Page 43

2016SummerShotcreteEMag

shotcrete) fall into the “moderate” rating. The fly ash cast concrete, cast wet-mix shotcrete, and shot wet-mix shotcrete all fall into the “low” rating. The fly ash shot wet-mix shotcrete and dry-mix shotcrete and all the silica fume mixtures fall into the “very low” category. IONIC MIGRATION TEST The ionic migration test (a modified chloride penetration test) was conducted in accordance with U.S. Navy Specification UFGS 03 31 29-3. Compared to ASTM C1202, rapid chloride penetration test, the ionic migration test employs a larger testing chamber (150 mm 6 in. diameter) that provides a more stable environment. Na(OH) solutions are placed in both the upstream and downstream containers to stabilize the Cl– ion and other species (Fig. 5). The measured values for current (I, in milliamp) is input into the STADIUM Lab program8 and the rate of diffusion for each chemical species is calculated based on Fick’s Second Law of diffusion. Results for the ionic migration test produce diffusion coefficient C-Wet-Mix-Cast 32.5 40.4 FA-Wet-Mix-Cast 29.3 39.3 SF-Wet-Mix-Cast 33.7 45.1 C-Wet-Mix-Shot 38.5 47.1 FA-Wet Mix-Shot 39.7 44.9 SF-Wet-Mix-Shot 38.1 51.5 C-Wet-Mix-Shot-5% 31.5 49.9 FA-Wet-Mix-Shot-5% 37.5 41.9 SF-Wet-Mix-Shot-5% 29.4 38.1 C-Dry-Mix-Shot 29.5 34.9 FA-Dry-Mix-Shot 32.2 52.6 SF-Dry-Mix-Shot 45.0 64.3 C-Dry-Mix-Shot-3% 24.6 35.9 FA-Dry-Mix-Shot-3% 26.6 43.5 SF-Dry-Mix-Shot-3% 30.3 47.9 Note: 1 MPa = 145 psi. Table 7—28-day compressive strength for shot versus cast shotcrete values for all of the species in the concrete, including OH–, Na+, K+, SO4 – Ca2+, Cl–, and enable a calculation of tortuosity and are listed in Table 11. The ionic migration test takes into account the species of OH–, Cl–, Na+, K+, SO4 2–, Fe(OH)4–, and H2SiO4 2–. OH– is one of the most representative species and the coefficient of diffusion (CoD) of all the species is represented by Diff OH–. CoDs are related to the porosity, which can be characterized by the volume of permeable voids (VPV). To take into consideration both CoD and VPV, a new parameter is introduced as Effective Coefficient of Diffusion (ECoD) = CoD × VPV Table 6—Compressive strength Mixture ID Compressive strength 7 days, MPa 28 days, MPa C-Cast 37.2 46.5 FA-Cast 36.6 48.8 SF-Cast 32.8 39.4 Cast concrete, MPa Cast wet-mix shotcrete, MPa Shot wet-mix shotcrete, MPa Increase of strength of shot shotcrete versus cast shotcrete, % Shot wet-mix shotcrete with 5% accelerator, MPa Increase of strength of shot shotcrete with 5% accelerator versus cast shotcrete, % Cement 46.5 40.4 47.1 17 49.9 24 Fly ash 48.8 39.3 44.9 14 41.9 7 Silica fume 39.4 45.1 51.5 14 38.1 –16 Note: 1 MPa = 145 psi. Fig. 4—Test results for boiled absorption and volume of permeable voids. SAhCotIc Mreatete •r Siaulsm Jmoeur r2n0a1l/6M ay-June 2016 37 491


2016SummerShotcreteEMag
To see the actual publication please follow the link above