PSI - Issue 11

Bárbara Belén Raggiotti et al. / Procedia Structural Integrity 11 (2018) 36–43 Raggiotti et al./ Structural Integrity Procedia 00 (2018) 000 – 000

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Resistance to compression of concretes containing zeolite was lower than the resistance reached by reference mixtures at virtually all ages, particularly at early ages (7 and 28 days). However, the reduction percentages were lower or even nil at higher ages of the concrete (90 and 180 days). This may be attributed to the zeolite's pozzolanic activity. The development of resistance in the master mixture ZN0 depends mainly on the speed of hydration of the clinker, while in the other mixtures, it depends on the combination of the hydration of the clinker and the pozzolanic activity of the zeolite (Perraki et al., 2010). As can be seen in Figure 6, the concrete made with NPC40 shows better performance to compression, at all ages, than that made with CPC40. The composition of the cement is an important variable in the performance to resistance of concrete. The lower resistances reached by the CPC40 can be put down to the lower content of non hydrated calcium silicates capable of reacting to the admixture forming new hydrated calcium silicates. The silicates, that made up about 75% of the common Portland cement, lead a dominant role in determining the hardening characteristics (rate of resistance development). Table 5 shows the results of the assays of traction by diameter compression and elastic module.

Table 5. Resistance to traction by diameter compression and elastic module Concretes

ZN0 ZN5 ZN10 ZN15 ZN20 ZC0 ZC5 ZC10 ZC15 ZC20

Traction [MPa]

4.5

3.8

3.8

4.2

4.5

3.9

3.9

3.2

3.8

3.8

Elastic module [GPa] 38.2 37.2 35.8 34.1 The mixtures showed variable behavior to traction by diameter compression, but with a common point between the two series of cements. The mixtures with 10% zeolite were those that presented the least resistance to traction. With a content of admixture greater than 10% the resistance increased gradually. The results of the elastic module show a dispersion of 1.26 and 1.94 corresponding to a mean of 37.5 and 36.9 GPa for NPC and CPC respectively. For the CPC series, as the zeolite increases, the material becomes more deformable, that is to say, the effort required to achieve the same deformation is lower. Table 6 shows the results of the durability indicators. 39.2 37.2 38.7 37.9 38.1 35.6

Table 6. Results of absorption, suction and speed of capillary suction and permeability to air

Concretes

ZN0

ZN5

ZN10

ZN15

ZN20

ZC0

ZC5

ZC10

ZC15

ZC20

Absorption [%]

3.9

3.4

4.3

3.8

3.9

6.5

6.8

7.3

7.6

8.3

Capillary suction [gr/m 2 ]

4133.8 4145.1 4549.7 4224.3 3491.5 7039.6 7444.2 7888.4 8143.1 8626.9

Suction speed [gr/m 2 .s 1/2 ] 8.4

8.7

9.9

8.5

6.7

15.9 3.40

14.1 3.55

17.5 3.75

18.4 3.48

19.5

Permeability to air [kT] 5.88 The permeability to air was determined with Permea-TORR (Swiss Standard SIA 262/1-E, 2003) equipment. The classes of permeability to air according to this standard are: PK1: very low (kT < 0.01), PK2: low (0.01< kT< 0.1), PK3: moderate (0.1< kT< 1.0), PK4: high (1.0< kT< 10.0), PK5: very high (kT>10.0). Analyzing the results shown in Table 6, there is an improvement in this property as from a 15% replacement of cement with zeolite in the NPC series; in the CPC series there is no decrease of permeability at a greater content of the admixture and the permeability of all the concretes remains within the same PK4 class, classified as "high." NPC concretes showed better behavior than CPC concretes in view of the transportation of water through the capillary suction mechanism. This may be correlated with the absorption results presented in Table 6. The phenomenon finds its explanation in the composition of NPC concretes, as the porous structure of the paste depends only on the interaction of the normal cement with the zeolite, while other admixtures are present in the CPC series. The properties analyzed improve in NPC concrete with replacements greater than 10%; while CPCs show an increase in the capacity for water absorption at a greater replacement of cement by the admixture, with a greater capacity for capillary suction and greater speed for capillary suction. 0.33 1.37 2.58 0.33 0.16