1 Introduction
2 Materials and Experiments
2.1 Materials
Chemical components (%) | Density (g/cm3) | Fineness (m2/kg) | LOI (%) | ||||||||
---|---|---|---|---|---|---|---|---|---|---|---|
SiO2 | Al2O | Fe2O | MgO | CaO | K2O | SO3 | Na2O | ||||
Slag | 35.30 | 12.58 | 0.79 | 3.19 | 41.30 | 0.63 | 4.75 | 0.33 | 2.84 | 420 | 0.32 |
Silica fume | 94.24 | 0.57 | 1.33 | 0.42 | 1.51 | – | – | – | 2.28 | 22,000 | 0.84 |
2.2 Experiments
10S | 5S5F | 10S-T | 5S5F-T | 5S5F-TA | 5S5F-TB | |
---|---|---|---|---|---|---|
Ready | Place all the mixing liquid (total water + total activator) in the bowl | Place all the mixing liquid (water/2 + activator/2) in the bowl | Place all the mixing liquid (water/2 + total activator) in the bowl | |||
1st-cycle | Add the 100% slag in the bowl and allow 30 s for the absorption of the liquid | Add the binder (slag + SF) in the bowl and allow 30 s for the absorption of the liquid | Add the 100% slag in the bowl and allow 30 s for the absorption of the liquid | Add the binder (slag + SF) in the bowl and allow 30 s for the absorption of the liquid | Add the slag in the bowl and allow 30 s for the absorption of the liquid | |
Start the mixer and mix at the slow speed (140 ± 5 r/min) for 30 s | ||||||
Stop the mixer for 30 s and during this time scrape down into the batch any paste that may have collected on sides of the bowl | ||||||
Start the mixer and mix at the medium speed (285 ± 10 r/min) for 30 s | ||||||
Stop the mixer and let the paste stand for 90 s. During the first 15 s of this interval, quickly scrape down into the batch any paste that may have collected on the side of the bowl; then for the remainder of this interval, close the mixer enclosure or cover the bowl with the lid | ||||||
Finish by mixing for 60 s at medium speed (285 ± 10 r/min) | ||||||
2nd-cycle | Stop for 30 s | Add the SF and liquid (water/2 + activator/2) in the bowl for 30 s | Add the SF and water/2 in the bowl for 30 s | |||
Start the mixer and mix at the slow speed (140 ± 5 r/min) for 30 s | ||||||
Stop the mixer for 30 s and during this time scrape down into the batch any paste that may have collected on sides of the bowl | ||||||
Start the mixer and mix at the medium speed (285 ± 10 r/min) for 30 s | ||||||
Stop the mixer and let the paste stand for 90 s. During the first 15 s of this interval, quickly scrape down into the batch any paste that may have collected on the side of the bowl; then for the remainder of this interval, close the mixer enclosure or cover the bowl with the lid | ||||||
Finish by mixing for 60 s at medium speed (285 ± 10 r/min) |
Test | Equipment | Measurement day (day) | Conditions |
---|---|---|---|
Pore structure (mercury-intrusion porosimetry; MIP) | AutoPore IV9500, Micromerities | 1, 28 | Surface tension : 485 dyn/cm, mercury (Hg) density : 13.534 g/mL |
Hydration products (X-ray diffraction; XRD) | Xpert3, PANalytical | 1, 28 | 5–60° (2θ), Cu-K radiation (k = 1.54443 Å), step size : 0.017 (2 θ) |
Thermal analysis (DSC) | SDT Q600, TA Instruments | 1, 28 | 30–800 °C, 20 °C/min, N2 gas environment |
Ultrasonic pulse velocity (UPV) | CCT-4, Proceq | 1, 28 | Prismatic bar (40 × 40 × 160 mm) |
Microstructure observation (scanning electron microscope/backscattered electron images; SEM/BSE) | SUPRA 40, Zeiss | 1 | Accelerating voltage : 15 kV, the high vacuum mode, energy dispersive spectroscopy (EDS) |
3 Results and Discussion
3.1 Compressive Strength
Age (day) | 5S5F-T/5S5F | 5S5F-TA/5S5F | 5S5F-TB/5S5F |
---|---|---|---|
1 | 116.6 | 114.9 | 133.0 |
7 | 108.8 | 115.0 | 126.5 |
28 | 105.5 | 109.9 | 127.2 |
3.2 Hydration products
3.3 Pore Structures
Age | 10S | 10S-T | 5S5F | 5S5F-T | 5S5F-TA | 5S5F-TB | |
---|---|---|---|---|---|---|---|
Total porosity (%) | 1 day | 36.9 | 34.9 | 33.4 | 33.0 | 31.3 | 31.8 |
28 days | 35.8 | 33.3 | 33.7 | 32.1 | 31.5 | 30.8 | |
Large capillary pores (10–0.05 µm) (%) | 1 day | 2.12 | 2.16 | 2.43 | 2.36 | 1.95 | 1.79 |
28 days | 1.98 | 2.35 | 1.94 | 1.53 | 1.79 | 0.88 | |
Medium capillary pores (0.05–0.01 µm) (%) | 1 day | 86.89 | 83.77 | 86.05 | 86.57 | 82.68 | 82.08 |
28 days | 86.76 | 82.31 | 82.02 | 82.34 | 82.08 | 81.51 | |
Gel pores (≤ 0.01 µm) (%) | 1 day | 10.99 | 14.07 | 11.52 | 11.07 | 15.37 | 16.13 |
28 days | 11.26 | 15.35 | 16.04 | 16.13 | 16.14 | 17.61 |
3.4 Thermal Analysis
3.5 Ultrasonic Pulse Velocity
3.6 Microstructural Analysis
4 Conclusion
- Increasing the mixing time promotes hydration due to the uniform distribution of slag and SF and the increase in the contact area and time of the activator with the slag particles. This action produces dense hydration reactants, reduces total porosity and increases compressive strength. Therefore, it was confirmed that the increase of the mixing time should be considered as a factor affecting the improvement of pore structure and mechanical properties by promoting the activation reaction of slag and increasing the formation of hydration reactants.
- The method of accelerating the slag using the activator of high alkali concentration in the 1st-cycle shows the highest compressive strength and the lowest total porosity. The promotion of slag activation in the early stages of mixing was effective to improve the mechanical properties. Therefore, the method of mixing slag prior to SF in a high alkaline environment by controlling the amount of mixing-water is an important factor in sufficiently improving the mechanical properties.
- Mixing SF in 2nd-cycle is done for slag paste already mixed in 1st-cycle. As a result, it can be estimated that SF is an effective step for homogeneous dispersion in slag paste by applying 2nd-cycle. Therefore, the filler effect and nucleation effect of SF help to show the improved mechanical properties. The effect of this action is demonstrated by 5S5F-TB method showing the highest mechanical performance and low total porosity.