Desulfurization gypsum is an industrial by-product gypsum obtained by desulfurizing and purifying the flue gas produced after the combustion of sulfur-containing fuel through fine lime or limestone powder slurry. Its chemical composition is the same as that of natural dihydrate gypsum, mainly CaSO4·2H2O. At present, my country’s power generation method is still dominated by coal-fired power generation, and the SO2 emitted by coal in the process of thermal power generation accounts for more than 50% of my country’s annual emissions. A large amount of sulfur dioxide emission has caused serious environmental pollution. The use of flue gas desulfurization technology to generate desulfurized gypsum is an important measure to solve the technological development of coal-fired related industries. According to incomplete statistics, the emission of wet desulfurized gypsum in my country has exceeded 90 million t/a, and the processing method of desulfurized gypsum is mainly piled up, which not only occupies land, but also causes a huge waste of resources.
Gypsum has the functions of light weight, noise reduction, fire prevention, thermal insulation, etc. It can be used in cement production, construction gypsum production, decoration engineering and other fields. At present, many scholars have conducted research on plastering plaster. The research shows that plaster plastering material has micro-expansion, good workability and plasticity, and can replace traditional plastering materials for indoor wall decoration. Studies by Xu Jianjun and others have shown that desulfurized gypsum can be used to make lightweight wall materials. Studies by Ye Beihong and others have shown that the plastering gypsum produced by desulfurized gypsum can be used for the plastering layer of the inner side of the outer wall, inner partition wall and ceiling, and can solve common quality problems such as shelling and cracking of traditional plastering mortar. Lightweight plastering gypsum is a new type of environmentally friendly plastering material. It is made of hemihydrate gypsum as the main cementitious material by adding lightweight aggregates and admixtures. Compared with traditional cement plastering materials, it is not easy to crack, stick Good binding, good shrinkage, green and environmental protection. The use of desulfurized gypsum to produce hemihydrate gypsum not only solves the problem of lack of natural building gypsum resources, but also realizes the resource utilization of desulfurized gypsum and achieves the purpose of protecting the ecological environment. Therefore, based on the study of desulfurized gypsum, this paper tests the setting time, flexural strength and Compressive strength, to study the factors affecting the performance of light-weight plastering desulfurization gypsum mortar, and provide a theoretical basis for the development of light-weight plastering desulfurization gypsum mortar.
1 experiment
1.1 Raw materials
Desulfurization gypsum powder: Hemihydrate gypsum produced and calcined by flue gas desulfurization technology, its basic properties are shown in Table 1. Lightweight aggregate: vitrified microbeads are used, and its basic properties are shown in Table 2. Vitrified microbeads are mixed in proportions of 4%, 8%, 12%, and 16% based on the mass ratio of light plastered desulfurized gypsum mortar.
Retarder: Use sodium citrate, chemical analysis pure reagent, sodium citrate is based on the weight ratio of light plastering desulfurization gypsum mortar, and the mixing ratio is 0, 0.1%, 0.2%, 0.3%.
Cellulose ether: use hydroxypropyl methylcellulose (HPMC), viscosity is 400, HPMC is based on the weight ratio of light plastered desulfurized gypsum mortar, and the mixing ratio is 0, 0.1%, 0.2%, 0.4%.
1.2 Test method
The water consumption and setting time of the standard consistency of desulfurized gypsum refer to GB/T17669.4-1999 “Determination of Physical Properties of Building Gypsum Plaster”, and the setting time of light plastering desulfurized gypsum mortar refers to GB/T 28627-2012 “Plastering Gypsum” is carried out.
The flexural and compressive strengths of desulfurized gypsum are carried out according to GB/T9776-2008 “Building Gypsum”, and the specimens with a size of 40mm×40mm×160mm are molded, and the 2h strength and dry strength are measured respectively. The flexural and compressive strength of light-weight plastered desulfurized gypsum mortar is carried out according to GB/T 28627-2012 “Plastering Gypsum”, and the strength of natural curing for 1d and 28d is measured respectively.
2 Results and discussion
2.1 The effect of gypsum powder content on the mechanical properties of lightweight plastering desulfurization gypsum
The total amount of gypsum powder, limestone powder and lightweight aggregate is 100%, and the amount of fixed light aggregate and admixture remains unchanged. When the amount of gypsum powder is 60%, 70%, 80%, and 90%, the desulfurization The results of flexural and compressive strength of gypsum mortar.
The flexural strength and compressive strength of light plastered desulfurized gypsum mortar both increase with age, indicating that the hydration degree of gypsum becomes more sufficient with age. With the increase of desulfurized gypsum powder, the flexural strength and compressive strength of lightweight plastering gypsum showed an overall upward trend, but the increase was small, and the compressive strength at 28 days was particularly obvious. At the 1d age, the flexural strength of gypsum powder mixed with 90% increased by 10.3% compared with that of 60% gypsum powder, and the corresponding compressive strength increased by 10.1%. At the age of 28 days, the flexural strength of gypsum powder mixed with 90% increased by 8.8% compared with that of gypsum powder mixed with 60%, and the corresponding compressive strength increased by 2.6%. To sum up, it can be concluded that the amount of gypsum powder has more effect on the flexural strength than the compressive strength.
