Graphene oxide (GO) has been utilized to strengthen composite materials. In this study, the effects of GO on hydration degrees, macro-mechanical strength and calcium-silicate-hydrate (C-S-H) ...structure of cement based composites were investigated through comprehensive experimental tests. In addition, the aggregation mechanism of GO was verified by alkaline solution simulations, using Ca(OH)2 and NH3·H2O. Based on the experimental results, it was found that the 3-day and 7-day compressive strengths of cement based composites with 0.2wt% of GO were increased by 35.7% and 42.3%, respectively as compared to the control. Moreover, the C-S-H structure of cement paste with GO was not observed to have undergone any change via qualitative and quantitative analyses combined with FT-IR, XRD and 29Si-NMR. Besides, the test results of TGA, DTG and 29Si-NMR showed that the hydrated degree of cement paste increased to 10.4% at 28days when incorporating with 0.1% of GO.
•The influence of NS on fresh properties and hydration characteristic of CBM has been reviewed.•Incorporation of NS can significantly enhance the mechanical strengths and durability of CBM.•There are ...three main reasons for the performance improvement of CBM with NS.•The addition of NS modified the microstructure and micromechanical strength of C-S-H.
Nowadays, many nanomaterials such as graphene oxide (GO), carbon nanotubes (CNTs), nano silica (NS) etc. have been introduced to improve the microstructures and performances of cement-based materials (CBM). Compared with other nanomaterials, NS has attracted much attention because of its pozzolanic reaction with calcium hydroxide (CH) to form calcium-silicate-hydrate (C-S-H) gel. Although several review papers have been published, the breadth and depth of literature coverage on NS and its effects on CBM is insufficient. This paper is aimed to keep researchers abreast of the latest research in the field. In particular, the influence of NS on CBM properties including workability, setting time, hydration characteristic, calcium leaching, porosity, mechanical strengths, and durability is critically reviewed. It is believed that this review paper will not only arouse new ideas to promote practical application of NS in construction materials but also provide some constructive guidance for similar research in the future.
•Sika-PCE is capable of keeping dispersed GO separated even in alkaline environment.•The dispersing process has a significant impact on the dispersion of GO.•GO can remarkably improve the flexural ...and compressive strength of cement mortar.•SEM and BSE images reveal GO leads to denser matrix and ITZ of cement mortar.
The effects of both the alkaline environment and calcium ions present in cementitious materials leads to the re-agglomeration of previously dispersed GO, and as a result decreases the dispersion of GO in cement matrix. To solve the aforementioned issues, this study compared 6 different kinds of superplasticizers (SP) to optimize the dispersion of GO in saturated Ca(OH)2 solution which can simulate the strong alkaline environment in the microstructure of cement matrix. And the mechanical properties and microstructures of the resulting cement mortar were investigated systematically. The experimental results present that, among the 6 SPs, Sika-PCE exhibits the best dispersibility with the optimal parameters found to be 30% ultrasonication energy and a SP-to-GO ratio of 1:1. Additionally, the dispersing process was found to have a significant impact on the dispersion of GO. The mechanical properties tests indicate that GO can remarkably improve the flexural and compressive strength of cement mortar in early age. The maximum improvement after 3d curing time was 15.48% for flexural strength with the addition of 0.02 wt% and 14.39% for compressive strength with the addition of 0.04 wt%. Scanning electron microscopy (SEM) and Back scattering images reveal that the incorporation of GO in the cement mortar leads to a denser matrix and stronger interfacial transition zone (ITZ) as compared to plain cement mortar. It can be also found that low GO dosage (0.02 wt%) contributes more to the hydration degree enhancement of the matrix of the cement mortar sample, while higher GO dosage (0.04 wt%) results in a denser ITZ in the cement mortar system. With the GO dosage increasing, energy dispersive X-Ray spectrum (EDS) results demonstrate a strong increasing trend in the Ca/Si ratio in both the interface and matrix regions.
