Research has focused on several subtopics: 1) modeling and experimental measurements on systems containing limestone fillers, 2) incorporation of the reactions for slag into CEMHYD3D, and 3) modeling of the pH and ion concentration of the pore solution during hydration. Substantial progress has been made on each of these topics.
Limestone additions to cement are commonplace throughout the world, with the exception of the U.S. In general, small (≤15%) quantities of limestone have no detrimental effects on cement properties and reduce both greenhouse gas emissions, and energy requirements. Additionally, in low w/c ratio concretes, there is insufficient space for all of the cement to hydrate completely, so that some of the cement may be acting as rather expensive reinforcing filler. The VCCTL consortium has been exploring the concept of replacing the coarsest cement particles by limestone fillers in low w/c ratio (≤0.3) concrete, via both computational and experimental research. From the modeling side, reactions for limestone have been added to the CEMHYD3D software. The limestone reacts with aluminates to form a calcium aluminate monocarbonate (AFmc) reaction product, reducing the monosulfoaluminate (AFm) content in the hydrated system (Klemm and Adams, 1990). The consortium has also experimentally examined the concept of replacing the coarsest fraction of the cement particles by limestone filler of a similar size (see Case Study I below for details).
A set of hydration reactions for slag has been incorporated into the latest version of the CEMHYD3D software. To accurately model a given slag, the user must obtain its particle size distribution and oxide composition. The hydration reactions for slag have been developed and partially validated based on materials received from consortium members. The slag reacts with a fraction of the calcium hydroxide produced from the cement hydration to produce a "slag"-gel hydration product containing calcium, silicon, aluminum, magnesium, and possibly sulfate. If the slag contains excess aluminum relative to its magnesium content (with regard to the formation of a hydrotalcite-type phase), the excess aluminate participates in reactions with the calcium sulfate in the cement to form ettringite and monosulfoaluminate (and hydrogarnet when sulfate is not readily available). Validation of these reactions has been based on measurements of chemical shrinkage of blended cements (typically 30% slag, 70% cement), measurements of calcium hydroxide production/consumption, and analysis of hydrated microstructures via X-ray diffraction and scanning electron microscopy. To date, good agreement between model predictions and experimental measures has been obtained.