Low Heat Cement Manufacturing
What is low heat cement? Low heat cement is also known as low heat Portland cement, code number P·LH. It is a type of hydraulic binding material made by mixing and grinding together ordinary Portland cement clinker, an appropriate amount of gypsum, and other admixtures. As its name indicates, low heat cement releases low heat of hydration. When it is mixed with water to form concrete, the temperature gradient established inside and outside the concrete surface is small, which is not easy to produce internal stress and then lead to small cracks. Besides, it also features high later strength, good durability, and strong corrosion-resistance, frequently applied in the construction of large-scale concrete structures and high strength concrete engineering.
Low Heat Cement Properties
Low heat Portland cement takes dicalcium silicate as the main mineral. The content is usually more than 40%. The content of Tricalcium aluminate is relatively low which no more than 6%. The free calcium oxide is less than 1.0%.
The early strength of low heat cement is low, but the late strength growth rate is fast. The minimum strength of low heat cement is 13.0 MPa at 7 days and 42.5 MPa at 28 days.
The initial setting time of low heat cement is 60 minutes (minimum) and the final setting time is 10 hours (max).
The hydration heat released by low heat Portland cement is low and the release process is gentle.
Low Heat Cement Uses
Low Heat Cement Features
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Low Heat Cement Manufacturing Process
Low heat cement is manufactured by adjusting the mineral constituent, grinding fineness, and blending materials of ordinary Portland cement. It has a small amount of tricalcium aluminate and a high percentage of dicalcium silicate.
Low heat Portland cement manufacturing process can be divided into five stages:
1. Raw material crushing
In the raw material crushing process, cement crushers assist to crush cement raw materials into a smaller size. The crushed materials are stored in a pre-homogenization storage yard.
2. Raw material grinding
70%-84% limestone, 10%-20% clay, 5%-10% sulfuric acid slag, and 1%-5% iron tailings are mixed in proportion and then fed into the raw mill for fine grinding.
3. Clinker calcination
Cement raw meals should be calcined in a cement kiln at 1350 ℃ to 1400 ℃ for 30 to 45 minutes and then cooled by a cement cooler to obtain cement clinker. If we adopt the new dry cement production process, we should set preheater and precalciner before the kiln.
4. Clinker grinding
In this stage, the cement clinker is ground in cement mills until reaches a standard fineness. During this process, it is allowed to add an appropriate amount of admixtures (less than 1%) without damaging the performance of cement.
5. Cement packing
Cement powder is usually stored in cement silos and then packed in bags by a cement packing machine.
Low Heat Cement Vs Moderate Heat Cement Vs Low Heat Slag Cement
There are three kinds of medium and low heat Portland cement: low heat cement, moderate heat cement, and low heat slag cement (containing 20%-60% blast furnace slag). They all have the characteristics of low hydration heat and are suitable for the construction of large structures.
Low Heat Cement
Ingredient: ordinary Portland cement clinker, an appropriate amount of gypsum, and mixed materials.
- Its hydration heat is low, which is more than 30% lower than that of ordinary Portland cement with the same strength grade.
- The early strength of low heat cement concrete is low, but its late strength is much higher than the moderate heat cement concrete. And the 90-day strength is more than 10 MPa higher than ordinary Portland cement.
- It has excellent mechanical properties, anti-cracking ability, and durability, as well as small dry shrinkage. The adiabatic temperature rise of low heat cement is 5-10 ℃ lower than moderate heat cement and ordinary Portland cement.
Application: hydraulic mass concrete engineering, high-performance concrete engineering, and other key engineering construction.
Strength grade: 42.5
Moderate Heat Cement
Ingredient:ordinary Portland cement clinker, an appropriate amount of gypsum, and mixed materials. The content of C3S in moderate heat cement should be no more than 55%, C3A is no more than 6%, and free calcium oxide is less than 1.0%.
- The hydration heat of moderate heat cement is more than 15% lower than the ordinary Portland cement with the same strength grade.
- Due to the low adiabatic temperature rise of the moderate heat cement concrete, the shrinkage cracks that may occur in the later cooling stage of the hardened concrete can be avoided or reduced.
- It has excellent long term strength and great chemo-resistance.
Application: large-scale construction works and engineering required for wear resistance, such as dams, bridge beams, and nuclear power plants.
Strength grade: 42.5
Low Heat Slag Cement
Ingredient: ordinary Portland cement clinker, an appropriate amount of gypsum, and blast furnace slag (20% ~ 60% by mass percentage). The content of C3A in low heat slag cement should be no more than 8%, free calcium oxide is no more than1.2%, and the magnesium oxide is less than 5%.
- The hydration heat of low heat slag cement is also low, mainly realized by adding mixed materials.
- Low heat slag cement has low early strength, good performance, and low cost. It can make great use of industrial waste, such as blast furnace slag.
Application: interior and underwater construction of large – scale structures.