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Winter Concreting - Canadian Practice
Turenne, R. G.; Sereda, P. J.
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ISSN 0 3 8 1 -4319
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WINTER CONCRETING CANADIAN
PRACTICE
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WINTER CONCRETING - CANADIAN PRACTICE by
R . G . Turenne and P . J . Sereda
A General Report p r e s e n t e d a t t h e Second l n t c r n a t i o n a l RILEM
Symposium on Winter Concreting October 14-16, 1975
Moscow, U.S.S.R.
DBR Paper No. 848 of t h e
Division of Building Research
WINTER CONCRETING
-
CANADIAN PRACTICE by R.G. Turenne and P . J . S e r e d a ABSTRACT To i l l u s t r a t e some of t h e c u r r e n t p r a c t i c e s b e i n g f o l l o w e d f o r w i n t e r c o n c r e t i n g i n Canada, t h e a u t h o r s have s t u d i e d t h r e e p r o j e c t s l o c a t e d i n d i f f e r e n t a r e a s of t h e c o u n t r y and i n v o l v i n g v a r i o u s s e c t o r s of t h e i n d u s t r y . Methods used by c o n t r a c t o r s t o p r o t e c t and c u r ec o n c r e t e under w i n t e r c o n d i t i o n s have been d e s c r i b e d . The p a p e r a l s o d i s c u s s e s some of t h e t e c h n i q u e s employed t o e n s u r e q u a l i t y , such as t h e h e a t i n g of t h e w a t e r and a g g r e g a t e s used i n t h e mix, t h e o n - s i t e t e s t i n g of t h e c o n c r e t e mix and c e r t a i n methods used i n m o n i t o r i n g t h e c o n c r e t e s t r e n g t h s . The b a s i c p r i n c i p l e used on a l l s i t e s c o n s i s t e d of
c o n t r o l l i n g t h e t e m p e r a t u r e of t h e c o n c r e t e a t t h e time of p l a c i n g and f o r a c e r t a i n p e r i o d of time t h e r e a f t e r t o e n s u r e t h e s a f e t y of t h e s t r u c t u r e . T h i s p r a c t i c e followed f a i r l y c l o s e l y t h e r e q u i r e m e n t s o u t - l i n e d i n CSA S t a n d a r d s . The a u t h o r s conclude t h a t t h e r e i s a need f o r a r e l i a b l e , n o n d e s t r u c t i v e method of o n - s i t e t e s t i n g t o m o n i t o r s t r e n g t h development t o d e t e r m i n e when t h e minimum r e q u i r e d s t r e n g t h h a s been r e a c h e d and e n s u r e t h a t t h e c o n c r e t e i s n o t c u r e d f o r a p e r i o d s h o r t e r t h a n r e q u i r e d o r l o n g e r t h a n n e c e s s a r y . T h i s would e l i m i n a t e t h e p r e s e n t u n c e r t a i n t y and p o s s i b l y r e d u c e c o n s t r u c t i o n t i m e .
p a r R.G. Turenne e t P.J. Sereda
A f i n de m o n t r e r quelques-unes d e s mgthodes u t i l i s g e s a u Canada pour l e bgtonnage pendant l ' h i v e r , l e s a u t e u r s o n t v i s i t 6 t r o i s c h a n t i e r s , dans d i f f g r e n t e s r 6 g i o n s du pays, m e t t a n t en j e u d i v e r s s e c t e u r s d e l ' i n d u s t r i e . Les mgthodes employ6es p a r l e s e n t r e p r e n e u r s pour l a p r o t e c t i o n e t l a p r i s e d u b g t o n dans d e s c o n d i t i o n s h i v e r n a l e s s o n t d g c r i t e s . Le p r g s e n t a r t i c l e examine Ggalement quelques-unes d e s
t e c h n i q u e s a s s u r a n t l a q u a l i r 6 , p a r exemple l e c h a u f f a g e d e l ' e a u e t d e s a g r g g a t s u t i l i s g s dans l e mglange, l e s e s s a i s i n s i t u du m6lange d e b g t o n e t c e r t a i n e s mgthodes d ' o b s e r v a t i o n c o n t i n u e d e l a r g s i s t a n c e du b g t o n . Le p r i n c i p e de b a s e pour t o u s l e s c h a n t i e r s e s t l a r g g u l a t i o n d e l a
t e m p g r a t u r e du b g t o n l o r s d e l a mise e n p l a c e e t q u e l q u e temps a p r s s e n v u e d ' a s s u r e r l a & c u r i t 6 d e l a c o n s t r u c t i o n . C e t t e m6thode s u i t d ' a s s e z p r 6 s l e s e x i g e n c e s d e s normes CSA. Les a u t e u r s c o n c l u e n t q u ' i l f a u d r a i t un procgd6 f i a b l e e t non d e s t r u c t i f d e m i s e 2 l ' e s s a i i n s i t u , p e r m e t t a n t d e s u r v e i l l e r l ' a u g m e n t a t i o n d e l a r g s i s t a n c e , de d g t e r m i n e r 2 q u e l
moment l a r g s i s t a n c e minimale s o u h a i t e g e s t a t t e i n t e e t d ' a s s u r e r que l a p g r i o d e d e p r i s e du b g t o n n ' e s t n i t r o p c o u r t e n i t r o p longue. C e l a G l i m i n e r a i t l ' i n c e r t i t u d e q u i e x i s t e a c t u e l l e m e n t e t r g d u i r a i t p e u t - s t r e
WINTER CONCRETING
- -
CANADIAN PRACTICEby
R . G . Turenne and P.J. Sereda
The degree of s e v e r i t y o f w i n t e r c l i m a t e i n f l u e n c e s t h e techniques used f o r w i n t e r c o n c r e t i n ~ . Although r e p o r t e d i n 1956, t h e c l i m a t i c
information p r e s e n t e d by
hens son'
i s s t i l l v a l i d f o r t h i s p r e s e n t paper. A diagrammatic r e p r e s e n t a t i o n of t h e s e v e r i t y of t h e Canadian w i n t e r i s presented i n Fig. 1, which shows i s o l i n e s of t h e f r e e z i n g index i ndegree-days. (The f r e e z i n g index i s defined a s t h e cumulative t o t a l of t h e monthly n e t f r e e z i n g and thawing degree-days during winter; a degree-day i s t h e u n i t of measurement of t h e d i f f e r e n c e between t h e d a i l y mean temperature
2 and t h e f r e e z i n g p o i n t o f w a t e r . )
The s o c i a l , economic and t e c h n i c a l r e a s o n s f o r maintaining c o n s t r u c t i o n i n year-round a c t i v i t y a r e well known and hence w i n t e r c o n c r e t i n g i s a
common n e c e s s i t y . A t p r e s e n t , w i n t e r c o n c r e t i n g i s c a r r i e d on i n Canada a s a r e g u l a r p r a c t i c e whenever r e q u i r e d by t h e circumstances o f a p r o j e c t . 3 The problems o f w i n t e r c o n c r e t i n g a l o n e a r e n o t considered reason enough t o d e l a y a c o n s t r u c t i o n p r o j e c t even when t h e requirements of t h e f i n i s h e d c o n c r e t e a r e a s demanding a s they were i n t h e c a s e of t h e CN Communication Tower (one of t h e c a s e s r e p o r t e d h e r e i n ) .
