GB/T 8077-2023Methods for testing uniformity of concrete admixtures (English PDF)

4.1 Number of tests and requirements

4.1.1 Each determination shall be tested twice. The absolute difference between the two results shall be within the repeatability limit; and the average of the two test results shall be used to represent the determination result. If the absolute difference between the two results exceeds the repeatability limit, a third determination shall be performed within a short period of time. Data exceeding the repeatability limit shall be discarded, and the average of the remaining two data shall be taken. If the third data is in the middle of the two values, the average of the three results shall be used to represent the determination result. If the deviation of all three determination results exceeds the repeatability limit, the test shall be repeated. Exceptions apply where otherwise specified.

4.1.2 For routine production control analysis, each determination may be tested only once.

4.1.3 The water used in this Document shall be no lower than the requirements of Grade III water specified in GB/T 6682-2008, except for cement paste fluidity and water reducing rate of cement mortar.

4.2 Blank test Using the same amount of reagent, without adding the specimen, the test shall be performed according to the same determination procedure; and the obtained determination results shall be corrected.

4.3 Ignition Place the filter paper and precipitate into a pre-ignited and constant-weight crucible. To avoid flame formation, slowly dry and ashed the precipitate in an oxidizing atmosphere until no black carbon particles remain. Then, place the crucible in a high-temperature furnace and ignite it at the specified temperature.

4.4 Constant mass After the first ignition or drying, cooling, and weighing, check for constant mass by repeatedly igniting or drying for 30 min each time, followed by cooling and weighing. Constant mass is achieved when the difference between two consecutive weighings is less than 0.0005 g.

4.5 Check for chloride ions (Cl-) (silver nitrate inspection) After washing the precipitate several times as prescribed, rinse the lower end of the funnel with a few drops of water. Wash the filter paper and precipitate with a few milliliters of water. Collect the filtrate in a test tube; add a few drops of silver nitrate solution (5 g/L); and observe whether the solution becomes turbid. If turbid, continue washing and testing until the solution is no longer turbid when tested with silver nitrate.

4.6 Reagent requirements

4.6.1 All reagents shall be no lower than analytically pure (unless otherwise specified). Reagents used for calibration shall be primary reagents.

4.6.2 For acids or ammonia specified no concentration in this Document, it refers to commercially available concentrated acids or concentrated ammonia.

4.6.3 The degree of dilution of reagents is expressed as a volume ratio. For example, ammonia (1+3) means a mixture of 1 volume of concentrated ammonia and 3 volumes of water.

4.6.4 The shelf life of standard titration solutions is no more than 6 months when sealed, and no more than 2 months after opening.

4.7 Data processing requirements Density and chloride ion calculation results shall be retained to three digits after the decimal point; pH and surface tension calculation results shall be retained to one digit after the decimal point; paste flowability calculation results shall be accurate to 1 mm; all other calculation results shall be retained to two digits after the decimal point, unless otherwise specified.

6.3 Test procedure

6.3.1 Shake the tested specimen thoroughly and pour it into a beaker. Carefully pour the specimen from the beaker into three 100mL stoppered graduated cylinders. When the liquid level in each stoppered graduated cylinder is close to the 100mL mark, use a dropper to titrate liquid to 100mL, accurate to 1mL; and then tighten the stopper.

6.3.2 Place three stoppered graduated cylinders horizontally at an ambient temperature of (20±2) °C, avoiding direct sunlight. After 28 d, directly read the volume of the supernatant, VL, (suspension) or the volume of the bottom precipitate, VS, (solution type).

6.4 Calculation and expression of results When the bottom precipitate is too small to be read directly after 28 days of standing of the solution-type liquid accelerating agent, pour the solution into another 100mL graduated cylinder; measure the solution volume, VL; and calculate the volume of the bottom precipitate according to Formula (1). Where. VS - volume of bottom precipitate, in mL; VL - volume of solution, in mL.

