Cement Types : The Key To Building
Cement is a key ingredient in the construction and strength of structures, it is the backbone of retaining walls, brick walls, pavement and pretty much any other type of strong structural foundation you can think of. When using cement is important to select the best quality and type for your job. But how to determine the right one ? To accomplish this mission we have set ourselves we must first look at the properties of each cement and the conditions of exposure, age to strength, and durability. Obviously quality comes first when choosing our cement as safety is a key concern in the buildings we surround ourselves in. Since we live most our life in our homes it is important they are quality built, durable and long lasting.
There are a wide range of cements available to consumers in the marketplace today. These include General Purpose Portland cement (GP) , High Early strength (HE), Low Heat (LH), Sulphate Resisting (SR), Low Shrinkage (LS) and Off–White cements. The use of mineral additives known as Pozzolans can also be combined to general purpose cements giving the desired advantageous properties to our cement, classifying these cements as General Blended cements (GB).
History of Cements
Before 1991 Type A cement was used as a general purpose cement. In addition Type B was of high early strength cement, Type C a low heat cement, and Type D a sulphate resisting cement. Today, manufacturers now blend mixtures of flyash, silica fume, limestone, and/or slag to achieve a low heat or suphate resisting cement.
The equivalent of classification of Australian cements to American is: Type I = GP, Type II = GB, Type III = HE, Type IV = LH and Type V = SR.
Below are a list of in-depth Cement types that Rafzan recommends for different applications:
Air Entraining Cement
This type of cement is produced by air entraining agents such as glues, resins, sodium salts of sulfate mixed with ordinary portland cement at 4 to 7 percent of the concrete volume, however this can be varied based on special conditions. They cause the entrainment of very fine air bubbles in a concrete, increasing the resistance of the concrete to freeze-thaw damage in cold climates by providing small chambers of air pockets for water to expand into when freezing.
Created by grinding 5 to 10 percent of white chalk minerals or clay free of iron oxide with white or ordinary gray portland cement, this type of cement is mainly used for interior and exterior decorative works. Disadvantage of colored cement is that it is much more costly that ordinary portland cement.
Its main use is for prestressed concrete ducts and grouting anchor bolts. Expansive cement advantage is that it does not shrink during or after the time of hardening, however it expands slightly with time, this expansion of concrete is compensated in shrinkage losses.
High Alumina Cement
HAC or High alumina cement is a special cement, that is produced by mixing aluminum ore and lime. This cement is very workable with its high compressive strength in comparison to ordinary portland cement. A disadvantage however is that HAC is prone to crystalline conversion, which could lead to reduced strength and vulnerability to chemical damage when exposed to water for prolonged periods.
This type of cement is manufactured by grinding portland cement clinker with film-forming substance to reduce the rate of deterioration when the cement is stored under unfavourable conditions such as high moisture areas. Hydrophobic cement is mainly used in constructing dams, spillways, and water tanks.
Low-alkali cement is a mixture of portland cement having a total content of alkalis below 0.6 percent. This cement is used where aggregates are suspect of containing reactive silica and so low-alkali cement balances the reactive silica to form a stable concrete.
Low Heat Cement
Less reactive with an initial setting time greater than that of ordinary portland cement, low heat cement is produced by increasing the proportion of C2S and decreasing the C3S and C3A content, and is mostly used in mass concrete construction.
Masonry Cements are a mixture of ground limestone, portland cement and another agent with an air entraining or water repellent additive, these cements are used for mortar, in the concrete process.
Oil-well cements are used in construction works such as in drilling oil wells where they are subject to exposure to high temperatures and pressures. They consist of portland or pozzolanic cement mixed with organic retardant to prevent cement from settling too quickly.
Portland Blast Furnace Cement
Manufactured by cement grinding clinkers mixed with blast furnace slag of 25-65% in weight for grinding, additionally a small percent of gypsum is added in order to control its time of setting. It is mainly used in marine and mass concrete works such as foundations, abutments of bridges, docks, harbors, jetties and dams. The properties in using this cement offer advantages in work ability, cohesiveness, plasticity, resistance to sulfates of alkali metals, produces low heat, and is economical.
Portland Pozzolana Cement
This type of cement is consisted of clinker and pozzolanic material such as volcanic ash, fly ash, ect, with gypsum or calcium sulfate. The pozzolanic materials do not have any cementing qualities when used alone, but when mixed with Portland cement, they react with cement components and form compounds with cementing properties. It has many properties similar to General use portland cement but also offers less production of heat, and offers greater resistance to sulfates and corrosive mechanisms of seawater. Thus this cement is used in constructing hydraulic and mass concrete works, and in sea water.
Rapid Hardening Cement
Contains a higher C3S content with a finer grinding that Portland cement. Rapid hardening cement is used in prefabricated concrete construction, and road works. It's greatest strength is in its early stage development. Know that even with the same water-cement ratio, this type of cement at 3 days is near the same as that of 7 days strength Portland cement.
Sulfate Resisting Cement
Used in soil foundation construction whereby subsoil contains high amounts of sulfate. It is produced by the reduction of C3A and C4AF content and is chosen for its high resistance to sulfate attack.
Waterproof Portland Cement
Used widely in constructing water-retaining structures such as swimming pools, dams, and reservoirs. Waterproof portland cement is manufactured by mixing portland cement or rapid hardening cement, added with a small portion of some metal composites.
When choosing which cement to buy, you must consider the purpose, location and application. As building a house, landscaping, or pavement have many different environmental factors.