A comprehensive study on the fire resistance properties of ultra-fine ceramic waste-filled high alkaline white cement paste composites for progressing towards sustainability

The most practical sustainable development options to safeguard the local ecology involve reducing the use of raw materials and guaranteeing proper recycling of the principal destroyed solid wastes. Preventing the creation of hazardous waste and the subsequent pollution that results from improper disposal is a top priority. Based on this, the study's authors recommend reusing the ultra-fine ceramic shards (CW). High-alkaline white cement (WC) has been partially replaced by ultra-fine CW because it is a cheaper, more abundant, and more lasting environmental material used in the production of trendy blended white cement pastes composites. In this context, we look at ultra-fine CW, a material that has been suggested for use as a hydraulic filler due to its high performance, physicomechanical qualities, and durability. XRF, XRD, FTIR, and SEM measurements are used to characterize the microstructure, thermal characteristics, and thermodynamics. Because of the effect of ultra-fine ceramic waste, the firing test reduces the mechanical strength by default, but with active filler, decreases slowly and increase its physicomechanical features and compressive strength compared to the control sample (WC), setting a new benchmark. The maximum amount of crystallization formed in the presence of ultra-fine ceramic waste in WC-matrix, resulting in a decrease in total porosity and early cracking. Together, the improved workability and energy-saving features of cement blends with ultra-fine ceramic waste, reflect their economic and environmental benefits, which may reduce building costs and boost the durability of the raw materials used in the mix.


Laboratory program Materials
The primary components used in this experimental protocol are ultra-fine ceramic waste (CW) and high-alkaline white cement (WC).CW came from El-Gawhara for ceramic and porcelane company (GCPCo), El-Saddat (Monfita, Egypt), and white ordinary cement (grades I, 52.5 R) came from Saini Cement, Cementier Holding Cement Company (CHCo.),Saini, Egypt.Table 1 displays the results of a comprehensive X-ray fluorescence (XRF) study of the raw materials.According to the bag of cement and confirmed by XRF analysis, the sodium equivalent of high-alkaline white cement is less than 0.6%.Ball milling the CW for 6 h yielded enough fine powder for microscaling.The particles sieved through a 45 µ sieve mesh.In addition to its physical and mechanical features of ultra-fine CW, are indicated in Table 2, the specific surface area determined by the fineness test, according to ASTM, C430-08 30 , was 4815 cm −2 g.The SEM and TEM images of CW were displayed in Fig. 1a,b.This study revealed that CW particles were spherical in shape, with sizes between 100 and 200 nm.
Mixing followed by cast using stainless steel molds with dimensions; (25 mm × 25 mm × 25 mm), start the hydration in 99 ± 1 percentage humidity (RH) at 23 °C.After 24 hs, prisms were stiffening and immersed directly  www.nature.com/scientificreports/ in tap fresh water for up to 28 days of continues hydration then thermally treated at varied temperature scales (250 °C, 500° C and 750 °C) as shown visually during synergistic process in Fig. 2. Our experimental study, described in greater detail elsewhere 31 , followed the ASTM standard, which highlights the significance of RH; on the hydration kinetics of the specimens.Estimates were made of the changes in compressive strength, porosity, and whiteness reflection that occur in white cement pastes under a wide range of high temperature conditions.Triplicate tests were run on the material's Compressive Strength (CS) in accordance with ASTM C109M 32,33 , with weight 5.00 tons and rating 20 kg per minute by (Shemizitu Machine test) with a loading rate of 25 kg/min.Reflectance measurements of whiteness (Ry) were taken using Elerpho French equipment in accordance with DIN 5033 standards 34 .Mercury intrusion data was used to complete the solidification of the prisms (porosity %, for example).Based on three different weightings, first, the dried sample was weighted (m1), after that, the sample is weighted after eliminating the air, using a desiccator, and saturated in a water tank for 72 h: denoted (m2).Third, the saturated sample is wiped superficially to remove surface water: denoted (m3).Finally, the sample total porosity is given as follow:

Physicals and mechanicals properties CW
Pore diameters were recorded and characterized, with a baseline established for each (macro-pores larger than 3500 nm, micro-pores in 0-15 nm, and meso-pores from 15 till 3500 nm) 35 .The small pieces from the burnt specimen was saved for later X-ray, infrared, and scanning electron microscopy (SEM); examination.In Fig. 3, we can see the experimental plan's scientific outline.

Instrumental Analysis
Specimen morphology conducted with (FEI Company, Netherlands) integrated with EDXA namely, "an energy dissipation X-ray analyzer".Other fired samples were pulverized, stored, dried, and passed from 25 µm mesh to (1) www.nature.com/scientificreports/determine the hydration phases after firing using X-ray diffraction (XRD, Philips PW3050/60) diffracto-meter order; 5 and 50 (2Ø), speed rate of 1 s step −1 and high resolution accuracy of 0.05° step −136 .The transmission electron ultra-microscopy (TEM) instrument reported that the effective particle size for CW is 100-200 µm.This indicated that, CW in micro-size powder, as shown in Fig. 1b, which a suitable particle size form mesopores of the WC blends.

