Effects of Blast Furnace Slag Powder and Limestone Powder on the Mechanical Properties and Durability of Shotcrete Using Monocalcium Aluminate Setting Accelerator.

In this study, the effect of fine blast furnace slag powder (SP) and limestone powder (LSP) as a mineral admixture in shotcrete using monocalcium aluminate (CA) as a quick-setting accelerator was evaluated. The shotcrete was prepared with up to 25 wt.% substitutions of mineral admixture, i.e., (SP and LSP), and then the CA accelerator was incorporated by 5 wt.% of binders. To examine the optimal mixing ratio for mineral admixture in shotcrete, penetration resistance, compressive strength, XRD analysis, and MIP analysis were performed on the mortar. On the other hand, compressive strength test, chloride diffusion coefficient, and freeze-thaw resistance were conducted on concrete to evaluate the field applicability of shotcrete. The study revealed the addition of LSP improved setting time and early compressive strength while the addition of SP increased long-term compressive strength. With the addition of both SP and LSP, the early and long-term strength was increased due to the influence of the properties of each admixture. Furthermore, the addition of SP and LSP improves the resistance of shotcrete to chloride ions and freeze-thaw.

Compressive Creep and Shrinkage of High-Strength Concrete Based on Limestone Coarse Aggregate Applied to High-Rise Buildings.

Concrete undergoes shrinkage regardless of the influence of external forces. The deformation of concrete is crucial for the structural stability of high-rise and large-scale buildings. In this study, the shrinkage and compressive creep of 70-90 MPa high-strength concrete used in high-rise buildings were evaluated based on the curing conditions (sealed/unsealed), and the existing prediction models were examined. It was observed that the curing condition does not significantly affect the mechanical properties of high-strength concrete, but the use of limestone coarse aggregate increases the elastic modulus when compared to granite coarse aggregate. The autogenous shrinkage of high-strength concrete is greater than that of normal-strength concrete owing to self-desiccation, resulting in a large variation from the value predicted by the model. The drying shrinkage was observed to be similar to that predicted by the model. Compressive creep was affected by the curing conditions, compressive strength, loading level, and loading age. The compressive creep of high-strength concrete varied significantly from the prediction results of ACI 209; ACI 209 was modified based on the measured values. The shrinkage and compressive creep characteristics of high-strength concrete must be reflected to predict the deformation of an actual structure exposed to various conditions.