The article presents the results of the research survey of the old rural constructions in the Koło Basin (Central Poland) and its closest vicinity, conducted by the authors in the period 2011-2013. From the beginning of the 19th century until the late 1960s, the population of that region tended to use for construction limestone, instead of wood which for centuries was the most common building material on Polish lowlands. Using the local deposits of limestone, excavated near Rożaniatow village, various structures were built, with the parts of the building most endangered by degradation made of ceramic bricks (for corners and window/door frames) or glacial erratics (for wall base), thereby forming structures with specific architectural and aesthetic features, unique to that region. The survey was conducted in 165 villages of the region, cataloguing more than 2,000 such structures - residential buildings, farm facilities, industrial buildings. Many of these buildings display a similar elevation style of same-coloured stones, making them one of the most specific elements of the landscape.
The analysed area, just like the majority of rural Poland, is currently undergoing socio-economic changes which started in the 1990s and intensified after Poland joined the European Union. Changes in production profiles and farm sizes, migration of rural population to cities or countries of Western and Northern Europe, and progress of suburbanization are some of the main factors which trigger significant changes in the settlement network of the country. This is the right moment to assess whether the traditional solutions applied in the rural construction of the Koło Basin are worth modern application or whether they are only an element of cultural heritage valuable just from the historical perspective.
The liquid limit - wL, the external surface area - Se, the concentration of exchangeable cations - Zi and the cation exchange capacity - CEC of seventeen clayey soils were determined. Finding the correlation between the liquid limit, external specific surface area and exchangeable cation concentration was the aim of this study. Experimental study performed using soils of the external surface area within the range of 4.1 to 118.5 m2·g-1. The relative content of sodium cation (i.e. Na+/CEC) varying between 0.03 and 1.0. Obtained results point to statistically significant relationship between these three properties. The greatest predictive power of linear regression was found for soils of external specific surface area larger than 60 m2·g-1. For the soils of comparable external surface area, the liquid limit increase with increasing the ratio of the content of sodium cation to the cation exchange capacity - Na+/CEC. For the soils of comparable composition of exchangeable cations the liquid limit increase with increasing the external surface area. These relationships indicates that interparticle forces have a prominent role in determining liquid limit of clayey soils.
The paper presents results of a study on the amount of water associated with the solid phase of the clay water system at the plastic limit. Two model monomineral clays, namely kaolinite, and montmorillonite, were used in the study. The latter was obtained by gravitational sedimentation of Na-bentonite (Wyoming).
The calculated mean number of water molecule layers on the external surface of montmorillonite was 14.4, and water in interlayer spaces constituted 0.3 of the water mass at the plastic limit.
The number of water layers on the external surface of kaolinite particles was 63, which was related to the higher density of the surface electrical charge of kaolinite compared to that of montmorillonite.
The calculations were made on the basis of the external surface area of clays and the basal spacing at the plastic limit measured by an X-ray diffraction test. The external surface area of clays was estimated by measuring sorption at a relative humidity p/p0 = 0.5.