According to T 312, what are the thermometer requirements for measuring the temperature of aggregates, binder, and asphalt mixtures?

• A. Range 0 to 100 C, accuracy ±0.5 C
• B. Range 20 to 250 C, accuracy ±5 C
• C. Range at least 10 to 230 C, accuracy ±2.5 C
• D. Range 200 to 400 C, accuracy ±2 C

Answer: (C)

Understanding how hot-mix asphalt temperatures are measured is essential because viscosity and workability of both binder and mix depend on accurate readings. The thermometer used for aggregates, binder, and asphalt mixtures must cover the temperatures typically reached during heating and testing, and do so with enough precision to detect meaningful differences.

The required specification is a thermometer that can read from at least 10 C up to 230 C, with an accuracy of ±2.5 C. This range comfortably encompasses the temperatures used for heating aggregates and asphalt binder in hot-mix operations, which often fall well above 100 C and can approach 200 C or more, while still being capable of reading cooler samples. The ±2.5 C accuracy ensures that temperature control is precise enough to maintain proper binder viscosity and mix consistency; small deviations can noticeably affect performance, so tighter accuracy helps keep tests reliable.

Ranging from 0 to 100 C would miss the high temperatures used in processing, and while 20 to 250 C might seem practical, the looser ±5 C accuracy is not in line with the tighter control required in practice. A range of 200 to 400 C is far outside the normal operating temperatures for asphalt materials.