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ROAD RESEARCH LABORATORY
Ministry of Transport
RRL REPORT LR 363
AIR-ENTRAINED CONCRETES:
A SURVEY OF FACTORS AFFECTING
AIR CONTENT AND A STUDY OF CONCRETE WORKABILITY
by
D. F. Cornelius, B.Sc.
Materials Section
Road Research Laboratory
Crowthorne, Berkshire
1970
CONTENTS
Abstract
PART 1:
1.
2.
o
4.
A survey of some factors influencing the efficiency of air-entraining agents Introduction
Effect of various factors on air content 2.1 General
2.2 Effect of sand grading
2.3 Effect of sand content
2.4 Effect of cement content
2.5 Effect of organic impurities 2.6 Effect of alkali
2.7 Effect of specific surface
2.8 Effect of temperature
2.9 Effect of concrete workability
2.10 Effect of transporting concrete
Effect of entrained air on concrete strengths
Possible additions to specifications for air-entrained concretes 4.1 General
4.2 Alkali content of cement
4.3 Specific surface of cement
4.4 Organic impurities in cement
4.5 Effect of concrete temperature
4.6 Effect of entrained air on strength
Summary of existing knowledge
A study of the workability of air-entrained concretes
o
PART 2:
6. Scope of work
7. Materials and mix design
8. Experimental method
9. Results and discussion
10. Comparison of Compacting Factors and Vebe values
11. Effect of aggregate properties on workability measurements
12. Conclusions
13. Acknowledgements
14. References
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Q CROWN COPYRIGHT 1970 Extracts [rom the text may be reproduced
provided the source is acknowledged
Ownership of the Transport Research Laboratory was transferred from the Department of Transport to a subsidiary of the Transport Research Foundation on I st April 1996.
This report has been reproduced by permission of the Controller of HMSO. Extracts from the text may be reproduced, except for commercial purposes, provided the source is acknowledged.
AIR ENTRAINED CONCRETES: A SURVEY OF FACTORS AFFECTING
AIR CONTENT AND A STUDY OF CONCRETE WORKABILITY
ABSTRACT
Air-entrained concretes are used extensively in modern road con- struction as they are able to resist damage by frost and by the use of de-icing salts. Variations in the amount of entrained air lead to changes in concrete workability and to loss of concrete strength or durability depending upon whether there is an excess or deficiency of entrained air. The first part of the Report giwes the results of a survey of the literature which was made in order to identify the factors affecting the yield of entrained air from a given amount of admixture; suggestions are made for limiting the influence of the more important factors on site. The effect of'entrained air on con- crete strength is also described.
The second part of the Report describes a study of the effect of entrained air on the workability of various concretes as judged by the Compacting Factor test and the Vebe test which has recently become a British Standard test. These workability studies showed that the relation between Compacting Factor and Vebe value depends markedly upon the aggregate used in the concrete. Additional data are therefore presented to show the dependence of the relations between these workability measurements on the shape and surface texture of the aggregates.
PART I: ASURVEYOFSOME FACTORS INFLUENCING THE EFFICIENCY OF AIR-ENTRAINING AGENTS
I . INTRODUCTION
Air-entraining agents are used extensively for modem concrete road construction to prevent damage
by frost and by the use of de-icing salts. They have consequently been the subject Of a considerable
volume of research, particularly in America Where they have been used for many years. In countries
where frost damage is not a problem, air-entraining agent s are often used to improve the workability
and to reduce segregation, bleeding and shrinkage of concrete.
Variations in the amount of air entrained in concrete cause changes in the workability and
this can lead to difficulties in its placement. Of even greater importance are the loss of concrete
durability when insufficient air is entrained and the loss of concrete strength when an excessive
amount of entrained air is present. It is obviously highly desirable, therefore, that the amount of
air entrained in concrete should be kept as constant as possible but site experience suggests that
• this is not always easily done. A literature review has, therefore, been carried out in order to
identify the factors influencing the yield (efficiency) of air, entraining agents, to indicate the extent
of their influence, and to consider the ways • in which such influence might be controlled on construc-
tion sites by appropriate Specifications. The effect that mixingprocedure and type of air-entraining
agent can have on the requirements for air-entraining agent is not discussed as in any given job these factors would not normally be varied.
The influence of air-entrainment on the flexural and compressive strengths of concrete is also described in this Report.
2. EFFECT OF VARIOUS FACTORS ON AIR CONTENT
2. I General Entrained air produces discrete cavities in the cement paste and these cavities do not normally
fill with water even in saturated concrete; They are thus able to relieve the hydraulic pressure
developed in capillaries in the paste in the initial stages of freezing. As freezing proceeds the
cavities limit the growth of microscopic bodies of ice in the cement paste, and thus protect thin
'shells ' of concrete surrounding them. It is therefore apparent that the thickness of cement paste
between adjacent air voids (bubble spacing) is critical, and this should be less than 0.25 mm 1 and
possibly as low as 0.05 mm 2. Bubbles should be as small as possible (their sizes usually range
from 0.05 mm to 1.25 mm in diameter) so that the total volume of entrained air is low and strength
losses due to the presence of entrained air are minimised. Although changes in the materials and
mix proportions of concrete can produce appreciable changes in the size distribution of entrained-air
voids 1,3,4,, about 9 per cent of air by volume of the mortar, properly distributed throughout the
cement paste, is usually sufficient to afford adequate durability 5.
Much of the fundamental research on factors influencing the efficiency of air-entraining agents
has been carried out on mortars but because the results of such research are equally applicable to
concretes,6, 7, data obtained with each type of material are given in this Report.
Several types of air-entraining agent are marketed and these have naturally been studied by
many research workers. However, rather more data are given herein for neutralised Vinsol resin
than for any other air-entraining agent as this is the type used most extensively in this country.
2,2 Effect of sand grading Sand grading has been reported as having a considerable influence on the quantity of air
entrained in sand-water mixtures 8, rather less influence on the air entrained in mortars and hardly
any on the air entrained in concrete 9. There is, however, conflicting evidence on this point as
Craven 10 reports that the amount of air entrained in concrete is dependent upon the quantity of sand
passing a sieve of 600 ttm aperture and retained on a sieve of 300/~m aperture (but he also varied
the cement content of his mixes at the same time and in a way that would enhance the effect attri- buted to sand grading). Walker and Bloem 11 found that the amount of air entrained in concrete is
related to fineness modulus; other studies suggest however that the relation is not general and that
it will differ for other sand gradings having the same fineness moduli.
2
The present considered view 12 is that no one size of particle or one size group can have an
independent effect in a mixture comprising many sizes; more probably the change in air content
of a mixture is due to change in void content and possibly void size between the aggregate part ic les .
