Study On Composite Modification And Application Of Solid Waste Based Sulfoaluminate Cementitious Materials

Under the background of the "double carbon" target,the large-scale application of sulfoaluminate cementitious materials is of great significance to the low-carbon development of the building materials industry.However,sulfoaluminate cementitious materials cannot meet the construction requirements of some projects because of their rapid setting time and too concentrated early hydration heat release,which limits the large-scale application of sulfoaluminate cementitious materials.Therefore,this study modified solid waste based sulfoaluminate cementitious materials(SSCM)by adding granulated blast-furnace slag(GBFS)powder and steel slag fine powder,studied the influence of GBFS powder and steel slag fine powder on the basic properties of SSCM materials,and explored the reaction mechanism of the modification of GBFS powder and steel slag fine powder.Finally studied the properties of composite cementing materials under pressure forming process,which provides a theoretical basis for the high-value application of composite cementitious materials under the pressure forming process.The main contents and conclusions are as follows.(1)SSCM material was modified by the single admixture,and the effects of GBFS powder and steel slag fine powder on hydration heat,standard consistency water requirement,setting time,compressive strength,hydration properties,and pore structure of SSCM material were investigated.The results show that the GBFS powder reduces the hydration heat release rate and cumulative heat release of the material,and prolongs the setting time of the material,while the steel slag fine powder accelerates the hydration heat release rate of the material and greatly shortens the setting time of the material.The addition of GBFS powder and steel slag fine powder both increases the standard consistency water demand of the material.In contrast,the increase in water demand for the composite material after the addition of steel slag fine powder is greater than that of GBFS powder.In the later stage of hydration,the addition of GBFS powder and steel slag fine powder did not change the type of material hydration products,but additional C-S-H gel was generated in the later stage of hydration,and both GBFS powder and steel slag fine powder could reduce the total porosity of hardened paste and the proportion of harmful pores and multiple harmful pores,which are beneficial to the development of compressive strength of materials.Therefore,both GBFS powder and steel slag fine powder can increase the compressive strength of the material in the later stage.The optimal dosage of GBFS powder is 15%(17.28%increase in strength),the maximum dosage is 25%,and the optimal dosage of steel slag fine powder is 20%(25.34%increase),the maximum dosage is 30%.(2)The SSCM material was modified by adding the mixture of GBFS powder and steel slag fine powder in different proportions,the reaction mechanism of the synergistic excitation effect of GBFS powder and steel slag fine powder was explored,and the hydration heat and compressive strength of SSCM materials modified by GBFS powder and steel slag fine powder were studied.The results show that the mechanism of synergistic excitation is that the hydration of steel slag fine powder increases the content of calcium hydroxide in the material,further stimulates the activity of the GBFS powder,and produces additional C-S-H gel,which is beneficial to the improvement of the mechanical properties of the material.In terms of hydration heat,the mixture of GBFS powder and steel slag fine powder reduced the accumulated heat release in the first 48 hours of SSCM materials.In the early hydration stage,the composite cementitious materials with low GBFS powder content and high steel slag fine powder content have better strength performance.And in the later stage of hydration,the strength improvement of the admixture compound mixing is not as large as the single admixture,but the total amount of the admixture is increased,which is due to the synergistic effect of GBFS powder and steel slag fine powder.The maximum content of the mixture can reach 40%.(3)Under the pressure forming process,the effects of different forming pressures on the properties of SSCM materials and composite cementitious materials were investigated.The results show that the higher the forming pressure,the higher the compressive strength of the test block,and the maximum content of mineral admixtures is increased under the pressure forming process.The maximum content of steel slag fine powder is increased to 40%,and the maximum content of mineral admixtures is increased to 45%.