16.7 QUALITY CONTROL AND QUALITY ASSURANCE
An important part of the production process is the testing of plant-produced material as part of the
quality control (QC) methods. QC sampling and testing are done on a regular basis to continuously
evaluate the produced material, by the material producer. The results of the QC process can be fed
back to the plant to correct or modify any setting, as required. Quality assurance (QA) tests are
generally conducted by the owner or a consultant agency (or sometimes even by the producer) at
longer time intervals to make sure that the produced material meets the specification.
The important tests and methods are presented in the following:
1. Standard test method for random sampling (ASTM 3665): This standard outlines the
process that can be used to eliminate bias during sampling. Sampling can be done either by
random procedure or stratified random procedure. In the latter process, the lot is divided
into sublots and then the random method is used to pick samples from each sublot. Tables
for picking random numbers, by selecting any two numbers and rows and columns, are
provided in ASTM 3665. Sampling should be done from different points, for example,
aggregates from a belt or truck or from in-place paving material.
2. Checking temperature of asphalt, HMA, and air: HMA and asphalt temperatures are
measured using dial- or digital-type thermometers (two thermometers) made with metal
stems (which are inserted into the material) and armored glass. AASHTO T-245 specifies the
requirements of the thermometers, which must be calibrated before use. Infrared thermometers,
when calibrated against conventional thermometers, could be used. HMA temperatures
are generally taken for each sample as well as at the start of the day, by pushing the stem to its
full depth into the material, after waiting for 3 min or when there is no appreciable temperature
difference between two readings at 1 min intervals. The same type of thermometer could
be used to check the temperature of the asphalt binder from sampling valves from the asphalt
tank. For measuring air temperature, the thermometer should be kept out of direct sunlight.