In any event, the nature of the relation between sand grading and the eff iciency of air-entraining
agents is unimportant as sand grading has only a small effect on the yield of air-entraining agents.
2.3 Effect of sand content
The amount of ~ r that is entrained in concretes increases as the sand content of the mix
increases for concretes made both with and without air-entraining agents 13. Typical ly an increase
in sand content from 35 to 45 per cent increases the total quantity of entrained air by about 1'/2
percent (e.g. from 4~ per cent to 6 per cent).
2.4 Effect of cement content
Work on cement pastes I and on concrete 13 has shown that the amount of entrained a i rodecreases
with increasing cement content, this effect being most marked with the leaner mixes. Typical ly an
increase in cement content of 90 kg//m 3.reduces the volume of entrained air in concrete by about
1 per cent of the volume of the concrete. However, as the cement and sand contents were varied
together in these studies on concrete it is possible that observed differences in air content could he attributed, at least in part, to changes in the sand content. .~.
2.5 Effect of organic impurities ~
It has been shown 6 that cements with organic impurities, as defined by their acid-chloroform-
soluble content, require greater dosages of air-entraining agent (irrespective of the type of air-
entraining agent used) to achieve a given air content. Organic impurities in the cement have been
known to originate from ingress of lubricant at the grinding plant and such contamination of the ~ -
cement by as little as 1 part of oil ifi 5,000 can double the air-entraining agent requirement of a
concrete mix (Fig. 1).
2,6 Effect of alkali
Both the alkali content of the cement and the alkali content of the air-entraining agent i tself
affect the efficiency of the air-entraining agent. The alkali content of the cement reduces the yield
of air-entraining agents for increasing concentrations of alkali (expressed as Na20) up to about
1.5 per cent iFig. 1); increases in alkali concentration above this value have no effect . The alkali
content of the air-entraining agent i tself acts in such a way that one part of Na0H to one part of
Vinsol resin in solution gives the most entrained air in concrete for a constant dosage of Vinsol
resin l l , and Greening 6 was able to attribute differences in air content of two concretes and two
mortars to small differences in the alkali content of two neutralised Vinsol resin solutions (Table 1).
Small changes in the alkali content of an air-entraining agent do not affect its yield when
high alkali cements are used.
TABLE I
Comparison of results with two different neutral ised Vinsol resin solutions
Na20 (per cent)
0.35
0.38
Per cent of air at equal amounts of neutralised
Vinsol resin
Concrete
5.5
7.4
Mortar
16.8
18.5
2.7 Effect of specific surface
The effect of the specific surface of cement on the yield of air-entraining agents has been
studied by grinding a single cement, with appropriate additions of gypsum, to different f inenesses .
Some of the resul ts of tes t s on a mortar and a concrete which were presented in tabular form in the
original paper 7 are given in Fig. 2. I t is clear from the regression lines of air content on specific
surface that the amounts of air entrained in both mortar and concrete are less when cement with a
high specif ic surface is used. The magnitude of this effect depends upon the type of air-entraining
agent used and can be such that the yield of an air-entraining agent is more than halved if the
specif ic surface of the cement is doubled from 2,500 to 5,000 cm2/g (Blaine).
2.8 Effect of temperature
The temperature of the mixed materials can have a marked and complex influence on the
eff iciency of air-entraining agents7,11,14. Although foaming (air-entraining) agents are usually
more effect ive in warm water than in cold and a given wieght of air occupies a greater volume at
high temperatures, these effects are more than offset by the greater loss of entrained air from the
concrete at the higher temperature and by the increase in chemical activity of the cement which
decreases the water available for the foaming process. Higher temperatures thus cause a reduction
in the amount of air entrained in the concrete for a given dosage of •admixture and Fig. 3 shows
that this decrease in air content with increase in temperature is the same for various types and
dosages of air-entraining agent. The size of this effect is such that the air-entraining agent
requirement at 20°C is about 30 per cent greater than that at 10°C.
2.9 Effect of concrete workability
A workable mix is able to hold more entrained air than a dry mix 15 but if the concrete is very
wet (slump greater than 200 ram) it is possible that the air may be mixed out of the concrete before
it is placed.
2.10 Effect of transporting concrete
Recent experience on road-construction si tes in the U.K. has clearly demonstrated that the
air contents measured in concrete are affected by the treatment received by the concrete before it
is sampled. If sampling is carried out at the mixer, where it is convenient to measure air content
for the purpose of controlling the mix, then the measured quantity of entrained air can be significantly
higher than if it is carried out after it has been transported to the paver (Fig. 4). Not surprisingly,
it has been argued 16 that measurements of air content should be made on concrete which has received
typical job treatment in handling and in the amount of vibration it rece ives , and that whenever
practicable, the sample of concrete should be taken from the forms after vibration.
3. EFFECT OF ENTRAINED AIR ON CONCRETE STRENGTHS
The flexural strength of concrete is affected less than the compressive strength by a given amount
of entrained air 17, 18, the percentage changes in flexural strength being somewhat smaller than those
in compressive strength. This is i l lustrated by the typical data 18 given in Table 2 for two maximum
sizes of aggregate and three cement contents. In most instances the loss of concrete strength with
increasing air content is not linear, the strength loss for each one percent of entrained air increasing
with the amount of air entrained; however, no satisfactory explanation of this effect is given in the reference.
TABLE 2
Effect of entrained air on the strengths of medium-workability concretes
Cement Maximum content aggregate (kg/m3) size (mm)
225 38 19
310 38 19
390 38 19
Change in Flexural strength -- per cent
Air content
3% I 4%
- 3 . 0 - 4.8 + 4.5 + 4.4
-12 .0 - 8.1
-10 .5 - 5.7
-16 .0 -10 .4
-14 .8 - 8.4
5% 6%
- 8.5 -12 .6 + 2.0 0
-20 .0 -13 .0
-11 .0
-24 .0 -16 .2
-14 .4
Change in Compressive Strength- - per cent
Air content
[
- 1 . 2 - 7 . 2 - 1 6 . 0
• + 6 . 6 i + 6 . 8 + 5 . 0
-15 .9 -10 .8
222.0 -29 .0 -15 .2 -19 .0
-12 .3 -20 .0 -
- 9 . 9 - 1 5 . 6 -21 .0
6%
-24 .6 0
-36 ,0 "23 .4
-27 .0
The loss of concrete strength resulting from air-entrainment becomes smaller as the maximum size
of aggregate is decreased and this effect is attributed to the larger reduction in water requirement
for concretes made with the smaller size of aggregate. Strength losses due to entrained air are also
less marked in the leaner mixes (less than about 235 kg/m 3 of cement) 18, 19, and for some lean
mixes a significant increase in strength is obtained when the water content of the mix is reduced
to counteract the effect of entrained air on concrete workability 20.
