Effect of medium-density fiberboard wastes ash on calcium silicate hydrate crystal of concrete

ABSTRACT

Due to the high consumption of Medium-density fiberboard (MDF), waste products of this material are growing worldwide. In this research, the feasibility of using Medium-density fiberboard waste ash (MDFWA) as part of cement in concrete was investigated. For this purpose, 0, 5, 10, 15, 20, and 25% of the cement in concrete was substituted with MDFWA. For all design mixes, the water/blind ratio and the volume of aggregates were same. The slump, compressive strengths, SEM, EDX, TGA, DSC, and FTIR tests were conducted on the samples. At 28 days, the results demonstrated that the compressive strength of the sample containing 20% MDFWA increased by 13.6% compared to the control sample. Furthermore, the microstructure of the concrete show that the voids of the sample containing 20% MDFWA reduced compared to the control sample and also more calcium silicate hydrate (C-S-H) crystal formed.

Implications: The significance of the present paper is to solve the environmental issue caused by large amount of Medium-density fiberboard waste ash (MDFWA) and produce also sustainable concrete. In addition, the replacement of cement with MDFWA increases the compressive strength and enhancement of the microstructure of concrete due to extra C-S-H products. Therefore, the findings confirm that by using 20% MDFWA, a more eco-friendly production, denser, sustainable, economical, and stronger concrete would be achieved.

Introduction

Today, the recycle of waste materials is considered in the engineering (Katare and Madurwar 2020). Since cement production is economically expensive and greenhouse gases are generated, some waste materials have the potential to substitute a part of cement in mix design (Adak, Sarkar, and Mandal 2017; Li and Hu 2020; Memon and Khan 2018). Additionally, by reusing these materials, not only is the environment protected but also eco-friendly, green, and sustainable concrete is produced (Collivignarelli et al. 2020; Iswarya and Beulah 2020; Kuroki et al. 2019; Nguyen et al. 2020).

One engineered wood product is Medium-density fiber (MDF) which is created by residuals of soft-wood or hard-wood as wood fibers. These wood fibers are combined with a resin binder as well as wax and then shaped into panels by applying pressure at high temperatures (Spence 2005). The MDF are measured and packed after cooling. Today, in addition to soft woods, other materials such as cereal stalks, rice, straw, sugarcane, and recycled papers are used to make MDF (Spence 2005). MDFs are used amongst other things for flooring, cabinets, and furniture. MDF production in the world has increased due to rising demand. For instance, 100 million cubic meters were produced worldwide in 2018 (Hagel et al. 2021).

Due to changes in consumer behavior from perceiving furniture, cabinets and decorations as durable items to fashion commodity, there is a great deal of MDF waste in furniture making, home remodeling, cabinet making, and flooring applications. Approximately 50 million cubic meters of MDF waste was accumulated until 2016 (Irle et al. 2019). To prevent environmental pollution and improve resource efficiency, this large volume of waste can be reused particularly in the cement industry as pozzolanic material.

Cement factories worldwide produce 7% of the total CO₂ emissions by. Approximately more than 700 kg of CO₂ is produced from the making of cement with one ton weight (Tamanna et al. 2020). To prevent the production of this volume of CO2 emissions, cement replacing materials such as pozzolans can be used in concrete. The feasibility of using new pozzolanic materials has always been of interest to researchers.

