The world’s increasing need is to develop smart and sustainable construction material, which will generate minimal climate changing gas during their production. The bottom-up nanotechnology has established itself as a promising alternative technique for the production of the cementitious material. The present investigation deals with the chemical synthesis of cementitious material using nanosilica, sodium aluminate, sodium hydroxide, and calcium nitrate as reacting phases. The characteristic properties of the chemically synthesized nanocement were verified by the chemical composition analysis, setting time measurement, particle size distribution, fineness analysis, and SEM and XRD analyses. Finally, the performance of the nanocement was ensured by the fabrication and characterization of the nanocement based mortar. Comparing the results with the commercially available cement product, it is demonstrated that the chemically synthesized nanocement not only shows better physical and mechanical performance, but also brings several encouraging impacts to the society, including the reduction of CO2 emission and the development of sustainable construction material. A plausible reaction scheme has been proposed to explain the synthesis and the overall performances of the nanocement.
The modern civil infrastructures undeniably depend on the cement based material. More than ever before, the world’s increasing need for the development of the new infrastructure demands the construction of efficient, sustainable, and durable building materials, generating minimal climate changing gas during their production. Based on the worldwide screening report, it is apparent that the Portland cement is the most common and widely used construction material and its current production is estimated to be ~2 billion tons per year. Reviewing the literature, it is anticipated that the abundant resource of the oxide composition (SiO2, CaO, Al2O3, and Fe2O3) present in the cement is the earth’s crust (~90%). The earth’s crust is used as a primary raw material for the production of cement [
Effect of different nanomaterials on the performances of the cement composite.
Primary material | Additives/procedure | Particle Size | Effect/performance | Reference |
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Portland cement | Nanosize ingredients such as alumina, silica particles, and carbon nanotubes were added | <500 nm | Nanocement can create new materials, devices, and systems at the molecular, nano- and microlevel | [ |
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Portland cement | Nano-SiO2, nano-TiO2, nano-Al2O3, nano-Fe2O3, and nanotube/nanofibres were added | ~20 nm and 100 nm | Can produce concrete with superior mechanical properties as well as improved durability | [ |
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Portland cement | Single wall and multiwall carbon nanotubes were added | — | Cement materials showed superior mechanical, electrical, and thermal properties | [ |
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Ordinary Portland cement | Spherical nanoparticle nano-SiO2, nano-Fe2O3, and multiwall carbon nanotubes were added | 1–100 nm | Significant improvement in compressive strength as well as Young’s modulus and hardness of the concrete | [ |
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Portland cement | Spherical nano-Fe2O3 and nano-SiO2 were added | 15 nm | Mortar showed higher compressive strength as well as flexural strength | [ |
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Nano-SiO2, nano-NaAlO2, and nano-Ca(NO3)2 | Using the hydrothermal method, a new type of cement material is produced | 167 nm | A new cementitious material is produced using pozzolanic material infused with hydrated alumina which avoids CO2 emission, able to control mechanical performance of the mortar | Present work |
Reviewing the literature, it is prophesied that the incorporation of the external nanomaterial into cement system has succeeded to improve physical characteristics, mechanical properties, and novel performances of cementitious materials; however, the process is unable to reduce CO2 emission during the production of cement. From the review of the existing literature, it is apparent that the production of the cementitious material without emitting CO2 has not been studied yet. In a previous study [
In this investigation, we have set a systematic experimental program to synthesize an alternative cementitious material (nanocement) using the hydrothermal method. For the synthesis of the nanocement using the hydrothermal method, initially, the raw materials were selected carefully, which did not emit CO2 in any step of the synthesis. Finally, the nanocement based mortar was fabricated and characterized.
The alternative cementitious material (nanocement) was synthesized using 99.9% pure nanosilica purchased from Asia Cement Manufacturing Co. Ltd., Daegu, Korea. The particle size, specific gravity, and surface area of the used nanosilica are reported to be 40 nm, 0.13, and 65 m2/g, respectively.
The other chemicals such as sodium aluminate, sodium hydroxide pellet purified (98%), triethanol amine (TEA), and calcium nitrate used for the synthesis of the nanocement were purchased from Sigma Aldrich, Korea.
Nanocement mortar was fabricated using the fine aggregate of the average particle size <0.6 mm. The specific gravity, fineness modulus, and water absorption of the used fine aggregate are estimated to be 2.63, 2.48, and 0.1%, respectively.
