Publisher’s version / Version de l'éditeur:
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.
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.
[Rilem/CIB 1965 Symposium: Moisture Problems in Buildings: Proceedings, p. 8,
1966-07-01
READ THESE TERMS AND CONDITIONS CAREFULLY BEFORE USING THIS WEBSITE. https://nrc-publications.canada.ca/eng/copyright
NRC Publications Archive Record / Notice des Archives des publications du CNRC :
https://nrc-publications.canada.ca/eng/view/object/?id=424861eb-51d3-4633-842f-a97f0be59f44
https://publications-cnrc.canada.ca/fra/voir/objet/?id=424861eb-51d3-4633-842f-a97f0be59f44
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
Damage to masonry constructions by the ice-lensing mechanism
Garden, G. K.
T}I1
N21t2
no. 22)
e . 2
BtDG
NATIONAL RESEARCH COUNCIL CANADA
CONSEIL NATIONAL DE RECHERCHES
DAMAGE TO MASONRY CONSTRUCTIONS BY THE ICE-LENSING MECHANISM by G . K . G a r d e n
A T { . A L Y Z I D
R I L E M / C I B S y m p o s i u m , H e l s i n k i , 1 9 6 5 r r M o i s t u r e Problems in Buildingsrl PREPRINT 2 - 6 T e c h n i c a l P a p e r N o . 2 2 5 of the D i v i s i o n o f B u i l d i n g R e s e a r c h O T T A W A J u l y 1 9 6 6 N R C 9 1 2 9 P r i c e 2 53 72271L'
T h i s p u b l i c a t i o n i s b e i n g d i s t r i b u t e d b y t h e D i v i s i o n o f B u i l d i n g R e s e a r c h o f t h e N a t i o n a l R e s e a r c h C o u n c i l . I t s h o u l d n o t b e r e p r o d u c e d i n w h o l e o r i . n p a r t , w i t h o u t p e r m i s -s i o n o f t h e o r i g i n a l p u b l i -s h e r . T h e D i v i s i o n w o u l d b e g l a d t o b e o f a s s i s t a n c e i n o b t a i n i n g s u c h p e r r n i s s i o n . P u b l i c a t i o n s o f t h e D i v i s i o n o f B u i l d i n g R e s e a r c h m a y b e o b t a i n e d b y r n a i l i n g t h e a p p r o p r i a t e r e r n i t t a n c e , ( a B a n k , E x p r e s s , o r P o s t O f f i c e N { o n e y O r d e r o r a c h e q u e r n a d e p a y -a b l e -a t p -a r i n O t t -a w -a , t o t h e R e c e i v e r G e n e r a l o f C a n a d a , c r e d i t N a t i o n a l R e s e a r c h C o u n c i l ) t o t h e N a t i o n a l R e s e a r c h C o u n c i l , O t t a w a . S t a r n p s a r e n o t a c c e p t a b l e . A c o u p o n s y s t e r n h a s b e e n i n t r o d u c e d t o r n a k e p a y -r n e n t s f o -r p u b l i c a t i o n s r e l a t i v e l y s i r n p l e . C c u p o n s a r e a v a i l -a b l e i n d e n o r n i n -a t i o n s o f 5 , Z 5 a n d 5 0 c e n t s , a n d m a y b e o b -t a i n e d b y r n a k i n g a r e r n i t t a n c e a s i n d i c a t e d a b o v e . T h e s e c o u p o n s r n a y b e u s e d f o r t h e p u r c h a s e o f a l l N a t i o n a l R e s e a r c h C o u n c i l p u b l i c a t i o n s , A I i s t o f a l l p u b l i c a t i o n s o f t h e D i v i s i o n o f B u i l d i n g R e s e a r c h i s a v a i l a b l e a n d r n a y b e o b -t a i n e d f r o r n -t h e P u b l i c a -t i o n s S e c -t i o n , D i v i s i o n o f B u i l d i n g R e s e a r c h , N a t i o n a l R e s e a r c h C o u n c i l , O t t a w a , C a n a d a .