Cement hydration is the reaction of the major components of cement, including tricalcium silicate (C₃S) and dicalcium silicate (C₂S), with H₂O resulting in the main products calcium hydroxide (C-H) and calcium silicate hydrate (C-S-H). In terms of rising strength, the C–S–H is more essential than C–H crystal. To delay corrosion, maintain a passive layer, and to preserve high concrete pH, the C–H crystal is important, but C–S–H enhances the compressive strength of cement-based materials (Faraj et al. 2020). By adding pozzolanic materials, additional calcium silicate hydrate creates and improves strength with increased curing time. Pozzolanic materials are silica and silica- aluminum materials that produce secondary C-S-H at normal temperatures if mixed with cement in the presence of water. Although pozzolanic concrete achieves its initial compressive strength more slowly than normal concrete, its ultimate strength is equal to or greater than that of normal concrete. Much research has been carried out on different pozzolanic materials such as fly ash (Branchn, Epps, and Kosso 2018; Hadi, Yu, and Al-Azzawi 2018; Hlaváček et al. 2018), rice husk ash (Chakraborty and Goswami 2015; Jung et al. 2018; Karim et al. 2013), wood ash (Chowdhury, Maniar, and Suganya 2015; Danraka et al. 2019; Pavlíková et al. 2018), and palm oil fuel ash (Awal and Shehu 2013; Salih, Ali, and Farzadnia 2014; Zeyad et al. 2016). According to the research literature, the feasibility of using MDF waste ash (MDFWA) as pozzolanic materials in concrete has not been investigated thus far. The question researched in this paper is whether MDFWA could be a replacement for the percentage of cement used in concrete.

The aim of this paper was to analyze the mechanical properties and undertake a microstructural analysis of concrete samples prepared by replacement of cement with 0, 5, 10, 15, 20, and 25% MDFWA. In all design mixes, the ratio of water to cement and the volume of aggregates were constant. To study the properties of the mixes, the fresh concrete slump and compressive strength, scanning electron microscope (SEM), energy-dispersive x-ray (EDX), thermo-gravimetric analysis (TGA), Differential Scanning Calorimetry (DSC), and Fourier transformed infrared spectroscopy (FTIR) of the samples were presented.

Materials and methods

Materials

Medium-density fiberboard waste ash (MDFWS)

Figure 1a shows raw medium-density fiberboard waste. In accordance with ASTM 305 (ASTM-C305-13 2013), the medium-density fiberboard wastes were dried in an oven at 80°C for 24 h. Next, dried medium-density fiberboard wastes were burned at 400°C for approximately three hours. In the third step, burned medium-density fiberboards waste were grinded and then by a 300-micrometer sieve were sifted. The specific surface areas, the medium particle size (D50), and the relative density of medium-density fiberboard waste ash (MDFWS) were 0.865 m ² /g, 9.00 μm, and 2.4 after grinding, respectively. In Table 1, the chemical compositions of cement and MDFWA analyzed by using the XRF test were tabulated. The chemical compositions of MDFWA depended on the type of original wood, its layer, resin and wax.

Figure 1. (a) Raw medium-density fiberboard wastes (b) MDFWS before grinding.

Table 1. XRF test of cement and MDFWS.

Chemical composition (%)	Cement	MDFWS
SiO2	19.87	48.56
CaO	63.22	26.56
Al2O3	4.19	2.87
Fe2O3	2.78	5.43
MgO	1.35	2.76
K2O	0.31	1.59
Loss on ignition (LOI)	-	1.89
Other	8.28	10.34
Physical properties
Specific gravity (g/cm^3)	3.15	2.79
Average size (Micron)	14	12

The chemical compositions in Table 1 illustrate that the SiO₂ component is high-level in the MDFWS material. SiO₂ component in MDFWS is 48.56. MDFWS is able to act with some part of CaO value of the cement which can generate secondary C–S–H crystal. Therefore, according to Reference (ASTM C618 2004), MDFWS can be classified as pozzolanic material. Furthermore, MDFWS contain 26.5% CaO, which can act as lime (Ca(OH)₂) (Salih, Ali, and Farzadnia 2014). Moreover, the value of losses on ignition (LOI) is less than 2%. Therefore, MDFWS material might be grouped as Class C ash according to Reference (Salih, Ali, and Farzadnia 2014). Additionally, Class C ashes can be replaced with cement in mixes at amounts of 5% to 50%.

