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Sequestration of carbon dioxide by RCAs 489

Figure 16.8 Relationship between compressive strength and strain rate.

ε

DIF f;C-NRCAs 5 1 1 0:0550Ulog (16.13)
ε 0
25
where ε 0 is the quasi-static peak strain, which is 10 /s in this study; ε is the strain
rate loaded. The results show that as the strain rate was increased by 10 times, the
DIF f of NRCAs specimens and C-NRCAs specimens was increased by 8.58% and
5.50%, respectively. It indicates that the strain-rate sensitivity of C-NRCAs speci-
mens was less significant than that of the NRCAs specimens.

16.3.4 Flexural strength

Fig. 16.9 shows the flexural strengths of the concrete mixes at 28 days. Compared
to the results of the static compressive strength, similar trends can be found:
Incorporating the C-NRCAs obviously enhanced the flexural strength of RAC.
Compared with the concrete prepared with 100% non-carbonated NRCAs, the flex-
ural strength of the concrete prepared with 100% C-NRCAs was increased by
28.7%. Moreover, over 40% C-NRCAs may be used in the new concrete to attain a
comparable flexural strength as the control concrete.

16.3.5 Microhardness of ITZ of RAC with C-NRCAs

In order to assess the micromechanical properties of RAC, the microhardness of the
new ITZs in RAC between NRCAs/C-NRCAs and the new mortar was determined
and compared. A digital Vickers microhardness tester was employed to measure the
microhardness across the new ITZs. The picture, shown in Fig. 16.10, of the
polished surface made for the microhardness test, illustrates one of the NRCAs in
RAC. The measured distance was up to 160 μm with a 20 μm spacing from the