Structuring of a foam concrete matrix from the perspective of fractal percolation theory on RLA, DLA, DLCA models

Abstract

Introduction. Foam concrete is a complex highly porous system, the structuring process of which (sol-gel transition) determines its physical, mechanical, and operational characteristics. Fractal percolation theory is a modern tool for describing and modeling the formation of the fractal pore structure and the cement matrix. Aim. To analyze the phase transition of the foam concrete matrix from a colloidal solution to a solid body from the perspective of fractal percolation theory using computer aggregation models (RLA, DLA, DLCA), as well as to experimentally study the effect of surfactants on the setting time. Materials and methods. The experimental part used Portland cement CEM I 42.5N, technical water, and a synthetic silicone foaming agent “Penta Pav 430A”. Cement paste (W/C=0.24) was prepared in a control mix and with a surfactant additive. Setting times were determined according to GOST 30744–2001 using a Vicat device. The theoretical part was based on the analysis of diffusion-limited (DLA) and reaction-limited (RLA, DLCA) aggregation models. Results. It was established that the introduction of a synthetic foaming agent in the range of 0.3–3 % increases the setting time of the cement paste by an average of 30 minutes. It is shown that the percolation transition (onset of setting) occurs when the concentration of chemically bound particles reaches 22 to 30 %. The presence of surfactants shifts the onset of setting, but the critical ratio of free to bound particles remains practically unchanged. Conclusions. It is concluded that to prevent sedimentation and form a strong framework, it is necessary to control the setting kinetics through the water-solid ratio and the introduction of chemical additives.