ASTM C94 Chapter 9 Measuring Materials
9.1 Cementitious material- When the quantity of cementitious materials exceeds 30 % of the full capacity scale, the measured quantity of the hydraulic cement shall be within ±1 % of the required mass, and the cumulative measured quantity of hydraulic cement plus supplementary cementitious materials shall also be within ±1 % of the required cumulative mass at each intermediate weighing.
9.2.1 For aggregates are measured in individual or cumulative weigh batches, when the required intermediate or final mass is less than 30 % of the scale capacity the mass of the aggregate shall be within ± 0.3 % of the scale capacity or within ±3 % of the required mass, whichever is less.
9.2.2 When the aggregates are measured in an individual weigh batcher and the required mass of aggregate is equal to or greater than 30 % of the scale capacity, the quantity of aggregates shall be within ± 2 % of the required mass. When aggregates are measured in a cumulative aggregate weigh batcher, and the required intermediate and final cumulative mass of aggregate components is equal to or greater than 30 % of the scale capacity, the quantity of the aggregate at each successive weighing shall be within ± 1 % of the required mass.
Note 11- The batching accuracy limit of 0.3 % of scale capacity establishes a reasonable minimum weighing tolerance limit that is independent of the quantity of material being weighed. It generally governs for smaller batch quantities weighed in weigh batchers (scale).
9.3 Mixing water shall consist of water added to the batch, ice added to the batch, water occurring as surface moisture on the aggregates, and water introduced in the form of admixtures. The added water shall be measured by weight or volume to an accuracy of 1 % of the required total mixing water. Added ice shall be measured by weight. In the case of trucks mixers, any wash water retained in the drum for use in the next batch of concrete shall be accurately measured; if this proves impractical or impossible, the wash water shall be discharged prior to loading the next batch of concrete. Total water (including any wash water) shall be measured or weighed to an accuracy of ± 3 % of the specified total amount.
Required accuracy of the batched water is a relatively tight ± 1 % of the total mixing water. Water meter calibrations are typically to a tolerance of ± 1 % of the actual batch water quantity going through the meter.
The NRMCA National Ready Mix Concrete Association Certification program includes a requirement that volumetric measuring devices for water at the plant be accurate ± 1.5 % of the target water quantity.
Admixture: most chemical admixtures contain approximately 70 % water and 30 % solids.
9.4 Chemical admixtures in powdered form shall be measured by mass. Liquid chemical admixtures shall be batched by mass or volume. Admixtures measured by either mass or volume, shall be batched with an accuracy of ± 3 % of the total amount required or plus or minus the amount or dosage required for 100 lb [50 kg] of hydraulic cement, whichever is greater.