Thermal conductivities of expanded shale and clay lightweight aggregates

(1)

Publisher’s version / Version de l'éditeur:

Vous avez des questions? Nous pouvons vous aider. Pour communiquer directement avec un auteur, consultez la première page de la revue dans laquelle son article a été publié afin de trouver ses coordonnées. Si vous n’arrivez pas à les repérer, communiquez avec nous à PublicationsArchive-ArchivesPublications@nrc-cnrc.gc.ca.

Questions? Contact the NRC Publications Archive team at

PublicationsArchive-ArchivesPublications@nrc-cnrc.gc.ca. If you wish to email the authors directly, please see the first page of the publication for their contact information.

https://publications-cnrc.canada.ca/fra/droits

L’accès à ce site Web et l’utilisation de son contenu sont assujettis aux conditions présentées dans le site LISEZ CES CONDITIONS ATTENTIVEMENT AVANT D’UTILISER CE SITE WEB.

Internal Report (National Research Council of Canada. Institute for Research in

Construction), 1987-09-28

READ THESE TERMS AND CONDITIONS CAREFULLY BEFORE USING THIS WEBSITE.

https://nrc-publications.canada.ca/eng/copyright

NRC Publications Archive Record / Notice des Archives des publications du CNRC :

https://nrc-publications.canada.ca/eng/view/object/?id=bdc75ba3-0b23-460d-9e85-dc0eda2f59d2 https://publications-cnrc.canada.ca/fra/voir/objet/?id=bdc75ba3-0b23-460d-9e85-dc0eda2f59d2

NRC Publications Archive

Archives des publications du CNRC

For the publisher’s version, please access the DOI link below./ Pour consulter la version de l’éditeur, utilisez le lien DOI ci-dessous.

https://doi.org/10.4224/20375389

Access and use of this website and the material on it are subject to the Terms and Conditions set forth at

Thermal conductivities of expanded shale and clay lightweight

aggregates

(2)

Ser

TH1

National Research Consell national

R427

1 *

_{Council Canada} _{d e recherches Canada}

n o . 5 5 6

c . 2 Institute for _Research_in lnstitut de BSDG _Construction _constructionrecherche e n

E E R M A I , COUDUCTlVl11ES

OF

E X P A N D E D L 4 I . E

AND CLAY

1,1(;lTi\vElmrr

AGGIU~GATES

L.E.

Goodrich and

T.L.

White

Internal Report No. I.R. 556

Date

of Issue:

28 September

1987

This i s an internal report of the Institute for Research in Construction. It is for personal use only and is not to be cited as a reference in any publication.

(3)

C O N F I D E N T I A L

INTERNAL REPORT

F i e l d Assessment of

THERMAL CONDUCTIVITIES OF EXPANDED

SHALE AND

CLAY LIGHTWEIGHT AGGREGATES

Prepared by

[

4. L a b k h

Prepared by

i~

Pdkd/.

T.L. Wh~te

L.E.

Goodr~ch

3-

Technical O f f i c e r

S e n i o r Researcher

Geotechnical S e c t ion

Geotechnical S e c t i o n

Submitted by

Approved by

W.A.

DALGLIESI4/

Head

Geotechnical S e c t i o n

Head Qua1 i t y %ssurance

I n s t i t u t e f o r Research

i n C o n s t r u c t i o n

A b s t r a c t

T h i s r e p o r t p r e s e n t s t h e r e s u l t s of a f i e l d e v a l u a t i o n of the thermal

c o n d u c t i v i t y of l i g h t w e i g h t c l a y and s h a l e - b a s e d aggregates from s t o c k p i l e s

exposed t o outdoor c l i m a t e c o n d i t i o n s . The d a t a i n d i c a t e d t h a t c o n d u c t i v i t i e s as

low a s 0.1

W1m.K

nay be expected f o r c o a r s e a g g r e g a t e .

Suggestions f o r

p o t e n t i a l a p p l i c a t i o n s of t h e m a t e r i a l a r e included along with p o s s i b l e ways of

improving t h e m a t e r i a l .

