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Evaluation of test methods for alkali-aggregate reactivity
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National Research
Conseil national
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1236
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EVALUATION OF TEST METHODS FOR ALKALI-AGGREGATE
REACTIVITY
*
by
P.E. Grattan-Bellew
Reprinted from
Danish Concrete Association
6th. International Conference
"Alkalis in Concrete: Research and Practice"
Technical University of Denmark
Copenhagen, 22-25 June 1983
Proceedings, p. 303
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Division of Building Research
L e s msthodes d ' e s s a i d e l a r h c t i o n a l c a l i - g r a n u l a t comprennent
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ALKALIS IN CQMCRlETlE
Research
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Paper reprinted from the
PROCEEDINGS
TECHNICAL UNIVERSITY
of Denmark
COPENHAGEN
22.-25.
J U N E
-
1983
EVALUATION OF TEST METHODS FOR ALKALI-AGGREGATE REACTIVITY P.E. Grattan-Bellew
D i v i s i o n of B u i l d i n g Research, N a t i o n a l Research Council Canada Ottawa, Canada K1A OR6
ABSTRACT
T e s t methods f o r a l k a l i - a g g r e g a t e r e a c t i v i t y c a n be d i v i d e d i n t o t h o s e t h a t determine t h e p o t e n t i a l r e a c t i v i t y of an aggregate ( t h e chemical t e s t and t h e proposed p e t r o g r a p h i c method f o r determining t h e undulatory e x t i n c t i o n a n g l e of q u a r t z ) and t h o s e t h a t p u r p o r t t o measure t h e e x p a n s i 9 i t y of a n a g g r e g a t e i n c o n c r e t e ( c o n c r e t e prism, mortar b a r , and rock c y l i n d e r methods). S e v e r a l m o d i f i c a t i o n s have been developed f o r t h e chemical method, ASTM C289, t o t a k e i n t o account r e g i o n a l v a r i a t i o n s i n aggregates. The main disadvantage of t h e methods measuring expansion is t h a t they t a k e a long t i m e . To t r y t o overcome t h i s problem, v a r i o u s methods of a c c e l e r a t i o n have been proposed, v a r y i n g from immersion of t h e samples i n s a l t s o l u t i o n a t an e l e v a t e d temperature t o autoclaving. Autoclaving methods must be regarded w i t h some c a u t i o n , however, because a t e l e v a t e d temperatures and p r e s s u r e s hydrothermal r e a c t i o n s occur t h a t do n o t t a k e p l a c e a t atmospheric pressure.
KEY WORDS: E v a l u a t i o n , T e s t s , A l k a l i , Aggregate.
1. INTRODUCTION
The i d e a l method of determining t h e p o t e n t i a l a l k a l i e x p a n s i v i t y of a n
aggregate i n c o n c r e t e should be a p p l i c a b l e t o a l l rock t y p e s , should be r a p i d , t a k i n g no more t h a n a few days t o complete, and must g i v e r e l i a b l e r e s u l t s . The q u e s t f o r t h i s t e s t h a s k e p t a number of r e s e a r c h e r s busy f o r many y e a r s , b u t l i k e t h a t of t h e a l c h e m i s t s b e f o r e them i t w i l l n o t succeed. M v e r s i t y i n t h e composition, g r a i n s i z e , and p o r o s i t y , and t h e presence o r absence of secondary cementing m i n e r a l s i n r o c k s p r e d i c a t e s a g a i n s t t h e development of a u n i v e r s a l l y a p p l i c a b l e , r a p i d t e s t method. Some t e s t s , f o r example t h e c o n c r e t e prism method, a r e a p p l i c a b l e t o a l l rock t y p e s b u t may t a k e s o l o n g t h a t t h e s t r u c t u r e w i l l be b u i l t b e f o r e t h e t e s t i s complete. Other tests, l i k e t h e mortar b a r and t h e chemical methods, a r e s u i t a b l e f o r a g g r e g a t e s e x h i b i t i n g c l a s s i c a l a l k a l i - s i l i c a r e a c t i v i t y but not f o r r e a c t i v e c a r b o n a t e aggregates. A s a r e s u l t , a number of d i f f e r e n t t e s t methods have been, and continue t o be, developed. This review w i l l examine t h e e f f e c t i v e n e s s and l i m i t a t i o n s of e x i s t i n g and proposed t e s t methods.
