To quote Apple's customer relations policy.
"nos clients ne sont rien d'autre qu'une vieille servante qui a l'habitude d'être violée et qui ne se bat pas beaucoup"
Would seem a lot cheaper to fill the barrels with sand. Also, making concrete is a process that in itself creates a massive amount of carbon emissions. Would be interesting to see what they can do when they start ironing out some of the wrinkles.