The synthesis of the alternative cementitious material (nanocement) using the hydrothermal process was performed subsequent to the preparation of the silica and alumina source materials. At the first step of the synthesis, 6.7 g of sodium hydroxide was dissolved in 100 mL of deionized water in a Pyrex flux. Afterwards, 3.8 g of sodium aluminate was added gently in the flux. The flux was then placed on a heating mantle for 10–15 min maintaining the temperature of the mantle at 90°C to dissolve the material in the solution. After completion of this process, the flux was then allowed to cool and left to attain the ambient temperature. Thereafter, 16.4 g of triethanol amine was added dropwise as an emulsifier to prevent the precipitation of the prepared alumina source. Subsequently, the prepared alumina source was then allowed to ripen for 24 h to produce a soft gel material. Additionally, in the second step of the synthesis, exactly 12.5 g of the pure nanosilica was added to 100 mL of deionized water in an another pyrex flux. The flux was then placed on a magnetic stirrer to prepare a thick gel of silica source material. Thereafter, the thick gel of the silica source material was allowed to ripen for 24 h at ambient condition. Subsequently, the prepared source materials of the silica and alumina were mixed together using a turbine mixture, followed by 3 h sonication to disperse the components homogeneously. Consequently, the compound synthesized in this process was then allowed to dry in oven at 105°C for 15 days. The crystallized product, thus obtained, was then washed with distilled water and filtered off using a membrane filter. Finally, the residue was allowed to dry in oven at 105°C for 6 h followed by grinding in a mortar pestle to obtain a powder material.
Typically, the Portland cement contains three principal ingredients such as SiO2, Al2O3, and CaO. The material synthesized in this investigation carried adequate amount of SiO2 and Al2O3; however, it did not contain CaO. In this context, the powder material was treated with the calcium nitrate (Ca(NO3)2) solution to increase the CaO content. Finally, the sample was allowed to centrifuge and filtered off, followed by oven drying at 105°C for 24 h. The product thus obtained was then ground to acquire a powder of the alternative cementitious material (nanocement).
Cement mortar was fabricated using chemically synthesized nanocement, fine aggregate, alkali activator, and water. In this investigation, the 50% sodium hydroxide solution was used as an alkali activator for the fabrication of the nanocement based mortar. The samples were prepared varying the water content, alkali activator content, and fine aggregate content. In a particular batch mixing of the nanocement based mortar, 100 g of nanocement was mixed with fine aggregate (varying amounts ~200 g–400 g) followed by the mixing with an alkali activator (varying amounts ~30 mL–95 mL) and water (varying amounts ~20 mL–50 mL). Additionally, a control cement mortar was fabricated using 100 g of the Portland cement, 314 g of fine aggregate, and 50 mL of water. Table
Formulation code and mix proportions of components for the fabrication of control as well as nanocement mortar.
Type of variability | Formulation code | Components | |||
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Cement (g) | Water (mL) | 50% NaOH solution (mL) | Fine aggregate (g) | ||
Control | CCM | 100a | 50 | — | 314 |
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Water variation | MN-W1 | 100b | 12 | 50 | 314 |
MN-W2 | 100b | 16 | 50 | 314 | |
MN-W3 | 100b | 20 | 50 | 314 | |
MN-W4 | 100b | 24 | 50 | 314 | |
MN-W5 | 100b | 29 | 50 | 314 | |
MN-W6 | 100b | 40 | 50 | 314 | |
MN-W7 | 100b | 50 | 50 | 314 | |
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Alkali activator variation | MN-A1 | 100b | 20 | 30 | 314 |
MN-A2 | 100b | 20 | 40 | 314 | |
MN-A3 | 100b | 20 | 50 | 314 | |
MN-A4 | 100b | 20 | 60 | 314 | |
MN-A5 | 100b | 20 | 70 | 314 | |
MN-A6 | 100b | 20 | 80 | 314 | |
MN-A7 | 100b | 20 | 90 | 314 | |
MN-A8 | 100b | 20 | 95 | 314 | |
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Course aggregate variation | MN-F1 | 100b | 20 | 50 | 200 |
MN-F2 | 100b | 20 | 50 | 245 | |
MN-F3 | 100b | 20 | 50 | 300 | |
MN-F4 | 100b | 20 | 50 | 400 |
The specific gravity and fineness of the chemically synthesized nanocement were analyzed in accordance with the Korean standard KS L 5110 [
Chemical compositions of the cementitious material synthesized in this investigation were analyzed using Rigaku NEX QC energy dispersive X-ray fluorescence (EDXRF) analyzer, Applied Rigaku Technologies, Inc., Austin, USA. Before the analysis, cement samples were dried in oven at 105°C and cooled to room temperature by storing the samples in a vacuum desiccator. The cement samples were analyzed packing the samples on a 40 mm rectangular hollow area of the sample holder. Thereafter, the analysis was performed in helium environment. In this instrument, a 50 Kv X-ray generator tube is used to generate the X-ray for the analysis of the sample and a high performance SDD semiconductor based recorder is used to detect the signal. The result obtained from this experiment was further clarified by the energy dispersive X-ray spectroscopy (EDX).
