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Alkali-aggregate reaction in Nova Scotia. II. Field and petrographic
studies
Duncan, M. A. G.; Gillott, J. E.; Swenson, E. G.
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CEMENT and CONCRETE RESEARCH. Vol
.
3, pp. 11 9-128, 1973. Pergamon Press, I n c . P r i n t e d i n t h e U n i t e d S t a t e s .ALKALI-AGGREGATE REACTION IN NOVA SCOTIA Kt. F I E L D AND P E T R O G R A P H I C STUDIES
M . A. G. Duncan, A t l a n t i c I n d u s t r i a l R e s e a r c h I n s t i t u t e , H a l i f a x , now with M i n i s t r y of R o a d s , S a l i s b u r y , R h o d e s i a ,
J . E . Gillott, Div. of Building R e s e a r c h , Nat. R e s . C o u n c i l of C a n a d a , now with Univ. of C a l g a r y , C a l g a r y , A l b e r t a , and
E.
G. Swenson, Div. of Building R e s e a r c h , Nat. R e s . C o u n c i l of C a n a d a .(Communicated by G . M. I d o r n ) ABSTRACT C e r t a i n s i l i c e o u s a n d s e d i m e n t a r y r o c k s in Nova S c o t i a , when u s e d a s a g g r e g a t e with h i g h a l k a l i c e m e n t , h a v e p r o d u c e d e x - c e s s i v e e x p a n s i o n of c o n c r e t e . L a b o r a t o r y s t u d i e s s h o w e d a t y p e of a l k a l i - a g g r e g a t e r e a c t i o n t o b e r e s p o n s i b l e . R o c k t y p e s i n s t r u c t u r e s a n d in a g g r e g a t e s o u r c e s w e r e i d e n t i f i e d b y p e t r o - g r a p h i c e x a m i n a t i o n , t h e m a i n t y p e s b e i n g s e l e c t e d f o r s t u d y of a l k a l i - r e a c t i v i t y . SOMMAIRE / E n Nouvelle-Ecosse,llutilisation d e c e r t a i n e s r o c h e s s i l i c e u s e s e t s h d i m e n t a i r e s c o m m e g r a n u l a t a v e c d u c i m e n t r i c h e e n a l c a l i a p r o d u i t une d i l a t a t i o n e x c e s s i v e d u bhton. D e s a n a l y s e s e n l a b o r a t o i r e en r e n d e n t r e s p o n s a b l e une s o r t e d e r g a c t i o n e n t r e l t a l c a l i e t l e g r a n u l a t . On a i d e n t i f i e c e s t y p e s d e r o c h e d a n s d e s s t r u c t u r e s e t s o u r c e s d e g r a n u l a t a u m o y e n c r e x a m e n s p e t r o g r a - p h i q u e s , e t on e n a c h o i s i l e s t y p e s p r i n c i p a u x p o u r Q t u d e d e r e - a c t i v i t h d e l r a l c a l i .
V o l . 3, No. 2 A L K A L I AGGREGATE REACTION, F I E L D STUDIES, PETROGRAPHY
I n t r o d u c t i o n
An i n v e s t i g a t i o n of t h e a l k a l i - a g g r e g a t e r e a c t i o n o c c u r r i n g i n Nova S c o t i a h a s a l r e a d y b e e n d e s c r i b e d (1, 2 ) . T h i s p a p e r d e s c r i b e s i n b r i e f t h e geology of Nova Scotia, t h e e x t e n s i v e field examination of s t r u c t u r e s and t h e d e t a i l e d p e t r o g r a p h i c a n a l y s i s of c o n c r e t e c o r e s and r o c k s f r o m a g g r e g a t e s o u r c e s i n t h e P r o v i n c e . An i m p o r t a n t p h a s e of t h i s i n v e s t i g a t i o n w a s t h e s e l e c t i o n of r o c k t y p e s f o r l e n g t h c h a n g e s t u d i e s , b a s e d on f i e l d and p e t r o - g r a p h i c e x a m i n a t i o n of a f f e c t e d a n d nonaffected s t r u c t u r e s a s w e l l a s on a g - g r e g a t e s o u r c e s . F i e l d e v i d e n c e of e x c e s s i v e e x p a n s i o n of c o n c r e t e h a d b e e n o b s e r v e d o v e r s o m e 3 5 y e a r s and s e v e r a l i n v e s t i g a t i o n s h a d b e e n m a d e without pinpointing t h e c a u s e . A l k a l i - a g g r e g a t e r e a c t i o n had b e e n s u s p e c t e d but t h e e x t r e m e s l o w n e s s of t h e e x p a n s i o n and t h e c o m p l e x geology of t h e a r e a m a d e t h i s s u p - p o s i t i o n difficult t o d e