Proceedings of the International rilem conference Materials, Systems and Structures in Civil Engineering 2016
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- 3. Durability Performance
- 3.1 Heat-rain test
370 International RILEM Conference on Materials, Systems and Structures in Civil Engineering Conference segment on Service Life of Cement-Based Materials and Structures 22-24 August 2016, Technical University of Denmark, Lyngby, Denmark
The drop trend in the strains begins from 28 days in BF-S1 and GF-S1 series, this trend was retarded to 56 days in S2 series. It is interesting that the strain capacities display similarities in GF-NC and –S2 series in 56 days and beyond it. Strain performances of GF-S1 and GF-S2 series are higher than BF-ones. The most positive effect of slag admixture is on the strains, the increase in flexural strengths is lower than NC-ones.
fibres with curing time for the replacements of nano clay (15%), and slag (50%, 80%).
371 International RILEM Conference on Materials, Systems and Structures in Civil Engineering Conference segment on Service Life of Cement-Based Materials and Structures 22-24 August 2016, Technical University of Denmark, Lyngby, Denmark
Durability tests were conducted in a suitable stage after 28 days until 90 days by considering production process of the firm where the experiments were conducted. For this reason, the flexural tests for reference specimens were also carried out prior to starting heat-rain or freeze-thaw cycles.
Heat-rain test is an accelerated weathering test to observe visible problems (cracks, delamination etc.) in the sheets and to determine the variation in the flexural characteristics after harsh exposure cycles. The test is composed total 50 cycles, and each cycle continues 6 hours. In each cycle, the sheets are exposed to about 1 l/m 2 /min. water spray for completely wetting face (2h 50 min 5 min) + radiant heating in 60 5 o C (2h 50 min 5 min) steps with 10 min. intervals. After reference sheet tests, total six (3+3) BF and GF-sheets for each mineral additive were fixed at the vertical position in computer controlled test cabin. The relevant sheets were taken outside in 8 th , 26 th and the last 50 th cycles. Herein, the findings from average values of flexural test results (Fig.4) are evaluated. Although nano-clay and slag replacement in BF-specimens retard the strain drop especially in earlier cycles compared with 100% cement one [11], the performance in the later cycles is poor and quiet similar to control specimens. It seems that this severe exposure may lead to increase the pullout resistance and overbonding by ongoing hydration and calcium silicate hydrate
( C-S-H) accumulation around basalt fibres. These conditions give rise to fast drops in the strains of BF-specimens during the ongoing cycles. The reference strengths (10.73 MPa, 9.52 MPa, 8.81 MPa) of GF-specimens in NC, S1 and S2 series are significantly lower than control specimen (13.37 MPa). However, the drop rate in strengths under continuous cycles is lower than those ones, even an increment is available as from 8 th cycles to be relevant with the adherence variation in the matrix-fibre interface. It is interesting that there is a noticable adherence-induced enhancement in strain capacity (up to about 1%) for 80% slag ratio (S2) as from the initial cycles.
fibres under heat-rain cycles. 372 International RILEM Conference on Materials, Systems and Structures in Civil Engineering Conference segment on Service Life of Cement-Based Materials and Structures 22-24 August 2016, Technical University of Denmark, Lyngby, Denmark
3.2 Freeze-thaw test In freeze-thaw test, each cycle continues 4 h to 6 h , max. 72 h interval between cycles which the plate specimens are stored in water at 20 °C. Ten plates for each series are exposed to total 100 cycles. In a cycle, first stage is to cool in the freezer down to (-20 ± 4) °C within 1 h to 2 h and holding at this temperature for a further 1 h; and the second stage is to heat in the water bath up to (20 ± 4) °C within 1 h to 2 h and hold at this temperature for a further 1 h. The relevant plates were taken outside in 25 th and last 100 th cycles. Herein, the findings from flexural test results (Fig.5) are evaluated. There is a different trend for BF-specimens in freeze-thaw cycles compared with heat-rain cycles. Brittle fracture trend due to C-S-H accumulation around fibres disappears and more ductile behaviour is under consideration in BF-NC, S1 and S2 series. In first cycles, the strength enhancement may be observed. It is noticed that the fibre-matrix integrity significantly degraded in GF-S2 series, thus, no value was displayed concerning 100 th cycle of GF-S2 series. The possible reason may be weakening bond between the matrix and fibres due to freeze-thaw cycles and the disintegrity of the matrix incorporated with fibre debonding.
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