2. CHEMICAL TEST
The chemical method, ASTM C289 111, was developed a s a r a p i d means of d i f f e r e n t i a t i n g between p o t e n t i a l l y r e a c t i v e and non-reactive s i l i c a - b e a r i n g aggregates. The c r i t e r i a f o r e v a l u a t i o n were developed from t h e r e s u l t s of p a r a l l e l s e t s of mortar b a r and chemical t e s t s on many a g g r e g a t e s from t h e United S t a t e s 121. The r o c k s t e s t e d included some c o n t a i n i n g o p a l , c h e r t o r chalcedony a s t h e r e a c t i v e component and o t h e r s i n which v o l c a n i c g l a s s was t h e r e a c t i v e component. A s t h e two main r e a c t i v e components, o p a l and v o l c a n i c g l a s s , c o n s i s t of c r y p t o c r y s t a l l i n e S i 0 2 and an a l u m i n o s i l i c a t e g l a s s , r e s p e c t i v e l y , i t i s s u r p r i s i n g t h a t one s e t of c r i t e r i a were found t o be a p p r o p r i a t e f o r e v a l u a t i o n of b o t h types.
The problem of o b t a i n i n g meaningful v a l u e s f o r t h e d i s s o l v e d s i l i c a (Sc) and t h e r e d u c t i o n i n a l k a l i n i t y (Rc) a r e complicated i f c a r b o n a t e s o r s u l p h a t e s , e.g., gypsum 131, a r e p r e s e n t i n t h e a g g r e g a t e because t h e y r e a c t w i t h NaOH t o
reduce its a l k a l i n i t y . The v a l u e s of Sc and Rc a r e a l s o very s u s c e p t i b l e t o o p e r a t o r influence. For example, i f t h e sample i s n o t properly s i z e d and a s i g n i f i c a n t amount of -150
um
m a t e r i a l is included i n t h e test, t h e value of Sc w i l l be markedly increased. Grinding q u a r t z t o s i z e s less t h a n about100
u m
g r e a t l y i n c r e a s e s i t s s o l u b i l i t y (Figure 1).The phenolphthalein i n d i c a t o r does n o t g i v e a s h a r p end p o i n t and t h e v a l u e of Rc determined is t h u s , t o some e x t e n t , dependent on t h e judgement of t h e operator. Soaie of t h e p r o b l e m i n h e r e n t i n t h e chemical test were d i s c u s s e d by Dent G l a s s e r and Kataoka 141. Their main conclusion i s t h a t t h e value of Rc, as c u r r e n t l y determined, i s r a t h e r meaningless s i n c e i t i n c l u d e s
reductions i n both OH- and t h e c o n c e n t r a t i o n of ~ a + i n t h e s o l u t i o n . They suggested t h a t t h e method should be a l t e r e d s o t h a t O H can be determined by a pH meter and ~ a + by a s p e c t r o s c o p i c method.
The q u e s t i o n a r i s e s a s t o t h e need t o d e t e r d n e t h e reduced a l k a l i n i t y , Rc;
i s determination of Sc alone s u f f i c i e n t f o r p r e d i c t i n g t h e p o t e n t i a l
r e a c t i v i t y of a n aggregate? To i n v e s t i g a t e t h i s , test r e s u l t s f o r a s e r i e s of q u a r t z sands containing varying amounts of opal 121 were p l o t t e d i n Figure 2; i t i s e v i d e n t t h a t expansion of mortar b a r s c o r r e l a t e s b e t t e r w i t h t h e f a c t o r Rc/Sc than with Sc alone, i n d i c a t i n g t h a t f o r t h e s e aggregates i t i s b e t t e r t o determine both Rc and Sc.
I t has been e s t a b l i s h e d t h a t t h e c r i t e r i a given i n C289 a r e n o t adequate f o r the e v a l u a t i o n of I c e l a n d i c sands containing volcanic g l a s s o r of Danish f l i n t g r a v e l s , f o r which l o w v a l u e s of t h e amount of d i s s o l v e d s i l i c a are i n d i c a t i v e of p o t e n t i a l r e a c t i v i t y . New c r i t e r i a were developed f o r t h e i r e v a l u a t i o n a s follows ( p e r s o n a l comnunication, Hakon Olaf sson) :
I c e l a n d i c sands:
non-reactive
-
Sc <I00 nsnol/Lp o t e n t i a l l y r e a c t i v e
-
Sc 100 t o 200 mmol/L r e a c t i v e-
Sc s200 mmol/L Danish g r a v e l s : non r e a c t i v e-
Sc <50 mmol/L p o t e n t i a l l y r e a c t i v e-
Sc 50 t o 200 mmol/~ r e a c t i v e-
Sc >200 mmol/L I n c o n t r a s t , i n B r i t a i n t h e Thames Valley f l i n t g r a v e l s y i e l d e d v a l u e s of Sc i n excess of 100 mmol/L y e t caused no problems i n concrete 131. It appears t h a t s e p a r a t e s e t s of c r i t e r i a need t o be developed on a r e g i o n a l b a s i s , even f o r e v a l u a t i o n of what a r e nominally t h e same rock types.I n t h e late-expansive a g g r e g a t e s of t h e Malmesbury Formation i n t h e Cape Peninsula of South Africa, i n which s t r a i n e d q u a r t z is t h e r e a c t i v e component, t h e c r i t e r i a s p e c i f i e d i n C289 a r e e f f e c t i v e f o r d i f f e r e n t i a t i n g r e a c t i v e and non-reactive aggregates; but i n t h e Tygerberg Formation from t h e same r e g i o n lower v a l u e s of Sc were obtained from r e a c t i v e aggregates. The r e s u l t s of the chemical t e s t on t h e s e aggregates, reported by Brandt,
Oberholster and Westra 151, a r e r e p l o t t e d i n F i g u r e 3. It i s e v i d e n t t h a t t h e d i v i d i n g l i n e between r e a c t i v e and non-reactive aggregates must l i e a t a value of Sc between 35 and 50 nnnol/L.
