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TECNOLOGÍA DEL CONCRETOAlumno: Lastra Amachi, Guimo Junior

PROPIEDADES QUÍMICAS:a. Reacc ión A lc ali -Sílic e

Los álcalis en el cemento están constituidos por el Óxido de sodio y de potasioquienes en condiciones de temperatura y humedad pueden reaccionar con ciertosminerales, produciendo un gel expansivo. Normalmente para que se produzcaesta reacción es necesario contenidos de álcalis del orden del 0.6% temperaturasambientes de 30°C y humedades relativas de 80% y un tiempo de 5 años para quese evidencie la reacción.

Existen pruebas de laboratorio para evaluar estas reacciones que se encuentrandefinidas en ASTM C227, ASTM C289, ASTM C-295 y que permiten obtenerinformaciónpara calificar la reactividad del agregado.

ASTM C227: Método de prueba estándar para determinar la reactividad potencialalcalina de cemento y agregados combinaciones (Mortero-Bar Method.)

ASTM C 227 Potential Alkali Reactivity of Cement-Aggregate Combinations(Mortar-Bar Method)Lab ID 65 Use Concrete prisms are fabricated and monitored to evaluate the susceptibility of an

aggregate for participation in the expansive alkali-silica reaction.Instructions Both coarse and fine aggregates should be sampled in accordance with ASTM D75. Send job cement and aggregates (coarse/fine) or CTLGroup will provide a highalkali cement or typical Type I cement. Need 7 kg (15 lbs) of cement and 25 kg (50lbs) of aggregate.Results Produced Percent length change of specimen.Time for Results Results are usually available within 120 working days (six to seven months totaltime).

Alternate Tests ASTM C 1260 accelerated detection of potentially deleterious expansion of mortarbars due to alkali-silica reaction.Related Tests

ASTM C 289 Potential Reactivity of Aggregates (Chemical Method) ASTM C 1293Potential Reactivity of Concrete Aggregates in ConcreteTest Designation

ASR - C227 Pot Reactivity, Mortar Meth

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Sample Type cement, aggregates (fine and coarse)

ASTM C289: Método de prueba estándar para el potencial de la reactividad álcali-

sílice de los agregados (método químico) ASTM C 289 Standard Test Method for Potential Alkali-Silica Reactivity of Aggregates (Chemical Method - Sample Preparation)Lab ID 260 Use To prepare samples for testing in accordance with ASTM C 289.Instructions Materials prepared for analysis or testing.Results Produced Fine material to make it ready for testingTime for Results Usually 1 day, depending on backlog and number of samples submitted.Alternate Tests NoneRelated Tests NoneTest Designation

ASR - C289 PreparationSample Type Siliceous aggregate samples that must be prepared especially for C289

ASTM C 289 Standard Test Method for Potential Alkali-Silica Reactivity of Aggregates (Chemical Method)Lab ID 34 Use

A rapid indication of potential alkali silica reactivity that should be used inconjunction with other tests or with history of the aggregate.Instructions Please supply a minimum sample mass of 1 kg (2.2 lbs), a larger sample lot isrequested if the sample has a lot of fine material. Additional price includescrushing, grinding, and sieving as required. If supplying material already preparedin accordance with ASTM C 289 please provide a sample mass of least 200 grams(1/2 lbs).Results Produced The potential performance of the aggregate is graphed and reported as"deleterious," "potentially deleterious," or "innocuous."Time for Results Results are usually available within 10 working days.Alternate Tests

ASTM C 227, Potential Alkali Reactivity of Cement-Aggregate Combinations(Mortar-Bar Method) ASTM C1260, Potential Alkali Reactivity of Cement-

Aggregate Combinations (Mortar-Bar Method) ASTM C1293 ASR Length Change

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Related Tests ASTM C 295 Petrographic Examination of Aggregates for ConcreteTest Designation

ASR - C289 Chemical MethodSample Type

siliceous aggregates

b. Reacción Alcali-carbon atos

Se produce por reacción de los carbonatos presentes en los agregados generandosustancias expansivas, en el Perú no existen evidencias de este tipo de reacción.Los procedimientos para la evaluación de esta característica se encuentrannormalizados en ASTM C-586.

ASTM C 586 Standard Test Method for Potential Alkali Reactivity of CarbonateRocks for Concrete Aggregates (Rock Cylinder Method)Lab ID 662Use This test is intended to provide a rapid indication for the potential expansion ofcertain carbonate rocks that may be used in concrete.Instructions Sample size must be 3?x3?x3 inches, sampling must be performed as obtained inSection 7 of ASTM C586.Results Produced Length change (%) over time. Measurements are taken weekly for first month andmonthly thereafter thru _____ months.Time for Results Testing can begin within 5 days of receipt of all necessary materials. Final reportissued upon completion of test with interim data provided as requested.Alternate Tests

ASTM C1105 - Length Change of Concrete Due to Alkali-Carbonate RockReaction.Related Tests

ASTM C295 - Petrographic Examination of Aggregates for use in Concrete. ASTMD75 - Sampling AggregatesTest Designation C586 Alkali-Carbonate ReactivitySample Type coarse aggregates including: calcitic dolomites, dolomitic limestones anddolostones.