react witha hardener at ambient temperature,whereas the hydraulicbinders,as
cement or lime,needwaterto harden.
Hydraulicbinder
The hydraulicbinder usedin the construction of flooringmaterial is cement. The
maindrawback of the use of hydraulic bindersis the highporositydue to water
evaporationduringhardening. Theaddition of a syntheticpolymer reduces
porosity, increases the mechanicalresistance and reducescrackingrisk.Cement
can be used in polymer-modified cementitiousscreedthat is definedas a `screed
where the binderis a hydrauliccement and whichis modifiedby the additionof
polymer dispersion or re-dispersiblepowderpolymerwitha minimumcontent
of dry polymerof 1% by massof the totalcomposition,excluding aggregate
particles largerthan5 mm'(Anon,2001a). Examplesare the acrylic-modified
cementitioussystemsthat are the mainsystems used in the meat industry in
France. The mainand greatadvantage of suchflooringsis that theycan be
applied ontoa damp substrate.
Cement is alsousedin associationwithresins,suchas epoxy resinand
polyurethane. In thosecases,resincontent is around 5% by mass of the total
composition.In suchfloors, cementis morea fillerthana binder, whichis why
theyare consideredto belongto the syntheticresinsfamily.
Syntheticresins
Epoxy resinsare the more frequently used syntheticbinders, followed by
polyurethaneand methacrylateresins.Polyesterresinsare seldomused,to the
author's knowledge,in the foodindustry.Characteristicsof the differentresins
change accordingto the formulationused. The formulationmaybe changedto
adaptto suchnon-optimalinstallationconditionsas temperature,relativehumidity
or timeavailablepriorto beingput into service.Specificformulationsproposed
mayhaveconsequenceson the resistanceof the finalproduct. It is therefore
difficult to give preciseruleson curing. The finalfloor system must be allowedto
cureaccordingto the manufacturer's instructions.Thesegenerallyrequire1±3
daysat 15±20ÎC beforetraffickingand 3±7 daysbeforewashing,beforecontact
withchemicalsor beforeany pondingtestsand hightrafficloads(Anon, 2001b).
The onlyresinthat clearlyescapesthis generalrule is polymethylmethacrylate
(PMMA),also calledmethacrylateor methylmethacrylate.It is characterisedby a
veryshorttimepriorto puttingin service:2 hours.It can be appliedat low
temperature (ˇ10 ÎC). However, this resinpossessesa strongodour at installation
that can irreversiblyalterfoodproductspresentnearby.
The climate abovethe uncuredresinshould be maintainedat least3 ÎC above
the dew point.The substratehumiditymustalso be correct. It must, for instance,
be smaller than 3% for an epoxyresin,or 7% for polyurethane±cementflooring.
Aggregates
Aggregatesare granular materialsthat do not contributeto the hardening
reactionof the mortar.Rolesof aggregatedependon theirsize and abrasion
170 Handbookof hygiene controlin the foodindustry