Internal curing is a technique to prolong cement hydration by providing internal water reservoirs in a concrete mixture. These reservoirs do not affect the initial water-to-cementitious materials (w/cm) ratio, but do provide water for curing throughout the thickness of the element. Benefits of this approach include improved mechanical properties as well as reduced risk of moisture gradients, thus reducing the potential for warping. The aim of this work was to assess whether joint spacings could be increased in slabs containing lightweight fine aggregate (LWFA) as a source of internal curing.