CC BY
12Magazine of Civil Engineering. 2023. 122(6). Article No. 12209
Magazine of Civil Engineering issn
2712-8172
journal homepage: http://engstroy.spbstu.ru/
Research article UDC 691.5
DOI: 10.34910/MCE.122.9
Performance of aluminium shaving waste and silica fume blended mortar
MO. Yusuf
Department of Civil Engineering, College of Engineering, University of Hafr Al Batin, Hafr Albatin, Saudi Arabia
M moruf@ uhb. edu. sa, moruff@.gmail. com
Keywords: compressive strength, hydration, thermal conductivity, supplementary cementitious materials, silica fume, microstructure
Abstract. This study investigates the impact of aluminium shaving waste (ASW or Ax: 0.0, 1.0, 1.5, 2 wt%) on the silica fume (SF or Sy: 0-10 %) blended ordinary Portland cement (OPC or C88-100%) mortar. The sample was designated as C100-x-ySyAx and the evaluations were done through their performances in terms of workability, compressive strength, thermal residual strength and microstructural characteristics in comparison with the OPC only mortar (C100S0A0). The increase in ASW/SF ratio enhanced the workability of SF blended (C90-xS1 0Ax). The unit weight of mortar reduced with increase in ASW/SF ratio so that 19.7 % was lost with the incorporation of 2 % of ASW. ASW induced effervescence of hydrogen gas in the fresh sample thereby leading to unit-weight reduction. The inclusion of 1 % ASW in ternary blending gave the optimum performances of 28-day strength (53.8 MPa) and residual thermal (300 °C, 1 h) strength of 56 MPa that had a comparable value to OPC mortar (55 MPa) unexposed to the thermal treatment. ASW also caused thermal stability in SF-ASW blended mortar as addition of 0.5, 1.5 and 2 % ASW caused 33.8, 15.6 and 33.4 % loss in 28-day strengths, respectively, while the least was observed in 1 % ASW sample with the loss of 8.8 %. Finally, ASW enhanced weight reduction (at 300 °C for 1 h) as the unit weight reduced by 1.75, 4.89, 3.30 and 1.86 % in C89.5S10A0.5, C89S10A1, C88.5S10A1.5 and C88S10A2, respectively, in comparison with C100S0A0. Mayenite and muscovite could be formed as products when ASW is used as supplementary materials in silica fume blended mortar production.
Acknowledgements: The authors would like to appreciate the remarks of the anonymous reviewer who has greatly improved the manuscript. The continuous support of University of Hafr Al Batin is appreciated.
Citation: Yusuf, M.O. Performance of aluminium shaving waste and silica fume blended mortar. Magazine of Civil Engineering. 2023. Article no. 12209. DOI: 10.34910/MCE.122.9
1. Introduction
Production of ordinary Portland cement that is used as a binder in mortar and concrete involves breaking down limestone with high amount of energy; this leads to proliferation of carbon dioxide, which causes global warming by damaging the ozone layer. The use of supplementary cementitious (SCMs) materials such as pozzolanic (fly ash, palm oil fuel ash, metakaolin and silica fume) and and other hydraulic materials such as ground granulated blast furnace slag (GGBFS) have been adopted by several researchers towards achieving cost efficiency and sustainable environment. Utilization of solid wastes has significantly reduced the volume of landfills in our environment. This solid waste could emanate from agricultural and industrial wastes. The industrial wastes such as iron-filling, cement kiln dust, and glass wastes have been recently reported to have contributed significantly to both fresh and hard properties of pastes, mortars, and concrete [1].
© Yusuf, M.O., 2023. Published by Peter the Great St. Petersburg Polytechnic University.
One of these industrial wastes is aluminium shaving waste (ASW), which is obtained through aluminium frames reshaping process by using lathe or turret mills. Aluminum (Al) is a non-ferrous metal reported to be light, conductive, and corrosion resistant. It can attract oxygen, and has viable potential for engineering applications since the end of the 19th century [2]. International Aluminium Institute (IAI) reported 5,273 thousand metric tons of aluminium production as of February 2023, while the main aluminium scraps came from construction and automobile industries [3]. The carbon dioxide equivalent (CO2e) owing to recycling of aluminium waste amounted to 22 million metric tons with substantial part obtained from the thermal energy source. It becomes imperative for civil engineers to develop a technique towards ensuring some aluminium wastes are safely used in concrete and mortar production.
