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This paper presents the results of natural radionuclide concentration and activity index study in materials used for construction in Latvia. Special attention is given to clay and clay ceramics. Concentrations of K-40 and Th- 232, U-238 radioactivity were determined using gamma-spectrometry method. In some building ware, maximal concentration of K-40 was 1440 Bq/kg, and of U-238 - 175 Bq/kg. In granite, the determined maximum concentration of Th-232 was 210 Bq/kg. It was found that radionuclide content in different period clay deposits can differ by more than two times, and up to five times in different clay ceramics. The results obtained are compared with analogous data from the other Baltic and North European countries.

Highly porous cordierite ceramic by using of talcum, kaolinite and γ-alumina was obtained by method of slip casting of concentrated suspension. Additives of amorphous silica and non-stabilized zirconia in the amount of 5 wt% were used. Sintering temperature of dried samples was in range of 1250 – 1450°C. All the samples contain crystalline phases of cordierite, mullite and corundum but, depending on the additives, as a result of sintering in addition forms spinel, cristobalite or zircon (ZrSiO4). Porosity of obtained materials changes in large scale from 42 to 59 per cent; it is influenced by both sintering temperature and composition. Compressive strength increases with the addition of zirconia. In comparison, compressive strength of samples without additives or with silica additive does not exceed 3.5 MPa. The increase of coefficient of thermal expansion depends both on the composition and sintering temperature. ZrO2 additive increases the coefficient of thermal expansion considerably.

Devonian clay of Liepa deposit (district of Cesis) and Quaternary clay of Laza deposit (district of Aizpute) was investigated. Pellets were fired at four different temperatures of 700, 800, 900, and 1050 °C. Porosity and surface area of pellets was determined by mercury porosimetry. The pH values after water immersion of fired pellets was determined with a pHmeter. The sorption ability of molecular substance (iodine) and ionic substances (ammonia and dichromate) were determined by titrimetric methods.The best sorption ability was found for iodine molecules. The entire amount of iodine in the water suspension was absorbed in two weeks, and the sorption ability reached 12.5 mg/g for samples fired at 700 and 800 °C temperature for the Liepa clay and 13.0 mg/g for the Laza clay. The sorption ability of these clay pellets for ammonia was lower and amounted to 3.0 and 2.5 mg/g, respectively. The sorption ability for dichromate ion was even less -only 0.6 mg/g for pellets of both clays.The investigated fired porous clay granules exhibited distinct sorption properties towards water-soluble ionic and molecular substances, which depended more on the firing temperature of granules and less on the source of clay.