The Boral Book of Concrete
The Boral Book of Concrete
The Boral Book of Concrete
Contents
Chapter 1 - What is Concrete?
Cement and concrete Are they the same? What is concrete? Strength of concrete Properties of fresh concrete What do you order? What makes good concrete?
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7 8 8 8 8 8
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Contents
Chapter 5 continued
Wearability Watertightness Curing of concrete Effects of curing Methods of curing Mechanical barriers absorptive covers Advantages of careful control of moisture concrete & temperature in concrete To sum up the advantages of careful control of moisture concrete and temperature in curing Points to keep in mind when curing 23 23 23 24 24 25
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31 33 33 33 34
Glossary of Terms
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Chapter 1
What is Concrete?
What is Concrete?
Cement and Concrete Are they the same?
Many people think that cement and concrete are the same product - they are not. Cement is a dry powdered chemical that, when mixed with water, slowly reacts to form a new hard, solid compound. On the other hand, concrete is a mixture of cement blended with water and various sizes of aggregates. The cement and water form a paste that glues the aggregates together when it hardens. Concrete, in its freshly mixed state, is a plastic workable mixture that can be formed into almost any desirable shape. It starts to slowly stiffen when mixed, but remains plastic and workable for several hours. This is a long enough period to allow it to be placed and finished. After it takes its initial set, it continues to gain strength for months and sometimes years if moisture continues to be present.
What is Concrete?
Concrete has two components; aggregate and paste. Aggregates generally are of two sizes; fine and coarse. Fine aggregates are those with particle sizes smaller than about 5mm, commonly known as sand, which can be natural or manufactured. Coarse aggregates are those with particle sizes greater than about 5mm. Gravel, crushed stone and blastfurnace slag are among the most commonly used coarse aggregates. Paste is composed of cement, flyash, water and sometimes entrained air. The cementing property of the paste results from a chemical reaction between the cement and water. This reaction is called hydration. It is a reaction that requires time and favourable conditions of temperature and moisture. Curing is the providing of favourable temperature and moisture conditions over a period of time long enough to allow the hydration process to approach completion. With proper curing, hydration takes place very rapidly at first, and then decreases slowly for a long time. This allows the concrete to develop good strength and durability. Remember, concrete needs continued moisture to harden properly. It should not dry out too quickly.
Chapter 1
What is Concrete?
Strength of Concrete
The compressive strength of concrete, measured by how much force is required to crush it, is important in the design of structures. In pavements and other slabs on ground, the design is usually based on flexural strength, (ie; how much force the concrete can withstand in bending before it breaks). In either case, the principal factors affecting strength are the water-cement ratio and the extent to which hydration has progressed. The addition of too much water to concrete (beyond the intended mix design) will reduce strength and durability of the concrete, even if it is properly placed, finished and cured.
Chapter 1
What is Concrete?
2. Fine and coarse aggregate of a predetermined quality is added to the cement-water paste in the batch to give bulk to the batch. They contribute significantly to the quality of the concrete. If all fine aggregate (sand) is used to make a one cubic metre batch, a large amount of cement-water paste is needed to coat and bond the particles. By adding coarse aggregate to the batch instead of a portion of the sand, the mixing water demand can be kept lower. This works to produce better quality concrete at an economical cement content. 3. Admixtures - many of these are used (often in combination) to impart specific qualities to the fresh or hardened concrete. Some admixtures make the concrete set faster or slower, or make it denser, or make it stronger or more durable. The most common is an air-entraining agent which develops millions of tiny air bubbles in the concrete. These improve durability and workability. Water-reducing admixtures are also very common. They help produce a medium slump, workable concrete, with less required mixing water. Superplasticisers are a relatively new breed of admixture which can greatly increase slump with a relatively small dose. Once added to the concrete this slump increase will last up to 2 hours, with the concrete eventually returning to its original slump. Its main uses are a) Flowing concrete (180mm plus slump) for ease of placement, labour savings and good off-form finish b) Medium slump concrete (100mm - 140mm slump) for exceptional pumpability (130 + metres high) c) Normal slump concretes (80mm) giving very low shrinkages due to reduced water content.
