This research investigated the latent heat and energy storage of lightweight concrete containing high contents of phase change material (PCM) (up to about 7.8% by weight of concrete). PCM – Polyethylene Glycol (PEG) with a fusion temperature of approximately 42–46 °C was impregnated into porous lightweight aggregates up to 24% by weight. The PCM aggregates were then used to replace normal lightweight aggregate at a rate of 0, 25, 50, 75 and 100% by volume. The samples were subjected to series of experiments such as compressive strength (EN12390-3 2002), flexural strength (ASTM C78), thermal conductivity (ASTM C518) and the thermal storage of phase change materials examined using a heat flow meter apparatus (ASTM C1784) at the age of 28 days...