Investigation of Hollow Block Production by Substituting Chicken Feather, Cotton and Rock Wool Waste Fibers for Pumice Aggregate

Abstract

Currently, natural resources are rapidly depleting as a result of increasing construction facilities. Increasing energy consumption with increasing construction is another serious issue. In addition, many problems that threaten the environment and human health arise during the disposal and storage of waste materials obtained in different sectors. The main objective of this study is to investigate the substitution of cotton (CW), chicken feather (CFF) and stone wool waste (SWW) from pumice aggregate in the production of environmentally friendly hollow blocks. To achieve this, CW, CFF and SWW were substituted for pumice at ratios of 2.5–5–7.5–10% in mass, and hollow blocks were produced with this mixture under low pressure and vibrations in a production factory. Various characterization methods, including a size and tolerance analysis, unit volume weight test, thermal conductivity test, durability test, water absorption test and strength tests, were carried out on the samples produced. This study showed that waste fibers of chicken feather and stone wool are suitable for the production of sustainable and environmentally friendly hollow blocks that can reduce the dead load of the building, have sufficient strength, provide energy efficiency due to low thermal conductivity and have a high durability due to a low water absorption value.

1. Introduction

In recent years, reducing the energy consumption in buildings has become a priority and an important issue. According to the reports of the Organization for Economic Cooperation and Development, buildings and their air conditioning are responsible for 40% of energy consumption [1]. Considering economic and environmental factors, the need to use construction materials with a high energy efficiency and superior thermal insulation properties in the construction sector becomes clear [2]. Lightweight building materials with an appropriate mechanical strength and high thermal insulation provide energy efficiency and help to reduce environmental pollution and reduce costs due to less fuel use [3,4].

The building envelope, which separates the indoor and outdoor environment and plays a major role in heat transfer control, is one of the most important parameters in achieving thermal comfort. Approximately 30% of the energy or heat loss in buildings occurs through the walls [5]. For this reason, the thermal conductivity coefficients of the materials used in the building envelope should be low. The heat conductivity coefficient of these materials depends on the porosity of the material. Since the heat conduction coefficient of the air inside the pores is very low, porous materials have high thermal insulation properties. As the number of pores increases, the density of the material decreases, while the thermal insulation efficiency increases [6]. Today, due to the high energy and construction costs, it is recommended to use low-density natural materials with a high thermal resistance. The aggregate used for the production of low-density building materials is divided into two types: natural (pumice, volcanic slag, diatomite, etc.) and artificial aggregate (perlite, shale, vermiculite, etc.) [7].

Pumice is a lightweight aggregate with many positive properties such as a low density, high thermal insulation, high fire resistance and incombustibility, acceptable compressive strength and reasonable flexibility due to its porous structure [8]. Pumice is widely used in Turkey and in many European countries in the production of lightweight building materials such as concrete blocks, bricks and panels in buildings, in exterior wall applications or as partition elements indoors. Lightweight building materials have important advantages such as reducing the dead load of the building, being cheap, providing heat and sound insulation and saving the timber, mortar, rebar and labor used in construction [9]. An important advantage of pumice concrete compared to normal concrete is its more elastic behavior against earthquake loads [10]. In addition, the existence of legal regulations that make insulation compulsory and the increase in energy costs are important reasons for the widespread use of lightweight building materials in the construction sector [11].

Since the production and use of lightweight block elements in buildings in order to reduce the dead load of the building will reduce the damage to living things during and after the earthquake, studies on this issue should be increased [12]. In reinforced concrete structures, various materials have been used until today to reduce the dry weight of the structure. Among the general properties sought in these materials, there should be important properties such as lightweightness, appropriate strength, a high thermal insulation and low water absorption. For this purpose, the use of lightweight materials with good thermal insulation properties is becoming increasingly common [13].

Liu et al. [14] investigated the production of lightweight composite blocks with granulated rubber and natural sand core. Galvin et al. [15] produced recycled vibro-compressed dry-mixed concrete blocks by substituting recycled aggregates (RAs) obtained from precast concrete block waste in different proportions for conventional aggregate. Al-Tarbi et al. [16] produced lightweight block material using perlite, vermiculite, slag and polystyrene instead of coarse aggregate and fine aggregate. Al-Tarbi et al. [17] produced hollow concrete blocks by replacing coarse aggregate with 20 wt% high-density polyethylene (HDPE), 20 wt% crumb rubber (CR) and 10 wt% low-density polyethylene (LDPE) and studied samples produced with the waste material. Al-Jabri et al. [18], in their study on the production of concrete blocks for thermal insulation in hot regions, produced block elements using ordinary concrete blocks and vermiculite lightweight aggregate and reported that vermiculite improved the properties of the block element.

In today’s world, all industries are trying to use and develop environmental friendly materials due to the increasing awareness of protecting the ecosystem and natural resources [19]. For this purpose, researchers are conducting various studies to minimize the use of synthetic polymers and to make the use of biodegradable waste natural fiber resources widespread. Natural fibers can be classified as plant, animal and mineral fibers according to their origin. Natural fibers offer a higher availability than man-made fibers due to their easy availability, low prices, low density and biodegradability [20].

Any substance that we do not need and remove can be defined as waste. Waste disposal requires a high cost and labor [17]. “Recycling” is the process of transforming waste materials into secondary raw materials by various physical and/or chemical processes and including them back in the production process. Owing to the recycling of wastes, natural resources are preserved, energy is saved, the amount of waste is reduced, the economy is contributed to, the damage to the environment and groundwater is reduced, and an investment is made in the future [21].

With the expansion of modern poultry farms, the disposal of keratin-containing chicken feather (CF) wastes has become an important problem [22]. Disposal methods for keratinous wastes generally include burial, open dumping, incineration, storage, composting and mechanical grinding [23]. However, each of these methods causes different levels of damage to the environment [24,25]. Considering the annual amounts of poultry wastes generated, the importance of converting these wastes from hazardous to usable and the necessity of widespread studies in this direction in the world and in our country can be understood [22].

