ISO 22873:2021 pdf download – Quality control for batching and mixing steel fibre-reinforced concretes.
7.2 Mixer equipment a) Mixers include stationary mixers or truck mixers. Agitators include truck mixers or truck agitators. b) Stationary mixers shall be equipped with a metal plate or plates on which are plainly marked the mixing speed of the drum or paddles, and the maximum capacity in terms of the volume of mixed concrete. If used for the complete mixing of concrete, stationary mixers shall be equipped with an acceptable timing device that does not permit the batch to be discharged until the specified mixing time has elapsed. c) Each truck mixer or agitator shall have attached thereto in a prominent place a metal plate or plates on which are plainly marked the gross volume of the drum, the capacity of the drum or container in terms of the volume of mixed concrete, and the minimum and maximum mixing speeds of rotation of the drum, blades or paddles. d) Stationary and truck mixers shall be capable of producing uniformly mixed concrete within the specified time or the specified number of revolutions. e) The agitator shall be capable of maintaining the mixed concrete in a uniformly mixed condition. f) Mixers and agitators shall be examined, or their mass determined, as frequently as necessary to detect changes in condition due to accumulations of hardened concrete or mortar and examined to detect wear of blades. 7.3 Mixing method 7.3.1 Add fibres to transit mix truck a) The wet mixture to be used is prepared first without the fibres. The slump of the concrete before fibre addition should be 50 mm to 75 mm greater than the final slump desired. Normally, the mixture would be prepared using the water-hydraulic cement ratio found to give the best results and meeting the specifications for the job. The use of a high-range water-reducing admixture can be advantageous, but is not essential.
8 Quality 8.1 Slump and air content a) Slump, air-content, and temperature tests shall be made at the time of placement at the option of the inspector as often as is necessary for control checks. In addition, these tests shall be made when specified and always when strength specimens are made. b) If the measured slump, temperature, or air-content falls outside the specified limits, a check test shall be made immediately on another portion of the same sample. In the event of a second failure, the concrete shall be considered to have failed the requirements of the specification.