5
t
A similar study 21 of the relations between strength and air content for eight different Portland
cements using concretes with nominal air and cement contents of 4, per cent and 330 kg/m 3 respec- tively showed that even for given air and cement contents the percentage of strength loss is not
constant but depends upon the source of cement. It has also been shown I0 that for given air
and cement contents the percentage loss in strength depends upon the actual air-entraining agent
used. Shacklock and Keene 9'2 have studied the effect of entrained air upon the flexural and com-
pressive strengths of concrete for materials used in this country. In general their findings agree
with published American data described above.
4. POSSIBLE ADDITIONS TO SPECIFICATIONS FOR AIR-ENTRAINED CONCRETES
4.1 General
From the foregoing discussion it is clear that the process of entraining air in concrete is
complex ancl is affected by many factors. Some of these, such as aggregate grading, either have
relat ively lit t le influence or, as with sancl and cement contents, are unlikely to vary much in any
given job. In any event, these particular factors can be controlled on site so the extent to which
variations in them affect air-entraining agent efficiency may, for all practical purposes, be ignored.
In contrast, the factors which have considerable influence on the efficiency of air-entraining agents
and which may vary considerably on site are :-
alkali content of cement
specific surface of cement organic impurities in cement and
concrete temperature.
Ways of limiting the influence of these factors are now considered.
4.2 Alkali content of cement
If variations in alkali content of the cement are to have no influence on the efficiency of air-
entraining agents, it will be necessary to specify a minimum alkali content of about 1.5 per cent
(Fig. 1). However not only would this be outside the normal range (0.4 to 1.3) of alkali contents
for ordinary Portland cements but it would inhibit the desired increase in concrete strength after
28 clays 93 and could, in certain circumstances, leacl to alkali-aggregate reaction.
The air-entraining agent requirement of a concrete can vary by up to about 100 per cent
depending upon the alkali level of the cement so it is clearly desirable for the alkali content of
each cement delivery to si te to be stated by the supplier. It should then be possible to predict
any changes in air-entraining agent dosage that are required to accommodate changes in the alkali
level of the cement.
4.3 Specific surface of cement
The information given in this Report on the effect of specific surface on air-entraining agent
efficiency suggests that a change in specific surface from 2 500 to 3 000 cm2/g can increase the
admixture requirement by up to 25 per cent. As it is possible that this order of variation in specific
6
surface can occur between batches of cement from the same works it is apparent that even greater
variations may be expected on sites where cement is received from two or more sources.
In order to control this source of variation it might be necessary to specify not only that the
cement should conform to B.S. 12 : 1958 (minimum specific surface of 2,250 cm2//g) but that an
upper limit to this specific surface should also be called for. Alternatively, and perhaps preferably,
cement supplied from a given source could be required to have specific surface values within a
limited range (+ 150 cm2//g, say). In these circumstances it may be an advantage on large construction
sites, where cement is obtained from more than one source, to use separate si los and mixers for
cements from different sources.
This type of system for separating the cements supplied from different sources would also help
when the alkali contents of the cements are appreciably different, and could, incidentally, reduce
the variability of the concrete production attributable to differences in the cements, particularly if
the mix proportions are suited to each particular cement.
4.4 Organic impurities in cement
It would appear from the data already considered that changes in the level of organic impurities
in the cement could give rise to the greatest changes in air-entraining agent requirement. Fortunately,
organic impurities are not likely to get into the cement in the normal course of production, so there
is little point in attempting to detect them, particularly as the normal methods of doing so are tedious
and can require extreme care. It is not envisaged, therefore, that the organic content of cements
would be measured as a routine site operation, but rather to cheek that organic impurities are not
getting into the cement (from whatever source) if large and inexplicable changes in air-entraining
agent efficiency should occur.
4.5 Effect of concrete temperature
Concrete temperature has a marked influence on the yield of air-entraining agents, reducing
their effectiveness by about 30 per cent as temperature increases from 10 ° to 20°C. However,
any changes in the temperature of the mix would normally occur slowly and therefore produce
quite small, and barely detectable, changes in the air content of concrete as discharged from the
mixer over a period of hours. It is thus quite easy to counter the effect of such changes in concrete
temperature by making small adjustments in air-entrainlng agent dosage from time-to-time during
the course of the concrete production.
4.6 Effect of entTained air on strength
The percentage change in concrete strength produced by a given amount of air depends upon
the maximum size of aggregate and the cement content of the concrete (Table 2). However, in any
given job only one maximum size of aggregate is normally used and the cement content is unlikely
to be varied significantly once the mix proportions have been established in trial mixes. The change
in concrete strength for a given amount of air should therefore remain sensibly constant in any one
construction job.
5. SUHHARYOF EXISTING KNOWLEDGE
For a given dosage of air-entraining agent, the amount of air entrained in concrete is increased by increasing:-
sand content
alkali content of cement up to 1.5 per cent (expressed as Na20 ) concrete workability;
is decreased by increasing:-
cement content
specific surface of cement
organic impurities concrete temperature
handling and vibration;
and is not appreciably affected by changes in sand grading.
The percentage loss in concrete strength for each one per cent of entrained air is greatest for:-
high air contents
high cement contents
large maximum sizes of aggregate.
Air-entrainment produces smaller changes in the flexural strength of concrete than in the compressive strength.
8
PART 2: A STUDY OF THE WORKABILITY OF AIR-ENTRAINED CONCRETES
6. SCOPE OF WORK
The present investigation was made to examine the effect of entrained air on the workability of
concrete for a range of concretes in order to obtain basic mix-design data, and to measure the
change in workability likely to arise on construction s i tes from changes in entrained-air con'tent of
the concrete within the limits of 3 - 6 per cent of entrained air permitted by the Ministry of
Transport 's 'Specification for Road and Bridge works'.
The opportunity was also taken to gain experience of the Vebe tes t which has been introduced
recently in the revised edition B.S. 1881 'Methods of Tes t ing Concrete ' as a method of measuring
concrete workability. Data relating the Compacting Factor to the Vebe value have, therefore, been
obtained for concretes with and without entrained air. Because it was found that the relat ions
between these two measures of concrete workability depended upon the aggregate used in the con-
crete, additional studies were made with plain concretes using aggregates widely different in shape
and surface texture.
7. MATERIALS AND MIX DESIGN
Three different coarse aggregates of 19 mm nominal maximum size were used. These were a rounded
quartzite gravel from Branston, Staffs., an irregular flint gravel from Chertsey, Surrey, and an
angular crushed granite from Charuwood, Leics .
The rounded and irregular aggregates were used with their own fine aggregates reconsti tuted
from single s izes of sand to give gradings approximately in the middle of Zones 2, 3, and 4 (Fig. 5).
