Theoretical background: see chapters 3 and 4 in Machiels (2010). Sample preparation method modified from Machiels et al. (2008).
The mineralogy and glass content of slags depend largely on the mode of cooling of the slags, e.g. slow cooling in a slag pot can result in a large amount of crystalline phases, and fast granulation in water can result in high glass content. A mineralogical analysis will thus only represent the mineralogy of a slag system for a certain grade of cooling and strongly different results can be obtained when cooling conditions are different between the different batches.
Even in a single slag pot, mineralogy and glass content can vary strongly. Taking a sample representative for a slag pot can be done by performing the sampling after a first size reduction of the bulk material or, by mixing representative parts of the slag pot (sides of the pot, center, near cracks, in center of slags, etc.)
1 Procedure of EDTA
A typical chemical reaction of a slag could be like the following [NIST, D.P Bentz],
C7.88S7.39M3A + 2.6CH + bH → 7.39C1.42SHmA0.046 + 0.66M4.6AHd
C=CaO, S=SiO2, M=MgO, A=Al2 O3, CH=Ca(OH)2, H=H2O.
The method EDTA (Ethylenediaminetetraacetic acid) has been described by Erntroy [Erntry, 1987]. The following is a short description of the method.
Better performance of slag concrete exposing to high temperatures
Concrete made with GGBS cement is much better than concrete made with 100% OPC at maintaining its compressive strength when exposed to high temperatures.
It is mentioned previously that the reactivity of slag is influenced by its fineness of grinding (specific surface area) that is determined by the sizes of slag particles. The finer the slag particles, the larger the surface area, which means higher hydration degree of slag.
However, if disregarding the fineness, in other words, take two slag particles with significantly different sizes (diameters of “spherical” particles) as the study target, do the reacting front layers of the two particles grow at same rate? The growing rate of reacting layer can be a good tool to calculate the hydration degree of slag at particle level.
Although it is somewhat difficult to measure the reaction degree of slag in slag blended cement comparing with the case in Portland cement, many researchers performed experiments on this field. A large body of literature can be found on the kinetics of Portland cement/slag blends.
Based on the modification of Takashima’s salicylic acid extraction method, Taylor collected some researchers’ data on the reaction degree of slag, as is showed in Table 1.