CONTROLLED LOW STRENGTH MATERIAL (CLSM) AS ROBUST BACKFILL MATERIAL

Soil or improved soil/ aggregates with predefined gradation (GSB, WMM) are primitively used for backfill, (both structural / non-structural back fill), pavement bases, void filling etc., with its inherent limitations of air voids, stiffness, need for compaction, susceptibility to water penetration, susceptibility of settlement etc. Controlled low strength material (CLSM) eliminates the drawbacks of soil backfill providing durability to the supporting structure. CLSM is compulsorily a back fill material and not a low strength concrete, rather it can be well defined as material which is designed as concrete with flow ability and strength as per the requirement and used as backfill to avoid the drawbacks of the soil or murum backfill. Contrary to the soil, the strength and thus the bearing strength of the fill can be controlled allowing with scope for future changes. ACI 116R defines CLSM as per the strength criteria, “CLSM as material that results in a compressive strength of less than 8.3 Mpa” CLSM can be designed with varying strength and density, considering the cost and future needs, low strength CLSM shall be necessary to allow future excavation, whereas if the there is no scope for future excavation the strength can be at higher side, further the density of CLSM can be modified as per the cost and material needs. Properties of CLSM can be enhanced as per the requirement to compensate particular need like corrosion resistance, Exacavatability, strength flow ability etc. Material properties such as shrinkage, subsidence and settlement are not considered as specification performance or requirement properties. These properties are considered as inherent to CLSM and as such; do not require the establishment of specification requirement.