Tecnologa de Epxicos

Tecnologa de Epxicos. Una Gua Bsica

Qu son los Epxicos?

Qu son los epxicos ?LOS EPXICOS ENDURECIDOS SON POLIMEROS HECHOS CON DOS RESINAS QUE SE COMBINAN PARA FORMAR UNA RESINA AN MS COMPLEJA.ESTE PROCESO SE CONOCE COMO RETICULACIN

La resina de base es mezclada con un endurecedor o Agente Endurecedor para lograr la ReticulacinEl epxico reticulado es muy denso y resistente en sus propiedades qumicas, comparado con el concreto

Los materiales epoxicos tienen 4 caractersticas sobresalientes:Adhesividad y cohesin excepcional Alta resistencia qumica y a los solventesResistencia trmica al calor seco entre 180-250FNo txicos una vez endurecidosQu son los epxicos ?

Qu son los epxicos?Los epxicos son resinas termoendureciblesCuando se endurecen y se vuelven a exponer al calor no se suavizarnOtras resinas son llamadas resinas termoplsticas Las termoplsticas se suavizarn cuando se expongan al calor, y se endurecern con el fro p.ej. polietileno, vinilos

Qu son los epxicos?Cuatro tipos comunes de resinas epxicas:Bisfenol A ms comn, de baja calidadmenor viscosidad, ms lento endurecimiento, mayor existencia qumica, resistencia al calorNovolacos multifuncional, ms alta densidad en la reticulacin, ms alta resistencia qumica, baja resistencia la radiacin uv, puede ser quebradizo,se utiliza en recubrimientosMezclas de las resinas antes mencionadas resultan en una combinacin de sus diversas propiedades

Qu son los epxicos?

Cinco tipos comunes de agentes endurecedores de epxicos:Poliaminas alifticas proporcionan alta reticulacin, buena resistencia qumica/a los solventes, mas larga vida de envase, moderada flexibilidad.Aminas alifticas Mayor resistencia qumica y trmica. Vida de envase ms corta, la relacin de mezcla es crtica. Sensible a la humedadAductores de amina los ms fciles de trabajar, mayor flexibilidad y tiempo de induccin, moderada resistencia qumica/a los solventes, pobre resistencia a la radiacin UV.Aminas cicloalifticas muy comunes, mejor resistencia qumica/trmica que las poliaminas, menos flexibles, se endurecen a temperaturas tan bajas como 35F. No las afecta la humedad, buenas para usarse en superficies hmedas.Amido aminas resistencia qumia moderada, resistencia trmica limitada, endurecimiento moderado a lento, mejor flexibiliad que las aminas

Qu son los epxicos?

Se aaden disolventes a la resina epxica para modificar sus propiedades; principalmente su viscosidad, flexibilidad y dureza.

Los disolventes se clasifican como:

No reactivos: se mezclan con las resinas, se entrelazan con las molculas del epxico pero no se reticulan

Reactivos: Reaccionan con las moleculas epxicas para reducir la viscosidad y modificar la densidad, incrementando as la flexibilidad

Para qu se utilizan los epxicos?Anclajes y adhesivos Alta adhesividad y resistecia tnsil para pernos de anclajeAgentes adhesivos Alta adhesividad con el concreto fresco y ya endurecido.Aglutinante Para morteros lechadas concreto polmeroRecubrimientos Protectores concreto y acero

Para qu se utilizan los epxicos?Reparacin de grietas Por gravedad e inyeccin, perfilado y sellado, sellado de superficiesRevestimientos y Acabados Para superficies de concreto, pisos de mortero epxicoSelladores de juntas / Selladores Horizontales y verticales, acabado de juntas, semi rgidoPavimento Broom & Seed, sistemas Thin Film

Inyeccin de Grietas con Epxico

Inyeccin de Grieta

Puerto de Inyeccin Mltiple

Instalacin de Mortero Epxico

Instalacin de Lechada Epxica

Instalacin de Mortero Epxico

Instalacin de Acabado Final Epxico

Acabado con Allanadora Mecnica

Piso Epxico Tipo Thin Film

Piso Epxico Terminado

Epxicos VS Polisteres

Epxicos VS PolisteresEpxicoBajo encogimientoBuena resistencia qumica en generalFrmulas que toleran la humedadBuena vida de envaseBuena flexibilidadPolisterAlto encogimientoPobre resistencia a las basesMuy corta vida de envaseRelativamente frgilesBuena resistencia a los cidos

