Methods of testing cem ent
BS EN 196-8-2003 pdf free.Methods of testing cem ent一 Part 8: Heat of hydration – Solution method.
Store anhydrous cement, from which metallic iron has been removed with a magnet, in a sealed container to avoid absorption of water or carbon dioxide. Bring the test sample to ambient temperature and carefully homogenize it before use.
4.4 Hydrated cement
Prepare the hydrated cement test sample by vigorously mixing, either manually or mechanically, (100,0 ± 0.1) g of anhydrous cement with (40.0 ± 0,1) g of distilled or deionised water for 3 mm at ambient temperature. Place the resulting paste in plastics or glass cylindrical vials (three for each hydration period to be tested) so that each vial contains 15 g to 20 g of material. Seal the vials by means of a stopper and, if necessary, with paraffin wax or similar material and store them horizontally in a thermostatic bath maintained at a temperature of (20,0 ± 0,2) °C.
NOTE The method does not deal with the standardization of the calorimetric apparatus, or the measuring instruments. Insulated flasks with a volume of about 650 ml have proved to be suitable.
A suitable calorimeter (see Figure 1) comprises the following:
a) Dissolution vessel, consisting of: an insulated flask (eg. Dewar flask), placed either in a heat insulated container set inside a box constructed of insulating material (e.g. wood, plastics), or immersed in a thermostatic water bath regulated to ± 0,2 °C; and an insulated stopper (made of cork or plastics) through which holes are provided for the thermometer, the stirrer and the funnel used for introducing the sample. The insulation of the calorimeter shall ensure that the thermal leakage coefficient. K, (determined in accordance with 6.3) is less than 0,06 kelvins per 15 mm for each kelvin above ambient temperature. The internal surface of the flask, that part of the thermometer immersed in the acid mixture and the lower part of the stopper, shall be acid mixture resistant.
b) Thermometer, either a Beckmann thermometer with a 5 °C to 6 °C scale and subdivisions every
0,01 °C or other measurement apparatus of an equal or higher accuracy such as a thermistor or
platinum resistance thermometer, positioned such that the end of the thermometer is at least
4 cm below the level of the liquid surface.
Express temperature readings with a resolution of ± 0.002 °C. Adjust the zero of the Beckmann thermometer so that the upper limit of the scale is approximately the ambient, or water bath, temperature. Calibrate the thermometer in a thermostatic bath against a 0,01 °C graduated and calibrated thermometer.
C) Funnel, of acid mixture resistant plastics, through which the sample is introduced into the flask and which extends below the lower part of the stopper by 5 mm to 6 mm and is sealed during the test.
d) Stirrer, of acid mixture resistant plastics, positioned such that the blades are as close as possible to the bottom of the flask and rotated by a motor at a speed of (450 ±50) min . The motor shall be low power rated (e.g. a motor of a few watts) so as to prevent any excessive heat emission from affecting measurements.
5.2 Thermostatic bath, e.g. water bath, for storing the hydrated samples at a temperature of (20.0 ±0,2) °C.
5.3 Mortar or electric grinder, for crushing the hydrated samples.
5.4 Plastics or glass vials, of capacity appoximately 20 ml, for storing the hydrated paste.
5.5 SIeve, of mesh size 125 pm.
5.6 Sieve, of mesh size 600 pm.
5.7 Chronometer, graduated in seconds, for timing the temperature readings.
5.8 Two platinum crucibles, of capacity approximately 20 ml, for ignition of samples.
5.9 Electric furnace, naturally ventilated, capable of operating at (950 ± 25) °C, for ignition of samples.
5.10 Analytical balance, capable of weighing to an accuracy of ± 0,0001 g.
5.11 Balance, of capacity 2 kg, capable of weighing to an accuracy of ± 0,2 g.
6 Calorimeter calibration
Calibration of the calorimeter is carried out in order to determine its thermal capacity and thermal leakage coefficient. These characteristics are determined by dissolving the ignited zinc oxide (4.2) in the acid mixture (4.1) and measuring the temperature of the calorimeter at fixed intervals of time. The temperature of acid mixture shall be so set that after the dissolution reaction the calorimeter temperature is at least 0.5 °C below the ambient temperature. Where a water bath is used the temperature of the bath is considered to be the ambient temperature for the calorimeter.
Calculate the thermal capacity, C, expressed to two decimal places, and the thermal leakage coefficient, K, expressed to four decimal places, as the mean values of five calibrations of the calorimeter. If K is not less than 0,06 K per 15 min per kelvin temperature difference then the calorimeter does not meet the requirements (see 5.1 a).
NOTE Calibration characteristics should be redetermined whenever:
-the thermometer has been recalibrated;
-either the thermometer, the stirrer or the flask have been renewed or modified;
the operator considers that it is necessary.
Remove the sample of hydrated cement (4.4) from the vial, and crush quickly, so that the whole sample passes the 600 pm sieve (5.6). When crushing by means of a rapid crusher operate this for (45 ± 15) s. Complete the reduction in not more than 15 mm so minimising contact with air and avoiding carbon dioxide absorption. Alternatively these procedures can be undertaken in a nitrogen atmosphere in a glove box.
Place the sample in a sealed container and homogenise by shaking, either manually or mechanically. Weigh the three samples from the same vial, required for the calorimetric determination and determination of bound water correction, in quick sequence to avoid loss of water or carbon dioxide absorption. Increase the quantity of the hydrated sample used to determine the heat of solution by 40 % over that used to test the anhydrous sample. Weigh the hydrated sample to ± 0,0001 g. Carry out the calorimetric determination as for the anhydrous cement (see 7.1.1).
Commence the heat of solution determination within the following times according to the specified hydration age:
a) ± 30 mm for hydration ages less than 3 d;
b) ± 1 h for hydration ages greater than, or equal to, 3 d and less than 7 d:
C) ±2 h for hydration ages greater than, or equal to, 7 d.
7.2.2 Correction for bound water
Correct the mass of the hydrated sample to its anhydrous mass by determining the bound water by igniting portions of the same sample of the anhydrous cement and a sample of hydrated cement from a vial as used for the calorimetric determination. Weigh two 2 g samples to ± 0,0001 g. Ignite using platinum crucibles, at (950 ± 25) °C for 1 h, then cool in a desiccator to ambient temperature arid weigh immediately.
The maximum deviation between the two determinations of percentage mass change on ignition for either the anhydrous, ma, or hydrated, ‘m,. cement shall not be greater than 0,1 %.
NOTE I Alternative instrumental methods such as thermogravimetry or automatic water and carbon dioxide analysers may be used for this delermination.
NOTE 2 The bound water correction may be determined from the calcium oxide. (CaO). content by chemical analysis or X-ray fluorescence, instead of by ignitmn. Calcium oxide determination requires greater accuracy as an error in the calcium oxide content affects the heat of hydration by a factor of two compared with the percentage mass change on ignition method.
NOTE 3 If the cement contains oxidizable components then the determination by calcium oxide content should be used.BS EN 196-8 pdf free download.Methods of testing cem ent