Green Line Extension to Medford & Union Sq

RandomWalk said:
The bike path has received a base coat of asphalt between the current terminus and Somerville Junction Park. I will take the under on one month before some folks ignore the fences.
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The grade transition where it joins the existing path is kind of awkward; hopefully they'll make that a little smoother. Nice to see the pavement there, even if we won't be able to ride it for almost another year.
 
ceo said:
The grade transition where it joins the existing path is kind of awkward; hopefully they'll make that a little smoother. Nice to see the pavement there, even if we won't be able to ride it for almost another year.
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It is only the base. There will be at least one more layer to bring it up to the level of the drainage structures.
 
It would be good if they had that. Would make it quicker to board the buses The present Charlie machines are just too damn slow!! :(
 
Arlington said:
I am expecting that the streaks of discoloration on the concrete mean they'll finish with some kind of power wash that will restore a more uniform patina?
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Based on this guy's PPE, this seems like some kind of acid wash to produce uniform appearance post-restoration (from today):

GL1.jpg
 
The consistency looks more like a poultice, which is similar to how people restore marble fireplace surrounds.
 
Charlie_mta said:
I still don't understand why they didn't go with a brownish integrally colored concrete. Some touch-up staining would have been required, but not so much.
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It actually seems like they're doing both. Those guardrails/balustrades up top seem to have been re-cast and replaced. They were completely removed, with rebar sticking up, and now they're back. They've definitely been cast with a color tinted concrete, and the patches are all tinted brown as well.
 
bigpicture7 said:
It actually seems like they're doing both. Those guardrails/balustrades up top seem to have been re-cast and replaced. They were completely removed, with rebar sticking up, and now they're back. They've definitely been cast with a color tinted concrete, and the patches are all tinted brown as well.
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You're right. The guardrails definitely look like they were replaced with integrally colored concrete. The same colored concrete should have been used for the archway portion (that the worker is shown applying the acid wash to).
 
bigpicture7 said:
Based on this guy's PPE, this seems like some kind of acid wash to produce uniform appearance post-restoration (from today):

View attachment 15532
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Hello, I've been lurking for a couple months but this was worth making an account for. The arches on this bridge are actually being strengthened with carbon fiber sheets. The white pasty stuff on the arch is the epoxy being used to adhere the carbon to the concrete, and the black sheet that the worker is holding up is the fiber that's about to go up. Then, the fiber will be sprayed with sand and painted over to match the concrete. I had a co-op the first half of this year working as a field engineer for the subcontractor doing this work. Here's the finished product on the span over the basketball courts, taken sometime late May:
IMG_4682.PNG
 
thepianoperson said:
Hello, I've been lurking for a couple months but this was worth making an account for. The arches on this bridge are actually being strengthened with carbon fiber sheets. The white pasty stuff on the arch is the epoxy being used to adhere the carbon to the concrete, and the black sheet that the worker is holding up is the fiber that's about to go up. Then, the fiber will be sprayed with sand and painted over to match the concrete. I had a co-op the first half of this year working as a field engineer for the subcontractor doing this work. Here's the finished product on the span over the basketball courts, taken sometime late May:
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Wow, really appreciate you making an account to share this. So, I am guessing that the portion of the arch in my photo to the right of the worker has been sanded smooth to accommodate this process?

Your photo above also shows what I was referring to regarding the old guardrails being removed.

Thanks again for joining aB and sharing this. One of the things that makes this forum great is the ability to learn details about projects like this that simply aren't available otherwise (or would be really difficult to find). Crazy how our 1910-vintage viaduct will have hidden cutting edge technology lurking within it that nearly every passerby will merely take for granted.
 
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bigpicture7 said:
Wow, really appreciate you making an account to share this. So, I am guessing that the portion of the arch in my photo to the right of the worker has been sanded smooth to accommodate this process?

Your photo above also shows what I was referring to regarding the old guardrails being removed.

Thanks again for joining aB and sharing this. One of the things that makes this forum great is the ability to learn details about projects like this that simply aren't available otherwise (or would be really difficult to find). Crazy how our 1910-vintage viaduct will have hidden cutting edge technology lurking within it that nearly every passerby will merely take for granted.
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Yeah, the existing surface had to be sanded down for the epoxy to adhere better. The guardrails were definitely replaced as well, though I don't know too much about the specifics of that that other than watching it happen.
It's a really cool system, I hadn't heard of using carbon fiber for structural applications at all before starting work on the job, it's mostly used for bridge or parking garage rehab as reinforcement.
 
thepianoperson said:
Hello, I've been lurking for a couple months but this was worth making an account for. The arches on this bridge are actually being strengthened with carbon fiber sheets. The white pasty stuff on the arch is the epoxy being used to adhere the carbon to the concrete, and the black sheet that the worker is holding up is the fiber that's about to go up. Then, the fiber will be sprayed with sand and painted over to match the concrete. I had a co-op the first half of this year working as a field engineer for the subcontractor doing this work. Here's the finished product on the span over the basketball courts, taken sometime late May:
View attachment 15537
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I had no idea they were refurbishing it this extensively, looks like theyre really investing for the long term here. Great first post!
 
Funny thing is: I remember the articles back in 2019 when they said they’d be using Carbon fiber wrap, but at the time (and since) I pictured wrapping steel elements, not big concrete with big cross sections.

googled up this link:
www.fenaghengineering.com

Lechmere Viaduct » Fenagh Engineering

The Lechmere Viaduct carries the MBTA Green line from Science Park Station to Charlestown Avenue in Boston and Cambridge, MA.
www.fenaghengineering.com www.fenaghengineering.com
 
Thanks to @thepianoperson 's info, I was inspired to take a closer look during my last walk by here.

Many of the arches now have their carbon fiber shells (this photo also shows the re-installed guardrails/balustrades at top):
GLV5.jpg


Upon closer look, a really nice carbon fiber weave (not unlike you'd see on the hood of my Civic drifter...if I had one):
GLV3.jpg


And now I know why I wasn't seeing the full picture before...you have to peer over the construction fence of the (temporarily shut down) basketball court area to see the first completed arch, which looks great:
GLV4.jpg


GLV2.jpg


And back to @Charlie_mta 's question from earlier; yes, they definitely appear to be using a sand-color tinted concrete for the cast-in-place repair work along with this carbon fiber/sand-coated work:
GLV1.jpg


GLV6.jpg
 
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