Application of cement-based foams for narrow-trench backfilling

Abstract

In modern urban traffic scene, it has become a necessity to cut the trenches for carrying service lines, especially cables for various uses, as narrow as possible in order to keep the disturbance to the traffic to the minimum. The rising cost of construction also demands that the time for, and cost of, such service line laying be kept to the minimum. These demands are well met by resorting to narrow trench cutting alongside the roads in use. However, the backfilling of such very narrow trenches requires that the backfilling material must satisfy certain engineering properties as opposed to the traditional earthfills. Cement-based foams are considered to be a good backfill material. This study characterises their mechanical performance, thermal shrinkage, and bonding with the bituminous substrate. Nine different mixtures ranging in density from 600 to were considered here. The hardened cement-based foam mixtures were tested first to ascertain their strength, modulus of elasticity and Poisson's ratio. This was followed by evaluating their drying shrinkage and coefficient of thermal expansion. Lastly, these mixtures were assessed for their bond performance with the asphalt concrete. The test outcomes were used to rank the mixtures on the basis of an analytic hierarchy process. The results show that the lightest mixtures yield the best performance and substantial benefit accrues from blending in fly ash into the binder. Aside from showing immense promise as a backfill material for narrow trenches, the results now constitute a valuable database to be used by future researchers for simulating and designing the back fills of narrow trenches as a composite structure.