In Figure 2, the XRD results of raw MDFWA with SiO₂ dominant phase are presented. As can be observed from this illustration, major phases of quartz diffraction were found. Furthermore, the locations of the major phases are between 20° to 40° (2 theta) due to an amorphous phase which has also been reported in other pozzolanic materials (Ibrahim et al. 2017; Salih, Ali, and Farzadnia 2014; Shahbazpanahi and Faraj 2020; Shahbazpanahi et al. 2021). To identify the microstructure of raw MDFWA, the SEM image is shown in Figure 3 by a TSCAN machine with 1.2 nm resolution. Separated shaped particles, irregular, crushed form, and rough surface were observed in raw MDFWA; however, holes can be observed in the SEM image. The microstructure of raw MDFWA has been reported in some pozzolanic materials (Adebakin, Gunasekaran, and Annadurai 2018; Shahbazpanahi 2019).

Figure 2. XRD pattern of raw MDFWA.

Figure 3. SEM images for raw MDFWA.

TGA test was performed to determine the weight loss of raw MDFWA. Figure 4 shows the TGA test results by Linseis (L81A1750) machine. Due to decomposition, the mass loss of raw MDFWA began at temperatures of 52 to 839°C. Due to the mixed water from C-S-H and dehydration of Ca(OH)2, the important mass loss occurred at approximately 427 to 460°C. This phenomenon has also been reported in previous work on pozzolanic materials (Salih, Ali, and Farzadnia 2014; Shahbazpanahi and Faraj 2020; Shahbazpanahi et al. 2021).

Figure 4. TGA test of raw MDFWA.

Cement, water, and aggregates

Type one Portland cement (grade 32.5) was used with 3.15 g/ cm ³ specific gravity at 100 min setting time and 2970 cm ² /g Blaine fineness according to ASTM C150 A (1999). Kurdistan Cement Company supplied the Portland cement consumed in present investigation the chemical and physical properties of which are listed in Table 1. Normal tap water with PH equal to 7 was used in the mixes. Crushed aggregates were consumed as the coarse aggregates of the mix with 0.30% water absorption, 2.7 relative density, and 12 mm maximum size. In the concrete mix design, the sand consumed had 0.42% water absorption and 2.35 relative density, according to ASTM C127 (1993) and ASTM C128 (2004). The grading diagram of aggregates used are shown in Figure 5.

Figure 5. Grading diagram of aggregates consumed in concrete samples.

Mix design of concrete

To reach the study aims, water/binder ratio, aggregate amounts, and all conditions were kept constant for all specimens. A partial of the cement was replaced by 5, 10, 15, 20 and 25% of MDFWA. Samples were classified in six groups including a control group (without MDFWA) and groups with 5, 10, 15, 20 and 25% with MDFWA replacement. To reduce error, five samples for 7, 28, and 90 days were made (Shahbazpanahi and Faraj 2020). The concrete mix design is shown in Table 2. In all the mix designs, the water to binder ratio and value of total binder were 0.25 and 400 kg/m³, respectively. To prepare samples of concrete, initially, coarse and fine aggregate were mixed for 3 minutes in a drum mixer. Then, MDFWA was added and mixed for 4 minutes, followed by adding water slowly. The drum mixer was continued for 5 minutes and then covered with a wet blanket for 1 minute (ASTM C511 2013). The next stage involved measuring fresh concrete slump; the concrete was poured in molds. The specimens were coated with plastic sheets for one day. In the last stage, according to ASTM C511 (2013), molds were separated, marked and cured in water tile testing days.

Table 2. Mix proportions.