Note:

This bdorking Paper i s prepared f o r i n f o r m a t i o n purposes a s p a r t of

a

(4)

/'

I n t r o d u c t i o n

/ Expanded shale and c l a y l i g h t w e i g h t aggregate m a t e r i a l has seldom been

used i n Canada f o r purposes o t h e r than l i g h t w e i g h t concretes. Yet i t s mechanical and drainage p r o p e r t i e s a r e such t h a t i t p o t e n t i a l l y has numerous o t h e r a p p l i c a t i o n s . This p o t e n t i a l has been e x p l o i t e d f o r a number of y e a r s i n a g r e a t d i v e r s i t y o f ways i n Western and Eastern Europe as w e l l as i n t h e S o v i e t Union.

I n J u l y 1987, W.P.L. Engineering o f Calgary requested a s s i s t a n c e from t h e N a t i o n a l Research Council o f Canada (NKCC) t o e v a l u a t e t h e thermal

c o n d u c t i v i t y o f t h e m a t e r i a l produced a t t h e Calgary and Edmonton f a c i l i t i e s o f C o n s o l i d a t e d Concrete Ltd. Since a f u l l c h a r a c t e r i z a t i o n o f t h e m a t e r i a l would e n t a i l a considerable number o f l a b o r a t o r y t e s t s

i t

was f e l t t h a t a programme o f i n s i t u t r a n s i e n t thermal c o n d u c t i v i t y probe measurements i n a number o f stock p i l e s l o c a t e d a t t h e Calgary f a c i l i t y would s u f f i c e t o q u i c k l y i n d i c a t e whether t h e m a t e r i a l had p o t e n t i a l as a thermal

i n s u l a t i o n , and would, a t t h e same t i m e , c o n f i r m o r r e f u t e t h e v a l i d i t y o f thermal c o n d u c t i v i t y values found i n t h e Russian l i t e r a t u r e .

A t o t a l o f 26 thermal c o n d u c t i v i t y t e s t s were made on f i v e d i f f e r e n t stock p i l e s , two o f which were composed o f c l a y b a s 4 aggregate brought

s

j e c i a1 l y from t h e Edmonton p l a n t o f Consolidated Concrete L t d .

The procedure o f measuring t h e thermal c o n d u c t i v i t y o f l o o s e p a r t i a l 1 y s a t u r a t e d m a t e r i a l i s complicated by t h e occurrence o f water vapour

t r a n s f e r , which takes place as a consequence o f t h e measurement process i t s e l f . Consequently t r a n s i e n t c o n d u c t i v i t y probe d a t a f o r such m a t e r i a l s are o f t e n d i f f i c u l t t o i n t e r p r e t . To compensate f o r t h i s d i f f i c u l t y many

(5)

measurements were made i n o r d e r t o c l a r i f y i n t e r p r e t a t i o n o f t h e b e h a v i o u r observed.

Most o f t h e data m a n i f e s t e d a s y s t e m a t i c decrease i n apparent

c o n d u c t i v i t y value when measurements were c a r r i e d o u t using increased power t o t h e probe heater. It i s t h e a u t h o r s ' b e l i e f t h a t , f o r a g i v e n sample,

t h e h i g h e r c o n d u c t i v i t y values o b t a i n e d are c l o s e t o t h e values which would o c c u r under f i e l d m o i s t u r e c o n d i t i o n s w h i l e t h e l o w e s t c o n d u c t i v i t i e s a r e an i n d i c a t i o n o f what might be achieved i f t h e m a t e r i a l were kept d r y .

DISCRIPTION OF

TEST METHOD

Thermal c o n d u c t i v i t y measurements were made u s i n g two d i f f e r e n t s t y l e s o f NRCC designed and c a l i b r a t e d thermal c o n d u c t i v i t y probes w i t h o v e r a l l a c c u r a c i e s o f approximately

-+4%.