m o n s t r a t e b y l a b o r a t o r y e x p e r i m e n t . Pr e l i r n i n a r y m i c r o s c o p i c e x a m i n a t i o n of c o n c r e t e c o r e s a n d r o c k s a m p - l i n g s w e r e m a d e a t t h e Nova S c o t i a T e c h n i c a l C o l l e g e ( 3 ) . M o r e d e t a i l e d p e t r o g r a p h i c a n a l y s i s w a s d o n e a t 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 of Canada, Division of Building R e s e a r c h . G e o l o e i c a l B a c k e r ound T h e r o c k s of t h e M a r i t i m e P r o v i n c e s of E a s t e r n C a n a d a a r e p a r t of t h e A p p a l a c h i a n p r o v i n c e which e x t e n d s f r o m c e n t r a l A l a b a m a t o Newfoundland. In Nova S c o t i a t h e r o c k s a r e m a i n l y of P a l a e o z o i c a g e and w e r e folded and r e - gionally m e t a m o r p h o s e d d u r i n g m o u n t a i n building m o v e m e n t s i n t h e l a t e r p a r t of t h a t p e r i o d . T h e r e a r e a l s o M e s o z o i c r o c k s and s u r f i c i a l d e p o s i t s f o r m e d d u r i n g t h e P l e i s t o c e n e ; t h e s e h a v e s i n c e b e e n r e d i s t r i b u t e d and e r o d e d t o s o m e e x t e n t .
L o w e r O r d o v i c i a n s e d i m e n t a r i e s and m e t a s e d i m e n t a r i e s belong t o t h e Megurna g r o u p which i s divided i n t o t h e o l d e r Goldenville F o r m a t i o n , and t h e younger H a l i f a x F o r m a t i o n . T h e o l d e r r o c k s c o n s i s t p r e d o m i n a n t l y of g r e y - w a c k e with m i n o r s l a t e , s c h i s t a n d c o n g l o m e r a t e . T h e o v e r l a y i n g H a l i f a x F o r m a t i o n c o n s i s t s m a i n l y of thinly bedded s l a t e s , a r g i l l i t e s , s i l t s t o n e s a n d
V o l . 3, No. 2 121 A L K A L I AGGREGATE REACTION, F I E L D STUDIES, PETROGRAPHY
In m u c h of s o u t h - c e n t r a l Nova S c o t i a t h e r e a r e L o w e r o r Middle Devoni- a n g r a n i t e s . T h e r e a r e a l s o b a s i c i n t r u s i o n s . I n n o r t h - c e n t r a l Nova S c o t i a the s e d i m e n t a r y r o c k s a r e m a i n l y of M i s s i s s i p p i a n and P e n n s y l v a n i a n a g e . They c o n s i s t of s h a l e s , s a n d s t o n e s , c o n g l o m e r a t e s , l i m e s t o n e s , c o a l m e a - s u r e s , gypsum, a n h y d r i t e and s a l t . T h e M e s o z o i c r o c k s occupy a f a u l t t r o u g h f r o m the Bay of Fundy to Chedabucto Bay. They a r e c o m p o s e d of c o n - g l o m e r a t e s , s a n d s t o n e s , s h a l e s , a m y g d a l o i d a l b a s a l t i c l a v a s and s m a l l o u t - c r o p p i n g s of a r e n a c e o u s l i m e s t o n e and c a l c a r e o u s s a n d s t o n e a t t h e top. T h e h a r d e r a n d m o r e r e s i s t a n t b a s a l t s f o r m t h e r i d g e of N o r t h Mountain. In t h e P l e i s t o c e n e , t i l l o r b o u l d e r c l a y and d r u m l i n s b l a n k e t the b e d r o c k . D e p o s i t s of t h i s s o r t a r e g e n e r a l l y l e s s s a t i s f a c t o r y s o u r c e s of c o n c r e t e a g - g r e g a t e b e c a u s e of t h e high p e r c e n t a g e of f i n e s .
Glacio-fluvial d e p o s i t s which include outwash p l a i n s , e s k e r s a n d k a m e s a r e a l s o w i d e s p r e a d in Nova S c o t i a and a r e m o r e s a t i s f a c t o r y s o u r c e s of f i n e and c o a r s e a g g r e g a t e f o r c o n c r e t e . (Maps of t h e s e d e p o s i t s a r e being p r e - p a r e d by the Nova S c o t i a R e s e a r c h Foundation,) B e a c h e s i n Nova S c o t i a a r e t h e r e s u l t of r e c e n t r e d e p o s i t i o n of g l a c i a l d e p o s i t s a n d p o s t g l a c i a l e r o s i o n of b e d r o c k .