Chicken feather fibers (CFFs) are composed of insoluble and highly durable keratin and have a hollow structure [26]. The keratin fibers in the structure of CF give the composite structure more rigid and strong properties, while the hollow structure provides lightweight and high thermal insulation properties. The thinness of the CFF allows the contact surface to be wider. It has a high resistance to degradation in a wet environment and tends to maintain its volume even when saturated with water. Due to these properties, it has become advantageous to expand its usage areas and employ it as a cheaper alternative to expensive fibers [27]. Keratinases obtained from the utilization of waste keratin are successfully used as biofertilizers and animal feed additives, in the production of detergents, in the cleaning of industrial wastewater by absorbing phenol commonly found in industrial wastewater, in the leather and textile processing industry, medical and pharmaceutical treatment, skin disease treatment and skin hair removal [28,29]. Its use for cladding and insulation (ceiling, slats, etc.) can increase the load resistance of the structure by reducing the weight on the beams. Lokesh et al. [30] used waste chicken feather as a reinforcement to develop synthetic fibrous composites with different fractions of reduced synthetic fibers. Yahyaoui et al. [31] investigated the feasibility of using processed chicken feather fibers to improve the performance of raw bricks. Mishra et al. [32] used chicken feathers as an auxiliary material to improve the fire-resistant and mechanical performances of polypropylene composites. Vaidya et al. [33] attempted to produce a hybrid composite consisting of glass fiber (GF) as reinforcement, CF powder as filler and epoxy as the matrix material. Rose et al. [34] used CF waste for sand soil stabilization and observed an increase in strength of 21–43%. Farhad Ali et al. [35] combined treated CFF, untreated CFF and crushed CFF waste (ZnO, CaCO₃ and Al₂O₃) with metal oxides to produce resin-based composites and showed that CFF positively improved the mechanical and water absorption properties of the composite material. Adediran et al. [36] investigated the effect of CFF and WSD (wood saw dust) on the properties of waste paper–cement-based composites. Pavithra et al. [37] presented the effect of CNSP in combination with CF as fibers in concrete on strength. Araya-Letelier et al. [38] produced adobe mixtures by adding 0–1% CFF to clay soil and reported that the physical and durability performance of the adobe mixtures increased as the CFF content increased. Ouakarrouch et al. [39] produced mortar by mixing gypsum plaster with CF waste to be used in building exterior walls and roofs in order to examine its thermal properties, and the results showed that the addition of composite material containing 5% by weight of CF waste reduced energy consumption by 24.8% in summer and 29.4% in winter.

Stone wool (SW) is an inorganic fiber consisting of glassy fibers with a typical diameters of 2–6 µm and average lengths of about 2–6 mm, obtained by melting and processing natural rocks such as basalt, diabase, dolomite, anorthosite and olivine sand at about 1450–1520 °C. SW, a glassy silicate mineral wool, is a versatile material that can be used in many different areas such as building insulation (facade insulation, roof insulation, partition walls), industrial and technical insulation for the process industry (electrical appliances), engineering fiber solutions, various applications including noise and vibration control [40] and greenhouses [41]. SW is widely used in building insulation to provide thermal comfort as well as fire resistance and acoustic comfort in all types of buildings. While a small portion of SW is obtained as a result of the production process, most of it is obtained as recycling from waste SW at the end of the construction and demolition process. The low density of stone wool waste (SWW) at the end of its life cycle requires large transportation and storage capacities [42]. Since it has unique advantages such as a low thermal conductivity, easy availability (rocks and waste from households and industry) and easy recycling, it is of great importance as a raw material in the production of new products in energy saving technologies [43]. Depending on its chemical composition and particle size, it can be used in many different applications such as the partial replacement of coarse and fine aggregates in concrete, cementitious materials and fiber-reinforced cement-based mortars or as a substitute for ultrafine fillers. This can save the cost of natural aggregates while minimizing the environmental impact of solid waste disposal [44]. Gutiérrez-Orrego et al. [45] activated rock wool fiber with alkali and also prepared a hybrid alkali-activated stabilized clay soil with rock wool and Portland cement. Klima et al. [46] used mineral wool waste (MWW) in the production of artificial aggregates. Korpoyev et al. [41] studied the substitution of SWW from greenhouse agriculture in different proportions for clay in the production of baked clay-based bricks and reported that SWW had a positive effect on the insulation and frost resistance of the brick. Liikanen et al. [47] evaluated the environmental impacts of wood-composite production with mineral wool waste and stated that the mechanical performance of the composites produced can be improved. Pavlin et al. [42,48] and Yliniemi et al. [49,50,51] presented new alternative research for the recycling of this waste material by activating SWW with alkalis.

With the rapid development of the textile industry and the improvement of people’s living standards, there has been a shift towards cotton textile production, and this has led to an increase in textile waste. Cotton is one of the most common textile materials, and waste cotton accounts for 24% of total textile waste. A large amount of the textile waste generated is buried or incinerated. This wastes a significant amount of resources and causes environmental pollution, with CO₂ impacts [52]. To manage this waste effectively, the recycling and reuse of waste cotton are common practices to reduce global waste generation [53]. Srinivasan et al. [54] produced composite panel specimens using areca nut shell fiber reinforced with a hybrid blend of desert cotton and bio-benzoxazine/epoxy resin, and its usability as insulation material in building construction was investigated. Peña-Pichardo et al. [55] studied polyester concrete containing waste cotton fibers. Kamble and Behera [56] reported that hybrid composites produced using cotton fibers derived from waste cotton textiles can be used instead of timber in buildings, where they are thermally stable.

Although the use of pumice in concrete has many advantages, pumice aggregate in the matrix reduces its mechanical strength and workability and increases drying shrinkage and water absorption, thus requiring methods to reduce the negative impact of pumice aggregate on concrete [8].

As shown by this literature review, CW (cotton waste), CFF (chicken feather fiber) and SWW (stone wool waste) wastes have a significant potential for various uses in different sectors. The construction sector is a suitable area for many different applications of these waste materials such as clay-based adobe bricks, plaster, artificial aggregate, composite material production and ground improvement. However, to the best of the author’s knowledge and as shown by this literature review, the use of these fibers by substituting them for pumice in the production of traditional hollow blocks widely used in the construction sector has not yet been fully investigated.

In this study, it is aimed to produce lightweight, environmentally friendly, economical and sustainable structural hollow blocks by substituting waste CFF, SWW and CW for pumice aggregate in certain proportions. In addition, protecting the limited natural resources used intensively in the construction sector and contributing to the utilization of waste by eliminating the disposal problem by recycling waste materials instead, and the production of building elements that increase insulation properties and reduce the building dead load without deteriorating the mechanical properties of the block element, are important study subjects in terms of the originality of this research.

