Fig. 39 and Fig. 40, Fig. 41 show the calculated πΎπ, ππ‘ and ππ. They are summarized for cement paste (CP) and for samples containing the fixed amount of 2.6 % by weight of cement for πΏ, π and π» polymer inclusions type, all 28 days old. It should be noted that each reactivity presents differently sized particles and different shapes, therefore only the stiffness of the element is significantly comparable.
These were assumed to come from normal distributions and were tested through one-sided Grubbs outlier tests [72].
Fig. 40. Work of fracture at 28 days, for samples with different HA inclusions reactivity.
The work of fracture keeping constant the quantity of HA and hydration age stays mostly unchanged, Fig. 40.
The change of polymer reactivity seems to have no influence also in tensile strength and stiffness. Only π reactivity shows a slight increase in strength that exceed the cement paste value. The increase in π can presumably be correlated with the higher bond strength manifested into the tensile test sub-section 4.1.
In the same way of Fig. 39 both tensile strength and stiffness (not independents quanti-ties) follow the same trend Fig. 41.
0 0,5 1 1,5 2 2,5 3
CP L2.6 M2.6 H2.6
Work of fracture [Nmm]
Work of fracture at 28 days
53
Fig. 41. Tensile strength and element stiffness at 28 days, for samples with different HA inclusions reactivity.
0 20 40 60 80 100 120 140
0 0,5 1 1,5 2 2,5 3
CP L2.6 M2.6 H2.6
Element stiffness [kN/mm]
Tensile strength [MPa]
Tesile strength at 28 days Element stiffness at 28 days
54
5 Conclusions and future developments
Some conclusions can be derived from the work presented in this study. Regarding the influence of lactate-derived self-healing particles on the fracture behavior of cement paste:
β’ The lactate-derived HA particles L and M show different levels of reactivity in the alkaline environment of cement paste, resulting in different bond strengths with cement paste. A failure within the layer of precipitates between polymer and cement paste seems to yield higher bond strength than a failure along the inter-face cement paste-polymer/precipitate.
β’ From the comparison between the development in time of stiffness, tensile strength and work of fracture of plain and self-healing cement pastes is sug-gested that the HA particles influence the hydration kinetics of cement or inter-act chemically with the surrounding paste over time.
β’ From the hydration age study on the L polymer, it was possible to notice that at 28 days the addition of HA particles resulted in negligible decrease in the tensile strength of 3 % and dramatically reduction of the work of fracture at around 80 % an increase in stiffness of 42 %,
β’ The study on the different quantity revealed that by changing quantity from 1.3 % to 3.9 % the work of fracture increased 9.8 times, negligible changes in the tensile strength and the stiffness of the element. With respect to the cement paste (with no inclusions in it) work of fracture increased by 2.1 times, it is pos-sible to assumed that such behavior is the result of defects introduction repre-sented by the SH particles.
The isothermal calorimetry provides additional proof of the reactivity between HA par-ticles components and cement paste.
The nanoindentation results prove that the embedded lactate-based capsules cause changes into the cement paste, and an interfacial transit zone of 75 Β± 10 ππ around the particle can be identified.
55
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