Hydration and Strength Behavior of Sugarcane-Baggase Ash Concrete Using Electrical Resistivity Measurement

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Table 1b. Chemical Composition of Baggase Ash

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Table 2. Mix Proportion for Different Concrete

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2.2. Experiments

Four different experiments were conducted on the concrete samples with and without baggase ash. The mix proportion is shown in table 2 and the experimental procedures are hereby presented.

2.2.1. Electrical Resistivity

A non-contact electrical resistivity apparatus was adopted and its operational principles were previously presented ^[5]. Four different mixes were prepared for the plain concrete 0, with 10, 20 and 30% of baggase ash with symbols of CBA0, CBA1, CBA2 and CBA3, respectively. Mixes were separately cast in the mould for resistivity measurement of 24 hours hydration period. Then, the mix was altered by replacing the percentage of each cement each of the mix, was tested for resistivity development and the whole data was collected, analyzed and presented under results section.

2.2.2. Compressive Strength

Similar samples were prepared and cast in 15x15x15 cm³ mould which were demolded after 24 hours from casting, then transferred to a moist room at 20 ± 2°C and 95 ± 5% relative humidity for curing before the test. The samples were crushed at 1, 3, 7 and 28 days using TYPE-2000A Compression testing machine in which their respective compressive strength were obtained.

2.2.3. Setting Time

The setting time test was conducted using penetration resistance test where the initial and final setting times for all the samples were determined by Vicat Apparatus ^[6].

3. Results and Discussion

3.1. Electrical Resistivity

Electrical resistivity development curve for different concretes during the first 24 hours is shown in Figure 1, it can be observed that all the curves followed the same trend and similar to the heat evolution curve of cement, with CBA3 having the higher resistivity throughout and CBA0 is the lowest which shows that with the increase in baggase ash quantity the resistivity also increases up to the 30% replacement level. Figure 2 shows a sample resistivity derivative curve in which four periods were identified based on the critical points pm, pa and pi upon which the hydration process was classified and these periods are dissolution period (I), an induction period (II), an acceleration period (III) and a deceleration/ diffusion controlled period (IV) which are similar to the previous findings ^{[7, 8]}, the interpretations of these periods are the same as those presented by^[8]. Therefore, it is proved that electrical resistivity measurement is an effective indicator of the hydration process of concrete as it has been established on cement pastes ^[7]. It also shows that, as the concrete is hydrating, the pores are decreasing, thereby making the mixture less conductive to electricity and the phenomenon continues throughout, and as such making it a semi conductor, another identified point on the curve is inflection point for the various samples as shown in Figure 3, it can be seen that the time upon which final inflection occurred is delayed as the baggase ash quantity decreases, this is quite clear when considering the inflection time of CBA3 as 16.38 hours which is earlier than those of CBA2, CBA1 and CBA0 which are 18.45 and 19.47 hours respectively, therefore this confirms the higher resistivity of mixture containing higher baggase ash quantity.

Figure 1. Electrical resistivity development for 24 hours

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Figure 2. The sample resistivity derivative curve

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Figure 3. The compressive strength development for all the concrete

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3.2. Compressive Strength

The result presented in Figure 3 shows that CBA3 has the highest compressive strength development from 1 to 28 days after casting which is observed to be decreased only with the decrease in the baggase ash quantity. This result agrees with the findings of the previous study ^[4].

3.3. Setting Time

It can be seen from Figure 4 that the setting time of the various concrete samples is delayed with the increase in the quantity of the baggase ash. Therefore, this delay ensures a steady strength development so that it would achieve its minimum working strength without experience rapid hardening. This indicates that the baggase ash can be used as a retarder in concrete.

Figure 4. Setting time for all concrete samples

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