Terminologa de Epxicos

DefinicionesDefinicin de Resina poxica:

Una resina que contiene o contuvo grupos epxicos (epoxido), principales responsables de su polmerizacin

DefinicionesDefinicin de Agente Endurecedor

Sustancia que causa la reaccin qumica en la que el sistema de resina fluida se transforma en un slido

DefinicionesDefinicin de pxico Endurecido:

Un epxico completamente endurecido es aquel en donde uno o ms de sus componentes reactivos ha sido completamente consumidoUna txico completamente endurecido es aquel que ha alcanzado un nivel aceptable de desempeo en un ambiente o propiedad particular

DefinicionesDefinicin de Vida de Envase de un Epxico:Es el tiempo til de la mezcla. El tiempo que transcurre despus de mezclar en el que el material epxico est en condiciones de ser trabajado apropiadamente

DefinicionesViscosidad:

Es el estado lquido o plstico de resistencia de un material para fluir a una temperatura dadaLa medida de la friccin interna de un lquido a una temperatura dada

Generalmente se mide y reporta en unidades IS llamadas centipoise. El IS del agua = 1 (uno) centipoise

Definiciones

ViscosidadAlta Viscosidad (geles)- Parches y anclajes Verticales y areosViscosidad Media Anclajes y uniones en generalBaja Viscosidad inyeccin de resinas y lechadas

DefinicionesPlastodeformacin:

La plastodeformacin es la deformacin del material (epxico) causado por una carga a lo largo del tiempoLa resistencia a la plastodeformacin puede ser incrementada reduciendo la lnea de unin del epxico al concreto y agregando rellenos y agregados

DefinicionesCalor de Desviacin

Temperatura a la que el epxico alcanza una desviacin arbitraria cuando se sujeta a una carga arbitraria

Endurecimiento de Epxicos

Endurecimiento de EpxicosDependientes de la masa y la temperatura

La mayora no endurece efectivamente cuando (reticulacin) < 50FAltas temperaturas y grandes masas resultan en menor tiempo de endurecimiento, menor vida de envase y tiempo de trabajoLa temperatura de endurecimiento ptima es ~ 65-80F

Endurecimiento de EpxicosEl endurecimiento de un epxico es producto de una reaccin qumica exotrmica (que produce calor)

Entre ms alta sea la temperatura ambiental ms rpido endurecer, entre ms rpido endurezca mayor temperatura tomar el epxico.Cuando se incorporan agregados, estos reducen y absorben el calor que genera la reaccin

Propiedades de los Epxicos

Propiedades Importantes de los EpxicosCompresivas y Tnsiles Mucho ms resistente que el concreto

Compresivas - 10 - 12,000 psi, (ASTM D- 692)

Tnsiles - comunmente 5 - 7,000 psi, (ASTM D-638)

Permeablidad muy baja, tasas

Propiedades Importantes de los EpxicosMdulo Alto o Bajo, medida de la rigidez de un material

Mdulo Bajo = suave = material tipo mortero de baja resistencia

Mdulo Alto = rgido = agente adhesivo de alta resistencia

MduloMdulo Bajo Bueno como mortero epxico, como pavimento y para uso exterior donde los cambios trmicos y de volumen sern mayores y de gran impacto

Mdulo Alto Bueno para reparar grietas, reparaciones estructurales en interiores, ciclo trmico bajo

