Modelling of 3D microstructure and effective diffusivity of fly ash blended cement paste
Modelling of 3D microstructure and effective diffusivity of fly ash blended cement paste
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DOI：
10.1016/j.cemconcomp.2020.103586
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发表时间：
2020-07
影响因子：
10.5
通讯作者：
Cheng Liu;Fazhou Wang;Mingzhong Zhang
中科院分区：
文献类型：
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作者：
Cheng Liu;Fazhou Wang;Mingzhong Zhang
准确预测粉煤灰水泥浆体的微观结构演变和离子扩散系数，对水泥混凝材料的实际应用和耐久性设计具有重要意义。本文提出了一个综合建模框架，用于模拟不同粉煤灰替代水平和水胶比（w/b）下混合水泥浆体的三维微观结构和有效离子扩散率。在此基础上，考虑C-S-H凝胶中毛细孔和凝胶孔对离子扩散的贡献，采用晶格玻尔兹曼（LB）扩散模型对有效扩散系数进行了模拟。对硅酸盐水泥与粉煤灰的形貌、水化过程和粉煤灰混合水泥浆体的孔隙结构进行了表征，并对有效离子扩散系数进行了测定。模拟结果在水化热、氢氧化钙含量、粉煤灰水化程度、孔隙率和有效扩散系数等方面与实验数据吻合较好，表明所建立的基于微观结构的LB扩散模型能够较准确地预测粉煤灰水泥浆体的离子扩散系数。粉煤灰的加入有助于降低水泥浆体的离子扩散率，特别是在发生毛细孔隙脱渗后，由于火山灰型C-S-H凝胶的扩散路径更为曲折。
Accurate prediction of microstructural evolution and ionic diffusivity in fly ash blended cement paste is significant for practical application and durability design of blended cementitious materials. This paper presents an integrated modelling framework for simulating 3D microstructure and effective ionic diffusivity of blended cement paste with various fly ash replacement levels and water-to-binder (w/b) ratios. A voxel-based hydration model using cellular automaton-like evolution rules was developed to simulate 3D microstructural development of fly ash blended cement, based on which the effective diffusivity was simulated using a lattice Boltzmann (LB) model for diffusion considering the contributions of both capillary pores and gel pores in C–S–H gels to ionic diffusion. A series of experiments were conducted to characterise the morphology of Portland cement and fly ash, hydration process and pore structure of fly ash blended cement paste and measure the effective ionic diffusivity. The simulation results agree well with experimental data in terms of hydration heat, calcium hydroxide content, degree of hydration of fly ash, porosity, and effective diffusivity, which suggests that the developed microstructure-based LB model for diffusion can predict the ionic diffusivity of fly ash blended cement paste with high accuracy. The addition of fly ash can help reduce the ionic diffusivity of cement paste particularly after the capillary porosity depercolation occurs due to the more tortuous diffusion paths in the pozzolanic C–S–H gels.