Ceramics-Silikáty 63, (4) 390 - 398 (2019)

It is important to select a certain type and amount of a superplasticizer (SP) for successful cement applications in concrete. The results show that the SPs ((lignosulphonates (LS), polyacrylates (PA) and polycarboxylates (PCE)) especially differ by their electrical conductivity (EC) values (from 2.5 to 4 times) and mostly influence the spreadability, viscosity, temperature and hydration course of the cement paste with an SP. Compared to the pure cement paste's viscosity, all the tested amounts of LS, PA and PCE lower the initial temperature of the cement paste, but only PCE and PA noticeably reduce the viscosity. It can be highlighted that LS, characterised with high EC values causes a rise in the cement paste temperature and a sharp growth in the viscosity. PCE and PA with much lower EC values, reduce the temperature and, correspondingly, the viscosity of the paste. EXO temperature tests revealed that the same amount of SP's (0.2 %) has a different effect on the course of the hydration, the EXO maximum time and the temperatures. Compared to the pure cement paste, LS reduced the EXO maximum time by 17 % and lowered the EXO maximum temperature by 6 °C, whereas PCE and PA extended the EXO maximum time by 11.3 % and 12.2 %, respectively.