Propiedades Importantes de los EpxicosRango de epxicos

Resistencia a la Compresin10 - 20,000 psi

Resistencia Tnsil1,000 - 13,000 psi

Resistencia a la Flexin4 - 20,000 psi

Expansin Trmica17 - 50 X 10-6

Rango del Concreto

Resistencia a la Compresin3 - 6,000 psiResistencia Tnsil200 - 500 psi

Resistencia a la Flexin 200 - 1,000 psi

Expansin Trmica 3 - 7 X 10-6

Compatibilidad de los Epxicos con el Concreto

Compatibilidad Epxicos/Concreto

Los Epxicos y el Concreto no son CompatiblesDiferencias en respuesta trmica, encogimiento y mdulo son las principales causas de problemas Entre ms espeso es el epxico, ms grandes son los efectos en el cambio de volumen

Los efectos son sustancialmente reducidos a travs de la formulacin del epxico, masa y el usuario final

Compatibilidad Epxicos/ConcretoFig. 3.3 Una capa de epxico (b) adherida a un espesor de concreto (a) Fig. 3.4 El efecto del incremento de la temperatura en un sistema de epxico concreto Fig. 3.5 El efecto de la disminucin de la temperatura en un sistema de epxico concreto

Fig. 3.6 El efecto de cambios en la relacin de agregados de arena aglutinante en un sistema epxico Relacin de agregados aglutinante ConcretoEpxico y arenaCoeficiente trmico x 106 in/in/F

Compatibilidad TrmicaCoeficiente lineal de expansin trmica ~ 5 - 8 X que el del concreto (ASTM D 696)

Epxico sin diluir = 40 - 50 X 10 - 6 in / in / FEpxico activado = 12 - 16 X 10 - 6 in / in / FConcreto = 2 - 8 X 10 - 6 in / in / FEl Epxico activado y el concreto tienen coeficientes de expansin ms cercanos

Compatibilidad TrmicaLa incorporacin de agregados a los morteros epxicos disminuye las diferencias en las tasas de expansin trmica, reduciendo la tensin en la linea de adhesin del epxico al concreto. Es comn encontrar tasas de aglutinantes epxicos de ~ 4 -7 partes por galn para baja viscosidad y ~ 1.5 -2 partes para geles de alta viscosidad

Epxicos :Especificaciones y Lineamientos

Sociedad Americana para Pruebas de Materiales ASTM C 881 ASTM C-881 Sistemas para Concreto a Base de Resina EpxicaUna especificacin de desempeo, que hace una clasificacin de los epxicos de acuerdo a:Tipo: I - II - III - IV - V, Uso y ExposicinGrado: 1 - 2 - 3, ViscosidadClase: A - B - C, Temperatura Ambiental

Tipos de Acuerdo a ASTM C-881 Tipo I - Sin capacidad de carga, se adhiere de slido a slido

Tipo II - Sin capacidad de carga, se adhiere de slido a fresco

Tipo III Recubrimientos antiderrapantes, que soportan trfico

Tipo IV Con capacidad de carga, se adhiere de slido a slido

Tipo V - Con capacidad de carga, se adhiere de slido a fresco

Grados de acuerdo a ASTM C 881Grado 1 Baja viscosidad, Agua a Aceite de Motor, Usados para reparacin de grietas por inyeccin/gravedad, morteros (2,000 cps max) Grado 2 Viscosidad Media, Almbar a Miel, Usados para Anclajes y como Adhesivo (2,000 - 10,000 cps)Grado 3 Viscosidad Alta, Gel a Mantequilla de Cacahuate, Usados como Adhesivo Vertical y en Techo

Clases de Acuerdo a ASTM C 881Clase A Aplicacin a Temperaturas < 40F

Clase B - Aplicacin a Temperaturas entre 40 - 60F

Clase C - Aplicacin a Temperaturas de 60F y ms altas

ASTM C 881 - EjemplosPasta Adhesiva Epxica, que no se Hunde Tipo IV I Grado 3 Clase A, B, o C

ASTM C 881 - EjemplosResina Epxica para Inyeccin, de Baja Viscosidad

Tipo IV Grado 1 Clase B o C

Instutito Americano del ConcretoACI 503 Comit de Adhesivos para Concreto (Lineamientos para su Instalacin y Uso)

503 R Uso de Compuestos Epxicos con Concreto 503.1 Adhesividad en Concreto Endurecido, Acero, Madera, Ladrillos y otros Materiales con el Endurecido con Adhesivos Epxicos Aplicados503.2 Adhesividad del Concreto Plstico con el Concreto Endurecido

