Expanding cement production
Expanding cement, also known as expansive cement, refers to hydraulic cementing materials that are ground by Portland cement clinker and proper amount gesso and expand agent.
Proportion: 86 ~ 90% (weight) of white limestone, 3 ~ 10% (weight) of lead-zinc dry waste, 3 ~ 8% (weight) of clay, 0 ~ 2% (weight) of iron powder.
What is the difference between Portland cement and expansive cement? In the hydration and hardening process to produce expanding cement, when general Portland cement hardening in the air, its volume will shrink. Shrinkage will cause micro-cracks in the structure of hardened cement paste, reduce the compactness of the structure of hardened cement paste, and affect the impermeability, frost resistance, and corrosion resistance of the structure. Expanding cement volume will not shrink in the hardening process, but also slightly expanded, can solve the adverse consequences caused by shrinkage. Expanding cement has wide applications.
How to use expanding cement? The waterproof concrete made of expansive cement is called expansive cement waterproof concrete. Due to the expanding cement produced ettringite in the early stage of hardening, the concrete volume expands, to improve the concrete pore structure under the constraint condition, and reduce the total porosity, capillary diameter, so as to improve the concrete compactness and impermeability.
6 Steps To Make Expanding Cement
How expanding cement is made? In a word, Portland cement clinker, expansive agent, and other additives are grounded together. The expanding cement production is similar to Portland cement plant, which can be divided into six steps: crushing, raw meal milling, homogenization, clinker calcining, cement grinding, packing and storing. Specific expanding cement manufacturing process as follows:
STEP1: Crushing
Cement raw materials will be crushed by cement crushers to meet the size requirement in the next section.
STEP2: raw meal milling
The pre-processed raw materials will be sent into raw mill for further grinding, there are four types of raw mill to be applied in the raw meal milling, including cement ball mill, cement vertical mill, Raymond mill, and coal mill in the cement plant.
STEP3: raw meal homogenization
The raw meal homogenizing keep the stability of raw meal into the kiln, and ensure the successful operation of clinker calcining.
STEP4: expanding cement clinker production
The preheating and precalcining system helps to process raw meal before entering cement kiln for energy-saving. Then, the cement kiln burns raw meal and other agents into clinker, there are cement rotary kiln or shaft kiln to be chosen according to real needs. In this step, there are also some auxiliary equipment needed, such as clinker cooler, cement dryer, bag filter, etc.
STEP5: expanding cement grinding
The clinker is discharged from the cement kiln and sent into the cement grinding plant to make finished expanding cement.
STEP6: packing and storing
According to different applications of expanding cement, it can be stored in a cement silo or bagged.
Expanding cement classification
The main components of cement, it is divided into silicate type, aluminate type, and sulphoaluminate type expanding cement. According to the expansion value of cement and its different uses, it is divided into contraction compensation cement and self-stressing cement.
There are some different types of expanding cement, such as the usual K-type expanding cement, M-type expanding cement, and S-type expanding cement.
K type expanding cement
K type expanding cement is ground by Portland cement clinker, expanding clinker containing anhydrous calcium sulforaluminate, gypsum or anhydrous gypsum together. In addition to the mineral anhydrous calcium sulphoaluminate, the expanded clinker also contains alite, Belite, iron phase, anhydrous gypsum and a small amount of free calcium oxide. The clinker is obtained by calcination at 1300℃ after mixing limestone, aluminized material and gypsum. It should be noted that not all sulphoaluminate cements containing anhydrous calcium sulphoaluminate will expand, some of which are characterized by quick hardening, early strength, and high late strength. This type of cement is made of limestone, gypsum, bauxite, silica sand and some iron ore after appropriate proportion, calcined at 1280℃.The clinker was ground to a specific surface area of 3700cm2/g, but gypsum was not added in the grinding process.
M, S type expanding cement
M-type expanding cement is made by adding aluminate cement or high alumina slag and lime to Portland cement.
The s-type expanding cement is made of Portland cement clinker with high C3A content. The C3A in S type expanding cement is quickly hydrated to form ettringite, but then the hydration rate is slowed down, and a certain amount of unhydrated C3A is still found after the age of 7 days. Therefore, the expanding of S type cement is not easy to control, and its use is also limited. In contrast, anhydrous sulforaluminate brining is more rapid than that of tricalcium aluminate, and maintains a higher hydration activity until it is completely consumed.
Expanding cement uses
Silicate expansive cement
It is mainly used to make waterproof sand pulp and waterproof concrete. Suitable for reinforcing structure, casting machine base or consolidating anchor bolt, and it also can be used for joint and repair works. However, it is prohibited to use in water engineering with sulphate erosion.
Low thermal micro expanding cement
Mainly used for low hydration heat and compensation shrinkage of concrete, mass concrete, but also for the projects with requirements of impermeability and sulfate resistance.
Sulphoaluminate expanding cement
Sulphoaluminate expanding cement is mainly used for casting member joints and concrete works for impermeability and shrinkage compensation.
Self-stressing cement
Mainly apply for self-stressing reinforced concrete pressure pipe and its fittings.
