Workability loss

Workability Loss Most WRA also have a retardation effect. Therefore, they reduce the workability loss, which is usually described in terms of slump (measure of concrete consistency) loss. For normal WRA, a distinction should be made between concrete mixes with a specified waterrcement ratio and a specified slump. At a given waterxement ratio the slump of concrete with WRA increases considerably. Although the rate of slump loss increases upon normal WRA use, the higher slump value at the beginning causes later slump values to be still higher than those of the concrete without WRA. On the other hand, for the same initial slump, the workability loss is more rapid in normal WRA incorporated concretes than that of control concretes. A similar but more pronounced effect of loss of workability is observed in high range WRA incorporated mixes. 

In order to study the effect of SO3 on slump loss in superplasticized cement, Khalil and Ward l adopted the conduction calorimetric technique. The heat effects were used to explain the workability loss. It was concluded that for cements cured at 25°C, the optimum SO3 content was higher in the presence of the superplasticizer. 

Masonry cements (80) are cements for use in mortars for masonry constmction. They are formulated to yield easily workable mortars and contain special additives that reduce the loss of water from the mortar to the porous masonry units. 

These limited results give some indication that it is possible to achieve high-workability material without a consequential loss in cohesion by the use of water-reducing admixtures of the lignosulfonate. 

The relationship of the concentration of the admixture to the water reduction produced has been found to be linear (Fig. 7.6). Two conclusions were reached from the study which included several brands of cement [15] (1) it is the addition rate of the admixture which is important, and (2) the chemical nature of the admixture does not play a part in water reduction, but is an important factor in determining the retention (or loss) of slump in concrete with age. For example, the extended workability of the more... 

The rapid decay of workability due to high slump loss, posing retempering (adding extra water on site) problems. 

EFFECT OF TYPE OF GYPSUM AND GYPSUM HEMIHYDRATE OR SOLUBLE ANHYDRITE RATIO (ABNORMAL SETTING AND LOSS OF WORKABILITY)... 

The thus obtained high-density Mn-Zn ferrite was investigated in detail from the view of physical and mechanical properties, that is, the relationships between the composition of metals (a,) ) and <5 the magnetic properties such as temperature and frequency dependence of initial permeability, magnetic hysteresis loss and disaccommodation and the mechanical properties such as modulus of elasticity, hardness, strength, and workability. Figures 3.13(a) and (b) show the optical micrographs of the samples prepared by the processes depicted in Fig. 3.12(a) and (b), respectively. The density of the sample shown in Fig. 3.13(a) reached up to 99.8 per cent of the theoretical value, whereas the sample shown in Fig. 3.13(b) which was prepared without a densification process, has many voids. 

Retorting of the total oil sand to produce cracked products was tested extensively, and other than the high heat loss to the sand, it appeared to be a very workable scheme. A combination scheme involving hot water washing to produce a wet bituminous froth followed by fluid coking of this froth was the basic operation recommended in the Blair report in 1950 (4). 

DILUENT. (I) An ingredient used to reduce the concentration of an active material to achieve a desirable and beneficial effect. Examples are combination of diatomaceous earth with nitroglycerin to term the much less shock-sensitive dynamite addition of sand to cement mixes to improve workability with no serious loss of strength addition of an organic liquid having no solvent power to a paint or lacquer to reduce viscosity and achieve suitable application properties. 

---