**Figure 4.**

*Palm oil clinker (a) large chunk of POC (b) fine POC (c) size distribution.*

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

**Figure 5.** *SEM micrograph.*


#### **Table 1.** *Proportion of mixtures.*

**Figure 6.** *Mixing of materials.*

another three minutes with water (**Figure 6**). Three 50x50x50 mm cubes specimens from each mix were moulded for density, porosity and compressive strength testing. Also, three 200 mm high cylinders specimens for each mixes were prepared for sound absorption test. Compaction done lightly to obtain good porosity by using the vibrating table. After demoulding of the specimens on the following day, they were all cured in water at room temperature.

The compressive test for all specimens was carried out for the concrete aged 7 and 28 days of moist curing in accordance with ASTM C109/C109M [24]. The porosity test was conducted on 50 mm diameter by 200 mm length cylindrical specimens representing all mixtures in 1st batch. Two types of porosity are measured using volume method; interconnected porosity ∅*int* and closed porosity, ∅*closed:* Total porosity, ∅*total* then calculated by summing interconnected and closed porosity.

The interconnected porosity test was done by applying the water displacement method to measure the accessible pores in concrete specimens i.e. displacing the absorbed water in concrete. Water absorbed into the concrete by interconnected pores can be beneficial information related to pore structure, and sound absorption performance by concrete. Meanwhile, the structure of the concrete pores is very important for strength material. The interconnected porosity is determined by using Eq. (1) [25].

$$\mathcal{Q}\_{int} = \left[\mathbf{1} - \frac{\mathbf{w}\_2 - \mathbf{w}\_1}{\rho\_\mathbf{w}\mathbf{v}}\right] \ast \mathbf{100} \tag{1}$$

where, w1: submerged weight of the porous specimen underwater (kg), w2 weight of dry porous concrete specimen (kg), ρw: density of water (kg/mm<sup>3</sup> ), v: volume of porous concrete specimen (mm<sup>3</sup> ).

The specimens were totally dried until no further reduction of weight. The closed porosity is determined by using Eq. (2) [25].

$$\mathcal{Q}\_{closed} = \left[\mathbf{1} - \frac{\mathbf{w}\_3 - \mathbf{w}\_1}{\rho\_\mathbf{w}\mathbf{v}}\right] \ast \mathbf{100} - \mathcal{Q}\_{int} \tag{2}$$

where, w3: totally dried weight of the porous specimen (kg),

where, w: weight of dry porous concrete sample (kg), w2: submerged weight of the porous sample underwater (kg), ρw: density of water (kg/mm<sup>3</sup> ), v: volume of porous concrete sample (mm3 ).

**Figure 7.** *Impedance tube set up for measuring specimen's sound absorption coefficient.*

Sound absorption coefficient (SAC) or *α* of specimens were obtained by using impedance tube Type 4206-A, **Figure 7**, which was in accordance with ASTM E1050–98 [26]. SAC was determined using transfer-function method in a twomicrophone method by placing the specimen at one end of the tube; involving the decomposition of a broadband stationary random signal into incident sound, Pi and reflected sound, Pr. The transfer function compensates for the possible gain and phase mismatch of the two microphones, then the measurement is repeated by interchanging the two channels. The complex reflection coefficient *R* is calculated by:

$$R = \left[\frac{H\_1 - H\_I}{H\_R - H\_1}\right] e^{j2k(l+s)}\tag{3}$$

Where *H1* is the frequency response function; *H1* is the frequency response function associated with the incident component; *HR* is the frequency response function associated with the reflected component; j is defined as ffiffiffiffiffiffi �**<sup>1</sup>** <sup>p</sup> , k is wave number, *l* is the distance to the first microphone location from the specimen and s is spacing between the microphones.

The normalised surface impedance ratio of specimen, ( *<sup>z</sup> ρc* ) and *α* can be calculated;

$$\frac{z}{\rho c} = \frac{1+R}{1-R} \tag{4}$$

$$a = \mathbf{1} - \left| \mathcal{R} \right|^2 \tag{5}$$

z is the surface impedance modulus of specimen which is obtained by calculating the characteristic air impedance *ρc*. Surface impedance implies the resistance of specimen surface to the sound energy. In this study *ρc* for temperature 25°C is 409 Rayls. Using this technique specimens' SAC in Eq. (5) were measured, and this was carried out by inserting the specimens in the impedance tubes and measuring the SAC absorption of the whole system.
