Application of X-Ray Micro-CT for Quantifying Degree of Hydration of Slag-Blended Cement Paste

Abstract

Quantifying the degree of hydration of mineral additives in a blended system has been a challenge in the concrete research community. This study attempted to calculate the degree of hydration of both clinker and ground granulated blast furnace slag in a slag-blended cement system based on nondestructive detection by X-ray micro–computed tomography (CT). Ordinary portland cement (OPC) pastes and slag-blended cement pastes were used with water-to-binder ratios of 0.3 and 0.5. The degree of hydration was calculated by comparing the volume fraction of the unhydrated phase with its original value. The key to quantification is to segment different phases (clinker, hydration products, and pores) in CT images, and then the volume fraction of the unhydrated phase can be obtained. Grayscale gradient–based edge detection was introduced for the first time to segment CT images of the cementitious materials. The degree of hydration quantified from the CT images was compared with that obtained from classical Thermogravimetric analysis (TGA). The use of X-ray CT to quantify the degree of hydration of OPC and slag-blended pastes was shown to be feasible. A suitable segmentation method for CT image of cementitious materials was recommended.