The crushed-granite aggregate was used with its fines reconst i tuted either to produce a Zone 2
grading of the material as supplied from the quarry (Fig. 5 - Curve A) or to have a Zone 1 grading
fairly typical of many that are produced by the crushed-rock industry24 (Fig. 5 - Curve B); it was
al-~o used with the rounded quartzite sand reconstituted to give a Zone 2 grading.
The concrete mixes were designed, where appropriate, to Road Note No. 425 for the level of
workability required. When Zone 3 and Zone 4 sands were used the proportions of the coarse aggre-
gate were obtained by extrapolation of data from Road Note No. 4. The proportions of coarse and
fine aggregate used in these experiments are given in Table 3.
TABLE 3
Percentages of aggregate used with various gradings of fine aggregate
Aggregate size
19 - 9.5 mm 9.5 - 4.8 mm Fines
35 45 55 65 70
23 20 15 10 10
42 35 30 25 20
Fines Zones
1 2 and 4 2 and 3 3 and 4
4
The effect of entrained air on concrete workability was studied for concretes with the combina-
tions of fine-aggregate grading and aggregate shape given in Table 4. Each concrete was used with
four levels of entrained air in the range 0 - 9 per cent and up to four aggregate/cement ratios in the
range 3.2 - 9.5. A free-water/cement ratio of 0.45 was used throughout unless otherwise indicated.
Neutralised Vinsol resin was used to entrain air in the plain concretes as designed. When
air-entraining agents were not used, the air-meter indicated that about 1 per cent of air was entrapped
within the concrete.
TABLE 4
Combinations of fine-aggregate grading and aggregate shape used at a free-water/cement ratio of 0,45
Fines
Zone
1
2
3
4
Percentage of fine aggregate
25 30 35
I
I R
AI* R
I
42
A
A = angular aggregate I = irregular aggregate R = rounded aggregate * = free-water/cement ratios of 0.40, 0.45, 0.50, 0.55
8. EXPERIHENTAL HETHOD
Coarse and fine aggregates were soaked separately for approximately 24 hours in order to obtain a
nominally complete state of absorption before mixing,'thereby preventing workability measurements
from being time-dependent as is the case when oven-dry aggregates are used. Air-entraining agent,
when required, was dispensed in about 10 per cent of the total mix water at the start of the mixing
process.
Concrete workability was measured by the Compacting Factor test and by the Vebe test as
described in B.S. 1881. Essent ia l ly the Vebe test consists of forming a slump cone within a
cylinder on a table and measuring the time in seconds required to remould the slump cone to the
shape of the cylinder when a given load is applied to the top bf the slumped concrete and the table
is subjected to precisely defined vibrations (Plates 1 to 4).
In general the degree of compaction at the end of the Vebe test is greater than that of the j
concrete in the slump cone, and so a distincti'6ii is made between the work done in remoulding the
concrete and that done in compacting it Bahrner 26 used a correction of the form:-
10
V1 Vebe degrees =
V2 x Vebe seconds
where V 1 = remoulded volume and V 2 = volume of concrete before vibration (assumed to be equal to the volume of the slump cone).
However, it is generally held 27, 28, 29 that this correction is unnecessary for the range of workabili-
t ies encountered in normal practice and it is not given in the Vebe tes t in B.S. 1881 : 1970; all
Vebe values given in this Report will therefore be Vebe seconds.
Some difficulty was experienced in measuring accurately Vebe values for very workable con-
cretes (Vebe values less than 2 seconds) so data obtained on concretes with Vebe values less than
this are not given. The end-point of tests on concretes of very low workability (greater than 50
seconds Vebe value) was difficult to judge precisely, and estimation of the end-point could vary by
up to _+5 seconds for different operators, but this apparently large difference appears reasonable when
considered as a proportion of the measured Vebe value. In the Compacting Factor tes t some rich
concretes had a tendency to stick in the hoppers, particularly when concretes were made with angular
aggregates which had a considerable percentage of fines passing a sieve of 150 gm aperture; on
these occasions the concrete was rodded through the hoppers .
The air content of each mix was measured by the pressure method 20 and compaction of the
concrete was achieved in a standard manner by using a vibrating table. With the very workable
concretes, measured air contents could possibly be slightly low because of the tendency to vibrate
some entrained air out of the concrete even with relatively short periods of vibration. With the
concretes of very low workability measured air contents would tend to be high because of the
difficulty in vibrating out the entrapped air; on the other hand, the high internal friction of such
concretes could possibly prevent effective pressure transmission to all the entrained and entrapped
air bubbles so that a low estimate of the air content could possibly be obtained. Because of the
difficulty of compacting fully the less workable concretes, even with long periods of vibration, the
weight of the concrete compacted in a Compacting Factor receiving cylinder could be low thereby
giving an enhanced Compacting Factor value. In this type of situation the measured compacted
weight was compared with the theoretical compacted weight calculated from the mix proportions and
specific gravities of the mix constituents (Fig. 6) and when any appreciable discrepancy occurred
the theoretical compacted weight was used to give an estimate of the measured weight at full
compaction.
9. RESULTS AND DISCUSSION
Altogether about 150 measurements of Compacting Factor and Vebe value were made. From these
it was clear that the relation between the amount of air entrained in the concrete and the change
in concrete workability was not greatly affected by the range of materials or mix proportions used
(Figs. 7 and 8), although there was a tendency for concretes of high water/cement ratio and those
made with angular aggregates to exhibit a greater change in Compacting Factor for the addition of
a given amount of entrained air; this trend was less noticeable for workabilities measured by the
Vebe test.
II
To a first approximation, the addition of 4~ per cent entrained air to a plain concrete increases
the Compacting Factor by about 0.06, and reduces the Vebe value by about two-thirds. It should be
noted, however, that a given change in the amount of air at low air contents produces a greater change
in workability than a similar change in the amount of air at high air contents. If the amount of
entrained air in a concrete production should vary from 3 to 6 per cent, as permitted by the Ministry
of Transport Specification for pavement-quality concrete, then the Compacting Factor will increase
by about 0.03, which is one half of the variation in Compacting Factor allowed by that specification.
The change in Vebe value (seconds) due to a comparable change in entrained air varies with the
workability of the concrete, but is such that the Vebe value for concretewith 3 per cent of entrained
air is about twice the Vebe value for the same concrete with 6 per cent of entrained air for any level
of concrete workability. Thus if limits are to be placed on workability, as measured by the Vebe
value, in any construction job it would appear more appropriate that they should be related to the
specified Vebe value by a geometric rather than an arithmetic progression.
