As one of the traditional inorganic cementitious materials, gypsum is widely used. Gypsum products have excellent characteristics such as lightweight, sound insulation, and fire resistance. They are green building materials that are vigorously developed all over the world. The industrial byproduct, phosphogypsum/desulfurized gypsum, has also been widely used in gypsum boards, gypsum blocks, and interior wall coatings. The theoretical water-to-cement ratio of semi-hydrated gypsum is 18.61%. Still, in actual use, the water consumption often reaches 65%~80%, which not only reduces the strength of gypsum products but also greatly increases the energy consumption of products during the drying process. To address this problem, the commonly used method is to add a certain amount of water reducer to the gypsum. On the one hand, it can effectively reduce water consumption when mixing gypsum while maintaining the same fluidity. On the other hand, the reduction of the water-to-cement ratio can reduce the energy consumption during the drying process.
Phosphogypsum PCE polycarboxylate superplasticizer and desulfurized gypsum
Polycarboxylate water reducer Application performance advantages in phosphogypsum
Phosphogypsum is a byproduct of the reaction between sulfuric acid and phosphate rock during the wet production of phosphoric acid. Domestic and foreign studies have shown that the resource utilization of phosphogypsum building materials is the main way to achieve its effective utilization. It can not only effectively utilize waste but also bring considerable economic benefits and effectively reduce the use of non-renewable natural gypsum. Chemical admixtures are key materials and technologies for the development of modern building materials in high-tech fields. Therefore, exploring the characteristics of the action of water reducers and phosphogypsum is of great significance to the widespread application of phosphogypsum.
The mechanism of action of different types of water reducers on gypsum-based materials
The mechanism of action of water reducers on gypsum-based materials has yet to be determined at present. It is generally believed that the sulfonic acid groups in the molecules of naphthalene-based water reducers are easily associated with water molecules in the form of hydrogen bonds, thereby affecting the water reducer on the surface of the hydrate. Adsorption equilibrium concentration. When a naphthalene-based water reducer is added to gypsum, it lies flat on the surface of the gypsum and adsorbs, relying on electrostatic repulsion to disperse the gypsum. While keeping the water-to-gypsum ratio unchanged, the addition of a water reducer can effectively break up the double-layer structure formed by dihydrate phosphogypsum, allowing the phosphogypsum particles to disperse with each other and release the free water wrapped between the particles, thereby achieving the purpose of water reduction. After adding the water reducer, the needle-like crystals in the crystal structure of the hardened gypsum are closely overlapped, the number of nodes increases and the contact points are well developed, thereby improving the hardened gypsum and increasing its strength. The polycarboxylic acid water reducer has many side chains, and the main chain reacts with calcium ions, which is chemical adsorption. The side chains form a three-dimensional adsorption structure on the surface of the particles, producing a steric hindrance effect, and cooperate with the electrostatic repulsion to disperse the particles to achieve a water reduction effect. After adding the homemade water reducer, It can transform more needle-shaped crystals into thick rod-shaped or sheet-shaped dense structures, and the large crystals are filled with originally small needle-shaped crystals, making the overlap between the crystals more compact and the macroscopic performance of the hardened body strength improvement.
From the above characteristics, different types of water reducers have different adaptability to phosphogypsum, among which polycarboxylic acid water reducer has a better effect, followed by naphthalene water reducer and melamine. Polycarboxylic acid water reducer has the characteristics of a good retarding effect, small loss of fluidity over time, and high strength improvement effect on phosphogypsum. Naphthalene water reducer has the characteristics of accelerating coagulation, large loss of fluidity over time, and certain strength improvement for hemihydrate phosphogypsum. It should be noted that before using a polycarboxylic acid water reducer on gypsum-based materials, its adaptability must be tested first because the water reducer suitable for cement may not be suitable for gypsum-based materials.
Trunnano polycarboxylate superplasticizer
Application performance advantages of polycarboxylic acid water reducer in desulfurized gypsum
Dispersibility
In desulfurized gypsum, the dosage of different types of water reducers varies greatly when the same water reduction rate is achieved. Among them, the required dosage of sulfonated melamine SM is the highest, and its dispersibility on desulfurized gypsum is the worst; the required dosage of naphthalene-based water reducer NSF is slightly lower than that of calcium lignin sulfonate M, and the dispersibility of naphthalene-based water reducer NSF is slightly better than that of calcium lignin sulfonate M. The required dosage of polycarboxylic acid water reducer PCE is the lowest. In terms of desulfurized gypsum dispersibility, PCE has a higher water reduction rate and excellent dispersibility.
Setting time
From the setting time of desulfurized gypsum, the addition of a naphthalene-based water reducer will not affect the initial setting time of gypsum but can effectively shorten the final setting time of gypsum; the addition of melamine has little effect on the setting time of gypsum, and basically does not affect the setting time; polycarboxylic acid water reducer will only slightly prolong the final setting time of gypsum slurry, showing a weak retarding effect; while calcium lignin sulfonate significantly prolongs both the initial and final setting times of gypsum, showing a strong retarding effect.
Gypsum strength
The water-to-cement ratio is the main parameter that affects the pore structure and strength of gypsum. Within a certain range, with the addition of a water reducer, the water-to-cement ratio (increase in water reduction rate) decreases. On the one hand, it can reduce the water-to-cement ratio and porosity, and on the other hand, it can improve the microstructure and crystal morphology of the gypsum hardener, thereby improving the compressive and flexural strength of the gypsum hardener; among them, the addition of polycarboxylic acid water reducer PCE has the most obvious increase in strength, but when the water reduction rate increases to a certain extent, there is no significant change in the growth of the strength of gypsum products. Therefore, the appropriate dosage of polycarboxylic acid water reducer needs to be controlled in the application of desulfurized gypsum.
Economic benefit analysis
In the production process of desulfurized gypsum products, if the water reduction rate is higher and the water consumption is less, the less water needs to be removed to dry the gypsum products to constant weight. The time required is also shorter, which will definitely greatly reduce the energy consumption generated by the gypsum products during the drying process. Increasing the dosage of polycarboxylate water reducer PCE can effectively reduce the water consumption of desulfurized gypsum powder, thereby greatly improving production efficiency and reducing production energy consumption, which has significant economic benefits.
