Preparation of Thermal Insulation Plaster with FGD Gypsum

Thermal insulation gypsum plaster was prepared from flue gas desulphurization (FGD) gypsum. K12 is more recommendable as foaming agent, when the mass fraction of K12 is around 0.1 %, the setting time and compressive strength meet the requirements of gypsum-based construction materials. In the meanwhile, the thermal conductivity is 0.18 W m−1 K−1, which can be used as a thermal insulation material. The hemihydrate mixtures obtained, allow the design of a new wall structure, which is more efficient as a thermal insulation system. The wall heat transfer coefficient test was carried out to compare thermal performance of two different thermal insulation systems. Compared with the thermal performance of a conventional system, the heat transfer coefficient of the new system was reduced by 5.6 %. Finally, energy-saving analysis of a building was carried out to compare the energy-saving effect of the conventional and new systems of building. The energy-savings of the building with the new system increased by almost 2 %, thus resulting in low energy consumption of the building.


Introduction
The emission of SO 2 is about 20 • 10 6 tons per year in China, of which about 50 % is generated from power plants.Acid rain caused by SO 2 leads to the pollution of the environment.To date, wet desulphurization technology has been used to precipitate the generated SO 2 from power plants.The limestone/lime-gypsum wet flue gas desulphurization process employs limestone/lime as an absorbent.Calcium in the limestone/lime absorbent reacts with the SO 2 existing in the boiler gases so that CaSO 4 • 2 H 2 O is formed in the spray absorber tower.Nonetheless, this method generates large amounts of FGD gypsum.This industrial by-product requires a large number of land resources, and causes serious environmental pollution if not treated properly.Calcined gypsum can be produced from waste FGD gypsum by its dehydration, which can be used as a building material.However, the utilization of FGD gypsum is insufficient considering the amount of its production.Calcined gypsum can be regarded as a green cement due to the considerable low costs and emissions during its manufacture in comparison with Portland cement.][6][7][8][9][10][11][12][13] However, with the improvement of the demand of building thermal environment, a gypsum plaster with an efficient thermal insulation function needed to be prepared.At present, there is little literature related to the preparation of thermal insulation gypsum plaster (TIGP).
In the preliminary study, the gypsum plaster for finish coating was prepared by adding a protein-based retarder (SC), a polycarboxylate-based water-reducing admixture (F10), and an ether-based water-retaining admixture (HPMC) to the hemihydrate from calcination of FGD gypsum.The initial setting time was 63 minutes, and the final setting time was 70 minutes, while the compressive strength was 11.5 MPa, which meets the requirements of the corresponding standard.The mass fractions of SC, F10, and HPMC was 0.25 %, 0.5 % and 0.1 %, respectively. 14sed on the preliminary study, thermal insulation gypsum plaster was prepared.The thermal performance and energy-saving impact of the new wall insulation system with thermal insulation gypsum plaster has been analysed.Overall, the work can be classified under the framework of applying innovative materials on wall thermal insulation systems.This paper is considered important for China, where energy consumption is continuously increasing in the hot-summer and cold-winter zone.

Preparation of Thermal Insulation Plaster with FGD Gypsum 2. Experimental 2.1 Materials
The material is the hemihydrate from calcination of FGD gypsum.The chemical composition of the hemihydrate is shown in Table 1, and the physical properties of the hemihydrate are shown in Table 2.The hemihydrate is produced by heating FGD gypsum to about 150 °C: The plaster starts as a dry powder which is mixed with water to form a paste that liberates heat and then hardens.The plaster can be easily manipulated with metal tools after setting.Its characteristics make it suitable for a finishing, rather than a load-bearing material.SC, F10, and HPMC were firstly added to the hemihydrate to prepare the common gypsum plaster based on the preliminary study.Secondly, in order to prepare thermal insulation gypsum plaster, rosin (C 19 H 29 COOH) and sodium lauryl sulphate (K12) were adopted as foaming agents, respectively.

Methods and equipment
The samples with different foaming agent were filled in 40 × 40 × 40 mm modules, and dried at 40 ± 2 °C in a muffle oven.Subsequently, the samples were cooled to room temperature.

Setting time:
The setting time was tested in accordance with the Chinese standard GB/T 17669.4-1999. 15The time interval of test was 5 min.
Compressive strength: The compressive strength was tested by a TYE-300 test device.The loading speed was 1.0 kN s −1 .The strength development was determined in accordance with the Chinese standard JC/T 517-2004. 16rphology: The morphology was observed by a scanning electron microscope (Quanta SEM 450).Firstly, sample powder was sprinkled on the double-sided tape.Secondly, silver powder was sprayed on the tape prior to observation.
Wall heat transfer coefficient: The test wall was placed between a hot chamber and a cold chamber to measure the air temperature, surface temperature, and power input to the hot chamber in the steady state.The heat transfer property of the test wall was calculated by the data.The wall heat transfer coefficient was determined in accordance with the Chinese standard GB/T 13475-2008. 17ergy-saving analysis: The heat transfer capacity of a building envelope was calculated using the reaction coefficient method by PBECA software.Internal surface temperature, external surface temperature, and heat flux in response to temperature disturbance of a triangular wave was calculated.Then, the reaction coefficient of the endothermic, exothermic, and transitive process was calculated.Finally, according to the temperature and heat flow calculated, the energy consumption and energy-saving efficiency of the building could be analysed.