2. Materials and Methods

2.1. Material

2.1.1. Pumice

Pumice aggregate with a light gray color and acidic properties used as aggregate for block production was obtained from the Kayseri-Talas (Turkey) region and used in 0–12 mm sizes. Sieve analyzes of pumice aggregates were carried out according to the TS EN 13055 (2016) [57] and TS EN 933-1 (2012) [58] standards. The grain sizes of the pumice aggregates were determined in accordance with ASTM C 330 [59]. Figure 1 shows the pumice aggregate used in the study, and

Table 1. Sieve analysis of pumice and limit values according to ASTM C 330.

Sieve Number (mm)	Sieved (%)	Limit Values According to ASTM C 330
		Sieve Number (mm)	Upper	Under
16	100	19	100	100
11.2	94.1	12.5	100	95
8	74.9	9.5	-	-
5.6	66.8	4.75	80	50
4	57.9	0.3	20	5
2	41.2	0.15	15	2
1	34.9	0.075	10	0
0.5	17.9
0.25	7.9
0.075	2.6

shows the granulometry curve of the aggregate used.

2.1.2. Cement

CEM I 32.5 R-type cement according to the TS EN 197-1 (2012) [60] standard was used in the production of hollow blocks in the study. The cement used in production was supplied from the CİMKO Cement and Concrete factory. The chemical and physical properties of the PÇ 32.5R-type cement used in this study are shown in

Table 2. Chemical and physical properties of PÇ 32.5R-type cement used in this study.

Chemical Properties
Oxides	Contents (%)
SiO2	8.54
Al2O3	4.65
Fe2O3	4.36
CaO	63.28
SO3	2.49
MgO	1.7
K2O	0.84
Na2O	0.32
MnO	0.12
TiO2	0.28
Cl	0.01
Loss on ignition (LOI)	3.41
Physical properties
Specific gravity (g/cm2)	3.13
Specific surface (cm2/g)	3646
Initial setting time (min.)	100–235
Final setting time (min.)	140–345

.

2.1.3. Natural Fibers

Chicken feather fiber (CFF), cotton waste (CW) and stone wool waste (SWW) were used as natural fibers in block production (Figure 2). Chicken feathers obtained from non-living chickens under ethical and humane conditions were used by Beyza Pilic factory in Adana/Turkey, CW was obtained from a textile factory in Kahramanmaras/Turkey, and SWW was obtained from Musyak Exterior, Sound and Thermal Insulation Systems, a company operating in Sanlıurfa/Turkey. The chicken feathers were first pre-washed to remove unwanted wastes, dust and blood, then placed in a sack and machine washed with non-ionic soap at 40 °C for 1 h. The reason for choosing 40 °C as the washing temperature is to prevent the deterioration of the unique micro-morphological structure of chicken feathers. After the pre-washing process, the chicken feathers were placed in ethanol, mixed vigorously and kept in this environment for 24 h. Afterwards, these feathers were dried at 30 °C for 8 h. The washing and drying process was repeated 3 times to completely remove unwanted pathogens in the feathers [61]. Then, the dried chicken feathers were cut with scissors and reduced to a size of 0–12 mm to replace the pumice aggregate used in the mixture. CW obtained from textile factories was washed and left to dry under natural conditions. Stone wool was used as supplied from the company without any processing.

Table 3. Properties of fibers.

	Pumice	CW	CFF	SWW
Unit weight (g/cm3)	2.15	1.45	0.82	0.35
Thermal conductivity (W/mK)	0.135	0.062	0.043	0.037
Water absorption (%)	34	65	14	6

shows the properties of the fibers obtained from Kahramanmaras Sutcu Imam University USKIM analysis center, and

Table 4. Chemical properties of pumice and SWW.

Component (%)
	SiO2	Al2O3	Fe2O3	TiO2	MnO	CaO	MgO	Na2O	K2O	Others
Pumice	68.60	15.95	2.97	0	0.10	1.93	1.79	4.80	2.88	0.98
SWW	43.47	20.70	4.52	0	0.51	18.01	7.13	1.52	0.81	3.33

shows the chemical properties of pumice and SWW.

According to ISO and CEN standards, the thermal conductivity coefficient (λ) is 0.065 W/mK, and according to DIN 4108 [62], materials with a thermal conductivity (λ) less than 0.1 W/mK are defined as thermal insulation materials, one of the determining criteria in the selection of thermal insulation materials [63]. Therefore, the selected fibers are found to be suitable for producing hollow blocks for insulation purposes.

2.2. Method

2.2.1. Block Production

Due to the high porosity and high water absorption of the pumice aggregate used in this study, the net water/cement ratio of the block element cannot be calculated with sufficient accuracy. For this reason, it is not possible to use a general mix calculation method suitable for block production and to apply standard concrete mix calculation methods exactly for pumice aggregate concretes. The method applied for block mixes is to know the optimum mix composition and the proportions of the materials used by a series of trial mixes on the basis of cement dosage. For this reason, while producing the reference block sample, the mixture ratios used by the plant in block production were taken as a basis, and the calculation was made accordingly. According to the results obtained from the literature reviews ([31], etc.) and preliminary study samples, it was decided to partially substitute pumice with CFF, CW and SWW at a rate of 2.5–5–7.5–10% by weight, which was determined as optimum and deemed sufficient, based on the cement dosage, in order to improve the properties of the blocks produced with pumice aggregate. Block mixtures were formed by ensuring a homogeneous mixing, and blocks were produced from these mixtures at a production facility in Kahramanmaras. In preliminary studies, due to the deterioration of the plasticity of the blend with more fiber substitution by mass, the substitution ratio was kept at a maximum of 10% in order to keep the w/c ratio constant, especially due to the deterioration of agglomeration upon CFF substitution. At higher ratios, fiber–matrix adhesion decreases due to the agglomeration of fibers. The blocks produced within the scope of this study are the standard blocks produced by the company, with dimensions of 18 × 36 × 18 cm and with 8 cavities and 3 rows of cavities. By using the block making machine in the facility, 12 blocks were produced on a pallet in each printing. The mixture ratios of the block samples produced are given in

Table 5. Mixing ratios of block samples.