In this regard, Ofuyatan et al. [4] used varied aluminium shaving waste (ASW) in volume of 1-2 % and studied its contribution to the bond strength of laterized concrete beams with a view to minimize industrial waste. They reported that ASW decreased compressive strength but increased bond strength of reinforcement with concrete. Lower diameter bar of 16 mm performed better than a 20 mm diameter bar. Gulmez [5] also used 1-4 wt% of ASW as fine aggregate with a noticeable decrease in bulk density while flexural strength and transport characteristics increased due to more porosity of the matrix. Tang Van et al. [6] also used the combination of 30 % fly ash (FA) and ASW to achieve production of aerated concrete with lower density and modulus of elasticity, but higher porosity. The 28-day compressive strength of 52.7 MPa was achieved due to silica and alumina interaction [7]. Shabbar et al. [8] also reported inclusion of 0.5 to 1 wt% of aluminium (Al) powder decreased the elastic modulus and density of concrete. Moghaddam et al. [9] also asserted that Al nanoparticles can react with portlandite to produce aluminosilicate-hydrate gel while its synergy with glass waste could reduce the absorption of the samples.
Furthermore, Kuziak et al. [10] investigated alumina powder in two different types of cement (CEM 1 and III) and discovered that the rate of hydrogen gas effervescence in Al-blended binder depends on the amount of portlandite that accompanied hydration process as this could have a negative effect on strength [11]. Moreover, incorporation of 1 wt% alumina into slag blended cement (CEM III) could cause cracks due to the interconnected pore formations. In addition, an introduction of alumina into a lime-dominated binder could also have a negative impact on strength and density of the binder, especially in an aerated concrete. Similarly, Ramamurthy et al. [12-13] indicated that lime/cement ratio plays a significant role for strength and density. Autoclave curing of aerated mortar with high aluminium content (0.6-0.8 %) could lead to coalescence of discreet pores thereby causing minimization of pore total surface areas, which in turn may result in a decrease in the strength of the products [14].
Narayanan et al. [15] asserted that curing methods for aerated concrete play a significant role in the microstructural properties, chemical compositions, and density of aerated concrete with the incorporated aluminium powder. Sabapathy et al. [3] incorporated 0.5-2 vol% aluminium fiber in concrete samples with a view to enhance the compressive and split tensile strengths at a water/binder ratio of 0.6 (M20), 0.45 (M30) and 0.4 (M40). The optimum fiber content for compressive strength and split tensile strength were 0.5 % and 2 %, respectively. Elinwa and Mbadike [16] also asserted that large aluminium waste (AW) content within 5-40 % in concrete can be used as a retarder with 10 % being the optimum for compressive and flexural strengths.
Moreover, Azarhomayun et al. [17] used Al powder to reduce free shrinkage and crack width in concrete but also increase the restrained drying shrinkage by 18 %. The presence of excessive AW embedded in concrete could cause cracks due to pressure exerted by Al corrosion products rather than effervescence of hydrogen [18]. Faez et. al. [19] found that alumina nanoparticles (2.5 %) blended with silica fume (10 % SF) enhanced 90-day compressive and split tensile strengths by 86 % and 47 %, respectively. Besides, adding aluminium nanoparticles with SF could reduce water absorption of concrete samples.
Despite the plethora of the studies on the incorporation of aluminium waste in aerated an lightweight concrete, little is known of the impact of the synergy between Al shaving waste (ASW) and SF in terms of strength, nature of the product, microstructure, and thermal performance of their combination in ternary blended mortar that comprises SF, ASW and OPC. It is expected that utilization of these solid wastes will reduce the amount of solid waste in landfill on one hand while it will also have a significant impact on the mechanical and microstructural properties of the final product.
This study is aimed at providing necessary information with a view to bridging the gap needed for the deeper understanding of the synergy of ASW and SF in mortar production. It also makes alternative materials available for repair and rehabilitation of concrete structure while ensuring a safe environment by limiting ASW in dumpsites or landfills.