I n S e r b i a t h e chemical method, ASTM G289, used by MitroviE and
~ u r i E I61 i n d i c a t e d t h a t t h e aggregates a r e p o t e n t i a l l y r e a c t i v e ( a s d i d t h e mortar bar t e s t ) , although
no
problems have been observed i n concrete. There a p p e a r s t o be some doubt concerning t h e v a l i d i t y of both methods f o re v a l u a t i n g t h e s e p a r t i c u l a r aggregates.
I n A u s t r a l i a , t h e c r i t e r i a s p e c i f i e d i n C289 a r e e v i d e n t l y s a t i s f a c t o r y ; they have been adopted
as
an A u s t r a l i a n standard, AS 1141 Section 39, 1954.2.1 Discussion
The c h e d c a l test i s t h e only rapid, currently a v a i l a b l e method, t h a t has been thoroughly evaluated. With some m d i f i r a t i o n of t h e c r i t e r i a used t o d e f i n e r e a c t i v e aggregates, and i n co-njuaction w i t h a p e t r o g r a p h i c
examination, it can be used t o e v a l u a t e t h e p o t e n t i a l r e a c t i v i t y of a wide
range of s i l i c e o u s aggregates. Improvements might be made i n t h e a n a l y t i c a l procedures s o t h a t t h e r e d u c t i o n s i n
OH-
and i n ~ a + a r e determined s e p a r a t e l y . There is some evidence t h a t determination of d i s s o l v e d s i l i c a a l o n e i ssufficient t o d i f f e r e n t i a t e between r e a c t i v e and non-reactive aggregates. Owing t o t h e wide d i v e r s i t y i n the conpositlo-n g r a i n s i z e and p e r m e a b i l i t y of rocks, it is most u n l i k e l y t h a t u n i v e r s a l l y a p p l i c a b l e c r i t e r i a can be developed t o d i f f e r e n t i a t e between r e a c t i v e and non-reactive aggregates; i n s t e a d , c r i t e r i a a p p l i c a b l e t o s p e c i f i e d rock t y p e s should be developed. 2.2 Modified chemical test
A d i f i e d c h e d c a l t e s t was developed f o r e v a l u a t i n g t h e p o t e n t i a l r e a c t i v i t y of a g g r e g a t e s i n she Schleswig-lblstein region of Germany. The aggregate i s d i v i d e d i n t o two s i z e f r a c t i o n s : 1-2 mm and 2-4 mm. These a r e d i g e s t e d f n NaOH s o l u t i o n f o r 60 d n a t BO'C. The samples are washed, d r i e d , and weight l o s s determined; t h i s r e p r e s e n t s t h e amount of s i l i c a d i s s o l v e d o u t by N&H and g i v e s , i n p r i n c i p l e , a measure of t h e p o t e n t i a l r e a c t i v i t y of t h e aggregate. The l i m i t a t i o n s of t h i s test have been d i s c u s s e d by Jensen, C h a t t e r j i , Christensen, Thaulow and Gudmndsson 171. It would be a p p l i c a b l e
only t o a g g r e g a t e s c o n t a i n i n g r e a c t i v e silica, i.e., opal, c h e r t o r chalcedapy and p o s s i b l y a l s o t o aggregate composed of v o l c a n i c g l a s s .
3. MORTAR
BAR
METHODThe mortar b a r t e s t , ASTM C227-8 / 8 / , i s t h e most widely used method of e v a l u a t i n g t h e p o t e n t i a l a l k a l i - r e a c t i v i t y of aggregates. A number of v a r i a t i o n s i n t h e method of e v a l u a t i n g t h e t e s t r e s u l t s a r e i n u s e by d i f f e r e n t o r g a n i z a t i o n s . Despite t h e almost u n i v e r s a l acceptance of t h e mortar bar method, i t h a s s e v e r a l shortcomings: It u s u a l l y t a k e s from s i x months t o a y e a r t o complete, except w i t h some opal-bearing aggregates t h a t c a n be e v a l u a t e d i n about t h r e e months. Such l o n g l e a d times f r e q u e n t l y do not e x i s t before c o n s t r u c t i o n i s s t a r t e d , even i n major s t r u c t u r e s f o r which t h e d u r a b i l i t y of t h e c o n c r e t e i s of c r i t i c a l importance.