The s m a l l e s t probe i s contained i n a s t a i n l e s s s t e e l sheath 3m i n diameter by

5

0

l o n g w h i l e t h e l a r g e r , u s i n g

~

a b r a s s sheath, i s 7mm i n diameter by 50cm long. Both probes use a b i f i l a r wound Constantan heater c o i l w i t h a temperature measuring t h e r m i s t o r mounted i n s i d e t h e c y l i n d r i c a l h e a t e r c o i l a t mid-length. An _{a c r y l i c p l a s t i c}

c a s t i n g r e s i n i s used f o r b o t h probes t o form t h e head, completely e n c l o s i n g s o l d e r e d connections t o t h e l e a d wires. This r e s i n i s a l s o used i n t h e case o f t h e s t a i n l e s s s t e e l probe t o f i l l i t s probe b a r r e l w h i l e t h a t o f t h e l a r g e r brass probe i s f i l l e d w i t h urethane foam. T y p i c a l probe c o n s t r u c t i o n d e t a i l s are shown i n F i g u r e

I.

T h e r m i s t o r s are chosen as temperature sensors because t h e i r s e n s i t i v i t y i s g r e a t l y s u p e r i o r t o t h a t o f thermocouples. Using r e a d i l y a v a i l a b l e

p o r t a b l e

5 +

d i g i t mu1 t i m e t e r s , temperature changes o f a few n i l li k e l v i n s a r e e a s i l y d e t e c t a b l e . This makes i t p o s s i b l e t o o p e r a t e t h e probes u s i n g

(6)

/

v e r y l o w power l e v e l s , thus reducing troublesome thermal g r a d i e n t s near t h e probe and d i m i n i s h i n g t h e associated d e l e t e r i o u s e f f e c t s o f m o i s t u r e

t r a n s p o r t (Goodrich, 1986).

F i e l d measurements were made u s i n g probes o f b o t h types w i t h a p o r t a b l e b a t t e r y - o p e r a t e d f i e l d i n s t r u m e n t a t i o n package. F i g u r e

2

shows t h i s f i e l d a p p a r a t u s which i n c l u d e s a d i g i t a l m u l t i m e t e r , a p r i n t e r capable o f simple g r a p h i c s , a manually operated ( i n t e g r a t e d - c i r c u i t - b a s e d ) r e g u l a t e d c o n s t a n t v o l t a g e source w i t h s w i t c h - s e l e c t a b l e o u t p u t v o l t a g e l e v e l s o p e r a t i n g from s e a l e d l e a d - a c i d b a t t e r i e s and a hand-held programmable c a l c u l a t o r w i t h i n t e g r a l d i g i t a l c l o c k .

The thermal c o n d u c t i v i t y probes were i n s t a l l e d h o r i z o n t a l l y i n t o t h e w a l l s o f s t o c k p i l e s o f t h e d i f f e r e n t t y p e s o f l i g h t w e i g h t shale and c l a y - based aggregates w i t h p r e c a u t i o n t a k e n t o b u r y t h e probes s u f f i c i e n t l y d e e p l y so as t o e l i m i n a t e any i n f l u e n c e froin t h e d r y o u t e r s u r f a c e - l a y e r , Thermal c o n d u c t i v i t y measurements were undertaken o n l y when t h e ambient t e q p e r a t u r e c o n d i t i o n s ' o f t h e aggregate m a t e r i a l around the probe had s t a b i l i z e d t o w i t h i n p l u s o r minus 5 mK over a 5 m i n u t e time period.

The p r i n c i p l e o f o p e r a t i o n o f t h e t r a n s i e n t probe i s s i m i l a r t o t h a t f o r a l i n e h e a t source. For an i n f i n i t e l y l o n g c o n s t a n t l i n e heat source of s t r e n g t h

Q/E

(power/length) embedded i n an i n i t i a l l y isothermal i n f i n i t e homogeneous medium, a f t e r a s u f f i c i e n t l a p s e o f t i m e , t h e temperature T becomes approximately p r o p o r t i o n a l t o t h e l o g a r i t h m o f time:

(7)

where T i s t h e probe t e m p e r a t u r e ( O C ) a t t i m e t ( s e c ) , q i s t h e power i n p u t p e r u n i t l e n g t h o f p r o b e (Wlm), and

k

_{i s t h e t h e r m a l c o n d u c t i v i t y o f t h e} medi um

.

