Abstract
The qualities necessary for the grouting paste for prestressed concrete are faculty of smooth flow, little bleeding and change of volume, high strength (compressive and bond) and resisting power for freezing. But those qualties, excepting the faculty of flow, are improved by the minimum use of water.
The current apparatus for measurement of fluidity of grouting paste are such as shown in Fig. 1∼Fig. 3, either of which is used, according to the enquête undertook by the Dutch Grouting Committee, in various foreign countries except in Holland.
The“International Recommendation”arranged by the same Committee has recently stated that“The water-cement-ratio must be as low as possible for a good workability. The fluidity of the grout may be measured with every kind of apparatus that gives reproducible results. Every type of apparatus must be calibrated in poises.”
But no apparatus has been calibrated in poise so far.
It is partly due to the thixotropic property of cement paste but mainly to the assumption that cement paste is nothing but a Newtonian liquid. The experiments which the writers have made with his coworkers on an assumption that cement paste is Bingham body clearly show that the measurements done with those apparatus can be expressed in terms of absolute unit.
The measurement has been done by means of BH type rotation viscometer (Photo. 1) at various rates of shear, that is, its number of rotation of rotor.
Investigation has also been made as to the change which the charactaristic values of ηpl and ν undergo by taking into consideration various conditions necessary for the presstressed concrete grouting, that is, mix proportion, types and numbers of rotation of mixer, mixing time and the fineness of cement.
Several results are shown in the following figures. From these experiments some conclusions have been obtained as follows:
(1) Cement paste behaves as Bingham body, and the fluidity of grouting paste is represented both by ηpl and ν.
(2) The values of these rheological properties are influenced by mixproportion, types and numbers of rotation of mixer, mixing time and the fineness of cement etc..
(3) The current apparatus for measurement of fiuidity of paste which are shown in Fig. 1∼ Fig. 3 will not be sufficient for measurement of ηpl and ν.