The e v a l u a t i o n of t h e r e a c t i v i t y of c o n c r e t e aggregate by t h e mortar b a r method assumes t h a t expansion of concrete i n t h e f i e l d c o r r e l a t e s w i t h expansion of test mortar bars. Although t h i s holds t r u e f o r some aggregates, t h e r e a r e exceptions. The carbonate aggregate from Kingston, Ontario, f o r example, shows much g r e a t e r expansion i n c o n c r e t e prisms than i n mortar b a r s , a s do late-expansive quartz-bearing aggregates such a s Malmesbury aggregate from t h e Cape Peninsula i n South A f r i c a and a greywacke from Nova S c o t i a , Canada 191 ( s e e Figure 4, #73-50).
3.1 I n t e r p r e t a t i o n of observed expansion
Recommended c r i t e r i a f o r e v a l u a t i o n of t h e r e s u l t s of t h e mortar b a r t e s t a r e given i n ASTM C33-82, Appendix XI.1.3
/lo/.
It must be s t r e s s e d t h a t t h e s e a r e recommendations, n o t a mandatory p a r t of t h e standard. Although they a r e f r e q u e n t l y i n t e r p r e t e d a s "limits," t h i s i s i n c o r r e c t .According t o C33, expansions a r e t o be considered e x c e s s i v e i f they exceed 0.05% a t t h r e e months o r 0.10% a t s i x months; t h e three-month d a t a should only be used, however, when a six-month t e s t i s n o t possible. The a l k a l i c o n t e n t of t h e cement should be 0.6%, pr p r e f e r a b l y 0.8%. With t h e h i g h a l k a l i cements now commonly i n use, an a l k a l i l e v e l of 1.0% o r g r e a t e r would be more
a p p r o p r i a t e . The problem w i t h t h e s e recommended maximum p e r m i s s i b l e expansions i s t h a t they assume a f a s t r a t e of expansion w i t h a s h o r t i n i t i a t i o n period. A slowly expanding aggregate may show mortar b a r
expansions w e l l below t h e v a l u e s considered t o be d e l e t e r i o u s , according t o C33, but t h e continuing slow expansion w i l l e v e n t u a l l y l e a d t o e x c e s s i v e s t r e s s and cracking.
A t y p i c a l example of expansion of a mortar b a r made w i t h Malmesbury
aggregate and a cement c o n t a i n i n g 0.82% a l k a l i i s shown i n Figure 5 ( p e r s o n a l comnunication, R.E. O b e r h o l s t e r ) . T h i s a g g r e g a t e i s known t o cause
d e l e t e r i o u s expansion i n c o n c r e t e made w i t h a high a l k a l i cement. The problem of e v a l u a t i n g t h e r e s u l t s of expansion of mortar b a r s made w i t h l a t e e x p a n s i v e aggregates has a l s o been discussed by Kennerly e t a l . 1111 and by Sims 131. 3.2 Corps of Engineers
The Corps of Engineers c r i t e r i a f o r e v a l u a t i o n of t h z r e s u l t s of t h e mortar bar t e s t a r e p o s s i b l y more a p p r o p r i a t e than t h o s e recommended i n C33.
EM 1110-2-2000 1121 s t a t e s t h a t expansion of 0.10% o r more a t any a g e should be considered d e l e t e r i o u s . An expansion of 0.05% o r more a t s i x months may a l s o be considered d e l e t e r i o u s . When expansions c l o s e t o t h e s e l i m i t s a r e recorded, t h e t r e n d of t h e time-expansion curve should be taken i n t o account. T h i s i s i n l i n e w i t h t h e concept of determining t h e r a t e of expansion proposed by Grattan-Bellew 191. Cracking of mortar b a r s i s g e n e r a l l y observed when expansion exceeds about 0.04%; i f c r a c k i n g i s accepted a s evidence of d e l e t e r i o u s r e a c t i o n , expansions of l e s s than 0.10% must i n d i c a t e p o t e n t i a l a l k a l i - a g g r e g a t e r e a c t i v i t y . The problem i s t h a t a t p r e s e n t n o t enough information on t h e c o r r e l a t i o n between expansion of mortar b a r s and f i e l d c o n c r e t e e x i s t s t o s e t r e a l i s t i c s a f e l i m i t s of expansion f o r mortar bars. 3.3 Canadian Standards Association
The Canadian s t a n d a r d (CAN3.A23.1-M77, Appendix B3.4 1131) s t a t e s t h a t expansions i n excess of 0.04% a t any age a r e t o be considered d e l e t e r i o u s . It a l s o n o t e s t h a t t h e shape of t h e expansion curve i s o f t e n of importance i n making a judgement. The 0.04% l i m i t f o r expansion i s i n agreement w i t h f r e q u e n t o b s e r v a t i o n s of c r a c k i n g when t h i s l e v e l of expansion i s exceeded; t h e l i m i t may, however, be too r e s t r i c t i v e f o r some aggregates f o r which expansion may j u s t exceed t h i s v a l u e and t h e n l e v e l o f f .