Examples	Pumice (kg)	Cement (kg)	CFF (kg)	CW (kg)	SWW (kg)	Water (kg)
R	55	6.5	-	-	-	15
CFF-2.5	53.625	6.5	1.375	-	-	15
CFF-5	52.25	6.5	2.75	-	-	15
CFF-7.5	50.875	6.5	4.125	-	-	15
CFF-10	49.5	6.5	5.5	-	-	15
CW-2.5	53.625	6.5	-	1.375	-	15
CW-5	52.25	6.5	-	2.75	-	15
CW-7.5	50.875	6.5	-	4.125	-	15
CW-10	49.5	6.5	-	5.5	-	15
SWW-2.5	53.625	6.5	-	-	1.375	15
SWW-5	52.25	6.5	-	-	2.75	15
SWW-7.5	50.875	6.5	-	-	4.125	15
SWW-10	49.5	6.5	-	-	5.5	15

. The mixtures prepared in accordance with the mixing ratios were automatically mixed homogeneously and then placed in the molds. The produced samples were compared with unadulterated reference samples produced in the same plant under the same conditions. The blocks were produced in accordance with the guidelines given in TS EN 771-3+A1 (2015) [64]. After applying compression and vibration for about 15 s with 70 kPa pressure, hollow blocks were produced. Waste fiber materials were substituted in 4 different weight ratios (2.5%, 5%, 7.5% and 10%) instead of pumice, and hollow briquettes were produced in 3 replicates for each group and each ratio. The block samples were left to dry in the natural environment in the stock area on the pallet after leaving the press. The briquettes were cured by watering one day after production. Irrigation procedures were applied once in the first week for all groups. Then, the samples were watered once three days a week. This process was continued until the experiment day (28 days). The mixtures used in the production of fiber-reinforced blocks are shown in Figure 3a, the production stage of the blocks is shown in Figure 3b, and images of the produced block samples in the storage area are shown in Figure 3c.

2.2.2. Dimension and Tolerance Analysis

Dimension and tolerance analyses were performed on the reference and waste fiber-reinforced block samples produced in accordance with the TS EN 771-3+A1 (2015) [64], TS EN 772-16 (2012) [65] and TS EN 772-20/A1 (2005) [66] standards. For determination of the blocks’ sizes, the length (l), width (w) and height (h) of the block were measured using a ruler. Afterwards, the difference of the measured values to the dimensions of 18 × 36 × 18 cm was determined, and it was determined whether it was within the tolerance value. In addition, the block was fixed on a flat table, and the diagonal length of each face was measured with a ruler. The ruler was placed on each diagonal in turn, and the gap between the block surface and the ruler was measured with a precision of 0.05 mm with a gap meter, and the surface smoothness was determined according to TS EN 772-20/A1 (2005) [66] (Figure 4).

Then, in accordance with the TS EN 772-16 (2012) [65] standard, the inner wall thickness, outer wall transverse thickness and outer wall longitudinal thickness of the block samples were measured with the help of calipers, and an average value was taken (Figure 5). The shape, surface gap and color properties of the produced block samples were determined by configuration analysis.

2.2.3. Unit Volume Weight Test

The block samples produced for the determination of unit volume weights were kept in the natural stock environment until they set. The block samples were then dried in an oven at a temperature of 105 ± 5 °C for 24 h and weighed with a precision of 0.1 g until they reached a constant mass. The approximate volume of the block sample was calculated by subtracting the volume of the cavity in the block from the volume obtained by multiplying the length, width and height values of the block sample measured with a precision of 0.1 mm, and the unit volume weights were calculated by dividing the mass value of the sample by the volume value of the sample according to the TS EN 772-13 [67] standard. According to the standard, the “gross dry unit volume mass” value is used in determining the transportation loading, sound and heat insulation and fire resistance of the block element, and the “net dry unit volume mass” value is used in the analysis of the acoustic properties of the block element (TS EN 772-13) [67].

2.2.4. Compressive Strength

Before the block sample taken from the stock area is subjected to the compressive strength test, any residue adhering to the surface on which the load will be applied is cleaned. If the surface does not meet the smoothness requirement, the block element is abraded until the desired smoothness is achieved, or it is subjected to the compressive strength test by making a cap. The net loading area, excluding gaps and pits, on the loading surface must be more than 35% of the gross slab surface area. If the block sample meets this condition, it is subjected to the test as it is without any action regarding the pits, and the net loading area is used in the calculation.

If the loading area of the block sample is equal to or less than 35% of the gross area, the voids of the samples are filled with mortar, capped and cured at room temperature. The calculation is based on the gross area. The samples are then dried at 105 ± 5 °C for 24 h until they reach a constant weight. After the dried samples are heat balanced at room temperature, they are placed between the loading plates, and the sample is crushed in accordance with the TS EN 772-1+A1 (2015) [68] standard (Figure 6). The loading rate was kept constant for all specimens, and a 0.6 MPa/s loading was applied, and the specimens were crushed.

2.2.5. Thermal Conductivity Coefficient

The thermal conductivity values of the 18 × 36 × 18 cm block samples were measured in the KSU USKIM laboratory with a KEM brand QTM-500 device (Figure 7) in accordance with the ASTM C 1113-90 (1990) [69] standard. In the experiment, the surface of the material is in contact with the sensor of the device, and the thermal conductivity coefficient of the material is determined from the temperature interaction between the sensor and the sample.

2.2.6. Water Absorption Coefficient

The porosity rate of the aggregates used in the production of block elements, the pore distribution and the degree of saturation of these pores affect the water absorption capacity and speed of the aggregate. This situation affects the parameters used in block element mixture calculations. Since the excess water retained in the pores of the block element, i.e., the high water absorption value, will adversely affect important properties such as mechanical and thermal properties and freeze–thaw resistance, it is desirable that the water absorption value of the materials used in the production of the block element, especially the aggregate, is low. The water absorption rates of the block samples produced were determined in accordance with the TS EN 772-11 (2012) [70] standard.