Stadium Australia
Chapter 2
The testing of Concrete
The Slump Test (AS 1012, Part 3) - Determining the consistency of Concrete
In many cases, the acceptance or rejection of a load of concrete depends upon a 15mm variation in the slump. This much variation can be, and often is, caused by poor slump test practices.
Sampling
If the slump test is to determine whether or not the concrete is to be accepted, the sample must be taken from the early part of the load. Never take the sample from the first concrete out of the mixer. Let out at least one fifth of a cubic metre before taking a test sample. If the test is to be representative of the entire load, samples should be taken from three well-spaced parts of the load by passing the bucket through entire discharge stream of concrete and remixing them on a non-absorbent surface.
Boral Book of Concrete
11
Chapter 2
The testing of Concrete
Right way to make a slump test
1. Moisten the inside of the cone and place it on a flat, level and firm surface - a piece of steel plate, concrete or stone slab, sheet or metal pan etc. This support should extend 50mm beyond the base of the cone to provide space for the concrete to spread when the cone is removed later. Hold the cone firmly in place when putting concrete in it by standing on the foot lugs.
2. Fill the cone with one-third of the volume (approx depth of 60mm) and rod the layer exactly 25 times with a round bullet-nosed steel rod of 15mm diameter, 600mm long. Rod uniformly over the entire concrete surface.
3. Fill the cone with the second layer until two-thirds full (approx depth of 150mm) and rod this layer 25 times uniformly over the entire concrete surface just penetrating into the underlying layer.
4. Fill the cone with the third layer until it slightly overflows and then rod this top layer 25 times uniformly over the entire concrete surface, just penetrating into the underlying layer.
5. Strike off the excess concrete from the top with a straight edge so that the cone is exactly filled. Remove spilled concrete from around the bottom of the cone.
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Chapter 2
The testing of Concrete
6. Lift cone straight up slowly and gently approximately 3 seconds after filling, rodding and strike-off are completed. Never jar the concrete in any way until after the slump is measured in order to avoid possible incorrect results of the test.
7. Measure the slump as shown in the diagram. If the top of the slump is irregular, do not measure the high point or the low point. Try to get the average. The slump shall be measured to the nearest 5mm for slumps 100mm and less, and to the nearest 10mm for slumps greater than 100mm.
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Chapter 2
The testing of Concrete
Filling and Compacting
The moulds are filled in two approximately equal layers and fully compacted usually by hand rodding for slumps of 40mm and above or by vibration for lower slumps down to 10mm. i) By rodding - each layer shall be fully compacted using the standard tamping rod 15mm diameter, 600mm long, tapered for a distance of 25mm to a spherical shape end having a radius of approximately 5mm, the strokes being distributed uniformly over the cross-section of the mould. The bottom layer shall be rodden throughout its depth and for the upper layer, the first ten strokes shall just penetrate into the underlying layer. The number of strokes per layer shall be 25. ii) Compaction by vibration - for standard cylinders two approx equal layers shall be used. All the concrete for each layer shall be placed in the mould before starting vibration of that layer. Vibration shall be continued only long enough to achieve full compaction of that layer. Over vibration shall be avoided.
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Chapter 3
Mixing water in Concrete
25
20
+20
+10
-15
-30
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Chapter 3
Mixing water in Concrete
In addition to the loss in strength, other results of excessive mixing water include: Excessive cracking resulting from high shrinkage and low tensile strength caused by too much water. Dusting and crazing of slabs caused by excessive bleeding bringing fines to the surface.
Remember: Stiff concrete is much less expensive when measured in man hours. It may require more labour initially to place, but it can be finished much sooner. Discharge concrete as soon as possible after it arrives on site. Prolonged mixing causes stiffening of concrete and may make it necessary to add water to maintain workability. Ensure that adequate manpower and equipment are available to place the concrete place it rather than pour it.
