3.1. Material characterization
The XRD patterns previously carried out for activated alum sludge waste changed significantly after being subjected to calcination at a temperature of 500 oC (AAS). The XRF for the chemical oxide compositions of OPC, the mineralogical phase compositions of OPC, and the oxide composition of AAS are outlined in Fig. 1. The pozzolanic activity of activated alum sludge waste (also known as AAS) was evaluated following the TS 25 standards by ensuring that it met the chemical and physical requirements of standards that apply to typical pozzolanic material. This was done to determine whether the waste possessed pozzolanic activity. The TS 25 standard suggests that SiO2 + Al2O3 + Fe2O3 should be at least 70%, that SO3 should be less than 3.0%, that CI should be less than 0.1%, and that the XRF study of AAS highlights the capacity of employing activated alum sludge waste (AAS) as supplemental cementitious materials (SCM) with qualities equal to those of a typical active pozzolanic material. In addition, the standard suggests the fact that XRF analysis was performed on the AAS brings this point home very clearly 49.
This investigation made use of a superplasticizer (SP) that was a modified polycarboxylate-based superplasticizer (PCsp) called Sika Viscocrete 5230 L. It has a specific gravity of 1.08 g/ml and was supplied by Sika Company in El-Obour City, Egypt. The evaluation investigated the effects of using an SP. SP superplasticizer is utilized not only as an agent for dispersing the nanoparticles but also to achieve the necessary level of workability in a variety of pastes. This is accomplished by utilizing the superplasticizer's dual-functioning ability to both disperse and work with the nanoparticles. The physical properties of the SP superplasticizer are broken out in further since its color is yellow-brown liquid, the percentage of solid residue is about 39.9%, the pH is ranged from 7.51 to 7.53 and finally, its specific gravity is about 1.08 g/ml. CuFe2O4 spinel nanoparticles (CFs NPs) with a nanoparticle size of 200 nm were created following the previously described approach as follows: utilizing commercial types of reagents and beginning components to lower the economic cost.
To determine whether the mixture was homogeneous, two moles of pure fine powder ferric acetate basic ((CH3COO)2 FeOH) were thoroughly combined in a ball mill for six hours with one mole of copper (II) acetate monohydrate ((CH3COO)2 CuH2O) 50. Following that, the mixture was dried at a temperature of 150 oC, and the sample was heated on a hot plate so that the acetates could be broken down more easily. To get copper ferrite nanocrystals, the sample was finally subjected to a two-hour-long heating process at a temperature of 100 oC. using SEM, the CFs NPs that had been produced at a size of 200 nm were subjected to a mechanochemical degradation process, which resulted in the generation of CFs NPs that had an average particle size of less than 50 nm as seen in Fig. 2.
The material was ball milled for forty hours to achieve this result, and then it was subjected to two hours of progressive heating in a muffle furnace at temperatures ranging from 300–500 oC. The CFs NPs that were obtained had a size of 50 nm and had a value of 39.1 emu/g for their saturated magnetic flux density (Bs), and 4.002 emu/g for their remnant magnetic flux density (Br), and 85.56 Oe for their high coercivity. Additionally, the CFs NPs had a value of 39.1 emu/g for their remnant magnetic flux density (Br) (Hc). The investigation revealed that it preserves a purity level of at least 99.0% throughout its operation. The characteristics and the general properties of CuFe2O4 spinel nanoparticles are studied since their crystallite size is about 49 nm, the remnant magnetic flux density is about 4.002 B r (emu/g), as well as the saturated magnetic flux density, is about 39.11 Bs (emu/g), and finally, its high coercivity is about 85.56 Hc (Oe). (CFs NPs). The design and the percentage composition of the different mixtures are outlined in Fig. 3.
3.2. Water absorption
The results of this experiment are depicted in Fig. 4a-d, and they may be summarized in the following way the following conclusions about the water absorption capacities of Mixes A–D were obtained from this experiment. The water absorption (WA) values of all the tested composites decreased as the aging process continued. Blended composites made from Mixes B0 and C0 displayed lower WA percentages as compared to neat OPC (Mix A), while Mix D0 showed comparable or slightly higher value after 28 days.