Construction and demolition waste (CDW) currently constitutes a waste stream with growing potential use as a secondary raw material in the manufacture of eco-cements that offer smaller carbon ...footprints and less clinker content than conventional cements. This study analyzes the physical and mechanical properties of two different cement types, ordinary Portland cement (OPC) and calcium sulfoaluminate (CSA) cement, and the synergy between them. These cements are manufactured with different types of CDW (fine fractions of concrete, glass and gypsum) and are intended for new technological applications in the construction sector. This paper addresses the chemical, physical, and mineralogical characterization of the starting materials, as well as the physical (water demand, setting time, soundness, water absorption by capillary action, heat of hydration, and microporosity) and mechanical behavior of the 11 cements selected, including the two reference cements (OPC and commercial CSA). From the analyses obtained, it should be noted that the addition of CDW to the cement matrix does not modify the amount of water by capillarity with respect to OPC cement, except for Labo CSA cement which increases by 15.7%, the calorimetric behavior of the mortars is different depending on the type of ternary and hybrid cement, and the mechanical resistance of the analysed mortars decreases. The results obtained show the favorable behavior of the ternary and hybrid cements made with this CDW. Despite the variations observed in the different types of cement, they all comply with the current standards applicable to commercial cements and open up a new opportunity to improve sustainability in the construction sector.
Dispersion of carbon nanotubes (CNTs) is a challenge for their application in the resulting matrixes. The present study conducted a comparison investigation of the effect of four surfactants: ...Alkylphenol polyoxyethylene ether (APEO), Silane modified polycarboxylate (Silane-PCE), I-Cationic polycarboxylate (I-C-PCE), and II-Cationic polycarboxylate (II-C-PCE) on the dispersion of hydroxyl functionalized multi-walled carbon nanotubes (MWCNTs-OH). Among the four surfactants, APEO and II-C-PCE provide the best and the worst dispersion effect of CNTs in water, respectively. Dispersion effect of MWCNTs-OH has been characterized by optical microscope (OM), field emission-scanning electron microscope (FE-SEM), and Ultraviolet-visible spectroscopy (UV-Vis).The OM images are well consistent with the UV-Vis results. Based on the chemical molecular structures of the four surfactants, the mechanism of MWCNTs-OH dispersion in water was investigated. For each kind of surfactant, an optimum surfactant/MWCNTs-OH ratio has been determined. This ratio showed a significant influence on the dispersion of MWCNTs-OH. Surfactant concentration higher or lower than this value can weaken the dispersion quality of MWCNTs-OH.
This work analyses the influence of fine concrete fractions (<5 mm) of different natures -calcareous (HcG) and siliceous (HsT)-obtained from construction and demolition waste (C&DW) on the behaviour ...of blended cement pastes with partial replacements between 5 and 10%. The two C&DW fractions were characterised by different instrumental techniques. Subsequently, their lime-fixing capacity and the physico-mechanical properties of the blended cement pastes were analysed. Lastly, the environmental benefits of reusing these fine wastes in the manufacture of future eco-efficient cement pastes were examined. The results show that HsT and HcG exhibit weak pozzolanic activity, owing to their low reactive silica and alumina content. Despite this, the new cement pastes meet the physical and mechanical requirements of the existing regulations for common cements. It should be highlighted that the blended cement pastes initially showed a coarser pore network, but then they underwent a refinement process between 2 and 28 days, along with a gain in compressive strength, possibly due to the double pozzolanic and filler effect of the wastes. The environmental viability of the blended cements was evaluated in a Life Cycle Assessment (LCA) concluding that the overall environmental impact could be reduced in the same proportion of the replacement rate. This is in line with the Circular Economy goals and the 2030 Agenda for Sustainable Development.
The dynamics of water confined in cement materials is still a matter of debate in spite of the fact that water has a major influence on properties such as durability and performance. In this study, ...we have investigated the dynamics of water confined in Portland cement (OPC) at different curing ages (3 weeks and 4 years after preparation) and at three water-to-cement ratios (w/c, 0.3, 0.4 and 0.5). Using broadband dielectric spectroscopy, we distinguish four different dynamics due to water molecules confined in the pores of different sizes of cements. Here we show how water dynamics is modified by the evolution in the microstructure (maturity) and the w/c ratio. The fastest dynamics (processes 1 and 2, representing very local water dynamics) are independent of water content and the degree of maturity whereas the slowest dynamics (processes 3 and 4) are dependent on the microstructure developed during curing. Additionally, we analyze the differences regarding the water dynamics when confined in synthetic C-S-H gel and in the C-S-H of Portland cement.
