ORCID ID: M. Yildirim (
In this study, compressive and flexural strength, thermal properties, and pore structure of mortars modified with two types of boron waste and different amounts of CuO nanoparticles were investigated. The binders were prepared with 3% of borogypsum or borax waste and nano-CuO at concentration up to 4%. The setting time, compressive and flexural strength at 3, 7, and 28 days, DTA/TG, XRD, BET, and water absorption tests were carried out, and optimal nano-CuO percentages were determined. It was observed that nano-CuO addition in the range 2%–2.5% can improve mechanical properties, reduce the amount of unreacted portlandite, increase water absorption resistance, and decrease the setting time for borogypsum-containing mortars. The optimum nano-CuO replacement ratio changes between 0.5%–1% for borax waste-containing mortars. The results showed that nano-CuO was able to promote hydration reactions, act as a nanofiller, and provide a kernel for nucleation reactions.
The use of industrial wastes as supplementary cementitious materials (SCMs) instead of cement, thereby eliminating 5% of the world’s carbon dioxide emissions, has grown in the last decades in line with sustainable and environmentally friendly production approaches. Researchers have approached the problem of improving properties to cement composites by using different SCMs, including fly ash, granulated blast furnace slag, rice husk ash, and silica fume (
Nanotechnology is an attractive research area with many applications because of the advantages of nanoscale (1–100 nm) materials. Nanoparticles, including nano-silica, nano-alumina, nano-titania, and nano-copper oxide, are used in cement composites to enhance mechanical and physical durability and chemical stability. Nanoparticles can be divided into two groups: nanoparticles that show pozzolanic activity such as nano-silica and nano-alumina, and those used as nanofillers and nano-nuclei such as nano-titania, nano-copper oxide, and nano-zinc oxide (
When nanoparticles disperse uniformly in the cement matrix, they produce a larger available surface area for hydration reactions. At early stages of hydration, nanoparticles act as a kernel, and hydration products envelop them tightly, resulting in a more compact, denser cement matrix. The generation of heterogeneous nucleation sites by nanoparticles promotes the formation of hydration products and limits the amount of Ca(OH)2. That results in improvement of the strength and durability of cement composites and reduced permeability through densification of the microstructures (
Many researchers have investigated the effects of nanoparticles on the mechanical and physical properties of cement composites. However, most of the studies have been concerned with application of silica, alumina, titania and iron oxide nanoparticles. Because of their pozzolanic effects nano-silica and nano-alumina are the most popular nanoparticles in the research. Li et al. reinforced cement composite with nano-alumina and revealed that the compressive strength and elastic modulus of mortars were improved by incorporating nano-alumina into matrix (
However, some studies have observed the influence of nano copper oxide on fresh and hardening features of cement-based materials. Nazari and Riahi (
Although there are studies incorporating CuO nanoparticles with cement composites, no study to date has examined the binary effects of boron waste and CuO nanoparticles on the fresh and hardened properties of cement mortar. The present study investigated the effects of boron waste and various amounts of CuO nanoparticles on the mechanical and thermal properties and the pore structure of cement mortars, evaluating both their compressive and flexural strength. Thermogravimetric analysis was used to evaluate the thermal properties, and the properties of the pore structure of mortars were determined by the Brunauer-Emmett-Teller (BET) method and water absorption test. The phase composition of mortars was determined by X-ray diffractometer (XRD) and Fourier transform infrared spectroscopy (FT-IR).
The researchers used borogypsum and borax waste provided by the Bandırma Boron Works (Eti Maden, Balıkesir, Turkey). Before starting the experiments, boron waste underwent a preparation process that included drying, grinding, and sieving. The prepared boron waste were identified by XRD and obtained patterns are given in
XRD patterns of boron wastes.
Borogypsum-containing mortars were prepared with clinker when borax waste–containing mortars were prepared with CEM 42.5 Portland cement. The binder materials were supplied from Akcansa Cement Factory, Istanbul, Turkey. Because of the gypsum content of borogypsum, clinker was used in the borogypsum-containing mortars.