2.2.7. Freeze–Thaw Testing (Endurance Feature)

Atmospheric events such as rain, snow, frost and sun rays and factors such as temperature, humidity changes and wind effects have effects on building elements. The most damaging of these events is the freeze–thaw effect. When the temperature drops below 0 °C, the water in the gaps in the material freezes and causes an increase in volume. With the pressure effect that occurs in the material, the material may disintegrate and crack, and spillage may occur. If this situation is repeated frequently, the material may become unusable. However, in cases where block elements are protected by processes such as coating and plastering in the field of use or where they are used in interior walls, the thermal expansion of the block element and resistance to freeze–thaw are not required [71].

The oven-dried pumice block samples to be subjected to the freeze–thaw test were kept in water for 24 h in accordance with TSE CEN/TR 15177 (2011) [72], and the cavities were completely saturated with water. The water-saturated block samples were kept in a freezer at −20 °C for 2 h so that the entire surface was in contact with cold air and then placed in a pool filled with water at +20 °C for thawing. At the end of 25 periods lasting a total of 3 h, frost resistance was measured by checking for mass loss and crack debris by observation.

3. Results and Discussion

The experimental results of the reference and fiber-reinforced block specimens produced with 18 × 36 × 18 cm dimensions were examined.

3.1. Size and Configuration Results

The length, width and height dimension values of the reference and fiber-reinforced block elements produced in accordance with TS EN 771-3+A1 (2015) [64], TS EN 772-16 (2012) [65] and TS EN 772-20/A1 (2005) [66] standards are given in

Table 6. Size analysis results of block samples.

Samples	l (cm)	ld (mm)	w (cm)	wd (mm)	h (cm)	hd (mm)	dss (cm)	dl (cm)
R	36.02	0.2	18.11	1.1	18.12	1.2	0.114	40.15
CFF-2.5	36.09	0.9	18.14	1.4	18.14	1.4	0.135	40.1
CFF-5	36.12	1.2	18.15	1.5	18.04	0.4	0.51	40.08
CFF-7.5	36.05	0.5	18.14	1.4	18.11	1.1	0.158	40.05
CFF-10	36.18	1.8	18.17	1.7	18.19	1.9	0.162	40.14
CW-2.5	36.09	0.9	18.03	0.3	18.03	0.3	0.124	40.24
CW-5	36.2	0.2	18.03	0.3	18.15	1.5	0.131	40.21
CW-7.5	36.14	1.4	18.04	0.4	18.08	0.8	0.129	40.07
CW-10	36.19	1.9	18.08	0.8	18.17	1.7	0.134	40.13
SWW-2.5	36.21	2.1	18.01	0.1	18.01	0.1	0.103	40.2
SWW-5	36.15	1.5	18.01	0.1	18.11	1.1	0.125	40.17
SWW-7.5	36.08	0.8	18.03	0.3	18.17	1.7	0.137	40.09
SWW-10	36.12	1.2	18.02	0.2	18.17	1.7	0.119	40.21

l: length, w: width, h: height, ld: length deviation, wd: width deviation, hd: height deviation, dss: determination of surface smoothness, dl: diagonal length.

.

Permissible deviation values according to the TS EN 771-3+A1 (2015) [64] standard are given in

Table 7. Permissible deviations (mm) according to the TS EN 771-3+A1 (2015) [64] standard.

Tolerance Class	D1	D2	D3	D4
Length	+3	+1	+1	+1
	−5	−3	−3	−3
Width	+3	+1	+1	+1
	−5	−3	−3	−3
Height	+3	+2	+1.5	+1
	−5	−2	−1.5	−1

.

When the height, width and length deviations of the produced block samples are examined, they comply with the D1 class according to the TS EN 771-3+A1 (2015) [64] standard. This shows that the molding and compression were performed appropriately since the fibers are compressible.

According to the TS EN 772-20/A1 (2005) [66] standard, the allowable surface deviation should not be more than 2 mm. The surface deviations of the block samples produced vary between +1.03 mm and +1.62 mm. The results are in accordance with the conditions stipulated in the TS EN 772-20/A1 (2005) [66] standard. The standard does not specify any limit value for diagonal length. The diagonal deviation values of the block samples produced vary between +2.4 mm and +0.5 mm.

The wall thickness of the uniformly shaped block samples produced was measured according to the measurement method stipulated in the TS EN 772-16 (2012) [65] standard, and an average value was determined. In the TS EN 771-3+A1 (2015) [64] standard, there is no limitation on the outer wall thickness of pumice block elements. However, in order to ensure that the maximum aggregate size used in the production of pumice block elements and the mechanical strength of the hollow block elements do not fall below a certain quality and do not give low strength, care should be taken to ensure that the outer wall thickness of the pumice block elements is at least 20 mm [64].

When the values in

Table 8. Wall thicknesses of block samples according to TS EN 772-16 (2012) [65] standard.

Samples	Feature
	Inner Wall Thickness (cm)	Outer Wall Thickness (Transverse) (cm)	Outer Wall Thickness (Longitudinal) (cm)
R	2.13	2.24	2.16
CFF-2.5	2.15	2.28	2.21
CFF-5	2.18	2.29	2.23
CFF-7.5	2.13	2.26	2.21
CFF-10	2.19	2.31	2.29
CW-2.5	2.14	2.25	2.27
CW-5	2.16	2.24	2.26
CW-7.5	2.15	2.26	2.25
CW-10	2.17	2.29	2.26
SWW-2.5	2.13	2.28	2.25
SWW-5	2.14	2.29	2.32
SWW-7.5	2.14	2.3	2.31
SWW-10	2.17	2.31	2.33

are examined, it is seen that the measured wall values are above 20 mm and are suitable for pumice block elements.

When the block elements are analyzed in terms of appearance, it is seen that the CW- and SWW-substituted samples are similar to the reference sample in appearance and can be accepted under market conditions. CFF-substituted samples have a hairy structure in appearance, but it is thought that this appearance will not pose a problem in flush-mounted use.

3.2. Unit Volume Weight Test

The unit volume analysis results of the reference and fiber-reinforced blocks produced are given in

Table 9. Unit weight values of block samples.

