| As the typical bulk industrial waste,a large amount of discharge and storage of steel slag,fly ash,desulfurized gypsum,etc.bring serious harm to the environment.The use of steel slag,fly ash,and desulfurized gypsum to prepare inorganic cementing materials to replace part of the cement for industrial production can not only promote the large-scale disposal of industrial solid waste,but also achieve the purpose of reducing cement production,consumption,and cost.In this paper,supersonic steam pulverizer is used to ultrafinely pulverize fly ash and steel slag.Through theoretical analysis and experimental research,the ultrafine pulverization mechanism of fly ash and steel slag and its mechanism of strengthening cementitious materials are clarified.At the same time,fly ash ultrafine powder and steel slag ultrafine powder are selected as the main cementitious materials,and desulfurized gypsum powder is used as auxiliary cementitious material and active activator to design a solid waste ternary cementitious system contain steel slag,fly ash and desulfurized gypsum(SS-FA-DG).The hydration products,reaction mechanism and reaction process of this cementitious system have been researched.The mechanical properties of the cementitious material have been further improved by optimizing the curing conditions and testing of enhanced carbonization.Finally,based on the theoretical research,the engineering application of SS-FA-DG full solid waste ternary cementitious system in high-performance and non-firing permeable bricks was explored.Major results included.(1)The characteristics of fluidized bed fly ash(CFBFA)and coal pulverized coal(PCFA)before and after ultrafine grinding were compared and studied.The results show that the ultra-micronization of fly ash not only increases its specific surface area,but also reduces the crystallinity and anionic polymerization degree of aluminosilicate minerals in fly ash.Research on the performance of fly ash-cement cementing block shows that,fly ash ultrafine powder is more conduciveto the improvement of compressive strength of cement cementation blocks than the original fly ash,especially the development of early compressive strength.Studies on the water absorption and thermal weight loss of the cementitious blocks show that fly ash ultrafine powder improves the compactness of the cementitious blocks and increases the C-S-H content in the blocks.Compared with PCFA,the degree of anionic polymerization of aluminosilicate minerals in CFBFA is lower.CFBFA is more conducive to improving the early compressive strength of cement blocks,while the active Si O2 and Al2O3 in the PCFA glass body are slowly released during the reaction and more conducive to improving the later-stage compressive strength of the block.(2)The ultra-fine crushing characteristics of supersonic steam pulverizer for steel slag were studied in detail.The results show that,after ultra-pulverizing the steel slag,the steel slag ultrafine powders with different particle sizes can be obtained by classified collection.Among them,the steel slag ultrafine powder with smaller particles is enriched with more Ca O and Si O2,has a lower degree of anionic polymerization,and has a smaller crystal size and a higher activity.It is more suitable for the preparation of cementitious materials.The effect of ultrafine powder of steel slag on the performance of cement-fly ash cementation block was studied.The results showed that the use of ultrafine powder of steel slag to replace part of the cement made the fly ash-cement binary gelling system into fly ash-steel slag-cement ternary cementitious system,the compressive strength,the frost resistance and the abrasion resistance of cementitious blocks have been greatly improved.(3)The synergistic of fly ash,steel slag and desulfurized gypsum was investigated with the compressive strength as the main index.The results show that the synergistic of different cementitious systems is:ternary system> binary system(steel slag-fly ash)> single system(steel slag).Using fly ash ultrafine powder,steel slag ultrafine powder,desulfurized gypsum fine powder with a ratio of 70:20:10 to prepare allsolid waste cementitious blocks,the block has high compressive strength(28 days compressive strength is 39.6 MPa)and good water resistance(softening coefficient is 1.09).The SEM,XRD and TGA analysis of the cementitious blocks show that the synergistic of the three kinds of fly ash,steel slag,and desulfurized gypsum is that the steel slag itself has self-gelling properties;the fly ash promotes the secondary hydration reaction of the steel slag to generate more C-S-H gels;desulfurized gypsum participates in the system reaction to generate ettringite crystals,needle-shaped ettringite crystals and C-S-H gels alternately grow to form a dense network structure,reduce the porosity of the block,and optimize the overall block structure,and the desulfurized gypsum has an active excitation effect on fly ash,which deepens the reaction degree,increases the C-S-H content in the block,and also promotes the conversion of hydrated calcium silicate with a high c/s to hydrated calcium silicate with a low c/s,thereby improving the mechanical properties of the cementitious block.(4)The reaction kinetics of the SS-FA-DG cementitious system was studied,and the effect of temperature on the reaction kinetic characteristics was investigated.The results show that the reaction of the SS-FA-DG cementitious system can be divided into five stages.In the first stage,the steel slag is hydrolyzed,and OH-and Ca2+ appear in the liquid phase of the system;in the second stage,the active Al and Si of the fly ash begin to dissolve under the stimulation of OH-,and H2 Si O42-and H2 Al O3-are formed in the solution;In the third stage,H2 Si O42-,H2 Al O3-,SO42-,and Ca2+ react in the liquid phase to produce products such as C-S-H and ettringite.The cementitious block begin to harden and produce a certain compressive strength.In the fourth stage,a large amount of C-S-H was generated,while a large amount of Ca(OH)2 was consumed,and C-S-H began to nucleate and crystallize.In the fifth stage,C-S-H and ettringite crystals continue to diffuse and grow inside the cementitious material to form a network structure,which makes thecemented block more compact and the compressive strength develops rapidly.The increase of curing temperature can shorten the reaction time of each stage of the SS-FA-DG cementitious system and accelerate the hydration reaction speed.At the same time,the increase in temperature increases the degree of polymerization of the hydration product,increases the degree of hydration,increases the amount of C-S-H produced,and makes the compressive strength of the cementitious block higher.(5)The curing conditions of SS-FA-DG ternary cementitious system was optimized.The results show that the compressive strength of the SS-FA-DG ternary cementitious block reached 35.8MPa in a short curing time(<4 days)under the humid and hot+autoclave curing condition,meeting the requirements of the national standard MU35.XRD,FT-IR and TGA analysis showed that hot and humid curing is beneficial to the rapid formation of C-S-H in cementitious blocks,while autoclaved curing promotes the conversion of C-S-H to tobermorite crystals.SEM analysis showed that C-S-H gelation and tobermorite crystals were linked to each other and tightly combined to form a denser microstructure,which resulted in higher compressive strength of the blocks.The cured cementitious block was subjected to enhanced carbonation,which resulted in a more compact cementitious block with its pores filled with nano-size calcium carbonate and thus further improvement in its compressive strength by 19.6%.The physical effect of enhanced carbonation on the cementitious block is increased mass by 1.95%,indicating that approximately 1.95% of CO2 of the mass of the respective cementitious block can be absorbed.(6)The self-developed new technology of "mechanical hole making-static press forming" is used to prepare high-performance non-fired permeable bricks with SS-FA-DG composite fine powder as the cementitious material and steel slag as the aggregate.The aggregatecement is 6: 4,and the water-cement ratio is 0.2,and the gradient autoclave curing condition is adopted.The results show that theperformance of the prepared permeable bricks meet or exceed the requirements of relevant national standards.The permeable brick products have been pilot-produced in Taiyuan Iron & steel(Group),and the pilot products have been laid on the ground in Xiangyuan,Shanxi.After a one-year life cycle,it was found that the long-term stability of the non-fired permeable brick developed by this project is good.It has a good market prospect and economic benefit prospect. |
