I would certainly think it would be fine, and in my trade, we drill in concrete hanging transformers weighing well over 20kg (44lb). To be sure, use
long wedge anchors.
If your previously filled holes were 50mm (2") deep, then 3" or 4" long wedge anchors will work. The width of the anchor would be 1/4".
VERY IMPORTANT NOTE #1: When your hammer drilling your holes, your drill bit should be EXACTLY width of hammer drill as the width of the anchor. If you choose to 1/4" wide anchors, then USE a 1/4" SDS hammer drill bit. DO NOT DEVIATE!!!
VERY IMPORTANT NOTE #2: When you drill the holes, drill them the entire depth of the wedge anchor. So, if your wedge anchor is 4" long, then drill the WHOLE 4" in depth.
VERY IMPORTANT NOTE #3: When your about to hammer the wedge anchor in, leave about 1/2" hanging out!! Do not hammer the anchor ALL the way in. Place your curtain hanger hardware over the exposed threads, and hand-thumb the nut/washers on. Then when you begin to torque the nuts down with a wrench, the anchor will begin to pull out. Don't worry.....as you torque more-and-more, the wedge anchor will resist more-and-more. Once it feels very snug, stop.....DONE.
Hope this helps.
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