Samples	l (mm)	w (mm)	h (mm)	Wd (kg)	Vv (mm3)	Vn (mm3)	γd (kg/m3)	Vg (mm3)	γg (kg/m3)
R	360.2	181.1	181.2	6.122	3,673,500	8,146,578	752	11,820,078	518
CFF-2.5	360.9	181.4	181.4	5.883	3,669,800	8,205,961	717	11,875,761	495
CFF-5	361.2	181.5	180.4	5.773	3,670,300	8,156,327	708	11,826,627	488
CFF-7.5	360.5	181.4	181.1	5.632	3,673,100	8,169,880	689	11,842,980	476
CFF-10	361.8	181.7	181.9	5.545	3,671,200	8,286,735	669	11,957,935	464
CW-2.5	360.9	180.3	180.3	6.015	3,670,400	8,061,770	746	11,732,170	513
CW-5	362.0	180.3	181.5	5.935	3,672,400	8,173,851	729	11,846,251	501
CW-7.5	361.4	180.4	180.8	5.853	3,673,100	8,114,438	721	11,787,538	497
CW-10	361.9	180.8	181.7	5.748	3,671,400	8,217,507	670	11,888,907	484
SWW-2.5	362.1	180.1	180.1	5.685	3,669,400	8,075,679	704	11,745,079	484
SWW-5	361.5	180.1	181.1	5.541	3,670,800	8,119,924	682	11,790,724	470
SWW-7.5	360.8	180.3	181.7	5.437	3,671,700	8,148,292	667	11,819,992	460
SWW-10	361.2	180.2	181.7	5.322	3,673,200	8,153,333	653	11,826,533	450

l: Length, w: Width, h: Height, Wd: Dry weight, Vv: Total void volume, Vn: Net volume, γd: Dry unit volume mass, Vg: Gross volume, γg: Gross dry unit volume mass.

in accordance with TS EN 772-13 (2002) [61].

According to the TS EN 772-13 (2002) [61] standard, the gross density values of block samples should not be more than 1000 kg/m³ maximum. The density values of all the waste fiber-reinforced block samples produced were found to comply with the relevant standard (Figure 8). After the reference sample, the sample with the highest gross density was CW-2.5 with 513 kg/m³, while the lowest gross density was obtained from SWW-10 at 450 kg/m³. The unit bulk densities of the block samples were found to be 4.4–5.8–8.2–10.5%, 1–3.3–4.1–6.7% and 6.5–9.3–11.2–13.1% lower in the block samples with CFF, CW and SWW substitutes, respectively. It is seen that the change in the unit weights of the block samples is related to the unit weights of the substitute fibers and the substitution rates. When the data obtained are examined, it is seen that the unit weights of the fibers used are lower than pumice, which contributes to the decrease in the gross weight of the block samples as the fiber contribution rate increases [43,73]. The low values of the unit volume mass value make an important contribution by reducing the building dead load.

3.3. Compressive Strength

The compressive strength of the block samples was used in accordance with TS EN 772- 1+A1 (2015) [68] by calculating the net area of the loading surface area.

According to TS EN 772- 1+A1 (2015) [68], no compressive strength requirement is required for non-load-bearing partition elements. However, it is still required to have a strength that will not deteriorate during transportation from the storage area to the usage area. The 28-day compressive strength values of the block samples are given in Figure 9. When the 28-day compressive strengths of the block samples are analyzed, the lowest value was obtained from the CW-10 sample with 1.23 MPa, while the highest strength was obtained from the CFF-7.5 sample with 1.49 MPa. The compressive strength of cotton waste-substituted block samples decreased by 3.7–6.6–7.4–9.6%, respectively, compared to the R sample. It was observed that the strength decreased with the fiber substitution rate. Gul et al. [74] stated that compressive strength is a function of density, and with decreasing density, porosity will increase in the composite structure, and this will cause a decrease in strength. In addition, inhomogeneous mixtures formed after the addition of waste materials also contribute to the low compressive strength of the composite material [75]. However, when the strength results of the CFF-substituted samples are examined, an increase of 5.1–8.08–9.6–8.09% was observed in the CFF sample compared to the R sample, and in the SWW-substituted samples, there was an increase of 2.2% in the SWW-2.5 sample compared to the R sample and a decrease of 0–2.2–3.7% in the other samples, respectively.

CFFs are composed of 91% keratin. This protein gives the feather a rigid structure and helps to improve fiber–matrix interfacial bonding [32]. CFF keratin bio-fibers allow a uniform distribution and adhesion within polymers due to their hydrophobic nature [76]. The amount of fiber determines the density of the composite material. The compressive strength of CFF increased up to a 5% fiber substitution into the block. However, in fiber substitution above this ratio, the fibers overlap each other, and the composite–fiber bond decreases. This causes the composite structure to weaken and the strength to decrease. Pavithra et al. [37] reported that the 28-day strength of concrete with chicken feather additions was 3.6% higher than standard concrete. Odusote & Dosunmu [77] reported that when 10% WCF was added to the ceiling panel, it increased the compressive strength. Salih et al. [73] found that the compressive strength of earth bricks reinforced with 7% WCF was much better than the control sample.

In SWW-substituted samples, an increase in strength was observed at a 2.5% fiber additive rate. It is thought that this is due to the SiO₂ content of very small sized pieces of SWW, which shows pozzolanic properties. Luo et al. [78] stated in their study that the addition of mineral wool increases porosity, but very small particles form a gel structure that strengthens the composite structure and increases the strength. The high compressive strength reduction in specimens with a high SWW content can be attributed to lower density, increased porosity and pore size distributions [79]. Ralegaonkar et al. [80] showed that 1–3 wt% is the optimal dosage for shredded SWW. The SWW surface is inert and smooth. For this reason, since it is easy for the fibers to intertwine in the cement matrix, it has been observed that the mechanical properties decrease as the fiber ratio in the mixture is concentrated in certain regions [81,82].

3.4. Heat Conduction Coefficient Values

Nowadays, many researchers are using industrially applicable materials to produce insulation materials in order to contribute to the solution of the increasing energy problem and to utilize waste materials. The thermal conductivity (TC) of the materials used plays an important role in preventing heat loss and saving energy. Bulk density and porosity are the main factors determining thermal conductivity. For this purpose, in this study, CFF, CW and SWW were used in the production of blocks for insulation purposes. The TC coefficients (λ) of the block samples are given in Figure 10, measured according to ASTM C 1113-90 (1990) [69].

