Use of Rapid-Hardening Cement for Controlled Low-Strength Materials for Pavement Applications

Controlled low strength materials (CLSMs) are engineered, cement based materials of growing interest in all trench backfilling and bedding applications where low stiffness, strength and density are required. Although 50 years have passed since its first application, the technology has been the source of continuous innovation. The challenge today concerns the excessive and undesirable long-term gain in strength of current CLSMs available on the market which leads to difficulties in the event of future removal and to unbalanced stress strain behavior with surrounding soils. In this investigation, the authors present a long-term laboratory study aimed at the creation of new formulations for pavement applications with the objective of avoiding or limiting any gain in stiffness and resistance over time. For this purpose, a rapid hardening cement has been used as a substitute for Portland cement. The particular formulation of cement adopted presents many advantages in terms of rapid set, high early strength development and insignificant gain in strength over long periods. All the mixtures studied were subjected to static and dynamic triaxial tests taking the mechanical characteristics of a reference granular soil as the mix design target for new CLSM formulations. The results deriving from the use of different admixtures and mixing procedures in terms of mixing time, batching sequence and type of mixer were also investigated.