Ordinary Portland cement is the most widely used type of cement in dry-mixed mortar products. Portland cement clinker is mixed with 6% ~ 15% mixed materials and the appropriate amount of gypsum to make a hydraulic cementitious material called ordinary Portland cement (referred to as ordinary cement), and its code is P ・0. The maximum amount of admixture in ordinary cement shall not exceed 15%, and it is allowed to replace with kiln dust not exceeding 5% of cement mass or inactive admixture not exceeding 10%. In addition, the maximum dosage shall not exceed 10% when mixed with passive mixed materials.
High alumina cement
Alumina cement is calcium aluminate cement (CAC) or alumina cement. As a special cement, different from ordinary Portland cement, it contains higher alumina (AI2O3), generally about 50%, the primary mineral materials CA, CA2, and a small amount of C2AS and iron phase. Because high alumina cement has the characteristics of early hardening and high-temperature resistance, it is often used to prepare self-leveling mortar, non-shrinkage grouting material, quick repair mortar, and plugging agent in dry powder mortar products. In addition, adding an appropriate amount of high alumina cement to ordinary cement can be used as a coagulant for regular cement.
Application of high alumina cement
(1) Field of Construction Chemistry
High alumina cement’s main characteristics are accelerated setting, high strength, chemical abrasion resistance, and weathering resistance. Therefore, high alumina cement is often used as a hydraulic adhesive for some unique products in the construction industry. Since the main component of high-alumina cement is calcium aluminate, it absorbs more water than ordinary Portland cement in the hydration reaction, solidifying faster and having higher early strength. The strength is higher than that of ordinary cement after 28 days, which can make the product put into use as soon as possible.
sewage treatment system
Since the hardened high alumina cement has low porosity, does not contain Ca(0H)2, and has a compact structure, it has good resistance to sulfate and seawater erosion. Therefore, various self-stressing pipes produced by high alumina cement have been very suitable as various pipe fittings for sewage and water-lifting stations for a long time. In addition, high-alumina cement has high early strength and can harden well in low-temperature environments, but when the temperature exceeds 30°C, the strength will drop sharply, opposite to Portland cement. Therefore, high alumina cement is usually used for emergency repairs and projects requiring high early strength and is not suitable for steam curing and construction at higher temperatures.
Gypsum
Dihydrate gypsum (hemihydrate gypsum) is used most in the construction industry. The chemical composition is about 32.5% CaO, 46.5% SO3, and 20.9% O. It is often granular and fibrous.
Gypsum powder products are commonly used in a dry-mixed mortar, divided into construction gypsum, plaster, caulking gypsum, and bonding gypsum according to their uses. Among gypsum powders, construction gypsum powder accounts for the most significant proportion, and it can be divided into two categories: gypsum powder is used to produce construction gypsum products, and the other is used as building plastering materials.
slaked lime
Slaked lime, scientific name calcium hydroxide Ca (0H) 2, is a cementing material and filler commonly used in dry-mixed mortar products. Slaked lime has strong alkalinity and hygroscopicity and is almost insoluble in water. It can gradually absorb carbon dioxide and form calcium carbonate when exposed to the air. Adding slaked lime to cement mortar and gypsum can increase the workability and has the advantages of improving the workability of the slurry, increasing the bonding strength, reducing cracking, and making up for micro-cracks. Since slaked lime is not used as the primary bonding material in dry-mixed mortar, it tends to act as an auxiliary filler, so it should be reasonable in the formulation system. Otherwise, it will affect the final compressive strength of the product.