Instutito Americano del ConcretoACI 503 Comit de Adhesivos para Concreto

503.3 Producir Propiedades Antiderrapantes en una Superficie de Concreto Utilizando Sistemas Epxicos

504.4 Reparacin de Concreto con Morteros Epxico

Mezclado de Epxicos

El Mezclado de los Epxicos es CrticoLa relacin de mezcla de la base de la resina, Parte A, con el endurecedor, Parte B, vara de acuerdo a la formulacin

Las relaciones de mezcla vara de producto a producto, 1:1 a 4:1, o ms en algunos casos

Se recomiendan variaciones < 2%

Entre ms alta es la relacin, es mayor la necesidad de ser muy precisos en el mezclado

El Mezclado de los Epxicos es CrticoLos materiales deben ser llevados a la temperatura adecuada antes de ser mezclados

La Base Parte A & y el Compuesto de curado Parte B deben ser mezclados por separado antes de combinarse

La mezcla final debe ser homognea, mostrando un color uniforme, sin rayas

Los morteros y lechadas epxicas deben ser mezcladas hasta que los agregados/arena estn completamente hmedecidos por la resina

El Mezclado de los Epxicos es CrticoLa mezcla inadecuada de un epxico puede provocar:

Curado Insuficiente

Resistencia Reducida

Resistencia Qumica Reducida

Resistencia Trmica Reducida

Suavidad en toda la superficie o en algunos puntos o reas

Diferencias en la apariencia

El Mezclado de los Epxicos es CrticoMezclado de los Adhesivos Epxicos para Inyeccin

Una vez que el Material ha sido Colocado no puede ser Movido

Requieren Extremada Precisin en el MezcladoBombas Medidoras de Componente Plural Proporcionan las dos partes a una cabeza o boquilla para ser mezcladasLas bombas medidoras deben ser calibradas antes de ser usadas

Equipo para Mezclar

El Mezclado de los Epxicos es Crtico

El Mezclado de los Epxicos es Crtico

El Mezclado de los Epxicos es Crtico

El Mezclado de los Epxicos es Crtico

Preparacin de la Superficie

Preparacin de la SuperficieEl concreto que va a ser reparado debe estar limpio y suficientemente poroso para alcanzar una adecuada adhesividad

El concreto debe ser resistente

Remueva cualquier concreto de apariencia friable, quebradiza y la suciedad

Prueba de Resistencia Tensil del Concreto y Adhesividad del Epxico

ACI 503R Define la Prueba de Traccin Tnsil

FIGURA 1recubrimientotaladrodisco de pruebaLa fuerza de tensin rompe el concreto

The epoxy molecule backbone consists of stable carbon to carbon & carbon oxygen bonds which makes epoxies inertEpoxy resins are linear molecules of long chain length terminated at each end with a reactive Epoxide Group( CH2 - CH - O ) The polar hydroxyl groups spaced evenly along backbone provide adhesion by hydrogen bonding with the substrateReacting of the epoxide Groups is the crosslinking, and is initiated by a curing agent.

Common Curing agents are:AminesPolyamineCycloaliphatic AmineAmide Polyamide

Crosslinking is the joining together of molecules to form larger tightly packed (dense) materialsThe greater the crosslinking, the greater the density, and therefore the greater the chemical and thermal resistanceAn increase in crosslinking usually results in an increase in brittleness, a decrease in flexibility

Adhesion develops because the Surfaces to which they are applied have a relatively strong positive + polarity (charge) over their surfaceDuring cure between the epoxy resin & curing agent there are many ether and hydroxyl groups that exhibit a negative - polarityThe negative ions are attracted to the positive + ions on the substrates surfaceThis is an actual electro-magnetic attraction of the ions called polar bondingThe bond is stronger than concrete itselfChemical resistance is high due to closely packed (dense) molecules from crosslinkingThermal degradation of the epoxy will take place > 230 - 250F depending on type of resin system & curing agent Curing agents are relatively toxic and can cause dermatitis. Diethylene triamine will burn skin in 5 min