The relative sensitivity of these tests to concretes of low workability is indicated by the
spacing of the curves in Figs. 7 and 8. The Vebe test shows much greater discrimination than the
Compacting Factor test between the two concretes represented by the circular symbols, and would
therefore appear preferable in assessing the behaviour of low-workability concretes under vibration.
The relations between workability and aggregate/cement ratio for concretes with no entrained
air and for concretes with 4~ per cent air are given in Figs. 9 and 10 for the Compacting Factor and
Vebe tests respectively. It can be seen that the addition of a given amount of air permits larger
increases in aggregate/cement ratio (for constant Compacting Factor) for concretes made with the
more rounded aggregates than for concretes made with angular aggregates. Conversely if a given
amount of air is added tO a concrete and no change in the aggregate/cement ratio is made then the
change in Compacting Factor is less for concretes made with the more rounded aggregates and
greater for concrete made with angular aggregate; this confirms the suggestion that this effect
exists30. These experiments do not support other data 20 which suggest that the change in Compact-
ing Factor due to a given amount of entrained air is influenced by the cement content of the concrete.
The effect of aggregate on the relation between the logarithm of the Vebe value and the aggregate/
cement ratio at different air contents is similar.
From the experimental data the relations between workability and water/cement ratio for con-
crete with no entrained air and concrete having 4~ per cent air are given in Fig. 11. With the
irregular aggregate used the addition of entrained air tends to produce a smaller change in work-
ability for the drier, less workable mixes (water/cement ratio less than 0.45) but produces about
the same change in workability for mixes with higher water/cement ratios; this is in broad agreement
with the findings of Wright 20.
10. COMPARISON OF COMPACTING FACTORS .AND VEBE VALUES
The Compacting Factor and Vebe values obtained in this study are plotted against each other in
Fig. 12 for concretes without entrained air and for those with more than 3 per cent air. Despite
the considerable scatter of the data, there appear to be separate Compacting Factor/Vebe relations
for concretes with and without entrained air although this type of effect has not been reported in
American studies31 on the relations between different methods of measuring concrete workability.
12
It would appear that the change in 'grading' associated with the inclusion of air bubbles in the
mortar phase is sufficient to change the relation between these two measures of workability.
The curves for plain and air-entrained concretes made with gravel aggregate and natural sand
intersect at a Compacting Factor of about 0.84. Thus for pavement-quality concretes an air-entrained
concrete would be judged to be equally workable by both Compacting Factor and Vebe measurements.
For concretes of higher workability, an air-entrained concrete would appear more workable when
judged by the Vebe test than would the concrete without entrained air, even though they may have
the same Compacting Factor.
There appears to be an anomaly in the way in which the Compacting Factor/Vebe relation is
affected by the addition of entrained air. For concretes made with the gravel aggregates the
relations" for plain and air-entrained concretes intersectwhereas those of concretes made with the
crushed-rock aggregates do not, and for a given Vebe value the air-entrained concretes always have
a lower Compacting Factor.
The effect of aggregate on the Compacting Factor/Vebe relation is considerable although this
was not noted by Hughes 29 when he obtained data on the relation between Compacting Factor and
Vebe value for concretes made from a range of aggregates. The curves in Fig. 12 for the different
aggregates "are such that the Compacting Factor test discriminates against concretes made from'
crushed materials at Compacting Factor values below about 0.88, i.e. concretes made from crushed
materials would be judged to be insufficiently workable by the Compacting Factor test in comparison
with concretes made from uncrushed materials even though they may have the same Vebe value.
However, as the vibration experienced by concrete in the Vebe test is more akin to that used to
compact concrete against formwork than the single jolt experienced by the concrete in the Com-
pacting Factor test, the Vebe test may be considered to give a more realistic assessment of concrete
workability, especially with dry mixes27, 31. Thus concretes made from crushed materials which
would be judged to be of low workability by the Compacting Factor test might not be so in practice.
In view of the results obtained in this study it was decided to investigate further the role of
the aggregates in producing the observed changes in the Compacting Factor/Vebe relation.
I I . EFFECT OF AGGREGATE PROPERTIES ON WORKABILITY MEASUREMENTS
For these experiments a crushed gritstone from Ingleton, Yorkshire, a crushed flint-gravel from
Long'field, Kent, and an irregular, uncrushed, flint-gravel from Chertsey, Surrey, were used. Most
of the work was done with the fine aggregates having a Zone 1 grading as this was the natural
grading of the materials from Ingleton and Longfield. A free-water/cement ratio of 0.50 was used
throughout these experiments and the workability of the concretes was varied by changing the
aggregate/cement ratio only; none of the concretes was air-entrained. Details of the materials
and the mix proportions are given in Table 5.
The relations between the Compacting Factors and the Vebe values for concretes made from
these materials are shown in Fig. 13. The effect of aggregate on these workability relations
confirms the data already presented and gives more information on the factors causing changes
in these relations. 13
W . J
I--
0
0
0
e~
N
e~
N
°,,~
0
~0
-=
0
O0
I
Ox
Ox
O0 CO O0 t~ l CO
0 0 0 ~0 0
C"x~ cq cq
~I I p , I p , I ~'b ~ i I
I~ I:I I:I I=I I= 0 0 0 0 0
l'q l'q N l~ DQ
~ ~ ~ ,
14
Changes in the surface texture of the aggregate from rough to smooth for crushed aggregates
with similar gradings and shapes, change the Compacting Factor/Vebe relation from the position of
Curve A to that of Curve B. Likewise, changing the shape of the aggregate from one that is flaky
and elongated to one which is irregular produces a shift in the Compacting Faetor/Vebe relation
from the position of Curve B to that of Curve C for aggregates with smooth surfaces. Clearly, the
shift attributable to changes in the surface texture of the aggregate may not necessarily be the same
for rounded aggregate as for the crushed aggregates used here, neither will the shift due to changes
in aggregate shape necessarily be the same for aggregates with rough surfaces as for those with
smooth surfaces used here. Nevertheless the data do give some idea of the change in Compacting
• Factor/Vebe relation attributable to changes in the surface texture and the shape of the aggregates.
If the coarse aggregate used to produce Curve A is combined with the fine aggregate used to
produce Curve C, then Curve E is obtained i.e. changing the coarse aggregate shifts Curve C hardly
at all. In contrast, replacing a natural, uncrushed, flint sand of irregular shape by crushed-rock
fines of the same nominal grading accounts for nearly the whole range of movement of the Compacting
Factor/Vebe relation (i.e. from position E to position A) observed in these experiments. This
result is not altogether surprising as, although the fine aggregate comprised less than half the total
aggregate used in the concrete, its specific surface was about 15 to 20 times as great as that of
the coarse aggregate; it is therefore to be expected that the fine aggregate exerts a controlling
influence on the relation between these two measures of workability.
