Publisher’s version / Version de l'éditeur:
Journal of the Canadian Ceramic Society, 35, pp. 92-95, 1967-07-01
READ THESE TERMS AND CONDITIONS CAREFULLY BEFORE USING THIS WEBSITE.
https://nrc-publications.canada.ca/eng/copyright
Vous avez des questions? Nous pouvons vous aider. Pour communiquer directement avec un auteur, consultez la première page de la revue dans laquelle son article a été publié afin de trouver ses coordonnées. Si vous n’arrivez pas à les repérer, communiquez avec nous à PublicationsArchive-ArchivesPublications@nrc-cnrc.gc.ca.
Questions? Contact the NRC Publications Archive team at
PublicationsArchive-ArchivesPublications@nrc-cnrc.gc.ca. If you wish to email the authors directly, please see the first page of the publication for their contact information.
NRC Publications Archive
Archives des publications du CNRC
This publication could be one of several versions: author’s original, accepted manuscript or the publisher’s version. / La version de cette publication peut être l’une des suivantes : la version prépublication de l’auteur, la version acceptée du manuscrit ou la version de l’éditeur.
Access and use of this website and the material on it are subject to the Terms and Conditions set forth at
The influence of efflorescence on decay and expansion of mortar
Ritchie, T.
https://publications-cnrc.canada.ca/fra/droits
L’accès à ce site Web et l’utilisation de son contenu sont assujettis aux conditions présentées dans le site LISEZ CES CONDITIONS ATTENTIVEMENT AVANT D’UTILISER CE SITE WEB.
NRC Publications Record / Notice d'Archives des publications de CNRC:
https://nrc-publications.canada.ca/eng/view/object/?id=892332e8-fdb3-417c-aab1-12b66bdf4987
https://publications-cnrc.canada.ca/fra/voir/objet/?id=892332e8-fdb3-417c-aab1-12b66bdf4987
The
Influence of
Efflorescence on
Decay and Expansion
of Mortar
by
T.
Ritchie
Efflorescence on brick masonry is usually considered to be a problem mainly as it affects the appearance of the building o n which it occurs. It is well known, however, that certain salts that frequently form a part of efflorescence, particularly sulphate salts, can be destructive to masonry materials. They may crystallize in a plane within the material as it dries and the resulting crystal growth causes scaling and decay. Similarly, sulphate salts are known to attack products of hardened portland cement, with resulting disruption of the material.
In certain studies of efflorescence carried out at the Division of Building Research, National Research Council, piers of brick- work were exposed to the weather. Subse- quent cracking and decay of the mortar appeared to be related to the soluble salts
contained in the bricks. A study was made,
therefore, of this occurrence of damage, and it led to additional investigations to deter- mine the influence of various bricks on the expansion of masonry mortars. It became evident that soluble salts in certain bricks caused abnormal expansion of mortars to take place. It is the purpose of this paper to describe the study of the decay of mortar in the brickwork piers and to describe the method of test used in determining the influence of bricks on mortar expansion.
Brick piers
Brickwork piers were erected in 1959 of combinations of two different bricks and three mortars in order to study the occur-
Abstract
A particular case of cracking and
spalling of masonry mortar was attri- buted to the migration of soluble salts from the brick to the mortar. Experi- ments with bars of masonry mortars showed that their expansion was in- fluenced by soluble salts in bricks. Efflorescence is therefore considered to be more than a problem of aes- thetics; it may affect the dimensional stability and durability of masonry. rence of efflorescence on brickwork in rela- tion to certain properties of the materials used. The piers were constructed of solid brickwork four bricks long (about 34 in.), a brick and a half wide (12 in.), and 20 courses high (52 in.). The top of the brick- work was covered by copper foil on which a concrete cap was set, and a similar sheet of foil was installed in the pier about 12 in. from the base to prevent the rise of ground water into the brickwork.