3.4 Accelerated Danish mortar b a r t e s t
T h i s t e s t , d e s c r i b e d by Jensen e t a l . 171, i s an a c c e l e r a t e d v e r s i o n of t h e mortar bar method C227 and i s used f o r Danish f l i n t g r a v e l s . The mortar b a r s a r e made i n t h e u s u a l way and cured i n a f o g room a t 23OC f o r 27 days. They a r e then placed i n s a t u r a t e d NaCl s o l u t i o n a t 50°C and expansion i s monitored w i t h time. No l i m i t s have been proposed. T h i s method i s r e p o r t e d t o be s a t i s f a c t o r y f o r t h e aggregates t e s t e d i n Denmark, but t h e r e a r e no r e p o r t s of
i t s use elsewhere.
3.5 Chinese autoclaved mortar bar t e s t
T h i s i s a n o t h e r a c c e l e r a t e d mortar b a r t e s t . Mortar b a r s 1 x 1 x 4 cm a r e prepared and cured f o r one day i n a fog room. Following t h i s , they a r e steam cured a t 100°C f o r 4 h and then immersed i n 10% KOH s o l u t i o n and autoclaved a t 150°C f o r 6 h. Expansions a r e recorded a f t e r each phase of t h e c u r i n g cycle. A l a r g e number of a l k a l i - s i l i c a r e a c t i v e a g g r e g a t e s were t e s t e d i n t h i s way by Ming-shu, Su-fen and Shi-hua 1141, who concluded t h a t t h e method i s capable of d i f f e r e n t i a t i n g between r e a c t i v e and non-reactive aggregates. More t e s t i n g should be c a r r i e d out t o e v a l u a t e i t s e f f e c t i v e n e s s f o r a wider v a r i e t y of rock types. Hydrothermal t e s t s must, however, be regarded w i t h some c a u t i o n
because of the possibility that the observed expansion might be distorted by hydrothermally induced reactions that would not occur in concrete under normal conditions.
3.6 Discussion
No firm limit of expansion can be specified that is applicable to all rock types. Cracking of mortar bars is frequently observed when expansion exceeds about 0.04%, and this value might be considered indicative of potentially deleterious expansion. In some cases, however, this could result in
classification of some aggregates that perform satisfactorily in concrete as deleterious. It would be desirable to have a time limit for the mortar bar test; owing, however, to wide divergences in initiation periods and in rates of expansion it is not possible to establish a universally applicable time limit. It is possible that regionally applicable time-expansion limits such as those proposed in C33 may be established for some suites of aggregates. Accelerated tests have so far not been evaluated for a wide enough range of aggregates to permit conclusions to be drawn as to their applicability.
4. CONCRETE PRISM TEST
The concrete prism test (CSA A23.2-14A 1151) was developed in Canada for evaluating the expansivity of reactive dolomitic limestones that do not cause significant expansion in mortar bars. The test has also been used success- fully for late-expansive siliceous aggregates and limestones containing reactive silica. Similar tests have been used in New Zealand and
South Africa. The criteria for evaluation of the test results are
specified
in CSA A23.1.M77, Appendix B3.5. Linear expansions of more than about 0.03% indicate potentially deleterious expansion. Appendix
3.5
concludes that some aggregates expand beyond the three-month period and that, where possible, the test should be continued until expansion has virtually ceased. This is sound advice, but it may often not be practical since with some late-expansive aggregates it may take up to two years for expansion to taper off. The use of the rate method of evaluating expansivity of aggregates 191 may help in evaluating the expansivity of concrete prisms before expansion tapers off. It is very desirable to carry out a petrographic examination in conjunction with the concrete prism test so that the type of reactivity to be expected can be determined; this helps in the correct evaluation of early test results if it is not possible to wait until the expansion has tapered off.The concrete prism method may be the most reliable test for all types of aggregate. In it, the aggregate is tested in the same size range and with the same cement:aggregate ratio that is used in field concrete. For some l a t e expansive siliceous aggregates and for carbonate reactive aggregates such as those from Kingston, Ontario, the concrete prism test is the only satisfactory method since these aggregates do not cause significant expansion in mortar bars. Expansion can be significantly accelerated by storage of the prisms at 38°C and 100% RH instead of at 23°C as specified.