CEN standard sand conforming to EN 197-1 was supplied by the Limak Trakya Cement (Kırklareli, Turkey) and was used in all mixtures as a fine aggregate. The chemical composition of raw materials was determined by PANalytical MiniPal 4 X-ray fluorescence (XRF), with parameters ranging from 4 to 30 kV (
Chemical composition of raw materials
Composition (%) | Clinker | Cement | Borogypsum | Borax waste | Sand |
---|---|---|---|---|---|
SiO2 | 14.00 | 13.00 | 4.10 | 20.00 | 90.80 |
Al2O3 | 3.00 | 2.00 | - | - | 5.70 |
Fe2O3 | 4.70 | 4.70 | 0.99 | - | 0.86 |
CaO | 76.50 | 71.80 | 45.10 | 57.30 | 0.41 |
SO3 | - | 2.90 | 48.70 | 22.00 | - |
MgO | - | 4.00 | - | - | - |
TiO2 | - | - | - | - | 0.87 |
K2O | 1.30 | 1.20 | - | 0.95 | 1.30 |
B2O3 | - | - | 1.10 | 1.30 | - |
LOI |
2.40 | 2.20 | 14.50 | 34.00 | 2.50 |
Loss of ignition
The nano-CuO used was synthesized from CuSO4.5H2O and NaOH by a hydrothermal method. The synthesis reaction temperature and reaction time were set at 70 °C and 4 hours after preliminary experiments with calcination parameters set at 400 °C and 2 hours, respectively. The morphological and crystallographic attributes of nano-CuO were determined by X-ray diffractometry (XRD), scanning electron microscopy (SEM); Micromeritics ASAP 2020 was used to measure the BET-specific surface area (SBET). The XRD pattern of synthesized CuO is presented in
XRD pattern of nano-CuO.
where
SEM image of nano-CuO.
Because of their large surface area, nanoparticles tend to agglomerate when in contact with water, and dispersing nanoparticles in the mortar matrix can be difficult (
The technical properties of superplasticizer admixture
Chemical admixture | Composition | Density (kg/L) | Alkaline Content (%) (EN 480-12) | Chloride Content (%) (EN 480-10) |
---|---|---|---|---|
MasterGlenium®51 | Polycarboxylic ether | 1.082–1.142 | < 3 | < 0.1 |
In total, 18 different mixtures with specified amounts of nano-CuO powder were prepared. The amounts of boron waste were kept constant as 3% of binder weight, which was determined as the optimum value according to previous studies (
Mixing proportions of mortar
Mix | Clinker (%) | Cement (%) | BJ (%) | BRX (%) | CuO (%) | Sand (g) | w/b |
---|---|---|---|---|---|---|---|
BJ-C-0 | 97 | - | 3 | - | 0 | 1350 | 0.35 |
BJ-C-1 | 96.5 | - | 3 | - | 0.5 | 1350 | 0.35 |
BJ-C-2 | 96 | - | 3 | - | 1 | 1350 | 0.35 |
BJ-C-3 | 95.5 | - | 3 | - | 1.5 | 1350 | 0.35 |
BJ-C-4 | 95 | - | 3 | - | 2 | 1350 | 0.35 |
BJ-C-5 | 94.5 | - | 3 | - | 2.5 | 1350 | 0.35 |
BJ-C-6 | 94 | - | 3 | - | 3 | 1350 | 0.35 |
BJ-C-7 | 93.5 | - | 3 | - | 3.5 | 1350 | 0.35 |
BJ-C-8 | 93 | - | 3 | - | 4 | 1350 | 0.35 |
BRX-C-0 | - | 97 | - | 3 | 0 | 1350 | 0.45 |
BRX-C-1 | - | 96.5 | - | 3 | 0.5 | 1350 | 0.45 |
BRX-C-2 | - | 96 | - | 3 | 1 | 1350 | 0.45 |
BRX-C-3 | - | 95.5 | - | 3 | 1.5 | 1350 | 0.45 |
BRX-C-4 | - | 95 | - | 3 | 2 | 1350 | 0.45 |
BRX-C-5 | - | 94.5 | - | 3 | 2.5 | 1350 | 0.45 |
BRX-C-6 | - | 94 | - | 3 | 3 | 1350 | 0.45 |
BRX-C-7 | - | 93.5 | - | 3 | 3.5 | 1350 | 0.45 |
BRX-C-8 | - | 93 | - | 3 | 4 | 1350 | 0.45 |
*BJ: Borogypsum, BRX: Borax waste, C: CuO
The preparation of specimens was carried out according to the EN 196-1 standard (
The setting time of fresh mortar was determined accordance with TS EN 480-2. The effects of different dosages of nano-CuO on the initial and final set time of the mortar were analyzed using a Vicat apparatus through measuring penetration of the metallic needles (