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Chapter 4
Vibration of Concrete
Vibration of Concrete
Concrete for any structure must have a degree of workability - while in a plastic state which will permit it to be moved into the final position where it will be allowed to harden. Normally the plastic concrete flows around reinforcing in the forms, into corners and other areas. However, when the concrete is too heavily reinforced, with small clearances between the bards and forms, some mechanical aid is required to assist in the placing. Here vibration provides the best method for consolidation of the concrete. Advantages of Consolidation by Vibration: Efficient placement of stiffer concrete mixes which will give higher-strength, better quality concrete. Savings in time/costs through ease of placement. Greater density in the concrete. Greater homogeneity in the concrete - uniform consistency can be maintained throughout. Absence of voids, stone pockets and air traps. Improved bonds with reinforcement. More complete combination of successive layers. Reduces shrinkage in the setting concrete.
Low-Slump mixes
The higher strength and quality of concrete obtained by vibration result largely from the fact that a drier concrete can be placed. Less free water, lower water-cement ratios, less volume change, all work for greater early and final strengths. Vibration periods of 5 to 15 seconds are usually sufficient. The amount of vibration needed in one spot can be gauged by the surface movement and texture of the concrete, by the appearance of cement paste at the sides of forms, by the approach of the sound of the vibrator to a constant tone, and by the feel of immersion vibrators in the operators hands.
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Chapter 4
Vibration of Concrete
Overvibration
There is little likelihood of overvibration when the slump of the mix is as low as practicable. When overvibration occurs, the surface appears very wet and in fact consists of a layer of mortar containing little aggregate. Generally, the slump, and not the amount of vibration, should be reduced. Overvibration of wetter mixes may result in horizontal stratification, with loss of durability. Obviously, mixes of air-entrained concrete, or stiff mixes made with lightweight aggregates, should receive the minimum amount of vibration needed for consolidation. Hand vibrators should not be used to transport concrete along a horizontal surface or to re-mix concrete in forms, as some segregation will occur. Systematic vibration of each new layer is essential. The vibrator should be used at regular intervals of space and penetrate vertically approx 50mm into the previous layer which should still be plastic. Penetration at haphazard angles, spaces and depths does not result in a monolithic combination of the two layers.
Correct
Incorrect
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Chapter 5
Curing of Concrete
Curing of Concrete
Whether as a test specimen or in the job, concrete must be cured. The following notes give some background to this necessity.
What is hydration?
When cement is mixed with water it undergoes a chemical change that transforms it into rock. When it hardens into a mass similar to rock, it is said to have hydrated. Therefore, hydration is nothing more than a chemical combination of cement and water. First, the outside of the cement particle hydrates and a cement gel (glue) is formed. As water continues to soak through this cement gel, further hydration takes place in the cement particle. This process goes on for many years just as long as moisture is present. The process of keeping the concrete damp and at about 21C is known as curing.
Average Comp Str. at 28 days MPa 27 days standard curing 6 days site curing then standard curing in lab 7 days site curing then standard curing in lab 13 days site curing then standard curing in lab 17 days site curing then standard curing in lab 19 days site curing then standard curing in lab 27 days site curing then standard curing in lab 22.7 19.7 17.7 16.7 15.6 15.0 14.2 % 100 86.7 77.8 73.5 68.6 66.2 62.6
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Chapter 5
Curing of Concrete
Wearability
Since evaporation occurs more rapidly from the surface of concrete, the surface is affected by the length of curing time more than by any other single item. For instance, surfaces moist-cured for 28 days produce floors twice as hard as those protected only 3 days.
Watertightness
A well proportioned and workable concrete mix generally contains about twice as much mixing water as is necessary for hydration of the cement. The reason is that one half of the water is used to make the concrete workable. As the cement and water hydrates, a gel is formed and the gel expands to fill the voids which are left by the unneeded water as it evaporates from the concrete. You can readily see what happens if curing is stopped at one of the intermediate stages. The voids that are normally filled by the gel are left at whatever stage curing is stopped, making the concrete porous.
Curing of Concrete
Concrete curing techniques fall into two groups: those designed to prevent loss of water, such as the application of impermeable membranes and those that supply moisture throughout the early stages of the hydration process, such as ponding or the application of wet sand or hessian.
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Mo
red 7 ist Cu
Days
30 25 20
Strength - MPa
No C u r i ng
15 10 5
Age - days
28
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Chapter 5
Curing of Concrete
Effects of curing
The longer concrete is moist cured the greater its strength. If the concrete is to gain high percentages of its potential strength and durability it must have: Sufficient water for hydration of the cement. A temperature conducive to maintaining the chemical reaction at a rapid, continuous rate.
