  ALICE (A Large Ion Collider Experiment) studies the Quark-Gluon Plasma (QGP):
a deconfined state of matter obtained in ultra-relativistic heavy-ion
collisions. One of the probes for QGP study are quarkonia and open heavy
flavour, of which ALICE exploits the muonic decay. A set of Resistive Plate
Chambers (RPCs), placed in the forward rapidity region of the ALICE detector,
is used for muon identification purposes. The correct operation of these
detectors is ensured by the choice of the proper gas mixture. Currently they
are operated with a mixture of C$_{2}$H$_{2}$F$_{4}$, i-C$_{4}$H$_{10}$ and
SF$_{6}$ but, starting from 2017, new EU regulations have enforced a
progressive phase-out of C$_{2}$H$_{2}$F$_{4}$ because of its large Global
Warming Potential (GWP), making it difficult and costly to purchase. CERN asked
LHC experiments to reduce greenhouse gases emissions, to which RPC operation
contributes significantly. A possible candidate for C$_{2}$H$_{2}$F$_{4}$
replacement is the C$_{3}$H$_{2}$F$_{4}$ (diluted with other gases, such as
CO$_{2}$), which has been extensively tested using cosmic rays. Promising gas
mixtures have been devised; the next crucial steps are the detailed in-beam
characterization of such mixtures as well as the study of their performance
under increasing irradiation levels. This contribution will describe the
methodology and results of beam tests carried out at the CERN GIF++ (equipped
with a high activity $^{137}$Cs source and muon beam) with an ALICE-like RPC
prototype, operated with several mixtures with varying proportions of CO$_{2}$,
C$_{3}$H$_{2}$F$_{4}$, i-C$_{4}$H$_{10}$ and SF$_{6}$ . Absorbed currents,
efficiencies, prompt charges, cluster sizes, time resolutions and rate
capabilities will be presented, both from digitized (for detailed shape and
charge analysis) and discriminated (using the same front-end electronics as
employed in ALICE) signals.
