**3. Result and discussions**

#### **3.1 Porosity**

Porosity is an important parameter in determining the sound absorption properties of materials. **Figure 8** shows the effect of increasing the percentage of POC in mixtures. Interconnected pores, mainly due to capillary pores [27], form channels to the other end surface that allow sound propagation, the same principle for the water penetration. While closed porosity occurs due to; (i) compaction that cause the air trap between the aggregate, (ii) POC pores and (iii) pores caused by hydrated cement. POC sand and natural river sand are covered with cement paste, thus makes closed pores in all specimens are identical. Without replacement, the interconnected porosity of specimen greater than that of 100% replacement of sand. This is also due to higher surface area of POC sand and its rough surface that makes the cement paste stick to the surface and cover micro-pores resulting in a decrease in interconnected pores. For substitution of 25–75% of natural sand results in a linear increasing relationship as shown in **Figure 9**.

The trend of changes of interconnected porosity and total porosity of mixture with POC 25–75% have very good relationship with the increment of POC

**Figure 8.** *Interconnected and closed porosities variation with the changes of POC percentage.*

#### **Figure 9.**

*Interconnected and closed porosities variation with the changes of POC percentage between 25–75%.*

percentage with R2 of 0.997 and 0.986, respectively. In this study, R<sup>2</sup> can be simplified as very good (>0.9), good (>0.8) [28], substantial (0.75), moderate (0.5), and weak (0.26) [29]. In summary, POC replacement between 50 and 75% increases interconnected and total porosity due to the angular shape and rough texture of POC sand, and the capillary porosity and connectivity of between capillary pores. **Figure 10** shows the irregular pores in both 100% sand and 50% POC replacement in samples. Based on these SEM micrographs, it is expected that the irregular pores for 100% sand has smaller diameters about 0.2 μm while 50% POC replacement with larger diameter of 0.6 μm. Larger pores was also created because of decrease of free water due to C-S-H bond formation and C–H gels crystallisation as surface area of POC is larger than natural sand.

*Palm Oil Clinker as Noise Control Materials DOI: http://dx.doi.org/10.5772/intechopen.98506*

**Figure 10.** *Morphology of sample 0% POC and 50% POC.*

#### **3.2 Sound absorption performance**

Performance of SAC on samples tested using impedance tube test is shown in **Figure 11**. In general, all specimen curves have 2 peaks. The first peak is higher with a frequency around 300–400 Hz while the second peak is relatively low at a frequency of 1000 Hz. Anti-resonance occurs at 500 Hz with a SAC less than 0.1. For specimens containing 100% natural sand, the second resonance is somewhat unstable. However with POC replacement, the curves for all three specimens are almost the same. Also, there is no significant change in the SAC curve when the percentage of POC replacement is increased from 25–100%. However, close examination revealed that at 1000 Hz, the SAC curves for all three specimens produced almost identical SACs.

**Figure 12** shows the average SAC for each sample containing 0%, 25%, 50%, 75%and 100%POC. Generally, as the % POC increase, the first dominant frequency shifts to a low frequency. It was obtained that the first dominant frequency and second dominant frequency can be described as follows;

$$f\_1 = \frac{C}{\beta 4h}; \text{where } \beta = 1.25 \text{-first dominant} \tag{6}$$

$$f\_2 = \frac{3C}{\beta 4h} \text{f}; \text{where } \beta = 1.35. - \text{second dominant} \tag{7}$$

These findings is in opposite with the previous researches [18, 30–32], that an approximate relationship between the thickness, h, and dominant frequency f, is numerically by *<sup>f</sup>* <sup>1</sup> <sup>¼</sup> *<sup>C</sup>* <sup>4</sup>*<sup>h</sup>; and f* <sup>2</sup> <sup>¼</sup> <sup>3</sup>*<sup>C</sup>* <sup>4</sup>*<sup>h</sup>;* for first and second dominant frequency, respectively. C is wave velocity in the medium and h is thickness. This is showed that POC had changed the frequency for the 1st and 2nd peak. The maximum 1st peak of SAC occurs at a frequency of 315 Hz, which is good value of SAC of 0.41 to 0.52. The increase due to POC sand is about 5%. 315 Hz is a category of middle frequency range that usually causes problems in the elderly if the sound intensity exceeds the allowable threshold. The source of the noise that causes problems at 315 Hz including road traffic and train noise.

The results show the 2nd peak of maximum SAC occurs at a frequency of 1000 Hz with a good value of SAC of 0.36 when the POC is 50%. At 1000 Hz, POC sand yield in a 30% increase in SAC although POC sand has a porosity of 6% compared to the natural river sand of only 3%. This can be used to reduce the traffic noise from heavy traffic which it dominant frequency is between 800 to 1250 Hz

**Figure 11.** *Effect of POC percentage on SAC curve.*

*Palm Oil Clinker as Noise Control Materials DOI: http://dx.doi.org/10.5772/intechopen.98506*

**Figure 12.** *Average sound absorption and POC percentage.*

**Figure 13.**

*Effect of POC percentage on NRC and 315 Hz.*

[18]. Result from this study showed that all specimens have better result of SAC compared to that of mosaic tiles that have a very low SAC in the frequency range of 400 Hz and above of between 0.028 to 0.1 [33]. Overall increase of SAC is between 5 to 30% identical with previous studies using porous aggregate by [14–16].

