When purchasing cement, one quickly finds that the benchmarks by which reputable cements are tested are ASTM Standards. There are over two hundred ASTM standard tests relating to cement and concrete, and in addition to these there are also standard specifications which outline the parameters within which cement must fall in order to deemed to be of good quality.
To the inexperienced eye, these standards may appear to be nothing but a jumble of letters and numbers which make little sense, and it is tempting to ignore these altogether focusing instead on more ostensibly important numbers, such as price. However one should have at least a cursory knowledge of applicable ASTM standards, as understanding what they mean can be imperative when one is committing to purchasing materials which can quite literally make or break a project.
Not all cements are made equal, and not all cements are suitable for all applications. Using the wrong cement can result in disaster, but fortunately ASTM standards ensure that there is a way to verify that the cement you are purchasing is of good quality and equal to the task it must perform.

What is the ASTM?

The American Society for Testing and Materials is an international organization which has been in operation for over a century, and which specializes in developing standards for various commodities and materials. Originally formed in the USA to address problems in the railway industry, where problems with cracking and breaking tracks lead industry professionals to realize that there needed to be standards for steel used in railway tracks, the ASTM soon began to formulate standards for other materials and commodities which suffered from related issues. Today ASTM standards are in place for a plethora of products ranging from adhesives, to cement, to leather, to sports and sport safety equipment, and many many more. In fact, ASTM standards have now been developed for over 60 categories of commonly traded goods.
ASTM standards are developed on a voluntary basis by contributors from around the globe. These contributors are academics, scientists, producers, consumers, and those with interest or expertise in certain fields.

What Is An ASTM Standard?

An ASTM standard is essentially nothing more than a document which outlines methods for testing, and the allowable results which if obtained, will mean that a product meets ASTM standards. Although ASTM has no authority in itself, because of the reliability and global efficacy of ASTM standards, many governing bodies in countries around the world refer to ASTM standards when setting guidelines for materials and products imported into or produced within their own countries.

ASTM Cement Standards

ASTM C 150 – 07 Standard Specification for Portland Cement
This is the ASTM standard which pertains to Portland cement, and outlines requirements for the eight basic types of Portland cement, which possess the following properties.
Type I – Basic general use cement. Can be used in low demand applications which do not come in contact with the ground or ground water, both of which often contain sulfates which deform Type I cement.
Type IA – Air-entraining version of Type I cement.
Type II – General use with added sulfate resistance and medium heat of hydration. This is the most popularly used type of Portland cement, as it is suitable for most construction applications, and can be used in projects which come into contact with the ground and ground water, such as pipes.
Type IIA – Air-entraining version of Type II cement.
Type III – High early strength.
Type IIIA – Air-entraining version of Type III cement.
Type IV – Low heat of hydration.
Type V – High sulfate resistance.

ASTM C 595 – 08 Standard Specification for Blended Hydraulic Cements

This is a general standard for blended hydraulic cements covering the gamut of blended hydraulic cements and including those made with slag, pozzolan, or a blend of the two combined with Portland cement, Portland cement clinker, and also slag with lime.

ASTM C1157 – 03 Standard Performance Specification for Hydraulic Cement

The most recent of the ASTM standards devised specially for hydraulic cements, this is perhaps the most useful type of ASTM standard as it is based entirely on performance testing, and not on chemical composition. Cements are classified under ASTM C1157 – 03 by type, and are based on requirements associated with the following desired properties:
General Use
High Early Strengthened
Sulfate Resistance
Heat of Hydration
Alkali Reactive Aggregate Reaction (Optional)

How Do I Obtain ASTM Standards?

ASTM standards can be purchased directly from ASTM. The bulk of ASTM’s income comes from selling standard documentation, so the information is not usually available freely. ASTM provides documentation on standard specifications, testing methods, and testing conditions so that producers and users seeking to verify the properties of a product can do so in a reliable and replicable fashion.
More information on ASTM standards and testing practices can be found at ASTM.org.

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Aluminous cement is also known as ‘calcium aluminate cement’, ‘high alumina cement’, and by its original French name, ‘ciment fondu’. Unlike traditional cements which are comprised largely of calcium silicates, aluminous cements are made with calcium aluminates. Aluminous cements were invented in France in the early 20th century, and patented in 1908. Originally, aluminous cements were invented as alternatives to existing types of cement which did not have good sulfate resistance, and would often expand and distort when they came into contact with the ground and ground water.

However soon after their invention it was discovered that over and above being resistant to sulfates, aluminous cements also develop strength very quickly, have a high chemical resistance, and some blends maintain integrity at high temperatures as well. Of course, the trade off for these high performance specifications is price, and aluminous cements are a great deal more expensive than ordinary Portland cement.

Uses of Aluminous Cement

Aluminous cement is only used in a very small number of applications, due to its special qualities and its high cost. The sort of construction projects which require the use of aluminous cement include those which will be exposed to high chemical levels, or high temperatures, or applications which require fast high strength development. Aluminous cement is also therefore quite often used as a component of various specialist construction concretes which are used to construct buildings and other structures which will be exposed to concentrated chemicals or extreme temperatures.

Making Aluminous Cements

Aluminous cements are made in a process similar to that by which Portland Cement is made, however instead of using limestone and silica as the primary raw materials, limestone and bauxite are commonly used instead. Refined alumina is also used in the case of white aluminous cement or refractory (high temperature) cements.