The l a t e r p a r t of a p l o t of p r o b e t e m p e r a t u r e r i s e a g a i n s t t h e l o g a r i t h m o f t i m e conforms t o a s t r a i g h t l i n e , t h e s l o p e o f w h i c h can b e u s e d t o c a l c u l a t e t h e t h e r m a l c o n d u c t i v i t y o f t h e medium. F o r c y l i n d r i c a l probes, i n c l u d i n g t h o s e used f o r t h i s f i e l d s t u d y , f a c t o r s such as n o n - n e g l i g i b l e h e a t c a p a c i t y o f t h e probe, i t s f i n i t e l e n c t h , t h e e x i s t e n c e o f c o n t a c t r e s i s t a n c e between t h e probe s u r f a c e and t h e c o a r s e t e s t medium, and m o i s t u r e m i g r a t i o n owing t o t h e imposed

t e m p e r a t u r e g r a d i e n t a l l m o d i f y t h e t h e r m a l response. N e v e r t h e l e s s by u s i n g l a r s e r d i a m e t e r t r a n s i e n t p r o b e s and a l i m i t e d i n t e r m e d i - a t e t e s t r u n t i m e span, t h e f o r m o f e q u a t i o n

[ I ]

r e m a i n s v a l i d and t h e t h e r m a l c o n d u c t i v i t y c a n be d e t e n i n e d f r o m t h e s l o p e of t h e l i n e a r response s e c t i o n o f t h e c u r v e o f p r o b e t e m p e r a t u r e r i s e v e r s u s l o g a r i t h m o f t i m e . I n p r a c t i c e , a l t h o u g h r e s u l t s a r e a l w a y s p l o t t e d i n o r d e r t o e l i m i n a t e ambiguous o r d e f e c t i v e d a t a , i t i s p o s s i b l e t o a u t o m a t e t h e r e m a i n d e r o f t h e a n a l y s i s p r o c e s s . T y p i c a l measurement and p r e l i m i n a r y a n a l y s i s t i m e s a r e o f t h e o r d e r o f 15 t o 20 n i n u t e s w h i l e t h e f i n a l a n a l y s i s g e n e r a l l y r e q u i r e s an a d d i t i o n a l s i m i l a r p e r i o d .

TEST RESULTS

I n s i t u t h e r m a l c o n d u c t i v i t y d e t e r m i n a t i o n s were made f o r t h r e e g r a d e s ( c o a r s e , medium and f i n e ) o f 1 i g h t w e i g h t s h a l e - b a s e d a g g r e g a t e fran t h e C a l ~ a r y p l a n t o f C o n s o l i d a t e d C o n c r e t e L t d . and two grades ( c o a r s e and medium) o f l i g h t w e i g h t c l a y - b a s e d a g g r e g a t e f r o m t h e Edmonton p l a n t .

(8)

M o i s t u r e c o n t e n t d e t e r m i n a t i o n s were p r o v i d e d f o r a l l stock p i l e s by

C o n s o l i d a t e d Concrete L t d . A d d i t i o n a l d e t e r m i n a t i o n s were made by NRCC from samples taken frm s i t e s B and E. It i s b e l i e v e d t h e Consolidated Concrete samples f o r these two s i t e s were n o t r e p r e s e n t a t i v e o f m o i s t u r e c o n d i t i o n s a t p r o b e b u r i a l depth and o n l y t h e NRCC d e t e r m i n a t i o n s are shown i n Table 1. A summary o f t h e thermal c o n d u c t i v i t y t e s t r e s u l t s based on both p r e l i m i n a r y a n a l y s i s completed i n t h e f i e l d and c a l c u l a t i o n s and p l o t s o f t h e data

r e p e a t e d i n t h e l a b o r a t o r y f o r a l l f i v e l i g h t w e i g h t aggregates are presented i n T a b l e 1. A t y p i c a l l a b o r a t o r y p l o t o f t h e t e s t d a t a i s presented i n F i g u r e 3. D e t a i l e d d i s c u s s i o n s o f t h e data f o r each s i t e f o l l o w .