Compressive and flexural strength tests were conducted in accordance with EN 196-1 (
The phase analyses of pastes prepared with nano-CuO and boron waste were carried out by XRD in the pattern range of 5° to 60° at a scanning rate of 0.006°/s. The inorganic crystal structure database (ICSD) patterns were used to identify crystalline composition of pastes. The X-ray tube voltage and current were set at 45 kV and 40 mA, respectively. Fourier transform infrared spectroscopy (FTIR) analysis was conducted in the range 450 to 4000 cm−1 to identify characteristic bonding of hydration products. FTIR can determine amorphous phases as well as crystalline phases (
The pore structure of mortars was investigated through the BET method. The BET surface areas (SBET) and total pore volume of all samples were determined by nitrogen adsorption on a Micromeritics ASAP 2020 instrument after degassing samples under vacuum at 105 °C. Also, to investigate the pore structure, water absorption analysis was conducted at 28 days curing time, in accordance with the BS 1881-122 standard (
Thermal analysis of samples was carried out using PerkinElmer Diamond TG/DTA equipment to measure the heat flow and weight change in the mortars as a function of temperature. Samples that had been cured for 28 days were heated from 30 °C to 1000 °C at a heating rate of 10 °C/min under an N2 atmosphere. The amount of CH formation during hydration progress was determined directly by TG analysis from the start and end points of the CH decomposition [5].
In
The initial and final setting time of mortars prepared with boron waste is shown in
Setting time of mortars with a) borogypsum b) borax waste.
The average compressive strength results of mortars containing borogypsum and borax waste for each nano-CuO ratio are presented in
Compressive strength of borogypsum containing mortars for different nano-CuO.
Compressive strength of borax waste-containing mortars for different nano-CuO ratios.
In contrast with borogypsum-containing mortars, the reference sample in which borax waste was used showed lower compressive strength as 37.56, 40.35, and 50.56 MPa for curing times of 3, 7, and 28 days, respectively. This phenomenon can be explained by different chemical compositions of boron waste and binders of clinker and cement. Except the sample prepared with 3% CuO, all samples had higher compressive strength than the reference sample. On the other hand, the highest compressive strength value was obtained for 1% nano-CuO replacement as 60.32 MPa for 28 days of curing. When the optimum amount of nano-CuO was added to the mortar matrix, it promoted cement hydration and increased the strength of gel formation. As a result, more hydration products were produced because of the kernel effect of nano-CuO; the compressive strength at 28 days increased up to 24% of the control sample. Similar to studies carried out with nano-CuO (
The flexural strength results of borogypsum- and borax waste-including cement mortars are given in
Flexural strength of borogypsum containing mortars for different nano-CuO ratios.
Flexural strength of borax waste-containing mortars for different nano-CuO ratios.
XRD patterns of mortars with a) borogypsum and b) borax waste.
The FT-IR spectra of mortars prepared with different nano-CuO ratios are given in
FT-IR spectra of mortars with a) borogypsum and b) borax waste for different nano-CuO ratios.