2 - 6
DAMAGE TO MASONRY CONSTRUCTIONS BY THE ICE.LENSING MECIIANISM G.K. GARDEN'}
N a t i o n a l ' R e s e a r c h C o u n c i l
D i v i s i o n o f B u i l d i n g R e s e a r c h , C o n s r r u c t i o n S e c t i o n , O t t a w a C a n a d a
Field studies of failures in dre cladding of buildings have provided conclusive evidence that ice-lensing occurs in masonry materials and that its excesive expansion accounts for the displacements and deterioration observed. It should have been possible from a knowledge of the ice-lensing mechanism in soils to predict the occurrence of ice lenses in building constructions. Although suggested by some writers, the possibility has not been widely recognized. This paper discusses rhe conditions required fcjr ice-lens growth, presents evidence of its occurrence in building constuctions, and considers some of the implications of these observations. Although not discussed in this paper, ice-lensing in the soil under building founda-tions is frequently responsible for structural movements producing masonry failures.
Extensive investigation of the mechanism of ice-lensing'with respect to frost heaving in soils has shown thrit it can occru in wet, fine-grained soils subjected to unidirectional freezing. Freezing of water, in causing a decrease in potential, induces water to migrate to the fteezing plane. The release of the heat of crystallization, upon freezing of the water which migrated to the freezing plane, acts to retard its rate of advance. So long as the advance of the frcezing plane is retarded by this means, water migrates between the ice and soil particles to freeze onto the ice, producing expansion far in excess of the normal expansion of water on fteezing with the accompanying heaving pressure.
Ice-lensing in a wet, frost-susceptible soil subjected to frcezing can be resisted by a load or tensile sfiength, by suction [1] at the freezing plane, or a combina-tion of both. The load or tensile strength required to prevent its occurrence is proportional to the heaving pressure attainable. The maximum heaving pressure in a material varies inversely with pore size but can only be developed when the
*)Construction Section, Division of Building Research, National Research Council, Ottawa, Canada
2
suction is essentially zero. With an increase in suction the rate of ice*lens gmtrrth' and the heaving pressure are both reduced with no ice-Iensing occurring when the suction is sufficiently high. When the potential rate of desiccation due to fteezing exceeds the rate of moisture migration through the unfrozen material, even though saturated, the suction at the f.reezing plane increases, resisting ice-lensing.
It should be enphasized that ice-lensing does not require that conditions,conduflve to ice-lens growth be maintained over a long period of dme for damage to occur. I t h a s b e e n s h o w n b y P e n n e r [ 2 ] t h a t a h e a v e o f 0 . 0 4 i n . ( 0 . J . c r n ) c a n o c c u r in less then half sn lt$ur in several different frost-susceptible soil samples only 3 in. (?. 5 cm) deep, with a cotal expansion of from 0. 3 to 1. 5 in. (0.75 to 3.25 cm) in two days. It is also important to note that, although sizable expansions in soil under roads can be tolerated, even small expansions in masonry can be quite serious since a strain of onlv 0.01 per cent can cause failure.
The conditions required to cause ice-lensing in soils - freezing, fine-pore structure, and moisture supply - frequently occur in building materials. ln walls of heated buildings the thermal balance required to retard the advance of the frcezing plane is not dependent upon the rate of moisture migration as it generally is for frost heaving in the ground. When this balance is essentially independent'of the heat of crystallization of water on fteezing a reduced rate of moisture migration may be of little significance in resisting ice-lensing. Furthermore, freeze=thaw cycling tends to produce a moisture accumulation in the zone of. freezing despite low permeance or periodic fluctuations of the moisture content of the unfrozen materials. Under these conditions a low suction can occur and the 'tensile strength of the material may then be the only condition resisting, ice-lens.growttr."If the exterior surface of a wall is highly permeable and drying can occur. by evaporation, a high suction may be maintairied and ice-lensing seldom occursJ' When',the exterior surface has a low permeability, however, the risk of low suction and ice-lensing is increased. Stone facings, flashings, and impermeable coatings-,are- instru-mental in many cases in producing accumulations of water which lead to severe ice lens.damage to masonry materials. When the moisture supply torthe f.rcezing zone is very great, however, ice-lensing can"occur even with a highly. permeable surface on che cold side.