The methods used by Canadian b u i l d e r s t o p r o t e c t and c u r e c o n c r e t e placed i n f r e e z i n g weather d i f f e r f o r d i f f e r e n t t y p e s o f j o b s and f o r d i f f e r e n t l o c a t i o n s . The t h r e e Canadian p r o j e c t s s e l e c t e d a s examples a r e considered r e p r e s e n t a t i v e of t y p e s of c o n s t r u c t i o n and c l i m a t i c c o n d i t i o n s . T h e i r l o c a t i o n s a r e shown i n F i g . 1.
Three g e n e r a l c o n t r a c t o r s agreed t o provide d e t a i l s of t h e i r w i n t e r
c o n c r e t i n g p r a c t i c e s on p r o j e c t s j u s t completed o r i n p r o c e s s of c o n s t r u c t i o n . The co-operation r e c e i v e d n o t only from c o n t r a c t o r s , b u t a l s o from d e s i g n e r s , owners, and t e s t i n g l a b o r a t o r i e s , i s g r a t e f u l l y acknowledged.
FERMONT PROJECT
The d e c i s i o n o f t h e Quebec C a r t i e r Mining Company t o work t h e i r o n o r e d e p o s i t s n e a r Mount Wright i n Northern Quebec a l s o e n t a i l e d t h e c o n s t r u c t i o n of a t o w n s i t e f o r t h e f i r m ' s employees. The f u t u r e p o p u l a t i o n o f t h e new town
of Fermont was e s t i m a t e d a t 5,000; accommodation would c o n s i s t o f s i n g l e - f a m i l y d w e l l i n g s , duplexes, townhouses and 3 1/2- and 5 - s t o r e y apartment b u i l d i n g s . The d e s i g n e r s joined a l l t h e apartment b u i l d i n g s t o g e t h e r t o form a windscreen, 600 m long, along t h e n o r t h e a s t edge o f t h e town ( F i g . 2 ) .
The r e g i o n has a f r e e z i n g index o f 2500 degree-days and
i t s
mean Januarytemperature i s - 2 0 ' ~ . Because of t h e s e v e r e c l i m a t e , t h e c o n s t r u c t i o n schedule, a s o r i g i n a l l y drawn up, e l i m i n a t e d w i n t e r c o n c r e t i n g . The e a r l y s t a g e s of t h e p r o j e c t were not s u i t e d t o winterwork and i t was thought t h a t t h e c o s t of hoarding and h e a t i n g c o n c r e t e over such a l a r g e p r o j e c t would be extremely
h i g h . Delays caused t h e schedule t o be modified, however, w i t h t h e r e s u l t
t h a t some w i n t e r c o n c r e t i n g became n e c e s s a r y . I t was r e s t r i c t e d t o t h e cons- t r u c t i o n o f t h e apartment b u i l d i n g s and confined t o two p r i n c i p a l a c t i v i t i e s : (a) p l a c i n g t h e 6-cm-thick e l e v a t e d colicrete s l a b s w i t h i n t h e 5 - s t o r e y
s e c t i o n ;
(b) c o n s t r u c t i o n o f t h e foundations f o r t h e 3 1 / 2 - s t o r e y wood-frame p o r t i o n .
O i l was s e l e c t e d a s t h e s o u r c e o f h e a t because i t was r e a d i l y a v a i l a b l e
l o c a l l y . (Gas would have t o be brought i n by r a i l from Seven I s l a n d s , some
400 km t o t h e s o u t h , and d e l i v e r i e s had a l r e a d y proved u n r e l i a b l e ; e l e c t r i c h e a t i n g was i m p r a c t i c a l a s t h e d i s t r i b u t i o n system was s t i l l under c o n s t r u c t i o n . ) Accordingly, some 40 h e a t i n g u n i t s i n s i z e s . r a n g i n g from 300 t o 500 M J were used.
The e x t e r i o r w a l l s of t h e 5 - s t o r e y apartment b u i l d i n g s were n o t t o be
e r e c t e d u n t i l a l l t h e i n t e r i o r f l o o r s had been concreted a s t h e y would t r a n s m i t any h o r i z o n t a l wind p r e s s u r e s t o t h e columns. Permission was given by t h e d e s i g n e r s , however, t o e r e c t t h e w a l l s a f t e r temporary c r o s s - b r a c i n g s were i n s t a l l e d a t a l l f l o o r l e v e l s . The e x t e r i o r w a l l s t h u s provided an e n c l o s u r e t o work i n . A s i t would be expensive t o h e a t t h e e n t i r c b u i l d i n g f o r t h e s o l e purpose of c o n c r e t i n g and f i n i s h i n g r e l a t i v e l y small f l o o r a r e a s , h e a t i n g was
l i m i t e d t o t h e r e q u i r e d a r e a s by suspending t a r p a u l i n s around t h e p e r i m e t e r o f t h e f l o o r t o be concreted and p l a c i n g h e a t e r s on t h e f l o o r below (Fig. 3 ) .
The h e a t was thug c o n c e n t r a t e d below t h e s l a b ; t h e light-gauge metal pans
s u p p o r t i n g t h e f r e s h c o n c r e t e o f f e r e d no r e s i s t a n c e t o t h e flow o f h e a t through t h e s l a b . The c o n c r e t e f l o o r s were f i n i s h e d , t h e n cured f o r seven days a t a minimum temperature o f 2 0 ' ~ . To reduce l a b o u r c o s t s , t h e h e a t e r s were a l l connected t o c e n t r a l o i l r e s e r v o i r s .
The c o n s t r u c t i o n o f t h e foundations f o r t h e 3 1 / 2 - s t o r e y wood-frame a p a r t - ments posed a d i f f e r e n t problem. A complete temporary e n c l o s u r e was r e q u i r e d i f p r o p e r c o n d i t i o n s were t o be maintained f o r a l l t h e v a r i o u s o p e r a t i o n s i n c l u d i n g f o o t i n g s , basement w a l l s , columns and s t r u c t u r a l f l o o r s l a b s and beams. A h o a r d i n g was t h e r e f o r e designed t o t a k e advantage o f t h e m a t e r i a l s on s i t e which would e v e n t u a l l y be i n c o r p o r a t e d i n t h e s u p e r s t r u c t u r e of t h e b u i l d i n g ( F i g . 4 ) . The wood t r u s s e s t h a t supported t h e r o o f provided a c l e a r
span w i t h l e a n - t o t s added on e i t h e r s i d e t o g i v e t h e r e q u i r e d width. Beams and p o s t s were laminated froni 4- by 14-cm lumber; f l o o r j o i s t s were used f o r t h e l e a n - t o r o o f s . Tile t r u s s e s were assembled i n t o panels and covered with p o l y e t h y l e n e p r i o r t o being h o i s t e d i n t o p l a c e . The e n c l o s u r e performed
s a t i s f a c t o r i l y ; i t even withstood, without damage, winds g u s t i n g t o 100 km/hr ( F i g . 5 ) .