Finally, the effect of aggregate grading on Compacting Factor/Vebe relation was examined
using the uncrushed, irregularly shaped, flint gravel. The different gradings used (Table 4) produced
a slight change in the workability relation (Curves. C and D in Fig. 13). This is mainly due to the
greater sensitivity of the Vebe test to changes in the grading of the aggregate, as it can be seen
from Figs. 14 and 15 that changing the grading produced less change in Compacting Factor for a
given aggregate/cement ratio than the marked change in Vebe value for a given aggregate/cement
ratio. It is also clear that for concretes of low or very low workability (Compacting Factor less
than 0.85), the Vebe test has the greater sensitivity to changes in the surface texture and shape
of the aggregate.
This study has shown that the Compacting Factor and Vebe tests give different impressions
of the workability of the concrete; the question is, which is the more suitable test?
The Compacting Factor test is extremely simple and does not require electric power to be
available; it is therfore very suitable for use on construction sites. On the other hand, the Vebe
test is more sensitive to changes in the surface texture, shape, and grading of the aggregate,
particularly for concretes of low or very low workability, but it requires a power supply to drive
its vibrating table. It would therefore seem that the Compacting Factor test is more suitable as a control test on construction sites whereas the Vebe test appears superior as an aid to designing
concrete mixes because it gives a more realistic assessment of the behaviour of the concrete to be
expected under the vibration used to compact it against the forms.
12. CONCLUSIONS
. The increase in Compacting Factor and the percentage increase in Vebe value produced by the
addition of a given amount of entrained air to a concrete is not affected greatly by either the 15
aggregate properties or the mix proportions of the concrete. There is, however, a tendency for
concretes made with the more rounded aggregates or lower water/cement ratios to exhibit
smaUer increases in workability for the addition of a given amount of entrained air.
2. To a first approximation, a change from 3 to 6 per cent in the amount of entrained air in a
concrete production increases the Compacting Factor by about 0.03 and halves the Vebe value
at all levels of worl~ability.
. The relation between Compacting Factor and Vebe value is most sensit ive to changes in the
surface texture of the fine aggregate. It is also affected by the shape and grading of aggregate
and by entrained air.
4. V'ebe value ismore sensit ive than Compacting Factor to changes in aggregate properties.
. The Vebe test is preferred for purposes of mix design and predicting the behaviour of concretes,
especial ly dry concretes, under vibration; but the Compacting Factor test is simpler to use
as a control tes t on site.
. When the workability of a concrete is specified as a Vebe value, it is more appropriate to choose
the upper and lower limits so that they form a geometric progression with the specified value
than that the specified value should be mid-way between them.
13. ACKNOWLEDGEMENTS
This Report was produced in the Materials Section of the Construction Division (Section Leader:
G. F. Salt). The experimental work was carried out by C. Corumluoglu and D. R. Hanger.
14. REFERENCES
. POWERS, T. C. Void sPacing as a basis fo r producing air-entrained concrete. J n l . Amer. .... "
Conc. Inst. 1954. 25 (9), 741-60.
2. POWERS, T. C. RILEM Bull. English Ed. 1958. 43/44, 97-9.
3. BRUERE, G.M. The relative importance of various physical and chemical factors on bubble
characterist ics in cement pastes . Aust. Jnl. App. Sc. 1961. 12 (1) 78-86.
4. TORRANS, P. H. and D. L. IVEY. Air void systems affected by chemical admixtures and
mixing methods. Highw. Res. Rec. No 226. Concrete admixtures, aggregates and durability.
47th Ann. Mtg. 1968.
. KLIEGER, P. Further studies on the effect of entrained air on strength and durability of
concrete with various s izes of aggregates. Highw. Res. Bd. Bul. 1956. 128, 1-19.
6. GREENING, N. R. Some causes for variation in required amount of air-entraining agent in
Portland cement mortars. Jnl. P.C.A Research and Devpt. Labs. 1967. 9 (2) 22-36.
16
.
.
.
10.
11.
12.
13.
14.
SCRIPTURE, E. W. BENEDICT, S. W. and LITWINOWICZ, F . J . 'Effect of temperature and
surface area of the cement on air entrainment.' Jnl. Amer. Caner. Inst. 1951. 23 (3) 205-10.
KENNEDY, H. L. The function of entrained air in Portland cement. Jnl. Amer. Coner. Inst. 1944. 15 (6) 515-7.
SCRIPTURE, E. W., HORNIBROOK, F. B. and BRYANT, D. E. Influence of size grading of sand on air entrainment. Jnl. Amer. Concr. Inst. 1948. 20 (3) 217-28.
CRAVEN, M. A. Sand grading influence on air entrainment in concrete. Jnl. Amer. Cone. Inst. 1948. 20 (3) 205-15.
WALKER, S. and BLOEM, D. L. Studies of concrete containing entrained air. Jnl. Amer.
Cone. Inst. 1946. 17 (6) 629-39.
POWERS, T. C. Mixtures containing intentionally entrained air. Jnl. P.C.A. Res. and Devpt.
Labs. 1964. 6 (3)19-42.
SCRIP33_IRE, E. W. and LITWINOWICZ, F. J. Some factors affecting air entrainment. Jnl.
Amer. Cone. Inst. 1949. 20, (6) 433-42.
CORDON, W. A. Freezing and thawing of concrete: mechanisms and control. Amer. Cone.
Inst. Monograph No. 3. (Amer. Concr. Inst. and Iowa State University Press).
15. NEVILLE, A. M. Properties of concrete. London, 1963 (Pitman and Sons Ltd), p. 364.
16.
17.
18.
19.
20.
21.
TUTHILL, L. H. Entrained air loss in handling, placing and vibrating. Jnl. Amer. Caner.
Inst. 1948. 19 (6), 504.
GONNERMAN, H. F. Tests of concrete containing air-eutraining Portland cements or air-
entraining materials added to batch at mixer. Jnl. Amer. Cane. Inst. 1944. 15 p.477.
KLIEGER, P. Effect of entrained air on strength and durability of concretes made with various
maximum sizes of aggregates. Highw. Res. Bd. Proc. 1952. 31, 177-201.
BLANKS, R. F., and CORDON, W. A. Practices, experiences, and tests with air-entraining
agents in making durable concrete. Jnl. Amer. Cone. Inst. 1949. 20 (6) 469-87.
WRIGHT, P. J. F. Entrained air in concrete. Proc. Inst. Civ. Eng. 1953. 2 Pt. 1, Paper
5915. 337-58.
JACKSON, F. H. Age-strength relations for air-entrained concrete. Public Roads. 1952.
27 (2) 31-36.
17
22.
23.
24.
25.
26.
27.
28.
29.
30.
31.