2.2 Effect of lightweight aggregate content on the mechanical properties of lightweight plastered desulfurized gypsum
The total amount of gypsum powder, limestone powder and lightweight aggregate is 100%, and the amount of fixed gypsum powder and admixture remains unchanged. When the amount of vitrified microbeads is 4%, 8%, 12%, and 16%, the light plaster Results of flexural and compressive strength of desulfurized gypsum mortar.
At the same age, the flexural strength and compressive strength of light plastered desulfurized gypsum mortar decreased with the increase of the content of vitrified microbeads. This is because most of the vitrified microbeads have a hollow structure inside and their own strength is low, which reduces the flexural and compressive strength of the lightweight plastering gypsum mortar. At 1d age, the flexural strength of 16% gypsum powder was reduced by 35.3% compared with that of 4% gypsum powder, and the corresponding compressive strength was reduced by 16.3%. At the age of 28 days, the flexural strength of 16% gypsum powder was reduced by 24.6% compared with that of 4% gypsum powder, while the corresponding compressive strength was only reduced by 6.0%. To sum up, it can be concluded that the effect of the content of vitrified microbeads on the flexural strength is greater than that on the compressive strength.
2.3 Effect of retarder content on setting time of light plastered desulfurized gypsum
The total dosage of gypsum powder, limestone powder and lightweight aggregate is 100%, and the dosage of fixed gypsum powder, limestone powder, lightweight aggregate and cellulose ether remains unchanged. When the dosage of sodium citrate is 0, 0.1%, 0.2%, 0.3 %, setting time results of light plastered desulfurized gypsum mortar.
The initial setting time and final setting time of light plastered desulfurized gypsum mortar both increase with the increase of sodium citrate content, but the increase of setting time is small. When the sodium citrate content is 0.3%, the initial setting time prolongs 28min, and the final setting time was prolonged by 33min. The prolongation of the setting time may be due to the large surface area of desulfurized gypsum, which can absorb the retarder around the gypsum particles, thereby reducing the dissolution rate of gypsum and inhibiting the crystallization of gypsum, resulting in the inability of the gypsum slurry to form a firm structural system. Prolong the setting time of gypsum.
2.4 Effect of cellulose ether content on the mechanical properties of lightweight plastered desulfurized gypsum
The total dosage of gypsum powder, limestone powder and lightweight aggregate is 100%, and the dosage of fixed gypsum powder, limestone powder, lightweight aggregate and retarder remains unchanged. When the dosage of hydroxypropyl methylcellulose is 0, 0.1%, 0.2% and 0.4%, the flexural and compressive strength results of light plastered desulfurized gypsum mortar.
At 1d age, the flexural strength of light plastered desulfurized gypsum mortar first increased and then decreased with the increase of hydroxypropyl methylcellulose content; at 28d age, the flexural strength of light plastered desulfurized gypsum mortar With the increase of the content of hydroxypropyl methylcellulose, the flexural strength showed a trend of first decreasing, then increasing and then decreasing. When the content of hydroxypropyl methylcellulose is 0.2%, the flexural strength reaches the maximum, and exceeds the corresponding strength when the content of cellulose is 0. Regardless of the age of 1d or 28d, the compressive strength of light plastered desulfurized gypsum mortar decreases with the increase of hydroxypropyl methylcellulose content, and the corresponding decline trend is more obvious at 28d. This is because cellulose ether has the effect of water retention and thickening, and the water demand for standard consistency will increase with the increase of cellulose ether content, resulting in an increase in the water-cement ratio of the slurry structure, thereby reducing the strength of the gypsum specimen.
3 Conclusion
(1) The hydration degree of desulfurized gypsum becomes more sufficient with age. With the increase of desulfurized gypsum powder content, the flexural and compressive strength of lightweight plastering gypsum showed an overall upward trend, but the increase was small.
(2) With the increase of the content of vitrified microbeads, the flexural strength and compressive strength of light-weight plastered desulfurized gypsum mortar decrease accordingly, but the effect of the content of vitrified microbeads on the flexural strength is greater than that of compressive strength strength.
(3) With the increase of sodium citrate content, the initial setting time and final setting time of light plastered desulfurized gypsum mortar are prolonged, but when the content of sodium citrate is small, the effect on setting time is not obvious .
(4) With the increase of hydroxypropyl methylcellulose content, the compressive strength of light plastered desulfurized gypsum mortar decreases, but the flexural strength shows a trend of first increasing and then decreasing at 1d, and at 28d It showed a trend of decreasing first, then increasing and then decreasing.
Post time: Feb-02-2023