PSI - Issue 17

Piotr Smarzewski / Procedia Structural Integrity 17 (2019) 5–12 Piotr Smarzewski / Structural Integrity Procedia 00 (2019) 000 – 000

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3. Results and discussion

3.1. Compressive strength

Tests were performed in accordance with PN-EN 12390-3:2011 to determine the compressive strength at 28 days. The details of the six mixtures with SF contents varying from 0 to 25% are given in Table 2. Among the specimens prepared from each mixture, 3 cubes were cast. The effect of the SF content on the compressive strength development is shown in Fig. 1. The bars denote the standard deviation.

Fig. 1. Variation of compressive strength with SF content.

The increase of HPC compressive strength was observed by increasing the silica fume content. The increases were determined as 6.7%, 13.1%, 13.4%, 14.1%, and 14.1% for 5%, 10%, 15%, 20%, 25% silica fume content, respectively. These results may be depend on the increasing bond strength of the cement paste – aggregate interface due to the filling effect of silica fume. It can be concluded that a nonlinear relation agrees very well with the test results.

3.2. Modulus of elasticity

Test were carried out according to ASTM C469/C469M-14 to obtain the static modulus of elasticity at 28 days. The variation in the modulus of elasticity with SF content is presented in Fig. 2a. With increasing silica fume content to 10%, increases in the elastic modulus of HPC were observed. Further increased SF content leads to increasing amounts of additional cementitious gel with progressive lower calcium-silicate ratio. For SF content to 20%, elastic modulus of HPC have higher values than elastic modulus of control HPC. The amount of gel formed will depend on the amount of calcium hydroxide produced from the hydrated cement which is available to reaction with SF. Excess of SF will not contribute to modulus of elasticity and strength development. A nonlinear relationship holds very well with the test results of elastic modulus. Fig. 2b shows the static modulus of elasticity versus the compressive strength. The modulus of elasticity appear to be notably affected by the SF presence above 10%. The measured mean modulus of elasticity increases 5% from 0 to 10% SF content and after that decreases 5% from 10% to 25% content of SF.

3.3. Tensile splitting strength

Examinations were carried out in accordance with PN-EN 12390-6:2011 to determine the tensile splitting strength of the various HPC used. The cube specimens were subjected to wet curing at 20 ºC, until they were tested at 28 days. Fig. 3a plots the splitting tensile strength against the SF content. The tensile strength increases with growing SF content up to 10%, and with further systematic change is reduction in HPC strength with SF contents between 10% and 25%. A nonlinear relationship fits quite well with the test results of splitting tensile strength.