{"id":60328,"date":"2026-05-18T08:00:12","date_gmt":"2026-05-17T23:00:12","guid":{"rendered":"https:\/\/norimen.net\/?p=60328"},"modified":"2026-05-16T19:25:43","modified_gmt":"2026-05-16T10:25:43","slug":"nail-head-cap-not-required","status":"publish","type":"post","link":"https:\/\/norimen.net\/en\/nail-head-cap-unnecessary\/","title":{"rendered":"The Argument Against Using Aluminum Caps for Rebar Insertion | 8 Reasons to Reevaluate NEXCO Specifications"},"content":{"rendered":"

<\/p>\n

Hello, everyone. This is Enta.<\/p>\n

The other day, at a slope construction site contracted by a company other than NEXCO, regarding the end treatment of rebar inserts,A worksite without a cap<\/strong>I saw it.<\/p>\n

\"Oh, so I've finally gotten this far,\" I thought, so I'm going to write another post about why I'm disliked by materials manufacturers lol<\/p>\n

To cut to the chase, it's about time...\"No head cap\" is the national standard<\/strong>That's what I want to happen.<\/p>\n

I\u2019ve covered this topic before in a blog poll, but I\u2019d like to take this opportunity to organize the evidence and write about it again.<\/p>\n

\"Reinforcing<\/p>\n

What is the purpose of a head cap, anyway?<\/h2>\n

The head cap for rebar insertion tools was originallyTo prevent \u201cthe rebar in the head from becoming exposed and rusting\u201d<\/strong>This is a component that was created.<\/p>\n

This design involves filling aluminum caps with rust-preventive oil to seal nuts, washers, and the heads of rebar.<\/p>\n

But today\u2019s topic is: When you really think about it, is this specification really necessary in this day and age?<\/p>\n

Let's look at each reason why a cap isn't needed, one by one.<\/h2>\n

1. Caps were first developed because, in the past, uncoated (unplated) materials were prone to rusting.<\/h3>\n

Around the 1980s and 1990s, when rebar insertion techniques began to gain popularity, prestressed concrete steel bars and deformed steel bars wereBasically, unplated raw material<\/strong>...was the norm.<\/p>\n

Exposed rebar ends corrode when exposed to rainwater and oxygen. That\u2019s why, back then, the standard practice was to build formwork and pour concrete into it.<\/p>\n

Alternatively, the prevailing practice was to bury the design within the legal framework.<\/p>\n

However, since I can't manage this (even though I'm not actually managing it, lol), I filled the aluminum caps with rust-preventive oil and<\/p>\n

That\u2019s how the idea of \u201csealing it and preserving it in oil\u201d came about.<\/p>\n

Given the technical standards at the time, this was a reasonable decision.<\/p>\n

The problem is that what was considered \u201creasonable at the time\u201d has remained unchanged as the standard specification to this day.<\/p>\n

\"Reinforcement<\/p>\n

2. Since everything is now hot-dip galvanized, it won't rust.<\/h3>\n

Currently, the reinforcement materials used in rebar insertion work areAlmost all are hot-dip galvanized<\/strong>That's it.<\/p>\n

In the past, plating was only done in coastal areas because the materials were too expensive to make it feasible elsewhere.<\/p>\n

But before I knew it, both the nut and the washer had been replaced with plated ones as well.<\/p>\n

In other words, the very nature of the materials has changed over the past 30 years.<\/p>\n

Put a rust-proof cap on a rust-resistant material. When you think about it objectively, this...Status of Dual Countermeasures<\/strong>That's it.<\/p>\n

The typical coating thickness is HDZ55 (550 g\/m\u00b2) or greater, and the level of corrosion resistance is fundamentally different from that of the era of bare steel.<\/p>\n

3. The plating will last for more than 50 years.<\/h3>\n

According to corrosion data from the Japan Hot-Dip Galvanizing Association,Approximately 60 years or more in rural areas, and about 30 to 50 years in industrial areas<\/strong>Its service life has been proven.<\/p>\n

A figure that fully covers the design service life (typically 50 years) of slope structures.<\/p>\n

The feeling that \u201cI\u2019m uneasy unless I wear a cap\u201d is just a holdover from my days as a raw material worker.<\/p>\n

4. Nuts (made of iron) are less likely to be stolen than those made of aluminum.<\/h3>\n

This is a point that doesn't get talked about much, but from a thief's perspective, it's actually pretty important lol<\/p>\n

During periods in the past when scrap metal prices soared,Cases Where Aluminum Caps Were Targeted for Theft<\/strong>There was one.<\/p>\n

On the other hand, if the steel nuts are exposed, their scrap value is low, so the risk of theft actually decreases.<\/p>\n

This actually goes against the intuition that \u201cleaving things exposed is dangerous.\u201d<\/p>\n

What's more, there's a high chance that the price will be reduced for galvanized steel!<\/p>\n

5. Just apply some anti-loosening adhesive, and you'll be fine.<\/h3>\n

To prevent nuts from coming loose, use a product like LoctiteAnaerobic Adhesive<\/strong>If you use this, vibration and loosening due to aging will practically never occur.<\/p>\n

And even if it does come loose, as long as the head is exposed, you'll notice it right away and can tighten it immediately.<\/p>\n

In fact, sealing it with a cap has the drawback that you can't see what's happening inside.<\/p>\n

\"Apply<\/p>\n

6. At NEXCO, head treatment is already done almost entirely without caps.<\/h3>\n

This might be the strongest piece of evidence.<\/p>\n

As you all know, NEXCO isA contracting agency that takes maintenance seriously<\/strong>It's one of them, isn't it?<\/p>\n

