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Technical Note (National Research Council of Canada. Division of Building Research), 1963-10-01
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Comments on Moisture Content of Concrete Masonry Units
Plewes, W. G.
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NRC Publications Record / Notice d'Archives des publications de CNRC:
https://nrc-publications.canada.ca/eng/view/object/?id=5dcf60f3-fa0f-43a2-b2da-b6da28e9e810 https://publications-cnrc.canada.ca/fra/voir/objet/?id=5dcf60f3-fa0f-43a2-b2da-b6da28e9e810
DIVISION OF BUILDING RESEARCH
NATIONAL RESEARCH COUNCIL OF CANADA
'f
EClHIN II CAlL
NOTlE
No.
406
PREPARED BY W.G. Plewes CHECKED BY WRS APPROVED BY NBH
DATE October
1963
PREPARED FOR National Concrete Products Association
SUBJECT ｃｏｾｾｅｎｔｓ ON MOISTURE CONTENT OF CONCRETE ｉｾｓｏｎｒｙ UNITS
The eighth draft of the CSA Standard for Hollow Load
Bearing Concrete Masonry Vnits (CSA A
165.1)
contains thefollowing Table which applies to "moisture controlled units" Types SH, PH and MH.
(Table
3
of Eighth Draft of CSA A165.1)
MOISTURE CONTENT REQUIREMENTS
FOR MOISTURE CONTROLLED UNITS
(Types
SH, PH
and ｾｬｬｩＩLinear Shrinkage Maximum Moisture Content, Per cent of
Total Absorption (Ave. of
5
Units)per cent ｾ... Average Annual Mean Relat1ve HUm1d1.ty,%
Over '{J "('j to 50 Under JO
Up to
0.03
40
40
35
0.03
to0.045
40
35
30
Over
0.045
35
50
25
The table specifies moisture content at time of
delivery as a percentage of total absorption for concrete units. Three categories of units are given according to their total linear shrinkage as determined by ASTM C426; the greater the
shrinkage the lower the specified moisture content. The specified
moisture contents also vary according to the average annual mean relative humidity at the site and for lower relative humidities
the specified moisture contents are lower. The purpose of these
requirements is to ensure at least some degree of drying of units before they are used in a structure and to make some allowance for the variable shrinkage properties of different units and the average humidity of the locality in which they are used.
It was suggested by one reviewer that the specified
moisture content values are too high. He pointed out that in
the Winnipeg area, although the winter outdoor relative humidity is high, the absolute moisture content of the air is low because
of the cold temperature. Under these circumstances the relative
humidities in heated buildings in Winnipeg can be very low, leading to nearly maximum shrinkages of concrete blocks.
'This point was well taken and it relates to a situation of which the Division of Building Research is well aware, i.e., that standards for concrete units do not adequately provide for
all possible actual climatic conditions within buildings. For
example, what are the relative humidities in a house, a manufact-uring plant, an office or a dairy etc. or for that matter in the
different parts of a building? What is the effect of
air-condition-ing? How does the relative humidity vary through the thickness
of an outside wall and what is the effect on permissible shrinkage? The complexity of these questions together with the lack of
adequate information on the properties of blocks makes it likely that more comprehensive standards will not be easily developed.
To explore the questions raised, the author performed calculations which seemed to shed some light on the subject and
which are presented in this Note for discussion. Information
giving the relationships between moisture content, relative
humidity and shrinkage as reported by Teonnies (1) was used and
climatic data was taken from Dept. of Transport "Climatic
Summaries" (2). Use was also made of standard psychrometric
charts.
Selection of Cities for Calculations
i
Table I shows climatic information for selected cities across Canada.