SHACKLOCK, B. W. and KEENE, P. W. Comparison of the compressive and flexnral strengths
of concrete with and without entrained air. Civ. Engng. and Publ. Wks. Rev. 1959. 54 (631)
77-80.
NEVILLE, A.M. Role of cement in creep of mortar. Jnl. Amer. Conc. Inst. 1959. 30 963-84.
d
TEYCHENNE, D. C. A survey of crushed stone sands for concrete. ]ournal of the British
Granite and Whinstone Federation. 1967, 7 (1), 53-60.
ROAD RESEARCH LABORATORY. Road Note No. 4. Design of Concrete Mixes. London 1950 H.M.S.O.
BAHRNER, V. Report on consistency tests on concrete made by means of the V.B. consisto-
meter. Joint Research Group on Vibration of Concrete. (Swedish Cement Assn. Malm~).
CUSENS, A. R. The measurement of the workability of dry concrete mixes. Mag. Concr. Res.
1956. 8 (22), 23-30.
KEENE, P. W. A preliminary examination of the V.B. consistometer. C. & C. A. Tech. Rep.
TRA/343 London 1960. (Cement and Conc. Assn.).
HUGHES, B. P. and B. BAHRAMIAM. Workability of concrete: a comparison of existing tests.
Jnl. of Mtls. 1967. 2 (3), 519-36.
CORDON, W.A. Entrained air - A factor in the design of concrete mixes. Jnl. Amer. Concr.
Inst. 1946. 17 (6), 605-20.
KLIEGER, P. Recommended practice for selecting proportions for no-slump concrete. Jnl.
Amer. Concr. Inst. 1965. 37 (1), 1-18.
18
[]
Data from Ref 6
Z$ Clinker 5
I ' - I ,,
V
O ,
4
u
O_
O3
t--
U1 O~ l_
-6 I/1 ¢-
>
2
3
z~
5 % gypsum
cold grinding
Z$ n
V
0 .02% air
'~ i v
V V /. 3
/No air
V
0 0.5 1.0 . 1.5 2"0
Concentration of alkali ( as Na20 ) ( per cent by weight)
Fig. 1 EFFECT OF ALKALI CONCENTRATION ON VINSOL RESIN REQUIREMENT TO GIVE 19 PER CENT AIR IN MORTARS
MADE FROM CEMENTS, LABORATORY-GROUND wITH AND WITHOUT OIL
2.5
i_
0
C
E UJ
18
16
1/,
12
10
Data from Ref. ?
~ D
Mortar (ASTM test )
Concrete (Constant workabi l i ty)
L
2000
Fig.2
3 000 4 000 Specific surface (cm2/gm) (Blaine)
EFFECT OF SPECIFIC SURFACEON AIR CONTENT OFAMORTAR AND A CONCRETE EACH WITH CONSTANT DOSAGE OF AIR-ENTRAINING AGENT (A.EA.)
5000
160
0 o
0
w-
c~
L.. o--
<
I/.0
120
100
80
60
A O 0
Data from Ref.11
0"008 percent Vinso[ resin 0.020 percent Vinsol resin 26 '5ml Darex/sack
10 20 30 /.0 Concrete temperature (°C)
Fig.3 AIR CONTENrT OF CONCRETE AT VARIOUS TEMPERATURES AS A PERCENTAGE OF THAT AT 21"C FOR CONSTANT DOSAGE OF AIR-ENTRAINING AGENT
50
0 Q
m "-M
r ' n
--,4
"-rt C )
( . n
0
~ 3 ¢0
Z
z - -4 m Z
U1
Q
Air content
~ o X
ET
gO
3 o" '10 4
0 " 0
'-'1
3 = - "10 0
¢D "10
0
( daily overage )
0
per cent
C~
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I
"7 J
I~ (J') ~ ( , q < Q < D
~ 3 ~ 3
Q
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" \ :g z
,
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o .,~
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",~,' o
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U O Q .
E O U
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13"6
13"5
13"4
13"3
i3'2
13.1
/
(6.5) O
(6.0} 0 /
'15.51} '/ /
/
/ /
/ /
/
I ReLation for~ f uL[ y- compacted concrete. ~
/ /
/
Mix details I rregutar, uncrushed flint - grovel aggregate 48 per cent of Zone 1 sand. Aggregate/cement ratios given in parenthesis Free- water / cement ratio = 0.50
13"1
Fig. 6
13"2 13"3 13"4 13"5 13"6 Measured compacted weight (kg)
COMPARISON OF MEASURED ANO THEORETICAL COMPACTED WEIGHTS FOR CONCRETES MAOE WITH VARIOUS AfGREGATE/CEMENT RATIOS
13"7
L) I:;I
O~ i -
U O Q.
E O
0'96
0'92
0"88
0"84
0"80
0 .76
0 .72 " 0
Aggregate shape
Angular
I r regular
Rounded
Irregular
Irregular
Irregular Irregular
Ag0rego,e/ J Wo, er, I ,ne, cement cement content
rat io ratio (per cent)
3-2 0.45 35
6-3 0.45 35
9.5 0.45 35
4-6 0'40 35
8.9 0.55 35
8.5 0.45 30 6 '6 0.45 25
Fines zone
2 2
2
2
2
3 4
trapped
1 2 3 4 5 6 7 Total (entrapped + en t ra ined) air (per cent)
Fig. 7. EFFECT OF ENTRAINEO AIR ON THE COMPACTING FACTORS OF VARIOUS CONCRETES
100
80
60
40
3O
20 (n
o
~ 10 ..Q
8
Agg regate
I Angutar I Irregular I Rounded I Irregular I Irregular
I I r r~utar 1 Irregul.ar
Aggregate/ cement
rat io
3-2 6"3
9.5 4'6 8.9
8'5 6"6
Water/ Fines cement content
ratio (per cent)
0"45 35 0"45 35
0.45 35 0.40 35 0.55 35
0.45 30 0.45 25
/ /
Entrapped
/ /
0 1 2 3 4 5 6 Total (entrapped + entrained) air (per cent)
Fig. 8. EFFECT OF ENTRAINEO AIR ON VEBE VALUES OF VARIOUS CONCRETES
? 8
0"96
No entrained air
/,1/2 per cent air
A= Angular ] I : Irregu[ar I aggregate R = Rounded
Free-water/cement ratio : 0'45
Fine aggrega te : - 35 percent Zone 2 grading
(,3
¢-
( 3 .