S i t e A:

The thermal c o n d u c t i v i t y probe was l o c a t e d i n t h e n o r t h (shaded) s i d e o f a s t o c k p i l e o f coarse shale-based aggregate, l m above ground surface, i n s t a l l e d h o r i z o n t a l l y 0.75111 i n t o t h e face o f t h e s t o c k p i l e .

Measured thermal c o n d u c t i v i t i e s ranged from 0.11 t o 0.12 W/m.K f o r two t e s t runs u s i n g an i n p u t power of 0.469 W/m. C o n s i s t e n t values o f 0.14 W/m.K were obtained when t h e h e a t e r power was reduced t o 0.154 W/m f o r f i v e t e s t runs. The dependence o f measured c o n d u c t i v i t y on t h e power l e v e l i s

a t t r i b u t e d t o s i g n i f i c a n t m o i s t u r e t r a n s p o r t away from the probe which r e s u l t s when a l a r g e temperature g r a d i e n t i s imposed by t h e h i g h e r i n p u t

(9)

/

S i t e B

The t h e r m a l c o n d u c t i v i t y probe was l o c a t e d i n t h e n o r t h facing w a l l of a s t o c k p i l e o f medium shale-based aggregate, l m above ground suface

i n s t a l l e d h o r i z o n t a l l y

0.75111

i n t o t h e face o f t h e s t o c k p i l e .

Measured thermal c o n d u c t i v i t i e s ranged f r o m

0.14

t o

0.17

W1m.K b u t w i t h no c l e a r l y s y s t e m a t i c dependence upon i n p u t powers f o r t h e f o u r i n d i v i d u a l t e s t runs, a l t h o u g h t h e average values i n d i c a t e decreased c o n d u c t i v i t y w i t h

i n c r e a s e d i n p u t power.

M o i s t u r e c o n t e n t values were h i g h e r

(13.1%)

t h a n f o r t h e coarse s h a l e based aggregate

(9.3%).

I n view o f t h e h i g h e r d r y d e n s i t y o f t h e medium grade aggregate p a r t i c l e s , t h e h i g h e r values o f t h e thermal c o n d u c t i v i t y compared w i t h those o b t a i n e d f o r t h e coarse aggregate appear reasonable. The g r e a t e r m o i s t u r e c o n t e n t would a l s o c o n t r i b u t e t o i n c r e a s i n g t h e thermal c o n d u c t i v i t y o f t h e medium grade m a t e r i a l .

S i t e s C and C C

Thermal c o n d u c t i v i t y probes c o n s i s t i n g o f t h e s m a l l e r diameter

s t a i n l e s s s t e e l sheath t y p e and t h e l a r g e r diameter brass sheath t y p e were l o c a t e d i n t h e n o r t h f a c i n g w a l l o f a s t o c k p i l e composed o f f i n e shale-based aggregate.

Measured thermal c o n d u c t i v i t i e s values u s i n g t h e small-diameter probe proved t o be ambiguous w i t h thermal c o n d u c t i v i t y values r a n g i n g form 0.22 t o

0.27

W/m.K

o r g r e a t e r f o r s i t e C. F a c t o r s such as poor c o n t a c t between t h e o u t e r w a l l o f t h e probe and t e s t medium and h i g h temperature g r a d i e n t s may b e r e s p o n s i b l e f o r t h e poor thermal response c h a r a c t e r i s t i c s observed.

(10)

/

Measured thermal c o n d u c t i v i t y values u s i n g the l a r g e r diameter brass

/

p r o b e ranged , from 0.17 t o 0.26 W/m.K f o r s i t e CC w i t h no c l e a r systematic dependence upon power i n p u t l e v e l b e i n g observed f o r t h e t h r e e i n d i v i d u a l t e s t runs s i m i l a r t o t h e o b s e r v a t i o n s f o r s i t e B.

M o i s t u r e c o n t e n t values (20.5%) were h i g h e r than t h e medium s h a l e based a g g r e g a t e (13.1%) and t h e coarse shale based aggregate (9.3%). I n a d d i t i o n t o t h e presence o f a h i g h percentage o f f i n e s t h e g r e a t e r m o i s t u r e c o n t e n t presumably c o n t r i b u t e d t o i n c r e a s i n g t h e thermal c o n d u c t i v i t y o f t h e f i n e grade m a t e r i a l as compared w i t h t h a t f o r a l l o t h e r s i t e s .