A l l m a t e r i a l s f o r c o n c r e t i n g o p e r a t i o n s were proportioned i n a c e n t r a l b a t c h i n g p l a n t and t r a n s p o r t e d t o t h e c o n s t r u c t i o n s i t e i n truck-mixers. The water, sand and a g g r e g a t e were heated. A l l c o n c r e t e was p l a c e d by means of a truck-mounted c o n c r e t e pump. The t r u c k was equipped with a boom which f a c i l i - t a t e d t h e o p e r a t i o n . The hose through which t h e c o n c r e t e was pumped was
completely wrapped i n i n s u l a t i o n t o p r o t e c t t h e f r e s h c o n c r e t e from c o l d t e m p e r a t u r e s . Although t h e c o n t r a c t o r had c e r t a i n r e s e r v a t i o n s about u s i n g a c o n c r e t e pump under s e v e r e w i n t e r c o n d i t i o n s , t h i s experience proved t o him t h a t pumping i s i n f a c t a n i d e a l method o f p l a c i n g c o n c r e t e d u r i n g c o l d weather.
I n t h e w i n t e r c o n c r e t i n g mix, 320 k g o f cement p e r c u b i c metre of c o n c r e t e
were used w i t h 1'6 calcium c h l o r i d e . Between 4 and 6% a i r entrainment was used depending on t h e exposure. A l l c o n c r e t e was cured f o r seven days a t
was a s s u r e d by a group o f q u a l i f i e d t e c h n i c i a n s . Concrete s t r e n g t h s were
determined from s i t e - and laboratory-cured c y l i n d e r s .
EDMONTON CENTRE
The C i t y o f Edmonton, l o c a t e d i n Western Canada, i s t h e most n o r t h e r l y of
a l l major Canadian c i t i e s ; it i s a l s o one of t h e c o l d e s t . Edmonton has a
f r e e z i n g index o f 1425 degkee-days and a mean January temperature of -lS°C. U n t i l r e c e n t l y , o u t s i d e c o n s t r u c t i o n work p r a c t i c a l l y stopped d u r i n g t h e
w i n t e r months i n Western Canada. However, a s p r o j e c t s became l a r g e r and more
complex and completion d a t e s l e s s f l e x i b l e , techniques were r e f i n e d and most b u i l d e r s now f a c e t h e p r o s p e c t of w i n t e r c o n c r e t i n g w i t h confidence, both
from t h e p o i n t o f view o f c o s t and of q u a l i t y . A good example o f t h i s a t t i t u d e i s found i n t h e c o n s t r u c t i o n o f t h e second o f f i c e tower o f t h e Edmonton Centre complex.
This o f f i c e tower, 29 s t o r e y s h i g h , measures 45.36 m by 30.35
m.
Thes t r u c t u r e c o n s i s t s o f a s t e e l frame w i t h i n t e r i o r s u p p o r t provided by a c o n c r e t e c o r e which c o n t a i n s a l l t h e s e r v i c e s , e . g . , e l e v a t o r s h a f t s , s t a i r w e l l s , wash- rooms and d u c t s p a c e s . The c o n c r e t e c o r e r i s e s 124 m above t h e basement f l o o r
and measures 26.26 m by 9 . 5 m a t i t s base. The w a l l t h i c k n e s s v a r i e s from
81.28 cm a t t h e b a s e t o 20.32 cm a t t h e t o p and t h e s p e c i f i e d c o n c r e t e s t r e n g t h from 34.5 t o 27.6 MPa. The schedule c a l l e d f o r t h e s t e e l t o be e r e c t e d i n t h r e e s t a g e s ; t h e c o n s t r u c t i o n o f t h e c o r e n a t u r a l l y had t o precede t h e s e s t a g e s .
Work s t a r t e d on t h e c o r e i n October 1974 and i t s w a l l s were c o n c r e t e d a t t h e r a t e o f one s t o r e y p e r week. The schedule c a l l e d f o r t h e p l a c i n g of concrete e v e r y Thursday, t h u s p r o v i d i n g c l o s e t o f o u r days o f h e a t i n g and c u r i n g a s t h e e x t e r i o r forms were n o t s t r i p p e d u n t i l t h e f o l l o w i n g Monday. 'Ihe c o n c r e t e was then exposed t o t h e ambient temperature without p r o t e c t i o n .
The forms f o r t h e core w a l l s were o f m e t a l . Because o f t h e d e c r e a s i n g w a l l t h i c k n e s s , s l i p f o r m i n g was i m p r a c t i c a l s o t h e f l y i n g form method was adopted. For w i n t e r c o n c r e t i n g o p e r a t i o n s , t h e e x t e r i o r form was sprayed w i t h polyure- thane foam i n s u l a t i o n t o a t h i c k n e s s o f 4 cm t o minimize h e a t l o s s e s . The 3.66-m-high forms complete with s c a f f o l d s a t v a r i o u s l e v e l s were supported by b o l t s c a s t i n t o t h e p r e v i o u s l y p l a c e d c o n c r e t e . The workmen were p r o t e c t e d from
c o l d weather and winds by t a r p a u l i n s t h a t enclosed a l l t h e o u t s i d e forms (Fig. 6 )
.
