PSI - Issue 41

Maria-Evangelia Stogia et al. / Procedia Structural Integrity 41 (2022) 744–751 Maria Evangelia Stogia et al. / Structural Integrity Procedia 00 (2019) 000–000

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2.2 Methods After the appropriate proportions of the building materials were finalized, the determination of mixing water and consistency through flow test was conducted in order to conclude on the appropriate Water to Binder (W/B) ratio. Taking into consideration the results of the flow table test, mixing and casting of the specimens followed, and then mechanical tests were performed. In order to assess the performance of these binders, an experimental protocol was implemented, including compressive and flexural tests. In order to determine the appropriate W/B ratio, the standard test method ASTM C141 (ASTM C 230-C 230M Standard Specification For Flow Table For Use in Tests of Hydraulic Cement, n.d.)] was followed. The experimental flow table test setup is shown in Fig. 2 2, where the table diameter is 300 mm, and the cone height is 60 mm. The truncated cone in which the top diameter is 70 mm, is removed, and the mix is dropped continuously from 10 mm height for 25 times in about 15 s. Five (5) different W/B were tested, from ratio of 0.60 to 0.80 with a step of 0.1. The 0.72 and 0.75 ratio were also investigated. The acceptability limits according to the above standard is in between the range from 100% to 115% and is calculated as the percentage of the cone base (100 mm).

Fig. 2. Mortar on the flow table test setup after the cone is removed

Taking into account the findings of previous researchers the W/B ratio was defined. Namely, Garijo et al. ( 2018) and Garijo et al. (2020) proved that high water-binder ratios produce structural weakening, increase the open porosity and reduce mechanical properties and proposed a lime/aggregate ratio equal to 1:3 and a water/lime ratio equal to 0.9. Moreover, Amenta et al. (2017) proved that by adjusting the amount of mixing water, the exceeding binder acts as ‘lubricant, decreasing the friction between aggregate particles and thus, enhancing the plasticity and workability of the mixture. In contrast, when a mixture lacks in binder its plasticity decreases, thus requiring more water to reach a satisfactory workability. The ternary paste with weight contents 35 wt% NHL5, 35 wt% Lime and 30 wt% CEM I was submitted in flow table test. The W/B ratio was selected to be within the green lines of (Fig. 3) that sets the upper and lower limit of paste flow according to the specification. To this end, the 0.75 ratio was selected and was kept constant in every paste of all the series of experiments described in this article so that comparison was feasible. After having determined the W/B, 6 cylindrical specimens of each composition, with a diameter of 30 mm and a height of 60 mm, were prepared for testing after 28 days of curing. The monotonic compression tests were performed at a 300 kN Instron SATEC loading frame (Fig. 4 4) according to the standard test method for compressive strength ASTM C39 (ASTM C 39/C 39M–01 S Standard Test Method for Compressive Strength of Cylindrical Concrete Specimens, n.d.). The four-point bending (flexural) tests were performed at a 10 kN MTS Insight testing machine according to the standard test method ASTM C78 [(ASTM C78, Standard Test Method for Flexural Strength of Concrete (Using Simple Beam with Third-Point Loading) (2002)., n.d.)]. The displacement rate of the crosshead was 300 μm/min during the whole conduction of the compression test and 0.001 mm/sec in the flexural test. The loading span was 1/2 of the support span. 3. Results and discussion 3.1 Compressive strength results The results of the compressive tests are presented in the diagram of (Fig. 5). The compressive strength of the L100 lime paste was found to be 1.6 MPa. The compressive strength of the L80-M20-C0 paste, the L47.5-M47.5-C5 and the L65-