S i t e

D

The thermal c o n d u c t i v i t y probe was l o c a t e d i n t h e - n o r t h f a c i n g slope of a s t o c k p i l e o f medium clay-based aggregate, again u s i n g t h e same probe b u r i a l procedure.

Measured medium clay-based aggregate thermal c o n d u c t i v i t i e s ranged from 0.14 W/rn.K u s i n g an i n p u t power o f 0.472 t o 0.17 W/mK f o r an i n p u t power l e v e l o f 0.155 W/m. The d i f f e r e n c e s i n c o n d u c t i v i t y a r e again c o n s i s t e n t w i t h m o i s t u r e t r a n s p o r t o c c u r r i n g i n response t o t h e higher temperature g r a d i e n t .

These v a l u e s a r e a l s o h i g h e r than f o r t h e coarse grade o f t h e same n a t e r i a l , as would be expected i n view b o t h o f t h e h i g h e r d r y d e n s i t y and t h e h i g h e r m o i s t u r e c o n t e n t (20.4%). It i s i n t e r e s t i n g t o note t h a t i n s p i t e o f t h e much h i g h e r m o i s t u r e c o n t e n t (20.4% i n s t e a d o f 13.1%) t h e t h e r m a l c o n d u c t i v i t y values a r e s i m i l a r t o those obtained f o r t h e medium

(11)

S i t e

E

The thermal c o n d u c t i v i t y probe was l o c a t e d i n t h e n o r t h f a c i n g s l o p e o f a s t o c k p i l e composed o f coarse clay-based aggregate using t h e same probe b u r i a l procedure as a t t h e shale-based aggregate stock p i l e s .

Very c o n s i s t e n t r e s u l t s were o b t a i n e d w i t h almost n e g l i g i b l e apparent change w i t h v a r i a t i o n i n a p p l i e d power. Thermal c o n d u c t i v i t i e s ranged from

0.10 t o 0.12 W1m.K f o r i n p u t power l e v e l s o f 0.472 W/m and 0.155 W/m

r e s p e c t i v e l y . The small decrease i n c o n d u c t i v i t y a t t h e h i g h e r power l e v e l i s c o n s i s t e n t w i t h a s l i g h t m o i s t u r e t r a n s p o r t and attendant d r y i n g

o c c u r r i n g i n t h e t e s t medium s u r r o u n d i n g t h e probe. I n t e r e s t i n g l y enough, a l t h o u g h t h e m o i s t u r e c o n t e n t (14.8%) i s considerably more than f o r t h e shale-based aggregate of t h e same grade ( 9 . 3 % ) , t h e thermal c o n d u c t i v i t y o f t h e clay-based m a t e r i a l i s s i m i l a r o r even s l i g h t l y lower.

D i s c u s s i o n

The thermal c o n d u c t i v i t y v a l u e s o b t a i n e d are c o n s i d e r a b l y lower than t h o s e f o r normal e a r t h m a t e r i a l s (see Table 11), although s t i l l

a p p r o x i m a t e l y t h r e e t o f o u r t i m e s t h a t o f expanded p o l y s t y r e n e i n s u l a t i o n . Iiumerous geotechnical a p p l i c a t i o n s can be imagined where an e n v i r o n m e n t a l l y s a f e m a t e r i a l w i t h good i n s u l a t i n g p r o p e r t i e s combined w i t h e x c e l l e n t

d r a i n a g e c h a r a c t e r i s t i c s and ease o f t r a n s p o r t and placement would be e x t r e m e l y d e s i r a b l e . Expanded c l a y and shale aggregate would appear t o possess many advantages f o r road b u i l d i n g and municipal works where

p r o t e c t i o n from f r o s t a c t i o n i s r e q u i r e d , s i n c e i t e l i m i n a t e s o r reduces a l l t h r e e o f t h e c o n d i t i o n s which can l e a d t o f r o s t a c t i o n , namely l o w

(12)

9

t e m p e r a t u r e s , poor d r a i n a g e and f r o s t s u s c e p t i b l e m a t e r i a l .

