Lattice Boltzmann based multicomponent reactive transport model coupled with geochemical solver for pore scale simulations

A Lattice Boltzmann (LB) based reactive transport model intended to capture reactions and solid phase changes occurring at the pore scale is presented. The proposed approach uses LB method to compute multi component mass transport. The LB multicomponent transport model is then coupled with the well-established geochemical reaction code PHREEQC which solves for thermodynamic equilibrium in mixed aqueous-solid phase system with homogenous and heterogeneous reactions. This coupling enables us to update solid phases volumes based on dissolution or precipitation using static update rules which, on pore scale, affects the change of potentially pore network geometry. Unlike conventional approach, heterogeneous reactions are conceptualized as volumetric reactions by introducing additional source term in the fluid node next to solid node, and not as flux boundaries. To demonstrate the validity of this approach several examples are presented in this paper

A combined data-driven, experimental and modelling approach for assessing the optimal composition of impregnation products for cementitious materials

The effectiveness of sol-gel based treatments for the protection of concrete depends on their capacity to penetrate into the material pores. Optimization of sol formulation to achieve maximum penetration depth is not a straightforward process, as the influence of different physical properties of the sol varies with the pore size distribution of each concrete. Thus, a comprehensive experimental programme to evaluate this large number of materials would require a significant number of experiments. This manuscript describes an approach, using combined computational and experimental approach to design tailor-made impregnation products with optimized penetration depth on concrete or cementitious materials with different pore size distributions. First, a process-based numerical model, calibrated experimentally for one sol composition and several cementitious material samples with different pore structures is developed. The model calculates the penetration depth for a specific pore structure. The optimization process utilizes the probabilistic and non-parametric Gaussian Processes regression method Gaussian Processes at two steps; first to make the choice of the optimal experimental design, and second to make predictions of physical properties based on the obtained training points. In the final step, the penetration depth is calculated for each mix combination in defined parameter range. The effectiveness of this approach is demonstrated on three cases. In the first instance, we optimized the impregnation product for the maximum penetration depth without any restrictions. With another two cases, we impose the restrictions on the gelation time, i.e. the time in which the sol reacts to gel. The validation of the procedure has been made by the use of a blind validation and shows promising results. The impregnation product penetrated significantly deeper with a product selected by using the described procedure compared to the considered best product before this optimization. The proposed procedure can be applied to a wide range of cementitious materials based on their pore size distribution data. This offers significant advantage compared to purely experimental approaches, where a set of experiments is required for each considered material

On the Effects of Relative Humidity and CO2 Concentration on Carbonation of Cement Pastes

Many environments to which concrete is exposed are highly aggressive due to various chemical components. In such environments, concrete is subjected to processes of chemical degradation, among which carbonation is one of the most frequently seen degradation processes. Though, the influence of saturation degree (or relative humidity - RH) of the specimen and CO2 concentration on the carbonation of cementitious materials is still not comprehensively described with respect to carbonation rate/degree as well as alteration in microstructure and mineralogy. This work aims at thoroughly investigating how these two key parameters affect the carbonation under accelerated conditions. Furthermore, the effect of initial moisture state of the specimen on the carbonation rate is also demonstrated. For such purpose, a numerical model at continuum scale is developed to investigate the effects of RH and CO2 concentration on the carbonation depth, phase changes in phases and porosity of hardened cement pastes due to carbonation under accelerated conditions. Verification with experimental results from accelerated carbonation tests shows a good agreement. The modelling results with supporting experimental data help to better understand the modification of material properties under different carbonation conditions and to optimize the carbonation conditions

The importance of physical parameters for the penetration depth of impregnation products into cementitious materials: Modelling and experimental study