- - - -- ｾ
3
-TABLE I
CLI1MTIC ｉｎｆｏｾｶｾｔｉｏｎ FOR SOME CANADIAN CITIES
Average Annual Mean Month of January
City R. H. , Dry Bulb fret Bulb R. H. , Dry Bulb Wet Bulb
ｾ
Tsmp,
F Tsmp,F%
TsmpFTsmp,
F Victoria81
50
47
87
37
35
Vancouver82
50
47
87
35
34
Prince Rupert84
46
44
84
35
34
Banff70.5
36
32
77
12
11
Ca1gaT1J65.5
38
33.5
70
15
13
Edmonton72
36.5
33
82
8
8
Regina76
36
32
91
5
4
Ninnipeg76
36
33
87
21
The Pas79
31
28
89
-3
-4
Ottawa74
43
39
82
14
15
rroronto75.5
45.5
42
83
22
21
Quebec75
40
37
78
12
11
Halifax79
44
41
82
25
23
Yarmouth84
43
41
84
27
25
st. John's86
39
38
87
24
23
Winnipeg was selected for calculation since it was involved in the original question: Toronto was chosen because its average temperatures are higher than for Winnipeg, although it has about the same average annual mean relative humidity. Calculations were also made for Calgary because that city has an average relative humidity lower than most Canadian cities. For comparison with annual conditions the climatic conditions for January in the three cities were also recorded because, although the rt.H. values will probably be as high or higher than the annual average, the associated temperatures are low, which would result in the greatest difference in R.H. values between outdoors and indoors.
In all the calculations it was assumed that no moisture is added to the system within a building due to its occupancy. EXPLANATION OF CALCULATIONS
The results of the calculations are given in Tables
II, III and IV. The term "outdoors" ref'ers to walls that are
Columns
6, 1, 8
and 9
-Similarly "indoors" applies to !.valls ･ｮｴｩｲ･ｬｾｲ within a bUilding,
such as partitions. ｾｯ consideration was given to walls that
have outside conditions on one side and inside conditions on the other.
ｬｾ･ values can perhaps be best explained by describing
the meaning of the various columns for Toronto (Malton) as an example
(Table
II).
At the top of the Table are given the outside meanannual R.H. and temperature and similar values for January. Also
shovm are the relative humidities ｴＺｾｴ would apply in a building
in Toronto heated to 12°F. These latter figures (29 and 12 per
cent) ｷ･ｾ･ obtained by the use of psychrometric charts.
ｃｯｬｵｾｾ 1 - Three categories of block are shown, termed average, low or high depending on their total linear shrinkage as determined according to the test methods of ASTINI
C426. The shrinkage values chosen correspond to
curves given by Toennies (1).
ｃｯｬｵｾｾ 2 - Moisture content of blocks as a percentage of their total absorptions when dried to equilibrium with average annual conditions, e.g. 36 per cent for an average hlock.
Column 3 - The percentage of the total linear shrinkage in Column
1 that will have taken place when a block has reached
outdoor equilibrium moisture content in Column 2, e.g. 29 per cent for an average block.
Column
4 -
Moisture content of blocks as a percentage of theirtotal absorptions when dried to equilibrium with indoor conditions, e.g. 12.5 per cent for an average block.
Column 5 - The percentage of total linear shrinkage in Column 1 that will have taken place when the block has reached indoor equilibrium moisture content, e.g. 86 per cent for an average block.
- Same as Columns 2 to 5 except based on January conditions.
Column 10- As delivered moisture content, taken from Table 3 of the Eighth Draft corresvonding to Average Annual Mean R.H. for Toronto.
Column 11- The percentage of the total shrinJmge of the block as given in Colur.m 1 T..,.hich 1,."ill have talren place when
it is in the CSA specified condition.
Column 12- SnvironElents ｢･ｴｾＧＬｲ･･ｮ which blocks ma;! be transferred
resul ting in shrinka[es (or expansions) as the:! ｣ｨ｡ｮｾ･
from equili'briUl'1 with one condition to equilibrium \."1i th another.