Use of t h i s

a g g r e g a t e c o u l d e a s i l y be imagined i n road beds a s well a s a s a b a c k f i l l f o r

sewer and water l i n e s o r t o reduce f r o s t j a c k i n g damage around manholes.

I t

C

_{c o u l d a l s o be very b e n e f i c i a l a s a b a c k f i l l f o r b u i l d i n g foundations and}

behind r e t a i n i n g w a l l s .

In permafrost c o n s t r u c t i o n t h e m a t e r i a l should be v a l u a b l e as an

i n s u l a t o r t o maintain f r o z e n ground under road beds, a i r s t r i p s and s l a b on

g r a d e b u i l d i n g f o u n d a t i o n s .

A

p o t e n t i a l l y important a p p l i c a t i o n i n t h e

North may be a s an i n s u l a t i n g d r a i n a g e m a t e r i a l i n s e c t i o n s of roads where

d r a i n a g e i s poor y e t c r i t i c a l l y important and normal c u l v e r t s a r e not

p r a c t i c a l ( a common p r o b l m i n many a r e a s ) .

Another advantageous

a p p l i c a t i o n might be a s an i n s u l a t i n g m a t e r i a l f o r p i p e l i n e s s i n c e l a b o u r

c o s t s and i n s t a l l a t i o n time could be s i g n i f i c a n t l y reduced.

With hot o i l

p i p e l i n e s t h e m a t e r i a l would t e n d t o dry o u t and hence maintain i t s thermal

i n s u l a t i o n v a l u e near t h e pipe.

For both roads and p i p e l i n e s t h e m a t e r i a l

c o u l d have s u b s t a n t i a l p o t e n t i a l f o r t h e thermal s t a b i l i z a t i o n of s l o p e s and

c u t s .

F i n a l l y , numerous s m a l l e r a p p l i c a t i o n s appear p o s s i b l e , such a s t o

p r o v i d e an i n s u l a t i n g f r e e - d r a i n i n g m a t e r i a l beneath t h e c h i l l e d a r e a of i c e

s k a t i n g a r e n a s and c o l d s t o r a g e p l a n t s .

Some p r a c t i c a l e x p e r i e n c e i n t h e use of expanded s h a l e o r c l a y a g g r e g a t e

f o r f r o s t p r o t e c t i o n of highways has been g a t h e r e d a l r e a d y in Europe

s t a r t i n g i n t h e e a r l y 1 9 7 0 ' s .

A

l i t e r a t u r e review i s now underway t o l e a r n

what, p r e c i s e l y was done and what d i f f i c u l t i e s i f any were encountered.

The v a l u e of t h e m a t e r i a l a s an i n s u l a t o r can be unambiguously

(13)

10

c a p e t i n g m a t e r i a l s . The presence o f m o i s t u r e i s probably u n d e s i r a b l e because i t i n c r e a s e s t h e thermal c o n d u c t i v i t y . This e f f e c t i s , however, p a r t i a l l y o f f s e t f o r seasonal f r o s t o r thaw p r o t e c t i o n by t h e f a c t t h a t t h e m o i s t u r e slows down t h e r a t e of p r o g r e s s i o n o f t h e 0°C isotherm. I n v i e w of p o s s i b l e breakdown under repeated freeze-thaw c y c l i n g , i t i s , on balance,

p r o b a b l y p r e f e r a b l e t o e l i m i n a t e t h e m o i s t u r e . P r a c t i c a l methods o f d o i n g so s h o u l d be c o n s i d e r e d as p a r t o f a f u t u r e study.

