The A5183 Watling Street in Radlett will be closed from A411 Elstree Crossroads North to the A414 North Orbital Road from 8pm this evening.
Thames Water has been dealing with a blocked sewer near Radlett Station under an emergency response permit since February 19.
The works have involved temporary two-way traffic signals being manually controlled during peak times.
The sewer, which is four metres down in the centre of the highway, has been completely blocked by concrete causing sewerage to back up. The sewer will now have to be replaced.
It is hoped the work will be completed by 8pm on Saturday, March 8.
Terry Douris, Cabinet Member for Highways, said: "We are doing everything in our powers to limit the disruption caused during this time. We are insisting that works be carried out 24/7 to minimise the duration of the closure with noisy works kept to a minimum during the night time periods.
"We are extremely frustrated that this situation has arisen due to what appears to be someone’s irresponsible actions and residents affected by this disruption have our sympathy. Due to the nature of these works council taxpayers will not be footing the bill."
Thames Water operations manager Mark Grimshaw said: "Normally blockages are caused by fat, oil and grease building up in the sewer but unfortunately in this case it’s concrete, so we can’t just jet it through.
"It’s in there and it’s set to the pipe, so unfortunately it means we need to remove the pipe and replace it with a new one. This is very frustrating and not the first time damage has been caused by private contractors pouring concrete into our sewers. "