The incorporation of CFs NPs within the OPC–AAS pastes induced the reduction in TP %, which caused declines in the water absorption value of the pastes and the results of the CS, BD, TP, and WA tests indicate that the nanocomposite with the composition 90OPC–10AAS–2CFs has the optimal composition for application and these test results were found. This is because it demonstrates the best possible physical characteristics in comparison to all the other mixes that were tested throughout most of the testing periods (86.94 Mpa for the CS test; 2.33 g/cm3 for the BD test; 35.12% for the TP test; and 12.99% for the WA test after 28 days of hydration) 51.
3.3. Bulk density
Figures 5a–d is a graphical representation of the findings that were obtained by measuring the bulk density (g/cm3) of a variety of various mixtures. The values of the bulk density (BD) during the hydration process indicated a steady increase from day one to day twenty-eight for each composite that was put through the test. These findings might be explained by the gradual stuffing of pores with accumulated hydration products over time, which allowed for the formation of a dense and thick framework. This occurred as a direct consequence of the buildup of hydration-related compounds. As can be seen in Fig. 5a, the BD values of Mixes B0 and C0 are either more than or comparable to those of the control (Mix A), however, the BD values of Mix D0 are either less than or comparable to the control (Mix A) and the results of this investigation agree with those found in the previous study (CS).
The BD values of the composites that were made from Mixes B0 and C0 increased because of the excessive amount of hydration products that were formed because of the pozzolanic reaction between calcium hydroxide that was liberated from cement clinker hydration and AAS waste. This reaction took place because of the pozzolanic reaction between calcium hydroxide that was liberated from cement clinker hydration and AAS waste. This is a consequence of the pozzolanic reaction that took transpired, which may be explained because these products are piled in most of the open spaces (pores) along with the hardened cement matrix, and the overall porosity of the hardened composites is reduced, which is a topic that will be covered in the subsequent section. At the same time, the BD values of the hardened composites are increased. In the case of the composite built from Mix D0, the number of extra hydration products generated because of the pozzolanic interaction between the available CH and AAS is lower than it is in the case of the composite built from Mixes B0 and C0 for the parameters that were previously indicated and listed in the section on compressive strength.
Because of this, the DB values of this mix were lower than those of (Mixes B0 and C0), but they were still comparable to those of the blank (Mix A) and the most significant discovery is that the hardened nanocomposites, which contain CFs NPs, have higher bulk density values than the materials that served as controls (Mixes A, B0, C0, and D0), and that the densification effect, which is characterized by high bulk density values, increases as the concentration of CFs NPs does as well mentioned in Figs. 5b–d. This finding can be attributed, without a shadow of a doubt, to the activation effect of CFs NPs. CFs act as foreign nucleation centers, which speeds up the hydration process and promotes the formation of an extra amount of C-S-H gel [calcium silicate hydrate (3CaO.2SiO2.3H2O], CASH, CAH [calcium aluminate hydrate 3CaO.AlO3.6H2O] (CuSH) 52.
3.4. Total porosity
These extra chemicals congregate in the pores that are accessible, which results in the formation of a structure that is denser, more compact, and with a greater BD. The results of the analysis of the total porosity of the different composites that were tested are presented graphically in Figs. 6a–d. As can be seen in Fig. 6a, the values of the TP % decreased steadily during the hydration process (which lasted anywhere from one to twenty-eight days) for all the mixes (A to D). This transformation took place as a natural consequence of the hydration process. The stacking of distinct hydrates that grew inside the accessible spaces coupled with the composite matrix is responsible for this decrease in size. Mix B0 and Mix C0 both have TP values that are lower than those of the control sample (Mix A). On the other hand, the TP values for Mix D0 are the same as those of the blank sample. This is an additional point of interest. These findings, along with the findings of the BD and CS, do correlate, and the reasoning behind this correlation may be found in the parts that were just described.
In addition, the incorporation of CFs NPs resulted in a discernible reduction in the total porosity of all the created nanocomposites in comparison to their control, and Figs. 6b–d demonstrates that this reduction in the total porosity percentage is proportional to the quantity of CFs that were mixed in. The integration of CFs NPs results in a decreased percentage of overall porosity. This may be because the CFs NPs perform the functions of both a filler and an activator 53.
3.5. Thermal resistivity
It was investigated what would happen if hardened composites made from OPC, OPC-AAS, and OPC-AAS-CFs were heated to higher temperatures (300, 600, and 800 oC) for 28 days. Figures 7a–b is a graphical representation of the CS values that were obtained for the various composites after being exposed to fire at various temperatures for 3 hours and then being left for gradual cooling in air. These values were obtained after the composites were left for gradual cooling in the air after being removed from the fire. The following is an account of the most important findings obtained. When compared to their recorded values after 28 days of hydration, the compressive strength values of all composites increased significantly during heating up to 300°C; however, these values decreased significantly during heating up to 600 and 800°C. The compressive strength values of all OPC–AAS composites increased significantly when compared to those of neat OPC cement (Mix A) at all testing temperatures.
