We finally got around to the second pour of the roadbed bricks. The first pour was not the best, and for a number of reasons. First was the quality of the form and the 3D printed mold inserts used to shape the concrete into a roadbed profile. Second, and more importantly, the quality of the actual concrete mix itself.
The form itself held up well, but the sides need to be tighter against the bottom if we’re going to try a wetter mix. Breaking down the form after the first pour reveals enough of the mix managed to get into the gaps between the sides and bottom. Gaps large enough that the concrete needs cleaned off the pieces before the form can be reassembled.
Closing those gaps is easy, just add more screws between the ones already there. The 3D printed profile molds now fit snugly as well, which should help hold the 3D printed dividers in place better than the first time around. The problem the first time around was the dividers moved on us, probably because of using the brick trowel to work the mix into the form and breaking them loose.
Fitting the molds and dividers in place takes the same amount of hot melt glue this time around as it the first time, one stick. That’s a dot on each of the four corners on the molds themselves and two or three dots on each divider. Somehow it seems more sturdy than the first time. Here’s hoping…
The weather is still pleasant enough to sit outside on the deck this time of year while we prepare the form for the pour. As you can see, the railing provides a suitable work surface for assembly. It can also slide back and forth on the railing as needed. The added bonus of easy access for Rocket to bring the Jolly Ball makes it even more enjoyable to sit outside in the Barkyard.
Enjoying it while we can. It won’t be long before the oppressive heat will keep us indoors all but early mornings and late evenings. We’ve already had a few record breaking days recently in the 98°-99° range. Soon it will be every day in the upper nineties, without relent, until Fall.
Time To Mix
Now that the form is ready, it’s time to mix the concrete. The first time around, we used ~5 quarts of water, not quite twice the maximum of three quarts recommended on the bag. This time we’re mixing it wetter, “soupy” is the term, “Thick as a milkshake, but not so thick that you can’t suck it up with a straw.” Now the only problem is how to translate that into quarts of water per 80# bag of concrete.
Starting with 6 quarts, the mix is still too “dry”, as in not wet enough for all the mix to be easily incorporated. Adding another quart still isn’t enough. One more quart makes it a total of 8, and finally wet enough to call “soupy”. Beginning to wonder if they meant three gallons and not three quarts. After all, eight quarts is two gallons.
A few more quarts would make a fairly thin mix, but still workable if pouring. Maybe nine quarts next time? Let’s not count the chickens before they’re hatched. It’s certainly something to consider, but let’s see how this batch turns out before making more changes. It would be nice if this batch wasn’t so crumbly like the first batch for sure.
Time To Pour
Well now we know eight quarts equals soupy. This time all it takes to fill the form is to shovel the mix into it. No working the mix into the form is required. It’s certainly hard not to be sloppy though! Each shovelful fills about two brick “slots”. Screeding the mix toward the next empty slot helps to level off with the top of the form.
It helps to angle the shovel toward the middle of the form to keep from pushing the excess mix over the edge and onto the driveway, but there’s no amount of careful that can prevent even a little spillage. We’ll wash that away with the hose when we’re done. It also helps to turn the mix over a few times before the next shovelful to keep the water from floating up and separating from the mix.
It’s about this point I remember I never sprayed the form with WD-40 as a release agent, even though I reminded myself twice before starting. Oh well. Too late now! Guess we’ll find out how much we really need a mold release agent. Hopefully it won’t cause too much trouble.
Once the pour is complete, it’s time to clean off the driveway, starting with shoveling the excess mix off of it. Next is a good wash down with the hose to push any remaining concrete off the edge of the driveway, carefully avoiding the fresh pour.
Now We Wait
Nothing left to do but wait for the pour to setup enough to remove from the form. Because the first pour was so crumbly, we’re waiting longer than a day. Besides, it’s way too hot the next evening to even think about doing anything with this latest pour. I do saturate the concrete with water to help keep it hydrated, but it will have to wait until tomorrow.
