The cement quality directly affects the quality of architecture and the durability. And what’s more, it is the key link of the quality control of concrete mixing plant. But the cement industry nowadays is in a mess: qualified clinker is commonly seen, it is also regular that the clinker content in the cement is far lower than the standard specified value and “small cement” can not be called cement and only can be call powdery grinding material.
1. Clinker. As for the standard requirements, calcium metasilicate mineral accounts for no less than 66%, the quality ratio between the calcium oxide and silicon oxide is nor smaller than 2.0. But many cement factories only do the strength experiment frequently.
2. Clinker content in the cement. In the standard requirements, the total content of ordinary silicate cement clinker and plaster should be not smaller than 80% and be smaller than 95%. But now, many large cement factories produce cement which contains only 65%-70% clinker, not alone many small cement factories all over our country. Generally, the cement in the small cement factories only contains 50% clinker. The small cement can not be called cement and it only can be called mixture.
3. Testing methods. Cement is in the supervision and administration of the Technical Supervision Bureau and the spot check is done every year, which can not restrain the production of cement factories. The necessary check items of national testing standard is only strength, setting time and safety, along with some chemical index, which is far from enough. What’s worse, some kinds of cement which have been taken some measures can satisfy these requirements easily.
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