The compressive strength values of all composites increased significantly when compared to those of the following is an example of one explanation that might be correct for these results and the high upgrading of the CS values after being subjected to 300°C could be attributed to the hydrothermal reaction (internal autoclaving) that takes place between the H2O vapor molecules generated from the evaporation of physically adsorbed water inside different pores along with the hardened cement matrix and the residual unreacted cement grains. This reaction takes place between the H2O vapor molecules generated from the evaporation of physically adsorbed water inside different pores along with the hardened cement. This reaction takes place between the molecules of H2O vapor that are produced because of the evaporation of water that has been physically adsorbed inside of certain pores.
The perfect dispersion of CFs NPs within the composite matrix can be attributed to the obvious improvement in the thermal stability of a variety of nanocomposites (especially Mix D3) at 300°C. This improvement can also be attributed to the composite matrix's efficiency in inducing the formation of large quantities of a variety of hydration products via its nucleation effect and activation of the internal autoclaving. Mix D3 exhibited the greatest degree of improvement in thermal stability mixture. The nanocomposite known as D3 is the one that has demonstrated the largest increase in its thermal stability. These products get lodged in the easily accessible gaps (both macropores and micropores) along with the hardened composite, which supports the creation of the hardened matrix, which possesses a high level of resistance to the damaging effects of fire. The decrease in CS values that were observed for all composites after being exposed to 600°C can be primarily attributed to the thermal degradation of nearly all fundamental products such as CSH composites after firing at 800°C can be attributed to the complete thermal degradation for all binding centers, in addition to the induction of several cracks along with the composite matrix. This was observed after the composites had been subjected to the temperature.
After exposing the composites to the temperature, this was the resultant observation was made. Figures 7a–b illustrates the change in CS values that occurred in several composites after being heated for three hours at temperatures of 300, 600, and 800 oC and then having their temperature dropped quickly (by immersion in cold water). These composites have CS values that are, beyond a reasonable doubt, significantly lower than those of their equivalents, which were fired at the same temperatures and cooled in the air (slowly). As the firing temperature was increased from 300 to 800 oC, it was observed that the CS of every composite material gradually decreased (Fig. 7a–b). This was the situation with every one of the composites.
The significant reduction in CS can be attributed to the formation of several cracks as well as the enlargement of the already generated crack (micro-cracks induced during the firing), both of which occurred because of the thermal shock that occurred during the rapid cooling process. Both events took place because of the rapid cooling that took place. In addition, the fact that the micro-cracks were caused by the firing process can be credited for the substantial drop in CS that was seen because of this action. When the temperature was raised from 300 to 600 oC, there was a discernible decline in the compressive strength of every composite that was evaluated, and this decline persisted until it reached zero oC when the temperature was raised to 800 oC. Despite this, the degree to which loss of strength occurs in blended samples, whether they include CFs NPs, is larger than that which happens in neat Portland cement pastes, whether they contain CFs NPs.
This is the case regardless of whether the blended samples contain CFs NPs. After a certain amount of time has passed, the percent relative compressive strength (RCS) (relative to their CS after 28 days) is displayed in Figs. 8a–b for all burned specimens. The RCS % values that were computed following firing at 300°C and 900°F are as follows: 125.16, 125.4, 125.53, and 128.79 for Mixes A–D0, respectively; 125.26, 125.31, and 125.43 for Mixes (A1–A3), respectively; 125.46, 125.58, and 125.61 for Mixes B1–B3), respectively; (Fig. 8a-b). These data make it abundantly evident that the nanocomposite material that is made up of 85% OPC, 15% AAS waste, and 2% CFs is the one that ought to be selected for use in thermal applications. The fact that this nanocomposite has the highest residual strength (the highest percent RCS) is the best conclusion from the point of view of both the economy and the environment. Figures 8a–b illustrates the percent relative compressive strengths (relative to their CS after 28d) of several different composites after they were subjected to fire and then rapidly cooled.