-e
- -
5
-Line D - Blocks conditioned outdoors nnder cover
and then moved inside a heated building. Line E - Blocks conditioned to the CSA specified
moisture content then le:ft outdoors under cover or used in a wall outdoors until they come to equilibrium.
Line F - Blocks conditioned to CSA specified moisture
content then moved to a heated indoor location and allowed to come to ･ｱｵｩｬｩ｢ｲｩｵｾＮ
Columns
-
Shrinkage differences:1.3,14,15
Line D
-
Column 5 minus Column 3 (Annual)Column 0 minus Column 7 (,January)
-'
Line T:I
Column '3 minus Column 11 (Annual)
i'...
-Column 7 minus -Column 11 (Januar;',l)
Line F
-
Column 5 minus Column 11 (Annual)Column 9 minus Column 11 (January)
DISCUSSIOlJ OJ? TABLES
It should be pointed out that in using the information given by Toennies the curves had to be extrapolated in the range
below 20 per cent R.R. It appeared, however, that in this range
the moisture contents were low and changed more slowly and the same applies to shrinkage, i.e. the curves were flattening out so that the
errors of extrapolation were not likely to be large enough to be
completely misleading. Too much emphasis should not be placed on
individual values but rather on their order of magnitude and the type of phenomena that occur.
Line D shows that:
(a) Units stored in protected locations outdoors long enough to come to equilibrium with the average
annual climate in ｴｾ･ locality will exhibit 50
to about
71
per cent of their total shrinkageafter they are later installed in heated indoor locations.
(b) HiGher shrinkage occurs with high shrinkage blocks
than ｾＧｊｩ th low ones.
(c ) Units in equilibriqm wit1, Januar;v conditions will
underr-:o even treater shrinkac:e, in some cases in
the order of 86.5 per cent, when placed in a heated
b1JildinS·
(d) Shrinkat!es in "nnnipeg wonld be a little higher than in Toronto for either ;:mnusl or Jannary
conditions. In ｃｅｬｾＸｲｹ the values would be
-e
oity along with reasonably hi[':h temperatures. Line E shows that:
Blooks dried to the o'ondi tions speoified in the eighth draft of CSA will undergo relatively small shrinkages or in some oases expansions
when used in an unheated wall. Expansions are
assooiated mainly with high shrinkage blooks. This is partly due to the lower moisture oontent speoified for these blooks and partly due to the
shapes of the ourves reported by Toennies. These
observations apply to Winnipeg, Calgary and Toronto which shows that the values given in the proposed standard are oonsistent.
Examination of Line F reveals that when used indoors, blooks dried to the CSA speoifioation will perform about the same as blooks allowed to oome to natural equilibrium with the looal
olimate (Line D). The speoifioation does, however, result in some
benefits with high shrinkage blooks where, in some oases, the values
are lower by about one third. The speoifioation again appears to
be reasonably oonsistent between the three oities.
Beoause the values in the Tables indioate that the moisture oontents speoified in the eighth draft of CSA Standard A 165.1 do not take oare of shrinkage in heated indoor situations
very well it is interesting ｾｯ note that for zero shrinkage to
ooour, blooks would, on an annual basis, have to be used at moisture oontents of 12.5, 8.5 and 17.5 per oent for average, low and high
shrinkage blooks in the Toronto area for example(Column 4). Similar
values apply in the other cities. These are very low moisture
oontents and raise the possibility of serious expansions in some
instances when higher R.H. oonditions return to the indoor environment in summer.
It may be argued that many oooupanoies do contribute moisture to bUildings and indoor R.H. values as low as 5 and 6 per
oent would seldom, if ever, apply. The figures in Line F for
annual and January oonditions, however, show that the resultant shrinkages are not likely to be muoh different unless the R.H. is
raised to about 20 per oent. This is due to the flattening out
of the R.H. (versus) shrinkage ourves in this range, (bearing in
mind the extrapolations disoussed). This indioates that there
may be no great value in ever oonsidering R.H. figures below about 20 per oent and that it is suffioient to oonsider annual l;lverage
olimate as is done in the eighth draft of CSA tandard A 165.1
In answer to the original question regarding ｾｩｮｮｩｰ･ｧＬ
the effeot of the values in Table 3 does not appear to be
signifi-oantly different for Winnipeg than for Toronto or Calgary. This
is partly due to the oharaoteristios of the ourves of R.H. and shrinkage as reported by Toennies.