A
few preliminaryexperiments to try and accelerate expansion by immersion of the prisms in NaCl solution, after the method of the Danish accelerated mortar bar test, were not very successful, but more research is needed before any firm conclusions can be drawn.
5. CONCRETE CUBE TEST
This test was developed in Germany 1161, and cracking is the criterion used to determine whether a cement-aggregate combination is reactive. There are two versions of it. In the first, 30-cm cubes are made and expansion is
a c c e l e r a t e d by s t o r a g e i n a f o g room a t 40%. Other exposure c o n d i t i o n s a r e a l s o used, f o r example, s t o r a g e on t h e roof of t h e r e s e a r c h l a b o r a t o r y .
I n t h e second v e r s i o n of t h e test, 10-cm cubes a r e s t o r e d a t 65%
RH,
with t h e Ibottom 1 c m immersed i n water a t 20°C. I n some samples c o n t a i n i n g r e a c t i v e I a g g r e g a t e marked c r a c k i n g was observed j u s t above t h e w a t e r l i n e .
I n B r i t a i n , a t t h e Cement and Concrete Association, a modified v e r s i o n of
the 10-cm cube t e s t is being i n v e s t i g a t e d (D.W. Hobbs, personal communica-
~
t i o n ) . Cubes a r e immersed i n a water b a t h a t 23'C and crack formation i sobserved. A temperature of 23'C i s reported t o be t h e optimum f o r s o l u b i l i t y of s i l i c a .
I n South A f r i c a , 30-cm cubes a r e used a t outdoor exposure s i t e s where they may be submitted t o v a r i o u s moisture and weather exposure conditions. T e s t s involving t h e o b s e r v a t i o n of cracking have a major advantage over tests r e q u i r i n g a c c c u r a t e measurement of l e n g t h change i n t h a t no e l a b o r a t e a p p a r a t u s i s required. This means t h a t t h e c o n c r e t e cube t e s t could r e a d i l y be c a r r i e d o u t by p i t , quarry o r ready-mix operators. The disadvantage i s
t h a t u n l e s s r a p i d l y expanding aggregates a r e being e v a l u a t e d i t would t a k e a n unacceptably long time f o r v i s i b l e cracks t o develop. From l a b o r a t o r y
o b s e r v a t i o n s by t h e a u t h o r i t is known t h a t a c o n s i d e r a b l e amount of expansion can f r e q u e n t l y be observed before cracks become v i s i b l e t o t h e unaided eye.
6. ROCK CYLINDER METHOD
1
The rock c y l i n d e r method (ASTM C586-69 1171) was designed t o e v a l u a t e t h e p o t e n t i a l r e a c t i v i t y of a l k a l i r e a c t i v e carbonate aggregates, but it has a l s o been used w i t h varying degrees of success t o e v a l u a t e t h e r e a c t i v i t y of a l k a l i - s i l i c a r e a c t i v e aggregates /5, 10, 18, 191. Paragraph 9.3 of C586 s t a t e s t h a t expansive behaviour of aggregate (carbonate) i n c o n c r e t e i s q u a l i t a t i v e l y p r e d i c t e d by t h e r e s u l t s of t h e rock c y l i n d e r t e s t .
Grattan-Bellew 1191 found moderate c o r r e l a t i o n between expansion of c o n c r e t e made with s i x samples of Kingston aggregate and expansion of miniature rock prisms made w i t h t h e same aggregates. Much poorer c o r r e l a t i o n was observed f o r expansion of c o n c r e t e prisms and t h a t of miniature rock prisms made with late-expanding s i l i c e o u s aggregates. Kennerley e t a l . 1111 found t h a t some prisms of New Zealand greywacke expanded e x c e s s i v e l y i n NaOH, but t h a t t h e same rock caused no expansion i n concrete.
It i s concluded t h a t t h e rock c y l i n d e r t e s t , o r v a r i a t i o n s of i t , can only be used t o e v a l u a t e t h e r e a c t i v i t y of c e r t a i n rock types. I t s optimum u s e would probably be f o r e v a l u a t i n g t h e p o t e n t i a l e x p a n s i v i t y of i n d i v i d u a l hori- zons i n a quarry containing a rock type f o r which c o r r e l a t i o n of expansion of rock c y l i n d e r s and t h a t of c o n c r e t e prisms has previously been demonstrated.