2. Methods and Materials
2.1. Materials
2.1.1 Aluminium shaving waste
Aluminium shaving waste (ASW) as shown in Fig. 1 is a by-product from an aluminium frame processing factory obtained through grinding and cutting by lathe machine (Fig. 1). The oxide composition mainly comprises alumina with traces of Fe2O3, CaO, MgO, SrO and TiO2 as shown in Table 1. Fig. 2 shows the X-ray diffractogram of the ASW.
Figure 1. Aluminium shaving. Table 1. Oxides composition of the raw materials.
Oxides Silica fume Cement Aluminium shaving waste
SiO2 95.85 20.17 -
AI2O3 0.26 5.58 99.10
Fe2O3 0.05 2.86 0.16
CaO 0.21 63.51 0.09
MgO 0.45 3.15 0.58
Na2O 0.40 0.12 -
K2O 1.22 0.57 -
SO3 1.00 2.56 -
SrO - - 0.01
TiO2 - - 0.04
SiO2+Al2O3+Fe2O3 96.16 28.61 99.26
Specific gravity (water) 2.25 3.15 1.18
LOI (%) 2.48 2.80 20.0
Figure 2. X-ray diffraction of aluminium shaving waste powder.
2.1.2 Cement
Type 1 ordinary Portland cement (OPC) was prepared in accordance with ASTM C 150 [20] with specific gravity (by water) of 3.15 and its oxides composition as shown in Table 1. The surface area and loss on ignition (LOI) are 329.5 m2/kg and 2.8 %, respectively, while SiO2, AI2O3, and Fe2O3 were summed up to 28.61 %. Fig. 3 shows the chemical compounds present in OPC as used in the study.
2-theta angle {Cu K-alpha)
Figure 3. XRD diffractogram of ordinary Portland cement (topmost) and the silica fume (bottom).
2.1.3 Silica fume
Silica fume (SF) is commercially obtained with a relative density, LOI and surface area of 2.25, 2.48 %, and 22,800 m2/kg, respectively with the sum of SiO2, AhO3, and Fe2O3 being 96.2 % as shown in Table 1, while Fig. 3 (bottom) shows its XRD diffractogram.
2.1.4. Fine aggregates
Natural sand in saturated surface dry (SSD) conditions whose moisture content and absorption were 3.43 and 6.14 %, respectively. The fine aggregate passes through a 2.36 mm sieve (No. 8) in accordance with ASTM C 157/C 157M - 08 [21]. The fineness modulus and relative density (water) were 2.8 and 2.71, respectively.
2.1.5 Superplasticizer
The superplasticizer (Glenium 51®) was used to enhance the consistency of the mixture. It is polycarboxylic ether and the proportion used was 1 % of the total binder (OPC, SF, and ASW).
2.2. Experimental tests
2.2.1 Workability
The consistency of the mortar sample was tested by using flow table in accordance with ASTM C 1437-20 [22].
2.2.2. Compressive strength
The compressive strength was determined by using 50 mm cubic samples, room-cured and subsequently exposed to thermal (300 °C for 1 h) treatment, in accordance with ASTM C 109 [23]. The testing was done by a universal testing machine at the ages 7, 14, and 28 days with the loading rate of 0.9 kN/s. The compressive strength was taken as the average of the three samples.
2.2.3 Unit weight of samples
The unit weight (KN/m3) of samples was determined by measuring the mass (kg) of the samples at specific days, multiplying it by the acceleration due to gravity (10 m/s2) and dividing it by the volume of the sample (125*10-6 m3).
2.3 Characterization and morphology of the samples
XRD Bruker apparatus model d2-Phaser with CuKa radiation (40 kV, 40 mA) was used to determine the compound present in the product of ASW-SF blended mortar with a scan speed of 2.5°/min and continuous scanning with 2-theta angle range of 10-80°. The raw and post thermally treated ASW powder were tested to understand its phase transformation. Fourier transform infrared (FTIR) spectroscopy measurements of ASW-SF paste were conducted by using Perkin Elmer 880 spectrometer. The scanning electron microscopy and energy dispersive spectroscopy (SEM+EDS) instrument model 5800 LV manufactured by JEOL was used at an accelerating voltage of 20 kV for the microstructural characterizations and elemental compositions of the paste samples.