A p l a t f o r m which completely covered t h e a r e a bounded by t h e w a l l s was supported by t h e i n t e r i o r forms. When t h e e x t e r i o r forms were r a i s e d t o t h e i r new p o s i t i o n , t h i s p l a t f o r m a c t e d a s a f l o o r f o r t h e workmen, e . g . , when
p l a c i n g t h e r e i n f o r c i n g s t e e l (Fig. 7 ) . When t h e i n t e r i o r forms were r a i s e d i n r e a d i n e s s t o p l a c e a new l i f t , t h e p l a t f o r m served both a s a f l o o r while p l a c i n g c o n c r e t e and a s t h e t o p of t h e hoarding f o r t h e purpose of h e a t i n g and c u r i n g t h e c o n c r e t e w a l l s . H e a t e r s p l a c e d on small panels suspended from t h e main p l a t f o r m burned n a t u r a l gas. These h e a t e r s , r a t e d a t 380 M J , were hooked o n t o a s t e e l p i p e , i n s t a l l e d i n s i d e t h e s t a i r w e l l , which c a r r i e d t h e n a t u r a l g a s t o t h e t o p o f t h e c o r e . This p i p e was extended i n 3.66-m increments
as
each new s t o r e y was completed. A s p e c i a l cap f i t t e d with s i x connections and v a l v e s was a t t a c h e d t o t h e t o p end of t h e p i p e . Rubber hoses were used t o connect t h e h e a t e r s t o t h e supply l i n e . The temperature w i t h i n t h e e n c l o s u r e was maintained a t 1 8 " ~ f o r t h e f o u r days o f h e a t i n g and c u r i n g .Floors f o r t h e t h r e e lower l e v e l s , which housed r e t a i l s t o r e s , were of r e i n f o r c e d c o n c r e t e . The s l a b t h i c k n e s s v a r i e d between 15 and 20 cm. Plywood was used t o form t h e s l a b , columns and beams. Heaters were p l a c e d below t h e
s l a b t o be cured and t h e a r e a enclosed w i t h p o l y e t h y l e n e and canvas. These h e a t e r s , which a l s o burned n a t u r a l gas, were l a r g e r than t h o s e used f o r t h e core; t h e y were r a t e d a t 1950 M J . The temperature w i t h i n t h e e n c l o s u r e was maintained a t about 1 8 " ~ . The s l a b s were n o t r e q u i r e d t o be trowel f i n i s h e d , they were merely s c r e e d e d t o t h e c o r r e c t e l e v a t i o n and given a l i g h t wood f l o a t f i n i s h . A s soon a s t h e c o n c r e t e had hardened s u f f i c i e n t l y , t h e f l o o r s were covered w i t h a 5-cm-thick i n s u l a t i n g b l a n k e t w i t h t h e p o l y e t h y l e n e cover a c t i n g a s a c u r i n g membrane (Fig. 8 ) . Although t h e s e s t r u c t u r a l s l a b s were h e a t e d f o r seven days, s t r i p p i n g o f t h e formwork g e n e r a l l y s t a r t e d on t h e
f o u r t h day. The s p e c i f i e d c o n c r e t e s t r e n g t h f o r t h e f l o o r s was 20 MPa. Columns were n o t heated b u t merely wrapped w i t h i n s u l a t i o n .
Concrete was s u p p l i e d by a f i n whose ready-mix p l a n t was l o c a t e d a s h o r t d i s t a n c e away ( a 10- t o 15-minute d r i v e ) . A l l c o n c r e t c d e l i v c r e d d u r i n g t h e l a t e autumn and w i n t e r was h e a t e d . The temperature o f t h e water, sand and
a g g r e g a t e was c o n t r o l l e d t o g i v e a mixing temperature o f 27OC. The w a t e r and c o a r s e a g g r e g a t e were heated t o about 24OC; t h e temperature o f 'the sand v a r i e d
between 27 and 3 8 ' ~ ~ depending on t h e ambient temperature. A s a r e s u l t , t h e
temperature o f t h e c o n c r e t e d e l i v e r e d a t t h e s i t e was g e n e r a l l y about 18°C. The c o n c r e t e mix was designed t o g i v e a 28-day s t r e n g t h some 15% g r e a t e r than t h e s p e c i f i e d s t r e n g t h . This p r a c t i c e ensured t h a t t h e 28-day s t r e n g t h would n o t f a l l below t h e d e s i g n s t r e n g t h even allowing f o r a 10 t o 12% devia- t i o n . Usually, two a d d i t i v e s were used: an a i r - e n t r a i n i n g a g e n t and a
water-reducing admixture. Calcium c h l o r i d e was a l s o added t o t h e mix occasion-
a l l y a t t h e r e q u e s t o f t h e p r o j e c t s u p e r i n t e n d e n t when a h i g h e a r l y s t r e n g t h
was r e q u i r e d . The amount v a r i e d between 1/2 and 2% i n increments of 1/2%.
Adding water t o t h e c o n c r e t e a t t h e s i t e was discouraged both by t h e c o n c r e t e s u p p l i e r and t h e c o n t r a c t o r . ~ h & n w a t e r had t o be added t o ensure adequate w o r k a b i l i t y , t h e p l a n t was n o t i f i e d immediately by two-way r a d i o and t h e d e l i v e r y s l i p s i g n e d by t h e s u p e r i n t e n d e n t .
A s a r u l e , t h e p l a n t monitored t h e s t r e n g t h of t h e v a r i o u s mixes d a i l y by t a k i n g samples i n o r d e r t o make a complete s e t o f t e s t s (slump and compression u s i n g t h r e e c y l i n d e r s ) f o r every d i f f e r e n t mix s u p p l i e d on any given day. One c y l i n d e r was t e s t e d a t 7 days and two a t 28 days.
A l l c o n c r e t e t e s t i n g a t t h e job s i t e was done by personnel o f an independent
t e s t i n g l a b o r a t o r y . A complete s e t of t e s t s included slump, a i r c o n t e n t ,
c o n c r e t e temperature, and u n i t weight, a s w e l l a s t h e making of t h r e e c y l i n d e r s . The t h r e e c y l i n d e r s were l e f t a t t h e s i t e f o r 24 h b e f o r e being taken t o t h e l a b o r a t o r y f o r c u r i n g . One c y l i n d e r was broken a f t e r 7 days and two a f t e r
28 days
.
Table I shows t h e d a t a o b t a i n e d from t h e c o n c r e t e t e s t r e p o r t s submitted t o t h e g e n e r a l c o n t r a c t o r by t h e t e s t i n g l a b o r a t o r y . These r e s u l t s a r e f o r e i g h t d i f f e r e n t c o n c r e t e b a t c h e s p l a c e d d u r i n g t h e months o f November and December 1974. The s p e c i f i e d c o n c r e t e s t r e n g t h was 34.5 MPa i n a l l c a s e s .
The average 7-day s t r e n g t h o f a l l e i g h t c y l i n d e r s i s 50.12 blPa o r 87.3% of t h e s p e c i f i e d 28-day s t r e n g t h and t h e d e v i a t i o n i s only 3%. The average 28-day s t r e n g t h on t h e o t h e r hand i s 39.76 MPa, which i s v e r y c l o s e t o t h e mix design
s t r e n g t h o f 39.67 MPa. The maximum d e v i a t i o n between c y l i n d e r s t r e n g t h and mix d e s i g n s t r e n g t h i s approximately 6%. These r e s u l t s i n d i c a t e good q u a l i t y c o n t r o l on t h e p a r t o f t h e c o n c r e t e s u p p l i e r .