XRD-patterns
Composites WC-pastes with CW powder hydrated for 28 days, then excesses to elevated temp. up to 750 °C, the phases of curing showed in Figs. 4 and 5, respectively.By using XRD-patterns the number of hydration, products before and after firing were evaluated.The X-ray diffractograms beaks showed that the hydration phases  mainly depended on the amount of CW content especially late ages of hydration 37 .Firstly, thee XRD-patterns of M5/500 °C, M5/750 °C, M0/500 °C and M20/750 °C plotted in Fig. 4. Clearly, the main hydration products responsible for compressive strength and bulk density such, as C-S-H and calcium hydroxide (C-H), were observed in all mixes with different ratios.Which responsible about the compressive strength and increase in the bulk density for both M0 and M5 at different thermal temperatures 38 .Due to the high replacement effect M20/750 °C caused low strength with the high total porosity.This may be attributed to the presence of high quartz content (un-reacted silica) appearing in the XRD patterns.The mixes containing 5.0% wt% of WCs fired at (M5/500 °C and M5/750 °C) presented highly C-S-H phase intensity comparing with anther mixes (M0/500 °C and M20/750 °C).This confirmed the results of compressive mechanical strength and high firing resistivity of the M5 blend.
Figure 5 shows the XRD patterns of hardened M0/250 °C, M5/250 °C and M20/250 °C pastes after 28 days of hydration.This proves that M5/250 °C shows higher workability and synergist properties verses M0/250 °C and M10-20/250 °C mixes.It can be attributed to; M5 has the maximum fill index, then other composites where further replacement has lower hydraulic impact and poor fire resistance.This might explain the high intensity peak of both C-S-H along C-A-H, in the case of M5/250 °C-mix.Additionally, M20/250 °C-mix possess low synergetic features as the dilution effect.This dilution led to high porosity with low firing resistivity.In the following order M5/250 °C > M5/500 °C > M5/750 °C > M20/250 °C ˃ M0/250 °C ˃ M20/750 °C ˃ M0/500 °C ˃ M0/750 °C, represent the synergic resistance features which is confirmed by other works too 39 .

FTIR spectra
Figure 6 shows the results of FTIR analysis performed on mixtures of M0/250 °C, M5/250 °C, and M20/250 °C.The symmetric and asymmetric O-H single bond found in water, yielding calcium hydroxide (C-H), is the source of the band at 3641 cm −1 .After being heated to 250 °C, the spectral absorption band at 1650 cm −1 in M0 was found to be related with ettringite.While the absorbance band vanished after being heated, the XRD data were consistent with the breakup of ettringite at high temperatures, demonstrating its thermal instability.Silica absorption bands emerge at 469 cm −1 , 785 cm −1 (present in the non-hydrated cement), and 1052 cm −1 (present in the hydrated cement) 40 , which is an intriguing finding illustrated by the two dotted lines.The polymerization of SiO 2 four units in Alite (C3S) and Belite (C2S) was responsible for this finding.M5F has the greatest and broadest absorption at 1050 cm −1 .This is consistent with the results of the compressive strength tests, and it may be attributable to the addition of the right amount of CW, which resulted in greater compressive strength compared to the others.As can be seen in M20F, the addition of additional CW decreased the compressive strength because of the presence of too much unreacted SiO 2 .
Comparing the spectra of control sample M0 with M5F at incarnation temperature 250 °C and 750 °C respectively, it is evident that a portion of C-H was re-structured to carbonate and the decomposition above 750 °C, band intensity decreased 41 .Finally, the intensity of C2S band was increased by raising the temperature and viceversa.The FTIR spectra of M5F as shown in Fig. 7 demonstrated a similar evolution as those of M0.Compared to the FTIR spectra of M5F, the peaks related to the vibration of O single bond − H in C-H at 3641 cm −1 cannot be observed in all FTIR spectra of M0.This demonstrates that C-H is used up in the pozzolanic process and that CW's pozzolanic activity is activated by heat.Eventually, ceramic waste replacement up to 5.0 wt% is suitable and reflects improved performance and energy saving qualities, lead to reduced construction costs and higher sustainability of raw materials.

