ConcRetE MateRiaL~~continue

STORAGE Cement should be stored off the ground in a

well-aired, clean, dry place.

Wrapping the cement bags in plastic sheets gives extra

protection,Bulk cement will normally be stored in silos.

AGGREGATES Aggregates are of two basic types:

COARSE: crushed rock, gravel or screenings.

FINE: fine and coarse sands and crusher fines.

Sand should be concreting sand and not brickies sand or plasterers sand.

Aggregates should be:

STRONG and HARD A stronger, harder aggregate will give a stronger final concrete. Never use a crumble or flakey rock like sandstone.

DURABLE to stand up to wear and tear and weathering.

CHEMICALLY INACTIVE so the aggregates

don’t react with the cement.

CLEAN Dirt or clay sticking to the aggregates

will weaken the bond between paste and aggregates.

GRADED Aggregates should range in size so that they fit together well.

This gives a stronger and denser concrete.

Rounded aggregates give a more

workable mix. Angular aggregates

make concrete harder to place, work and compact,

but can make concrete stronger.

STORAGE Aggregates should be stored where they will stay clean, separated from other

materials and dry. If the aggregates are very wet use less water in the mix.

WATER Water is mixed with the cement powder to form a paste which

holds the aggregates together like glue.

Water must be clean, fresh and free from any dirt, unwanted chemicals or

rubbish that may affect concrete.

Many concrete plants now use recycled water.

Always check bore water before use.

Don’t use sea water as it may rust the steel

reinforcement in the concrete.

ADMIXTURES Admixtures are mixed into the concrete to change or alter its properties, ie

the time concrete takes to set and harden, or its workability.

HOW THE PROCESS WORKS Measured amounts of the coarse and fine aggregates are

mixed together.

A measured amount of cement is added and mixed in.

Enough water is added to make the mix workable. All the materials are then mixed

together well. The cement powder and water form a paste which bonds the aggregates

together like glue.

ConcRetE MateRiaL

CONCRETE is made by mixing:

CEMENT

WATER

COARSE AND FINE AGGREGATES

ADMIXTURES (if required).

The aim is to mix these materials in measured

amounts to make concrete that is easy to:

TRANSPORT

PLACE

COMPACT

FINISH

and which will set, and harden, to give a strong

and durable product.

The amount of each material (ie cement, water and

aggregates) affects the properties of hardened concrete.

CEMENT The cement powder, when mixed with water,

forms a paste.

This paste acts like glue and holds or bonds the

aggregates together.

There are six major

types of cement sold

in Australia:

Type GP (General Purpose Portland cement)

Type GB (General Purpose Blended Cement)

Type HE (High Early Strength cement)

Type LH (Low Heat cement)

Type SR (Sulfate Resisting cement)

Type SL (Shrinkage Limited cement)

Each type of cement will produce concrete with different properties.

The most common types of cement are Type GP and Type GB.

Blended cements contain portland cement and more than 5% of

either fly ash, ground slag, silica fume, or a combination of these.

ConCretE BaSICs

Foreword

Concrete is widely used in domestic, commercial, recreational, rural and

educational construction.

Communities around the world rely on concrete as a safe, strong and simple

building material. It is used in all types of construction; from domestic work to

multi-storey office blocks and shopping complexes.

Despite the common usage of concrete, few people are aware of the

considerations involved in designing strong, durable, high quality concrete.

Concrete Basics aims to provide a clear, concise explanation of all aspects of

making quality concrete; from the Materials and Properties involved through

Planning, Preparation, Finishing and Curing.

Concrete Basics addresses the needs of unskilled and semi-skilled persons

undertaking general concreting projects including home and handyman projects.

Concrete Basics also assists owner builders in the supervision of construction.

It aims to develop an understanding of highly technical terms through clear

definition accompanied by simple illustrations. A general understanding of these

terms will help to facilitate communication within the building industry.

Concrete Basics will help to generate a higher standard of workmanship on-site

and facilitate better communication among construction workers, builders,

engineers, building surveyors, architects and anyone interested in understanding

the processes involved in making quality concrete.

SLumP TeSt PrOcEduRe

What is a concrete test?

A concrete test is a test which is performed to learn more about the properties of a specific sample of concrete. A number of different tests can be performed on concrete, both on a job site and in a laboratory.

Because concrete is an important structural element, testing is mandatory in many regions of the world, and construction companies must provide documentation of their testing and results when asked to do so by government representatives. Test results are also kept on file in case a problem develops in the future.

One of the most classic concrete tests is a slump test. In a slump test, concrete is tamped into a cone which is then removed to see how far the concrete sinks or slumps without the support of the cone. Changes in slump height between batches of concrete can indicate a consistency problem. There are also slump requirements for different types of construction; low slump height concrete, for example, cannot be used to build roadways. Thus, the slump concrete test is both a quality control measure and a consistency measure.

Other types of concrete test can include laboratory analysis of the components of concrete, to confirm that concrete contains what the manufacturer claims it contains, and to learn more about properties such as durability and permeability. Concrete must meet specific standards, especially for high stress projects like bridges and high rise buildings, which makes lab testing important to confirm that concrete is safe to use and that it will withstand years of stress.

Materials testing in general is designed to make sure that materials meet quality control standards, comply with any laws which may be relevant, and contain the components people claim they contain. If concrete fails a concrete test, it may mean that part of a construction project needs to be redone to remove the faulty concrete, or that a batch of concrete needs to be discarded before it can be used in construction.

People have been testing concrete for strength, durability, and workability since Roman times. Curiously, reports about falsification of concrete test results pop up in the news on a regular basis, with construction companies being accused of cutting corners to avoid having to replace work performed with faulty concrete. Reputable companies use third parties to test their concrete so that the results are neutral, ensuring that there will be no doubts about the safety of the concrete in the future.

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