I n s u m m a r y , t h e s o u t h e r n half of the P r o v i n c e i s u n d e r l a i n ' b y g r e y w a c k e s , q u a r t z i t e s , s l a t e s and phyllites, invaded by g r a n i t e s of a t l e a s t two a g e s and by m i n o r b a s i c i n t r u s i v e s ; the n o r t h e r n half i s u n d e r l a i n by r o c k s of t h e Ap- p a l a c h i a n type on which w e r e d e p o s i t e d a l t e r n a t i n g t e r r e t i l l and m a r i n e s e d i - m e n t s . S u r f i c i a l d e p o s i t s of s a n d s , g r a v e l s a n d t i l l w e r e d e p o s i t e d b y f l u v i o - g l a c i a l a c t i o n a n d . i n m a n y c a s e s c o n s i s t of m a t e r i a l s f r o m widely s e p a r a t e d s o u r c e s .
F i e l d C o n c r e t e
E v i d e n c e of e x c e s s i v e expansion i n f i e l d c o n c r e t e s in Nova Scotia could be d e t e c t e d only a f t e r s o m e 12 t o 15 y e a r s of s e r v i c e . U s u a l m a n i f e s t a t i o n s w e r e h o r i z o n t a l off-setting, s q u e e z i n g out of e x p a n s i o n joint f i l l e r , warping of s t r u c t u r a l c o m p o n e n t s , and m i s a l i g n m e n t of m a c h i n e r y . M e a s u r e m e n t s i n e a r l y s t u d i e s showed c l e a r l y t h a t expansion i n s o m e h y d r a u l i c s t r u c t u r e s was continuing a t a s i g n i f i c a n t r a t e a f t e r 3 0 o r m o r e y e a r s . M a p c r a c k i n g
V o l . 3, N o . 2 A L K A L I AGGREGATE R E A C T I O N , F I E L D S T U D I E S , PETROGRAPHY a n d o t h e r f o r m s of d e t e r i o r a t i o n w e r e c o n s e q u e n c e s of e x c e s s i v e e x p a n s i o n b u t could n o t b e u s e d a s d i r e c t e v i d e n c e b e c a u s e of o t h e r d e s t r u c t i v e m e c h a - n i s m s t h a t m i g h t h a v e b e e n p r e s e n t . F r o s t a c t i o n had c l e a r l y b e e n r e s p o n s i b l e f o r c o n s i d e r a b l e d a m a g e t o c o n c r e t e and i t s a c t i o n i n m a n y s t r u c t u r e s tended t o o b s c u r e e x p a n s i o n d u e t o a l k a l i - a g g r e g a t e r e a c t i o n . M o s t of the s t r u c t u r e s w e r e b u i l t b e f o r e a i r - e n t r a i n m e n t w a s widely used, m a k i n g i t c e r t a i n t h a t m u c h d e t e r i o r a t i o r w a s c a u s e d by f r e q u e n t f r e e z e - t h a w cycling p r e v a l e n t i n t h i s r e g i o n . R e c o r d s of s o u r c e s of c e m e n t and a g g r e g a t e , of m i x p r o p o r t i o n s , and o t h e r i n f o r m a t i o n on c o n c r e t e u s e d w e r e r a r e l y a v a i l a b l e . A s often a s not, a g g r e g a t e s u s e d i n t h e o r i g i n a l c o n s t r u c t i o n w e r e t r a n s p o r t e d o v e r c o n s i d e r - a b l e d i s t a n c e s . A g g r e g a t e s w e r e c o m m o n l y m a d e f r o m g r a v e l and b e a c h d e - p o s i t s and i n v a r i a b l y c o n t a i n e d a h e t e r o g e n e o u s m i x t u r e of r o c k t y p e s a s c a n b e e x p e c t e d f r o m the geology of t h i s p a r t of the A p p a l a c h i a n s .
S t r u c t u r e s which showed t h e c l e a r e s t e v i d e n c e of e x c e s s i v e expansion, a n d which could b e e x p e c t e d to b e s u s c e p t i b l e b e c a u s e of t h e a v a i l a b i l i t y of e x c e s s i v e m o i s t u r e , included g r a v i t y d a m w a l l s , s p i l l w a y s , p o w e r h o u s e s , c a n a l s a n d b r i d g e s .