Epoxies (thermosetting resin) decompose or degrade when heated beyond their thermal limits of approx. ~ 250F. dry heat, and 150-180 F wet is where decomposition can start. Epoxies will char (carbonize) at > 500 - 550F

Thermoplastics molecules do not crosslink, but slip amongst each other when heated, and in time will flow like a liquid or plasticBis - A Resins are the reaction products of phenol & either acetone, condensed with epichlorohydrin. The common workhorse of epoxies. Most common not usually used in demanding conditions This reaction results in diglycidyl ethers of bisphenol A or DGEBA (Bis - A epoxy resin)Epoxy characteristics change with changes in molecular weight (backbone chain lengths)Bis - F Resins are lower molecular weight (lower viscosity), and react slower than the Bis A Resins. They have better chemical resistance than Bis - A resinsNovolacs are a reaction product of phenol with formaldehyde, and have more reactive groups on the backbone chain resulting in much greater crosslinking, therefore higher chemical & thermal resistance. Bis-F & Novolacs are suitable for high solids & 100% solids formulations.Other various epoxy types include:Water miscible and dispersible polyamidesEpoxy esters (single package) can saponify in an alkaline environmentEpoxy functional silanesAcrylic, vinyl, silicones are added to increase flexibilityThe above listing of curing agents is far from inclusive. Many more types and variations of types are available

Aliphatic-Amines often moisture sensitive, have very good wetting properties, moderate chemical resistance, better flexibility than aminesCyloaliphatic Amines Are A Variation Of An Amine. Many variations.Cyloaliphatic amines provide increased adhesion to damp cool surfacesLow temp curing down to 40F.Mixing ratios of 1:1 are most commonHigh solids formulations possible

Other materials such as polysulfides, phenols, tertitary amine catalysts, and alcohol's are used in curing agents to extend or diminish pot life, accelerate or retard cure time, and add other desirable properties such as flexibility to the cured epoxy

A common non - reactive diluent is benzyl alcohol. Between 10 -15% is common in the resins. Other diluents may include:Non reactive polymers and plasticizers, vinyl resins, silicones, acrylic resins, phthalates, phenolics, and other thermoplastic resins

Reactive Diluents become an integral part of the cured epoxy resinReactive diluents include:Epoxidized oils, or pre-reactions of epoxy with resins such as butyl nitrile rubbers,titanates, and silanesUsually some chemical, solvent, and thermal resistance of the cured epoxy is lost when used with diluents. This requires careful formulation and judicious use

Four Basic End Use Epoxy Systems:

Adhesives & Bonding - bonding concrete together Fresh/Fresh, Hardened/Hardened, Fresh/Hardened and anchoring resins. When used for anchoring the annular space should be ~ 1/8 or less otherwise Creep (time dependant deformation under load) of the epoxy will occur over time. This concept should also be observed when using epoxy in a bonder situation, keep the epoxy thin not thickMortars & Grouts - epoxy is used as the aggregate binder instead of cement. Used in place of, and to repair concrete or in base plate grouting. Very high strength in short time, much better chemical resistance than cement base mixtures Interior use hi or low mod, exterior use low mod to accommodate thermal cycling

Polymer Concrete AKA Epoxy Concrete is very much the same as epoxy mortar, but larger aggregate is used

Coatings & Overlays - wide variety of formulations. Used to protect concrete and steel from chemical and mechanical attack. Epoxy coatings are used to coat and resurface concrete floors and decks. They can be top- coated with urethanes for increased chemical and UV resistance. Thin Film Systems are applied at up to 30 mils thick Epoxies are non-breathable. Moisture vapor test for slab on grade applications, elevated slabs are not affectedSealants - provide flexibility and high strength for joint sealing. Wide variations in hardness and flexibility available, self leveling and non-sag gels. Semi-Rigid for control joints. Concrete should be >28 days old, 40 -60% of concrete shrinkage occur during the first three months

