The bush is at least 20 years old and up until this year has been beautiful. My neighbor put in a concrete driveway within 2' of bush. Now it looks burnt and blooms were very sickly looking.
Yellow, Burnt Looking Mature Hydrangea
Certified GKH Gardening Expert
Chemicals from the concrete may be affecting it or it may be that the root system was damaged when it was put in.
Either way, the best thing you can do for the plant is to start watering it deeply on a regular basis. This will leach away the chemicals if that is what is hurting it or will help support the plant while it is regrowing damaged roots. Make sure to regularly fertilize while you are doing this as nutrients will also be leached away.
I will let you know how things go.