The   TX-Pro   Texas   Overlay   Tester   (TOT)   addresses   a   major   issue   in asphalt     pavements:     premature     surface     cracking.     While     the Hamburg   wheel   test   has   guided   rutting-resistant   mix   design,   a complementary    test    for    cracking    resistance    has    been    lacking. Developed   in   the   1970s,   TOT   uses   pill-shaped   specimens   cyclically loaded    to    simulate    pavement    distress    and    evaluate    material performance. Recent   improvements   by   the   University   of   Texas   at   El   Paso   for   TxDOT have   significantly   enhanced   the   test’s   reliability   and   accuracy.   Data analysis   now   separates   crack   initiation   from   propagation,   more   closely reflecting   real   pavement   behavior   than   single-shot   tests   like   SCB   or IDEAL   CT.   Specimen   preparation   and   procedures   were   also   refined   to reduce   variability.   A   Round   Robin   study   in   Texas   in   November   2021 showed   excellent   repeatability   and   reproducibility   across   12   machines at   multiple   locations.   These   advancements   confirm   TOT   as   a   robust, practical    tool    for    assessing    reflective    cracking    resistance,    helping engineers design longer-lasting, more durable asphalt overlays.

One   of   the   principal   performance   concerns   with   asphalt   mixture pavements     is     premature     cracking,     particularly     of     surface mixtures.   For   many   years   agencies   have   used   the   Hamburg   wheel test   to   design   more   rutting-resistant   mixtures.   Due   to   a   lack   of suitable    candidates,    a    complementary    test    to    produce    more cracking-resistant mixtures has been difficult to find. Balanced   mix   design   developed   with   the   advent   of   monotonic   cracking tests,     but     there     is     some     concern     over     their     reliability.     More fundamental   tests   such   as   flexural   fatigue   are   still   in   general   use,   but at   research   rather   than   routine   testing   level.   The   Texas   Overlay   Test (TOT)   has   existed   since   the   70s.   It   was   developed   to   investigate   the reflective   cracking   resistance   of   asphalt   mixture   overlays   on   concrete pavements.   In   the   test,   a   Superpave   gyratory   compactor   puck   is   cut into   a   pill   shape   and   glued   to   two   platens.   They   are   secured   into   the overlay    machine.    A    fixed    displacement    triangular    wave    with    an amplitude   of   0.635mm   is   then   applied   to   the   pill.   This   develops   cracks through   the   center   of   the   pill,   which   results   in   a   small   reduction   of   the load   required   to   pull   the   pill   apart   on   each   cycle.   The   curve   of   this   load reduction   v   cycle   provides   an   indication   of   the   material   performance in the road. Variability   in   the   test   results   has   been   a   major   area   of   concern   with   the overlay   test   in   the   past.   A   new   approach   to   data   analysis   has   been developed   by   the   University   of   Texas   in   El   Paso   for   TxDOT.   It   is   similar in   concept   to   the   methods   employed   in   tests   such   as   I   FIT   and   IDEAL CT,    but    as    the    test    is    cyclical    the    pill    is    repeatedly    loaded    in    both tension   and   then   compression.   This   far   more   accurately   simulates   the distresses    which    occur    in    the    pavement    over    single    shot    SCB    and IDEAL   CT   tests.   Previously   only   load   reduction   was   measured   in   the overlay   test,   which   led   to   variability.   Now   the   first   cycle   is   assessed   as crack     initiation     and     subsequent     cycles     are     analyzed     as     crack propagation. Additional   improvements   were   made   to   the   specimen   preparation   and test   procedure.   In   a   Round   Robin   performed   in   Texas   in   November 2021    excellent    repeatability    and    reproducibility    were    demonstrated between 12 machines at various locations. • Market-leading overlay with excellent accuracy and repeatability • New ergonomic touch-screen display • EMT1    electromechanical    actuator    produces    silent,    accurate, repeatable performance • Peltier   temperature   control   modules   ensure   silent   temperature stability throughout tests • Our technical staff are able to analyze overlay test data • Small footprint MAIN APPLICATIONS Determination   of   cracking   in   asphalt   mixtures,   crack   initiation,   crack propagation, balanced mix design, specifications, QC/QA research applications RESEARCH APPLICATIONS Although   the   TxPro   was   designed   specifically   for   contractors   and   DOT labs   it   utilizes   a   sophisticated   electromechanical   actuator   and   Peltier temperature    control    system.    If    more    versatility    is    required,    please enquire.