Tricalcium aluminate (C
A) is the most reactive component of the Portland cement and its hydration has an important impact on the workability and early strength of concrete. Recently, nanomaterials ...such as nano-silica (nano-SiO
) have attracted much attention in cement-based materials because of its pozzolanic reactivity and the pore-filling effect. However, its influence on the hydration of C
A needs to be well understood. In this study, the hydration kinetics of C
A mixed with different percentages of nano-SiO
were studied and compared with pure C
A. The hydration products were examined by different characterization techniques including XRD, XPS, and NMR spectroscopy and isothermal calorimetry analyses. The XRD results showed that the addition of nano-SiO
promoted the conversion of the intermediate product C
AH
. The isothermal calorimetry results showed that the addition of nano-SiO
significantly reduced the hydration exotherm rate of C
A from 0.34 to less than 0.1 mW/g. With the presence of nano-SiO
, the peaks for Q
were observed in
Si MAS-NMR measurements, and the content of Q
increased from 6.74% to 30.6% when the nano-SiO
content increased from 2 wt.% to 8 wt.%, whereas the proportion of Q
gradually decreased from 89.1% to 63.6%. These results indicated a pozzolanic reaction provoked by the nano-SiO
combined with aluminate structures generating C-A-S-H gel.
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•Ultra-low dosage of alkaline activator was achieved by introducing mold-pressing technology.•High performance for heavy metals solidification by mold-pressing AAM.•High compressive ...strength can be obtained.
The safe disposal of municipal solid waste incineration fly ash (MSWIFA) has become the weakest link of the circular economy of MSW due to its hazardous nature. In this study, we focused on the heavy metals solidification of MSWIFA by using alkali-activation technology and introducing a mold-pressing method. The influence of alkaline activator (AA) including alkali concentration and dosage of sodium silicate solution were well designed and studied. MSWIFA before and after alkali-activation, as well as the sample treated by commercial chelating agent (CA), were contrastively studied the performance of heavy metals solidification. The results show that the alkali-activated MSWIFA exhibits superior solidification for heavy metals than the blank control and the CA treated ones. With mold-pressing technology, the alkali-activated MSWIFA shows a core-shell structure, in which a thin layer that is composed of mainly N-A-S-H gel is as the shell and acts as a protective layer to inhibit the leaching of heavy metals. Besides, the introduced mold-pressing technology is beneficial for the improvement of materials strength and the reduction of AA dosage. The optimal AA composition is that the net concentration of NaOH is ∼4 M and sodium silicate dosage is ∼65 wt% in alkaline activator, and the total alkaline activator requirement is only 32 wt% of MSWIFA, yielding 7.9 MPa compressive strength at 10.2 MPa molding pressure. In summary, this work paves a potential new way for safe and recycling use of hazardous MSWIFA, which will be of great significance to environmental sustainability.
•Combining the fine fraction of CDW (glass and concrete) yields viable pozzolans.•Their use at 7% replacement level gives cements compliant with current standards.•Blended mortars show slightly lower ...mechanical strength and resistivity values.•Calcareous concrete wastes increase capillary absorption more than siliceous ones.
The serious technical and environmental problems associated with the management of construction and demolition wastes (CDW) have led to a worldwide growing interest in the recycling of that waste stream as secondary raw material for sustainable building applications.
This research work investigates the physical and mechanical behaviour of mortars made with ternary cements containing 7% of a binary recycled CDW mixture comprising the fine fraction (<5 mm) of recycled concrete waste (both siliceous and calcareous nature) in combination with recycled laminar glass in three different proportions (1/1, 1/2, and 2/1, respectively). To this end, the chemical composition and fineness of the anhydrous ternary cements were analysed, as well as their behaviour in paste and mortar matrices, in both fresh and hardened states, verifying the requirements established by the applicable standards.
The results attest to the viability of using these ternary cements, as their performance is comparable to that of an ordinary Portland cement (OPC), without evidencing any significant dependence on the glass content. The compressive strength values decrease by 7–8% with respect to that of the OPC mortar, revealing the prevalence of the filler effect over the pozzolanic reaction. The ternary cements analysed in this study met the chemical, physical and mechanical requirements for the elaboration of future eco-efficient cements.
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