Ceramics-Silikáty 50, (2) 115 - 122 (2006)

In this work, the ability to reduce the harmful influence of wood extractives using the pozzolanic mineral additive, carbonated opoca, was investigated. The influence of various wood species extracts on the setting time and the hardening of two types of Portland cement, CEM I 42.5 R and CEM II/A-L 32.5, was searched. It has been found that cement hydration, setting and hardening depend upon wood extract concentration and do not depend on wood species and preparation method. The influence of extractive additives on binding material (pure cement and cement with opoca additive) was estimated according to the setting time of binding material paste, active portion of the reaction products of cement hydration changes, cement stone strength and X-ray diffraction of hardened cement stone. The investigation data show that wood extractives decrease the hydration of cement and pozzolanic additives effectively minify this influence. The expediency of employing mineral additives (opoca) with a large specific surface was confirmed and that opoca surface was found to influence the binding rate of CaO. The opoca specific surface influences its pozzolanic activity and adsorption ability. At the initial stages of cement hardening the strongest influence of the particle fineness of opoca additive was observed on its adsorption properties. At later stages of hardening the influence of opoca additive particle fineness on its pozzolanic properties (binding of separating Ca(OH)₂) increased.