Gypsum is added in appropriate amounts to Portland cement clinker, and the mixture is then ground into four different grades: 425, 525, 625, and 725. This type of cement has an early strength that is 5-10% higher than other types of Portland cement. It also exhibits excellent resistance to frost and wear, making it ideal for high-grade concrete applications. It is commonly used in important civil engineering projects where durability and performance are critical.
2. Ordinary Portland Cement
1) Concept
Ordinary Portland cement is a hydraulic cementitious material composed of Portland cement clinker, 6% to 15% of mixed materials, and an appropriate amount of gypsum. It is commonly referred to as ordinary cement, with the code P·O. The quantity of mixed materials added depends on their level of activity. According to Chinese standards, when active materials such as granulated blast furnace slag, volcanic ash, or fly ash are used, the maximum allowable addition is 15% by weight, with no more than 5% kiln dust allowed (which refers to dry powder collected from the kiln exhaust). Alternatively, if inactive materials are used, the maximum addition should not exceed 10%. Ordinary Portland cement is available in six grades: 275, 325, 425, 525, 625, and 725. It is widely used in the production of various mortars and concretes.
2) Technical Requirements
The fineness of the cement must not exceed 10% passing through an 80-micron square hole sieve; otherwise, it is considered non-conforming. The initial setting time should be no less than 45 minutes, and the final setting time should not exceed 10 hours. If the initial setting time is too short, the product is classified as waste. If the final setting time is too long, it is considered non-conforming. Volume stability must be confirmed through testing, and any cement failing this test is deemed unsuitable. Ordinary Portland cement is categorized into three strength classes—32.5, 42.5, and 52.5—based on compressive and flexural strength at 3 days and 28 days. Each class is further divided into normal and early-strength types.
3) Basic Performance and Application
Ordinary Portland cement shares similar applications with standard Portland cement, but some types of ordinary cement cannot be used in place of Portland cement. As a result, it is the most widely used type of cement in the construction industry due to its versatility and cost-effectiveness. Its balanced performance makes it suitable for a wide range of building and infrastructure projects, from residential to commercial and industrial structures.
3. Slag Portland Cement, Pozzolanic Portland Cement, Fly Ash Portland Cement
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