Although most of the conditions required {ot i.ce-lens growth freqqently occurt damage to materials may not resulL It has been proposed that for' ice'lensing to occur in a sound porous material its structure must first be damaged by freezing while in a highly satutated state. This would appear to be of importance when the tensile strength of the material exceeds. the potential heaving pressure but not necessary for the mechanism to operate in a matetial with low tensile strength, such as mortar. There is not enough evidence, however, to say that the failures to be discussed were not influenced in any way by prior history of freezing.
The following examples, chosen from many such cases, are included to show how ice-lensing is instrumental in cases of severe deterioration of masonry materials and constructions. Granite facing stones on a row of exterior columns, rising out
2 - 6
F i g u r e 1 . G r a n i t e fa c i n g b r o k e n b e c a u s e o f i c e - l e n s i n g in the back-up mortar.
of a poorly drained roof terrace, were displaced during the first winter after con-stuction. The steel columns had been infilled to provide a square masonry column and the space between masonry and facing stones was filled with an over-watered mortar. The stones were installed in such a manner that the back-up mortar connected with the mortar bed of the temace topping materials. The heat loss from the space below prevented the freezing of water in the terrace mortar bed and in the base of the columns. Water from the terrace could migrate through the mortar behind the column cladding stones to a trcezing plane a short distance above the base. The appearance of the mortar; its low strength and fine pore structure, the existence of an ample supply of water and unidirecdonal freezing led to the assumption that ice-lensing was responsible for the failure. The following summerr displaced stones-were removed and relaid, using new mortar throughout, and the space behind facing stones was again filled with mortar. Early the following winter similar displacement occurred and some stones 4 in. (10 cm) thick were broken by the force (Figure L). Some stones were immediately reuroved and examination of the mortar back-up showed many ice lenses between wafers of solid material, typical of ice-lensing damage (Figure 2), confirming the assumption made the previous year.
On the saffre terrace there were low walls of a highly absorptive brick, faced with large stone slabs, the space between being filled with mortar..f: These walls were built on the roof membrane in contact with the terrace topping materials. The same displacement of stones occurred but, in addition to the-ice:lensing in the mortar, a laminar break-up of the brick occurred.
Air leakage outward at the top of a humidified building caused excessive con-densation [3]. The condensate was absorbed by the bricks and mortar in the 8-in.
Figure 2. Ice lenses in firortar beirind granite facing stones of Figure tr.
F i g u r e 3 . M a s o n r y d e t e r i o r a t i o n d u e to ice-lensing in the mortar joints.
2 - 6
Fig ure 4. Laminar break-up of masonry units which were covered by a metal flashing.
(20 cm) high parapet and several coruses of brick below. Ice-lensing occurred, causing expansion in the mortar joint and disruption of the brickwork (Figure 3). The bricks at the back of the parapet were covered by the roof membrane and flashing and suffered a laminar break-up typical of ice-lensing damage. This break-up did not occur in the exposed face bricla because of drying to the atmos-phere. Similar mortar failures and masonry disruption also occurred at window sills in the upper pan of the building where condensation due to air leakage had been occurring.
On a building where roof leaks were permitting water to enter the wall, ice-lensing catrsed laminar failure of the bricl<s behind a base flashing. Above the flashing the bricks were not damaged because the partial drying and their tensile strength were sufficient to resist ice-lensing but the mortar joints were damaged. Figure 4 shows the wall with the flashing removed.
A high humidity was produced by plastering and finishing operations in a building under construction which was closed in by the permanent exterior walls and heated [4]. During frcezing weather the exfiltration of air with a high moisture content through spaces between the windows and the inner wythe and through the wall cavity resulted in excessive condensation on the back of the glazed brick exterior wythe. Within a few weeks ice-lensing in the mortar joints had caused severe disruption of the face brick (Figure 5) with the expansion causing breakage of many panes of window glass.
Examinations were made of a window assembly in a residence where a large pane of glass had broken early in the winrer, in both the first and second years after construction. The pattern of fracture indicared edge loading and. it was observed that the wooden sill had been forced upward at the middle. Examination
Figure 5. Damage to masonry and windows frorn ice-lensing in mortar join*. High moisture condltion was due to condensation from air leakage.
of the brickwork below the window sill disclosed evidence of ice-lensing in the mortar ioirts. As the relative humidity irl the house was being held at b0 per cenr, the air leakage under the window sill produced continual cqndensation in cold weather. with this high moisftre supply neirher drying ro rhe exrerior nor rhe tensile strength of the mortar were sufficient to resist ice-lensing, at least for some period of time.
