Cement is a common material in construction industry. It is so common that sometimes people do not border to study it. When you ask someone “What is cement?", probably he/ she will just answer “A grey powder to bind materials together”.
The Malaysian Standard MSEN 197-1 defines cement as a hydraulic binder, i.e. a finely ground inorganic material which, when mixed with water, forms a paste which sets and hardens by means of hydration reactions and processes and which, after hardening, retains its strength and stability even under water. It is a versatile substance that is primarily used to bind aggregates together in mortar and concrete. When it is mixed with fine aggregates and water, it produces mortar. When it is mixed with fine and coarse aggregates, water and admixtures, it forms concrete.
Portland cement was developed in England by bricklayer Joseph Aspdin in 1824. It gets its name from its resemblance upon hardening to the famous Portland limestone obtained from quarries on the Isle of Portland. Portland cement is the most important cement in terms of the quantity produced. The main “raw material” to produce Portland cement is Portland cement clinker. Portland cement clinker is produced by heating a mixture of lime, iron, silica and alumina in a rotary kiln at temperature up to 1450oC. When the materials sinters, it partially fuses into clinker balls. The clinker balls are then cooled and ground to a fine powder together with a small amount of gypsum and the resulting product is Portland cement.
Cement Standards and Types of Cement
There is no universal international standard for cement because every country has its own standards. For example, the cement standard used in Malaysia is MSEN 197-1 (Malaysian Standard for Cement - Composition, specifications and conformity criteria for common cements) which is adopted from the European Standard. There are 27 types of common cement specified in MS EN 197-1 and they are grouped into 5 main cement types as below:
CEM I Portland cement
CEM II Portland-composite cement
CEM III Blastfurnace cement
CEM IV Pozzolanic cement
CEM V Composite cement
Although MSEN197-1 is the main cement standard used in Malaysia, the American Standard ASTM C150 (Standard Specification for Portland Cement) is also sometimes being specified in some projects. Both MSEN 197-1 and ASTM C150 classified cements into 5 main types namely Type I to V. However, the way these two standards classifying the type of cement is very different. MSEN classification is based on composition while ASTM classification is based on potential phase composition and application. Below is a summary of the types of cement classified in both standards for easy reference.
In addition to the type of cement, it is important to know the strength class of the cement you are using as well. There are 3 standard strength classes specified in MSEN 197-1 i.e. 32.5, 42.5 and 52.5. On top of that, 3 classes of early strength (2 days or 7 days) are included for each class of standard strength, a class with ordinary early strength, indicated by N, a class with high early strength, indicated by R and a class with low early strength, indicated by L. Class L is only applicable for CEM III cements. These are the distinct low early strength blast furnace cements. Table below shows the strength requirement for each strength class specified in MSEN 197-1.
Cement is sold both in bulk and bagged. The bagged cements sold in Malaysian market are generally classified into three types, namely the Ordinary Portland Cement, Portland Composite Cement and Masonry Cement. The Portland cements are general purpose cement which can be used for structural works and have to comply to MSEN 197-1. Masonry Cement which is used for plastering work has to comply to MSEN 413-1 (Malaysian Standard for Masonry Cement - Composition, specifications and conformity criteria) which is specifically for Masonry Cement. Masonry Cement is good for plastering work but cannot be use for structural work due to its low strength. In order to differentiate the Masonry Cement from the Portland cements, it is commonly associate with red bag in the packing.
Factors to Consider
Different types of cement have different characteristics. The most important variables are the rate of hardening, the strength gain pattern, the heat of hydration, the resistance of the hardened cement to sulfate chloride attack and other durability aspects. Construction documents often specify a cement type based on the required performance of the concrete or the placement conditions. Factors to be considered when selecting the right cement are :
a) Type of construction
b) Speed of construction
c) Compressive strength requirement
d) Strength development
e) Specific requirements such as chloride & sulfate environment, permeability tests, control of ASR, etc.
Although the process for cement manufacturing is relatively similar across the world, the standards requirement can be vary. There are different types of cement and sometimes it can be difficult to determine the suitable cement for your project. When ordering cement for construction projects, do not extrapolate performance data for one cement as representing all cements. Work with your cement supplier to verify that the cement is suitable and meeting the requirements for the project and application.
Thank you
コメント