Study On Effects Of Activators On Gypsum Composite Cementitious Materials

Gypsum composite cementitious materials is the new gelled material preparedwith raw materials of gypsum,slag or fly ash and ordinary Portland cement etc.Gypsum composite cementitious materials prepared with desulfurization gypsum, slagand ordinary Portland cement consume lower energy during the process of productionand utilize mass industrial by-product gypsum. But setting time is long, poormechanical properties and water resistance of gypsum composite cementitiousmaterials using the original desulfurization gypsum preparation. So this paper choosesNaOH, KAl（SO₄）₂.12H₂O, Al₂（SO₄）₃·18H₂O and CaCl₂as activators to research settingtime, mechanical performance and water resistance and study on effects of activatorson gypsum composite cementitious materials by using XRD and SEM test methods.Because of gypsum composite cementitious material is a system of high sulfur, addingactivators may cause bad soundness, so this article researched the effect ofKAl（SO₄）₂.12H₂O, Al₂（SO₄）₃·18H₂O and CaCl₂on volume stability of gypsumcomposite cementitious material.The results are as follows:Alkali activators such as lime, NaOH and cement, both shorten the setting timeand increases the compressive strength of gypsum composite cementitious material,especially the cement, But the dosage of cement should not be more than10%,otherwise it will lead to volume stability significantly worse.Activators such as KAl（SO₄）₂.12H₂O, Al₂（SO₄）₃·18H₂O and CaCl₂shorten thesetting time; KAl（SO₄）₂.12H₂O and Al₂（SO₄）₃·18H₂O activator improve the bleedingof gypsum composite cementitious material significantly, but CaCl₂increases thebleeding rate slightly. Whether water, air or steam curing, KAl（SO₄）₂.12H₂O,Al₂（SO₄）₃·18H₂O and CaCl₂both increase the strength of gypsum compositecementitious material, especially the early strength.KAl（SO₄）₂.12H₂O, Al₂（SO₄）₃·18H₂O and CaCl₂activator significantly improvethe water resistance performance of gypsum composite cementitous material, makingthe softening coefficient of the specimens above0.85. When KAl（SO₄）₂.12H₂Oactivator content is1%, the softening coefficient can reach0.91; When content was1.5%, the softening coefficient decreases but is still higher than specimen not mixedactivator. Al₂（SO₄）₃·18H₂O present the same rules. Specimen’s water resistance increased with the dosage of CaCl₂increased.When water curing, KAl（SO₄）₂.12H₂O, Al₂（SO₄）₃·18H₂O and CaCl₂activatorrestrain inflation of specimens; When air curing, KAl（SO₄）₂.12H₂O restrain shrinkageof specimens; Al₂（SO₄）₃·18H₂O and CaCl₂slightly increase the shrinkage of thespecimens, When steam curing, specimen’s shrinkage was less than air curing.By XRD and SEM know adding KAl（SO₄）₂.12H₂O, Al₂（SO₄）₃·18H₂O and CaCl₂activator in the gypsum composite cementitious material don’t change hydrationcategories, but make the specimen more hydration products generated and the structuremore compacted; This mainly because adding KAl（SO₄）₂.12H₂O, Al₂（SO₄）₃·18H₂O and CaCl₂activator improve the ion concentration of the system accelerating thehydration of slag.