The RCS percent values for these composites are as follows: 95.17, 95.29, 95.79, and 91.12 for Mixes A–D0, respectively, 96.75, 97.45 and 97.62 for Mixes A1–A3, respectively, 96.77, 97.51, and 97.63 for Mixes B1–B3); respectively. After being fired at 300 oC then rapidly cooled. As a result of these observations, the idea is that CFs have a good effect on strengthening the fire resistance of a range of OPC–AAS blended pastes, such as I and II, CAH, CASHs, AFm, Aft, CFSH, and CH, receive additional support. Finally, a noticeable drop in CS levels was observed across the board for all the samples that were analyzed 54.
3.6. Compressive strength
To undertake an examination of the treated specimens' ensuing mechanical qualities, the compressive strength (CS) values of the specimens were measured at various points throughout the hydration process. This was done so that the values could be compared with one another. In Figs. 9a-d, the CS values of the hardened composites that were produced by replacing OPC with 0%, 5%, 10%, and 15% of activated alum sludge waste (AAS) (respectively, Mixes A, B0, C0, and D0) are shown. These values were obtained by creating the hardened composites with Mixes A, B0, C0, and D0. These values were achieved by exchanging OPC for waste products generated during the manufacturing of activated alum. In general, the CS values exhibited a consistent pattern with a growing hydration period across the board for every one of the mixes that were put through the testing process.
This continuous increase in the strength values can be generally attributed to the hydration of different phases that are present in Portland cement clinker and the formation of hydration products, primarily in the form of calcium silicate hydrates, calcium aluminate hydrates, alumino ferrite monosulfate hydrate, calcium aluminosilicate hydrate, and calcium ferrite trisulfate, also known as ettringite C6A0. In addition, when contrasted with the control (pure OPC) paste, the compressive strength values recorded by the pastes generated by substituting OPC with 5 and 10% of AAS (mass % (Mixes B0 and C0, respectively) recorded the highest values possible at each testing hydration time. These values were determined by comparing the values recorded by the control paste to the values recorded by the pastes generated by substituting OPC with 5 and 10% of AAS (Figs. 9a-d).
The higher strength values that were reported for these composites are linked to the presence of excessive amounts of nearly amorphous and illcrystalline CSH as the main product. This was obtained through the pozzolanic interaction between AAS waste (alumina and silica phases) and calcium hydroxide, which was obtained from the hydration of cement clinker 55. These greater strength values are associated with the presence of an excessive quantity of almost amorphous and ill-crystalline CSH as the principal product.
This CSH is the culprit behind the higher strength values. These hydrates not only operate as binding sites between the un-hydrated grains that are still present in the system, but they also fill the pores that are present along with the matrix. The matrix is not completely hydrated. On the other hand, increasing the quantity of AAS waste to 15% (Mix D0) causes the CS values to become comparable to, or even lower than, those of blank after 28 days. This occurs because the CS values are affected by the amount of AAS waste. This is since the waste from the AAS gets diluted (Mix A) and this decrease in the CS can be attributed to the dilution effect of PC as a result of its replacement with high percentages of AAS waste, which in turn reduces the amount of Ca(OH)2 liberated as a secondary hydration product from C3S and -C2S phases that required activating the AAS waste. In other words, the amount of Ca(OH)2 liberated as a secondary hydration product from C3S and -C2S phases.
The substitution of PC with significant percentages of AAS waste is to blame for the diluting impact since PC has this discovery is compatible with the findings that have previously been published by many studies, and the results of the CS revealed that the optimal replacement ratio of OPC by AAS is 10%; this finding was also verified by the results of the CS. Figures 9a–d provides clarification of the influence that additions of 0.5, 1.0, and 2.0% CFs NPs have on the CS values of neat OPC pastes. The CFs NPs were added to the pastes. There is an illustration of the mixtures A1–A3, B1–B3, C1–C3, and D1–D3. When compared to the values of their references (Mixes A–D0), the addition of different dosages of CFs NPs to OPC or OPC substituted by different masses of AAS waste leads to a significant increase in the compressive strength values of the composite material (Figs. 9a–d).
This can be seen by comparing the values of the composite material to the values of their references. These findings can be attributed to the nanoparticle characteristics of CF spinel, which include a large specific surface area of 66 m2/g, a nano dimension of 50 nm, and, finally, the good distribution of it along with the cement matrix. These characteristics enable it to fill the nano- and micropores existing among different hydration products, which results in a dense and compact structure with higher strength values than those of their control samples (Mix A). Additionally, CFs nanoparticles perform the function of active nucleation centers, which has the effect of accelerating the hydration process of cement grains to produce new and increased quantities of a variety of hydrated phases.
