Dipayan Jana Construction Materials Consultants, Inc. Greensburg, PA USA

Transcription

1 DELAYED SETTING OF CONCRETE A PETROGRAPHIC AND CHEMICAL INVESTIGATION Dipayan Jana Construction Materials Consultants, Inc. Greensburg, PA USA

2 Some Common Applications of Set-Retarding Admixtures in Concrete Hot weather construction Construction of Large Concrete Structure Oil-Well Cement Exposed Aggregate Finish

3 Lignosulfonic acids and their salts - Modifications and derivatives of lignosulfonates Hydroxylated carboxylic acids (OH, COOH) and their salts (e.g., Gluconic, Citric, Tartaric, Malic, Salicylic, Tannic acids) - Modifications and derivatives of hydroxylated carboxylic acids Carbohydrates (e.g., Glucose, Sucrose, Polysaccharides)

4 Reduction in the dissolution rate of the rapidly dissolved anhydrous components of cement (i.e., C3A & C4AF) Formation of insoluble and impermeable film around the hydrating cement particles Delay in bond formation among the hydrates

5 Delayed Setting of ASTM C 494 Type D Retarding and Water Reducing Admixture Setting Time (hrs) Final Set Initial Set Admixture Dosage by Mass of Cement (liters/kg) From Rixom, M.R. Concrete Admixtures: Use and Applications 1978

6 Effect of Type D Admixture in Improving Compressive Strength of Concrete (Water-reducing Effect) Compressive Strength (MPa) DAY 7-DAY 3-DAY = W/C Admixture Dosage by Mass of Cement (liters/kg) From Rixom, M.R. Concrete Admixtures: Use and Applications 1978

7 Hot weather construction Placement of a concrete slab-on-grade on a busy interstate highway Severe delay in final set to achieve an acceptable final tyned surface finish Settlement cracking during form release Plastic shrinkage cracking Low 3-day compressive strength

8 Ingredients Portland Cement, ASTM C 150 Type II Fly Ash, ASTM C 618 Class F Sand, ASTM C 33 Crushed Gravel, ASTM C 33 Water Retarder, Daratard 17 Darex II AEA DCI-S Corrosion Inhibitor Amount/Cubic Yard 520 pounds 124 pounds 990 pounds 1800 pounds 250 pounds 21.4 ounces 7.7 ounces 7 pounds/gallon of water

9 Daratard 17 is a blend of lignosulfonates and corn syrup (carbohydrate) Complies with ASTM C 494 Type D admixture retarder & water reducer Recommended dosage that varies from 130 to 520 ml/100kg (2 to 8 fl oz/100 lb) of cement. Set retardation by forming a thick, dense impermeable film around the hydrating cement particles (stabilizing ettringite films around calcium aluminate).

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11 Petrographic examinations [ASTM C 856] - Visual examinations - Examinations of freshly fractured surfaces and lapped sections of concretes by using a stereomicroscope - Examinations of oil immersion mounts and thin sections by using a petrographic microscope Chemical Analysis - UV-visible spectrophotometer scan in the region of 190 to 1100 nanometers

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13 Reference Sample - Pastes = Type I/II Portland cement, Fly ash, Daratard 17 - w/cm = percent fly ash - Retarders dosages 0, 3, 6, 9, and 18 oz per 100 pounds of cementitious material. - Moist-cured for seven days. Test Sample (Concrete Cylinders) - Approximately 160 grams of paste-rich fractions of concrete was ground to pass through the No. 100 sieve.

14 Pulverized to Minus No. 100 size fraction Digested in 120 ml. deionized water was added, stirred, boiled for 20 minutes Vacuum filtered while hot; the residue was washed with denatured ethanol; and the filtrate was dried on a hot plate in a 250 ml. glass beaker. The dried solids were dissolved in 25 ml. reagent grade sulfuric acid; a 5 ml. aliquot of this solution was added with 5 ml. of beta-napthol reagent in a 15 ml. glass test tube. The test tube was boiled for one hour. After cooling, the solution in the test tube was scanned in a UV-Visible spectrophotometer. The absorbance bands at 590 to 600 nm were used to determine the amounts of sugar and salts of hydroxylated compounds in the sample.

15 Lignosulfonate Carbohydrate