#### *3.2.1 Relationship between SAC and POC content*

The average of SAC coefficient at 250 Hz, 500 Hz, 1000 Hz, 2000 Hz or noise reduction coefficient (NRC) is shown in **Figure 13**. NRC has weak linear relationship with increase of POC percentage with R<sup>2</sup> = 0.14 but surprisingly, SAC at 315 Hz has significant relationship with R<sup>2</sup> = 0.78, significant at 0.05 with the following expression;

$$\text{SAC at 315 Hz} = -0.523 - 0.098 \ast \text{POC } \left( \text{R}^2 = 0.761, 0.05 \right) \tag{8}$$

#### *3.2.2 Relationship between porosity and sound absorption coefficient*

**Figure 14** shows the relationship between interconnected porosity and the first peak, second peak SAC and NRC. All showed that interconnected porosity relatively

#### **Figure 14.**

*Effect of interconnected porosity on NRC, 315 Hz and 1000 Hz.*

**Figure 15.** *Density of specimens with POC content.*

has low relationship with SAC and NRC. This is indicated that interconnected porosity is not the factor influence the sound absorption. This finding is in disagreement with finding of Zhang et al. [16] that interconnected porosity has a significant relationship with the sound absorption properties of the concrete.

#### **3.3 Density**

As known, the specific gravity of the POC is lower due to micro-pores, and as a result, the replacement of natural sand with POC decreased the density of the specimens. The densities ranged from 1878 to 2070 kg/m<sup>3</sup> for replacement of POC percentage 25 to 100%. It can be seen that POC50–100% fell within the range of light weight concrete (between 900 to 2000 kg/m3 ) while in previous work by Kanadasan et al. [34] 100% POC still resulted density more than 2000 kg/m<sup>3</sup> . This could ideally fall under sustainable and energy efficient materials category [35].

Based on the density results, it can be observed that there is a direct relationship between the density and the percentage of POC as the density decreases linearly (**Figure 15**) as shown by Eq. (9). Such behaviour can be explained by taking into account the light weight properties of fine POC with high pore content [12], which

*Palm Oil Clinker as Noise Control Materials DOI: http://dx.doi.org/10.5772/intechopen.98506*

reduces the mass per unit volume of mortar. It should also be noted that the POC itself is approximately 25% lighter than river sand [10], as mentioned in sect 1.

$$\text{Density} = -240.4 \ast \text{POC} + 2118.8 \left( \text{R}^2 = 0.994; \text{p} = 0.000 \right) \tag{9}$$

**Figure 16** shows the relationship between SAC at 315 Hz, 1000 Hz, NRC, and density of specimens containing POC of 0%, 25%, 50%, 75% and 100%. NRC has weak relation with density and this result opposite with findings from Gonzalez et al. [22] and Tzer el al. [21]. On the other hand, density has very good relationship with SAC at frequency 315 Hz with the following;

$$\text{SAS at 315 Hz} = -0.356 + 0.0004 \ast \text{density} \,(0.785, 0.045) \tag{10}$$

## **3.4 Compressive strength**

**Figure 17** shows the changes of compressive strength for 7 and 28 days. As can be seen, there is constant development of compressive strength within 7 and 28 days. At 28 days, the compressive strength of specimen decreases more

**Figure 16.** *Relationship between density and SAC.*

**Figure 17.** *Effect of POC percentage on compressive strength.*

significant (p = 0.001) as the percentage of POC replacement increases. It is noted that all specimens meet the range for compressive strength of 5 N/mm<sup>2</sup> according to Specification for masonry units Part 2: Calcium silicate masonry units [36].

The relationship of compressive strength (fc) and POC content at 28 days is as follows:

$$\mathbf{f\_c} = -0.081 \ast \text{POC} + 17.592 \begin{pmatrix} \mathbb{R}^2 = 0.952; \mathbf{p} = 0.004 \end{pmatrix} \tag{11}$$

The reduction of compressive strength is due to reduction of density as explain in 3.3. The strength gradually reduced and almost 44% of strength was lost when replacement was 100%. This is due to fine POCs having micro pores in the internal structure have affected the strength capacity leading to a reduction in the strength of the mortar, this is also obtained by Kanadasan et al. [34]. Therefore, the higher the percentage of POC used then the more macro pores and this makes the mixture have even higher strength reduction. Regression analysis on compressive strength is statistically significant (p = 0.006) governed by density:

$$\mathbf{f\_c = 0.034 \* density - 53.57 \left(R^2 = 0.938; p = 0.006\right)}\tag{12}$$

**Figure 18** shows specimen containing 50% POC failure in compression occurs quicker than specimen with 100% sand river due to porous POC contribute to lower density and lower strength which is in agreement with Eq. (11). Also, since the crushing value of aggregate (ACV) for POC is three times lower than that of ordinary [12, 34], this has given maximum effect of compressive strength compared to mixtures with river sand where the pores in POC allow greater crack spread than conventional aggregate. This type of failure similar with that of previous research [37–39].
