Density of Cement & More Cement FAQs
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What is cement?
Cement is made by heating limestone (calcium carbonate) with small quantities of other materials (such as clay) to 1450°C in a kiln. The resulting hard substance, called 'clinker', is then ground with a small amount of gypsum into a powder to make 'Portland Cement', the most commonly used type of cement.
Portland cement is a basic ingredient of concrete, mortar and most non-specialty grout. The most common use for Portland cement is in the production of concrete. Concrete is a composite material consisting of aggregate (gravel and sand), cement, and water. As a construction material, concrete can be cast in almost any shape desired, and once hardened, can become a structural (load bearing) element. Portland cement may be grey or white.
Courtesy of Wikipedia.
What is the difference between cement and concrete?
While the terms cement and concrete are often used interchangeably, it is important to note that cement is actually an ingredient of concrete. Cement is the powder added to concrete that provides the basis for the glue that holds the concrete together. Concrete is a mixture of aggregates (stones) and sand and the paste is water and cement. Through a process called hydration the cement and a portion of the water will undergo a chemical reaction and harden into a rocklike mass.
Contrary to popular belief, concrete “sets” or “hardens” as a result of the chemical reaction between the cement and the water – it doesn’t just dry out.
What is the difference between General Purpose Cement (GP) and Builders (GB) Cement?
General Purpose Cement (or GP Cement) is straight cement. GP cement is manufactured from Portland cement clinker, gypsum and limestone. GP cement is used in all types of building and construction. Our General Purpose Cement exceeds the requirements specified in Australian Standard AS3972 for Type GP cement.
Builders Cement (or General Purpose Blended (GB) cement) contains both GP cement and a nominal mass of fly ash. Concrete made with Builders Cement delivers improved workability, later-age strength, enhances the durability performance of concrete and provides a lower carbon footprint. Early rates of strength gain may be lower than GP cement and curing may be more critical for full strength development. Builders Cement is used in all types of building and construction. Builders Cement is a uniform blend of Portland cement and Fly Ash that exceeds the requirements specified in Australian Standard AS 3972 for Type GB cement.
Does cement have a use by date?
The recommended shelf life of grey cement products is approximately 6 months from the date of manufacture. It is recommended that Off White Cement is used within 3 months of manufacture. These timeframes are based on the understanding that the product has been stored unopened and off the ground away from moisture. Cement is recommended to be stored indoors out of the weather and the pallet wrap is always maintained around the product. It is essential to ensure that stock of this product is rotated by Stockists and the oldest pallet is always used first.
Can you add placticiser to mortar and does it strengthen the mortar?
Plasticiser was developed to make mortar more workable or more “plastic”. Plasticisers that are based on a water reducing admixture action may improve strength, whereas excessive use of plasticisers that entrain air will reduce strength and bond.
TIP – A simple way to tell the difference between a plasticiser and a water reducing admixture is to shake the container. If the liquid produces a froth that does not quickly dissipate, then it is an air entraining product.
Why should a shovel not be used to measure concrete or mortar materials?
Cement is a dry product and is free flowing whereas damp sand tends to clump together. Cement tends to lie flat on the shovel and has less volume than the sand. Using a shovel does not ensure that materials are measured equally and it is recommended that proportions of raw materials are measured with a container such as a bucket.
Always use an accurate measure to add your water too as the most common mistake made when mixing concrete, render or mortar is to add to much water.
Too much water ruins the strength of concrete, mortar and render.
Which cement product should I use if I want a very light coloured finish?
When you need a light or pastel coloured finish for your cement-based job, use Off White or White Cement as your base product and select the palest sand you can find.
What are Supplementary Cementitious Materials (SCM’s) and why are they used?
SCM's are by-products from other industries that can partially substitute for cement in concrete, and help to improve the performance of the concrete.
Flyash is used as a SCM in some of Cement Australia’s Packaged Products and is rich in silica and / or alumina and these oxides combine with lime in the presence of water to form compounds that are virtually identical to the compounds in hydrated Portland cement.
Flyash is the dust collected in electrostatic precipitators used to clean the flue gases from black coal burning power stations. Flyash is a waste product and it is difficult to find practical, economic and environmentally sensitive ways to dispose of it. It is beneficial to the environment to utilise these waste materials and they have a positive influence on plastic and hardened concrete properties.
Supplementary cementitious materials have been used in building construction for many years. The original term used to describe these materials was pozzolan. Pozzolans are rich in silica and/or alumina and these oxides combine with lime in the presence of water to form compounds that are virtually identical to the compounds in hydrated Portland cement.
What is the density of cement?
The bulk density is the mass of the material related to a specific volume and for cement is normally expressed as “kilograms per cubic metre”. The bulk density reflects the volume taken up by the cement plus any air trapped between the particles. The relative density or specific gravity is the weight of the material particles themselves and for cement, this density is typically 3.11. When used in concrete, the space around the cement particles is taken up by water so there is no air around the particles and the bulk density is not important. The weight of the particles and their volume is important so the relative density value is used in concrete mix calculations. The bulk density of bagged GP cement is approximately 1000-1300kg/m3 and Builders cement is approximately 1000-1250kg/m3.
Which products can be used to line areas exposed to extreme temperatures such as pizza ovens?
Hardened concrete, mortar and plaster can be damaged at high temperatures. It is recommended that a product called Cement Fondue is used. This product is a High Alumina Cement and is available from specialty cement suppliers.
Cement Australian strongly recommends that unless you are experienced in using specialty cement products you should seek technical advice before using these products.
What is the best cement to use to mix your own concrete?
If you’re looking to mix your own concrete at home, add Cement Australia Builders Cement to your sand and aggregate for a more creamy, easy to work concrete that will give a really smooth surface finish.