2.3. Sample preparation
2.4.1 Sample designation
The samples were composed of OPC (88-100%), ASW (0, 0.5, 1, 2 %) and 10% SF. The sample was designated as Copc%Ssf%Aai%, and thus a sample that contained 88 % OPC, 10 % SF and 2 % ASW, was designated as C88S10A2, while the control was taken as the sample that contained OPC only, labelled as C100S0A0.
2.4.2 Mix design
Mix design of the sample is given in Table 2 with the total binder of 350 kg/m3 such that the water/binder ratio is 0.4. The binder/sand ratio was maintained at 2.5 while ASW/binder ratio varied from 0 to 2 % at the interval of 0.5.
2.4.3 Mixing procedure
Mixing was done in the following way. OPC, SF, and ASW were mixed dry for 3 mins. Half of the needed water together with the superplasticizer was poured into the mixer and then mixed for 3 mins to form a grout. Fine aggregates were then added and mixed for additional 2 mins before adding the other half of the water mixed with superplasticizer for 3 mins to achieve a homogenous mixture. Steel moulds with the dimensions of 50*50*50 mm were then oiled for easy demoulding, and to receive the fresh mortar. The cast specimens were left in the moulds for 24 h before being demoulded and then placed in the curing tank for a specified number of days (7, 14, 21 and 28 days) before being tested for compressive strength at a loading rate of 0.9 kN/s.
Table 2. Mixture proportion of aluminium shaving waste blended mortar.
Designation Cement kg/m3 Silica fume kg/m3 Aluminium shaving waste kg/m3 Sand kg/m3 water kg/m3 SP kg/m3
C100S0A0 350.00 0 0.00 875 140 3.5
C90S10A0 315.00 35 0.00 875 140 3.5
C89.5S10A0.5 313.25 35 1.75 875 140 3.5
C89S10A1 311.50 35 3.50 875 140 3.5
C88.5S10A1.5 309.75 35 5.25 875 140 3.5
C88S10A2 308.00 35 7.00 875 140 3.5
3. Results and Discussions
3.1. Oxide compositions and compound in aluminium shaving waste
Table 1 shows the oxide composition of aluminium shaving waste, and it is mainly composed of 99 % alumina with traces of calcium, magnesium, iron, titanium, and strontium oxides. The ASW is very stable at thermal exposure to the tune of 1000 °C; the loss on ignition (LOI) was 20 % while the specific gravity (water) is 1.18. The presence of graphite in the X-ray diffraction (XRD) diffractogram as shown in Fig. 2 increased the value of LOI recorded while the observable main crystalline phases in ASW are graphite (COD#1200018), calcite (C0D#1010962), titanium (COD# 9011600), and a-alumina (a-AhOa) (C0D#1533936).
The crystalline phases include graphite and Ti-6Al-4V (TC4) at the 2-theta angle of 27 °C and 39 °C, respectively. Upon subjecting it to 1000 °C as shown in Fig. 4, graphite and T4 phase disappeared thereby leading to the formation of more crystalline phases of K-AhO3 and a -AhO3 and spinel (COD#9001364). This resulted in lowering of the amorphous content of ASW [24]. It has been reported that 8- and y-
alumina could transform into more crystalline phases of a - and 0-alumina with low surface area [24]. Comparing Figs. 2-4 makes it apparent that subjecting ASW to elevated temperatures transforms it into more crystalline phase.
Figure 4. Phases of compounds formed upon subjecting ASW to 1000 °C.
3.2. Workability of the mortar
From Fig. 5, OPC mortar (C100S0A0) had a flow diameter of 225 mm, which decreased by 20 % upon adding SF. The incorporation of 0.5 % ASW to OPC mortar (C99.5S0A0.5) increased the consistency by 11.11 % whereas that of 10 % SF-ASW blended mortar reduced it by 6, 4.8 and 2.0 %, upon adding 0.5,
I, and 1.5 % ASW, respectively. As ASW became 2 %, no change was observed in the consistency of the mortar. Therefore, flowability of ASW-SF blended mortar was increasing with ASW/SF ratio. With reference to C100S0A0, the consistency of 10 % SF-ASW blended mortar increased by 4.4 %, 5.8 %, 8.9 %, and
II.11 % as ASW was 0.5, 1, 1.5 and 2 %, respectively.