Among t h e s e v e r a l f i e l d s u r v e y s m a d e d u r i n g t h i s i n v e s t i g a t i o n w a s a s y s t e m a t i c "condition s u r v e y " of 176 c o n c r e t e s t r u c t u r e s . Of t h e 117 t h a t p r e d a t e d 1940, 101 w e r e judged unsound and of t h e s e 63 a p p e a r e d t o h a v e
s u f f e r e d e x c e s s i v e expansion, p r e s u m e d t o b e d u e t o a l k a l i - a g g r e g a t e r e - a c t i o n . Of the 59 s t r u c t u r e s postdating 1940, 30 w e r e judged t o b e unsound a n d of t h e s e 15 a p p e a r e d t o b e a f f e c t e d by a l k a l i - a g g r e g a t e r e a c t i o n . F i g u r e 1 s h o w s a n e x a m p l e of a type of d e t e r i o r a t i o n a s s o c i a t e d with t h e Nova S c o t i a
r e a c t i o n . P e t r o g r a p h y of C o n c r e t e s S e v e n t y - f i v e c o r e s w e r e t a k e n m a i n l y f r o m a f f e c t e d f i e l d s t r u c t u r e s , b u t a l s o s o m e f r o m s t r u c t u r e s judged to h a v e b e e n unaffected by a l k a l i - a g g r e g a t e r e a c t i o n . T h e c o r e s w e r e e x a m i n e d m i c r o s c o p i c a l l y f o r e v i d e n c e of a l k a l i - a g g r e g a t e o r o t h e r r e a c t i o n and to d e t e r m i n e t h e r o c k t y p e s p r e s e n t a s a g g r e g a t e s . S u b s e q u e n t l y 45 of t h e s e c o r e s w e r e s u b j e c t e d to m o r e d e t a i l e d
V o l . 3 , N o . 2 1 2 3 A L K A L I AGGREGATE REACTION, F I E L D S T U D I E S , PETROGRAPHY
FIG. 1
P a t t e r n c r a c k i n g i n c o n - c r e t e of a b u t t r e s s p i e r i n a Nova S c o t i a d a m .
p e t r o g r a p h i c a n a l y s i s , using m a t e d thin and p o l i s h e d s e c t i o n s . T a b l e I shows t y p i c a l e x a m p l e s of a n a l y s e s of r o c k t y p e s p r e s e n t i n f i v e c o n c r e t e c o r e s t a k e n f r o m widely s e p a r a t e d s t r u c t u r e s in t h e p r o v i n c e . T A B L E I Aggregate A n a l y s e s of F i v e C o r e s Showing T y p i c a l D i s t r i b u t i o n of R o c k T y p e s i n Nova S c o t i a C o n c r e t e s 0 . 6 1 6 . 2 1 . 4 1 0 . 5 0. 6 S y e n i t e s C a r b o n a t r s S l a t c s T o t a l p c r c c n t 1 0 0 . 0 3 . 6 1 0 0 . 0 9 9 . 9 0 . 5 1. I 9 9 . 2 3 . 7 9 9 . 9
V o l . 3, No. 2 A L K A L I AGGREGATE REACTION, F I E L D STUDIES, PETROGRAPHY
T h e c o r e e x a m i n a t i o n s , i n d e p e n d e n t of t h e m o r e d e f i n i t e c o n f i r m a t i o n o b - t a i n e d i n s u b s e q u e n t l e n g t h - c h a n g e s t u d i e s , s h o w e d t h a t o n e o r m o r e of c e r - t a i n r o c k t y p e s w e r e a l w a y s p r e s e n t w h e r e e x p a n s i o n a n d c r a c k i n g h a d o c c u r - r e d a n d t h e c a u s e a p p e a r e d t o b e d u e to a n i n t e r n a l r e a c t i o n . T h e s e r o c k t y p e s w e r e m a i n l y t h e g r e y w a c k e s , a r g i l l i t e s a n d p h y l l i t e s , w i t h o t h e r r o c k t y p e s s u c h a s s c h i s t s , r h y o l i t e s and s o m e q u a r t z i t e s a l s o involved i n r e a c t i o n a n d e x p a n s i o n . L a t e - r v o l u m e c h a n g e d a t a c o n f i r m e d a n d m o r e c l e a r l y p i n - p o i n t e d t h e r o c k t y p e s t h a t w e r e a l k a l i - e x p a n s i v e t o a n e x c e s s i v e d e g r e e . I n i t i a l m i c r o s c o p i c e v i d e n c e f o r t h e p r e s e n c e of a l k a l i - a g g r e g a t e r e - a c t i o n w a s s o u g h t i n t e