Well, if a structure were to fail on a highway that\u2019s open to traffic, that would definitely lead to a major accident.<\/p>\n

The fact that NEXCO has determined that \"caps are unnecessary\" and has standardized this practice. (There is a precedent where caps were eliminated based on past data.)<\/p>\n

Why do they continue to demand specifications that are stricter than NEXCO\u2019s for prefectural, municipal, and forest roads with similar or even less demanding usage conditions?<\/p>\n

Don't you think that's inconsistent? (Or am I just not thinking things through??)<\/p>\n

7. The service life of rust-preventive oil is approximately 5 to 10 years.<\/h3>\n

This is another little-known fact, but even if you seal it with a cap,The rust-preventive oil inside has evaporated and deteriorated<\/strong>I'll keep doing that.<\/p>\n

It is generally said that the protective effect of rust-preventive oil lasts for about 5 to 10 years. (As I mentioned in a previous blog post.)<\/p>\n

What's the point of applying rust-preventive oil that wears off in 10 years to a plating that lasts 50 years? lol<\/p>\n

In fact, when we open them up during maintenance, we often find that the rust-preventive oil has dried up and become crusty.<\/p>\n

The punchline is, \u201cWhen I opened the lid, nothing was protected.\u201d<\/p>\n

\"Service<\/p>\n

8. At the end of the day, it's a waste of taxpayer money<\/h3>\n

In terms of public works cost estimates, each aluminum cap\u2014including the anti-rust oil\u2014costs around 2,500 yen.<\/p>\n

If it's 100 bottles per site, that comes to roughly 250,000 yen.<\/p>\n

On an annual basis, the total value of construction projects nationwide ranges from several hundred million to several billion yen.<\/strong>That brings us to the topic of...<\/p>\n

If that money can be used to add even one more reinforcement bar, it will definitely improve disaster prevention effectiveness.<\/p>\n

Since public works projects are funded by tax dollars, it\u2019s not really acceptable to keep spending money on unnecessary specifications, is it?<\/p>\n

What exactly are these economic comparisons we're doing in design...<\/p>\n

It turns out the same applies to conduit and terminal caps as well.<\/h2>\n

We've been talking about head caps up to this point, but actually...The same principle applies to the sheath tube and the tip cap.<\/strong>\u3002<\/p>\n

Now that galvanized rebar has become the standard, its significance for corrosion protection has diminished considerably.<\/p>\n

The same applies to the tip cap; assuming it will be completely filled with the injection material, there is virtually no reason to protect the tip.<\/p>\n

In other words, this isn't just about the head treatment; there are several components throughout the entire rebar insertion process that \"simply follow past specifications.\"<\/p>\n

If you take another look at this,The number of reinforcement bars can be increased by several to over a dozen per site.<\/strong>That's the calculation.<\/p>\n

Furthermore, the presence of the tip cap and sheath means that grout has not adhered to those parts. (No adhesion)<\/p>\n

\"Grout<\/p>\n

It's just that the design practices haven't been updated<\/h2>\n

Please don't get me wrong\u2014I'm not trying to speak ill of consultants.<\/p>\n

In design, there is a \"play it safe\" logic that involves following precedents, and I can understand that in itself.<\/p>\n

Still, even though both the materials and technology have changed, it does feel a bit off that the drawings and specifications are still stuck in the past, just as they were 30 years ago, doesn't it?<\/p>\n

Given that the NEXCO specification has already proven itself with the \u201ccapless\u201d design, I think there\u2019s plenty of reason for other contracting agencies to follow suit.<\/p>\n

To summarize the reasons for not using a head cap:<\/h2>\n
    \n
  • The material does not rust (all parts are plated)<\/span><\/strong><\/span><\/li>\n
  • The plating will last for over 50 years.<\/span><\/strong><\/span><\/li>\n
  • The rust-preventive oil will reach the end of its service life first.<\/span><\/strong><\/span><\/li>\n
  • NEXCO is already toll-free<\/span><\/strong><\/span><\/li>\n
  • In fact, the risk of theft is lower with steel nuts.<\/span><\/strong><\/span><\/li>\n
  • Glue is sufficient to prevent loosening.<\/span><\/strong><\/span><\/li>\n
  • Waste of Taxpayer Money<\/span><\/strong><\/span><\/li>\n<\/ul>\n

    I think you'll find that convincing lol<\/p>\n

     <\/p>\n

    Simply by removing the conduit and cap, you can use the money saved to install even one more reinforcement bar.<\/p>\n

    This serves as disaster prevention infrastructureA purely positive story<\/strong>Right?<\/p>\n

    I think things would change significantly if the client, consultant, and contractor\u2014the three parties involved\u2014simply discussed the question, \u201cDo we really need this?\u201d just once for each job site.<\/p>\n

    It would be fastest if major general contractors and major consulting firms took the lead, but,<\/p>\n

    Things won't change unless we on the front lines speak up, right?<\/p>\n

     <\/p>\n

    However, there are exceptions.<\/p>\n

    We recommend flat caps in areas where contact with a car could be dangerous or where there is a risk of contact with people.<\/p>\n

    NEXCO also uses flat caps on the lower sections near the vehicle.<\/p>\n

    \"Flat<\/p>\n

     <\/p>\n

    See you later.<\/p>\n

    The final and most critical step in ground anchor installation is applying anti-rust oil to the head!<\/a><\/p><\/blockquote>\n