Ice-lensing' although responsible for many cases of severe deterioration of masonry materials and constructions, cat be controlled. Since the four basic conditions - fine pore structure, low tensile strength, fteezing, and high moisture content - are required simultaneously, sufficient modification of any one can prevent the growth of ice lensei;.If economy in building is a factor, as itgenerally is' available materials must be used as they are. Consequently it is not reasonable to consider modification of the pore structure or tensile strength if the problern can be controlled in other more economical ways. Coating all the interior surface of a porous material with a compound to reduce the surface energy might reduce the potential heaving force but sufficient information is not yet available upon which to base a positive statement and furthermore the cost of such an operation could
2 - 6
be prohibitiuet Since 'the, 'requlred*atensile{$trength*,and {he*'tedrrction."of . strength due to freeziag in a saturated state ,are .both indeterminate it may be unwise to rely on sftength alone to.prevent the occunence of ice-lensing. oy positioning the: insulation as far to the cold "side ,as posible,. rbe *emperature in most materials of a wall can,.be kept above.{reezim a tef i'al $'; irr il 1 {'fi e
,Sueh*f,. wallr .onlv the exterior facing:;
L--tSSS#fi de" iensirig conside
rablf
redue#. Ice;lenSing sbannotdS6curr{fi'4ryttnadfidls$n0'.*the contfol of the moistudb content of materials.exposed 4o freezingean also.be employed to prevent its occurrence.The best way to prevent ice-lensing damage to {nasonly construction is by designing so as ro minimiz4'the quantity.of fnh6rials;rirubjeeted to freezing and to maintai.n the moisture 4content .of ,[hess, as low €s.,posslble. A cavity-type wall with insulation 'applied ,to .the,outside surface of thdlnnelwyrhe has great possibility for success. With the insulation as far to the outsidg as. practical, most of the wall can be kept from freezing;,. The moisturerrcontent.iof {h6: exterior wythe can be kept low if the mechanisms produei.ng tain.peflgBation.havg;been properly controlled and adequate.-ventilation of ijre cavity: 1o outslde has"been pfovided. Ventilation of the,cav'ir-y;i"1n "additi*tf1 Ff.Siging irilgarltrol-.'pf.-tairdfetteuafion, permits drytr-rg *' of the outer wyrhe.frorrii botti;.{iide$; Itdsd.acts.toi$rahsport water vapour out of the wall' promoting a dry conditldn. .Air leakage tthrougtrths inner wythe musr, however, be kept small anil':itater 'entry to the face" materials by contact with the ground or by faulty flashings.-$hould not .be .petr4lfted.
Although" ice-'leh3inB. has{tbet-tor.fhd fu ebe*fesliqxi${btb fbr many cases of ma;onqp deterioration; rh6lndpfrahir6lijsanS6tfoptnol{dd*$6 ftighilegree by good wal[. design. ,As in"rnany'tbr0ildiag;prob1erfrs#heicohtfol.&S'1,rtatet ls nf vital impor.tance^
This paper is a contribution from the DiVision of Building Research, National Reseatch Council'of.Canada and is-,publtshed:wittr,Che approval of the Director of the Dlvision.
8
. REFERENCES
1. Penner, E., Soil moisture.,suctioff- its.importance;and'msasursment. Pro-ceedings, A-merican -Sqeiety' for'"Testin$'Materials,r 58(1958); pp. 1205 -' 121?. (Reprinbd as NRC 4994).
'2. Penner, E., Soil moisture'tension and. ice segregadon. Highway Research Board, Bulletin 168(195?), PP. 50-'64. (Reprinted as NRC 4738).
3 . W i l s o n , A . G . a n d G . K . G a r d e n , M o i s t u r e a c c u m u l a t i o n i n w a l l s d u e t o air leakage. Paper presented at the RILEM/CIB Symposium, "Moisture Problems in Buildings", Helsinki, August 1965.
4. Crocker, C.R., Moistureproblems.duringwinterconstruction Paperpresented ar rhe RILEM/CB Symposium, "Moisture Problems in Buildings"' Helsinki, August 1965.
