Figure 8-24.–Smear test of asphalt cutback. Smear Test The    smear    test    is    used    to    separate an    RC    from    an    MC    or    SC.    The    test    is primarily    based    on    the    fact    that    RCs    are cutback     with     a     highly     volatile     material (naphtha    or    gasoline).    You    can    determine whether    a    sample    is    an    RC    or    not    by smearing    some    of    the    sample    in    a    thin layer   on   a   nonabsorbent   surface,   such   as   a piece of glazed paper. The volatile substance    evaporates    within    a    few    minutes and   the   surface   becomes   so   tacky   that   when touched, the specimen, paper and all, sticks    to    your    fingers    and    can    be    lifted into    the    air    (fig.    8-24). Checking     the     reverse     side     of     the paper,   you   will   find   that   the   RC   did   not penetrate   through   the   paper   as   MCs   or   SCs do.    MCs    and    SCs    on    smear    tests    remain fluid    and    oily    for    time    periods    that    vary from   hours   to   days,   depending   on   the   type and   grade   of   material.   If   an   800   or   3,000 grade   MC   or   SC   is   present,   they   may   become sticky    in    a    few    minutes    since    there    is such     a     small     amount     of     cutterstock     in them. When such a viscous grade is present, it is well to confirm the identification    of    the    sample    by    a    prolonged smear   test.   Generally,   the   MCs   and   SCs   will penetrate   through   the   paper   while   the   RCs will not. You can determine this by observing   the   back   side   of   the   paper. In    a    prolonged    smear    test,    a    thin smear    is    made    on    nonabsorbent    paper    and allowed    to    cure    completely.    If    the    viscous cutback is all RC-3000, it will cure completely   in   about   3   hours.   When   the   spot has    cured    completely    (the    cutterstock    has almost all evaporated), the smear will be    almost    pure    asphalt    cement    (AC)    and will     be     hard     and     no     longer     sticky.     If the    viscous    sample    were    an    MC    or    SC- 800    or    3,000,        the    spot    would    still    be Figure 8-25.—Stone-coating test for emulsions. uncured     and,     therefore,     very     sticky,     even after    24    hours,    while    the    RC    smear    will have   become   a   hard,   glazed   spot. Heat-Odor Test A heat-odor test is used to distinguish between medium-curing and slow-curing     asphalt     cutback     by     identifying the    cutter    stock    as    kerosene,    fuel    oil,    or diesel    oil.    A    sample    of    the    material    is heated    in    a    closed    container    to    retain    the vapors.  (CARE  MUST  BE  TAKEN  TO  AVOID  THE USE   OF   TOO   MUCH   HEAT).   Medium-curing asphalt   cutback   will   have   a   strong   odor   of kerosene.     Slow-curing     asphalt     cutback     will lack    the    kerosene    odor,    but    a    faint    odor of   motor   oil   may   be   present. Field Penetration Test The field penetration test is performed to determine the approximate hardness    of    the    asphalt,    not    to    pinpoint the    exact    penetration    number    for    it.    To determine   if   the   number   falls   in   the   hard, medium,    or    soft    group    is    sufficient. To     perform     this     test,     attempt     to push    a    sharpened    pencil    or    nail    into    the container of asphalt (at about 77°F), using a firm strong pressure of approximately    10    pounds.    If    only    a    slight penetration is made with considerable difficulty, a hard asphalt cement is present. When the penetration is made slowly but without great difficulty, a medium    asphalt    cement    is    present.    If    the penetration   is   made   with   ease,   the   asphalt cement   is   a   high   penetration   scale   (a   soft AC). Stone-Coating Test When   a   material   has   been   tested   and found    to    be    an    emulsion,    the    stone-coating test    is    performed    (fig.    8-25).    This    test    is conducted   to   determine   if   the   emulsion   is   a 8-26