I n accord w i t h usual Canadian c o n c r e t i n g p r a c t i c e , no attempt was made t o determine t h e i n - p l a c e s t r e n g t h o f t h e c o n c r e t e by t e s t i n g cored samples o r by n o n - d e s t r u c t i v e t e s t methods. I t can be determined from l a b o r a t o r y - c u r e d c y l i n d e r s i f t h e r i g h t c o n c r e t e mix was used i n t h e c o n s t r u c t i o n . I f t h i s proves t o be t h e c a s e , it i s assumed t h a t , p r o v i d i n g t h e f r e s h c o n c r e t e i s given adequate p r o t e c t i o n f o r a c e r t a i n p e r i o d o f time, i t w i l l e v e n t u a l l y develop approximately t h e same s t r e n g t h a s t h e test c y l i n d e r s . The e x p e r i e n c e o f b u i l d e r s i n Canada b e a r s t h i s o u t ; most f a i l u r e s i n v o l v i n g r e i n f o r c e d
c o n c r e t e s t r u c t u r e s experienced i n t h i s c o u n t r y have r e s u l t e d from inadequate c u r i n g immediately f o l l o w i n g t h e p l a c i n g o f t h e c o n c r e t e . I t i s obvious t h a t , from a p r a c t i c a l p o i n t of view, t h e f i r s t t h r e e o r f o u r days o f c u r i n g a r e c r i t i c a l i f t h e c o n t r a c t o r i s t o s t r i p and r e - u s e t h e forms according t o a predetermined s c h e d u l e . The o n l y way t h i s can be done w i t h confidence i s by p r o v i d i n g an environxcnt condccive t o r a p i d c u r i n g .
I t should a l s o be noted t h a t very l i t t l e calcium c h l o r i d e was added t o t h e
c o n c r e t e . The p r a c t i c e ori t h e p r o j e c t was t o add calcium c h l o r i d e o n l y when h i g h e a r l y s t r e n g t h s were r e q u i r e d (when s t r i p p i n g o f forms had t o proceed w i t h i n 24 h , f o r example, o r where anchors were c a s t i n t h e c o n c r e t e which might have t o be loaded v e r y e a r l y ) . Otherwise, i t was b e l i e v e d t h a t t h e 4
t o 7 days o f c u r i n g were s u f f i c i e n t f o r t h e c o n c r e t e t o develop adequate s t r e n g t h without t h e u s e o f calcium c h l o r i d e .
CN COMMUNICATION TOWER, TORONTO
Because o f i t s geographical l o c a t i o n , t h e C i t y o f Toronto enjoys a r e l a t i v e - l y mild w i n t e r . The mean January temperature i s -5°C. The temperature
o c c a s i o n a l l y f a l l s t o -20°C o r climbs t o 10°C d u r i n g t h e month. Winds a r e normally l i g h t , averaging 17 km/h. They seldom exceed 65 km/h with g u s t s of
100 km/h.
The CN Tower i n downtown Toronto (Fig. 9) c o n s i s t s o f a hexagonal c o r e 11 m i n diameter w i t h 61-cm-thick c o n c r e t e w a l l s r i s i n g 446 m above t h e foundation.
The c o r e i s supported by t h r e e b u t t r e s s e s p r o j e c t i n g r a d i a l l y 120' a p a r t .
These b u t t r e s s e s measure 27.4 m by 7 m a t t h e b a s e ; the 1.5-m-thick end w a l l s
t a p e r inwards u n t i l they i n t e r s e c t t h e main c o r e a t t h e 342-m l e v e l . S i d e and i n t e r m e d i a t e w a l l s o f t h e wings a r e 46 cm t h i c k . Sleeves t o r e c e i v e t h e
t e n s i o n i n g c a b l e s were c a s t i n t h e c o r e w a l l s and i n t h e i n t e r m e d i a t e and
end walls o f t h e wings. The tower was p o s t - t e n s i o n e d a t t h e 55-, 170-, 342-,
417- and 451-m l e v e l s .
The tower, i n c l u d i n g t h e wing w a l l s , was c o n s t r u c t e d by t h e s l i p f o r m
method. C a s t i n g began i n l a t e June 1973, and was completed i n February 1974.
I n i t i a l l y , it had been planned t o complete t h e p l a c i n g o f t h e c o n c r e t e by t h e
end o f November, t h u s avoiding w i n t e r c o n c r e t i n g . Progress was slowed down ,
by v a r i o u s f a c t o r s , however, i n c l u d i n g t h e u s e o f s l o w e r - s e t t i n g Type-40 low-heat cement which was used e x c l u s i v e l y f o r t h e f i r s t 122 m. T h e r e a f t e r , t h e low-heat cement was r e p l a c e d by normal p o r t l a n d cement Type 10 i n 10% increments a s t h e weather g o t p r o g r e s s i v e l y c o l d e r . The l a s t 12% of t h e volume o f c o n c r e t e used o n l y normal p o r t l a n d cement.
When it was decided t o c o n t i n u e w i t h t h e c o n s t r u c t i o n o f t h e tower d u r i n g t h e months o f December, January and February, m o d i f i c a t i o n s had t o be made t o t h e s l i p f o r m t o provide h e a t f o r c u r i n g t h e c o n c r e t e a s w e l l a s f o r t h e
comfort o f t h e workmen. The s p e c i f i c requirements o f t h e p r o t e c t i o n system
were:
( a ) t o allow t h e c o n c r e t e t o c u r e a t an e l e v a t e d temperature f o r a p e r i o d o f about 4 days i n o r d e r t o a t t a i n a s t r e n g t h of about 60% o f f i n a l when c o n c r e t i n g was proceeding a t normal r a t e ; and
(b) t o prevent an extreme change i n temperature i n t h e c o n c r e t e when
i t was exposed t o outdoor c o n d i t i o n s
.
I f s l i p f o r m i n g were t o proceed a t t h e r a t e o f 3.65 m p e r day, t h e second requirement would be s a t i s f i e d by suspending an 11-m-high i n s u l a t e d s k i r t from t h e s l i p f o r m . This s k i r t , shown i n Fig. 10, was c o n s t r u c t e d a s follows:
t o p s e c t i o n , 6 m high, o f 2.5-cm-thick r i g i d p o l y s t y r e n e sandwiched between
2 s h e e t s of plywood; middle s e c t i o n , 2.5 m high, o f 1.25-cm-thick s h e e t o f
p o l y s t y r e n e between two s h e e t s o f plywood; bottom s e c t i o n , 2.5 m h i g h , o f plywood. T h i s provided adequate p r o t e c t i o n f o r i n i t i a l s t r e n g t h g a i n . I t
a l s o allowed t h e c o n c r e t e t o cool s u f f i c i e n t l y b e f o r e being exposed t o t h e a t ~ o s p h e r e t o avoid temperature g r a d i e n t s s e v e r e enough t o cause c r a c k i n g ( F i g . 1 1 ) . Some h e a t was provided t o t h e i n t e r i o r of t h e c o r e by a 7,000 M J h e a t e r i n s t a l l e d a t t h e b a s e o f t h e tower.
The s p e c i f i c a t i o n s c d l l e d f o r a minimum c o n c r e t e s t r e n g t h o f 34.5 MPa a t
28 days. The following c o n c r e t e mix p r o p o r t i o n s were s e l e c t e d : kg/rn3
Cement 36 8
Coarse aggregate 1127 (19.5 mm crushed d o l o m i t i c limestone)
Fine sand 712 ( n a t u r a l sand)
Water 154
No a d d i t i v e s were used except f o r an a i r - e n t r a i n i n g agent and a water-reducing
admixture. The water/cement r a t i o was 0.45 and t h e s p e c i f i e d slump 100 mm 212
mm. A i r c o n t e n t was 5% t l .
