Once you have your gravel, use robots to make a path and compact the regolith. Put down the gravel over the compacted regolith, and there's your road. I have no idea if that would actually work or not, but it's interesting to think about.
I feel like maybe I'm missing something, but isn't this just a compactor? What am I missing? Does hydraulic pressure need gravity?
If your compaction includes application of force vertically, top down, you need something opposing that force. On the Earth it's usually gravity, and on the Moon it could be the same, just the gravity on the Moon is ~1/6 the Earth one.
I am legitimately confused by what you're getting at. I feel like maybe we're not even talking about the same thing.
If the compactor is only pushing down, and it is not secured to the ground, then yes, it needs gravity to hold it in place. But most compactors are secured to a frame, so the force is produced between the hydraulic ram and that frame.
Most (all?) road equipment is held down by gravity: if it weighs 10 tons, then it can't apply more than 10 tons of downward force. However, if you need to apply more downward force, the easy answer is to secure your compactor to the ground.
Followed by aluminum! You could sinter (?) Al out of bauxite. Imagine a metal road!
Similar to what we can get from the Earth (The mineral composition of the two bodies is similar), with the key difference being that terrestrial construction sites don't turn undifferentiated piles of rocks into buildings, doors, windows, elevators, and roadways.
There's a colossal supply chain that turns those piles of rocks into usable building materials. We're likely to see moon roads sometime after we get flying cars, and economically viable fusion energy.
"Concrete" normally refers to rocks that are bound with cement, without having to use high temperature and/or pressure.
The paper does not explain how such a cement could be made from lunar rocks.
The Portland cement and most other usual cements, which are used on Earth, require water, which is not available in most places on the Moon.
What could be done is to extract the calcium oxide (quicklime), or other similar oxides, e.g. magnesia or yttria, from the lunar rocks.
Without water, these oxides cannot be used to make cement, i.e. a binder that becomes solid without applying high temperature or pressure, but due to chemical reactions at low temperature.
Nevertheless, these oxides can be used as binders in making ceramics, by sintering at a high temperature and moderate pressure, like making bricks on Earth.
Thus one can make ceramics or glass on the Moon, which should be the cheapest materials, but not cement or concrete. There is no chance of making a building by pouring concrete, like on Earth. It should be possible to make a building from bricks, which might have shapes holding them together, but which must also use some metal parts, e.g. bolts or rivets, to ensure that they stay in place, in the absence of cement that could be applied like on Earth.
It might be possible to seal the spaces between ceramic bricks with some kind of easily fusible glass, to make them airtight.
Bringing hydrogen from Earth in quantities large enough to allow wasting it in construction materials, instead of using it only for making precious food and drinking water, for making water and acids used in certain chemical processes, for certain plastic materials used in small quantities and for fuel, is a completely impractical idea (this being a polite way of not calling such a solution for making construction materials on Moon as completely stupid).
Hydrogen, nitrogen, carbon and sulfur will be the most expensive materials on the Moon, so they will be reserved for things where they are irreplaceable, not for construction materials, which are needed in huge quantities in comparison to the materials needed for any other application, so they must be made from the most abundant materials that can be found around.
This dust would probably be a physical challenge to equipment used to build infra.