Performance of silica fume shotcrete

1. Thickness and rebound loss of bond damage

The incorporation of silica fume in shotcrete can improve the adhesion to the bonded surface and the cohesion within the shotcrete; thus the thickness of shotcrete on the top and vertical surfaces can be greatly increased.

In the study of wet mix shotcrete, if not mixed with silica fume, the top surface of the bond damage thickness of 90 mm; if mixed with compacted low-density silica fume, the maximum value of up to 280 mm. the top surface of the bond damage thickness is generally greater in dry mix shotcrete, if mixed with non-compacted silica fume, the maximum value of dry mix shotcrete up to 380 mm, while the top surface of dry mix shotcrete without silica fume The top surface rebound of dry shotcrete is 42.7% for shotcrete without silica fume, which can be reduced to 21.4% with the addition of silica fume. The amount of springback on the vertical surface: 45.5% for shotcrete without silica fume; can be reduced to 22.8% with the addition of silica fume. In all shotcrete, the percentage of rebound of wet mix is lower.



2. Compressive and flexural strength

The compressive strength of wet-mix shotcrete with silica fume has a significant increase. At 63d, the compressive strength of shotcrete without silica fume was 44MPa, while the average compressive strength of shotcrete with silica fume was 66.lMpa, an increase of about 50%.

The same is true for dry shotcrete, i.e., the compressive strength of shotcrete with silica fume is higher than that of shotcrete without silica fume, although the higher percentage is not as large as that of wet shotcrete.

The same is true for the flexural strength of wet-mix and dry-mix shotcrete, with the increased flexural strength of the wet-mix silica fume shotcrete being the greatest. The flexural strength of dry-mixed silica fume shotcrete is also greater than that of shotcrete without silica fume, but the increase is smaller.

3. Boiling water absorption and permeability porosity

The incorporation of silica fume greatly reduces the boiling water absorption rate and permeability porosity of dry shotcrete, but not for wet shotcrete. All of the test results of the water absorption of wet shotcrete, can be examples of "good" and "excellent" between; all dry shotcrete test data are very low, belonging to the "excellent "range.

4. Fast chloride ion permeability

The chloride ion permeability and resistivity is a very important feature in evaluating the ability of shotcrete to be used in rehabilitation projects in order to retard or prevent corrosion of reinforcing steel.

Although shotcrete without silica fume has fairly good strength, water absorption, and permeability porosity data, the rapid chloride permeability of wet shotcrete is 6800 C, while dry shotcrete is 2573 C. These values are in the "high" and "medium" chloride permeability ranges, respectively. of" range. According to historical data, the durability of concrete of this quality in aggressive chloride environments is very poor.

In contrast, the average values of chloride ion permeability of wet and dry shotcrete mixed with silica fume fall to 371C and 192C, respectively.

5. Resistivity

The measured values of resistivity show that the shotcrete mixed with silica fume has considerable improvement over the shotcrete without silica fume. The average resistivity of shotcrete with silica fume is 55290 Ω-cm, while that of shotcrete without silica fume is only 5490 Ω-cm, taking the dry mix as an example.

The chloride ion permeability of both wet-mixed and dry-mixed shotcrete with silica fume is 10 to 20 times less than the corresponding shotcrete without silica fume. This observation, coupled with the resistivity data, is good evidence that the use of silica fume is very advantageous in the repair of reinforced concrete structures with shotcrete.

6. Dry shrinkage rate

The data at 56d showed that the dry shrinkage of shotcrete mixed with silica fume was minimal. The dry shrinkage of dry shotcrete is lower than the corresponding value of wet shotcrete, which can be explained by the lower water requirement of dry shotcrete.

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