Influence of curing conditions on engineering properties of controlled low strength material made with cementless binder

As an evaluation of the use of Controlled Low Strength Material (CLSM) in highway construction applications (e.g., backfill, utility bedding, void fill and bridge approaches), the need for adequate curing conditions of CLSM cannot be overemphasized. The aim of this paper is to assess the influence of different curing conditions on the engineering properties of CLSM using ponded ash as fine aggregate and Cementless Binder (CB). CB is manufactured with granulated blast-furnace slag and other alkali activators (e.g., phosphogypsum and waste lime). It was used a binder material to replace Portland cement fully in the CLSM production. Various CSLM mixtures were prepared with variable ranges of water to CB ratios (W/CB) and tested through a series of laboratory experiments. A good flowability of higher than 20 cm was first confirmed for all CLSM mixtures by flow tests as reported in the American Concrete Institute (ACI 229R). Subsequently, in order to evaluate influence of curing conditions to engineering properties of CLSM, the following tests including Unconfined Compressive Strength (UCS) and thermal conductivity were performed. Herein, in addition to UCS, thermal conductivity of CLSM was considered due to the fact that in highway construction, the breakdown of cable insulation can be unexpectedly caused if heat generated from transmission of underground power cables could not be discharged effectively through the backfill material. The prepared CLSM specimens were subjected to three different curing conditions: wet chamber curing with the relative humidity of 100% (WCC-RH100); wet chamber curing with the relative humidity of 50% (WCC-RH50) and Saturated Curing (SC). As a result, it was observed that the curing environments significantly affected the UCS and thermal conductivity of CLSM mixtures. In particular, the wet chamber curing conditions (WCC-RH100 and WCC-RH50) led to higher compressive strength but lower thermal conductivity than those of mixtures cured at the SC condition. This finding is very important when determining a proper curing condition playing a significant role in achieving optimum performance and full potential from the given CLSM mixtures in highway construction.