A b a t c h i n g p l a n t was assembled on t h e s i t e and a l l c o n c r e t e used f o r t h e foundations (7,646 m3) and t h e tower (30,584 m3) was mixed a t t h e job s i t e , As
a r e s u l t , t h e e n g i n e e r s had e x c e l l e n t c o n t r o i o v e r a l l t h e various phases of t h e
c o n c r e t i n g o p e r a t i o n , i n c l u d i n g p r o p o r t i o n i n g o f t h e i n g r e d i e n t s , mixing time, and t h e time r e q u i r e d f o r p l a c i n g t h e c o n c r e t e .
A s t h e ambient temperature d e c r e a s e d , t h e w a t e r used i n t h e c o n c r e t e was h e a t e d , and e v e n t u a l l y t h e sand and aggregate had t o be heated a s w e l l . Maximum
water temperature was s e t a t 5 7 ' ~ ; t h a t of t h e sand was s e t a t 55OC. Although
it was r e l a t i v e l y easy t o maintain a f a i r l y uniform temperature i n t h e sand,
steam h e a t i n g t h e l a r g e r aggregate produced h o t cone-shaped patches surrounded
by c o l d a g g r e g a t e . The heated aggregate t h e r e f o r e had t o be moved t o a n o t h e r
p i l e where i t was thoroughly mixed and l e f t t o reach an even temperature.
An i n - p l a c e c o n c r e t e temperature of about 3 2 " ~ was aimed f o r a s o b s e r v a t i o n s had shown t h a t t h e c o n c r e t e gained s t r e n g t h f a s t e r when p l a c e d a t t h a t tempera-
t u r e than a t , s a y , 20°C. To prevent e x c e s s i v e l o s s of h e a t d u r i n g t h e p l a c i n g of c o n c r e t e , a l l t h e c o n c r e t e was h o i s t e d i n s i d e t h e core s o t h a t t h e bucket
was n o t exposed t o t h e cold a i r and wind on i t s way t o t h e t o p . The conveyor
b e l t which t r a n s p o r t e d t h e c o n c r e t e from t h e t r u c k s t o t h e bucket was h e a t e d by i n f r a r e d lamps.
A f u l l y equipped t e s t i n g l a b o r a t o r y s e t up on t h e s i t e was s t a f f e d 24 h a day d u r i n g s l i p f o r m i n g o p e r a t i o n s . Four qua3 i f i e d t e c h n i c i a n s a s s u r e d
q u a l i t y c o n t r o l . Concrete s t r e n g t h s were determined from c y l i n d e r s measuring
15 cm by 30 cm. Five c y l i n d e r s were c a s t f o r every 57 m3 o f c o n c r e t e . n o
were s u b j e c t e d t o a c c e l e r a t e d t e s t i n g a f t e r 48 h u s i n g t h e autogenous method
developed by Smith and Tiede. ?he o t h e r t h r e e c y l i n d e r s were cured by
s t a n d a r d l a b o r a t o r y fog room methods. One was t e s t e d a t 7 days, two a t 28 days
and one a t 90 days. The c o e f f i c i e n t o f v a r i a t i o n o f a l l c y l i n d e r s t e s t e d a t 28 days based on a mean s t r e n g t h o f 47.6 MPa was 6 . 1 .
With a planned r a t e o f r i s e of 3.65 m p e r day, t h e 2-day a c c e l e r a t e d t e s t s d i d n o t e n a b l e t h e r e s i d e n t e n g i n e e r t o monitor c o n c r e t e s t r e n g t h s as they
developed. I t was t h e r e f o r e decided t o adopt t h e m a t u r i t y t e s t i n g concept
along w i t h t h e 2-day a c c e l e r a t e d t e s t s . A s t r e n g t h m a t u r i t y curve f o r t h e c o n c r e t e mix i n u s e was e s t a b l i s h e d . Thermocouples were i n s t a l l e d i n t h e c o n c r e t e d u r i n g each s h i f t (1.2 m v e r t i c a l s p a c i n g ) . The thermocouple w i r e s were c o i l e d on f r e e - t u r n i n g r e e l s a t t a c h e d t o t h e s l i p f o r m framework s o t h a t t h e w i r e s unwound a s t h e form r o s e and readings could be t a k e n a t r e g u l a r i n t e r v a l s w i t h i n t h e e n c l o s u r e . I n d i v i d u a l thermocouple r e a d i n g s were p l o t t e d a g a i n s t t h e p r e v i o u s l y e s t a b l i s h e d s t r e n g t h - m a t u r i t y curve a s a f u n c t i o n of time and temperature s o t h a t t h e i n - p l a c e s t r e n g t h o f t h e c o n c r e t e could be p r e d i c t e d a s it developed (Fig. 1 2 ) . V e r i f i c a t i o n o f t h e i n - p l a c e s t r e n g t h and of t h e m a t u r i t y concept was o b t a i n e d from t h e t e s t i n g of c o n c r e t e c y l i n d e r s cored o u t o f t h e tower w a l l s .
These two t e s t i n g methods, a c c e l e r a t e d c u r i n g and s t r e n g t h m a t u r i t y measure- ment, demonstrated t h e adequacy o f t h e c o n c r e t e and t h u s t h e s a f e t y o f t h e s t r u c t u r e . The c o n c r e t i n g crew, however, could not w a i t f o r t h e s e r e s u l t s t o determine t h e s a f e r a t e o f c o n c r e t e p l a c i n g a t any given time. I t was n e c e s s a r y t o determine q u i c k l y and a c c u r a t e l y i f t h e 8-h-old c o n c r e t e was hard and s t r o n g enough t o be s l i p p e d o u t of t h e forms; n e i t h e r t e s t i n g method could provide t h i s
information. A s a r e s u l t , a very simple t e s t was devised which proved r e l i a b l e .
I t c o n s i s t e d i n having a man push a smooth s t e e l b a r 1 cm i n diameter i n t o t h e f r e s h c o n c r e t e and measure t h e depth o f p e n e t r a t i o n t o t h e hardened c o n c r e t e .
depth o f t h e s l i p f o r m . The depth of p e n e t r a t i o n was o b t a i n e d by measuring t h e v e r t i c a l d i s t a n c e between t h e t o p of t h e form and t h e mark on t h e b a r . When t h e measured l e n g t h was l e s s t h a n 60 cm, t h e r a t e o f pour was a c c e l e r a t e d ; when t h e l e n g t h was g r e a t e r t h a n 60 cm, t h e r a t e was slowed down.
