the eastern hub, has been carried out in an orderly manner, and the key and difficult control project of Lixiang Section of Yunnan-Xizang Railway, Habaxueshan Tunnel, will soon be completed, the track laying of Changjinghuang high-speed rail will be completed, the box girder erection of Weiyan High-speed Railway will be completed, and the joint commissioning and testing of Xiamen Jindao Liaison Line Project of Fuzhou-Xiamen high-speed rail will begin.. Recently, there have been frequent reports of success in key railway projects.
Railway is a national strategic, leading and key infrastructure, known as the "locomotive" driving economic growth. In the first quarter, the national railway completed infrastructure investment of 75.6 billion yuan, an increase of 6.7% over the same period last year. In 2023, the national railway is expected to put into operation more than 3000 kilometers of new lines, including 2500 kilometers of high-speed rail.
Railway construction is in full swing, people can not help but wonder, what is the cement used in railway construction, and what is the difference between ordinary Portland cement? Because of the particularity of
railway construction, especially high-speed rail engineering technology, the requirements for materials used are becoming more and more stringent. The special low-alkali cement for high-speed rail is different from the general low-alkali cement we often talk about, not only to meet the national standard GB 175-2007 "General Portland Cement", but also to meet the Chinese railway construction industry standards, referred to as the railway standard, such as TB/T 3275-2018 "Railway Concrete", TB/T 3275-2018 Amendment No.1, and TB/T 3275-2018. TB 10404 — 2018 "Standard for Constructional Quality Acceptance of Railway Concrete Engineering", TB/T 3432 — 2016 "High-speed Railway Prefabricated Post-tensioned Prestressed Concrete Simply Supported Beam". According to the requirements in 3.2.2 of
TB/T 3432 — 2016, low-alkali Portland cement or low-alkali ordinary Portland cement with stable quality and strength grade not less than 42.5 shall be used. The admixture in cement is limited to ground slag powder or fly ash, the alkali content should not be greater than 0.6%, and the specific surface area should be 300 ~ 350 m2 /kg. The C3A content in clinker shall not be greater than 8.0%, and other technical requirements shall comply with the provisions of TB/T 3275.
Low-alkali cement refers to the cement with low content of alkali metal oxides (potassium oxide and sodium oxide). The total alkali content is calculated by equivalent sodium oxide (Na2O + 0.658K2O ), and the total alkali content (equivalent sodium oxide) of low-alkali cement is required to be less than 0.6%. The differences between the special low-alkali cement for high-speed rail and the general purpose cement are as follows:
1. The clinker minerals have changed
. The special low-alkali cement for high-speed rail requires that the C3A content in the clinker should be less than 8.0% in general and less than 5.0% in special cases. This increases the difficulty of batching and calcination.
2. There is no requirement for the free calcium oxide
in the cement in the general cement, only the soundness is qualified, but in the special low-alkali cement for high-speed rail, not only the soundness is qualified, but also the free calcium oxide is less than 1.0%, which increases the difficulty of clinker calcination and cement batching. The clinker calcination operation shall be strictly controlled, the free calcium oxide shall be controlled at 0.5% ~ 0.8%, the sintering shall be complete, the kiln condition shall be stable, and there shall be no underfired material. The saturation ratio of clinker ingredients should be moderate. If the saturation ratio is too high, it is easy to make the free calcium oxide exceed the index. If the saturation ratio is too low, the strength of clinker is low. Therefore, the ingredients should be moderate and stable.
3. Requirements
for specific surface area high-speed rail the requirements for specific surface area of special low-alkali cement is 300 ~ 350 m2 /kg. However, the specific surface area of general-purpose cement is generally controlled in the range of 350 ~ 400 m2/kg. On the surface, the grinding quality of cement is required, but in fact, the quality of clinker is also assessed. The production of general-purpose cement often relies on the method of increasing the specific surface area of cement to improve the strength of cement. However, the specific surface area of special cement for high-speed rail is limited, and it is not feasible to improve the early strength by increasing the specific surface area, which can only be achieved by improving the strength of clinker itself, which undoubtedly increases the difficulty of clinker calcination.
In practical application, according to the adaptability of concrete, users require the specific surface area to be 320 ~ 340 m2/kg, which is a narrower range, we call it the "ideal range", and requires homogeneity and stability, which puts forward higher requirements for grinding process control. Therefore, the control index of (325 ± 15) m2/kg is formulated to meet the needs of users.
4. The requirements
for the types of admixtures strictly restrict the types of admixtures, "only ground slag powder or fly ash", and stipulate the indicators of slag powder and fly ash, whether in the types of admixtures or in the inspection items, there are strict requirements. Various indexes are far higher than index requirements of general cement. The dosage of slag powder is also limited, because the specific surface area of slag powder is generally 400 ~ 420 m2/kg, the dosage will affect the specific surface area of cement, so the dosage should be strictly controlled in 8% ~ 10%.
5. The requirement
for alkali content R2O is less than 0.6%, which is obviously strict for raw materials.
6. Cement factory inspection
, cement factory inspection, one vehicle inspection. For the delivery inspection of general cement, according to the provisions of the national standard GB 175-2007, the scale of annual production of 1 million tons of cement should be 1:1 000 tons as a number. Because of the particularity of high-speed rail construction, the cement tanker is driven into the bulk tank on the construction site, each tanker is 30 tons, the specific surface area of each tanker must be sampled and inspected, and the unqualified bulk tank is not allowed to enter the construction site, which is equivalent to 1 000 tons to 30 tons as an inspection frequency, which undoubtedly improves the requirements of the homogeneity and stability of cement quality.
To sum up, due to the special application scenarios of low-alkali cement, its indicators have more stringent standards, and a little carelessness in production can not meet the requirements of low-alkali cement indicators. This also makes the builder realize that choosing a better and better low-alkali cement brand is an important factor that must be measured when purchasing.
Among the domestic enterprises that can provide high-quality low-alkali cement, Fangcheng Wanbei Cement (Group) Co., Ltd., located in Nanyang, is undoubtedly one of the best.
It is reported that Wanbei Cement has excellent mine resources and advanced production technology, and has obvious advantages in the development of low-alkali cement. It is widely used in key national projects such as South-to-North Water Transfer Project, Zhengzhou-Wanzhou high-speed rail, Xinyang Minggang Airport, Zhounan Expressway, Xuxin Expressway, Zhengfu high-speed rail and Tianchi Pumped Storage Power Station in Henan Province, which ensures and improves the construction quality of these large-scale projects.
At present, Wanbei Cement can not only produce ordinary Portland cement and low-alkali cement, but also successfully develop special cement such as medium and low heat slag Portland cement and oil well cement.
In the "Qianli Jiangshan Map" of Chinese-style modernization, the construction of railways, especially high-speed rail, has contributed a lot. In the future, Wanbei Cement will continue to provide more customers with high-quality low-alkali cement products, adding a strong color to this "Qianli Jiangshan Map".
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