PSI - Issue 64

Laurena De Brabandere et al. / Procedia Structural Integrity 64 (2024) 97–104 Laurena De Brabandere et al./ Structural Integrity Procedia 00 (2019) 000 – 000

98 2

1. Introduction Recently, more and more research is focused on how to decrease the environmental impact of concrete and to increase its durability. Supplementary cementitious materials (SCMs), such as blast furnace slag, silica fume, fly ash, and calcined clays, are widely studied and used to partially replace Portland cement in concrete to reduce carbon dioxide emissions and to increase the durability (Juenger & Siddique, 2015). The influence of these SCMs on the durability of concrete can be measured via different test methods, including water absorption, water permeability, chloride permeability, electrical resistivity and gas permeability (Hakeem, Althoey, & Hosen, 2022; Liang & Yin, 2021). The addition of blast furnace slag in concrete usually leads to a reduction of the pore volume and a finer pore size distribution (Alderete et al., 2017; Bijen, 1996). Cyr (2013) summarized that the results on the effect of SCMs on concrete permeability in literature were quite scattered, with some studies obtaining an increase in permeability, while others noticed a decrease. Limestone is often studied and added as a partial cement replacement to improve its properties due to its filler effect (Tsivilis et al., 2000; Wang et al., 2018). Wang et al. (2018) summarized that the sorptivity of concrete decreased with an increased limestone replacement rate of up to 20% cement replacement. On the other hand, the results also showed that an increase in cement replacement by limestone increased the chloride diffusion coefficient. Based on the findings in the literature, it is not known whether the test method influences the measured performance of a material. Therefore, this study compares the durability of concrete with different binders and different water-to-cement ratios via 4 different test methods which are frequently used in literature, namely, two unsaturated flow methods (capillary imbibition and diffusion) and two gas permeability tests (CEMBUREAU and Torrent method) and compares the obtained performance. The binders used in this research are a CEM I (100% Portland cement), CEM II (up to 20% limestone) and CEM III (up to 65% blast furnace slag). 2. Materials In this research, 6 different concrete mixes were made, with 3 different cement types (CEM I, CEM II and CEM III) from Holcim, Belgium, and two water to cement (w/c) ratios (0.4 and 0.7). The mix compositions are shown in table 1. In the mixes with a w/c of 0.4, a PCE-based superplasticizer was added to increase the workability during casting. From each mix, 3 concrete slabs 400x400x120 mm 3 were cast and compacted with a vibrating needle. After casting, the slabs were cured in a climate-controlled chamber (20 °C, > 95 % relative humidity (RH)) and demoulded after 24 hours. Then, they were again stored in the climate-controlled chamber until the age of 28 days was reached.

Table 1. Mix design. Materials

0.4-I

0.4-II

0.4-III

0.7-I

0.7-II

0.7-III

CEM I 52.5 N

320

-

- -

300

-

- -

CEM II/A-LL 42.5 R CEM III/A 42.5 R

- -

320

- - -

300

-

320 2.65

- -

300

Superplasticizer MasterGlenium 27con 20%

2.90

2.65 661 775 550 128

-

Sand 0/4

670 650 465 210

Coarse aggregates 2/8 Coarse aggregates 8/16

Water

3. Methods 3.1. Capillary imbibition

Cylinders with a diameter of 100 mm were drilled from the concrete slabs. After drilling, the bottom part of the cylinder was removed to obtain cylinders with a height of 100 mm. Subsequently, the circumference was coated