The r a t e o f hardening of t h e c o n c r e t e was a f f e c t e d by t h e temperature
w i t h i n t h e e n c l o s u r e . Although t h e c o n t r a c t o r t r i e d t o maintain t h e temperature a t about 20°C, e x c e s s i v e a i r leakage d u r i n g high wind c o n d i t i o n s sometimes
caused t h e temperature t o drop considerably. Operations u s u a l l y had t o be suspended when t h e i n s i d e temperature.approached t h e f r e e z i n g p o i n t a s t h e c o n c r e t e was no longer s e t t i n g p r o p e r l y . The winds t h a t caused such drops i n temperature were u s u a l l y s o s t r o n g a s t o make t h e use of t h e tower crane
hazardous. A s no more than a one-hour supply of r e i n f o r c i n g s t e e l could be s t o c k - p i l e d i n t h e working a r e a a t o p t h e tower a t any t i m e , c o n c r e t i n g o p e r a t i o n s u s u a l l y had t o s t o p .
The c o r e was topped on 22 February 1974; s t i l l t o be added was t h e 4.88-m- t h i c k s l a b t o r e c e i v e t h e s t e e l antenna. Although t h e e x t r a c o s t i n terms of p r o t e c t i o n , h e a t i n g and reduced p r o d u c t i v i t y because o f a slower r a t e of pour was high, t h i s w i n t e r c o n c r e t i n g o p e r a t i o n was v e r y s u c c e s s f u l , and prevented t h e u n d e s i r a b l e e f f e c t s t h a t a t h r e e - o r four-month shutdown might have had on t h e p r o j e c t ' s u l t i m a t e completion.
GENERAL DISCUSSION AND CONCLUSIONS
The t h r e e p r o j e c t s d e s c r i b e d i n t h i s p a p e r p r e s e n t evidence t h a t , i n
Canada, w i n t e r c o n c r e t i n g i s c a r r i e d o u t s u c c e s s f u l l y on a l l t y p e s of c o n s t r u c - t i o n from housing u n i t s t o l a r g e s t r u c t u r e s such a s t h e CN Tower.
The survey showed t h a t t h e methods t o p r o t e c t c o n c r e t i n g i n c o l d weather d i f f e r on d i f f e r e n t t y p e s o f c o n s t r u c t i o n ; however, a l l t h e methods follow one b a s i c p r i n c i p l e , i . e . , t h a t t h e temperature o f t h e c o n c r e t e a t t h e time of p l a c i n g and f o r a p e r i o d t h e r e a f t e r i s c o n t r o l l e d t o allow t h e development of t h e minimum s t r e n g t h r e q u i r e d t o ensure t h e s a f e t y o f t h e s t r u c t u r e .
Canadian c o n c r e t i n g p r a c t i c e i s o u t l i n e d i n s t a n d a r d s o f t h e Canadian 5
Standards A s s o c i a t i o n . P a r t i c u l a r emphasis is p l a c e d on t h e temperature of t h e mix and t h e p r o t e c t i o n requirements. Tables I 1 and I 1 1 a r e based on t h i s
s t a n d a r d . Canadian Standards a l s o provide f o r t h e a d d i t i o n o f a c c e l e r a t i n g a g e n t s such a s calcium c h l o r i d e by up t o 2% by weight o f cement i n t h e c o n c r e t e mix. This i s normally a t t h e d i s c r e t i o n o f t h e engineer i n charge. The u s e of calcium c h l o r i d e i s not allowed i n p r e s t r e s s e d c o n c r e t e n o r i n s u l f a t e - r e s i s t i n g c o n c r e t e . Only two o f t h e t h r e e c a s e s d i s c u s s e d i n t h i s paper made u s e of an a c c e l e r a t i n g agent and i n amounts l e s s t h a n t h e l i m i t set by t h e s t a n d a r d .
Other u s e f u l s o u r c e s of information a r e t h e p u b l i c a t i o n s o f t h e American 1 Concrete I n s t i t u t e , e . g . , r e f s . 7 and 8.
As t h e r e have been only few s t r u c t u r a l f a i l u r e s r e s u l t i n g from w i n t e r c o n c r e t i n g i n t h e p a s t 25 y e a r s , i t can be concluded t h a t p r e s e n t p r a c t i c e i s adequate t o ensure good r e s u l t s . Nevertheless, i t w i l l n o t be p o s s i b l e t o a s s e s s a c c u r a t e l y t h e l e v e l of s a f e t y a t t a i n e d o r whether t h e s e p r a c t i c e s a r e e x c e s s i v e u n t i l such time a s n o n - d e s t r u c t i v e methods o f t e s t i n g of s t r e n g t h development have been adopted f o r f i e l d i n s p e c t i o n . Current t e s t i n g of
c o n c r e t e c y l i n d e r s ensures o n l y t h a t t h e c o n c r e t e has t h e p o t e n t i a l t o develop t h e d e s i g n s t r e n g t h and n o t t h a t i t w i l l i n a p a r t i c u l a r s i t u a t i o n . Experience of c o n t r a c t o r s , however, g i v e s confidence t o t h e b e l i e f t h a t c o n c r e t e which i s given t h e minimum r e q u i r e d p r o t e c t i o n i n t h e f i r s t few days w i l l eventua1J.y develop t h e s t r e n g t h i n d i c a t e d by t h e s e t e s t s .
I
ACKNOWLEDGEMENTSThe a u t h o r s g r a t e f u l l y acknowledge t h e co-operation of t h e following d e s i g n e r s , c o n t r a c t o r s , owners and engineers i n providing information t o t h e D i v i s i o n and wish t o thank them f o r t h e i r c o n t r i b u t i o n t o t h i s paper:
Surveyer, Nenniger & Chenevert I n c .
,
Montreal ; Pentagon Construction (1969) Co. Ltd., Montreal; Poole Construction Limited, Edmonton; R.M. HardyG
Associates L t d . , Edmonton; Alberta Concrete Products Co. L t d . , Edmonton; N i c o l e t , C a r r i e r , DresselG
Associes, Montreal; The Foundation Conlpany o f Canada Limited, Toronto; C . N . Communication Tower, Toronto; The Trow Group-
Construction T e s t i n g S e r v i c e s Limited, Toronto.This paper i s a c o n t r i b u t i o n from t h e Division o f Building Research,
National Research Council o f Canada, and i s published with t h e approval of t h e D i r e c t o r of t h e Division.
REFERENCES
1 Swenson, E.G. Weather i n r e l a t i o n t o w i n t e r c o n c r e t i n g . Proceedings of t h e RILEM Symposium on Winter Concreting, Theory and P r a c t i c e , Copenhagen, 1956.
2 Boyd,
D.W.
Normal f r e e z i n g and thawing degree-days f o r Canada 1931-1960. Canada, Dept o f t h e Atmospheric Environment S e r v i c e , CLI 4-73.3 Crocker, C.R. Winter c o n s t r u c t i o n i n Canada. Build I n t e r n a t i o n a l , Vol. 4 ,
No. 6 , Nov-Dec 1971, p. 326-330.
