Canadian Council of Independent Laboratories (CCIL) Practice Exam 2025 - Free CCIL Practice Questions and Study Guide

The significance of the 28mm sieve in slump flow sample preparation primarily relates to its role in indicating particle size retention. This sieve is used to assess whether the material meets specific gradation requirements for optimal workability in concrete mixtures. By retaining larger particles while allowing smaller particles to pass through, it ensures that the sample's particle size distribution is appropriate for achieving desirable flow characteristics and stability during application.

In slump flow testing, uniformity and the right proportions of coarse and fine aggregates are crucial for ensuring the material's performance, especially in applications like self-consolidating concrete (SCC) where fluidity is essential. Thus, utilizing the 28mm sieve helps to ensure that only the particles suitable for the intended use remain in the sample, which ultimately contributes to the quality and integrity of the concrete mix.

The other options highlight concepts that, while important in the broader context of concrete testing and characterization, do not directly pertain to the sieve's role in preparing slump flow samples. For example, the sieve does not measure the fluidity of a sample or determine its temperature, nor is it employed specifically for strength testing. Instead, its primary function is focused on filtering out larger aggregates to maintain the intended particle size distribution crucial for achieving the best performance characteristics