154434 Reliability and Reproducibility

In order to check the reliability of the apparatus, the experimental results of 0.1 N KCl standard solution obtained by the electrodeless resistivity apparatus was compared with the standard resistivity value provided by the international Chemistry and Physics Society [32]. The international standard value of 0.1 N KCl solution, electrical resistivity is 78.3699 Q cm at 24.5°C. The measured value using the electrodeless resistivity apparatus is 78.6782 Q cm at 24.5°C. It can be seen that the experimental result is in good agreement with the international standard value. The difference is only 0.3934%. It indicates that the electrodeless resistivity measurement apparatus provides an accurate method.

Figure 15.16 plots the resistivity against time curves for three specimens with an identical formula. The similarity of the three curves showed that the measurement method had very good reproducibility.

15.4.4.4 Applicability

The electrical resistivity developments over time have been measured by using the electrodeless resistivity apparatus for hundreds of HPC mixtures. The typical electrical resistivity curves are shown in Figure 15.17 and Figure 15.18.

Based on the measured results, four periods with their own characteristics can be clearly defined as shown in Figure 15.17 and Figure 15.18 [33]. The first period is from the mixing time to t(m), corresponding to the M point shown in Figure 15.18. The second period is from t(m) to time t(l) corresponding to the L point marked in Figure 15.18. The third period begins from f(l) to t(i) corresponding to the I point, and the fourth period begins from t(i) onwards. Their characteristics are described in Table 15.10.

It is found that the four characteristic periods defined by the electrical resistivity curves are consistent with those obtained by other methods such as hydration heat test, ultrasonic waves. However, electro-deless resistivity measurements are much easier to operate and the apparatus is so sensitive, accurate, and

Time, min

FIGURE 15.16 Reproducibility check on three batches of the same mix.

Time, min

FIGURE 15.16 Reproducibility check on three batches of the same mix.

Time, min

FIGURE 15.17 Development of resistivity during the first 1440 min after mixing [33].

Time, min

FIGURE 15.17 Development of resistivity during the first 1440 min after mixing [33].

TABLE 15.10 Characteristics of Four Periods of Hydration

Period name

Range

Characteristics

Dissolving period (I) Competition period (II) Setting period (III) Hardening period (IV)

t< t(m) t(m) < t < t(t) t<7) < t< t(i) t> t(i)

dp/dt < 0, dissolution of cement in water dp/dt = 0, competition balance between dissolution and precipitation 0 < dp/dt < dp(i)/dt, continuous formation of hydrates 0 < dp/dt < dp(i)/dt, slow and steady formation of hydrates

effective that the effects of the chemical admixtures, mineral admixtures, alkaline content, and temperature on the hydration process of HPC can also be quantitatively recorded. It is because of the above reasons that great attention has been placed on electrodeless resistivity apparatus across the world. Some papers and patents have also been published and the corresponding apparatus commercially available.

0 20 40 60 80 100 120 140 160 180 200 220 Time, min

FIGURE 15.18 Development of resistivity during the first 200 min after mixing.

0 20 40 60 80 100 120 140 160 180 200 220 Time, min

FIGURE 15.18 Development of resistivity during the first 200 min after mixing.

0 0

Post a comment