4 Smith, P , , and Tiede, H. E a r l i e r d e t e r m i n a t i o n o f c o n c r e t e s t r e n g t h p o t e n t i a l . Highway Research Board, HRB Record No. 210, Washington, D.C.,
1967, p . 29-66.
5 Canadian Standards Association,CSA Standard A23.1-1973. Concrete m a t e r i a l s and methods o f c o n c r e t e c o n s t r u c t i o n . [Tables 1 2 and 13)
.
6 Canadian S t a n d a r d s ~ s s o c i a t i o n , CSA Standard A266.4, Guidelines f o r t h e u s e of admixtures i n concrete'.
? American Concrete I n s t i t u t e , A C I Standard 306-66. Recommended p r a c t i c e f o r c o l d weather c o n c r e t i n g ( r e a f f i r m e d 1972).
8 American Concrete I n s t i t u t e . Behavior o f c o n c r e t e under temperature extremes. ACI P u b l i c a t i o n SP-39, 1973.
TABLE I
RESULTS OF CONCRETE TESTS
Calcium
A i r Unit c h l o r i d e ,
Slump, e n t r a i n e d , w t . , Temperaturc,'C C o n c r e t e s t r e n g t h , MPa
O
(by w t .cm % kg/m3 ' Mix A i r 7 d a y s 28 days128 days o f cement)
I
7 . 6 2 . 8 2335 1 9 . 5 - 0 . 5 30.77 n o t a v a i l a b l e 1 / 2 6 . 3 2 . 5 2345 20.0 1 . 0 29.19 39.81 38.78 1 / 2 7 . 0 2 . 6 2313 21.0 - 4 . 5 30.15 40.50 40.36-
10.2 3 . 0 2307 2 1 . 0 0 30.02 40.64 41.74 1 / 2 8 . 9 4 . 5 2307 1 8 . 0 0 . 5 29.88 39.05 3 7 . 3 3 - 7 . 6 2.8 2307 1 8 . 0 - 6 . 0 30.84 41.88 40.85-
8 . 9 3 . 2 2326 1 8 . 0 1 . 0 29.81 39.54 40.50-
10.2 3 . 7 2323 12.0 0 29.39 38.09 37.60-
TABLE I 1 CONCRETE TEMPERATURES FOR COLD WEATHER CONSTRUCTIONI
T e m p e r a t u r e sI
Maximum A l l o w a b l e Gradual Drop o f C o n c r e t e T e m p e r a t u r e C o n c r e t e a s P l a c e d , For Each 2 4 - h r p e r i o d a t L e a s t Dimension Miniinum/Maximum,*
T e r m i n a t i o n o f P r o t e c t i o n o f S e c t i o n Degrees C Degrees C Less t h a n 0 . 3 0 TPI
I 13/32 I 2 8 G r e a t e r t h a n 1 . 8 0 m t 4 . 5 / 2 1I
11" C o n c r e t e t e m p e r a t u r e a t
time
o f mixing s h a l l n o t exceed t h e maximumshown i n T a b l e . C o n c r e t e t e m p e r a t u r e a t time o f p l a c i n g s h o u l d b e
TABLE I11
PROTECTION AND CURING REQUIREMENTS FOR COLD WEATHER CONSTRUCTION
.. . - .-
Outside Air Temperature Least Dimension of Section
During Protection Feriod Less than 0.90 m Greater than 0.90 m
Below -12'~ see Note 1 see Note 2
From -12OC to -l°C see Note 2 see Note 3
From -l°C to 10°c see Note 3 see Note 4
Notes
1. Complete housing plus supplementary heat or adequate insulation.
2. Enclose with suitable covering plus supplementary heat or adequate insulation.
3 . Enclose with suitzble covering with supplementary heat in readiness or adequate insulation
1 , 5 ARE 3 112 STOREY APARTMENT BUILDINGS
2 , 3 . 4 ARE 5 STOREY APARTMENT B U I L D I N G S
F I G U R E 2 W I N D S C R E E N L A Y O U T . F E R M O N T P R O J E C T INSULATED BUILT-UP WALLS ERECTED BEFORE CONCRETING OF FLOORS WAS STARTED F I G U R E 3 S E C T I O N T H R O U G H 5 S T O R E Y W I N D S C R E E N B U I L D I N G , F E R M O N T P R O J E C T :
6.10 m 1 2 . 8 rn 2 . 6 m
-
BASEMENT ONLY - 3 112 STOREY APARTMENT BUILDING WITH MALL ' PATIO AT UNDERGROUND PARKING
GROUND LEVEL
ROOF TRUSSES, FLOOR JOISTS AND WALL STUDS USED I N ERECTING THIS TEMPORARY SHELTER
GROUND FLOOR SLAB
I I 1 I I I I I I I r - l L-,-U- - - - _ . A - - - - A F I G U R E 4 C R O S S - S E C T I O N T H R O U G H F O U N D A T I O N OF 3 112 S T O R E Y W I N D S C R E E N B U I L D I N G S H O W I N G O U T L I N E O F T E M P O R A R Y S H E L T E R . F E R M O N T P R O J E C T
F I G . 5 Temporary e n c l o s u r e , Fermont p r o j e c t ( c o u r t e s y Pentagon Construction (1969) Co. L t d . )
F I G . 6 Photograph o f c o n c r e t e c o r e showing p r o t e c t i o n around formwork, Edmonton C e n t e r
r * u I 1 1 E X T E R I O R F O R M I N ' I
/
R A I S E D P O S I T I O N I Y W O O D P L A T F O R M A C T S A S D E C K,
, W H I L E P L A C I N G C O N C R E T E . 1 1 R E I N F O R C I N G B A R S , S L E E V E S , ETC A N D A S E N C L O S U R E W H I L E C U R I N Gi /
C O N C R E T E W A L L S 1 1I
W O O D F R A M E A N D l N T E R l O R C A N V A S E N C L O S U R E F O R M W O R K I N C O N C R E T I N G A N D C U R I N G P O S I T I O N E X T E R I O R F O R M S P R A Y E D W I T H P O L Y U R E T H A N E F O A M I N S U L A T I O N C O R E W A L L ' S T H I C K N E S S V A R I E S F R O M 8 1 . 2 8 crn A T B A S E T O 2 0 . 3 2 crn A T T O P E X T E R I O R F I G U R E 7 T Y P I C A L S E C T I O N T H R O U G H E X T E R I O R W A L L A N D F O R M W O R K O F C O N C R E T E C O R E . E D M O N T O N C E N T E RFIG. 8 I n s u l a t i n g b l a n k e t s p r o t e c t i n g newly p l a c e d c o n c r e t e f l o o r , Edmonton Centre
F I G . 9 View o f tower showing w i n t e r p r o t e c t i o n and working a r e a a t t h e t o p o f t h e s l i p f o r m , CN Communication Tower (Courtesy CN Tower)
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