US unleashes 30,000-pound bunker-busters on Iran — but scientists say Tehran’s concrete may have won the day

US unleashes 30,000-pound bunker-busters on Iran — but scientists say Tehran’s concrete may have won the day

While the United States launched Operation Midnight Hammer on Iran amid the ongoing war between Israel and Iran to attack its nuclear facilities, it is still not known if Iran’s nuclear program is actually destroyed, as per a report.

America’s Biggest Bomb Makes Its Combat Debut in Iran

The US military used Massive Ordnance Penetrators (MOPs), massive 30,000-pound bombs, to strike key Iranian nuclear sites, including the Fordow fuel-enrichment plant, the Natanz nuclear facility, and the Isfahan nuclear technology center, according to a Popular Mechanics report.

The Pentagon’s operation marks the first-ever use of the MOP, which can only be carried by the B-2 stealth bomber, and it has been considered the only country capable of destroying Iran’s underground nuclear facilities, but whether it actually accomplished that feat is still unclear, as per the report.

While US president Donald Trump declared the operation "completely and totally obliterated" the sites, Iranian officials have dismissed his claims, according to the Popular Mechanics report. Even early US intelligence has revealed that the level of damage inflicted based on satellite imagery alone is not clear, and a CNN report mentioned that the strikes on Iran did not destroy the country’s nuclear program and has instead only set it back by a matter of months, reported Popular Mechanics.

Decades-Old Arms Race: Concrete vs. Bombs

According to the Popular Mechanics report, history suggests Iran's underground nuclear facilities could be partially or wholly intact, "because up until now, in the quiet arms race between concrete and bombs, the concrete has been winning."

In the late 2000s, a bunker-buster bomb failed to penetrate an Iranian bunker due to Iran's advancements in Ultra High Performance Concrete (UHPC), which is the latest concrete advancement and could not be impacted with a standard bunker buster, as per the report.

Stephanie Barnett, Ph.D., of the University of Portsmouth in the US, who is involved in developing stronger concrete to protect civilian buildings from terrorist attacks, said that military personnel are not pleased with the advancement as she shared that, “One officer told me, ‘If you make this stronger blast- and impact-resistant material, we need to think about how to get through it,’” quoted the Popular Mechanics report.

Bunker-Buster Technology

The US Air Force introduced its first modern bunker buster in 1985, these bombs have a thicker casing and fewer explosives than general-purpose bombs, concentrating weight on a smaller area to smash through concrete, according to the report.

Eglin Steel, developed in the early 2000s, with low-carbon, low-nickel steel with traces of tungsten, chromium, manganese, silicon, and other elements, became the gold standard for bunker-busting munitions, as per the Popular Mechanics report. However, in recent years, Eglin Steel has been supplemented by a new USAF-96 steel, which offers similar performance but is easier to produce, as per the report.

The Concrete Advantage

Phil Purnell, Ph.D., an expert in concrete technology at the University of Leeds, explained that concrete is brittle, with a weakness in its tensile capacity and toughness, according to the Popular Mechanics report. He said, "It is good at being squashed, not being stretched. The weakness is in its tensile capacity and toughness,” as quoted in the report.

However, UHPC has changed this, withstanding 40,000 pounds per square inch (psi) or more, compared to the previous high-strength rating of 5,000 to 10,000 psi, as reported by the Popular Mechanics report.

The addition of steel or other fibres turns concrete into a composite material, preventing cracks from spreading, as per the report. Barnett explained that, “Instead of getting a few large cracks in a concrete panel, you get lots of smaller cracks,” adding, “The fibers give it more fracture energy,” quoted the Popular Mechanics report. The report defined the meaning of fracture energy as the amount of energy needed to split a material open.

Past Efforts

In 1991, the US developed a 5,000-pound bomb in six weeks to penetrate Iraqi bunkers protected by reinforced concrete, as per the report. In 2012, the USAF studied the challenge posed by UHPC bunkers and developed its own version, Eglin high-strength concrete, for testing, according to the Popular Mechanics report. While the results are classified, a Chinese study showed that UHPC targets survived projectile impacts with only minor cracking, as per the report.

The Air Force received the Massive Ordnance Penetrator (MOP) in 2011 and has upgraded it multiple times, according to the report. However, Gregory Vartanov, Ph.D., of Toronto-based Advanced Materials Development Corp, said that high-grade UHPC is too strong for bombs made with existing steels, according to the Popular Mechanics report.

Vartanov wrote in a February 2021 piece in Aerospace & Defense Technology magazine that, "Penetrators with monolithic cases made from materials such as … Eglin Steel … cannot penetrate bunkers made from UHPC,” as quoted in the report.

However, the US Air Force will not disclose its current bunker-busting capabilities or how they stack up against potential targets in Iran, China, or elsewhere, reported the Popular Mechanics report.

FAQs

Can current bunker-busters penetrate UHPC?

Not reliably. Some experts believe UHPC may be too strong for existing steel-based bombs.

What bombs were used in the US strike on Iran?

The US dropped Massive Ordnance Penetrators (MOPs)—30,000-pound bunker-busting bombs, as per the report.

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