r m s of t h a t p r e v i o u s l y f o u n d i n c a s e s of a l k a l i - s i l i c a r e a c t i o n s ; t h i s w a s t h e p r e s e n c e of known d e l e t e r i o u s l y r e a c t i v e m i n e r a l s a n d r o c k t y p e s , t h e d e g r e e of g e l f o r m a t i o n , t h e p r e s e n c e of r e a c t i o n r i m s on a g g r e g a t e s , a n d c e r t a i n t y p e s of m i c r o f r a c t u r e i n t h e r o c k p a r t i c l e a n d c e - m e n t p a s t e . I t w a s found t h a t p o t e n t i a l l y a l k a l i - s i l i c a r e a c t i v e m i n e r a l s a n d r o c k t y p e s s u c h a s o p a l a n d c h e r t , a n d s i l i c a - r i c h c r y p t o c r y s t a l l i n e a n d g l a s s y v o l c a n i c r o c k s , e . g . , s i l i c a - r i c h r h y o l i t e s , a n d e s i t e s , a n d t h e i r tuffs, w e r e p r e s e n t only i n r e l a t i v e l y s m a l l a m o u n t s a n d i n only a f e w i n s t a n c e s . G e l f o r m a t i o n s i n c o n c r e t e a r e g e n e r a l l y p r o d u c t s of r e a c t i o n b e t w e e n a l k a l i h y d r o x i d e s a n d s i l i c e o u s p h a s e s i n t h e a g g r e g a t e s . T h e s e s i l i c a t e p r o - d u c t s t e n d t o i m b i b e w a t e r a n d s w e l l , p r o d u c i n g p r e s s u r e s t h a t c a n p r o d u c e r u p t u r e of t h e c o n c r e t e u n d e r e x t r e m e c o n d i t i o n s . When t h e c o n c r e t e i s d r i e d o r p a r t i a l l y d r i e d , t h e s e s i l i c a t e s f o r m a c e r a m i c - l i k e d e p o s i t i n v o i d s . T h e i r r e l a t i v e a b u n d a n c e h a s b e e n c o n s i d e r e d a s proof of a l k a l i - s i l i c a r e - a c t i o n a n d o b s e r v e d d i s p l a c e m e n t and c r a c k i n g . I n t h e Nova S c o t i a c o n c r e t e s , g e l s w e r e a b u n d a n t i n s o m e c o n c r e t e s a n d a l m o s t l a c k i n g i n o t h e r s . No c o r - r e l a t i o n w a s found b e t w e e n l e n g t h - c h a n g e r e s u l t s on t e s t m o r t a r s a n d c o n - c r e t e s a n d t h e a m o u n t of g e l a s s o c i a t e d w i t h t h e r o c k t y p e s . G e l s w e r e n o t u s u a l l y a b u n d a n t e v e n i n c o n c r e t e s which h a d e x p a n d e d e x c e s s i v e l y , e x c e p t w h e r e r h y o l i t e s a n d tuffs w e r e p r e s e n t i n s i g n i f i c a n t a m o u n t s . R e a c t i o n r i m s w e r e d e t e c t a b l e on s o m e Nova S c o t i a r o c k p a r t i c l e s i n a g e d c o n c r e t e s . T h e y w e r e p r e s e n t , h o w e v e r , b o t h i n c o n c r e t e s t h a t w e r e s e r i o u s l y a f f e c t e d b y a l k a l i - a g g r e g a t e r e a c t i o n a n d t h o s e t h a t w e r e n o t . In l a b o r a t o r y s p e c i m e n s c o n t a i n i n g e x p a n s i v e r o c k t y p e s , r e a c t i o n r i m s , when
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they o c c u r r e d , w e r e p r e s e n t with high a l k a l i c e m e n t and t o a l e s s e r e x t e n t with low a l k a l i c e m e n t . I t w a s c l e a r t h a t r i m f o r m a t i o n , l i k e g e l f o r m a t i o n , w a s not in i t s e l f r e l i a b l e e v i d e n c e of a l k a l i - e x p a n s i v i t y in t h e s e r o c k s . A p a r t f r o m a f e w i s o l a t e d i n s t a n c e s of s o - c a l l e d classical'^ a l k a l i - s i l i c a r e a c t i v i t y , a s with s o m e of t h e r h y o l i t e s , t h e r e l a t i o n s h i p b e t w e