Bleeding of cement pastes

A b s t r a c t I n v e s t i g a t i o n s on the bleeding of cement pastes were carr i e d out wi t h d i f f e r e n t cements. Studies w i t h customary cements showed a c l e a r tendency to decreasing bleeding w i t h i n c r e a s i n g s p e c i f i c surface, but se v e r a l u n c e r t a i n t i e s i n regard to the spread of r e s u l t s r e q uired f u r t h e r research wit h cements produced i n the laboratory. By keeping i n f l u - encing f a c t o r s other than fineness constant, the spread was reduced d i s t i n c t l y . A d d i t i o n a l strong i n f l u e n c e s of type and amount of calcium sulphate on the tendency of cement pastes to bleed were i l l u s t r a t e d at v a r i e d temperatures. The d i f f e r e n t s o l u b i l i t y of hemihydrate and anhydrite, which i s again e f f e c t e d by temperature, caused changes i n the s t r u c t u r a l development. Keywords : Bleeding, Cement Paste, Fineness, Calcium S u l - phate M o d i f i c a t i o n , Hemihydrate, Anhydrite, Temperature

1 Introduction

1.1 General Bleeding, i . e . the process of settlement of s o l i d s and exp u l s i o n of water w i t h i n f r e s h concrete, i f i t exceeds a normal r a t e and leads to the formation of channels or water lenses under coarse aggregate p a r t i c l e s or reinforcement, i s considered to be disadvantageous to concrete q u a l i t y . Any excessive upward stream of the bleeding water w i l l carry w i t h i t f i n e p a r t i c l e s of cement and sand, thus forming the more or l e s s harmful l a i t a n c e on the h o r i z o n t a l surface or b r i n g i n g about spotted v e r t i c a l surfaces and leading to heterogeneous hardened concrete.