At the beginning of the manufacture of aluminous cement, the raw materials are transported from various silos by use of a conveyor belt, which carries them to a raw mill. The purpose of the raw mill is to grind down the chunks of raw material into small pieces which are all of a similar size. It is important that the materials be of similar size so that when they melt in the kiln, they do so evenly.

Once they have been thoroughly ground up in the raw mill, the raw materials are sent on to the blender, where they are mixed together. The blended raw mix is analyzed carefully at this stage to ensure that the correct portions of materials are present. Perhaps the most important aspect of any form of cement production is controlling the relative ratio of raw materials in the raw mix. If the raw materials are present in the wrong proportions when the raw mix enters the kiln, the resulting product will be faulty.

Once blended, the raw mix is then sent through into the kiln where it is melted and where calcium aluminates form in the extreme temperatures. The result of the firing process are small pebble looking nodules of material which are called ‘clinker’.

In order to transform the clinker into cement, it must be ground thoroughly until it is a very fine powder. This is carried out inside a rotating cylinder where the clinker is mixed with hard balls, and gradually broken down to a very fine powder. This powder is aluminous cement, and is ready for use.

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As lower cost alternatives to Portland Cement, blended cements are increasingly being used in a great many construction applications. Blended cements are made by inter grinding Portland cement with another material. Fly ash, blast furnace slag, and condensed silica fume are all common components of blended cements, and each of them results in a different type of blended cement with an unique set of properties.

Blended cements are not a new idea. As far back as Roman times, pozzolanic materials such as volcanic ash were being added to cements in order to create long lasting strong concretes. To see the evidence of how long wearing these cements were, one merely needs to visit Rome and see some ancient cements still standing their ground against time and the elements.

Modern blended cements have been slow to gain popularity for a variety of reasons. For a long time there were no real standards for blended cements, so it was hard to source a reliable product. In many cases the additives which were blended with Portland cement to create blended cements actually weakened the end product and made it less reliable due to unforeseen alkali aggregate reactions.

More recently however, blended cements have come into their own as increasing care has been taken to develop high quality, high performance blended cements which far outperform traditional cements at a far lower price.

Why Blended Cements?

Portland cement is the most widely used cement on the globe, and there are several types of Portland cement which can successfully be used in almost any construction application, so why use blended cements at all?

Here are a few reasons why blended cements are being both developed and used more and more frequently.

Blended cements:

• Are cheaper than Portland cement.
• Are more long lasting and durable than Portland cement.
• Have higher strength tolerances than Portland cement.
• Have less drying shrinkage than Portland cement.
• Can, unlike Portland cement, be made to the buyer’s specifications.
• Are more environmentally friendly than Portland cement, as they are comprised of recycled materials.

Blended cements have been developed to both lower the cost of cement, and also to combat problems which are traditionally encountered with OPC (Ordinary Portland Cement) such as susceptibility to sulfates, cracking, steel corrosion, and susceptibility to freezing failure and carbonation.

Warning: As will be discussed in the section on blended cement standards, there are a myriad of ways in which cements are classified and standardized. There are relatively few blended cements available on the market which meet the specifications of the most recent and reliable standard, ASTM C 1157, but it is recommended that purchasers seek out cements which do meet this standard, as those which do not may be entirely unsatisfactory.

Blended Cement Standards

There are a plethora of cement standards around today, and most of them are wildly confusing to those who are not experts in the field. With three or four different standards, and several subtypes within each standard, it is easy to become quickly confused.

However, finding good quality blended cement is not as difficult as it might seem at first, due to the inception of a new standard specifically designed for blended cements. This is the ASTM C 1157 Standard, and it is recommended that buyers wishing to purchase blended cements check for compliance with this standard first before going any further with their investigations.

Unlike previous standards, which were based on the composition of the cement, ASTM C 1157 is based on performance, making it more reliable and easy to understand than previous standards. There are only two major subtypes within this standard, blended cements which meet the ASTM C 1157 standard, and blended cements which meet the standard and also will not react with alkali-reactive aggregates. These types of cement will be marked with [R].

Various types of cement under the ASTM C 1157 standard are defined by the compressive strength which they attain at the standard one, three, seven and twenty eight day marks.

Fly Ash Pozzolanic Blended Cements

Blended cements made with fly ash are pozzolanic cements. Pozzolanic materials are silica or alumina based materials which are not cements on their own, but which react with calcium hydroxide at room temperature to form cementious compounds. A relatively popular component of blended cements, fly ash in the form of coal ash is often used as an additive in blended cement production, especially in China and the United States.

Blast Furnace Slag Blended Cements

Blast furnace slag is a material which is high in silicates. When silicates are combined with Portland cement they improve the workability of concrete, and create a product which has low permeability, and does not allow alkali aggregate reactions to take place.

Condensed Silica Fume Blended Cements

A waste product from silicone production, condensed silica fume is perhaps the best additive of the three substances commonly used to create blended cements. Silica fume blended cements are high performance cements which have very little permeability and very high strength. Because silica fume is so effective at increasing the performance of cement, small amounts of silica fume may also be added to other types of blended cement as a secondary additive to develop the overall quality of the cement.

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