Setting in injection ports with a gel epoxyInjecting under pressure through an injection portInjecting numerous ports simultaneously, a technique called manifolding allows a contractor to inject cracks for extended periods and still get the production needed to make the job profitableExample: If a contractor were to inject one port at a time for a duration of 7 minutes, it would be costly.for a 1 foot spacing, production would be little more than 8 lineal feet per hour. However, if the contractor can inject 9 at once, the production rate will soar to 75 lineal feet per hour. High production is the contractors key to profitsThis Floor has three coats. An epoxy prime coat, an epoxy body or build coat, and a urethane finish coat. Total system thickness ~18-20 mils (0.001) Polyesters are generally less user friendly to install than epoxiesPolyesters are very sensitive to installation conditionsPolyesters are subject to saponification at higher pH ranges due to the ester linkages in their molecular structure. They basically turn to soap due to the saponification Words and terminology commonly used in association with epoxiesEpoxies are a class of organic chemical bonding systems used in the preparation of special coatings, or as adhesives for concrete or as binders in epoxy resin mortars, grouts, and polymer concreteEpoxide Group molecule = ( CH2 - CH - O )The Epoxy Resin is usually referred to as the Part A or sometimes Part 1 of the two components, Resin & Curing Agent The curing agent is the Part B When the two parts are combined and mixed together polymerization occursCuring agents accelerate or directly participate in the curing of epoxiesCrosslinking agent -A substance that increases the molecular weight of epoxies by chemically linking and bridging together polymer molecular chains, i. e., polymerizationCatalysts- increase the rate of a chemical reaction such as crosslinkingEpoxies generally take from 5 7 days at 75 degrees F. to achieve full cure and develop full physical propertiesThe pot life can be extended by keeping the epoxy cool, and mixing in small quantitiesEpoxy viscosity is determined by ASTM D 2393

Viscosity is determined by the molecular weight of the materialThe molecular weight is a measure of the molecules chain length

The longer the length of the molecule, the easier and greater the entanglement of the molecules becomes, and the more difficult it becomes for the molecules to slide over and around each other.

An increase in temperature decreases viscosity, while a decrease in temperature will increase viscosity

A materials viscosity is determined at a specified and accurately measured temperature ~ 70-75F. Acetone = 0.3 cpsXylol/xylene = 0.6 cpsDistilled water = 1 cps30 wt. Motor oil = 200 cps60 wt. Motor oil = 1,000 cps Honey = 3,000 cpsKetchup = 110,000 cpsPeanut butter 250,000 cps

ASTM D 2393 Method for viscosity of epoxy resins and related components. Uses a Brookfield Viscometer

Polymers such as epoxies always have greater creep than inorganic materials such as a concreteThe amount of filler or aggregate that can be added to reduce creep is limited by the degree that workability is reducedCreep resistance is important when anchoring epoxies are employed under loadGenerally the thinner the bond line the less the creep The HDT can be a good indicator of glass transition temperature, although these may not be the same Sustained loads in excess of ~ 18F. above the HTD can result in creep to failureTypical HDT for epoxies range from 120 130 degrees F. HDT is the service temperature limitation under loadDesirable for structural bonding applications when service temperatures places the material in a ridged state (at least 30F below the HDT)Working Time and Cure Time are affected by the ambient air and surface temperatures at the time the epoxy is applied.Pot life and Open Time are two elements which make up Working Time.

Pot life is the time a pre-determined quantity of mixed epoxy is workable in the mixing vessel.Open Time is the period between the application of the epoxy and the expiration of the ability of the epoxy to bondThe use of aggregate in the epoxy resin in addition to absorbing heat will occupy space in a given volume normally taken up by the heat producing epoxyGenerally, a specified cure time will half or double respectively when the temperature increases 18F or decreases 18F Epoxies do not breath, that is, readily pass water vapor.Breathability is also referred to as permeability, and is measured in a unit called Perms A perm is the rate of water vapor transmission of 1 grain per square foot per hour per inch of mercury vapor pressure differentialEpoxies have perm ratings of less than 1 perm, i.e. 0.15 -0.05 permsEpoxies can develop blistering from vapor pressure when applied to concrete slabs on grade where a vapor pressure differential exists across the slab