Mix design	Cement kg/m^3	Water kg/m^3	MDFWA kg/m^3	Coarse aggregate kg/m^3	Fine aggregate kg/m^3
Control	400	100	0	990	815
MDFAW 5%	380	100	20	990	815
MDFAW 10%	360	100	40	990	815
MDFAW 15%	340	100	60	990	815
MDFAW 20%	320	100	80	990	815
MDFAW 25%	300	100	010	990	815

Results and discussion

Slump test of fresh concrete

In accordance with ASTM C511 (2013), slump test results of fresh concrete are shown in Figure 6. The control specimen had 61.1 mm slump value. The slumps were reduced to 57.2, 54.4, 52.1, 47.4, and 47.3 mm for samples with 5, 10, 15, 20, and 25% of MDFWA replacement, respectively. Due to the small size, pozzolanic properties and higher specific surface area of the MDFWA, replacement of cement with MDFWA leads to a decrease in the slump. Similar performances have been reported in earlier work on pozzolanic materials (Farajr, Sherwani, and Daraei 2019; Omrane et al. 2017; Siddique 2012; Sun et al. 2019).

Figure 6. Fresh concrete slump.

Compressive strength of samples

Based on ASTM C39 (ASTM C39/C39M 2014), compressive strength test results at 7, 28, and 90 d are shown in Figure 7. The control sample compressive strength was 28.1 MPa at the age of 7 days. However, at early age, compressive strengths of samples containing 5, 10, 15, 20, and 25% MDFWA were 26.7, 25.3, 23.2, 22.2, and 22.1 MPa, respectively. Due to a delay in the process of hydration by using a higher value of MDFWA, compressive strengths were decreased at the age of 7 days. A same procedure was also reported in previous research on other concrete material containing pozzolanic materials (Ahsan and Hossain 2018; Jang et al. 2018; Shahbazpanahi and Faraj 2020). The reason for this delay is the alkali activation released from the cement at early ages which stops the formation of C-S-H (Salih, Ali, and Farzadnia 2014; Zhang et al. 2017). Therefore, the incorporation of 20% MDFWA replacement decreased the compressive strength by 16.8%, relative to the control sample at age of 7 days.

Figure 7. Results of compressive strength tests.

At 28 days, 5, 10, 15, 20 and 25% MDFWA-replacement led to compressive strength of 32.9, 33.2, 34.7, 35.3, and 35.1 MPa, respectively. The compressive strength of the control sample was 31.5 MPa at 28 days. Therefore, with 20% MDFWA replacement, at the age of 28 days, the compressive strength was increased by the value of 13.6%. Improvement of the compressive strengths can be due to three reasons: first, the presence of high-level value of SiO₂ in MDFWA replacement (Table 1) which reacts with the CaO of the blind and raises the value of C-S-H formation (Li, Farzadnia, and Shi 2017; Shahbazpanahi et al. 2021). Second, MDFWA fine particles might be used as filler materials and fill pores, voids, and interfacial transition zone (Salih, Ali, and Farzadnia 2014; Shahbazpanahi 2019). Third, the presence of high-level value of CaO in MDFWA (Table 1) could act as lime (Tamanna et al. 2020; Thomas, Hasan, and Arel 2017). In Figure 7, it can be observed that the compressive strength of 25% MDFWA-replaced sample increased by 12.7% that is less than the amount corresponding for 20% substitution. This could be due to the absence of enough cement for producing the hydration procedure due to the high value of MDFWA. As a result, cement replacement with 20% MDFWA resulted in the best compressive strength at the age of 28 days. This pattern was also observed at 90 days. For instance, cement replacement with 20% MDFWA rose the compressive strength by 15.6% relative to the control specimen at 90 days.

SEM image

The SEM image is presented in Figure 8 for the control sample and in Figure 9 for the sample containing 20% MDFWA at 28 days. Figure 8 depicts C-H, micro-cracks, voids, partially reacted particles, interfacial transition zone (ITZ), and non-activated material (Farzadnia et al. 2018; Ibrahim et al. 2017; Shahbazpanahi et al. 2021). Due to the existence of abundant lime in the cement, non-activated materials were formed (Salih, Ali, and Farzadnia 2014). Amorphous phases could just be detected on the control sample surface which has been reported in previous research (Pan et al. 2019). As observed from Figures 8 and 9, replacement of cement with 20% MDFWA decreases the voids, micro-cracks, and non-activated material. It was also observed that 20% MDFWA replacement increases the C-S-H formation and crystal phase. Compared with the control sample, the Si amounts in the MDFWA could increase the C-S-H formation. The results of SEM images clearly define the recorded compressive strength.