The performance of impregnation treatments used for protection and remediation of porous building materials relies on sufficient penetration depth. The penetration of sol-gel impregnation products into partially saturated porous material is driven by capillary suction and depends on material properties, such as pore size distribution on one hand, and on the other hand on sol physical properties, viscosity, density, surface tension and contact angle, along with the time in which the sol gels. In this work we analyse, by the way of modelling and experiments, the penetration depth of a sol-gel impregnation product as the function of pore size distribution and sol properties. The main goal is to determine the importance of sol's physical properties for the penetration depth for a specific pore size, which will serve as a basis of the optimization of impregnation products to maximize their penetration depth. The model is first calibrated in terms of penetration depth and sol uptake by the experimental data obtained from mortar samples each with a specific pore-size distribution. The correlation between penetration depth and physical parameters is then established by the use of Monte-Carlo method. The results show that the most important parameters for the optimization are surface tension, whose influence increases for larger pores, and gelation time, which with decreasing importance for larger pores. (C) 2020 The Author(s). Published by Elsevier Ltd

Influence of Micro-Pore Connectivity and Micro-Fractures on Calcium Leaching of Cement Pastes — A Coupled Simulation Approach

A coupled numerical approach is used to evaluate the influence of pore connectivity and microcracks on leaching kinetics in fully saturated cement paste. The unique advantage of the numerical model is the ability to construct and evaluate a material with controlled properties, which is very difficult under experimental conditions. Our analysis is based on two virtual microstructures, which are different in terms of pore connectivity but the same in terms of porosity and the amount of solid phases. Numerical fracturing was performed on these microstructures. The non-fractured and fractured microstructures were both subjected to chemical leaching. Results show that despite very different material physical properties, for example, pore connectivity and effective diffusivity, the leaching kinetics remain the same as long as the amount of soluble phases, i.e., buffering capacity, is the same. The leaching kinetics also remains the same in the presence of microcracks

Podmol pri Kastelcu - novo večplastno arheološko najdišče na Krasu, Slovenija

The paper concerns the results of trial excavation in the new Holocenc archaeological cave site at Podmol on the Petrinjc Karst in Slovenia. Stratigraphie sequence is 8 metres deep. Eleven Holoccnc layers yielded numerous finds from Ncolithic, Copper, Bronze, Roman and Mediaeval Age. This is the most complete archaeological stratigraphy of Holoccne period in Slovenia till now, especially for Copper Age and the Copper-Early Bronze Age transition. Radiocarbon dates do not exist. Many aspects of the site and its finds were analised: pcdological-scdimcntological, archaeological, palaeofaunistical and palaeobotanical.V prispevku so obdelana poskusna izkopavanja v novem arheološkem jamskem najdišču Podmol na Petrinjskem Krasu v Sloveniji. Ugotovljen je bil 8 m debel stratigrafski niz, obsegajoč obdobja neo- in eneolitika, bronaste dobe, antike l n srcdnjcga veka. Trenutno je lo najdišče z najpopolneje ohranjeno stratigrafijo za holocensko obdobje v Sloveniji. To velja še posebej za eneolitik in za prehod iz eneolitika v zgodnjo bronasto dobo. Najdišče radiokarbonsko ni datirano. Podmol je bil vzorčno kompleksno obdelan: narejene so bile pedološko-sedimentološke raziskave ter paleovegetacijske in paleofavnistične analize. Vse so dale prepričljive preliminarne rezultate

Diffusion velocity lattice Boltzmann formulation applied to transport in macroscopic porous media

This paper describes the application of a single relaxation time (SRT) lattice Boltzmann scheme to the transport in porous media with large spatial variations of diffusion coefficients. Effective diffusion coefficients can vary substantially within porous media because of their dependence on porosity and tortuosity which can span over several orders of magnitude, depending on pore size and connectivity. Moreover, when mass is transported with pore-water in porous media, the hydrodynamic dispersion, which depends on Darcy's velocity, contributes additionally to the usually anisotropic variation of the dissipative term. In contrast to the traditional treatment of spatially variable diffusion coefficient by the variation of a SRT, here the variability is accommodated through the use of diffusion velocity formulation which allows for larger variabilities of diffusion coefficient. The volume averaged properties of mass transport in macroscopic porous media are resolved through the additional source term which is similar to the existing force adjusting methods. The applicability of both the proposed schemes is demonstrated on two examples. The first demonstrates that the method is accurate for the large variation of diffusion coefficients and porosities. The second example introduces mass diffusion in a real, geometrically complex system with spatially contrasting properties