Modulus is a measure of the amount of movement of a fully cured epoxy before fracture occursHigh Modulus good for vertical and overhead anchoringMedium Modulus good for anchoring/bondingLow Modulus good for crack injection & mortars

Modulus is affected by temperature especially at or near to the Heat Deflection Temperature (HDT) . Below the HDT the change in modulus is insignificant Low modulus materials should be used on exterior projects where thermal cycling is prevalentLow modulus epoxies will bend or deflect slightlyHigh modulus epoxies are relatively brittle when compared to low modulusHigh modulus materials do not deform under load

When an external load is applied perpendicular to the bond line, a difference in modulus usually does not cause a problem

When the load is applied parallel to the bond line deformation of the lower modulus material transfers the load to the higher modulus material which may fracture

Concrete repair materials should exhibit a modulus close to that of the concrete to be repaired3-7 X 10 6 = 0.000,003 0.000,007"Thermal shock can cause ruptures between the epoxy and concreteThermal cycling can cause ruptures between epoxy and concrete. Freeze thaw cycling may be in excess of 100 times per yearRuptures will typically occur at the epoxy to concrete interface locus zoneModulus of elasticity should be low enough to accommodate the volume change differences between the epoxy and concrete without inducing excess stress Sufficient volume change cycling can fatigue materials even though the induced stress may be have been smallThe thermal expansion coefficients for epoxy and concrete are differentThe epoxy expands and contracts at a different rate than the concrete when subject to changes in temperature

Epoxy thermal expansion rate is ~ 8 X that of concreteThe addition of sand or other aggregate brings the thermal coefficient of epoxy closer to that of the concrete.Not only the amount (ratio) of sand or aggregate used , but the mineralogy of the sand or aggregate will effect the thermal coefficient of the epoxy.Bulking the epoxy with aggregate will bring the thermal coefficients closer together. Bulking rates up to 50-60% are commonThe type of aggregate used also have an effect on the overall thermal coefficients achieved.

Average Concrete has a thermal Coefficient of ~ 5 X 10 - 6 which is expressed as a decimal of 0.000005.

Thermal Compatibility is evaluated by:ASTM C 884 - Test Method for Thermal Compatibility Between Concrete and Epoxy-Resin Overlay ASTM C881 can be used as a helpful means of selecting an epoxy for a particular use or environmentType refers to the intended exposure conditions and it end use

Types I & IV are useful and appropriate for crack injection

Type IV Spec requires a minimum Heat Deflection Temp. of 120F.

Heat Defection Temp. is the temp. At which the epoxy changes from rigid to elastomeric . ASTM D648 is test standardConsideration must be given to situations where the internal temp. may exceed 100F. as a mean.

Grade refers to the viscosity, flowability of the mixed epoxy,Low viscosity resins are best suited for the injection of fine hairline cracks, but may leak out when used on cracks > 0.01 in.The class refers to the temperature limits at the time of placement, for both ambient air and the surfaceA non sag paste is also defined as a gel and is defined by ASTM C-881 as having a viscosity of greater than 2,000 cps and not more than 10,000 cpsepoxies exhibiting viscosity's greater than 10,000 cps are gels or otherwise pastesLow viscosity is < 2,000 cps as defined by ASTM C-881Do not mix quantities larger than 1 quart by hand mixing. Always use a power mixer Do not let the mixed material set in the bucket or in a pile. This is an increase in the mass of the mixed material therefore pot life, working time will be significantly reduced.The epoxy mass in the bucket will exotherm (heat up) and speed up the cure (crosslinking) Mixing each part separately before combining togetherDetermines what the strength (axial tensile) of the concrete top surface is. The strength of the concrete at the surface is considerably weaker than if the aggregate is not exposed and the laitance removedDetermines what the relative strength of the coating topping or repair material installed over the epoxy isPerform the test at ~ 1 per 100 sq.. ft.According to where the tensile break occurs determines the weakest link in the chainTensile breaks can occur:1. Within the concrete surface (cohesive failure)2. Within the coating, topping, or repair material (cohesive failure)3. At the material to epoxy interface line (adhesive failure)4. A glue failure (cohesive)