Issue 54

A. Sirico et alii, Frattura ed Integrità Strutturale, 54(2020) 297-316; DOI: 10.3221/IGF-ESIS.54.22

Batch

Flexural Strength [MPa]

Fracture Energy [N/mm]

Compressive Strength [MPa]

14 days

50 days

14 days

50 days

14 days

50 days

M 0%

4.21±0.33

5.37±0.26

0.078±0.005

0.089±0.003

38.68±0.68

47.51±1.59

M 1%

4.20±0.35

5.05±0.54

0.068±0.009

0.082±0.005

38.55±0.80

49.82±1.00

M 2.5%

4.90±0.39

5.37±0.49

0.091±0.010

0.091±0.005

38.15±0.85

48.16±0.69

N 0%

6.62±0.49

6.62±0.15

0.115±0.012

0.098±0.006

86.82±1.44

90.37±3.83

N 1%

7.04±0.80

7.2±0.12

0.111±0.007

0.109±0.015

86.36±2.58

93.82±3.07

N 2.5%

6.53±0.24

7.15±0.30

0.118±0.007

0.125±0.029

83.01±1.01

83.06±4.38

Table 8: Mechanical properties of cement mortars.

1000

1000

(b)

(a)

Load [N]

14 days curing

Load [N]

14 days curing

800

800

M 1% - Sample 1 M 1% - Sample 2 M 1% - Sample 3

M 0% - Sample 1 M 0% - Sample 2 M 0% - Sample 3

600

600

400

400

200

200

CMOD [mm]

CMOD [mm]

0

0

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

1000

1000

(c)

(d)

Load [N]

Load [N]

14 days curing

14 days curing

800

800

M 2.5% - Sample 1 M 2.5% - Sample 2 M 2.5% - Sample 3

M 0% - Mean M 1% - Mean M 2.5% - Mean

600

600

400

400

200

200

CMOD [mm]

CMOD [mm]

0

0

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

Figure 15: Load P – CMOD curve as obtained from 3PBT at 14 days for: (a) M 0% (plain batch); (b) M 1%; (c) M 2.5% and (d) comparison between the mean values of the three batches. Biochar addition of 2.5% by weight of cement leads to a general increase of both flexural strength and fracture energy for mortar type M, especially at 14 days curing, as shown in Fig. 16a and Fig. 17a. By comparing the results of flexural strength and toughness of all batches of mortar type M, it can be seen that even if their values tend to increase, as expected, with curing age, this increment is lower as biochar percentage increases. As a matter of facts, biochar particles can act as an accelerator that produces beneficial effects on early age development of mechanical properties, as outlined in the literature [21]. As regards compressive strength, the addition of biochar does not particularly influence the results, as shown in Fig. 18a-b. Therefore, it seems that for mortar type M the higher percentage of biochar considered (2.5%) is the most suitable, since it increases flexural strength and toughness, without diminishing compressive strength. These results suggest considering also different percentages (and in particular higher) of biochar for future research. However, it is worth noticing

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