The pore volume and specific surface area of cement mortars are given in
BET specific area and pore volume of specimens
Mix | SBET (m2/g) | Pore Volume (cm³/g) |
---|---|---|
BJ-C-0 | 1.1739 | 0.008533 |
BJ-C-1 | 4.5244 | 0.016379 |
BJ-C-2 | 4.6515 | 0.014364 |
BJ-C-3 | 3.0636 | 0.010302 |
BJ-C-4 | 3.8215 | 0.011939 |
BJ-C-5 | 2.2284 | 0.009201 |
BJ-C-6 | 1.8825 | 0.009098 |
BJ-C-7 | 1.6418 | 0.010851 |
BJ-C-8 | 1.8759 | 0.008138 |
BRX-C-0 | 3.7321 | 0.011914 |
BRX-C-1 | 4.7800 | 0.013069 |
BRX-C-2 | 7.6775 | 0.014358 |
BRX-C-3 | 6.8768 | 0.018347 |
BRX-C-4 | 6.0937 | 0.015007 |
BRX-C-5 | 3.3164 | 0.013952 |
BRX-C-6 | 3.6724 | 0.013733 |
BRX-C-7 | 1.6714 | 0.013261 |
BRX-C-8 | 3.6879 | 0.015282 |
Among the mortars containing borogypsum, all samples had a greater specific surface area compared with the control sample; as a result of this phenomenon, these samples showed a higher total pore volume. When the ratio of nano-CuO increased, a decrease was observed in both specific surface area and total pore volume, which can be caused by the lack of uniform distribution of this nanofiller.
The mortars containing borax waste displayed a significant difference in the values of specific surface area and total pore volume in comparison with mortars with borogypsum. Considering the increasing specific surface area, a more compact mortar matrix was obtained in this experimental set except for the BRX-C-7 sample. In parallel with the results of the strength tests, BRX-C-2 had the highest SBET, at 7.6775 m2/g.
To the contrary, although mortars containing borogypsum showed higher compressive and flexural strength, borax waste-containing mortars had a denser structure.
The water absorption test results of borogypsum and borax waste-containing mortars are given in
Water absorption of borogypsum containing mortars.
Water absorption of borax waste containing mortars.
Although the total pore volume of borax waste-containing mortars is greater than the reference mixture indicated by the BET analysis, the water absorption resistance of borax waste-containing mortars was improved by replacement of nano-CuO. The mortar without nano-CuO absorbed 7.68% water; at 3% nano-CuO, water absorption replacement decreased to 1.41%. The decrease in the water absorption by increasing the amount of nanoparticle can be explained by the reduced porosity.
The comparison of the water absorption results of mortars with different boron waste contents shows that using borogypsum with nanoparticles has a considerable impact on water absorption compared with the borax waste-containing mortars. The water absorption test results conform with compressive and flexural test results in which nano-CuO–modified borogypsum-containing mortars showed higher strengths than those with addition of borax waste. The higher amount of the C–S–H gel formation in the presence of well-dispersed nano-CuO can ensure a denser packing by filling the space between cement and aggregates, in addition to providing higher mechanical strength.
DTA results of borogypsum containing mortars.
DTA results of borax waste containing mortars.
