Iran may have used UHPC concrete in the missile cities . This can mean that even the biggest non-nuclear bombs may not break it enough .
A bunker-buster bomb failed got stuck on the surface
Article from June 14, 2012 :
Super concrete shielding Iranian nukes?
The Economist Mar 3rd 2012 :
Smart concrete
Is Iran’s UHPC Concrete Too Tough for U.S? Even ‘Mother of All Bombs May Not Break It
A bunker-buster bomb failed got stuck on the surface
Quote:UHPC concrete is stronger and too strong for today's bombs
UHPC is a type of concrete that is way more advanced than regular concrete. Earlier, concrete rated as "high strength" had a yield of 5,000 pounds per square inch (psi). There were some that went up to 10,000 psi. But UHPC can withstand 40,000 psi or more. This is because in this technology, concrete is turned into a composite material by adding steel or other fibres. They hold the concrete together and prevent it from cracking. Stephanie Barnett, Ph.D, of the University of Portsmouth in the UK, who works to develop stronger concrete to protect civilian buildings from terrorist attacks, told Popular Mechanics, "Instead of getting a few large cracks in a concrete panel, you get lots of smaller cracks. The fibres give it more fracture energy."
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An open-source Chinese study compared normal high-strength concrete with fibre-reinforced UHPC. It noted that projectiles smashed through the reinforced concrete targets, but the UHPC targets only had minor cracking. The bombs “either embedded in or rebounded from” the targets.
The United States Air Force had also launched a project to study bunkers made of UHPC. It was reportedly feared that even the 5,000-pound bombs would not get through UHPC. Then it got the 21,000-pound Massive Ordnance Air Blast, "mother of all bombs". This is the biggest bomb one can fly, with only the B-2 Spirit strategic bomber capable of doing so.
Experts say that even the biggest and toughest bomb could not get through UHPC. Gregory Vartanov of Toronto-based Advanced Materials Development Corp claims that current bombs cannot break down the high-grade UHPC. "Penetrators with monolithic cases made from materials such as … Eglin Steel … cannot penetrate bunkers made from UHPC,” he wrote in Aerospace & Defense Technology magazine in February 2021.
Article from June 14, 2012 :
Super concrete shielding Iranian nukes?
The Economist Mar 3rd 2012 :
Smart concrete
Is Iran’s UHPC Concrete Too Tough for U.S? Even ‘Mother of All Bombs May Not Break It