7
-If it was desired to strike a balance between outdoor and indoor conditions the moisture contents in the proposed
standard appear to be somewhat too high. ,The reviewer's contention
that no blocks should be used at moisture contents above 30 per cent would seem to be a valid average condition for high shrinkage
blocks but it should be noted that moisture contents of 30 and 35
per cent for high s.hrinkage blocks resulted in as much or greater shrinkage for high shrinkage blocks as drying to 40 per cent for low shrinkage blocks according to the calculations (Line F).
It should also be noted that for annual Toronto conditions, as an example, although low shrinkage blocks had lower absolute shrinkage than high shrinkage blocks, i.e. 0.016
as compared to 0.028, the percentage shrinkage is greater, 65
per ceBt as compared with 51 per cent. If it was desired to
obtain the same percentage benefits from drying, it may well be that low shrinkage blocks should be del ivered at lower moisture
contents than high shrinkage units. This is also apparent from
inspection of Toennies curves. Further study may indioate that
the progression of values in the vertical columns of Table 3 is
in the wrong direction for optimum results.
Observation of Column 2 of Tables II, III and IV for all
three cities indicates that a case could perhaps be made for requiring all blocks to be delivered at a moisture content of 30
per cent. For Toronto and Winnipeg annual conditions this would
be about the equilibrium ｾｯｩｳｴｵｲ･ content for low shrinkage blocks
and below that value for average and high shrinkage blocks. Low
shrinkage blocks would benefit the least which is on the right
side. A value of 30 per cent would not be of much benefit to
Calgary area but it would be better and in the right direotion. CONCLUSION
It is not proposed that any ohange be made at this time in the eighth draft of the CSA standard on Hollow Load-Bearing
Concrete Masonry Units. In the first place other records should
be studied, particularly the relationships between moisture content,
relative humidity, and shrinkage at low R.H. values. This would
require a good deal of testing of Canadian blocks.
More information is also required concerning the H.R. conditions obtaining through the thickness of the exterior walls of an actual bUilding where most units are likely to be used.
Although the moisture contents proposed at present appear to be somewhat too high, it is not clear at the moment
what the best values would be. There is hardly any doubt that
blocks should be dried to moisture contents below 40 per oent but the selection of the optimum values to use is still partly
in the realm of guesswork. The proposed specification is a step
in the right direction and should condition suppliers and users to the importance of moisture content pending more stringent requirements in the future.
More needs to be known as well about the effects
of storage. For example, if blocks were delivered to a site
at 25 per cent moisture content how long could they be stored on the site in a climate having an equilibrium moisture content
of
40
per cent before the benefits of drying would be lost?Presumably it would be some function of the size of the pile, method of stacking, protection method, and other factors •
. For all the conditions assumed in the calculations, the moisture movements of low shrinkage blocks is about half
that for high shrinkage blocks. So far as shrinkage is concerned
there is no real ｳｵ｢ｳｴｾｴｵｴ･ for a low shrinkage block.
REFERENCES
-e
(1)
(2)
Toennies, Henry, Concrete Masonry Shrinkage,
Publication of National Concrete Masonry Association,
Washington
7,
D.C.Climatic Summaries for Selected Meteorological stations in Oanada, Vol II (Revised), Humidity and Wind, Department of Transport, Meteorological Branch, Toronto, 1959.
e
TORONTO (MALTON)ｾ
-Average Annual Average Annual Average Annual Indoor Temp. Indoor R/H Mean R/HMean Dry Bulb Temp. Mean Wet Bulb Temp.