Setting time
The influence of the two foaming agents with different mass fractions on final setting time of the gypsum plaster is shown in Fig. 1.It can be observed that K12 has better retarding effect on the hemihydrate.When the mass fraction of K12 was 0.1 %, the final setting time was 83 min (≤ 8 h), which meets the requirements of gypsum-based construction materials.

Compressive strengths
Fig. 2 shows the influence of the two foaming agents on the compressive strength of gypsum plaster.It can be observed that the strength of the resulting gypsum decreases when the foaming agent is added.With more foaming agent, the acquired strength is lower.In addition, the extent of the compressive strength decline is relatively small when K12 is added as the foaming agent, which further proved that K12 was more suitable as foaming agent.When the mass fraction of K12 was 0.1 %, the compressive strength was 7.2 MPa (≥ 6 MPa), which meets the requirement of building walls.
Fig. 3 presents the microstructure of gypsum plaster when K12 is added as foaming agent.The figure shows obvious generation of porosity.Therefore, the reason for the decrease in compressive strength is further explained from the microscopic point of view.

Thermal conductivity
The thermal conductivity coefficient of insulation material is usually lower than 0.2 W m −1 K −1 .This is an important index for evaluation of the thermal performance of a material.The thermal conductivity coefficients of gypsum plaster with the addition of rosin and K12 is shown in Fig. 4. As expected, the thermal conductivity coefficient decreases with increased foaming agent.When the mass fraction of K12 was 0.1 %, the thermal conductivity coefficient was 0.18 W m −1 K −1 .
In summary, K12 is more recommendable as foaming agent, when the mass fraction of K12 is around 0.1 %, the setting time and compressive strength meet the requirements of the standard.In the meanwhile, the thermal conductivity coefficient is 0.18 W m −1 K −1 , which can be used as a thermal insulation material.

Wall heat transfer coefficient
Thermal insulation gypsum plaster is applied on the inner surface of walls, which can be used as the heat insulation layer and plaster layer of finish coating.The layer of conventional systems (from outer surface to inner surface) is 20 mm cement mortar, 200 mm conventional ACB, 15 mm cement mortar, 20 mm EPS, 5 mm cement mortar, and 5 mm putty.Combined with TIGP, a new type of wall insulation system is put forward.The layer of the new system (from outer surface to inner surface) is 5 mm thin-layer mortar, 5 mm waterproof interface agent, 250 mm lightweight ACB, and 5 mm TIGP.The new system can realize the objective of self-insulation.
The heat transfer coefficient of the new wall insulation system was tested compared with that of the conventional system.The test results of temperature in conventional and new wall insulation systems are shown in Fig. 5 and Fig. 6, respectively.As shown in the mentioned figures, the test results of temperature tend to be stable with increasing test time.The final test result of surface temperature on the hot side is higher than that on the cold side, which forms the condition of one-dimensional steady-state heat transfer.
Based on the one-dimensional heat transfer theory, the wall heat transfer coefficient can be defined as: ( where T ni and T ne are the ambient temperatures of the hot side and the cold side, respectively; Q represents total heat transfer capacity; A represents the wall test area.In this test, total heat transfer capacity through conventional and new insulation systems were 53.98 W and 50.96W, respectively.The test area of wall was 1.44 m 2 .
The ambient temperatures of the hot side and the cold side are defined as: ( where T sai and T sae are the air temperatures of the hot side and cold side, respectively; T mi and T me are the mean radiant temperatures of the hot side and the cold side, respectively; T sis and T ses are the surface temperatures of the hot side and the cold side, respectively; h i and h e are the radiation heat transfer coefficients of the hot side and the cold side, respectively; ε is the emissivity of inner surface, which in this test was a constant value of 0.85.
According to the test results, we could calculate that the heat transfer coefficient of the conventional wall insulation system was 0.644 W m −1 K −1 , while the heat transfer coefficient of the new system was 0.608 W m −1 K −1 , which represents a reduction of 5.6 % compared with that of the conventional system.The thermal performance of the new wall thermal insulation system had improved substantially.

Energy-saving analysis
Energy-saving analysis of a building was carried out to compare the energy-saving effects of the conventional thermal insulation system and the new system of a building.The analysis is based on an actual building.The building type was shear wall structure, located in a hot-summer and cold-winter zone in China.The design standard for residential buildings of low energy consumption (in accordance with the Chinese standard DB42/T 559-2013) 18 was used in the energy-saving design.Calculation parameters were as follows: (1)

Conclusion
Thermal insulation gypsum plaster was prepared from flue gas desulphurization (FGD) gypsum.The obtained hemihydrate mixtures allowed the design of a new wall structure, which is more efficient as a thermal insulation system.Compared with the thermal performance of a conventional wall insulation system, the heat transfer coefficient of the new system had reduced by 5.6 %.Due to this reason, the energy-savings of the building with the new system had increased by almost 2 %, thus resulting in the building's low energy consumption.

Table 2 -
Physical properties of the hemihydrate from calcination of FGD gypsum Tablica 2 -Fizikalna svojstva hemihidrata nastalog kalcinacijom FGD-gipsa work is supported by the National Science and