Figure 8. SEM image of the control sample at 28 days.

Figure 9. SEM image of the sample containing 20% MDFWA at 28 days.

EDX results

To recognize the components in the samples at 28 days, EDX test was conducted. The EDX results of the control and 20% MDFWA-replacement sample are shown in Figures 10 and 11, respectively. The main chemical components include Ca, Si, Fe, Na, K, and O as shown in the diagrams. Components identified by the EDX test matched to the properties of MDFWA (See Table 1). According to Figure 10, the Si amount is lower than that of the Ca amount, while a reverse trend is observed in Figure 11. The extreme intensity of Si in the EDX test of samples containing 20% MDFWA and a very small intensity of other components could display that MDFWA led to C-S-H formation (Vishwakarma and Ramachandran 2018) and not creating other weak structures (Pan et al. 2019; Salih, Ali, and Farzadnia 2014; Shahbazpanahi and Faraj 2020).

Figure 10. EDX of control sample at 28 days.

Figure 11. EDX of20%MDFWA-replacement sample at 28 days.

TGA test

Figure 12 displays the TGA results of the control and 20% MDFWA-replaced samples at 28 days at range of 32–839°C. Due to free water and the bound hydration at the first stage, loss of heat at ranges 60 −70°C occurred (Salih, Ali, and Farzadnia 2014; Shahbazpanahi and Faraj 2020). In the next stage, main loss of heating at ranges 4790 to 4900°C occurred due to Ca(OH)₂ dehydroxylation (Pane and Hansen 2005). As a result of de-carbonation, the decreasing trend continued slightly in the last stage. It was also observed that the 20% of MDFWA replacement in the control samples increased the mass loss due to the formed C-S-H. Furthermore, due to pozzolanic reactions, the rate of hydration increased by using 20% MDFWA replacement at 28 days. Such an effect has also been reported in earlier research on pozzolanic materials (Alehyen, Achouri, and Taibi 2017; Branchn, Epps, and Kosso 2018; Farzadnia et al. 2018; Shahbazpanahi and Faraj 2020; Shahbazpanahi et al. 2021). The results of the TGA test were in agreement with those of the compressive strength, SEM, and EDX tests.

Figure 12. Results of TGA test of control and 20% MDFWA-replaced samples.

DSC thermograms

To recognize the endothermic peaks, the DSC thermogram was measured with NETZSCH Company, HP-Phoenix 204 instrument. The release of waters of raw MDFWA with minimum energy was measured by DSC diagram in Figure 13. As can be seen from this illustration, the mass change of raw MDFWA was detected at approximately 100°C due to moisture evaporation previously reported in other Pozzolanic materials (Alehyen, Achouri, and Taibi 2017; Alsubari et al. 2018; Salih, Ali, and Farzadnia 2014). Furthermore, DSC analysis of control and MDFWA 20% samples at the age of 28 days are shown in Figure 13. One main endothermic peak can be observed in Figure 13. This main peak centered at 105°C and 99.28°C for the control and MDFWA 20% samples, respectively due to the evaporation of bound water, degradation of C-H, and C-S-H dehydration (Salih, Ali, and Farzadnia 2014). The endothermic results were −4.32 and −8.13 for the control and MDFWA 20% samples, respectively. In addition, Figure 13 demonstrates that as 20% of MDFWA was added to the mix, extra energy was required for degradation of C-H to the C-S-H crystal. The increase of the endothermic peak of MDFWA 20% sample displays the better degradation of C-H and more stable system compared with the control sample (Farzadnia et al. 2018; Pacewska and Wilińska 2020). The results of the DSC test for raw MDFWA illustrates only one major peak due to pozzolanic activity at 105°C which has been reported in previous work (Salih, Ali, and Farzadnia 2014). The findings of the DSC thermograms are like-minded with the results of the TGA tests.

