,the investment is low,the energy consumption is low,the pollution is small,and the utilization rate of the slag is high,which has become a research hotspot in the field of cementitious materials.In this paper,slag and fly ash are used as raw materials,liquid water glass,Na OH,solid water glass,sulfate,phosphate,and organic alkali are used as activators,and naphthalene water reducer and polycarboxylic acid water reducer are used as additives.The alkali-activated slag/fly ash cementitious material is prepared below.Study the effects of different types of exciter dosage,fly ash content,slag type,and naphthalene water reducer dosage on the mechanical properties and working performance of cementitious materials;the preparation of the type of exciter is preferred to study the Na2O dosage and modulus The influence of hydration heat,hydration products and pore structure of alkali-activated cementitious materials;the types and contents of stimulants are preferred to prepare alkali-activated concrete,and the effects of fly ash content and water-binder ratio on the mechanical properties and working performance of alkali-activated concrete Influence;C50concrete ratio is preferred to make alkali-excited concrete and ordinary concrete simply-supported beam members,to study the crack development,strain and deflection of alkali-excited concrete and ordinary concrete simply-supported beam under static load.The main conclusions of this article are as follows:1.The optimal Na2O content of liquid water glass excited slag/fly ash cement material is6%,the modulus of 1.00 is 28 d,the compressive strength is 63.0MPa,and the bending strength is 12.2MPa;the solid water glass excited slag/fly ash glue The optimum content of Na2O is 4%,the modulus of 0.50 is 28 d,the compressive strength is 20.5MPa,and the flexural strength is 6.3MPa.The compressive strength is 22.3MPa and the flexural strength is6.5MPa;the optimal content of the solid water glass mixed K2HPO4 excitation slag/fly ash cementing material is 6%,the 28 d compressive strength is 39.5MPa and the flexural strength is 8.0MPa.2.The naphthalene-based water-reducing agent has a significant retarding effect on alkali-activated slag/fly ash cementitious materials.With the increase of the amount of naphthalene-based water-reducing agent,the setting time of the cementitious material gradually increases.The naphthalene-based water-reducing agent The initial setting time was362 min,the final setting time was 392 min,and the interval was 30 min.3.The main hydration products of liquid and solid water glass excited slag/fly ash cementing materials are quartz(Si O2),calcite(Ca CO3),mullite(3Al2O3·2Si O2),CSH gel,CASH gel,water Talc(Mg6Al2(OH)16CO3·4H2O)and other components.4.Liquid water glass stimulates the hydration process of slag/fly ash cementitious materials can be divided into early hydration period,induction period,acceleration period,decay period,and slow period.Accelerated exothermic peak appears;the hydration process of solid water glass excited slag/fly ash cementitious material can be divided into early hydration period,decay period,and slow period,without obvious induction period and acceleration period,and appears only at the early stage The instantaneous initial heat release peak,the heat release rate at the initial stage of hydration is large,and then the heat release rate of hydration decreases rapidly.5.The pore structure of liquid water glass excited slag/fly ash cementitious material is mainly gel pores,medium capillary pore content is next,and large capillary pore content is almost no;solid water glass excited slag/fly ash cementitious material The pore structure is mainly medium capillary pores,followed by large capillary pores,and the gel pore content is relatively small.The pore structure distribution of the hardened paste of the cement material is consistent with the compressive strength,and the liquid water glass activator has good excitation effect on the slag/fly ash cement material?6.Liquid water glass excited slag/fly ash concrete 7d concrete compressive strength54.7MPa,28 d concrete compressive strength 62.3MPa.7.Alkali-excited slag/fly ash concrete beams have cracks and develop rapidly at 45 KN,ordinary concrete beams have cracks and develop slowly at 40 KN,and the cracking load is increased by 12.5%;under the same static load,alkali-activated slag /Fly ash concrete beams have greater strain and deflection than ordinary concrete beams.Alkali slag/fly ash concrete enhances the beam's crack resistance and tensile properties.