Microstructure And Water-oil Transfer Characterization Of Cement Stone Based On NMR Relaxation Method

At present,with the rapid development of sponge city construction,research on different functional building materials has become a hot topic of academic research.In this study,a series of highly adsorptive cement stones with high water absorption and oil absorption were prepared.It is used for the bonding of permeable concrete coarse aggregate in slope protection engineering and the filling of open grade asphalt pavement in pavement engineering.Through nuclear magnetic resonance relaxation method,a corresponding calibration method of adsorption of water,diesel,soybean oil,and engine oil onto cement paste was proposed.Based on the calibration results,the NMR data are analyzed to explain the mechanism of fluid transport and diffusion in the cement paste,and the flow and transmission characteristics of interlayer pores,gel pores,hydrate pores,and capillary pores of cement-based materials are described.A pore transport model based on the NMR relaxation method is proposed.The main research contents are as follows:(1)From the perspective of pore microstructure regulation,a series of cement stones with discontinuous particle size grading of different mineral admixtures were prepared using P·Ⅱ42.5 Portland cement and four types of cementitious materials,namely grade II fly ash,S95 slag,and S105 slag.Based on the capillary water absorption and oil absorption coefficient and compressive strength as indicators,macroscopic capillary water absorption and oil absorption experiments and compressive bending strength experiments of cement stone were designed.The results showed that a water cement ratio of 0.5,with 70% grade II fly ash and 10% S95 slag added,can significantly improve the adsorption performance of cement paste and maintain necessary strength.Cement stones with a pore size ratio of over 50% in the range of 200 nm to4000 nm characterized by mercury intrusion are called high adsorption cement stones.(2)Based on the oil absorption characteristics of oil absorbing materials and existing research on the hydrophilicity of cement-based materials modified with external additives,adding 3% polyethylene glycol inside and outside of high adsorption cement stone can further enhance the oil adsorption capacity of cement stone.However,as the amount of polyethylene glycol added increases,its oil absorption performance slightly weakens.(3)By combining the nuclear magnetic Hahn echo experiment,nitrogen adsorption experiment(BET),and mercury intrusion experiment(MIP),the single-layer water film calibration method,BET specific surface area calibration method,and mercury intrusion volume accumulation curve calibration method were completed.Analyzed and studied the characterization characteristics of NMR pore distribution curves obtained by different calibration methods.Based on the testing principle of low field nuclear magnetic resonance,a new method for pore calibration of cement-based materials,namely the nonlinear joint calibration method,is proposed.By establishing a power Exponential function model jointly calibrated by BET and MIP,the corresponding relationship between BET,MIP and NMR pore distribution curves is achieved,and the conversion model between transverse relaxation time T2 and pore fluid(water,diesel,soybean oil,engine oil)diameter d is completed.(4)The NMR technology is used to monitor the state of fluid penetration into the pore structure,and characterize the adsorption characteristics of the interlayer pores,gel pores,hydrate pores,and capillary pores of cement-based materials during the water absorption process.The interlayer pore water and gel pore water of highly adsorptive cement paste increase alternately during the adsorption process;The pores between hydrates quickly reach saturation adsorption capacity;The adsorption effect of capillary pores is strong,and pore fluid permeates from small capillary pores to large capillary pores.Fluid is transported through small capillary pores,rather than the most probable capillary pores.(5)The monitoring results of the process of self infiltration and water absorption,diesel,soybean oil,and engine oil using high adsorption capacity cement stone showed that different oil substances can also enter the full type of pores of cement stone,and the process of adsorbing diesel and water is similar.Diesel can accelerate the evolution of interlayer pores and promote the formation of more interlayer pores;The pore fluid movement of soybean oil and engine oil is relatively similar,mainly diffusing in the pores.