The thermal c o n d u c t i v i t y v a l u e s c l e a r l y increased f o r t h e denser grades. Even w i t h i n a s i n g l e grade, v i s u a l i n s p e c t i o n i n d i c a t e d v e r y

n o t i c e b l e v a r i a t i o n s i n d e n s i t y o f t h e i n d i v i d u a l p a r t i c l e s . Therefore, i t

s h o u l d be p o s s i b l e t o s u b s t a n t i a l l y reduce t h e thermal c o n d u c t i v i t y o f t h e m a t e r i a l by e l i m i n a t i n g t h e denser f r a c t i o n . This procedure ought n o t t o

s i g n i f i c a n t l y a f f e c t mechanical p r o p e r t i e s such as c r u s h i n g s t r e n g t h , s i n c e t h e s e p r o p e r t i e s presumably a r e l a r g e l y c o n t r o l l e d by t h e weakest p a r t i c l e s .

It may a l s o be t h a t f o r a s i m i l a r p a r t i c l e d e n s i t y t h e c o n d u c t i v i t y o f t h e shale-based m a t e r i a l i s n o t s i g n i f i c a n t l y g r e a t e r than f o r m a t e r i a l produced fran c l a y .

I f m o i s t u r e can n o t be e l i m i n a t e d t h e n i t i s i m p o r t a n t t o r e c o g n i z e t h a t f r o z e n wet m a t e r i a l w i l l have a n o t i c e b l y g r e a t e r c o n d u c t i v i t y t h a n f o r w e l l - d r a i n e d thawed m a t e r i a l and t h i s aspect needs t o be examined f u r t h e r .

For some a p p l i c a t i o n s i t may be necessary t o consider e n c a p s u l a t i o n o r s i m i l a r concepts t o reduce thermal c o n d u c t i v i t y degradation. I n o t h e r a p p l i c a t i o n s however, such as c o n t r o l o f p e r m a f r o s t temperatures, an

i n c r e a s e i n f r o z e n c o n d u c t i v i t y i s g e n e r a l l y d e s i r a b l e and c o u l d be

a

u s e f u l advantage o f t h e m a t e r i a l .

(14)

C o n c l u s i o n ,,'

/

The thermal c o n d u c t i v i t y v a l u e s o b t a i n e d f o r t h e medium and coarse grades o f b o t h shale- and c l ay-based 1 ig h t w e i g h t aggregates i n d i c a t e c l e a r l y t h a t t h e s e m a t e r i a l s are s u f f i c i e n t l y good i n s u l a t o r s t o be p o t e n t i a l l y v e r y

u s e f u l f o r c o n t r o l of ground temperatures. The f i n e grade o f shale

aggregate, however, gave poor r e s u l t s . The clay-based coarse grade gave t h e l o w e s t thermal c o n d u c t i v i t y o f a l l t h e samples t e s t e d . The data suggest t h a t f o r t h e same grade o f m a t e r i a l t h e clay-based aggregate i s a b e t t e r

i n s u l a t o r than the shale-based m a t e r i a l even when i t s m o i s t u r e content i s s u b s t a n t i a l l y greater. The d a t a o b t a i n e d by o p e r a t i n g t h e equipment a t b o t h l o w and h i g h power i n p u t y i e l d e d an i n s i g h t i n t o t h e e f f e c t o f m o i s t u r e c o n t e n t on t h e apparent thermal c o n d u c t i v i t y b u t d i d n o t n e c e s s a r i l y

i n d i c a t e t h e f u l l range.

A l a b o r a t o r y e v a l u a t i o n s h o u l d be undertaken i n o r d e r t o f u l l y c h a r a c t e r i z e t h e thermal c o n d u c t i v i t y o f t h e coarse and medium grade aggregate. Neasurements should be made i n b o t h s a t u r a t e d and oven d r y c o n d i t i o n s t o l e a r n t h e f u l l range p o s s i b l e . I n a d d i t i o n , i t would be i m p o r t a n t t o measure c o n d u c t i v i t i e s o f t h e f r o z e n m a t e r i a l i f i t i s t o be used as an i n s u l a t o r against cold. F u r t h e r work should be done t o determine t h e reasons f o r the s u p e r i o r r e s u l t s found w i t h t h e c l a y based m a t e r i a l as w e l l as t o determine what improvements might be o b t a i n e d by s o r t i n g t o r e t a i n o n l y t h e l i g h t e s t d e n s i t y m a t e r i a l . F i n a l l y , methods f o r