122
E. Janowska-Renkas and D. Matyjaszczyk
3 Results of Testing and Their Analysis
Analysis of test results obtained showed that application of hydrophilic and
hydrophobic nanosilica without and with participation of silica fume and polycarboxylate superplasticizer had the impact on properties of both fresh concrete and
hardened concrete. Therefore amodification of the test (reference) concrete mixture
(M1) with hydrophilic and hydrophobic nanosilica content used in amounts of: 0.5%
and 1.5% by mass (in mixtures: M3, M4, M9, M10), affected the cone slump increase
about from 3 to 6 cm, which caused a change of consistency class from S3 (determined for the M1 test mix) to S4. Also the concrete mixtures containing 8% by mass
of silica fume and 0.4% by mass of superplasticizer SP (M7, M8, M13 and M14)
had the S4 consistency class. Whereas concrete mixtures that apart from the silica
fume contained the HI hydrophilic nanosilica (M5 and M11) or HF hydrophobic
nanosilica (M6 and M12), used in the amount of 0.5 and 1.5% by mass, showed the
reverse effect, i.e. the slump reduction by ca. 4–7 cm compared to the test mixture,
and thus the change of the consistency class from S3 class to S2 class.
For concrete mixes containing nanosilica, the vibration time determined by means
of the Vebe method, was shorter than 5 s, which proves the lack of reliable results and
excludes application of this method to determine consistency of the above concrete
mixes (Table 1).
The admixture of both hydrophilic and hydrophobic silica to the concrete mix
without and with the silica fume and superplasticizer (M3-M14) increased in general
the density of mixtures tested compared to the density of the test specimen of pure
CEM I 42.5R Portland cement (M1). Only the modified mix with 8% by mass of
silica fume—M2—had lower density (Table 1).
It was found that with lower content of nanosilica (0.5% by mass) (Table 1), the
air content in the concrete mix is lower in the presence of M3 hydrophilic nanosilica
(1.5%) than with the M4 hydrophobic nanosilica (1.9%). On the other hand, increase
of the nanosilica amount from 0.5 to 1.5% by mass causes a reverse effect demonstrated by higher air content in the mix containing M10 hydrophilic nanosilica (1.9%)
than in case of the mixture with M9 hydrophobic nanosilica (1.6%). Increase of
air content along with the increase of nanosilica amount was also observed in the
paper [15]. It was demonstrated that introduction of silica fume to the concrete mix
containing the hydrophobic nanosilica, used in 0.5% by mass, caused reduction air
content by over twice in M6 mix (0.8%). Whereas in the presence of polycarboxylate
superplasticizer, concrete mixes containing the nanoadmixture and silica fume (M7M13 and M8-M14) showed increased and comparable air content (ca. 1.7–1.9%)
regardless of the nanosilica type (Table 2).
The impact of hydrophilic and hydrophobic nanosilica, used both in the amount
of 0.5 and 1.5% by mass, on the density increase of hardened concretes (B3, B9,
B4 and B10) was found. Density of those concretes was identical and amounted to
2370 kg/m
3 , which compared to density of B1 test concrete (2210 kg/m
3 ) gave the
increase by 160 kg/m
3 .
E. Janowska-Renkas and D. Matyjaszczyk
3 Results of Testing and Their Analysis
Analysis of test results obtained showed that application of hydrophilic and
hydrophobic nanosilica without and with participation of silica fume and polycarboxylate superplasticizer had the impact on properties of both fresh concrete and
hardened concrete. Therefore amodification of the test (reference) concrete mixture
(M1) with hydrophilic and hydrophobic nanosilica content used in amounts of: 0.5%
and 1.5% by mass (in mixtures: M3, M4, M9, M10), affected the cone slump increase
about from 3 to 6 cm, which caused a change of consistency class from S3 (determined for the M1 test mix) to S4. Also the concrete mixtures containing 8% by mass
of silica fume and 0.4% by mass of superplasticizer SP (M7, M8, M13 and M14)
had the S4 consistency class. Whereas concrete mixtures that apart from the silica
fume contained the HI hydrophilic nanosilica (M5 and M11) or HF hydrophobic
nanosilica (M6 and M12), used in the amount of 0.5 and 1.5% by mass, showed the
reverse effect, i.e. the slump reduction by ca. 4–7 cm compared to the test mixture,
and thus the change of the consistency class from S3 class to S2 class.
For concrete mixes containing nanosilica, the vibration time determined by means
of the Vebe method, was shorter than 5 s, which proves the lack of reliable results and
excludes application of this method to determine consistency of the above concrete
mixes (Table 1).
The admixture of both hydrophilic and hydrophobic silica to the concrete mix
without and with the silica fume and superplasticizer (M3-M14) increased in general
the density of mixtures tested compared to the density of the test specimen of pure
CEM I 42.5R Portland cement (M1). Only the modified mix with 8% by mass of
silica fume—M2—had lower density (Table 1).
It was found that with lower content of nanosilica (0.5% by mass) (Table 1), the
air content in the concrete mix is lower in the presence of M3 hydrophilic nanosilica
(1.5%) than with the M4 hydrophobic nanosilica (1.9%). On the other hand, increase
of the nanosilica amount from 0.5 to 1.5% by mass causes a reverse effect demonstrated by higher air content in the mix containing M10 hydrophilic nanosilica (1.9%)
than in case of the mixture with M9 hydrophobic nanosilica (1.6%). Increase of
air content along with the increase of nanosilica amount was also observed in the
paper [15]. It was demonstrated that introduction of silica fume to the concrete mix
containing the hydrophobic nanosilica, used in 0.5% by mass, caused reduction air
content by over twice in M6 mix (0.8%). Whereas in the presence of polycarboxylate
superplasticizer, concrete mixes containing the nanoadmixture and silica fume (M7M13 and M8-M14) showed increased and comparable air content (ca. 1.7–1.9%)
regardless of the nanosilica type (Table 2).
The impact of hydrophilic and hydrophobic nanosilica, used both in the amount
of 0.5 and 1.5% by mass, on the density increase of hardened concretes (B3, B9,
B4 and B10) was found. Density of those concretes was identical and amounted to
2370 kg/m
3 , which compared to density of B1 test concrete (2210 kg/m
3 ) gave the
increase by 160 kg/m
3 .