OPERATIONAL PROPERTIES OF ORGANIC COMPOSITIONS (LIGNIN SULFONATE) IN PORTLAND CEMENT - A COMPARATIVE STUDY WITH GYPSUM IN PORTLAND CEMENT

This study is aimed to examine the methodology of producing of gypsum-free Portland cements, which are prepared from standard white cement clinker with a low percentage of Fe2O3 content. Gypsum-free Portland cement is a binding agent based on Portland cement clinker, in which gypsum with its regulating effect is substituted by the composition of sodium lignin sulfonate and alkali metals such as carbonates.GF cement-based binders have the outstanding property of allowing well workable mixtures to be prepared at very low water to cement ratios. Gypsum-free cement is characterized with short setting time and high initial strength. The lowest water to cement ratios are obtained in a sample that contains 1.2 wt.% of sodium lignosulfonate acid and 1 wt.% of sodium carbonate. The addition of sodium carbonate at 1% into gypsum-free Portland cement can increase its plasticity. Furthermore, 1% sodium carbonate can reduce the initial setting time of gypsum-free Portland cement (for instance, the initial time will decrease to 70 minutes). More sodium carbonate (up to 3%) has a decreasing effect on the properties of initial setting time and final setting time, which will reach to 15 and 20 minutes, respectively. X-ray diffraction pattern for the hydrated pastes of gypsum-free cement and standard white cement clinker shows the reduction of amorphous Ca(OH)2.