72° (say) 75.5% 45.5°F 42°F ＲＹｾ Jan. RJH
Jan. Dry Bulb Jan. Wet Bulb Indoor Temp Indoor R/H 83% 22°F 21°F 72°F 12%
ｾＪ Percent of total shrinkage occurring between saturation and
stated conditions.
SHRINKAGES OCCURRING ｂｅｮｾｅｅｎ STATED ENVIRONMENTAL CONDITIONS
*
Percent of Total absorptionAvge. Block Low S Block High S Block
12 . 0.038 13 0.024
14
0.055 15D Ditf. Between Shrinkages Annual Bas is 57% • 022 in. 54.5% .013 in. 64% .035 in •
(Indoors - Outdoors) January Basis 78 .030 69 .017 82 .045
E Ditt. Between CSA AnnuB.l Basis 8 .003 10.5 .002 -13 -.007
t
Spec. & Outdoor Condit. January Bas is -1 -.0004
l'
4 .001 -24 -.0131(Outdoor - eSA)
F Ditt. Between CSA Annual Basis 65 .025 65 .016 51 .028
C""" _ _ .. T ...ｾＢＬＬＢｉｏＧｬｴｯ ＬＮＬＢＧｾｾｾｾ T n ...""I"":l"ltt"l"'lT ｏｬＢｬｬｲｴＢＧｾ '7'7 /"I')C '7') /"I' A ｾａ /"I')') I
PERCENT MOISTURE CONTENT AND SHRINKAGE AT EQUILIBRIUM WiTH ENVIRONMENT AS DELIVERED M.C.
BASED ON MEAN ANNUAL BASED ON JANUARY AND SHRINKAGE AS
CONDITIONS CONDITIONS SPECIFIED IN 8th
BLOCK OUTDOORS INDOORS OUTDOORS INDOORS DRAFT OF CSA SPEC
1 Total EquiL -::-
to ....
o'"h-,r Equil. ｾ EquiL%
Equil.%
ｓｨｲｩｾｫ｡ｧ･ M.C. Shrink. M.C. Shrink. ｉｾＮ C. Shrink. M.C. Shrink. . M.C. % She
(ASTM C426) 2 3 4 5 6 7 8 9 10 11 A ｾＮＢｻＭｧ･Ｎ Block Ｓｾ ｾＹ 12.5 86 43 20 7 98 40 21 Q.038
:a
Low 29 37.5 8.5 9237
31 4 100 40 I 27 0 .. 024 Q ｈｾＱＬＮｧｨ 42 27 17.5 91 49 16 12 98 35 40 0._055 ..- , ... - ｾ .. ...I o.Jp'OV. ex. ,L.UUVV.l· VVUU,L.V. uQ.u ....a..l·J
ＮｵｑＮｾＮｌＧＢ
II . V ' - 7 1-1 . v . v ;.IV .V..)C-II
I (Indoor CSA) I I
...J
ｾ Negative sign denotes expansion
I
I
I I I I I I II
Ie
Average Annual Average Annual Average Annual Indoor Temp. Indoor R/H Mean R/HMean Dry Bulb Temp. Mean Wet Bulb Temp.
72°F (say) 76r{o 36°F 330F 20% Jan. R/H
Jan. Dry Bulb Jan. Wet Bulb Indoor Temp. Indoor R/H ＸＷｾ 2 F lOF 720F 5%
e
*
Percent of Total AbsorptionPERCENT MOISTURE CONTENT AND SHRINKAGE AT EQUILIBRIUM WITH ENVIRON}illNT AS DELIVERED r-l.C.
BASED ON MEAN ANNUAL BASED ON JANUARY AND SHRINKAGE AS
CONDITIONS CONDITIONS SPECIFlf-:D IN 8th
DRAFT OF CSA
BLOCK OUTDOORS INDOORS OUTDOORS INDOORS SPEC.