The TC coefficients (λ) of the block samples contain values between 0.1863 W/mK and 0.2471 W/mK. The highest TC value was obtained from the R sample, while the lowest thermal conductivity value was obtained from the SWW-10 sample compared to the reference. The decrease in the thermal heat coefficient of CFF-substituted block samples was 10.5–12.8–15.2–14%, and it was 5.5–8–11.2–12.7% for CW-substituted samples and 12.5–14.9–18.2–24.6% for SWW-substituted samples, respectively, in comparison to the R sample. All of the block samples prepared in this study have better values than the TC value that the building elements used as partition walls should have today, and they are within the acceptable thermal conductivity value (0.5 W/mK) according to TS 825 [83] standards.

The TC of a material depends on the closed pores in the material, the size and distribution of these pores, the amount of air contained in the pore, the thermal conductivity of the solid material and the density and TC of the additional materials [84]. In addition to these properties, the interaction between the matrix and the reinforcement will also affect the thermal properties. When fibers are added to the composite, they act as pore formers. The type of porosity (open or closed), pore size and distribution affect the TC, which can be shown by the fluctuation that occurs with increasing SWW. A more uniform and densely distributed porosity can contribute to increased insulation [85]. Increasing the porosity in the microstructure increases thermal insulation as air is trapped in the pores [86]. In general, a decrease in density leads to a decrease in the thermal and mechanical properties of the composite material [87]. Korpayev et al. [41] produced clay bricks with SWW additions in their study. They stated that the addition of SWW creates porosity in the clay mass and therefore the bulk density decreases. They commented that the reduction in density has a positive effect on the thermal insulation of the bricks. Taurino et al. [86] stated that the addition of up to 10% SWW increases the porosity and reduces the bulk density of the brick samples and consequently reduces the TC coefficient of the samples, which improves the thermal insulation properties of the bricks.

The honeycomb structure of CFF’s body and barbs is the main reason for its use as a thermal insulator [88,89]. This honeycomb structure creates air voids in the feather and body, giving the material a low density and low TC [90]. Therefore, biomaterials made of chicken feathers have a low thermal conductivity [91]. Bessa et al. [92] showed in their study that CFF exhibits superior performance in thermal insulation when used as a reinforcement in composite material due to its morphological structure, with hollow protein fiber properties. Ouakarrouch et al. [39] showed that the addition of 5% chicken feather waste to gypsum plaster for use in wall and ceiling mortars provides up to a 36% increase in thermal insulation. Cheng et al. [44] showed that the addition of CFF increased the thermal stability of composites compared to pure PLA. Khaleel et al. [61] reported a 17% improvement in the thermal insulation performance of rigid polyurethane foam material containing 3% turkey feathers.

The decrease in the TC value is due to the hollow microstructures of the chicken feathers, as well as the additional closed microcells formed by the thick outer walls of the well-distributed CFF. The presence of closed cells with a considerable amount of wall barriers reduces both the molecular velocity and the free movement of air molecules inside the cell, resulting in a reduced material-to-material heat transfer. However, when the CFF substitution exceeds 7.5%, this favorable situation in TC starts to change. This is thought to be due to the loss of homogeneity of the distribution as a result of the high amount of CFF substitution and the concentration of CFFs in certain regions; as a result, the void structure deteriorates and disintegrates. These imperfect microstructures cause an increase in heat transfer as they cause air flow between the cells. In addition, due to the high heat conductivity of the conductive thick walls of the CFFs concentrated in certain regions, more heat conduction is provided [61].

3.5. Water Absorption

If building materials are to be exposed to harsh weather conditions, water absorption is one of the most important properties to consider [93]. Water absorption is a durability indicator that reveals the open porosity of a sample [79]. The water absorption values of R samples with and without waste fiber additives were determined in accordance with TS EN 772-11 (2012) [70] and are given in

Table 10. Water absorption values of block samples.

Samples	Initial Dry Weight (g)	Water-Saturated Weight After 24 h (g)	Water-Saturated Weight After 48 h (g)	Weight Saturated with Water (g)	Water Absorption (%)
R	6122	6887.25	7242.33	7395.38	20.8
CFF-2.5	5883	6594.84	6888.99	7030.19	19.5
CFF-5	5773	6448.44	6719.77	6846.78	18.6
CFF-7.5	5632	6262.78	6504.96	6640.13	17.9
CFF-10	5545	6127.23	6382.30	6504.29	17.3
CW-2.5	6015	6869.13	7163.87	7332.29	21.9
CW-5	5935	6819.32	7104.20	7270.38	22.5
CW-7.5	5853	6766.07	7041.16	7210.90	23.2
CW-10	5748	6679.18	6949.33	7121.77	23.9
SWW-2.5	5685	6338.78	6605.97	6713.99	18.1
SWW-5	5541	6128.35	6405.40	6505.13	17.4
SWW-7.5	5437	5948.08	6247.113	6350.42	16.8
SWW-10	5322	5785.01	6093.69	6189.49	16.3

.

According to TS EN 772-11 (2012) [70], the water absorption rate should not be more than 20%. When the obtained values are analyzed, the lowest water absorption rate was obtained from the SWW-10 sample with 16.3%, and the highest water absorption rate was obtained from the CW-10 sample with 23.9% (Figure 11). Pumice aggregate has a high water absorption capacity due to its porous structure. The water absorption value of the cotton fiber-substituted samples was found to be 5.3–8.2–11.5–14.9% higher than the reference sample. It was observed that the water absorption value increased as the cotton fiber substitution rate increased. This can be explained by the high water absorption capacity of cotton fibers [94]. In addition, with the increase in the amount of fiber, the settlement problem arises due to the difficulties arising in processability, and since hollow structures are obtained, the water absorption value was observed to be the highest in the series with the highest fiber ratio. However, this situation was reversed in CFF- and SWW-substituted samples. Chicken feather and stone wool fibers are hydrophobic, and their water absorption is lower than pumice. The lowest water absorption rates were found in stone wool fiber-substituted block samples. The water absorption value decreased by 13–16.4–19.2–21.6% in stone wool-substituted block samples compared to the reference sample. As the stone wool substitution increased, the unit weight decreased and porosity increased but water absorption decreased. Poor adhesion between the fiber particles and the composite caused a decrease in strength and increased porosity, but the non-absorbent hydrophobic property of the fiber material caused a decrease in water absorption [95]. Waste stone wool fibers are hydrophobic due to resin binders [96]. Due to the open fibrous structure of stone wool, when water penetrates the fibers, it only replaces the air between the fibers, and this ensures that the water does not affect the fibers. Therefore, when stone wool becomes wet during storage, during the construction phase and even during the operation phase of the building due to structural failures, if it is given enough time to dry, it returns to its original state and maintains its insulation properties [97]. In the chicken feather-substituted samples, the water absorption value was found to be 6.3–10.6–13.9–16.8% less than the reference sample. Chicken fibers have a high keratin content and are hydrophobic fibers [27]. The protein layer in the keratin structure wraps the fiber from the outside and ensures that the water absorption of the fibers is low. Adediran et al. [36] emphasized that water absorption decreases as the ratio of CFF, which shows hydrophobic properties, increases compared to WSD, which showed hydrophilic properties in the composite material they produced. However, water retention occurs over time from the structural voids of the fibers exposed to water effects, and this causes some water absorption of the fibers. Farhad Ali et al. [35] obtained results supporting this conclusion in their study.