ClOOSOAO C90S10AÜ C99.5WA0.5 C89,5510A0,5 C89S10A1.0 C88.5S10A1.5 C8&510A2 ■ workability 22 5,00 ISO. CO 25(100 235.00 233.00 245,00 250.00
Sample designation
Figure 5. Consistency of SF-ASW blended mortar.
Furthermore, by comparing 10%SF-x%ASW blended mortar with SF-OPC mortar (no ASW), the workability increased by to 30.56, 32.22, 36.11 and 38.89 % with ASW content (x) of 0.5, 1, 1.5 and 2 %, respectively. This suggests that incorporation of ASW enhanced the flowability of SF-OPC mortar as shown in Fig. 5. The increase in the consistency of the mortar could be due to the reaction of portlandite with Al [25, 26] as shown in Eq. (1) thereby leading to the formation of entrapped hydrogen gas (Fig. 6) that formed a spherical ball within the matrix.
Figure 6. Formation of spherical bubble due to formation of hydrogen gas.
The presence of Al also enhances the formation of ettringite Ca6Ah(SO4)3(OH)12-26H2O due to its interaction with portlandite and water to form calcium aluminate hydroxide and liberation of hydrogen gas as shown in Eq. (1):
2Al + 3Ca (OH)2 + 6H2O ^ 3CaO.Al2O3.6H2O + 3H2. (1)
The formation of hydrogen gas led to internal bubble formation that later caused pore formation due to the effervescence of the gas as shown in Fig. 6. This reaction becomes spontaneous due to formation and oxidation of Al(OH)3 that accompanies dissolution of OPC that leads to the formation of hydroxyl ions.
The presence of hydroxyl ion oxidizes Al(OH)3 to become Al(OH)4 ion thereby making ASW undergo continuous corrosion as shown in Eq. (2) [27]. The corrosion of ASW and effervescence of hydrogen gas led to loss of fluidity of the mortar. This phenomenon depends on the concentration and quantity of ASW present in the mixture.
OH- + Al(OH)3 ^ Al(OH)-. (2)
At lower ASW incorporation of 0.5 % without the presence of SF, the workability increases due to attachment of Al to OH ions thereby causing disintegration of hydrogen bonding within the ettringite formation. The presence of ASW led to formation of Al-OH thereby decreasing OH"/Al ratio, which induces ionic repulsion within ettringite. This explains why C100S10A0.5 has better consistency (250 mm) compared to C100S0A0 (225 mm) as shown in Fig. 5. Upon introducing SF into the mixture, silicic acid (Si(OH)4) would be formed thereby reducing the pH of the mixture. The presence of SF-ASW reduces the viscosity of the mixture. This is further enhanced by the fineness of SF.
3.3. Unit weight of samples
Inclusion of the ASW and SF decreased the unit weight of the blended and OPC mortar due the specific gravity and escape of hydrogen from the pores within the matrix. With reference to C100S0A0 (Fig. 7), the unit weight of OPC mortar increased from by 1.65 % within the 1 to 7 days, while it was 2.1 % in 10%SF-OPC mortar. The addition of 0.5, 1, and 1.5 % ASW made the increment to be 0.68 %, 3.93 %, and 4.33 %, respectively in 10%SF+ASW blended mortar. Upon increasing the ASW to 2 %, there was a decrease in unit weight by 5.42 %. Within the interval of 7-14 days, the increment became 0.24 % in C100S10A0 but increased to 0.68 % in C90S10A0. Inclusion of 0.5 % ASW led to an increase in the unit weight by 0.68 %, but reduced by 2.7 %, 2.8 %, and 5.9 %, upon adding 1, 1.5, and 2 % ASW, respectively. Within the interval of 14 to 28 days, the unit weight of OPC mortar and SF-blended mortar increased by 0.89 % and 0.34 %, respectively. The unit weight in 10%SF+ASW reduced by 0.08, 0.35, 1.06 and 0.64 % in C89.5S10A0.5, C89S10A1, C88.5S10A1.5 and C88S10A2, respectively.