Methods of curing
We have given some of the reasons why it is necessary to cure concrete. Below are listed some of the methods to cure concrete. All the methods have advantages and disadvantages. The one used should be the one that will be the cheapest and most effective for the particular conditions under which the concrete is to be placed.
Methods
Sprinkling with water or covering with wet hessian.
Advantage
Excellent results if constantly kept wet.
Disadvantage
Likelihood of drying between sprinklings. Difficult on vertical walls.
Straw.
Insulator in winter.
Curing Compounds.
Sprayer needed inadequate coverage allows drying out; film can be broken or tracked off before curing is completed; unless pigmented, can allow concrete to get too hot. Can dry out, removal problem.
Moist Sand.
Cheap.
Waterproof Paper.
Cost can be excessive. Must be kept in rolls, storage and handling problem.
Plastic Film.
Should be pigmented for head protection. Requires reasonable care and tears must be patched, must be weighed down to prevent blowing away.
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Chapter 5
Curing of Concrete
Mechanical barriers absorptive covers
The use of waterproof building papers or plastic film (polyethylene sheeting) will also prevent the evaporation of moisture from concrete. An absorptive medium such as sand, hessian or canvas will hold water on the concrete surface while curing progresses. Plastic sheeting also has advantages of flexibility. It is easy to drape over complex shapes; and the progress of curing and conditioning of the concrete can be checked easily at any time.
To sum up the advantages of careful control of moisture concrete and temperature in curing
The strength of concrete increases with age if curing conditions are favourable. Compressive strength of properly cured concrete is 80 to 100% greater than the strength of concrete which has not been cured at all. Properly cured concrete surfaces wear well. Drying shrinkage is greatly reduced and cracking is avoided. Greater watertighness of constructions is assured.
cracking.
If during curing the concrete is allowed to dry out as may happen in hot weather the chemical
change stops right at the point where the concrete loses its moisture.
The ideal curing temperature is a constant 21C. Cure concrete for at least 7 days.
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Chapter 6
Hot and cold weather Concreting
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Chapter 6
Hot and Cold weather Concreting
Cold weather Concreting
Few areas in Australia experience temperatures low enough to warrant elaborate and expensive protection of freshly placed concrete. But frosts, abrupt drops in ambient temperature and/or prolonged periods of cold weather, are common in our winter seasons. Harmful effects of these conditions on new concrete can be avoided by relatively simple measures in ordering, placing and curing. Placed concrete is a gel formation which hardens over a period of weeks. Generally, the lower the ambient (surrounding) temperature, the slower the rate of hardening. At an ambient temperature just above 0C the development of strength in unprotected freshly placed concrete is very slow. If the ambient temperature drops to or below 0C some of the water in the concrete may freeze, setting will virtually stop until it thaws and this interruption of hydration increases porosity and reduces final strength and durability. Because some heat is generated during the hydration process, ordinary concrete has a minor inherent resistance to the freezing of its water content after placing. But when the temperature of the concrete surface itself falls below freezing point, the water content near the surface will solidify in an almost instantaneous surge, increasing its volume by about 10% and causing tensile pressure as high as 210 MPa in concrete which is no longer plastic. Scaling or spalling will follow, and will become more severe if several freezing/thawing cycles occur. The use of aggregate of high porosity in concrete can increase scaling/spalling problems.The aggregate particles near the surface will expand when frozen. Moreover, as most porous aggregates have poor abrasion resistance, the damage will be intensified by separation of particles from the cement paste. Air entrained concrete mixes have excellent resistance to surface scaling or bursting after freezing because, as ice crystals begin to form, residual water under pressure moves into the millions of small air cells in the concrete, thus relieving stress. The addition of any air entrainer increases slump, the obvious answer will be to reduce the amount of water in the mix and thus derive an even greater benefit in terms of increased durability.
