Since joining Rand, Loial has shown the ability to fight and drive back shadowspawn such as Trollocs and Myrddraal. It is known that Ogier are peaceful creatures and are not used to weapons. I've seen Loial using a weapon made from a tree stick. However, I don't remember him using any other weapon in their journey.
If it is not the weapon, is it the size of his body that makes him so great at fighting?
In The Shadow Rising, it is written:
“Loial,” Faile said, standing up from behind one of the banks of flowers with a book in her hands, “is a hero.”
Perrin jumped; the flowers had masked her scent completely. Loial made shushing noises, his ears twitching with embarrassment, and waved his big hands at her, but she went on, her voice cool but her eyes hot on Perrin’s face.
“He gathered as many children as he could—and some of their mothers—into a large room, and held the door alone against Trollocs and Myrddraal through the entire fight. These flowers are from the women of the Stone, tokens to honor his steadfast courage, his faithfulness.” She made “steadfast” and “faithfulness” crack like whips.