Field emission scanning electron microscopic (FE-SEM) images of the synthesized nanocement and commercially available Portland cement were recorded using JEOL JSM-6700F, JEOL USA Inc., USA. In this microscope, the electrons are emitted from a bent tungsten filament (withstand high temperature without melting). The emitted electrons are accelerated by the application of high voltage (maximum 30 kV) which in turn leads to strike on the surface of the sample; consequently, the electrons are liberated from the outer shell of the sample. The liberated electrons are termed as secondary electron, focused by electromagnetic lenses with a maximum magnification capacity 1000000x. The scanning of the electron beam over the sample surface is controlled by deflecting the electron beam using a scanning coil. During this investigation, a very thin gold was sputter coated on the surface of the moisture free dried samples to avoid charging. Thereafter, samples were placed on the SEM stub and allowed to analyze. The digital scanning electron micrographs were recorded in 10–20 kV accelerated voltage and 15 kx magnification.
Setting times (initial and final) of the newly synthesized cementitious material (nanocement) as well as Portland cement were estimated in accordance with the standard KS L 5108 [
The structural characteristics of the chemically synthesized cementitious material were examined using an X-ray diffractometer (Ultima III, Rigaku Inc., Japan). The CuKα radiation (40 kV, 40 mA) and Ni filter were used to produce the X-ray. The X-ray diffractograms of the samples were recorded in the 2
The compressive strength of the nanocement based mortar as well as control cement mortar of the dimension 50 × 50 × 50 mm3 was measured using a universal testing machine with a loading rate 0.06 MPa/min in accordance with the Korean standard KS F 2405 [
Table
Physical properties of the synthesized nanocement as well as commercially available different types of cement.
Properties | Type of cement | |||
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Ordinary Portland cement | Blast furnace slag cement | Fly ash based cement | Synthesized nanocement | |
Particle size ( |
10~30 | 10~30 | 20~30 | 0.167 |
Specific gravity | 3.15 | 3.03 | 2.94 | 2.11 |
Fineness (cm2/g) | ~2800 | ~2600 | ~2500 | 3582400 |
Particle size distribution pattern of the chemically synthesized nanocement.
Subsequent to the analysis of the physical performances, the chemical compositions were also analyzed to assess the basic chemical characteristics of the synthesized cementitious material. Typically, cement contains dicalcium silicate (C2S), tricalcium silicate (C3S), tricalcium aluminate (C3A), and tetracalcium aluminoferrite (C4AF) phases [
Oxide composition (%) present in nanocement as well as ordinary Portland cement.
Type of cement | Chemical composition (%) | |||||||
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CaO | Na2O | SiO2 | Al2O3 | MgO | Fe2O3 | SO3 | Loss of Ig | |
Ordinary Portland cement | 64.33 | — | 20.36 | 5.77 | 2.05 | 2.84 | 2.51 | 2.0 |
Chemically synthesized nanocement | 3.71 | 5.31 | 42.8 | 21.9 | 0.41 | 2.37 | — | 0.32 |
Figures
Identification of the chemical constituents of the nanocement by EDX.
Type of the cement | Chemical constituents (%) | ||||
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Ca | Na | Al | Si | O | |
Nanocement | 10.09 | 2.00 | 25.05 | 32.62 | 30.24 |
FE-SEM micrographs of the (a) ordinary Portland cement and (b) chemically synthesized nanocement.
EDX analysis of chemically synthesized nanocement.
Setting time of the cement is one of the important characteristics and provides the information of how long concrete maintains its liquidity. It is an output of the hydration reaction occurring among the chemical phases of the cement in the presence of water as reacting medium. In this investigation, setting of the chemically synthesized nanocement is occurring due to the condensation reaction of the reacting phases in the presence of an alkali activator (50% NaOH solution). In the present investigation, the cementitious material was synthesized from the pozzolanic material (nanosilica) infused with hydrated alumina using the hydrothermal method. Therefore, the occurrence of the hydration reaction among the chemical phases is difficult in the presence of the water only. Hence, the use of an alkali activator in aqueous solution may achieve driving force to allow the hydration reaction and leads to setting of the cementitious material. Figure
Initial and final setting times of the ordinary Portland cement at 30°C and the variation of the initial and final setting times of the chemically synthesized nanocement with increase in curing temperature.