Two types of red clay brick were used. They were similar in water absorption
properties, but differed in compressive
strength and in the tendency to produce efflorescence. Mortars of three compositions were used in constructing the piers: the first was prepared from lime and sand (in pro- portions 1:3 by volume); the second from cement, lime and sand in proportions 1: 1:6 by volume; and the third from masonry cement and sand in proportions 1:3 by volume.
Mortar decay and cracking
During the first winter following construction of the piers trouble developed in the mortar joints of one of the two piers constructed of 1ime:sand mortar. Flakes of mortar were observed coming from the joints, and the
The author, T. Ritchie, is research ofiicer, Inorganic Building Materials Section, Division of Building Research, National Research Council, Canada.
~ieu;e 1 w 6 c h show t h i t the mortar
-.o--- ., - - - ~ - -
around the bricks of one pier is badly cracked while the mortar in the other pier is apparently sound.
Salts in bricks
Before the piers were constructed samples of the bricks were tested for efflorescence. This test was made by the ASTM method, in which a brick is placed for 7 days in a pan o f distilled water 1 in. deep. Water moves through the brick and dissolves salts in it so that they are deposited on the surface when the water evaporates. In this test one of the bricks was heavily marked by salt deposits, but the other was only slightly affected (Figure 2). The five bricks on the left side o f each row were placed in distilled water for 7 days, then dried; the five bricks o n the right are "control" bricks, which were not wetted.
The brick heavily marked by efflorescence was that used in the pier that developed severe mortar cracking. Chemical analysis showed that this brick contained 1 per cent
SO.: the other brick contained less than -- -
0.0: per cent. The compound formed by the Figure 2: Efflorescence test of bricks used in the
sulphate in the brick was not determined. piers.
Salts in mortar
Three years after construction of the piers samples were taken of both the decayed and cracked mortar and of the apparently sound mortar of the corresponding pier built with the second brick. Chemical analysis showed that there was considerably more sulphate salt in the decayed mortar than in the sound mortar. (The identity of the sulphate com- pound could be determined by neither X-ray analysis nor differential thermal analysis.) Chemical analysis of the lime used in the piers of 1ime:sand mortar indicated no sul- phate present, so that the sulphate content of the mortar must have been derived from the brick used with it, although there is a slight possibility that the sand may have contained sulphate salts. Chemical analysis of samples of the cement:lime mortar and of the masonry cement mortar similarly indi- cated considerably higher content of sulphate salts in those samples taken from the piers of the brick of higher sulphate content. These mortars, because of the gypsum con-
tained in the portland cement, would be expected to contain sulphate salts when
originally prepared. A comparison of the
sulphate content of the mortars of the piers
is given in Table I.
The piers therefore provided evidence that there was a migration of sulphate salts from the brick to the mortar, and that t h e presence of such salts in the mortar of lime: sand composition had been the cause of its decay and severe cracking. T h e greater sus- ceptibility of the lime mortar to cracking and decay was probably due to its relatively low strength, which would make it less capable of resisting internal pressure.
Tests of mortar bars
The influence of bricks o n the expansion of mortar was studied by the use of mortar bars of "standard" size, 1 in. square and 10 in. effective length, fitted with metal reference pins in the ends. The bars were stored in a room of high humidity (73"F, 100 per cent RH) until they were tested. T h e tests were started from one to four days after the bars
S U L P H A T E CONTENT O F M O R T A R S I N B R I C K P I E R S M O R T A R L X P A N S I O N A N D S U L P H A I E C O N T E N T 5 0 4
1
M O R T A RI
B R I C KI
I N M O R T A RI
1%) L ' L i m e C-
P o r l l a n d c e m e n t..,,,
,., h l C M a s o n r y c e m e n t S-
S a n d TABLE Ihad been moulded; their length was meas- ured using a standard comparator, after which they were placed in plastic trays and covered with water. Companion bars were placed in a similar tray in which a layer of crushed brick had been spread over the bottom; water was poured into the tray to cover the bars. Periodically the bars were removed from the trays and their length was measured.
The crushed bricks contained no particles
larger than X in., and the amount of brick
used with each mortar bar was such that the ratio by weight of mortar to brick was 1.0 to 1.6 approximately the proportion of mor- tar to brick in brickwork.
