Modelling of 3D microstructure and effective diffusivity of fly ash blended cement paste

Abstract

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 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.

Lattice Boltzmann modelling of ionic diffusivity in non-saturated limestone blended cement paste

“…The intra-particle chemical phase distribution of Portland cement was determined by analysing the scanning electron microscope (SEM) images of well-polished cement powder. The distribution corresponding to the autocorrelation functions of mineral phases is consistent with that reported in [33]. LP was regarded as pure CaCO3 with a density of 2.71 g/cm 3 , the particle size distribution of which is also presented in Fig.…”

“…A LB model for diffusion [33] was used for the second step to simulate the ionic diffusion through 3D microstructure and estimate the ionic diffusivity in partially saturated limestone blended cement paste. To simulate the ionic diffusivity, the ionic diffusivity in capillary pore water and C-S-H gel of cement paste as inputs needed to be determined.…”

Analysis of Strength and Microstructural Characteristics of Mine Backfills Containing Fly Ash and Desulfurized Gypsum

“…Thus, exploring the feasibility of using FA and DG to prepare mine backfilling is the main purpose of this study. Scholars have so far used backfill samples with ecofriendly binders [30,31] and cement-based composites [32] on a single or combination of FA [33,34] and DG [35,36] as industrial waste.…”

Microscopic Modelling of Permeability in Cementitious Materials: Effects of Mechanical Damage and Moisture Conditions

“…Afterwards, the cellular automa-ton-like evolution rules with pre-defined dissolution and reaction probabilities were employed to manipulate the movement and phase transition of basic voxels accounting for the reactions in the system, which simulates the cement hydration process and leads to the microstructural development. More details about the modelling procedure can be found in a previous publication (Liu et al 2020c). For the attributes of binder used in the simulations, Portland cement with Blaine fineness of 369 m 2 /kg consists of 53.72% C 3 S, 24.09% C 2 S, 7.61% C 3 A, 8.98% C 4 AF and 5.60% CaSO 4 •2H 2 O.…”

“…However, the remaining experimental data (Wong et al 2009;Hamami et al 2012;Tracz 2016) are far smaller than the simulation results. One of the reasons is that the experimental porosity was measured using the water displacement method, which can be regarded as the total porosity including gel pores and capillary pores (Liu et al 2020c). Treating the average gel porosity of C-S-H in cement paste as 0.28 (Powers 1958), the gas permeability can be expressed as a function of total porosity (Fig.…”