Investigated on predictive compressive strength model and setting time of controlled low-strength materials

Most of the pipelines in Taiwan lie beneath road pavements. Maintaining existing pipelines and establishing new pipelines inevitably leads to the wide-scale excavation and backfilling, which can greatly interfere with traffic patterns. Controlled low-strength material (CLSM) is commonly used as backfill material because it is highly fluid, self-filling, ideally suited to re-excavation, and does not require ramming. According to American Concrete Institute (ACI) specification, CLSM requires load-bearing capacity sufficient to avoid surface settlement and/or rutting. The water-to-cement (W/C) ratio, water-to-solid (W/S) ratio, curing time and temperature were all shown to affect compressive strength. Besides, the temporarily restore surface have to pave quickly due to the heavily traffic volume in situ. Therefore, the road response is strongly related to the initial compressive strength of CLSM after backfilling. Rushing the setting time can compromise strength; however, extending the setting time can adversely affect traffic flow. To understand the parameters effect, we consider different W/C, W/S, curing time and temperature of CLSM specimens in this study. The soil extracted through excavation was used as the aggregate for CLSM and conducted compressive strength experiments on CLSM. By the experimental data, we build a regression model considered the parameters effect and predicted the compressive strength of CLSM precisely. Furthermore, we used Linear Variable Differential Transducers (LVDT) and program to plot the stress-strain curves; it can get Young’s Modulus from the curves and build the relationship of Young’s Modulus and compressive strength of CLSM. These models can be used in the finite element analysis and analyze the pavement response after the backfilling.