Figure 7. Change in unit weight of SF-ASW blended mortar with age.
Fig. 8 shows the OPC samples exposed to thermal (300 °C) treatment lost 13.0 % of unit weight, and upon incorporating 10%SF and ASW, the loss in unit weight reduced to 12.0 %, 4.2 %, 4.3 % in C89.5S10A0.5, C89S10A1, and C88.5S10A1.5, respectively, while a 4.4 % increment in unit weight was recorded in C88S10A2. The loss in unit weight was due to removal of water from the capillary of the matrix and the disappearance of the embedded hydrogen gas. By comparing the unit weight of OPC sample (C100S0A0) subjected to 300 °C, inclusion of ASW in SF blended mortar increased post-thermal unit weight by 1.75, 4.89, 3.30 and 1.86 % in C89.5S10A0.5, C89S10A1, C88.5S10A1.5 and C88S10A2, respectively.
Sample designations
Figure 8. Unit weight of samples due to room curing and thermal treatment.
3.4. Compressive strength of ASW-SF blended mortar
As seen in Fig. 9, the presence of ASW without SF (C99.5S0A0.5) reduced the 7, 14 and 28-day strengths by 23.3, 8.7 and 16.7 %, respectively, in comparison with OPC mortar (C100S0A0). Upon adding only SF into OPC mortar (C90S10A0), the 7 and 14-day strengths reduced by 14.2 and 14.6 %, respectively, while its 28-day strength increased by 7.1 % due to secondary hydration process of pozzolanic material in the matrix.
Figure 9. Compressive strength of ASW-SF blended mortar.
However, blending 0.5 % ASW with SF (C89.5S10A0.5) further reduced the 7, 14 and 28-day strengths in comparison with C100S0A0 by 36.1, 26.8 and 29.2%, respectively. In C89S10A1, the reductions in strengths compared to C100S0A0 were 32.3, 9.1 and 2.3 %, respectively. Increasing the ASW to 1.5 % and 2 % caused further reduction of 7, 14 and 28-day strengths to 22.8, 25.2 and 9.6% (C88.5S10A1.5), and 46.7, 27.4 and 28.7 %, respectively (C88S10A2) compared to C100S0A0. Besides, the rate of strength gain in C100S0A0 increased from 7 to 14 days and from 14 to 28 days by 11.1 and 12 %, respectively. For SF+OPC mortar, the rate from 7 to 14 days reduced by 4.8 % and 31.3 % in C90S10A0 and C88.5S10A1.5, respectively while the strength increased by 189.8, 146, 343 and 361.8% in C99.5S0A0.5, C89.5S10A0.5, C88S10A1, and C88S10A2, respectively. The rate of strength gain from 14 to 28 days increased by 237.53, 70.14, and 194.6 % in C90S10A0, C89S10A1 and C88.5S10A1.5, and decreased by 81.43, 29.81 and 16.61 % in C99.5S0A0.5, C89.5S10A0.5 and C88S10A2, respectively, in comparison with C100S0A0.
This implies that ASW contributes to the strength development through their attachment with free silica to form aluminosilicate products. This aluminosilicate network contributes to the skeletal framework to induce strength gain as indicated in Fig. 9. Moreover, the portlandite that ought to react with SF to produce additional CSH was consumed by ASW (Eqs. (1), (3)) thereby leading to the evolution of hydrogen that caused the reduction in the unit weight of the samples as shown in Fig. 7.
CS + H ^ CSH + CH.
(3)
The ASW-SF blended OPC mortar (C89S10A1) performs better than SF blended mortar (C90S10A0). The optimum quantity to foster performance in ASW-SF blended mortar is 1%, since the Sulphate/Al ratio plays a key role in the formation of aluminoferrite mono-sulphate (Afm), unlike low density Aft with pore filling characteristics, which can improve the compressive strength [28]. Afm has greater density due to increase in Sulfate/ASW ratio at lower substitution up to 0.5 %, that can cause weak microstructure. Lower sulfate/ASW ratio could also lead to lower compressive strength due to more porosity that accompanies the evolution of hydrogen gas within the matrix. This explains the reason why C88.50S10A1.5 and C88.50S10A2 have lower strengths in comparison with C89S10A1. The presence of ASW reduces the dilution effect of SF during pozzolanic reaction in mortar production.