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Chapter 6
Hot and Cold weather Concreting
An interesting comparison can be provided between: 1. An ordinary concrete mixed and cured at 5C and 2. An identical concrete mixed and cured at 21C. The 3 day strength of the first concrete (5C) could be expected to be only 30% of the 3 day strength of the second concrete. At 7 days the relative strength of the low temperature concrete might be 50% and at 28 days 80%. Ordinary concrete mixed at 21C but placed in an ambient 5C will gain strength fairly rapidly if the surrounding temperature increases.
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Chapter 7
Cracks in Concrete
Cracks in Concrete
Concrete, when placed is a mass containing more water than is required for hydration of the cement it contains and for subsequent curing. When the concrete hardens and starts to lose the excess water, shrinkage begins. If the concrete is unrestrained no cracks due to drying shrinkage should develop. But it is virtually impossible to support a structure of any appreciable size without some restraint. The cracking phenomenon is complex and depends upon a number of things rate and amount of drying, drying shrinkage, tensile strength, tensile strain, creep, elasticity, degree of restraint and other factors. In the laboratory, drying shrinkage tests are the most easily and most frequently performed tests in relation to shrinkage/cracking problems. However, there is sometimes too much emphasis on the drying shrinkage of hardened concrete as the criterion of susceptibility to cracking.
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Chapter 7
Cracks in Concrete
Types of Cracks
1. Shrinkage cracks avoid by cutting contraction joints along dotted lines. 2. Shrinkage cracks caused by stress concentration at corners prevent by placing expansion joint along dotted line, or by using reinforcing steel. 3. Settlement crack caused by movement of sub-grade or footings. 4. Cracks due to heaving under slab through poor drainage of sub-grade. 5. Expansion cracks prevent by placing expansion joints at dotted lines. 6. Shrinkage cracks in feathered sections. Narrow feathered sections should be avoided. 7. Plastic shrinkage cracks, due to quick loss of water to dry sub-grade or to the atmosphere. 8. Shrinkage cracks at door or window corners avoid by use of reinforcing steel or (in solid concrete walls) by careful placement of low slump concrete.
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Chapter 7
Cracks in Concrete
Cracks before and during hardening
Plastic shrinkage cracks occur when wind velocity, low relative humidity, high air temperature, or a combination of all three, cause water to evaporate from a concrete surface faster than it can be replaced by bleeding to the surface. The rapid evaporation which causes this cracking can be checked by windbreaks, shading and efficient curing.
Shrinkage cracks cannot always be prevented, but they can be controlled by making planes of weakness to establish the direction of cracking when contraction occurs. This is done by cutting grooves one third the thickness of the slabs, and is done as soon as the concrete is hard enough to resist damage by the saw.
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Chapter 7
Cracks in Concrete
In Summary:
The majority of cracks occur within 72 hours after concrete has been placed. These are preventative measures which will minimise cracking in this period. See that the sub-grade is well compacted. Check that form work is firm. Ensure that sub-grade and form work are moist before placing concrete. Do not add water to ready-mixed concrete in placing. Adequately compact the concrete. Cut sufficient contraction joints to allow for shrinkage and/or provide crack inducers to control location of cracking at early ages. Provide expansion joints where necessary. Start curing as soon as possible. Maintain proper curing for an adequate period.
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Glossary
Glossary
Glossary of Terms
Admixture a material other than water, aggregates and cement, used as an ingredient of concrete to
alter its basic characteristic.
Accelerator a chemical which, when added to concrete shortens the time of set, or increases the rate
of hardening or strength development.
Aggregate granular material such as sand, gravel, stone and slag, which when bound together by
portland cement paste forms concrete.
Aggregate, Heavyweight a heavier than normal aggregate such as barite, magnetite, limonite,
ilemenite, iron or steel used to produce extra heavy concrete.
Aggregate, Lightweight a lighter than normal expanded aggregate made from basic materials such
as clay, slate, fly ash, vermiculite, pumice or scoria used to produce lightweight concrete.
Air Entraining Agent an admixture for concrete which causes air to be incorporated in the form of
minute bubbles in the concrete during mixing, usually to increase its workability and frost resistance. Normally expressed as AEA.
Batch Plant an installation of equipment including bins, batchers and/or mixers as required for batching
or for batching and mixing concrete materials; also called mixing plant when equipment is included.
