Assessing hydration disturbances from concrete aggregates with radiation shielding properties by isothermal calorimetry

Spallation sources create a large amount of neutrons with energies up to the GeV range. To shield for these neutrons, steel and concrete are important materials. By adding different aggregates to normal concrete, one can improve the shielding effect of the concrete. Some of these aggregates can influence the rate of hydration (reaction) of the cement or even completely inhibit the hydration. It is thus good practice to start the investigation of new shielding concretes by assessing the rate of cement hydration in the presence of new aggregates. This is preferably made with isothermal (heat conduction) calorimetry. In this paper we describe such tests made with a large number of different potential aggregates for a shielding concrete. We found a full range of influence on the hydration, from no influence to severely disturbed. In some cases smaller particles gave more disturbance.

Figure 1

Schematic illustration of how a calorimetric measurement of the hydration of a neat cement (solid line) can be changed by additions causing retardation (dashed line), lowered rate of the main reaction (dash-dotted line), or serious hydration disturbances (dotted line).

Figure 2

Results of isothermal calorimetry on cement paste (no aggregate) discussed in the text. (a) Twelve repeats of hydration measurements made over a 140 day period. (b) Results for different water/cement ratios.

Figure 3

Results from tests with isothermal calorimetry of compatibility between hydrating cement and different materials used for radiation shielding. The samples and the used concentrations are given in Table 1 and the results are described in Table 2.

Figure 4

The same result for cement paste with colemanite ore as in Fig. 3, but the hydration curves have been shifted in the y-direction to emphasize that the sulfate depletion peak at the arrow changes when the colemanite ore is added.