E 0
(..3
0 92
0'88
0"84
080
0"76
0"72
A
.I
I l l l l
l \
'A
3 Z, 5 6 ? 8 9" Aggregate/cement ratio
Fig9 EFFECT OF AGGREGATE/CEMENT RATIO ON COHPACTING FACTOR FOR COHCRETES MADE WITH VARIOUS SHAPES OF AGGREGATE FOR NO ENTRAINED AIR
AND l, V2 PER CENT AIR(DERIVED DATA)
10
(.,1 U~ 03 O
CO
OJ
100
80
60
40
30
20
10
8
6
No entrained air
41/2 per cent air
A = Angular I = Irregular R = Rounded
aggregate
Free-water/cement ratio = 0"45
Fine aggregate : - 35 percent Zone 2 grading
~A
A /
/ /
I I
/ /
R
// t l
r l /
/
4/ ,/
l / / I / / ,"'
/,,r / / II
II
II l I/ I
3 4 5 6 ? 8
Aggregate/cement rat io
Fig.lO EFFECT OF AGGREGATE/CEMENT RATIO ON VEBE VALUES FOR CONCRETES WITH VARIOUS SHAPES OF AGGREGATE FOR NO ENTRAINED
AIR AND 1,1/2 PER CENT AIR (OERIVEO OATA)
MADE
10
U ~
c~N
O l ~ " "
. _ u 0
L- e -
O
I I I
.L. "~
r -
Z ",.t
. /
/ /
J
/ . /
/ /
/ '
/
/
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alOeS 6Ol (s) aqaA
\ \
\ \,\
0
O
0 0
E
0
-4" ~
w
w ~
r¢~ i,=m
W Q , .
W
0
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c~..o
E
E u
. !
0 "4"
6
&.m.l
w
.m
O~ aO aO aO r'- • . . . . .
Jo~o~ 6u!~ooduJoo
100
80
60
z,O
30
20
~ 10 O u
8
~ 6
0.72
Fig.12
0.76 0.80 0.8/, " 0.88 G92 G96 Compacting factor
RELATIONS BETWEEN COMPACTING FACTOR AND VEBE VALUE FOR CONCRETES MADE WITH ANO WITHOUT ENTRAINED AIR FOR DIFFERENT TYPES OF AGGREGATE -
0 U
. 0
200
100
80
60
~.0
30
20
10
8
6
4
3
A
E :
o I
1.6/,
Symbot Description of aggregate Fines zone
[]
Angular, rough texture
Angutar, smooth texture Irregular, smooth texture
Irregular, smooth texture Coarse:as • Fine :as n
Free-water/cement ratio = O. 50
% ' [ ]
0.88 O. 92 O- 96 0.76 0.80 0.8&
Compacting factor
0.72 0.68
Fig. 13 EFFECT OF AG6REGATE PROPERTIES .ON RELATION BETWEEN COMPACTING FACTOR AND VEBE VALUE
u O
O3 t -
O -
E O
(J
0.96
0.92
0.88
0.8/*
0.80
0.76
0-72
0.68
0.64
Symbol Description of aggregate Fines zone
• Angular, rough texture 1 A Angular, smooth texture 1 D Irregular.smooth texture 1 [] Irregular, smooth texture 3
[a~ [] Coarse as • " 1 Fine : as []
l i '~ ~ Free-water/cement ra t io=0.50
' ) .
3 4 5 6 ? 8 9 Aggregate/ cement ratio
Fig. 1/, EFFECT OF AGGREGATE / CEMENT RATIO ON COMPACTING FACTOR FOR CONCRETES MAI]E WITH VARIOUS AGGREGATES.
10
0 u u~
o.
OJ .a
>
200
100
80
,60
/.0
30
20
10
8
6
3
Symbot
A rl
[]
Description of aggregate Fines zone
Angutar, rough texture Angutar, smooth texture Irregutar, smooth texture Irregutar, smooth texture Coarse:as • Fine: as A
1 1 1 3 1
Free-water / cement-ratio = 0.50
/
Fig.15
j ,,. l/:/ . / I,. ' 1 . 1 ~ /
/ , ;/j/ //7' ' ;
i I
A 5 6 ? 8
Aggregate / cement ratio
EFFECT OF AGGREGATE /CEHEII.T RATIO OH VEOE VALUE FOR CONCRETES NAOE WITH VARIOUS ~,G'GREGATES.
/
10
e ,
, 7 : . ¸
PLATE 1 General view of Vebe apparatus
Neg No B2013/69
S
PLATE 2 Neg No H2908/69
Concrete ready for workability measurement in Vebe apparatus
I
PLATE3
End of Vebe test
Neg No H2909/69
.g
.Q O
"6
c O
"6
.o u
0 u
0 u c
@
~D
0 Z
(1549) Dd635272 3,500 10170 H.P. Ltd. G1915 P R I N T E D IN E N G L A N D
ABSTRACT
Air-entrained concretes: a survey of factors affecting air content and a study of concrete workability: D . F . CORNELIUS, B.Sc.: Ministry of Transport, RRL Report LR 363: Crowthorne, 1970 (Road Research Laboratory). Air-entrained concretes are used exten- sively in modern road construction as they are able t o resis t damage by frost and by the use of de-icing salts. Variations in the amount of entrained air lead to changes in con- crete workability and to loss o f concrete strength or durability depending upon whether there is an excess of deficiency of entrained air. The first part of the Report gives the results of a survey of the literature which was made in order to identify the factors affect- ing the yield of entrained air from a given amount of admixture; suggest ions are made for limiting the influence of the more important factors on s i t e . The effect of entrained air on concrete strength is also described.
The second part of the Report describes a study of the effect of entrained air on the workability of various concretes as judged by the Compacting Factor test and the Vebe test which has recently become a British Standard test. These workability s tudies showed that the relation between Compacting Factor and Vebe value depends markedly upon the aggregate used in the concrete. Additional data are therefore presented to show the dependence of the relations between these workability measurements on the shape and surface texture of the aggregates.
ABSTRACT
Air-entrained concretes: a survey of factors affecting air content and a study of concrete workability: D. F . CORNELIUS, B.Sc.: Ministry of Transport, RRL Report LR 363: Crowthorne, 1970 (Road Research Laboratory). Air-entrained concretes are used exten- sively in modern road construction as they are able to. resis t damage by frost and by the use of de-icing salts. Variations in the amount of entrained air lead to changes in con- crete workability and to loss 'of concrete strength or durability depending upon whether there is an excess of deficiency of entrained air. The first part of the Report gives the results of a survey of the literature which was made in order to identify the factors affect- ing the yield of entrained air from a given amount of admixture; suggest ions are made for limiting the influence of the more important factors on site. The effect of entrained air on concrete strength is also described.
• The second part of the Report describes a study of the effect of entrained air on the workability of various concretes as judged by the Compacting Factor test and the Vebe test which has recently become a British Standard test. These workability s tudies showed that the relation between Compacting Factor and Vebe value depends markedly upon the aggregate used in the concrete. Additional data are therefore presented to show the dependence of the relations between these workability measurements on the shape and surface texture of the aggregates.