XRD in Fig. 10 shows the possible formation of mayenite (Ca12Al14O33), ettringite and muscovite (K2(Al2Oa)a(SiO2)6H2O), which further justify the possibility of Eq. 1. The dual presence of ettringite and mayenite due to reaction of ASW with gypsum and other cement compounds could be responsible for the decrease in the compressive strength in comparison with C100S0A0 and C89S10A0. It also shows that the presence of ASW does not prevent the formation of calcium silicate hydrate (CSH) and portlandite (Ca(OH)2) as clearly shown in Fig. 10, while the presence of C4AF, alite (C3S) and belite (C2S) could be
due to the presence of unreacted cement within the matrix. The removal of hydrogen gas led to more microstructural voids that induced carbonation thereby leading to the formation of calcium carbonate or calcite (CaCO3).
] CSH
CSH c A CSH A Ca3SiCL-
G _i_ M P B F ? B - Ca;Si04 C CaCOj E - Ca6AI:(S04)3(OH)l:-26H;O F 4CaAl:0,Fe:03
1 p Mil A
G CaS04.2H;0 M - Cal:Al140 ,3 Mu - KJ(AI;0i)i(Si0;)6(H;0) P - Ca(OH):
0 ID 20 30 40 50 60 70 80
2-theta angel (K-alpha)
Figure 10. X-ray diffractogram of the SF-ASW ternary blended paste.
Fig. 11 shows the Fourier transform infrared (FTIR) spectroscopy and indicates asymmetric stretching of Al-O bond and AhO3 vibration at 1119 cm-1 and 997 cm-1, respectively, while wavenumber 874 cm-1 indicates C-O vibration from the carbonate source. Besides, C-O vibration due to carbonation (region B) is indicated in the wavenumber 2336 cm-1 [18, 29]. Similarly, region A and C point to OH and HOH vibration were due to the presence of portlandite. The presence of ASW does not appear to affect the C-O band at 1420 cm-1, but in contrast, it has significant impact on Si-OH and HOH bending mode vibration in water at 1638 cm-1 due to interaction with tricalcium aluminate (C3A) to form aluminosilicate bonds [30]. The calcium aluminate phase has been assigned by Tarte [26] to the wavenumber with 700-900 cm-1 for condensed aluminate CaO.AhO3, 12CaO.7AhO3 and theta-AhO3, which was further supported by Yusuf [29], and Fernendez-Carrasco et al. [25, 29].
Figure 11. FTIR of ASW blended paste in comparison with OPC cement paste.
The isolated and condensed octahedral AlO4 were identified at wavenumber 650-800 and 530400 cm-1, respectively [26]. Therefore, the peak at point G in Fig. 11 can be said to be due to the presence of calcium aluminate hydroxide (CAH). Besides, the OH/HOH vibration was noted at 3422 cm-1 while the absence of ASW in the control sample (hydrated cement) led to the presence of OH peaks at 3642 cm-1, which was absent in ASW blended mortar.
3.5. Thermal residual strength of ASW-SF blended mortar
By comparing 28-day strength, addition of ASW into OPC mortar caused reduction in compressive strength at room temperature (Fig. 12). There is a decrease in the residual thermal strength in OPC due to microstructural disintegration as the thermal residual 28-day strength was 37 % less than that at room temperature. However, under thermal treatment (300 °C for 1 h), addition of 0.5, 1, 1.5 and 2 % ASW caused increase in strength by 18.5, 29.2, 2.4, 11 and 26.2 % in comparison with C100S0A0 as noted in C99.5S0A0.5, C89.5 S10A0.5, C89S10A1, C88.5 S10A1.5, and C88S10A2, respectively. Both SF and ASW have positive
impacts on thermal treatment by incorporating 0.5, 1, 1.5 and 2 % ASW, through the achievement of positive strength gains of 39.8, 43.5, 61, 50.4 and 29.7 %, respectively.
