Cement Chemical Characteristics
Cement hydration (adding water) leads to a complex chemical reaction that is accompanied by thermal expansion. The UK revised standards for Portland Cements that are commonly used for repairs are as follows:
- Portland cement–grade 42.5; based on BS 12: 1991 (CEM 1)
- Portland cement – grade 52.5; based on BS 12: 1991
- Portland cement – grade 42.5 R; based on BS 12: 1991
- Sulfate-resisting Portland Cement-grade 42.5; based on BS 4027: 1991
- Building cement: BS 5224: 1995-ENV 413-1
The letter “R” indicates high initial resistance.
Revised versions are mainly related to testing methods and specific terms, and they aim to comply with the European Cement Standard (ENV 197-1). Minor changes to the composition are also introduced. If the required cement is Ordinary Portland cement, then Portland cement grade 42.5 based on BS12: 1991 is required.
If Portland cement is required with a fast hardening, then either Ordinary Portland cement grade 52.5 based on BS12: 1991 or Portland Cement grade 42.5 R, based on BS12: 1991, are advised.
The above types of cement are almost exclusively for repairing. In 1990 and 1991, a complete correction version of BS 5328: 1991 was issued for concrete in four sections.
The above types of cement are almost exclusively for repairing. In 1990 and 1991, a complete correction version of BS 5328: 1991 was issued for concrete in four sections.
What is Portland cement? Portland cement mainly consists of calcium silicate and calcium aluminate compounds. The amount of calcium silicates is always between 55% and 85%
Also, the amount of tricalcium aluminate is between 7 to 12% and iron hydroxide is also between 6 to 10%. C
ement is made from burning gypsum and clay mixture in a rotary kiln under high temperature.
Clinker is the main material and gypsum stone is added to control sulfur, which, according to the BS 12, is equal to 3.5%. When examining the possibility of sulfate attack on concrete or mortar, Portland Cement containing sulfate is of great importance. In the following we will present further information on the reaction between different sulfate groups (calcium, magnesium and ammonium).