Test results
In the first tests undertaken four different mortars were used with four different bricks. The mortars differed in the type of cement- ing material used and in the proportions of cementing material to sand. The bricks were from four sources and were selected because
h i O R T A R M O R T A R S T O R A G E
C O N D I T I O I I
1 1 I Y E A R 1 I
they were in common use in Canadian construction.
The expansion of the mortar bars used with each of the four bricks is shown in Figure 3. The length of the bars, as meas- ured periodically after the start of the test, is expressed as a percentage of the original length. These graphs show that the expan- sion of the mortar bars stored in water and of those stored in water and crushed bricks
"A",
"C"
anddid not differ much;
brick "B", however, caused greatly increased
expansion of the mortar bars. T h e graphs
also indicate that the influence of brick "B"
on the expansion of the mortars differed among the four mortars used.
Samples of some of the mortars were analysed for sulphate content. I t was found that sulphate content varied, depending o n whether the bar was stored in water alone and on which brick had been added to the
water. A typical example is shown in Table
11, in which the expansion of a mortar bar after one year and the sulphate content of that bar is given in relation to its conditions of storage whether in water, in water plus brick "A", o r in water plus brick "B". It may be seen that the greater expansion in the last case is associated with greater sul- phate content of the mortar.
\'t a l e r \ ' t a l e r + B r i c k A W a l e r B r i c k B B r i c k B 'l 0 B r i c k s A. C. D W a t e r -0.020 0 100 200 300 400 5 0 0 600 700 0 100 200 300 400 5 0 0 600 700 D A Y S D A Y S
Figure 3: Influence o f brick o n expansion of mortar.
TABLE I1 0 0 4 0 0 5 . 0 2 2 0. 36 0. 39 0. 91
Additional tests
In further tests nine additional bricks from various plants in Canada were used with several mortars to determine the influence of the bricks on mortar expansion. The method of test was the same as that described, and the results were similar in that certain bricks caused greater expansion of the mortars.
The bricks were tested for sulphate con- tent by placing 25 grams of the crushed brick in a beaker with 50 cc of water which was at room temperature. The beaker was shaken and then allowed to stand for
!I
hour, when the water was poured off through a filter paper and the filtrate collected. Another 50 cc of water was added and the procedure was repeated. A third 50 cc of water was added and allowed to stand over night before the water was poured off. These wash solutions were collected and analysed for sulphate content.The sulphate content of the bricks as determined in this way was plotted against the expansion of the mortar bar after one year of storage in water to which that par- ticular brick had been added. The results are shown in Figure 4, the expansion plotted being that directly attributed to the influence of the brick (that is, the difference between the expansion of the mortar bar in water to which crushed brick was added and that of the mortar bar in water alone). The results for two mortars are shown in the graph. In each case there appears t o be a close relation between mortar expansion and sulphate con- tent of the brick.
Conclusions
A study of brickwork piers showed that migration of sulphate salts from bricks into mortar can take place and that this may lead to cracking of the mortar and its decay. A study of the influence of various bricks on the expansion of masonry mortars showed that there may be a significant increase in mortar expansion owing to the brick. The tests again indicated that the abnormal ex-
-0.004 1 I I 1 I
0 1 0 0 2 0 0 100 4 0 0 5 0 0 600 1 0 0
C O N T t N T 0 1 SO4 I N B R I C K ' S W A S H S O L U T I O N . P . P . h l .
Figure 4: Effect o f soluble sulphate o f bricks o n
mortar expansion.
pansion was due to the migration of sulphate salts from the brick into the mortar. Efflores- cence in bricks, therefore, is important not only with regard to the appearance of brick- work, but also with regard to the durability and dimensional stability of brick masonry.
Acknowledgments
The author wishes to thank E. C. Goodhue of the Division of Applied Chemistry, Na- tional Research Council, for the chemical analyses referred to in the paper.
This paper is a contribution from the Division of Building Research, National Research Council, and is published with the approval of the Director of the Division.