3.6. Freeze–Thaw Testing

The void structure of concrete, the number and size of voids, their distribution in concrete, freezing rate, permeability of concrete and water absorption rate are the most important factors affecting the cracking and disintegration behavior of hardened concrete at the end of the freeze–thaw effect. The greatest risk is that the micro, macro and capillary void structure of concrete are saturated with water as a result of water absorption. Cavities that are not filled with water will act as a kind of cushion. As a matter of fact, the volume increase with freezing water will grow towards these voids, and no stress will occur. Freeze–thaw damage to concrete starts as physical damage and continues by causing greater durability problems. For this reason, the use of materials and admixtures to reduce the water absorption of concrete is important to reduce the damage of this effect [98].

The endurance strength results of the block samples according to TSE CEN/TR 15177 (2011) [72] are given in

Table 11. Freeze–thaw mass loss values of block samples.

Samples	wi (kg)	we (kg)	Examinati on for Rashes and Cracks	Mass Loss (%)
R	6.122	5.985	No rashes and crack s observed	2.23
CFF-2.5	5.883	5.757		2.15
CFF-5	5.773	5.656		2.02
CFF-7.5	5.632	5.523		1.94
CFF-10	5.545	5.450		1.72
CW-2.5	6.015	5.857		2.63
CW-5	5.935	5.730		3.45
CW-7.5	5.853	5.622		3.95
CW-10	5.748	5.463		4.96
SWW-2.5	5.685	5.575		1.93
SWW-5	5.541	5.438		1.85
SWW-7.5	5.437	5.341		1.77
SWW-10	5.322	5.235		1.63

wi: Initial dry weight, we: End of experiment dry weight.

. When the freeze–thaw test results are analyzed, the highest mass loss in the block samples is observed in cotton-substituted samples. This can be explained by the fact that the water absorption of cotton is higher than pumice. Therefore, since the amount of water absorption increased, the highest mass loss after freeze–thaw was observed in CW-substituted samples. The use of hydrophobic CFF and SWW instead of pumice aggregate reduced the water absorption of the blocks and increased the frost resistance of samples. Vrána & Gudmundsson [96] stated that stone wool fibers are less affected by freeze–thaw than cellulosic fibers due to their hydrophobic properties.

According to TS EN 771-3+A1 (2015) [64], freeze–thaw resistance is not required if the product is fully protected against water penetration at the intended place of use (such as with an appropriate plaster layer or coating or use on the inner wing of the sandwich wall or interior walls of the building). However, this study has shown that the freeze–thaw resistance of blocks can be increased by using SWW and CFF.

4. Conclusions

In this study, the usability of pumice aggregate and 2.5–5–7.5–10% substitutes of CW (cotton waste), CFF (chicken feather fiber) and SWW (stone wool waste) in hollow block production was investigated. The following conclusions may be drawn from the data analysis:

• This study has shown that the deviation values of length, width and height are in accordance with the permissible deviation values according to the TS EN 772-16 (2012) standard. This shows that CW, SWW and CFF fibers can be used instead of pumice aggregate due to their compressible and moldable properties.
• According to the TS EN 772-13 (2002) standard, the gross density values of the block samples should not exceed a maximum of 1000 kg/m³. When the unit weight values are examined, it is seen that the unit weights of all fiber-substituted samples comply with the standard. Since the unit weights of the fibers used are lower than pumice, the gross weight of the block samples decreased as the fiber substitution rate increased. The lowest unit weight was obtained from the SWW-10 sample, with a value of 450 kg/m³, due to its low density. The use of lightweight blocks in buildings will result in a significant reduction in the dead load caused by the weight of the building itself, thus reducing the damage to the occupants during an earthquake.
• Although there is no compressive strength requirement for non-load-bearing partition elements, they are expected to have a robustness that will not deteriorate from the storage area to the usage area. When we look at the compressive strength results, it is seen that the strength decreases in CW and SWW substitution. (However, there is a 2.2% increase in strength in SWW-2.5 substitution compared to the reference sample.) In CFF-substituted samples, an increase of 5.1–9.6% in strength was observed due to the strong keratin structure of CFF.
• It is seen that the fiber-substituted block specimens have lower thermal conductivity (TC) values than the TC values required for traditional building elements used as partition walls today. The best TC value was obtained in the SWW-substituted specimens, which decreased by 12.5–24.6% compared to the reference specimen.
• Due to the high water absorption ability of CW, as the fiber substitution rate increased, the water absorption value increased by 5.3–14.9% compared to the reference sample. However, due to the hydrophobic character of SWW and CFF, the water absorption values decreased by 13–21.6% in SWW-substituted block elements and by 6.3–16.8% in CFF-substituted blocks.
• Freeze–thaw resistance is not required if the block elements are completely protected against water penetration, such as with a suitable plaster layer or cladding or use in the inner wing of the sandwich wall or in the interior walls of the building. However, SWW- and CFF-substituted block elements have reduced mass losses due to the freeze–thaw effect due to their hydrophobic character.

The results of this study clearly show that the CW-, CFF- and SWW-substituted block specimens have superior properties to the reference block specimen without fiber substitution produced under the same conditions. The produced blocks can be produced as lightweight blocks that can be properly molded, non-bearing, with satisfactory mechanical performance and freeze–thaw resistant due to low water absorption. At the same time, they will save on heating costs with their high thermal insulation value.