DTA/TG results of Ca(OH)2 decomposition
Mix | Initial Temperature (°C) | Final Temperature (°C) | Mass loss (%) | Ca(OH)2 content (%) | Total heat (kJ/kg) |
---|---|---|---|---|---|
BJ-C-0 | 370.78 | 436.79 | 1.09 | 4.48 | 39.05 |
BJ-C-1 | 379.09 | 458.04 | 0.83 | 3.42 | 34.19 |
BJ-C-2 | 379.46 | 450.72 | 0.95 | 3.91 | 32.55 |
BJ-C-3 | 400.50 | 481.14 | 0.61 | 2.51 | 32.15 |
BJ-C-4 | 375.96 | 446.62 | 0.85 | 3.49 | 30.42 |
BJ-C-5 | 401.55 | 469.92 | 0.98 | 4.03 | 37.35 |
BJ-C-6 | 402.40 | 485.00 | 1.01 | 4.15 | 31.93 |
BJ-C-7 | 394.02 | 491.04 | 1.62 | 6.66 | 37.25 |
BJ-C-8 | 398.05 | 462.00 | 1.09 | 4.48 | 39.23 |
BRX-C-0 | 394.78 | 466.60 | 1.95 | 8.02 | 75.83 |
BRX-C-1 | 395.51 | 461.50 | 1.36 | 5.59 | 47.35 |
BRX-C-2 | 395.27 | 460.99 | 1.63 | 6.70 | 65.17 |
BRX-C-3 | 400.89 | 468.63 | 0.93 | 3.82 | 37.23 |
BRX-C-4 | 391.40 | 456.24 | 1.79 | 7.36 | 75.13 |
BRX-C-5 | 387.14 | 455.28 | 1.64 | 6.74 | 67.27 |
BRX-C-6 | 401.31 | 454.52 | 1.61 | 6.62 | 63.09 |
BRX-C-7 | 390.71 | 456.40 | 1.99 | 8.18 | 80.91 |
BRX-C-8 | 401.36 | 468.31 | 2.05 | 8.43 | 77.97 |
The released heat amount resulting from CH dehydration changed as a function of the amount of decomposed CH. In accordance with mass loss, the incorporation of borax waste into nano-CuO in mortars caused higher released heat resulting from the decomposition of CH.
The researchers in this study examined the effects of nano-CuO on the properties of boron waste (borogypsum and borax waste)-modified cement mortars. Based on the results, the following conclusions can be drawn:
The replacement of CuO accelerated the hydration progress and reduced setting time; even boron-containing waste is known to be materials that have retarding effects on Portland cement hydration. For borax waste-containing mortars, 1% nano-CuO replacement shortened the final setting time by 38.5% compared with the reference sample. Conversely, nano-CuO could not show a positive impact on the setting of borogypsum-added mortars.
The addition of 2% nano-CuO provided 67.89 MPa compressive strength after 28 days of curing, which was 6% higher than the reference sample when borogypsum was used. Likewise, the compressive strength increased up to 19.3% of the reference sample for borax waste-containing mortars for 1% nano-CuO addition.
BET analysis showed that the pore volume and specific surface area of borogypsum-modified mortars were improved by incorporating nano-CuO at all ratios. However, a non-linear change was observed for the values owing to the non-uniform dispersion of nano-CuO. According to BET results of borax-containing mortars, the combination of borax waste and nano-CuO ensured denser packing.
Water absorption results demonstrated that the replacement of nano-CuO was significantly effective in reducing the water absorption of borogypsum-containing mortars, especially for the nano-CuO ratio of 2%. Also, the same effectiveness was observed for borax-containing mortars when the nano-CuO ratio was 3%.
The amount of available portlandite (CH) was determined by DTA/TG analysis; addition of nano-CuO in the range 0.5%–3% could decrease the amount of unreacted CH.
Experimental results showed different chemical compositions of boron waste enhanced properties to the mortars. Compared to the borax waste, the addition of borogypsum into the mortar composition improved the mechanical properties. Also, BJ-C-0 sample showed 126.53% bigger resistance to the water absorption than BRX-C-0.
The results emphasize the significance of choosing the optimal nano-CuO ratio to obtain cement-based composites with desired properties, by reason of the difficulty of the homogeneous distribution of nanoparticles in the composite matrix. According to obtained results, the appropriate nano-CuO ratio range was determined to be between 2% and 3%.
This research was supported by Yildiz Technical University Scientific Research Projects Coordination Department, with project number of 2015-07-01-DOP04 and authors wish to extend their sincere thanks to “The Scientific and Technological Research Council of Turkey (TÜBİTAK)” for its Ph.D. scholarship support for the first author.