Compressive mechanical strength (CMS)
Results of CM's verses during periods for WC-pastes incorporated with ultrafine-CW at different thermal temperatures are depicted in Fig. 8.As shown in figure, the CM's of specimens blended with or without ultrafine-CW at various thermal temperatures increased with increasing hydration age.For hardened prism still 5% (M5F) replacement at 25 °C, the blend's compressive mechanical strength increases with hydration progress yielding extra products, leading of extra species of hydration products, particularly C-S-H, which is responsible for solidification features 42 .When tested against other mixtures and the neat sample (M0), the hardened paste M5F had the highest mechanical compressive strength.It might be concluded to the Pozzolanic features of CW during the late age of the hydration process, consuming high content of Ca(OH) 2 accompanied by extra production of C-S-H gel, where it was observed as (honeycomb-like) on WC-surface and pores as the nucleation effect leads to densification in microstructure 43 .www.nature.com/scientificreports/speeds up the hydration process of the un-hydrated WC-clinker.Clearly, all WC-pastes benefited from the tested temperature range of 0-250 °C.In addition, self-autoclaving WC-pastes increases the polymerization degree of C-S-H 41,44 .At temperatures as high as 750 °C, compressive strength significantly decreased.This is mostly because the strength-giving hydration stages have broken down.In contrast, M5F had the maximum compressive strength at both 500 and 750 °C during firing, and it was the strongest overall.This is because an excessive amount of hydration products formed, which countered the firing effect.When compared to the M5F-mix, all of the WC-pastes in which 2, 5, 10, 15, and 20 weight percent of CW was substituted had the same syndrome: low fire resistance across the board.This is attributed to the increment of WC-pastes porosity due to the highest coarsening of MF's pore size distribution and decomposition of hydrated phases, formed an amorphous Portlandite (poor crystalline structure) and Gehlenite (Ca 2 Al 2 SiO 7 ); at thermal load up to 750 °C.However, the M20F mix presented the lowest compressive strength regression especially, at 500 °C and 750 °C.This is explained the dilution of WC-matrix with low hydration products.It can be proven that, each hydration product and the compact are central to the variations in compressive strength under firing temperatures 45 .

Total porosity (TP)
After 28 days of hydration and exposure to increased temperatures up to 750 °C change in porosity is calculated.Figure 10 displays the differences in porosity between blended WC-pastes with and without CW.Up to 250 °C, it was evident that the porosity of all WC-pastes (with or without CW) was slightly reduced.Self-autoclaving WCpaste is a process that reduces the number of micro-pores in the material's matrix.On the other hand, for all WCpastes, porosity differences greatly increased after 250 °C, especially at 750 °C.The expansion and proliferation of microscopic holes and fissures is to blame.An increase in the crystallinity degree (CD) of hydration products (HP) occurs at higher temperatures, and this is manifested as the formation of open pores in the WC-matrix 46 .
In comparison to the other mixtures, the WC-paste with 5.0 wt% CW (M5F) showed the least amount of porosity across the board.The impact of CW, which closes down pores and reduces micro-cracks, is responsible for this.These results tied in with the ones for compressive strength and demonstrated the universal link between the two variables.When comparing M20F and M15F pastes, it was clear that a different pattern emerged, with the M20F sample displaying the maximum porosity up to 750 °C.These results shed light on why CW affects the permeability of WC-pastes.Lower porosity WC-pastes had greater firing resistance and compressive strength.These findings validated the probity and firing resistance of CW, which were a reflection of its filling and nucleating capabilities 47,48 .

Weight loss
Weight loss identification is an important parameter to be noted while adding any supplementary materials.and exposure to increased temperatures up to 750 °C.Notably, the weight loss variation for all pastes dropped up to 500 °C, then increased up to 750 °C, as the temperature was increased.This is accompanied by the fire effect, which causes the disintegration of hydration products and the loss of free water (FW) at 100 °C and combined water (CPW) up to 600 °C.At 250 and 500 °C, all WC-pastes showed the lowest weight losses regardless of whether or not they contained CW.This points to a drop in FW and CPW proportions.Weight loss was greatest for the M20F mixture, despite its high CW content, and lowest for the M5F sample.This lends credence to the idea that CW-filling causes an excessive amount of hydration products (HP) to be present in the WC-matrix.This forms C-S-H and Ca (OH) 2 which decompose at around (300-400 °C).According to instrumental analysis in the previous figures, CaCO 3 was formed as a hydration product resulting from CW-hydration and normal carbonation [49][50][51] .This product begins to decomposition at 600 °C.This confirms the increment in weight loss at 750 °C in case of M20F comparing with M5F.The weight losses of WC-Pastes containing CW except M20F are lower than this paste (M20F) and the control sample (M0).especially at 500 °C.This may be attributed due to the presence of additional hydration products (C-S-H and C-H) in WC-matrix, which are de-hydroxylated at range (300-400 °C) 52 .

