The present investigation has been carried out in order to find the significant factors or characteristics for improvement of water resistance of set gypsum. Asphalt-Wax emulsion (emulsified by cationic surface active agent in Hurrel Homogenizer) was employed as the water resistant material. Bulk density, porosity, setting time, compressive strength and water absorption of specimens admixed this water resistant material were determined and the correlation between these physical properties and the factors such as addition amount of Asphalt-Wax emulsion, water/plaster ratio, penetration of asphalt used, Wax/Asphalt ratio in the emulsion and addition of potassium sulfate was discussed.
The results are summarized as follows;
(1) The mixture of asphalt and wax has the synergistic effect on the improvement of water resistance of set gypsum, showing maximum effect when Wax/Asphalt ratio was 30% in the present experiment. (2) The results of analysis of variance executed to estimate the factor effect on water resistance showed that the Wax/Asphalt ratio in the emulsion was the most effective factor and in sequence, addition amount of K
2SO
4 and addition amount of the emulsion were effective. (3) Bulk density and porosity of set mass and setting time are not in substantial conjunction with water absorption, but predominated by the effectiveness of water resistant materials admixed. (4) For all factors except water/plaster ratio, under the more effective condition to improve water resistance of set gypsum, the more decrease in compressive strength was observed.
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