Study On The Mechanism Of Sepiolite-Fly Ash System In Cement-Based Materials

The concept of green and sustainable development has a profound impact on the development trend of modern cement-based materials and started the application of supplementary cementitious materials represented by industrial waste.With the wide application of traditional supplementary cementitious materials,the development and research of new materials have attracted more and more attention.Sepiolite as an excellent functional mineral materials,has been well applied in sewage treatment and functional carrier and its application research in cement base material is not yet perfect.In order to expand the application of sepiolite in cement-based materials and widely promoted the role of sepiolite on cement-based materials.,The mechanism of sepiolite-fly ash system in cement-based materials is studied systematically in this paper.First,the effects of sepiolite species and calcination conditions on chlorine adsorption were analyzed in the functions of sepiolite on chloride ions adsorption.The mechanism of sepiolite on the adsorption of chloride ions was investigated by using the multiple analysis methods.Such as the microscopic analysis?SEM?,the pore structure analysis?BET/MIP?,composition analysis?XRD/IR?and the First principle.Then,the influence law of sepiolite and fly ash on the strength and durability of cement mortar under the conditions of single and compound mixing was investigated.The adsorption results showed that sepiolite had a good adsorption effect on chloride ions.Among them,the mean adsorption values of chlorine ions on three types of sepiolite were up to 5.88 mg/g;Calcination is an effective way to improve the adsorption of sepiolite on chloride ions,and the appropriate calcination temperature is 400?600?.After calcination,the average adsorption value of sepiolite to chlorine ions was increased to 5.93 mg/g.In addition to the characteristics of the sepiolite,the adsorption process of sepiolite on chlorine ions is related to the temperature of the adsorption environment,but is not sensitive to the adsorption time.The pore structure of sepiolite?BET/MIP?shows that the change of pore structure and the increase of specific surface area are the main reasons for calcining to enhance the adsorption of chlorine.composition analysis?XRD,IR?shows that physical adsorption plays a leading role in the adsorption of sepiolite on chlorine ions.At the same time,through modeling analysis?MS/VASP?,it is demonstrated that the Mg²⁺which between sepiolite layers may be the active site for sepiolite to absorb chlorine ions.The results of mechanical properties show that the mixing of sepiolite is beneficial to the strength development of mortar,and has a significant effect on the early strength improvement of mortar.At the 3d curing age,the flexural strength and compressive strength of the mortar mixed with 25%sepiolite increased by 48.3%and 49.1%of the strength of the base group?JZ?respectively.Compared with 20%fly ash alone,when the composite ratio is 20%fly ash and 25%sepiolite,the 3d flexural strength of mortar increased by 69.1%and the compressive strength increased by24.3%.After curing for 28d,the flexural strength and compressive strength of mortar mixed with 25%sepiolite can still be increased by 30.3%and 18.1%of the strength for the JZ group,respectively.Meanwhile,sepiolite and fly ash can both reduce the effect of mortar shrinkage.In addition,the mixing of sepiolite and fly ash has a good synergistic effect on reduce the mortar shrinkage.When the content of fly ash is 20%and sepiolite is 30%,the shrinkage rate of mortar 21d is reduced by 32.5%and25.3%of the shrinkage rate of mortar for the JZ group and the group of single admixture fly ash with 20%.In terms of durability,sepiolite can improve the carbonization resistance of mortar.the mortar has the best carbonization resistance when sepiolite mixed with15%.Compared with the JZ group,the 28d carbonization depth is decreased by37.8%.In sepiolite-fly ash composite system,mix in sepiolite can effectively improve the carbonization resistance of fly ash mortar of which ever made the carbonization resistance of mortar deterioration.The incorporation of sepiolite and fly ash effectively improved the anti-chloride erosion ability of the mortar.When the fly ash and sepiolite content were both 20%,the diffusion rate of chlorine ions in the mortar was only 30%of the JZ group and showing excellent synergistic effect.The microstructure analysis of cement-based materials shows that:?1?The distribution of multi-scale fibers in sepiolite and sepiolite firm cementing effect between the hydration products?SEM?,and the effect on cement hydration?XRD/IR?are the main reasons for the improvement of the strength of cement mortar;?2?Sepiolite plays a key role in improving the durability of mortar by optimizing the matrix structure of dense cement and the distribution of matrix aperture?BET/MIP?;?3?The potential internal curing function of sepiolite was found to be an important factor for its excellent performance in mortar.