Whiteness reflection (Ry)
While CW appeared white after milling, its reflectance using the "Elerpho" apparatus was inadequate, normally on the Rz-axis that causes green color reflection, as shown visually in Fig. 12: Ha = − 7.23 (very pale yellow) versus Ha = − 1.06 (very crimson green white).This solid proof supports the role of consumption in the reversal of the whiteness reflection of the blends (Ry).Table 4 and Fig. 13 show the findings of measuring the Ry; of WC incorporate with ultra-fine CW powder.Elerpho reflected that the whiteness reflection values were decreasing with an increasing in the CW powder content.It can be summarized as: Ry-M0 > Ry-M2.5F> Ry-M5F > Ry-M10F > Ry-M15F > Ry-M20F, conform to DIN 5033 (relative to 100% Rx, Ry and Rz) 53 .The Ry; values vary from 86.70% of (M0) for WC without CWpowder to 80.11% of (M20F) with increasing the content of CW-powder replacement.Moreover, the whiteness level of (M2.5F) reported a better green reflection on Rz-axis value by 85.90%.This can be attributed to, the negative green reflection and positive yellow reflection of CW-powder, which equal to 82.25%, may marginally affect the whiteness level of WC-blends.Frankly, CW can be proposed as a possible additive for the production of white cement up to 5%, without any negative defects at the level of whiteness of the final product [54][55][56] .After 28 days of curing blends have been fired at different thermal temperatures.Small species were collected to check the whiteness reflection level; it was noticed that all blends have affected negatively after firing.Ry of WC shows the best performance, i.e.: Ry slightly moved from 86.70 to 86.10.In the contrary; others Ry results decrease by 4.09, 5.30, 6.24, 8.67 and 10.62 respectively for M2.5F to M20F.XRF analysis of CW shows high content of ferric oxide higher than WC content by 92.70%, which may have a stronger effect on Ry reduction of blends after fire, ferric turns into ferrous, i.e.: turns pale yellow orange-red when heat treated.

Morphology and microstructure
The microstructure variations during thermal treatment from 250 °C up to 750 °C, were examined by SEMphotos as shown Fig. 14.According to compressive strength results, 500 °C is regarded as a critical firing temperature, that determines the dual effect of nucleating and Wt., percent CW on the performance of WC-pastes under elevated temperatures.It can be shown that more densification in the microstructure in the case of firing at 250 °C reflected a significant effect on the performance of WC-pastes under elevated temperatures [57][58][59] .The SEM-photos proved the higher compaction of M5F at 250 °C microstructure compared with M0 and M20F at the same temperature, confirming the positive impact of CW on the microstructure densification as well as the performance under elevated temperatures.The SEM micrograph of the paste made from neat WC at 250 °C reveals the formation of well-developed hydration products such as calcium hydroxide (C-H) crystals intermixed  www.nature.com/scientificreports/with small wrinkled fibres of calcium silicate hydrate (C-S-H); and calcium sulphoaluminate hydrate (Ettringite).Besides, the pore spaces are still available for depositing new hydration products 60 .In the same direction, the morphology of M5F fired at 500 °C found to be denser with more compact than M0 and M20F at the same temperature.This confirms the fact that, the composition of cementitious materials as binder represents as good impact on the firing resistivity.Although CW has a good effect on microstructure densification due to its increased nucleating sites effect, the microstructure of all mixes at 750 °C appears to be less compact than the

Conclusion
The improvement of solid waste recycling to produce eco-cement is a goal of the sustainability aspects which is practiced by many researchers.One of the way to use waste materials is to impregnate them in productive materials such as concrete, building materials etc. Huge quantities of ceramic waste produced as byproduct of industries need to be utilized and it need further research to maximize its benefits.This work represents one such solution of reuse of the CW as a complementary raw material in white cement production without a negative impact on its whiteness reflection (Ry) degree.Five suggested patches of cw were studies, physico-mechanical features and microstructure investigations were studied to understand the impact of adding ceramic waste into white cement.Combination M5F reported increases in mechanical strength, whiteness reflection (Ry), setting and synergetic properties compared to others mixes.WC replaced by 2.5, 10, 15 and 20 with a weight of CW shows a similar syndrome; poor thermal resistivity, which may have attributed to increases in paste porosity and the decomposition of hydrated phases form of amorphous Portlandite (poor crystalline structure) and Gehlenite (Ca 2 Al 2 SiO 7 ); at thermal load up to 750 °C leads to crack formation and decreases of its strength values.It recommended that 5.0% of CW is applicable with additional physic-mechanical features.This work provides information related to the dosage and method of utilizing ceramic waste into cement production.

Figure 3 .
Figure 3. Methodology flow chart indicating the research method.

Figure 11 Figure 10 .
Figure 10.Porosity of blended WC-pastes with or without CW of 28 days of hydration at different thermal temperatures

Figure 11 .
Figure 11.Variation of weight loss of blended WC-pastes with or without CW of 28 days of hydration at different thermal temperatures.

Table 4 .
Ry for pastes on dray base.