ABSTRACT
15 Conclusions 1. Dutch d r a f t standard recommendations (3) contain recommendations, s p e c i f i c a t i o n s and r u l e s f o r t e s t i n g and a s s e s s i n g the s u i t a b i l i t y of crushed masonry rubble as aggregate f o r concrete. However, compliance with these s p e c i f i c a t i o n s i s not s u f f i c i e n t i n i t s e l f and acceptance t e s t s must be c a r r i e d out i n any case. I n the F e d e r a l Republic of Germany according to DIN 4226 crushed b r i c k rubble may be used as aggregate f o r production of ligh t w e i g h t aggregate concrete. However, crushed masonry rubble made from d i f f e r e n t s o r t s of b r i c k s and blocks may not n e c e s s a r i l y f a l l under the j u r i s d i c t i o n of that s t a n - dard and an a u t h o r i z a t i o n i s re q u i r e d f o r t h e i r use i n each i n d i v i d u a l case. 2. The proportion of harmful i m p u r i t i e s i n crushed masonry rubble should not exceed the l i m i t i n g v a l u e s according to (3) or DIN 4226, p a r t 2. According to the Dutch d r a f t standard the proportion of paper, p l a s t i c , g l a s s , e t c . should be l i m i t e d to a maximum of 1% by weight and 1% by volume. 3. R e l i a b l e f i g u r e s f o r the water absorption of the aggregate must be determined where the c h a r a c t e r i s t i c value a f t e r 30 minutes i s not r e l i a b l e . An accurate estimate of the water absorption necessary for maintaining the cons i s t e n c y of f r e s h concrete and for maintaining the requ i r e d water/cement r a t i o i s made d i f f i c u l t by the varying value of the water absorption of aggregates. For mixes with a f l u i d c o n s i s t e n c y and produced with l a r g e water contents more water may be absorbed by the aggregate and should be deducted from the quant i t y of mixing water when the f r e e water/cement r a t i o i s c a l c u l a t e d , than would be the case for s t i f f mixes. 4. Wherever p o s s i b l e , i t i s recommended th a t porous crushed masonry rubble should be pre-wetted, f o r i n s t a n c e by means of s p r i n k l e r s i n a s t a r s i l o . Care must be taken to ensure that the water s a t u r a t i o n of the aggregate i s uniform. T h i s r e q u i r e s s u f f i c i e n t time. 5. Aggregate must not be used f o r production of concrete while soaking wet, i n order not to l o s e c o n t r o l of the f r e e water/cement r a t i o . 6. The p a r t i c l e d e n s i t y of crushed b r i c k rubble i s between 1,200 and 1,800 kg/m3 and the bulk d e n s i t y i s between 1,000 and 1,500 kg/m3. The p a r t i c l e d e n s i t y compared with other l i g h t w e i g h t aggregates may be c h a r a c t e r i z e d as medium. For crushed masonry aggregates, the expected range of p a r t i c l e d e n s i t i e s i s even l a r g e r . Where the proportion of crushed concrete i s l a r g e , the upper l i m i t of 2,200 kg/m3 as
