The bonding strength developed between two cement treated crushed rock layers has been investigated in a laboratory testing project undertaken by the University of South Australia and Transport SA. Samples were prepared to represent several field construction practices and interlayer treatments to indicate which methods provided the better bonding condition between cemented layers of a flexible pavement. The tested materials were bound with 4 percent (by mass) blended cement (GB) prepared both with and without retarder. The interface boundary was lightly brushed to simulate construction brooming, and left either damp or dry prior to the next layer placement. While no proprietary bonding agents were evaluated, a low cost curing compound (Calcure) was investigated to determine its effect on bond development. The effects of the delay in placement time between layers was also studied by simulating same day, next day, three-day, and seven-day field placement. In general, the bond strength between the cemented layers was observed to decrease with an increased time delay in placement of the second layer. Hence it was concluded that consecutive CTQR layers should be placed on the same day, preferably as soon after each other as possible. It was also found that both CTQR layers should be treated the same in relation to inclusion or exclusion of the retarder and that Calcure did not prove effective as a potential bonding agent. The recommended same day placement of consecutive cemented layers is consistent with the standard construction specifications in use by TSA over the last decade. Some quantification of the relative effects on bond development caused by unavoidable delays in final layer placement, has also been achieved. (a)
Samenvatting