XRD/Rietveld Analysis of the Hydration and Strength Development of Slag and Limestone Blended Cement

The X-ray diffraction (XRD)/Rietveld method was applied to analyze the hydration progress of cement paste prepared with blast furnace slag powder (BFS) and limestone powder (LSP). The Rietveld method can be used to quantify the amount of amorphous phase as well as crystalline phases. However, in cement paste containing BFS, two kinds of amorphous phases, unhydrated BFS and C-S-H, are included and the Rietveld method cannot distinguish them. In order to discriminate these two phases, a selective dissolution method was used to quantify the amount of unhydrated BFS. By combining these two methods, it became possible to quantify the amount of BFS and C-S-H in hydrated cement. The analysis results show that BFS accelerates the hydration of C3S, C(3)A, and especially C(4)AF. The strength increasing effect of LSP is more pronounced in the ordinary Portland cement (OPC) - BFS system than in the OPC system. This is attributed to the higher amount of calcium aluminate hydrates generated in the BFS contained system compared to the system without BFS. The additional calcium aluminate hydrates fill pores as calcium carboxaluminate by the reaction with LSP, increasing the compressive strength. These results show the effectiveness of the XRD/Rietveld method as an analysis tool for cement hydration relating to various properties of cement materials.