Increasing the thermal efficiency of structures and decreasing deterioration in concrete pavements due to harsh changes in temperature have been the topic of much research. Using phase change materials (PCMs) in buildings decreases the energy lost and increases occupant comfort. In addition, using PCM in concrete pavements decreases thermal deterioration due to freeze/thaw cycles. To investigate the capacity of PCMs to increase the thermal inertia of mortar, a series of laboratory test were conducted. Three different kinds of PCMs with different melting points and latent heats were used. Lightweight Aggregate (LWA) was used as a carrier unit for PCMs and a guarded longitudinal calorimeter (GLC) was used to measure heat flow during both heating and cooling. The results show that using LWA to incorporate PCM in mortar prevents PCM interference with the hydration reaction between cement and water and therefore the compressive strength of the mortar does not decrease drastically. In addition, adding PCM to mortar increases the thermal mass and delays temperature changes. (C) 2015 Elsevier B.V. All rights reserved.