Figure 12. Compressive strength of alumina blended mortar.
Inclusion of ASW contributed significantly to the thermal residual strength as compressive strength by 8, 27.6, 3.8, 3.5 and 11.1 % in C99.5S0A0.5, C89.5 S10A0.5, OsgSioAi, C88.5 S10A1.5, and C88S10A2, respectively. There is no observable physical deterioration in any of the samples. Therefore, the optimum thermal performance was observed when the ASW inclusion is 0.5 % in the presence of SF (C89.5S10A0.5) even though the maximum thermal strength was obtained with 1 % ASW. This indicates that the presence of ASW+SF improves thermal performance due to attachment of Si to Al in tetrahedral coordination to induce the formation of zeolite-like product (CASH) as observable in geopolymer synthesis [31-33].
3.6. Microstructure and elemental ratio of ASW-SF blended paste
Fig. 13 shows the contribution of ASW to the microstructural morphology and the elemental compositions of the product formed. The region 1 and 3 indicate that the general spectrum of ASW-Si blended paste was such that Ca/Si ratio was 1.83 and 2.9, respectively, while the region 4 at which Aft or ettringite was formed had the Ca/Si ratio of 3.34. At the region 2 where the bubbles formed, the Ca/Si ratio decreases to 0.76. The low Ca/Si ratio in this region causes a decrease in the compressive strength recorded when compared to SF-ASW based samples. Calcium to carbon (Ca/C) ratios are 1.25 and 1.68 at regions 1 and 3 while the region 4 (where Aft formed) had 1.40. The presence of graphite in ASW as noticed in the XRD in Fig. 2 was supported by the presence of carbon in the energy dispersion spectroscopy (EDS) (Fig.13). The presence of a bubble could make the matrix susceptible to carbonation thereby causing Ca/C to be 0.76 (region 2). The presence of Fe in region 1 pointed to the possibility of unreacted cement powder that contained tetracalcium aluminoferrite (F-C4AF) as shown in the XRD in OPC raw powder (Fig. 2).
4. Conclusions
This paper investigates the impact of the synergy of silica fume (SF) and aluminium shaving waste (ASW) on the strength and thermal performance of ternary blended mortar comprising ordinary Portland cement, aluminium shaving waste powder and silica fume (OPC+ASW+SF). The following conclusions can be drawn:
1. Silica fume reduced the workability of mortar and concrete whereas the use of ASW enhanced the consistency of the binder by up to 32 % at the level of 0.5-2 % without compromising the strength significantly.
2. ASW enhanced the formation of calcium aluminate hydrate (CAH) together with calcium silicate hydrate (CSH). This is established by the presence of mayenite and muscovite among the peaks identified by X-ray diffractogram.
3. Thermal exposure of ASW-SF sample to 300 °C for 1 hr significantly reduced the unit weight of the samples by 12.03, 4.16 and 4.27 % for 0.5, 1 and 1.5 %, respectively while 2 % ASW led to an increase
in the unit weight of the sample by 4.4 %. It implies that 0.5 % ASW had the most significant effect on the density of the sample.
4. The strength gain in 10%SF-0.5%ASW and 0%SF-0.5%ASW blended mortar exposed to 300 °C for 1 hr were 8 % and 26 % when compared to those produced at room temperature. Exposing ordinary Portland cement (OPC) to similar condition led to 37 % decrease in strength compared to those prepared at room temperature.
5. The optimal 28-day strength performance of the mortar of 53.8 MPa was obtained in the sample produced with 10%SF, 1 % ASW and 89 % OPC. There was 3.9 % gain in strength when the samples were exposed to 300 °C for 1 hr.
Figure 13. Morphology of SF-ASW blended mortar.
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Information about authors: Moruf O. Yusuf, PhD
ORCID: https://orcid.org/0000-0002-8134-5435 E-mail: moruf@uhb.edu.sa E-mail: moruff@gmail. com
Received 03.05.2023. Approved after reviewing 08.08.2023. Accepted. 14.08.2023
