MARTIAN CONCRETE: An abstract on ISRU concrete production for use on the Moon and Mars.

An unfortunate snag in the use of ISRU concrete is the heavy machinery required to produce cement on a large scale, as detailed here.

While small "starter" units could be built for use on Mars -- self-contained units small enough to be launched from Earth in one go -- the smaller size could become a limiting factor on the rate at which an initial settlement could grow. The same could be said of the equipment required to produce steel and other primary materials. A Martian settlement will likely find itself bootstrapping from these small imported factories, using their outputs to first build larger facilities capable of producing these materials on an industrial scale for use in settlement construction. Either way, the availability of primary materials will be a bottleneck for the construction of early settlements, one that doesn't seem to get a lot of attention in the usual literature.