Accelerating agent refers to a setting regulating agent that can speed up the setting and hardening of concrete and mortar.
According to the chemical composition of their compounds, accelerated agents can be divided into two categories: inorganic and organic. The leading accelerating agent in China is primarily inorganic salts, and the main component is sodium aluminate ( Aluminum-oxygen clinker). Other inorganic salts with rapid setting include sodium carbonate, calcium aluminate, calcium fluoroaluminate, magnesium fluorosilicate, sodium silicate, sodium fluorosilicate, ferrous chloride, aluminum sulfate, trifluorosilicate, and aluminum chloride. Organic substances used as accelerating setting agents include triethanolamine and soluble resins such as polyacrylic acid, polymethacrylic acid, hydroxyacrylic acid, and calcium acrylate.
As concrete accelerating agents, the above-mentioned single compounds are rarely used. Commonly used are mainly compounds with accelerating assessing effects. These accelerating agents can be divided into four categories according to their main components: Aluminum-oxygen clinker-based accelerating agents, water glass accelerating agents, new inorganic low-alkali accelerating agents, and new composite liquid accelerating agents.
The accelerating agent with alumina clinker as the main component is currently the most widely used accelerating product. According to its different accelerating mechanisms, it can be divided into alumina clinker and carbonate series and composite sulfoaluminate systems. The main components of the alumina clinker and carbonate series are alumina clinker, sodium carbonate, and quicklime. Its primary disadvantage is its high alkali content, which significantly impacts the later strength of concrete. However, after adding a certain amount of anhydrite, it can be improved to a certain extent; there are wide varieties of composite sulfoaluminate accelerating agent, including blended sulfoaluminate varieties with alumina clinker, vitriol mud and quicklime as the main components and sodium aluminate, tricalcium silicate, dicalcium silicate, calcium oxide and zinc oxide alumino-oxygen clinker, alunite and other varieties. This accelerating agent performs similarly to the alumina clinker and carbonate accelerating agent, but the alkali content is reduced. The latter uses sodium aluminate, tricalcium silicate, and dicalcium silicate as the clinker part, is made by calcining bauxite and Glauber’s salt. Adding zinc oxide improves the later strength, but the early strength development is slightly slower. The above-accelerating agents based on alumina clinker are all solid powder products with high alkali content. Therefore, the reagents are developing into low-alkaline, liquid reagents to overcome the alkali-aggregate reaction, facilitate construction, reduce pollution and harm to the human body, and accelerate setting agents.
The main component of water glass accelerating agent is water glass (sodium silicate). Adding a small amount of potassium dichromate, sodium nitrite, and triethanolamine can reduce viscosity. The product is characterized by fast setting, hardening, high early strength, and impermeability. It is durable and can be constructed under low-temperature conditions but can increase concrete shrinkage.
The new inorganic low-alkali accelerating agent is a new type developed to overcome the shortcomings of traditional ones with high alkali content and adverse effects on the strength of concrete. This type of agent has low alkali or no alkali and hurts concrete. It has no impact on stability, easy availability of raw materials, and simple production processes. Its composition includes the following: sodium metaaluminate, gas ash, silica powder, alumina clinker, calcined alunite, zinc sulfate, anhydrite, quicklime, aluminum sulfate, calcium fluoride, alumina, calcium oxide, and silica.
New types of composite liquid accelerating agents represent the development direction, including inorganic accelerating agents and organic diluents, mixed varieties of inorganic and organic accelerating agents, and some using water-soluble resins. The main component is the low-alkaline organic accelerating agent.
The accelerating agent used in dry-mixed mortar is in powder form. Its application range includes waterproof leak-proofing mortar, self-leveling mortar, quick-drying tile adhesive, and leveling mortar.
Defoaming agent
Defoaming agent is a type of admixture that helps release air bubbles entrained or generated during mortar mixing and construction, increase compressive strength, and improve surface conditions.
The defoaming agent can prevent the mortar from generating bubbles during the mixing process, thus improving the wetting process of the powder. The defoaming agent can also prevent the mortar from causing bubbles during the construction process, thereby improving the compressive strength of the mortar, preventing defects on the mortar surface, and improving the leveling performance of the self-leveling mortar series.
The defoaming agent is a surfactant that inhibits or eliminates foam. It has good chemical stability; its surface tension is lower than that of the medium to be defoamed; it has a particular affinity with the medium to be defoamed, and it has good dispersion. Effective defoaming agents can not only quickly break the foam but also can destroy the foam and prevent its regeneration for a long time.
Many types of defoaming agents, such as silicones, polyethers, fatty acids, and phosphates, but each has its adaptability. Dry mortar is strongly alkaline, and a defoaming agent must be selected for alkaline media. The defoamer used in dry mortar is a water-soluble powdery additive that can construct hydraulic adhesives. The product reduces undesirable bubbles during formulation and application. It is suitable for neutral and alkaline systems and compatible with most other additives, such as surfactants and derivatives including cellulose, starch, and starch ethers—water-soluble polymers such as polyvinyl acetate.
Defoaming agents can be used in all dry-mixed mortar formulations based on cement, gypsum, and lime, like gypsum-based fillers and caulks, gypsum-based and cement-based floor leveling, and cement-based self-leveling compounds. In dry-mixed mortar materials, the powder-defoaming agent that should be added generally uses hydrocarbons, polyethylene glycol, or polysiloxane, and its dosage is 0.01% to 0.2% of the cement dosage. The specific dosage should be determined according to the materials used, and the parameters can be determined after experiments.