Subsequent to the analysis of the physical, chemical, and fresh properties of the synthesized material, the mechanical performance of the chemically synthesized nanocement has been elucidated measuring the compressive strength of the nanocement based mortar. In this investigation, different mortar samples were fabricated varying the water content, alkali activator content, and fine aggregate content. In this investigation, the compressive strength of the nanocement mortar is compared with the control cement mortar fabricated using ordinary Portland cement. Comparing the compressive strength of the nanocement mortar with the ordinary Portland cement, it is assessed that the nanocement based mortar performs similarly or better as compared to that of the ordinary Portland cement. Figure
Compressive strength of control mortar and variation of the compressive strength of nanocement based mortar with increase in water content.
Compressive strength of control mortar and variation of the compressive strength of nanocement based mortar with increase in alkali activator content.
Compressive strength of control mortar and variation of the compressive strength of nanocement based mortar with increase in fine aggregate content.
As it seems from the setting time analysis the setting of the nanocement occurs very fast at high temperature (~90°C). Keeping the effect in mind, a nanocement based mortar was prepared using 100 g cement, 95 g of alkali activator (50% NaOH solution), and 314 g of fine aggregate and allowed to cure in two different temperatures to evaluate the effect of high temperature on the mechanical performance of the mortar. Analyzing the result, the compressive strengths after 3 days and 7 days curing of the mortar fabricated using the above-mentioned mix design and cured at 90°C are estimated to be ~62.6 MPa and 65 MPa, respectively, whilst the compressive strengths after 3 days and 7 days curing of the mortar fabricated using the same mix design and cured at normal temperature (30°C) are estimated to be ~56 MPa and 61.5 MPa, respectively. The rapid development of the compressive strength at high temperature confirms the fast occurrence of condensation reaction of the chemical phases present in nanocement.
In addition to the effect of curing temperature, the effect of curing time on the compressive strength of nanocement based mortar has also been investigated. Figure
Variation of the compressive strength of the nanocement based mortar as the function of curing time.
Viewing in light of the above results, it is revealed that the method used in this investigation is an innovative scheme to produce an alternative cementitious material of the nanoscale particle size. In fact, in this investigation, an alternative pathway is followed instead of the clinkering to produce a cementitious material using pozzolanic material (nanosilica) infused with hydrated alumina. Based on the results reported above, we are trying to explain plausible chemical reactions involved in the synthesis of nanocement and its overall performances as well. Figure
Plausible model for chemical synthesis of the nanocement using bottom-up nanotechnology.
Plausible reaction scheme for the synthesis of nano cement.
X-ray diffraction pattern of the chemically synthesized nanocement.
Plausible model based on hydration of nanocement and probable structure of the expected hydrated product, that is, sodium-calcium-aluminosilicate hydrate.
Viewing in light of the hydrothermal synthesis of the cementitious material (nanocement), it is apparent that the raw materials used in this investigation are not carbon based. Accordingly, the process steps followed to produce nanocement are not responsible to emit CO2. Therefore, it is confirmed that the CO2 will not emit during the synthesis of the nanocement using the hydrothermal method. However, it is reported elsewhere that during the production of the 1 ton of Portland cement, ~700–800 kg CO2 is liberated [
The present investigation offers an innovative idea to synthesize nanocement utilizing the hydrothermal method instead of the high temperature clinkering method which emits enormous carbon dioxide during the production of cement. In this investigation, the hydrothermal synthesis of the nanocement from nanosilica and sodium aluminate is considered as a bottom-up nanotechnology. Based on the physical properties analyses, the particle size, specific gravity, and fineness of the synthesized material are estimated to be 167 nm, 2.11, and 3582400 cm2/g, respectively. Hence, from the result, it is assessed that the product obtained by the chemical synthesis method is a nanomaterial. Additionally, FE-SEM analysis proves that the average particle size of the synthesized material is retained at nanoscale level. Additionally, based on the chemical composition analysis in conjugation with EDX analysis, it is revealed that the synthesized material contains identical chemical oxide phases with commercially available cement. Therefore, it is considered that the synthesized material is a type of cementitious material. Furthermore, based on the setting time measurement, it is concluded that the synthesized nanocement follows Korean standard in its setting behavior. Finally, viewing in light of the mechanical property analysis, it is assessed that the newly developed material shows cementing ability with superior mechanical performance as compared to that of the commercially available cement. Based on the critical analysis of the results, a plausible model as well as a reaction scheme has been established in favor of the synthesis and hydration of nanocement. Finally, it is concluded that the chemically synthesized cementitious material (nanocement) not only improves the physical and mechanical performance of the mortar and concrete but also brings several encouraging impacts to the society, including reduction of the CO2 emission.
The authors declare that there is no conflict of interests regarding the publication of this paper.
The authors would like to acknowledge BK21, Republic of Korea, for their financial support to pursue this research program.