Question

1. Explain the process that leads to raveling of aggregate in asphalt concrete pavements in the field that are exposed to heavy rains.

2. Explain why defects (such as knots) are much less significant in engineered wood products than in sawn timbers.

Answer 1

1. When moisture content by way of rain, fog or high humidity etc comes during or after laying down of the pavement a film of moisture forms on the coated aggregate particles and prevents the development of a strong bond. And hence finer aggregates starts dislodging due to the deterioration by the moisture and advances to the loss of larger aggregate sizes.

2. The Sawn timber comes directly from the tree cutted and converted into logs the natural defects like knots and rots etc comes as such and very less chances that these can be eliminated.

But engineered wood comes from the proper seasoning of the timber then we convert the logs into sub-layers which can be of the same species, or of different species. The grain of each layer runs in different directions, which makes it very stable and hence eliminates the defects.