Required density has been achieved after three passes, but on the fourth pass, aggregate begins to break down and density diminishes. This leaves the paving foreman with a decision. During production, the roller operator can make three passes over the mat and reach required density with the breakdown roller alone. However, according to the first fundamental rule of conducting test strips, the other rollers in the paving train must also be taken into account.

Experience from previous jobs tells the foreman that rolling this type of mix with a pneumatic roller in the intermediate zone will provide 2- to 3-percent more density. Therefore, when the breakdown roller reaches 91.8-percent required density after two passes, the pneumatic roller could be used to complete the compaction and reach the desired density. With the extra density provided by the pneumatic roller, the mat would reach up to 94.6-percent required density - well within parameters for 100-percent pay while also increasing the chance for a performance bonus. Though one might assume that making three passes with the breakdown roller followed by the pneumatic roller will result in an even greater amount of density, the risk of breaking down the aggregate and missing the density requirement entirely is too great. With so much on the line, assumptions have no place in road construction - and test strips ensure that you have a factual baseline on which to rely.

Need for Speed
Another important aspect of establishing test strips is to operate at the appropriate travel speed to balance all machines in the paving operation. This helps to ensure that the rollers always work within their defined zones of effectiveness, while also maximizing overall production efficiency.