Sulphate Resisting Cement Manufacturing

Sulphate resisting cement (SRC cement) is a type of hydraulic binding material with resistance to sulfate ions. It is manufactured by fine grinding of Portland cement clinker, an appropriate amount of gypsum, and blast furnace slag. Compared with other Portland cement, it features high sulfate resistance, strong frost resistance, and low hydration heat.

Sulphate resisting cement has low tricalcium aluminate and tetracalcium aluminoferrite content and high tricalcium silicate content. This structure reduces the formation of sulfate salt thus improving the performance of concrete stones for sulfate attack and enhancing their durability in most aggressive environments. It is suitable for seaport engineering, water conservancy engineering, and underground construction, which are easily affected by sulfate corrosion, freeze-thaw, and dry-wet alternation.

Properties of Sulphate Resisting Cement

Sulphate resisting Portland cement can be divided into moderate sulphate resisting cement and high sulphate resisting cement. Their strength grades are 32.5, 42.5, and 52.5.

Moderate sulphate resisting cement (code P-MSR) can resist the corrosion of sulfate ions with a medium concentration. The content of tricalcium silicate does not exceed 55.0%, and the tricalcium aluminate is no more than 5.0%. High sulphate resisting cement (code P-HSR) can resist the corrosion of sulfate ions with a high concentration. The content of tricalcium silicate and tricalcium aluminate is less than 50% and 3%, respectively.

Compressive strength	Ignition loss	Free lime content	Magnesium oxide content	Undissolved substance content	Specific surface area	Initial setting time	Final setting time
10Mpa at 3 days, 16Mpa at 7 days, and 33Mpa at 28 days	≤3%	≤1.0%	≤5%	≤1.5%	≥280m2/kg	≥45min	≤10h

Sulphate Resisting Cement Uses

Concrete prepared from sulfate resistant cement has a strong resistance to pure sulfate whose concentration of sulphate ion is less than 2500mg/L. It is ideal for concrete engineering in contact with acidic soil, groundwater, seawater, etc. The use of SRC cement is recommended for the following applications:

Underground structures; Tunnels, culverts, and bridge foundations engineering;

Sea walls, dams, and reservoirs construction; Water and sewage pipelines and treatment plants;

Food processing, chemical, and fertilizers industries; Mines and other acidic soil environments;

Normal concrete works where ordinary Portland cement is used;

Sulphate Resisting Cement Features

It has excellent workability and pumpability.

Sulphate resisting cement features low water demand.

The content of C3A and C3S in sulfate-resistant cement clinker is small so the hydration heat is low.

The concrete prepared from sulfate resistant cement has great compressive strength and an economic mix design.

The sulfate resistant cement enables concrete to maintain high-level performance and structural integrity in aggressive environments thus prolongs the service life.

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Sulphate Resisting Cement Manufacturing Process

Raw materials needed in the production of sulfate-resistant cement are basically the same as ordinary Portland cement, mainly including calcareous materials, clayey materials, and ferriferous corrective materials. However, their mineral composition is very different from ordinary Portland cement.

1. The hydration product of C3A is the component that is most susceptible to corrosion in cement. As the corrosion resistance of C4AF is stronger than C3A, it partially replaces C3A in sulfate resistant cement to improve the non-corrodibility.

2. CH produced in the hydration process of C3S is another factor leading to corrosion. Therefore, appropriately reducing the content of C3S and correspondingly increasing C2S which has better performance is also an effective measure to improve the corrosion resistance of sulfate-resistant cement.

The manufacturing process of sulphate resisting cement is almost the same as ordinary Portland cement. It can be divided into:

Raw Material Preparation

Limestone, clay, and other raw materials should be first crushed into raw mill feed size by cement crushers. After that, they are stored in a pre-homogenization storage yard and then mixed in proportion, and fed to a cement raw mill for subsequent fine grinding. The fine-ground raw meal will be stored in storage bins waiting for calcination.

Clinker Calcination

In the calcination process, cement raw meals will first enter the preheater and precalciner to complete the preheating and partial carbonate decomposition. Then they are sent into the cement kiln for formal calcination until the clinker is formed. After that, the hot clinker will be cooled to a normal temperature in a cement cooler placed behind the kiln.

Cement Grinding

Cement clinker is usually mixed with gypsum and other admixtures for a specific property before sent into the cement mill. In a cement mill, they are finely ground until reach the fineness required for cement products. After grinding, cement powder is stored in cement silos and then packed in bags by cement packing machines.