Variation of pulse velocity with expansion

The variation of pulse velocity with expansion for the concretes in series B to E is shown in Figures 3.15 to 3.18. It is again emphasised that the fluctuations in the measured pulse velocities shown in these figures are due to the cyclic environmental exposure regime of the concretes, which alternately activated and suppressed the reaction, and therefore controlled the development of the resulting expansion.

The data in Figures 3.15 to 3.18 are summarised in Tables 3.11 and 3.12. Table 3.11 shows the maximum expansions measured while the test specimens were still in the hot room and the corresponding pulse velocities and ages. Table 3.12 presents data on expansions measured after the specimens had been removed from the hot room and returned to ambient temperature and humidity, and the corresponding pulse velocities and ages. Figures 3.15 to 3.18 and the data in Tables 3.11 and 3.12 show that the progress of alkali-silica reactions and the resulting expansions can be monitored satisfactorily by pulse velocity measurements in concrete without and with mineral admixtures. The data also reveal that both the increase in expansion and its suppression are realistically reflected in these measurements.

The data presented in Figures 3.15 to 3.18 and Tables 3.11 and 3.12

image37

image38

Подпись: Figure 3.16 Influence of fly ash on pulse velocity and expansion of ASR-affected concrete (series C).

image40

Figure 3.18 Variation of pulse velocity with expansion of ASR-affected concrete containing

microsilica (series E).

emphasise two very important aspects of ASR which may not be readily recognised by researchers and practising engineers. Firstly, when the exposed environmental conditions change, resulting in the cessation of measured expansions or even their reduction, this is not immediately reflected in an increase in the measured pulse velocities. The reason is that the pulse velocity reflects the internal structural damage through microcracking and other effects, and it may take some time before healing of the internal structure begins. It can be readily seen why measured pulse velocities in real structures

Table 3.11 Maximum measured expansions and corresponding pulse velocities.

Test series

Maximum measured values*

Age

(days)

Expansion

(%)

Pulse velocity (km/s)

В—ASR

41

0.736

3.50

C—ASR+PFA

39

0.164

4.53

D—ASR + slag

35

0.314

3.77

E—AST + MS

36

0.273

4.04

*Measured in hot room.

PFA, fly ash; MS, microsilica.

Test series

Final measured values*

Age

(days)

Expansion

(%)

Pulse velocity (km/s)

B—ASR

43

0.732

3.03

C—ASR + PFA

42

0.136

4.36

D—ASR + slag

42

0.311

3.51

E—ASR + MS

38

0.256

4.04

*Measured under ambient conditions after removal from hot room.

PFA, fly ash; MS, microsilica.

undergoing ASR can, if taken in isolation, result in confusion515254. It very much depends at what point during the progress or cessation of chemical reactions the pulse velocity measurements are taken. Thus spot or isolated values of pulse velocity may not make much sense except to give an overall assessment of the extent of ASR deterioration or loss of engineering properties45.

The second significant point is that there appears to be no unique relationship between expansion and pulse velocity, resonant frequency or dynamic modulus of ASR-affected concrete45,48-50. As pointed out earlier, since the rate of ASR is influenced by a host of parameters, including the nature, type and particle size distribution of the reactive aggregate as well as the unpredictable variations in the ambient environment, losses in pulse velocity do not occur at the same rate or in proportion to expansion. This is particularly true when mineral admixtures are incorporated in concrete, so that the time required to reach a given expansion (for a given set of reactive

Table 3.13 Estimated pulse velocity at different expansions.

Pulse velocity (km/s)

Expansion

(%)

В

(ASR)

c

(ASR + PFA)

D

(ASR + slag)

E

(ASR+MS)

0.05

4.43

4.20

4.32

4.50

0.10

4.23

4.40

4.27

4.53

0.15

3.90

4.50

4.08

4.47

0.20

3.64

3.91

4.30

0.25

3.41

3.83

4.13

0.30

3.33

3.78

aggregate and concrete alkali conditions), and hence a given pulse velocity, will not be the same. This is illustrated by the data in Table 3.13, which summarises the pulse velocity for the concretes of series B to E to reach different rates of expansion. It should, however, be appreciated that the values of pulse velocity shown in Table 3.13 are necessarily approximate as they have been interpolated from the measured values for the expansions quoted in the same table.

Updated: 16 сентября, 2015 — 4:31 пп