Calcium aluminate hydrates (C3AH6), calcium aluminosilicate hydrate (Ca-(A)-SH), and calcium ferrosilicate hydrate (like ilvaite, CaFe2+) are some examples of the hydrated phases that may be found here CFs nanoparticles since it has been shown that the enforcement impact of CFs NPs increases as the quantity of addition of these NPs increases (from 0.5 to 2%), which is represented as an increase in the CS values for all investigated mixtures. This is a general observation that can be made because of the finding that the quantity of addition of these NPs increases. This improvement can be due to the filling influence that the CFs NPs had on the cement matrix, which led to a decrease in the porosity of the material. In other words, the CFs NPs filled the pores in the cement matrix. In addition to this, the high alkalinity of the composite matrix, which had a pH of more than 12, encouraged the partial ionization of CFs NPs into Cu2+ and ferric anion.
These ions have an interaction with Ca(OH)2 in the presence of amorphous SiO2, which is present in the AAS waste. This interaction results in the generation of an excessive amount of new hydrates, such as copper silicate hydrate Cu2Si2O7(OH)4.nH2O (CuSH), calcium ferrosilicate hydrate (such as ilvaite, CaFe2 + Fe3+SiO7O(OH), (CFSH), which strongly findings will be supported by the XRD analysis that was performed on a variety of different composites that were put through their paces. In conclusion, the research showed that composite material is known as Mix C3, which is comprised of 90% PC, 10% AAS, and 2% CFs NPs, could be regarded as the most advantageous option for use in applications relating to general construction.
This was why it demonstrated the highest CS values when compared to all the other nanocomposites that were tested at nearly all ages. This was the case since it was tested at almost all ages. The substitution of 90% of the OPC with 10% of the AAS contributes to the reduction of costs associated with the disposal of waste (landfill tax), the provision of an alternative use for recycled water-treated plant sludge, without making any assumptions about either its cost or its quality, and the protection of the environment through the conservation of energy and the reduction of the number of harmful gases (CO2 and NOx) and other air pollutants emitted. There is no question that this composite (90 OPC–10AAS–2 CFs) provides a multitude of benefits, from the point of view of both the economy and the environment 56.
3.7. Morphology and textural characteristics
The SEM-photographs provided by EDX-analyses of OPC, OPC-AAS-2 CFs NPs at 7 and 28-days of curing are represented in Figs. 10 and 11, respectively. The improvement in hydration products forming escorted by microstructure compaction is a sign of the permanence of hydration with curing intervals at all hardened samples. A low compact microstructure is the mean feature of both of OPC -AAS and OPC-AAS-2 CFs microstructures at 7 days, and this is agreeing with the results of compressive strength, which proved that a small amount of hydration products, as C-S-H, as well as a large amount of unreacted clinker grains closely can be detected. After 28-days of hydration, OPC-AAS-2 CFs exhibits microstructure compaction better than those of OPC -AAS at both 7- and 28-days, which is attributed to dense matrix composed of the excessive generation of force-giving phases (C-S-H, C-A-S-H, and C-F-S-H) 57,58.
3.8. Corrosion resistance for the blinded material
The accompanying Fig. 12a-d demonstrates how the hydration time it takes for cement to set may have a significant impact on the corrosion rates of mild steel. The investigation revealed that the corrosion rates have decreased over the course of time, which was supported by the obtained data. Along with the inherent properties of these combinations, in which the pH values were recorded at the neutral level, which decreased the corrosive influence of the surrounding mild steel medium, since the water content of cement will decrease with time, which will result in a reduction in the corrosion rates by diminishing the direct contact between the mild steel surface and the surrounding environment. Both factors will contribute to a reduction in the overall corrosion rates. The presence of mild steel in this medium makes it less corrosive than it otherwise would be as a result, the pace at which corrosion occurs slows down; this was proved by the gained results that were provided earlier in the discussion. It was also found that the corrosion rates in the mixtures shown in Fig. 12d are a considerable amount lower than the rates that were reported for the mixtures in Figs. 12a, b, and c correspondingly. This was one of the findings that was shown in Fig. 12d since these data give evidence that increasing the concentration of sludge in the combination has a favorable effect on more than one property, with a reduction in the rates of corrosion being the predominant advantage brought about by this combination.