Alternative Setting Retarders for Portland Cement Clinker

摘要

Other compounds than gypsum to regulate the setting of Portland cement clinker have been investigated. This will potentially improve particle packing of such a cement since elongated ettringite needles should NOT form on the surface of the cement grains in the fresh stale as with gypsum as set regulator. It has been demonstrated that small dosages of citric acid (0.2%), lignosulphonate (0.3%) and tannic acid (0.05%) can be viable alternative set regulating admixtures to 3.5%) gypsum in Portland cement clinker. It has been proven for paste specimen cured for 90 days that the porosity of clinker paste with w/c = 0.45 using 0.05% tannic acid has more than 20% reduced porosity compared to paste made with the normal 3.5% gypsum dosage of clinker mass at the same w/c. In addition to reduced total porosity, the pore openings were also finer.