Development of Gypsum Block of Energy Conservation and Waste Utilization

Waste, parings and scraps (WPS) in shoemaking industry are difficult to deal with by traditional approaches, which will pollute the environment and results in waste of resources if not handled properly. In this paper, WPS, after modification, is used as reinforcing material in gypsum block, in which livestock-waste based retarder is used to control setting time. The result showed that the proper mass ratio of hemi-hydrate gypsum to WPS is 95:5. The optimal dosage of retarder is 0.23% (on the basis of total solid). The addition of modified WPS remarkably improved the characteristics of anti-cracking, water absorption, dry shrinkage and thermal conductivity of the gypsum block, with little decrease in mechanical strength values.


Introduction
The acceleration of urbanization has promoted the vigorous development of the construction and building industry, and the corresponding building energy consumption is also increasing. According to statistics, 99 % of existing 40 billion square meters of buildings and more than 95 % of new buildings in China belong to high energy consumption buildings. In recent years, as a lightweight material, gypsum block gradually replace the traditional clay brick as non-load bearing interior walls, partition walls, cavity walls, skin walls and pillar casing indoors, which not only can utilize waste gypsum, but also has the advantages of heat preservation, comfortable, and fire-resistant, etc.
In order to further improve the performance of gypsum, some admixtures were added [1,2]. Considering the cost, solid waste is the first choice. At present, a large number of shoe-making plants produce large amount of waste, parings and scraps which will pollute the environment and results in waste of resources if not handled properly. Analysis shows that the main components of them are rubber, adhesives and fiber etc. The combined use of these wastes with gypsum to produce construction block may be a possible approach considering the properties.
The aim of this work is to use WPS in gypsum block, giving full play the synergistic effects between different materials [3,4]. In order to reduce water requirement and increase the compatibility with gypsum, WPS is modified beforehand [5].

Experimental
a Corresponding author : zhaofq3366@126.com MATEC Web of Conferences

Raw materials
The construction gypsum was provided by shijiazhuang changan jiayi building materials Co. Ltd, which is obtained by the desulfurization gypsum calcined at 150-170℃. See Fig. 1. Table 1 gives the composition. Shoe-making industry waste is from the Xiong'an District, see Fig. 2. Gypsum retarder was prepared from livestock-waste [6]. Citric acid, sodium hexametaphosphate and other chemical reagents were bought on the market.

Methods
(1)Modification of WPS. Potassium methyl silicate, VAE emulsion and water are mixed to form modification liquid, in which small WPS fragments are soaked, air dried.
(2)Preparation of gypsum block sample [7]. Construction gypsum, modified WPS fragment, retarder and water are mixed to form gypsum slurry. The slurry is put into mold, then de-mold, curried and air dried to obtain the final product. Fig. 3 gives the flow-sheet of the preparation of gypsum block. T2542-2512. The thermal conductivity of the specimen was determined on DRM thermal conductivity tester [8,9].

Effect of retarder on setting time and mechanical strength
In this work, gypsum retarder was prepared using slaughter plant waste, by hydrolysis and neutralization process [1]. Based on the same initial setting time, the effects of four retarders on the bending and compressive strength of desulphurization gypsum were observed, See table 2. It can be seen from table 2 that, the slaughter plant waste based retarder has less negative effect on the mechanical strength of gypsum, compared to the other three retarders.

Effect of modified WPS on the properties of gypsum block
The first choice is the larger size of the scraps, through the exploration of different dosage, testing the density, water absorption, bending and compressive strength. As can be seen from Fig. 5, with the increase in WPS scraps content, the water absorption of block gradually decreased, indicating that WPS has a significant effect on gypsum system after modification, and the water absorption rate is reduced by 10% compared with the blank experiment.  Figure 7 and Figure 8 show the cross section morphology and profile of the block. It can be predicted that the addition of WPS can improve the crack resistance of the test block.

Effect of scraps on dry shrinkage value and thermal conductivity
The dry shrinkage value and thermal conductivity were tested for addition of WPS scraps in the gypsum. See table 3. As can be seen from table 3, compared with the blank, the dry shrinkage and thermal conductivity of the gypsum system decrease by 43 % and 9.4 % respectively.
That is to say, the addition of WPS scraps can effectively improve the thermal insulation effect of gypsum blocks and reduce the dry shrinkage value [10,11].

Summary
(1)A kind of environment-friendly gypsum insulation block of energy conservation is prepared by using desulphurization gypsum, WPS in shoemaking industry and slaughter plant waste based retarder, realizing solid waste utilization.
(2)The slaughter plant waste based retarder has good retarding effect on construction gypsum and has less negative effect on the mechanical strength of gypsum, compared to the other three retarders.
(3)The addition of modified WPS improved the characteristics of anti-cracking, water absorption, dry shrinkage and thermal conductivity of the gypsum block. In this case, the mechanical strength values of the block decrease [12][13][14].