Figure 13. Results of DSC test of row MDFWA, control, and 20% MDFWA-replaced samples.

FTIR test

To study the important variations in the location of C-S-H peaks, the FTIR test was used. Figure 14 shows the FTIR test at the range 2400–600 cm⁻¹ for the control and the 20% MDFWA-replaced samples after 28 day. The bending stretch over the range 1665–1693 cm⁻¹ is due to being associated with H-O-H (Liu et al. 2016; Shahbazpanahi et al. 2021). As can be seen from Figure 14, replacement with 20% MDFWA has the effect of increasing bending stretch. MDFWA porous resulted in increased water molecules in this bond (Salih, Ali, and Farzadnia 2014). It was also observed that another asymmetrical -OH bond was vibration bands at 1416 cm⁻¹ which has also been previously reported (Fernández-Jiménez and Palomo 2005; Shahbazpanahi et al. 2021). The next peak at range of 960–1200 cm⁻¹ could denote Si–O stretching vibration. The latter peak was detected at the range 680–800 cm⁻¹ which is distinctive. This strong bond might be attributed to symmetric Si–O–Si stretching vibration. The Si–O–Si bond has been reported in previous research on pozzolanic materials (Salih, Ali, and Farzadnia 2014; Shahbazpanahi 2019; Shahbazpanahi et al. 2021). This band denotes the structure of C-S-H (Salih, Ali, and Farzadnia 2014). Therefore, the results showed that a greater amount of C-S-H was formed by the presence of 20% MDFWA. The results from the FTIR test demonstrated that MDFWA was a pozzolanic material to use as partial cement replacement.The results from the FTIR test were in agreement with those of EDX, TGA, and DSC observation.

Figure14. FTIR results of control and 20% MDFWA-replaced samples.

Conclusions

To use partial substitution of cement in mixes design, the present investigation presents MDFWA as pozzolanic material. Mixes design were prepared by replacement of cement with MDFWA in the volumes of 0, 5, 10, 15, 20, and 25%. To do so, the slump of the fresh concrete, compressive strength, SEM, EDX, TGA, DSC, and FTIR tests were performed. Accordance with the results of the tests, the following conclusions were reached:

• The results of test on raw MDFWA show that it can be used as partial replacement material for cement.

• The results of the fresh concrete test illustrate that the slump of the control sample was greater than that the sample containing MDFWA.

• Compared with the control sample, MDFWA-replaced sample demonstrated less compressive strength at 7 days.

• With 20% MDFWA replacement, the compressive strength was increased by 13.6% relative to the control sample at the age of 28 days. In addition, higher replacement amounts of MDFWA improved only the compressive strength until 12.7%. The same trend for compressive strength was observed at 90 days.

• SEM test indicated that the 20% MDFWA decreases the number of voids, micro crack, and non-activated material. It was also observed that 20% MDFWA replacement increases the C-S-H formation and crystal phase.

• The results of EDX test showed the amount of silica in the sample containing MDFWA was greater than the Ca intensity and new components. This might induce the secondary C-S-H formation and usage of MDFWA as pozzolanic materials.

• As recognized by the FTIR test results, cement replacement by 20% MDFWA enhances the bands related to C-S-H formation.

• The results of DSC test showed that the increase of the endothermic peak of the sample containing 20% MDFWA displayed better degradation of C-H and a more stable system compared with the control sample.

• Therefore, the findings confirm that by using 20% MDFWA, a more eco-friendly production, denser, sustainable, economical, and stronger concrete would be achieved.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

The data that support the findings of this study are available from the corresponding author upon reasonable request.

Additional information

Funding

This research received no external funding.