In o rd er to c e n tre specimens p rio r to t e s t , numbers are provided on the lower loading s t r i p , (zero a t the c e n tre , in c re a sin g outw ards a t h. inch in te r v a ls ) , and by referring to th e se , specimens can
be lo c ated c e n tr a lly w ith re sp e c t to th is s c a le . To f a c i l i t a t e c e n trin g in a d ire c tio n p e rp e n d icu la r to th i s , the system i l l u s tr a te d in p la te 4 (b ) was u sed. A s u ita b ly dim ensioned support and backstop arrangem ent was provided on both th e upper and lower cross-m embers such th a t when the s te e l c e n trin g p la te was in s e rte d and p o sitio n e d a g a in s t the b ack sto p s, and a specimen h eld in c o n ta c t w ith i t (as in p la te 4 b ) , th e specimen was th en c e n tr a l w ith
re s p e c t to th e loading s t r i p s . The arrangem ent allow s fo r the
p la te to rem ain in p o s itio n u n t i l load is being taken by the specim en, a t which p o in t, i t can be removed. Thus c e n trin g can be achieved w h ils t leav in g a sm all gap between the specimen and the upper
loading s t r i p , thus allow ing s u f f ic ie n t time fo r machine tak e-up to occur p rio r to any reco rd in g being made, (as in the M arshall t e s t ) .
P rio r to t e s t , specimens were brought to a tem perature o f 25°C by p la cin g them in a th e rm o s ta tic a lly c o n tro lle d w a te r-b a th fo r a t le a s t 45 m in u tes. Using the set-u p p re v io u sly d e sc rib e d , i t is n o t p o ssib le to b rin g any of the equipm ent to t e s t tem pera tu re p rio r to te s t in g . However, as the t e s t tem perature (25°C) was only s lig h tly above normal room tem p eratu re, the au th o r c o n sid ered th is to be unnecessary provided te s tin g was c a rrie d out as
q u ick ly as p o s s ib le .
Having p re v io u sly c a lib ra te d the re co rd in g equipment (see Appendix B), each specimen was in tu rn cen tred between the load in g s t r i p s ,
leav in g a gap of approxim ately 4 mm between the specimen and the upper loading s t r i p . The te s tin g machine was sw itched on, and as soon as load was being taken by th e specim en, the c e n te rin g p la te was removed. The fo rce being e x e rte d was measured c o n tin uously by the load c e l l and a Force v s. Time graph produced by the c h a rt re c o rd e r. When the specimen f a ile d , the te s tin g mach ine was sw itched o f f , the specimen unloaded and the o p e ra tio n s rep eated as q u ick ly as p o ssib le u n t i l a l l specimens had been te s te d .
A ty p ic a l Force v s. Time graph is shown in fig u re 10. Knowing the c a lib r a tio n o f the equipm ent, the fo rce a t f a ilu r e can be determ ined in the same manner as in the M arshall t e s t .
C a lib ra te d fo r f u l l sc a le d e fle c tio n = 12.5 kN 1 in on c h a rt = 1.25 kN
D istance on c h a rt re p re se n tin g maximum fo rce (SD) = 6.55 inches (see fig u re 10)
Maximum fo rce(P ) = 1.25 x 6.55 = 8.19 kN
hence, knowing the dim ensions of the specim en, the In d ire c t-T e n s ile S tren g th ( I .T .S .) can be c a lc u la te d :
Diameter (D) = 101.6 mm H eight (H) = 63.2 mm
I.T .S . = 2P = 2 x 8 .19xl03 = 0.812 N/mm2 TfDH 3.142x101.6x63.2
The v e r tic a l deform ation undergone by the specimen a t f a ilu r e
(AD) was determ ined from the c h a rt re c o rd in g , in a manner id e n tic a l to th a t by which M arshall Flow was determ ined, i . e . assuming a c o n sta n t ra te of ram movement (50.8 mm/min), a c o n sta n t ra te of
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