# Water Impermeability of Self-Compacting Fly-Ash-Containing Concrete
## 1 Introduction
The experimental data are well approximated by a power law of the type [15]:  
\[FC=K_{c}\cdot f_{c}^{m} \tag{4}\]  
where \(f_{c}\) is the strength of concrete, \(K_{c}\) and \(m\) are coefficients influenced by the characteristics of concrete mixtures, hardening conditions, hardening duration, etc. Considering the wide variety of factors affecting concrete's water impermeability, the coefficients \(K_{W}\) and \(\mathrm{m}\) in Equation (4) should be experimentally determined when predicting water impermeability and designing concrete compositions. [PERSON] proposed [16] to predict the concrete water impermeability using the equation:  
\[\mathrm{W}=\mathrm{A}\cdot(R_{\mathrm{c}\mathrm{m}}/100)\cdot(\mathrm{C}/ \mathrm{W}-0.5) \tag{5}\]  
where W is the water impermeability class of concrete (MPa\(\cdot 10^{-1}\)), \(R_{\mathrm{c}\mathrm{m}}\) is the compressive strength of cement (MPa), and C/W is the cement-water ratio. It is proposed to take the coefficient A for the reference composition equal to 1 and for other compositions to be determined by a special nomogram that considers the effect of W/C, water consumption, active and inert additives, and air pore volume. However, this equation does not objectively reflect the effect of active mineral additives on water impermeability. In some cases, it is necessary to assess the change in the water impermeability of concrete under prolonged exposure to water pressure. Many authors have noted the increase in concrete water impermeability in the natural environment [17]. For example,data on the water impermeability of concrete, determined on cores drilled at different times from Italian dams, indicate a decrease in the concrete filtration coefficient by three orders of magnitude from 90 days to 27 years [15]. The increase in concrete water impermeability in the later stages of hardening can be significantly higher than the relative increase in concrete strength. To achieve significant and stable growth in concrete water impermeability over time, it is necessary to ensure sufficient humidity of concrete during hardening [18]. Adding organic and inorganic additives to the concrete mix is an effective way to reduce its permeability. Surfactants and polymer additives are the most commonly used organic additives. When reducing the overall permeability of concrete and increasing the water impermeability, surfactants reduce the W/C, increase the density, and reduce the average capillary radius. In addition, most surfactants promote air entrainment of the concrete mixture, which contributes to forming a conditionally closed capillary-porous structure and reduces permeability [19]. Dispersed mineral additives, acting as active concrete fillers, significantly impact the formation of the cement stone structure and the pore structure of concrete, which should accordingly affect its water impermeability. As is well known, the water impermeability of concrete significantly depends on the value of sedimentation porosity, which is also considerably affected by active mineral additives. In turn, the sedimentation porosity of concrete is primarily determined by the water separation of the concrete mix. Ensuring resistance to stratification is particularly important for self-compacting concrete mixes. This study's aim, the results of which are presented in the paper, was to investigate the influence of the main factors of the concrete mixture's composition and the dispersion of fly ash as an active mineral additive on the water impermeability of concrete and to establish a correlation between water impermeability and compressive strength for self-compacting fly-ash-containing concrete. The technological factors' influence on the concrete mixture's water separation was also studied.