Bonding Agent a substance applied to an existing surface to create a bond between it and a
succeeding layer as between a sub surface and a terrazzo topping.
Broom Finish the surface texture obtained by stroking a broom over freshly placed concrete. Bush Hammer Finish a finish on concrete obtained by chipping off the surface mortar. Cement Content quantity of cement contained in a cubic metre of concrete. Cement, Expansive a special cement, which when mixed with water, forms a paste that tends to
increase in volume at an early age used to compensate for volume decreases due to drying shrinkage.
Cement, High Early Strength cement characterised by producing earlier strength in concrete than
regular cement.
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Glossary
Cement, Hydraulic a cement that is capable of setting and hardening under water, such as normal
portland cement.
Cement, Portland hydraulic cement obtained by combining and burning limestone and clay to form
amounts of gypsum, is then ground to produce a powder.
Central Mixed Concrete concrete which is completely mixed in a stationary mixer before it is
transported to the job. It can be transported in mixer trucks, agitators or dump type trucks.
Chute a rounded trough or tube for sliding concrete from a higher to a lower point. Compressive Strength the measured maximum resistance of a concrete specimen to compressive
loading expressed in megapascals (MPa).
Concrete a composite material which consists mainly of aggregate, portland cement and water,
normally weighing 2200-2300kg per cubic metre.
Concrete, Foamed concrete made very light and cellular by the addition of a prepared foam or by
generation of gas within the unhardened mixture.
Concrete, Lightweight concrete made with lightweight aggregate; the unit weight of the resulting
concrete is in the range of 1500 to 1950kg per cubic metre.
Concrete Pump an apparatus which forces concrete to the placing position through a pipeline or hose. Concrete, Reinforced concrete construction which contains mesh or steel bars embedded in it. Construction Joint a normally keyed joint formed by a bulkhead between successive placements
of concrete.
Contraction Joint (Control Joint) a joint or deep groove separating concrete in a structure or
pavement designed to prevent formation of cracks elsewhere in concrete.
Conveyor a device for moving materials; usually a continuous belt, system of buckets, a confined
screw or pipe through which material is moved by air or water.
Core Test compression test on a concrete sample cut from hardened concrete by means of a core drill.
37
Glossary
Corrosion disintegration or deterioration of concrete or reinforcement by electrolysis or by
chemical attack.
Craze Cracks fine, random cracks or fissures caused by shrinkage which may appear in a concrete
surface within a few days of placement.
Curing maintenance of moisture and temperature of freshly placed concrete during some definite
period following placing, casting or finishing to provide enough moisture and the proper temperature level to promote continued hydration within the hardened concrete.
Drum Speed (RPM) the various rates of rotation of the drum of the mixer when used for charging,
mixing, agitating or discharging. These various drum speeds are usually outlined on the mixer rating plate.
Drying Shrinkage contraction caused by moisture loss from hardened concrete sometimes resulting
in cracks in the concrete occurring days, weeks, or months after placement.
Dusting a defect in a slab surface; the powdering of the surface under foot or vehicle traffic. Usually
caused by overtrowelling wet concrete.
Efflorescence a deposit of salts, usually white, formed on a surface, the substance having emerged
from below carried by water vapour.
Entrained Air microscopic small air bubbles intentionally incorporated in concrete during mixing to
improve durability and workability.
Entrapped Air large air voids in concrete which are not purposely entrained; generally larger than
1mm and are usually due to incomplete consolidation.
Expansion Joint a separation in the concrete filled with compressible material to allow room for the
expansion of the concrete in hot weather or movement due to other causes.
False Set premature stiffening of freshly mixed portland cement concrete. Plasticity can usually be
regained by further mixing with no additional water.
Flash Set the rapid development of rigidity in freshly mixed portland cement concrete, usually building
up considerable heat. Rigidity cannot be dispelled nor can the plasticity be regained by further mixing without addition of water.
Flexural Strength the ability of concrete to withstand bending measured by breaking a test beam. 38
Boral Book of Concrete
Glossary
Float a tool, usually of wood, aluminium or magnesium, used in finishing operations to impart a relative
even (but not smooth) texture to a fresh concrete surface immediately after placement and strike off.