6.1 Accelerated rock prism test
I
An a c c e l e r a t e d rock prism t e s t f o r e v a l u a t i o n of t h e p o t e n t i a l r e a c t i v i t y of carbonate aggregates has been developed by Kazimir 1201 and adopted a s Czechoslovakian s t a n d a r d CSM 72 1160. Rock prisms 1 x 1 x 3 cm a r e prepared and autoclaved i n NaOH s o l u t i o n a t 215OC and 2.1 MPa f o r 6 h. This t e s t
i s
r e p o r t e d t o be s u c c e s s f u l i n d i f f e r e n t i a t i n g between expansive and non- expansive carbonate aggregates. Some r e s e a r c h was conducted by t h e author on t h e a p p l i c a b i l i t y of t h i s t e s t t o late- expanding s i l i c e o u s aggregates, but i t
was discontinued a f t e r a f e l d s p a r - l i k e phase was found t o have formed i n t h e prisms. Expansions occurred, but a s r e a c t i o n s were t a k i n g p l a c e ( t h e s e do n o t occur a t one atmosphere) i t seemed most u n l i k e l y t h a t t h e observed expansions would c o r r e l a t e w i t h expansions of t h e same prisms under atmospheric
conditions. More r e s e a r c h should probably be done a t various temperatures and p r e s s u r e s t o see whether an a c c e l e r a t e d t e s t could be developed f o r l a t e - expansive s i l i c e o u s aggregates.
7. GEL PAT TEST
This test was developed in England as a rapid method of identifying
potentially deleterious minerals such as opal or chert in mortar samples.
It does not give any indication of the expansivity of the aggregate.
As reported by Sims 131, a smoothed, sawn surface of the mortar is prepared
and immersed face down in alkali for three days. Gel forms on the reactive
particles, which can thus be readily identified and counted to yield a measure
of the percentage of reactive component in the aggregate.
A somewhat similar test, CSN 72-1162 1211, is used in Czechoslovakia to
accelerate rim development around prisms of siliceous aggregates embedded in
mortar. It is useful for preliminary screening of potentially alkali-silica
reactive aggregates, but additional tests would
benecessary to obtain a
measure of the expansivity of the aggregate in concrete.
8. PETROGRAPHIC EXAMINATION
Petrographic examination, ANSIIASTM C595 1221, has been changed from a
technique for determining the mineralogical composition of a rock to a
semi-quantitative method of determining the potential reactivity of certain
rock types by Dolar-Mantuani's development of a technique for determining the
undulatory extinction angle, UE, and relating it to the expansivity of
aggregate 1231. Following on earlier work 124-261, describing the development
of the technique for measuring strain in the quartz lattice by means of the
undulatory extinction angle, Dolar-Mantuani suggested that aggregates with
undulatory extinction angles of less than 15 deg may be characteristic*
nowreactive aggregates.
Recent unpublished results obtained by the present author show that some
South African aggregates (a quartzite from the Witwatersrand, a greywacke, and
a spotted slate from the Malmesbury Formation in the Cape Peninsula, all of
which cause excessive expansion in concrete) have UE angles of 36, 36 and
43 deg, respectively, indicating that there is some correlation between high
UE
angle and the reactivity of the aggregates. More research into this method
should be carried out. It has great potential as a rapid method of evaluating
the potential reactivity of quartz-bearing aggregates, particularly the late-
expansive types common in Precambrian terrains. It would be useful to conduct
a series of interlaboratory measurements of UE angles on reference samples so
that participants could adjust their measuring techniques to ensure results
consistent with those of other operators. In a limited test carried out in
Ottawa, a variation of 10 deg was found among measurements made by three
participants on the same quartz grains in a thin section. Such a wide
variation may have resulted because one or more of the participants measured
the extinction range, ER, rather than the undulatory extinction angle, UE, as
defined by DolarMantuani.
8.1
Use of scanning electron microscope
Use of the scanning electron microscope (SEM) to extend the scope of the
petrographic method by permitting characterization of texture and composition
of fine argillaceous rocks may, in due course, make it possible to distinguish
between expansive and non-expansive horizons in a particular deposit.
Figure 6 shows micrographs of two rocks from the Pittsbury quarry near
Kingston, Ontario. Figure 6a shows the highly expansive dolomitic limestone
characterized by isolated dolomite rhombs in a matrix of calcite; Figure 6b
shows a dolostone, which is non-expansive. This sample is composed almost
entirely of a more coarse grained dolomite. Electron probe analysis showed
that the Ca/Mg count rate ratio was different in the two samples
i n t h e r e a c t i v e dolomite; i t i s , t h e r e f o r e , a m e t a s t a b l e protodolomite 1271. The SEM h a s one g r e a t advantage over o t h e r techniques, (e.g., p e t r o g r a p h i c microscopy), t h a t i s , t h e speed w i t h which o b s e r v a t i o n and a n a l y s i s can be done; i n about h a l f a n hour a c h i p of rock can be coated, examined, and analysed by an expqrienced o p e r a t o r .