e n m i c r o f r a c - t u r e s and a l k a l i - a g g r e g a t e r e a c t i o n i n t h e s e d i m e n t a r y and m e t a s e d i m e n t a r y r o c k s in a g e d Nova S c o t i a c o n c r e t e s w a s found t o be d i f f i c u l t t o a s s e s s . T h e e x t r e m e l y s l o w r e a c t i o n had i n a l l p r o b a b i l i t y a l l o w e d c r e e p , p l a s t i c flow, a n d a u t o g e n o u s healing t o a c c o m m o d a t e and o b s c u r e m i c r o f r a c t u r e s within t h e m o r t a r . C h a r a c t e r i s t i c i n t e r n a l p e r i p h e r a l c r a c k s and t r a n s v e r s e c r a c k s could f r e q u e n t l y b e o b s e r v e d , h o w e v e r , within t h e l a r g e r s u s p e c t p a r t i c l e s . F r o m a n e x a m i n a t i o n of f i e l d c o n c r e t e s , a deduction m u s t b e b a s e d on e v i d e n c e of m e c h a n i c a l d i s p l a c e m e n t , s u p p o r t e d i n s o m e c a s e s b y o t h e r f a c - t o r s s u c h a s r i m s and g e l s . Such m e c h a n i c a l d i s p l a c e m e n t m a y b e on a m i - c r o s c o p i c s c a l e i n t h e l a b o r a t o r y o r on a m e g a s c o p i c s c a l e in t h e f i e l d . T h u s t h e i n t e r p r e t a t i o n of d i a g n o s t i c f e a t u r e s g e n e r a l l y a s s o c i a t e d with t h e b e t t e r known a l k a l i - s i l i c a r e a c t i o n should b e r e - e x a m i n e d i n t h e c a s e of a f f e c t e d Nova S c o t i a c o n c r e t e s . T h r e e p r e v i o u s l y r e p o r t e d c a s e s (4, 5, 6), two of which involved Appalachian r o c k s , a p y e a r t o b e r e l a t e d t o t h e Nova S c o t i a
d e s c r i b e d i n t h e p r e s e n t study. P e t r o g r a p h y of R o c k s
T h e g r e y w a c k e s e x a m i n e d a r e d a r k , f i n e - t o - m e d i u m - g r a i n e d , m a s s i v e r o c k s which often w e a t h e r to a l i g h t e r g r e y o r g r e e n i s h c o l o r s o m e t i m e s s h o w - ing i r o n s t a i n i n g . The s a n d - s i z e c o n s t i t u e n t s a r e c o m m o n l y i n t h e 0. 1 t o 0 . 2 m m s i z e r a n g e and a r e g e n e r a l l y q u a r t z and f e l d s p a r with a c c e s s o r y a m o u n t s of r o c k f r a g m e n t s . T h e y tend to e l o n g a t e p a r a l l e l t o t h e s h e a r - i n d u c e d a l i g n - m e n t of t h e p l a t y m i n e r a l s i n t h e m a t r i x . The m a t r i x c o n s t i t u e n t s a r e l e s s than 20 p m and g e n e r a l l y c o m p r i s e q u a r t z , f e l d s p a r , m i c a , c h l o r i t e and i r o n m i n e r a l s s u c h a s l e u c o x e n e , p y r r h o t i t e , m a g n e t i t e and l i m o n i t e . M i c r o f r a c -
t u r e s a r e f a i r l y c o m m o n . G r a p h i t i c m a t e r i a l i s p r e s e n t in s o m e of t h e r o c k s . M a n y of t h e g r e y w a c k e s c o n t a i n p o r p h y r o b l a s t s of a b r o w n m i c a - t y p e
1 2 6 V o l . 3 , N o . 2 . A L K A L I AGGREGATE REACTION, F I E L D S T U D I E S , PETROGRAPHY
n a t i o n i n d i c a t e s t h a t t h i s m i n e r a l i s m o r e c l o s e l y r e l a t e d t o v e r m i c u l i t e t h a n b i o t i t e . V e r m i c u l i t e i s known t o f o r m a t t h e e x p e n s e of b i o t i t e by w e a t h e r i n g o r h y d r o - t h e r m a l a c t i o n . In s o m e of t h e g r e y w a c k e s t h e b r o w n l a y e r s t r u c - t u r e s i l i c a t e s a r e p a r t l y a l t e r e d t o p a l e g r e e n c h l o r i t e .
