ISO 22873-2021 pdf free download – Quality control for batching and mixing steel fibre-reinforced concretes.
5Mixture proportioning
5.1General
As with conventional concrete, SFRC mixtures employ a variety of mixture proportions depending onthe end use.Because of the unique properties of SFRC, slump requirements are somewhat differentfrom those of conventional concrete.Some modifications for mixture proportions of SFRC compared tothe conventional concrete are required.
5.2 Proportioning methods
Steel fibres shall be added without any changes to the conventional mixture proportions used by ready-mix suppliers for the required concrete compressive strength. Where very large numbers of fibres perunit volume are used, some adjustments can be required. To provide better workability of the concrete,more paste is needed in the mixture.Therefore, the ratio of fine-to-coarse aggregate is adjusted upwardaccordingly. To prevent wet fibre balls, avoid overmixing and using a mixture with too much coarseaggregate (more than about 55 % of the total combined aggregate by absolute volume).
Another method of improving SFRC workability has been to use pozzolans such as fly ash, slag or silicafume in addition to or as a partial replacement of hydraulic cement.
6Batching
6.1 Measuring materials
a)Hydraulic cement, aggregate, water, mineral and chemical admixtures shall be measured with eachscale. Water weighed with chemical admixture in advance shall be measured together.
b) Fibres shall be batched by mass or volume with an accuracy of -3 % and +5 % of the amountrequired per batch.
c) When fibres are to be measured by mass, bags, boxes or like containers provided that such like
containers are sealed by the fibre manufacturer and have the mass contained therein clearlymarked.No fraction of a container delivered unsealed, or left over from previous work, shall beused unless weighed.
6.2 Batching plant
a) Bins with adequate separate compartments shall be provided in the batching plant for fine and for
each required size of coarse aggregate.Each bin shall be designed and operated so as to dischargeefficiently and freely, with minimum segregation, into the weighing hooper.
b) Scales shall be considered accurate if load indicated relative to applied test load is within ±0,15 %
of the total capacity of the scale or 0,4 % of the net applied load.
c)Indicating devices shall be in full view and near enough to be read accurately by the operator while
charging the hopper. The operator shall have convenient access to all controls.
d) All exposed fulcrums, clevises and similar working parts of scales shall be kept clean.7Mixing
7.1General
There are some important differences in mixing SFRC in a transit mixer or revolving drum mixercompared to conventional concrete.One of these is that, to obtain good dispersion of the fibres and toprevent fibre balling, the fibres should be added to a fluid mix.
7.2Mixer 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 mixedconcrete. If used for the complete mixing of concrete, stationary mixers shall be equipped with anacceptable timing device that does not permit the batch to be discharged until the specified mixingtime 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 interms of the volume of mixed concrete, and the minimum and maximum mixing speeds of rotationof 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 todetect wear of blades.ISO 22873 pdf download.