Release of internal curing water from lightweight aggregates in cement paste investigated by neutron and X-ray tomography

A sealed sample of cement paste containing a pre-wetted and a dry lightweight aggregate (LWA) particle was investigated in the period between 0.5 and 20.3 h after mixing. Changes in the local water distribution in the sample during hydration were evaluated using the subtraction of 3D images obtained by subsequent neutron tomographies (NT). As both water retention in the LWA and its release to the cement paste are influenced by the pore structure of the aggregate, a high-resolution image of the sample was subsequently captured by X-ray tomography. The internal curing water released from the LWA traveled at least 3 mm from the LWA into the cement paste in the first day. Hardly any gradient in the water content of the cement paste against the distance from the LWA was observed. This suggests that the release of water for internal curing (IC) is relatively fast and the water is distributed fairly homogeneously from the LWA for at least 3 mm within the hydrating cement paste.