A r g i l l i t e s and p h y l l i t e s a r e n o t t h e d o m i n a n t r o c k type i n Nova S c o t i a c o n - c r e t e a g g r e g a t e s s e l e c t e d f o r study. Nonetheless, they a r e f r e q u e n t l y p r e s -
e n t . The a r g i l l i t e s c o n t a i n a n h e d r a l q u a r t z and f e l d s p a r g r a i n s of s i l t - s i z e i n a f i n e m a t r i x of s e r i c i t e and s u b h e d r a l l a t h s of m u s c o v i t e . A p p r o x i m a t e l y
1 m m p o r p h y r o b l a s t s of t h e v e r m i c u l i t e - t y p e m i n e r a l s i m i l a r t o t h o s e found in t h e g r e y w a c k e s , a r e p r e s e n t . P y r i t e s o m e t i m e s o c c u r s a s a n a c c e s s o r y . T h e f i n e m i c a s in t h e g r o u n d m a s s often show s o m e r e c r y s t a l l i z a t i o n and p r e f e r r e d o r i e n t a t i o n i n d i c a t i n g a g r a d a t i o n i n t o phyllite. T h e p h y l l i t e s a r e s i m i l a r b u t m o r e s t r o n g l y m e t a m o r p h o s e d t h a n t h e a r g i l l i t e s . I n s o m e s a m - p l e s t h e r e a r e p o r p h y r o b l a s t s of t h e b r o w n l a y e r - s t r u c t u r e s i l i c a t e . Hand s a m p l e s of Nova S c o t i a q u a r t z i t e s a r e f i n e - t o - m e d i u m g r a i n e d , m a s s i v e , h a v e good c o h e r e n c e and a r e g e n e r a l l y l i g h t g r e y b u t s o m e t i m e s a r e b r o w n i s h . I r o n s t a i n s a r e c o m m o n on w e a t h e r e d s u r f a c e s and a r o u n d f r a c t u r e s . T h e q u a r t z c r y s t a l s a r e c o m m o n l y l e s s than 1 m m i n d i a m e t e r and f r e q u e n t l y h a v e i n t e r l o c k i n g b o u n d a r i e s with t h e i r n e i g h b o r s . I n s o m e r o c k s t h e c r y s t a l s a r e c l e a r b u t i n o t h e r s i n c l u s i o n s and b o u n d a r y i n t e r g r o w t h s with m i c a a r e c o m m o n ; m a n y of t h e c r y s t a l s show s t r a i n . F e l d s p a r i s c o m m o n i n t h e s a m e a p p r o x i m a t e s i z e r a n g e a s t h e q u a r t z . Brown m i c a , m u s c o v i t e and c h l o r i t e a r e i m p o r t a n t a c c e s s o r i e s . The m a t r i x v a r i e s f r o m 1 o r 2 p e r c e n t t o 10 o r 15 p e r c e n t . I t i s g e n e r a l l y c o m p o s e d of f i n e q u a r t z a n d f e l d s p a r c r y s t a l s with m u s c o v i t e , c h l o r i t e and s o m e t i m e s b i o t i t e l a t h s . A c c e s s o r y a m o u n t s of t o u r m a l i n e , p y r i t e , h e m a t i t e , l e u c oxene and l i m o n i t e a r e c o m m o n . Q u a r t z i t e s w e r e n o t g e n e r a l l y found t o b e a l k a l i - e x p a n s i v e b u t t h e r e w e r e s o m e n o t a b l e e x c e p t i o n s . M i c a s , c l a y m i n e r a l s and f e l d s p a r s a r e a l k a l i - containing m i n e r a l s . D e e r , Howie and Z u s s m a n ( 7 ) r e p o r t an a v e r a g a c o n - t e n t of 1. 270 Na 0 and 7. 1% K 0 f o r i l l i t e s w i t h s m e c t i t e s and c h l o r i t e s c o n -
2 2
taining s m a l l e r q u a n t i t i e s . It i s p o s s i b l e t h a t i n t h e C a - r i c h e n v i r o n m e n t of h y d r a t i n g c e m e n t p a s t e s o m e s m a l l q u a n t i t i e s of a l k a l i s m a y b e r e l e a s e d f r o m t h e p h y l l o s i l i c a t e s by c a t i o n exchange.
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Only a f e w s a m p l e s of volcanic r o c k s w e r e e x a m i n e d ; t h e s e included b a s a l t , rhyolite, t r a c h y t e and tuff.
S e l e c t i o n of Rock T y p e s f o r Expansion S t u d i e s
A t o t a l of 54 l o c a l r o c k s and s a n d s s u i t a b l e f o r c o n c r e t e w e r e s a m p l e d f r o m v a r i o u s p a r t s of the p r o v i n c e . The r o c k t y p e s w e r e s e l e c t e d on the b a s i s of o c c u r r e n c e in c o n c r e t e f i e l d c o r e s and in c u r r e n t s o u r c e s of c o n c r e t e a g g r e - g a t e in the p r o v i n c e . T h e s e r o c k s w e r e used a s a g g r e g a t e s in m o r t a r s and c o n c r e t e f o r s t u d i e s of expansion c h a r a c t e r i s t i c s and m e c h a n i c a l and o t h e r p r o p e r t i e s . T h e s c o p e of t h i s investigation did n o t p e r m i t a n evaluation of new s o u r c e s of potentially n o n - r e a c t i v e a g g r e g a t e .
