Sample Management and Preparation Flashcards

A field technician must obtain a representative sample from a large, conical stockpile of coarse aggregate. According to CSA A23.2-1A, which of the following methods is the most appropriate to minimize the effects of segregation?

Answer: Combining at least three increments taken from the top, middle, and bottom thirds of the stockpile.

CSA A23.2-1A specifies that to obtain a representative sample from a stockpile, increments should be taken from different levels (top, middle, and bottom) to account for segregation, where coarser particles tend to roll to the bottom and finer particles concentrate in the middle. The other methods are prone to bias and will not yield a representative sample.

According to standard practices such as AASHTO T 248, what is the primary purpose of the quartering method when handling a large field sample of aggregate?

Answer: To obtain a smaller, representative specimen that has approximately the same composition as the original large sample.

The fundamental goal of sample reduction techniques, including quartering and splitting, is to reduce a large field sample to a manageable test size while ensuring the reduced portion remains representative of the original material's characteristics and gradation.

Which of the following is a critical requirement for the *initial curing* of newly molded concrete test cylinders in the field as per CSA A23.2-3C, before they are transported to the laboratory?

Answer: Cylinders must be stored in a manner that prevents moisture loss and maintains a temperature between 15°C and 25°C.

CSA A23.2-3C requires that during the initial curing phase on-site (up to 48 hours), concrete cylinders must be protected from freezing, moisture loss, and physical disturbance. They must be maintained within a specific temperature range, which for most concrete is 15°C to 25°C, to ensure proper hydration. The other options describe incorrect or harmful practices.

A technician receives a bulk sample of loose hot-mix asphalt from a plant. According to standards for reducing sample size (e.g., AASHTO T 248), what is the mandatory first step before quartering or splitting the sample?

Answer: Thoroughly mix the entire sample on a clean, hard surface to ensure it is homogeneous.

Before any reduction in size, the entire bulk sample must be thoroughly remixed to counteract any segregation of aggregates and binder that may have occurred during transport. This ensures that any subsequent smaller portion taken for testing is representative of the whole batch.

In the context of a CCIL-certified laboratory, what is the primary purpose of maintaining a strict chain of custody for construction materials samples?

Answer: To provide a chronological and legally defensible record of sample possession, handling, and storage.

A chain of custody provides a formal, documented history of a sample from collection to disposal. Its primary importance is to ensure the integrity of the sample and the test results, providing traceability and legal defensibility by showing who had the sample and what was done with it at all times.

A technician is preparing a fine aggregate sample for a sieve analysis (CSA A23.2-2A). The field sample is visibly moist. Which of the following preparation steps is essential for an accurate dry sieve analysis?

Answer: Drying the sample to a constant mass in an oven at a temperature of 110 ± 5 °C.

A standard dry sieve analysis requires the test to begin with a known dry mass. The sample must be dried to a constant mass at a specified temperature (110 ± 5 °C) to ensure all moisture is removed. Wet particles would clump together and not pass through the sieve openings correctly, leading to inaccurate gradation results.