2024, the State Administration of Market Supervision and Administration (Standardization Administration of China) approved and issued the national recommended standard of GB/T21372-2024 Portland Cement Clinker , and the implementation date of the standard is October 1, 2024. It replaces the GB/T21372-2008 version issued in 2008. Compared with the old standard, the new standard adds clinker varieties, clinker strength grades and physical indicators of characteristics, and at the same time adds the limit requirements of harmful components, paying more attention to the impact on people and the environment. The main changes are as follows:
1. The corresponding technical indexes are required
in detail, and the clinker varieties are added to the road cement varieties. The specific technical index adopts the content of clinker tricalcium aluminate (C3A ) stipulated in GB/T 13693-2017 Road Portland Cement, which should not be greater than 5%. The content of tetracalcium aluminoferrite (C4AF ) shall not be less than 15.0% and the content of free calcium oxide shall not be more than 1.0%. At the same time, the calculation formula of silicate minerals is specified in more detail.
2. Two indicators
of chloride ion and radioactivity are added. Compared with the 2008 edition, two indicators of chloride ion and radioactivity are added. More attention is paid to the requirements of safety and environmental impact. It is also to correspond to the newly published cement standards such as GB-175 2023.
3. The selective index
of "water-soluble chromium (VI), heavy metal content and leachable heavy metal content" is added. Considering the requirement of water-soluble hexavalent chromium in the recently issued GB-175 2023 standard for general Portland cement, the proportion of clinker used in subsequent cement grinding is different. At the same time, it can also be treated by chromium reducer and other technical means, so this index is a selective index. At the same time, considering that many kiln lines adopt solid hazardous waste co-disposal at present, the selective index of heavy metal content and leachable heavy metal content is increased, so that the purchaser has the right to know and can choose high quality and high price when buying and selling.
4. The indexes
of "insoluble matter" and "loss on ignition" have been changed. The insoluble matter has been reduced from 0.75% to 0.5%, and the loss on ignition has been reduced from 1.5% to 1.0%. The main reason is that most enterprises can meet the requirements of this technical index because they are all new dry cement production lines at present.
5. The strength grade of clinker is subdivided
and the strength grades of general cement clinker, low-alkali general cement clinker and road cement clinker are added, which are divided into two grades of 42.5 and 52.5, while other clinker has only one grade of 42.5. At the same time, the 3-day strength and 28-day strength of different types of clinker are specified in detail, and the 3-day strength of some clinker varieties is reduced; It is originally stipulated that the 28-day strength of general and low-alkali cement clinker shall not be less than 52.5MPa. Considering that the 28-day strength of clinker of some enterprises or clinker under special circumstances is less than 52.5MPa, qualified cement products of 42.5 grade and below can also be produced. Therefore, the strength of clinker is graded, which can be selected at high quality and high price when buying and selling.
6. The physical requirements
for the characteristics of sulfate-resistant cement clinker, medium-heat cement clinker and low-heat cement clinker are added. The particularity of special cement lies in the requirements for characteristic indicators. There are corresponding provisions in the standards of special cement, which must be extended to the strict requirements for special clinker. Therefore, this standard increases the physical index requirements of special clinker, increases the requirement of 14d linear expansion rate for medium and high sulfate-resistant cement, and makes specific requirements for 3D and 7d hydration heat of medium and low heat cement, which are consistent with the requirements of special cement.
7. The physical property test method stipulates that the strength index is very important in the physical properties of
clinker, so the new standard adds specific requirements for the grading and weight of steel balls in the strength test mill to prevent disputes over the test data.
Summary: The impact
on the industry Portland cement clinker has been revised again in 16 years. As a whole, it keeps pace with the development of the times, revises the standards cautiously and strictly, and pays more attention to the impact on people and the environment. From the perspective of specific indicators, it is synchronized with several cement standards revised and issued in recent years. Under the background that the state vigorously advocates and promotes special cement, the specific indicators of special cement clinker are more clear, which makes the standard more referential for commodity clinker buyers and sellers, and reduces quality disputes in trade.