9. CONCLUSION
There i s a d e f i n i t e t r e n d towards m o d i f i c a t i o n of t h e s t a n d a r d ASTM t e s t s f o r use i n c e r t a i n r e g i o n s and f o r s p e c i f i e d types of aggregate. This h a s come about a s a r e s u l t of inadequacies i n t h e s t a n d a r d t e s t methods, e i t h e r because they f a i l t o p r e d i c t c o r r e c t l y t h e r e a c t i v i t y of an aggregate o r because t h e t e s t t a k e s t o o long t o complete. The t e s t methods have been modified i n two ways: expansion h a s been a c c c e l e r a t e d , a s i n t h e Chinese autoclaved mortar b a r t e s t ; t h e c r i t e r i a f o r t h e chemical t e s t , a s
recommended, have been modified t o p r e d i c t t h e r e a c t i v i t y of l o c a l a g g r e g a t e s more a c c u r a t e l y , a s i n I c e l a n d and Denmark where s p e c i f i c l i m i t s on t h e d i s s o l v e d s i l i c a have been proposed.
Modified c r i t e r i a f o r e x i s t i n g t e s t methods may be l i m i t e d t o s p e c i f i e d aggregates i n c e r t a i n regions. For example, t h e proposed Danish c r i t e r i a f o r e v a l u a t i n g t h e r e s u l t s of t h e chemical t e s t of f l i n t a g g r e g a t e s , t h a t
Sc values between 50 and 200 mmol/L a r e i n d i c a t i v e of p o t e n t i a l r e a c t i v i t y , would be q u i t e u n s u i t e d f o r t h e e v a l u a t i o n of Thames Valley f l i n t s , which a r e non-expansive i n c o n c r e t e d e s p i t e having Sc v a l u e s i n excess of
100 mmol/L.
There i s s t i l l a g r e a t need f o r b e t t e r , more r a p i d methods of diagnosing p o t e n t i a l l y r e a c t i v e aggregates. For reasons a l r e a d y o u t l i n e d t h e new t e s t s w i l l probably be developed f o r t h e e v a l u a t i o n of c e r t a i n a g g r e g a t e s i n s p e c i f i c regions. The most promising f o r f u t u r e development a r e t h e chemical method, i n conjunction w i t h improvements i n techniques f o r p e t r o g r a p h i c e v a l u a t i o n , and p o s s i b l y some type of a u t o c l a v e a c c e l e r a t i o n f o r mortar o r c o n c r e t e expansion t e s t s .
Acknowledgement
The a u t h o r i s indebted t o P.J. Lefebvre f o r h i s enthusiasm f o r t h e work and t h e p r e c i s i o n w i t h which he c a r r i e d o u t t h e experiments r e p o r t e d i n t h i s paper. T h i s i s a c o n t r i b u t i o n from t h e D i v i s i o n of B u i l d i n g Research, National Research Council Canada, and i s published w i t h t h e approval of t h e D i r e c t o r of t h e Division.
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p.87-100.
1261 M A ~ R ;
K., Presentation at Symposium on Alkali-Aggregate Reactivity.
Annual Meeting of Transportation Research Board, Washington, D.C., 1976.
/27/ SWENSON, E
.G. and GILLOTT, J. E
.
,
Alkali-Carbonate Rock React
ion. Highway
F i g u r e 1 E f f e c t of g r a i n s i z e of q u a r t z on the a o u a t af d i s s o l v e d s i l i c a determined by t h e chemical method, ASTM C289
1 0 0 0 5 0 0 300 2
-
=
aoa 0 4 8 1 2 16 20 24 % OPAL I N QUARTZ S A N D l l . l L , ! l ,- b
-
-
1
-
\ \-
-
F i g u r e 2 P l o t showing v a r i a t i o n i n Sc and Rc/Sc determined by t h e chemical t e s t , ASTM C289, and l e n g t h change of m o r t a r b a r s of q u a r t z sand c o n t a i n i n g v a r i o u s amounts of o p a l E 6 0
-
\-
3 0 '\ 1 5 --
-
-
5 0 m200 " 1 4 0 0 ' t "6 0 0 " 800 1 0 0 0 MEAN G R A l N S 1ZE, ,LL m 2 5 0 1 1 1 1 1 1 1 1 1 2 0 0-
1 5 0-
INNOCUOUS 1 0 0-
t
a DELETERIOUS4
D I S S O L V E D S I L I C A S c , m m o l l lFigure
3
R e s u l t s of chemical t e s t , ASTM C289, f o r s o w r e a c t i v e and non-.
r e a c t i v e South A f r i c a n aggregates. Non-reactive: No ( n o r i t e ) andWS ( q u a r t z sand)
.- . . . Y e ? - . ; - . .
.
- -. -.- -=-
-
- - . . .. . - -- .
. : ...-
- - 5 --
The Fare Bridges
Construction site visited during the Conference Excursion
Trykt I Vejdlrektoratet K~benhavn