6.5 Determination of test results The suspended liquid accelerating agent is represented by the median value of three read VL values; the solution-type liquid accelerating agent is represented by the median value of three read or calculated VS values.

7.1 Drying method

7.1.1 Principle Water is vaporized at a temperature of 100°C~105°C, thereby achieving the purpose of drying.

7.1.2 Instruments The required instruments and requirements are as follows:

a) Balance. Graduation value of 0.0001 g;

b) Drying oven. Temperature range from room temperature ~ 200 °C;

c) Weighing bottle with lid;

d) Desiccator. Filled with color-changing silica gel.

7.1.3 Test procedure

7.1.3.1 Place the clean, lidded weighing bottle in the drying oven and dry it at 100 °C ~ 105 °C for 30 min. Remove it and place it in the desiccator to cool for at least 30 min before weighing. Repeat the above procedures until a constant mass is obtained; the mass is m0.

7.1.3.2 Weigh approximately 5 g of the specimen into the constant-weighted weighing bottle, accurate to 0.0001 g. The total mass of the liquid specimen and the weighing bottle is m1.

7.1.3.3 Place the weighing bottle containing the liquid specimen into a drying oven; open the cap; heat to 100°C~105°C (except for special varieties) and dry for at least 2 h. Cover and cool in a desiccator for at least 30 min; then weigh. Place in an oven and dry for 30 min; cover and cool in a desiccator for at least 30 min; then weigh. Repeat the above procedures until a constant mass is obtained; the mass is m2.

7.1.4 Calculation and expression of results The solid content, omegas, is calculated according to Formula (2). Where. omegas - solid content; m2 - mass of the weighing bottle plus the dried specimen, in g; m0 - mass of the weighing bottle, in g; m1 - mass of the weighing bottle plus the specimen, in g.

7.1.5 Repeatability and reproducibility limits The repeatability limit is 0.30%; and the reproducibility limit is 0.50%.

7.2 Dilution-drying method

7.2.1 Principle The diluted test specimen is placed in a constant-weighed petri dish and dried to a constant mass at a specific temperature. The mass of the specimen before and after drying is measured.

7.2.2 Instruments The required instruments and requirements are as follows:

a) Balance. Graduation value of 0.0001 g;

b) Drying oven. Temperature range from room temperature ~ 200 °C;

c) Weighing bottle with a lid;

d) Desiccator. Filled with color-changing silica gel.

7.2.3 Test procedure

7.2.3.1 Place a clean, capped weighing bottle in a drying oven and bake at 100°C~105°C for 30 min. Remove and place in a desiccator; cool for at least 30 min; then weigh. Repeat the above procedures until a constant mass is obtained; the mass is m0.

7.2.3.2 Diluting the test specimen. Shake the test specimen thoroughly. Accurately weigh W0 (8.0000 g~10.0000

g) of the test specimen using a small spoon and place it in a beaker. Add distilled water W1 (30.0000 g~50.0000

g) to dilute the specimen.

7.2.3.3 Thoroughly stir the diluted test specimen; take approximately 5 g of the diluted test specimen with a small spoon, accurate to 0.0001 g; and place it into a constant-weighed weighing bottle. Cover the bottle and accurately weigh the total mass of the specimen and the weighing bottle as m1.

7.2.3.4 Place the weighing bottle containing the specimen into a drying oven; open the weighing bottle cap; heat to 100 °C~105 °C to dry. Cover the bottle; and place it in a desiccator to cool for at least 30 min before weighing. Repeat the above procedures until a constant mass is obtained; the mass is m2.

7.2.4 Calculation and expression of results

7.2.4.1 The solid content of the diluted specimen is calculated according to Formula (3). Where. omegad - solid content of the diluted specimen; m2 - mass of the weighing bottle plus the dried specimen, in g; m0 - mass of the weighing bottle, in g; m1 - mass of the weighing bottle plus the specimen, in g.