Fly ash the fine ash resulting from the burning of powdered coal in electric utility plants, sometime
used as a mineral admixture.
Groover (Jointing Tool) a tool used to form grooves or weakened lane joints in a concrete slab
before hardening to control crack location.
Gross Vehicle Load the weight of a vehicle plus the weight of a load thereon. Grout a mixture of cement and water with perhaps some fine material used to fill cracks and voids in
concrete or to prime concrete pumps.
Hardener a chemical applied to concrete floors to reduce wearing and dusting. Hairline Cracking (Crazing) small cracks of random pattern in a concrete surface caused by too
rapid surface drying.
High Early Strength Concrete concrete which, through the use of high-early-strength cement or
admixture, is capable of attaining specified strength at an earlier age than normal concrete.
Mineral Admixture (Pozzolan) a fine powdered material such as flyash which may be used to
improve workability or strength characteristics of concrete.
Mixer Capacity the volume of concrete permitted to be mixed or carried in a particular mixer
or agitator.
Mortar usually consisting of cement, water and sand; no coarse aggregate. Plastic Shrinkage Cracks cracks which appear in fresh concrete during or just after finishing. They
are often at an angle to side forms but parallel to each other.
Pile a long slender timber, concrete or steel structural element driven, jetted or otherwise embedded
on end in the ground for the purpose of supporting a load or of compacting the soil.
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Glossary
Rubbed Finish a finish obtained by using an abrasive to remove surface irregularities from concrete
walls or columns.
Schmidt Hammer (Trade Name), Swiss Hammer, or Rebound Hammer a device used to estimate
the compressive strength of hardened concrete by measuring surface hardness.
Screed a tool for striking off the concrete surface. Segregation a) separation of the coarse aggregate from the mortar portion of the concrete;
b) improper balance of the aggregate sizes from stockpiles or bins resulting in stony or sandy mixes.
Shrink-Mixed Concrete concrete which is partially mixed in a plant mixer to intermingle the
materials and observe consistency; it is then discharged into a truck mixer where mixing is completed.
Slump a measure of consistency or wetness of freshly mixed concrete. Slurry a wet mixture of water and portland cement; usually containing no aggregate. Spalling a chipping or peeling off of concrete surface or corners. Swirl Finish a nonskid curving texture imparted to a concrete surface during final finishing. Topping a) a layer of high quality concrete placed to form a floor surface on a concrete base, or
b) a dry shake application of a special material to produce particular surface characteristics.
Truck-Mixed Concrete concrete, the mixing of which is accomplished in a truck mixer. Vibrated Concrete concrete compacted by vibration during and after placing. Water Reducing Agent a material which either increases workability of freshly mixed concrete
without increasing water content or maintains slump with a reduced amount of water.
40
Glossary
Products
Products
Architectural
Products such as Boralstone, Colori and Expos are among the many specialised architectural products available. The extensive range of products are available to add unique and creative alternatives for flooring, driveways, external areas and pool surrounds. It truly is creativity in concrete, limited only by your imagination.
High Performance
Developed with the assistance of Boral's highly respected Concrete Research and Development laboratory, Boral's high performance concretes have been used in many technically demanding projects around Australia.
Normal Concrete
Boral's range of Normal concrete products is designed for general purpose applications such as slabs on ground, footpaths, foundations and general paving.
Special Purpose
With over 60 years experience in concrete manufacturing, Boral has developed a wide range of Special Purpose Concrete products designed to help you deliver your project on time.
Boral website:
Visit the Boral website for the full range of Boral products www.boral.com.au or for specific concrete information visit www.boral.com.au/concreteproducts For your nearest concrete plant log onto www.boral.com.au/concretelocations
Customer Service:
at Boral we are committed to excellence in service so for further information please contact: QLD 1300 50 59 80 NSW 1300 55 25 55 VIC 133 006 TAS 03 6336 1366 SA 08 8425 0400 WA 13 2675 (13 BORL) NT 08 8947 0844
General information:
To contact a customer service person please phone or email your particular state: concreteQLD@boral.com.au concreteNSW@boral.com.au concreteSA@boral.com.au concreteVIC@boral.com.au concreteWA@boral.com.au concreteNT@boral.com.au
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