F o u r t e e n of the b e d r o c k s a m p l e s w e r e obtained f r o m f o u r q u a r r i e s of the Nova S c o t i a P o w e r C o m m i s s i o n who initiated t h e s e s t u d i e s b e c a u s e of p r o b - l e m s with c o n c r e t e in i t s h y d r a u l i c s t r u c t u r e s . T h e s e r o c k s c o n s i s t e d m a i n l y of a r g i l l i t e s , g r e y w a c k e s , s u b g r e y w a c k e s , q u a r t z i t e s , phyllites and s c h i s t s . S a m p l e s w e r e t a k e n f r o m m a r i n e - w o r k e d g l a c i a l t i l l s c o m p r i s i n g b o u l d e r s , c o b b l e s and s a n d s . T h e s a m p l e s w e r e v a r i o u s m i x t u r e s of a r k o s e s , s a n d s t o n e s , g r e y w a c k e s , s u b g r e y w a c k e s , a r g i l l i t e s , s c h i s t s , phyllites, q u a r t - z i t e s , b a s a l t s , r h y o l i t e s and g r a n i t e s . Inland g l a c i a l t i l l s s a m p l e d included s a n d s , n a t u r a l b a l l a s t and c r u s h e d r o c k s f r o m e s k e r s , k a m e s , outwash p l a i n s and d r u m l i n s . O u t c r o p s a m p l e s c o n s i s t e d of s o m e of the above v a r i - e t i e s of rock. F i g u r e 2 shows the location of the t e s t a g g r e g a t e s o u r c e s .
3 E D a O C K O U i Q R Y A M A R I N E : l / O Q K ~ D TILLS 0 I N L A N D TILLS A SOURCE ROCKS FIG. 2 Location of t e s t a g g r e g a t e s o u r c e s in Nova S c o t i a
128
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Concluding S t a t e m e n t
R o c k s u s e d a s c o n c r e t e a g g r e g a t e a r e of t h e t y p e t o b e e x p e c t e d f r o m t h e geology of Nova S c o t i a
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a g l a c i a t e d p o r t i o n of t h e A p p a l a c h i a n p r o v i n c e . Mi- c r o s c o p i c e x a m i n a t i o n s of c o n c r e t e c o r e s f r o m m a n y s t r u c t u r e s , and r o c k a n d s a n d s a m p l i n g s f r o m w i d e l y s e p a r a t e d p a r t s of Nova S c o t i a show t h a t g r a v e l a n d b e a c h d e p o s i t s h a v e f r e q u e n t l y b e e n u s e d a s a g g r e g a t e s o u r c e s ; h e n c e m a n y of t h e c o n c r e t e s c o n t a i n a h e t e r o g e n e o u s m i x t u r e of A p p a l a c h i a n r o c k t y p e s . T h e f i e l d s u r v e y s along with p e t r o g r a p h i c e x a m i n a t i o n s i n d i c a t e c o n c r e t e d i s t r e s s c a u s e d by a n a l k a l i - a g g r e g a t e r e a c t i o n i n w i d e l y s e p a r a t e d p a r t s of t h e P r o v i n c e . T h e m o s t c o m m o n r o c k s i n a f f e c t e d c a s e s a r e g r e y - w a c k e s , a r g i l l i t e s , p h y l l i t e s , a n d s o m e q u a r t z i t e s a n d s c h i s t s . T h e s e f i n d - i n g s w e r e c o n f i r m e d b y l e n g t h c h a n g e e x p e r i m e n t s on m o r t a r b a r s , c o n c r e t e p r i s m s a n d r o c k c y l i n d e r s . R e f e r e n c e s1. M. A. G. Duncan, E . G. Swenson, J. E. Gillott, a n d M. R. F o r a n . Cem. a n d C o n c r . R e s . , Vol. 3 , No. 1 ,
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55
(1973).2. M. A. G. Duncan and E . G. Swenson. I n v e s t i g a t i o n of C o n c r e t e E x p a n s i o n i n Nova S c o t i a . T h e P r o f . Eng. i n Nova S c o t i a , Vol. 10, No. 2, M a y 1969,
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p. 16-
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