I was curious to see if the lack of a mold release agent will keep the concrete from pulling away from the sides like it did the first time. I was surprised to see that not only did it NOT keep the concrete from pulling away from the sides, it actually caused a jagged separation line, like part of the concrete wanted to stick to the sides while the rest pulled away from it.
It’s disappointing to say the least. I’m wondering if maybe I should have worked the mix into the form better. Maybe the mix didn’t fully fill the form, leaving it weak enough to separate in that jagged fashion. Doesn’t quite explain why it did it along one side and not the other though.
Mixed Results
Noting the telltale cracks above the dividers, it’s time to release this batch of bricks from the mold. Taking most of my lunch hour to remove them, I drag the form through the gate onto the back stoop, where I can sit and work on it. The bricks fall right out of the form one by one, splitting cleanly along the crack at the dividers without fail.
But I find another problem related to the lack of a release agent. While the bricks may be popping right out, the 3D printed molds are sticking to them like glue. For the most part, the dividers pop off without issue. All but two. Those crack along the ear on one or the other, snapping apart at the ear that’s still stuck to the concrete.
It takes quite a bit more force to pry those 8″ molds loose from the concrete though. It acts like a vacuum tight fit, where once the seal is broken, the rest of it peels right off. But even those suffer damage from overstressing the glued joints, often splitting the joint, sometimes for the full length. A number of them are now separate pieces again and will need to be reassembled.
Better Results
While these bricks are crumbling along the jagged separation line, they are NOT crumbling anywhere else. The bricks from the first attempt would have broken with the amount of force it took to remove the molds from this time. These bricks have much more strength. They’re holding up well to the strong arm handling.
In fact, they’re resisting my attempts to trim where the dividers didn’t quite reach the top of the form. That’s one change we’ll be making for the batch. I’ll need to print a couple of replacements for the broken ones anyway.
Another thing that worked quite well was the placement of the dividers and they stayed where I put them. Not working the mix into the form with the brick trowel seems to have saved us from having misshapen bricks. They also peeled right off with the bricks and didn’t require removing the sides of the form like the first batch.
The best part is the 100% yield! All 12 bricks came right out of the form and none of them are cracked or broken. I can even read the writing from the embossed text on the dividers! Round two is a success! We’ll give them the rest of the week to cure and put this idea to the test.
Time To Lay Bricks
Well, almost. First we need to clear a path for the bricks to sit on. The two concrete blocks with the chunk of 2×6 across them is to protect the puppies’ paws from the sharp ends of the track. We’ve been losing ground lately with three puppies pounding things to pieces, having to remove more and more track to keep it from getting damaged and them from getting hurt on what’s left.
In fact, all that’s left are the stringers that survived where the track used to lay. This “experiment” is meant to mitigate that damage and provide a means to protect the track and the pups. Time to pull the stringers out of the way and replace them with the roadbed bricks.
It only takes removing a few screws and the first stringer is free, after releasing it from the join with the next stringer of course. Now we need to lay out the bricks and cut the turf along the edges to make room for them. But first we need to rake all those leaves out of the way!
A leaf blower will just make a huge mess everywhere and a big rake won’t fit, so it’s a good thing we have a “mini” rake that’s about as wide as the bricks are. It makes quick work of moving just the leaves we want out of the way. Pretty handy. Not our first either. IIRC this is our third.
Bumps In The Road(bed)
Anyway, time for the Dremel saw. It does an adequate job of cutting the turf without much effort. If there is a single complaint, it would be the lackluster locking mechanism for the foot. It’s a flip / twist handle that gets cinched down to lock the foot and set the depth of cut, but the damned thing is at its end of travel before it actually tightens, constantly coming loose!
It would do a great job if the depth of cut didn’t need constant attention. You may think you’re cutting, but guess what? That damned foot is once again set to not cut at all! This time it’s taking two, three, even four tries to get a cut, and the cuts are now crooked and ragged. But enough “belly aching”, it’s just another unnecessary annoyance due to poor quality control.