Total Equil.-!} ＥｾｾｾＺＮ Equil.
%
Equil. % Equil.%
Shrinkage M.C. Shrink. M.C. Shrink. M. C. Shrink. M.C. Shrink. N. C. 10 She
(ASTN C1.J.26 A Avge. Block 36 29 9 90 46 16 5 100 40 21 0.038 B Low 29 37.5 7 100 40· 29 3 100 40 27 0.024 C High 42 27
14
98 53 12.5 9 99 35 40 0.055*-!} Percent of total shrinkage occurring between saturation and
stated conditions.
SHRINKAGES OCCURRING BETWEEN STATED ENVIRONMENTAL CONDITIONS
Avge. Block Low S Block High S Block
0.038 0.024 0.055
D Diff. Between Shrinkages Annual Basis 617& .023 in. 62.5 .015 in. ＷＱ［ｾ .039 in.
(Indoors - Outdoors) January ]?asis 84 .031 71 .017 86.5 .047
E Dift. Between CSA Annual Bas is 8 .003 10.5 .003 -13 • 007 't
Spec.
&
Outdoor Condit. January Basis -5 -.002"*
2 .0 -27.5 -.015t
(Outdoor - CSA)
F Diff. Between CSA Spec. Annual Bas is 69 .026 73 .018 58 .032
&
Indoor Condit. January Basis 79 .030 73 .018 59 .032e
TABLE IV• CALGARYe
I. Average Annual Average Annual Average Annual Indoor Temp. Indoor RIH Mean R/H Mean Dry Mean Wet 720p Bulb Temp. Bulb Temp. (say)65.5)0
38°F 33.5°P 1950 Jan. RIBJan. Dry Bulb Jan. ltlet Bulb Indoor Temp. Indoor RIB ＷＰＯｾ l5°P l30P 720P 6.Jf /0
PERCE:-IT tfl,OISTURE ｃｏｎｔｾ［ｎｔ Al\ID SHRINKAGE AT EQUILIERIUN WITH ENVIRONHENT AS DBLIV2HED
N.C. Aim
SEHD;-BASED ON MEAN ANNUAL BASED ON JANUARY KAGE AS
SPECI-CONDITIONS CONDITIONS FIBD IN 8 DRA?'T
BLOCK OUTDOORS INDOORS OUTDOORS INDOORS OF CSA SP3:C.
lotal ｅｱｵｩｬＮｾＺﾷ ＥＮＺＬｾｾｾ Equil. % Equil. % Equil. /0
H. C.
I
ｓｨｲｩｮｫ｡ｾｧ M.C. Shrink. M.C. Shrink. M.C. Shrink. 1'-;.C. Shrink.
%
She(AS :'1':
e4
)
A Avge. Block 28 42 8 92 31 37 5 99 35 29 0.038 B Low 22.5 50 6 100 25 46 J 100 40 27 0.024 C High 33.5 44 14 96 37.5 36.5 10 99 30 53 0.055*
Precent of Total Absorption ｾｈｾ Percent of Total Shrinkage occurring between saturation andstated conditions.
SHRINKAGES OCCURRING BETWEEN STATED ENVIRONMENTAL CONDITIONS
p
r
Avge. Block Low S Block High S Block
1
0.038 0.024 0.055
i
D Diff. Between Shrinkages Annual Basis 50% • 019in. 50;h .012 in . 52% .029 in.
i
62 .024 54 .013 62.5 .034 ,
(Indoors - Outdoors) January Basis
.
,jE Diff. Between eSA Annual Basis 13 .005 23 .006 -10 -.006
r
I
Spec.
&
Outdoor Condit. January Basis 8 .003 19 .005 -16.5 -.009 -F(Outdoor - CSA)
F Diff. Between CSA Annual Bas is 63 .024 73 .018 43 .024
Slec & Indoor)Condit. January Basis 70 .027 73 .018 46 .025
( ndoor - CSA 1
