The Influences of Gypsum Water-Proofing Additive on Gypsum Crystal Growth

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The influences of gypsum water-proofing additive on gypsum crystal growth

Abstract
The gypsum water-proofing additives were composed of organic emulsion that were emulsified by polyvinyl alcohol and stearic acid and saline water-proofing additive made of alunite, carboxylic acid sodium, aluminium sulfate, etc. Using modern testing instrument, such as SEM, EPS, the influences of gypsum water-proofing additives on the crystal growth of gypsum products and its water-proof mechanism were analyzed from the perspective of the crystal changing of gypsum after adding gypsum water-proofing additive. Such results show that organic emulsion can be adsorbed selectively on the gypsum crystal surface, inhibiting the crystal growth along axis c. Besides, anion RCOO −

, cations Na
+
and Al
3+
in
saline water-proofing additive can be adsorbed selectively to crystal section (111) to coordinate, slowing down the growth speed along axis c, which could balance the speed in all directions and turn the crystal into a short hexahedron pole. © 2006 Elsevier B.V. All rights reserved.

Keywords: Gypsum water-proofing additive; Crystal growth; Adsorption; SEM 1. Introduction
At present, all kinds of gypsum products are widely used in the building trade because of their various fine performances. How- ever, their low strength and weak performances in both water- proof and damp proof are clearly found [1]. The water-absorbing rate of the ordinary gypsum products is generally about 50%, and the intenerate coefficient is only about 0.2 – 0.3, so the products are easily deformed after being dampened; besides, it causes building walls to soften and rot. Those shortcomings have been greatly hampering the development of the gypsum products.

For this reason, a large amount of research [1 – 7] on the water- proof performance of gypsum products has been carried out at home and abroad, and a great deal of achievements have been
made. One method was to mix organic water-proofing additive
agent (such as silica gel) into gypsum materials in order to reduce the water-absorbing rate of the gypsum material; another was to add cement directly into the building gypsum so that the gypsum could be transformed into a water rigid material. Unfortunately, the results of those methods were unsatisfactory. Later new

methods were tried, such as painting an organic water-proofing additive on the gypsum board or choosing a water-proof layer, but they just had a temporary effect, and failed to solve the funda- mental water-proof problem of the gypsum products.

Here, a new type of gypsum water-proofing additive was crea- ted by emulsifying polyvinyl alcohol and stearic acid together, and mixing with alunite, carboxylic acid sodium, aluminium sulfate, etc. as the saline water-proofing additive. This new water-proofing additive turned out to be quite satisfactory. It can be mixed with gypsum and water directly and causes the crystallization of the gypsum. Recently, too much attention was paid only to the water- proofing additive and the effects; researches only analyzed the reason, theory and the mechanism, ignoring the crystallization process. They omitted the influences of the gypsum water-proofing Materials Letters 61 (2007) 872 – 876

www.elsevier.com/locate/matlet
⁎ Corresponding author. Tel.: +86 531 8276 5974.
E-mail address: ligz5974@163.com (G. Li).
Table 1
Composition of the raw material
Sample
number
Gypsum
(g)
Organic emulsion
(ml)
Saline water-proofing
additive (g)
Water
(ml)
1 1200 0 0 750
2 1200 0 12 750
3 1200 60 0 690
4 1200 60 12 690
0167-577X/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2006.06.005
additive on the crystallization and the water-proof effect, etc. As regards to this purpose, we carried out the following research. 2. Raw materials and experiment method
2.1. Raw materials
The building gypsum produced in Shandong Pingyi Jinxin
Gypsum Company of China was chosen. SO 3 holds...
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