Part of the problem is uneven terrain and cutting along the edge of the bricks, laid out in the circular pattern where they’ll sit. That uneven terrain is also causing an “elevation” problem with the first few bricks after the track leaves the 4×4 roadbed. The problem is twofold. First is having to make up for the height of the 4×4 itself and second is the 4×4 is sitting proud of where it should.
You can see how the track is dangling off the end of the 4×4 in the picture above. Those PVC pipe risers were also in the way and have been removed. Because the first batch of bricks is so crumbly, it begs the idea of crumbling them into “rubble” to restore the elevation needed.
Rocket is helping too, making sure to pace me by “pestering” me to throw the Jolly Ball… Constantly! But that’s okay. He didn’t get much play time this last week because we’ve been so busy with the latest “emergencies” at work. “We must overreact immediately!” comes to mind. Can’t wait to retire and kiss all that constant chaos goodbye!
On the plus side working remotely still has its advantages. After all, I was able to spend my lunch hour to get these bricks out of the form and ready to work with now. We get to stay home with the pups so they don’t have to go to “Doggy Daycare”, and we still get to play with them during the day, even if it’s not as often as they’d like.
Crumbling Infrastructure
What was originally a disappointment is quickly turning into an advantage, an opportunity to use those crumbly bricks in a way they were not originally intended. Where’s my hammer? My favorite place. Somewhere. Oh well, hopefully the “mini” hammer will do the trick. Let’s finish the job of crumbling them into rubble.
The idea is to crumble them the rest of the way and use them as fill to make up the height difference at the end of the 4×4 roadbed. One won’t be enough. Turns out even two isn’t enough. Three? Nope. More. In the end, all but four of them are pulverized to become fill beneath those four that remain. But not all at once.
I start with a first course of crumbled bricks, spreading it even and level until more is needed. Then start the next course, levelling it, and so on. As I sit there pounding those bricks into rubble, I continue to test fit until pleased with the progress.
One thing’s for sure, that 4×4 needs to sit down in the ground at least another ½”, if not more. The track doesn’t like bending over the edge of that 4×4 much. Side to side, sure. But not a sudden drop of ½” or more. A concrete block coerces it into position for now. Maybe the tie strips can be adjusted to leave an opening so the track will sit down over the end of the 4×4.
Lessons Learned
- DO NOT FORGET THE MOLD RELEASE!
- Tamp the mix into the form with the shovel to ensure complete fill, then screed.
- Vibrate the mix to remove trapped air and eliminate gaps.
- Make the dividers extend all the way to the top of the form (redesign).
- Increase the font size for the end marks or just assume one size fits all?
The first two are fairly self explanatory, plus I covered them earlier. What I didn’t cover was the amazing amount of detail the wetter mix captured. I can see the layer lines from 3D printing the molds in the concrete! The only thing that spoils it is air bubbles and “inclusions” where the concrete didn’t quite fill the gaps. Need to try vibrating the form once tamped and screeded next time.
Making the dividers tall enough to meet the tops of the 1×4 sides of the form should avoid having to snap off the jagged excess by hand to make the ends flush. That means a redesign of the divider model then printing more with the new STL. Some of them broke and need replaced anyway.
While we’re at it redesigning the dividers, it’s time to think about a one size fits all approach. Rather than having bricks of varying degrees of curvature and having to stock many different types, including tangent, why not have one that can be used for everything? The difference between the various curves is at most 3.75°, so a small gap one way or the other will barely be noticeable.
Another bonus is tangent track can be accommodated by alternately rotating the bricks 180°, such that the angles point left, then right, alternating to effectively create a straight section. If you look close in the picture with Rocket inspecting things, you’ll see I had to do that in a few places to help adjust accumulated error in the curvature, a straight section as part of a curve.
More to come, so stay tuned.