At the start of WWII, the British attempted to armor some of their merchant ships using layers of concrete paving stones up to six inches thick, but these were found to be virtually worthless against armor-piercing machine gun bullets. Concrete as a material is excellent in compression but very weak in tension and sheer (in reinforced concrete this weakness is overcome by the embedded rebar), which makes its ability to resist being separated and displaced by the incoming shell negligible.

The British quickly invented a replacement for the concrete armor, a substance called plastic armor, which was essentially just a variant of asphalt road material. They mixed bitumen with limestone and chunks of granite and stuck the material to unarmored parts of the ships in layers several inches thick. When an AP machine gun bullet hit the material, the granite chunks would cause the bullet to tumble and thus not penetrate the thin steel backing plate.

They used plastic armor heavily for ship protection since the material was cheap and they had plenty of road workers with the skills to handle it. It was considered for use in tanks, but it was of no use against anything larger than machine guns and it weighed roughly twice as much as comparable steel armor.

Not a direct answer to your question, but is it possible that your friend might have been confused by the term "cemented armour"?

During the final decades of the 19th century various companies developed types of steel armour where the face of the armour plate would be hardened through a process of cementing. This involved treating one side of the steel plate with high temperatures over a period of days or weeks, gradually increasing the carbon content of that side relative to the other. The end result would be armour plate which was hardened on the outside, but flexible on the inside, thus giving cemented armour greater strength than other contemporary steel armour plates.

Not being an expert on tanks I'm not aware of cemented armour being used to protect vehicles. It did however remain common in warship construction well into the cold war period.

In any official armor packages, no. Like others have said concrete's properties aren't well suited to defeating kinetic tank arounds. However that didn't stop tank crews from trying it anyways.

There are plenty of instances of many Sherman crews covering the front of their tank in concrete and was one of the more common forms of infield appliqué armor, along with sandbags and tracks.

In Late 1944 (around September IIRC) a study was done among several US divisions about their current feelings of armor protection as well as the effectiveness of such improvised armor. What they found is that while the Sherman was still acceptably protected versus its contemporaries such as the StuG and the Pz. IV, newer tanks, despite their shortcomings, such as the Panther created an intense desire for a more protected vehicle. What they also found is that concrete armor was almost completely ineffective against the most common German infantry anti tank weapon, the Panzerfaust. On top of that it was extremely heavily and badly overloading the suspension of the Sherman. This led to an immediate order from the War Department for all tank crews to stop using concrete armor.

This eventually lead to the development of the M4A3E2 armor package which added a 1.5" appliqué steel plate to the front of the Sherman's hull as well as a new cast turret and gunshield. While still not ideal for the Sherman's suspension, it was very popular among tank crews.