Canadian Council of Independent Laboratories (CCIL) Practice Exam

Placing concrete into moulds for a flexural test requires careful consideration of the uniformity and consolidation of the material to ensure accurate testing results. The correct method of placing the concrete in two equal lifts is essential for several reasons. When concrete is placed in two equal lifts, it allows for better control over the compaction of each layer, leading to a more homogeneous mix within the mould. This method reduces the risk of segregation and voids, which might compromise the integrity of the test sample. Additionally, by allowing the first lift to unset before placing the second lift, it ensures that there is a bond between the layers, enhancing the strength of the sample. Proper curing of the concrete also benefits from this approach, allowing for a more accurate flexural strength measurement once the testing begins. This method strikes a balance between achieving adequate fill and ensuring proper consolidation without excessive vibration, which could introduce air pockets or uneven density. In smaller moulds, like those measuring 200mm or less, this careful method of placement is critical to produce reliable test specimens that reflect the true performance of the concrete under flexural loads.