Investigation on the Mechanical, Microstructural, and Electrical Properties of Graphene Oxide-Cement Composite

Nanotechnology refers to the use of the materials or particles ranging from a few nanometers (nm) to 100 nanometers (nm) in a wide range of applications. Use of nanomaterials in cement composite to enhance the mechanical properties, fracture toughness and other functionalities has been studied for decades. In this regard, one of the carbon-based nanomaterials, Graphene Oxide (GO), has received attentions from researchers for its superior mechanical properties (e.g. tensile strength, yield strength, and Young\u27s modulus). Although GO is not lucrative in increasing electrical conductivity (EC) of cement paste compared to that of graphene- another derivative of GO, reduced graphene oxide (rGO), might be a solution to increase EC. Another derivative of GO is the solution to the problem. In this research, the compressive strength and flexural strength of GO-cement composite (GOCC) and rGO-cement composite (rGOCC) have been investigated with 0.01% and 0.05% GO and rGO content. GOCC-0.05% showed 27% increase in compressive strength compared to the control cement paste after 28 days (d) of hydration. GOCC-0.01% showed only 3.4% increase in compressive strength compared to the control. rGOCC-0.05% showed 21% increase in compressive strength and 15.5% increase in Modulus of Rupture (MOR) compared to the control cement paste after 28 d of hydration. On the other hand, rGOCC-0.01% showed 7% increase in compressive strength and 0.35% increase in MOR after 28 d. GOCC-0.05% showed increasing trends in compressive strength after 28 d indicating continuation of hydration. Similarly, rGOCC-0.05% also showed increasing trends in compressive and flexural strength after 28 d, possibly due to the reason described earlier. Microstructural investigation on GOCC-0.05% and GOCC-0.01% by X-ray Diffraction (XRD) illustrated that the crystallite sizes of tobermorite-Å and jennite, which are mineralogical counterpart of disordered Calcium-Silicate-Hydrate (C-S-H), increases from 3 d to 28 d, representing the crystallite growth due to continued hydration. However, the crystallite size of GOCC-0.05% was smaller than that of GOCC-0.01% at both 3 d and 28 d, indicating finer nucleated grains. According to Hall-Petch equation, mechanical strength increases with decreasing particle size. Finer particles or grains can increase the strength in cement composites in several other ways: (1) GO acted as heterogeneous nucleation sites because of reactive functional groups. Activation energy was decreased by these defects in the cement paste, and consequently, numerous nuclei of C-S-H. with high surface area were formed, (2) because of finer grains, cracks are forced to move along a tortuous path, which makes the structure difficult to fail, and strength increased consequently (3) Finer grains of GOCC-0.05% created compacted hydration products decreasing porosity which can indirectly increase the strength. The above reasons, separately or in conjunction, might increase the strength of GOCC-0.05% and proved that GO is responsible for increasing heterogeneous nucleation sites during cement hydration. Early age hydration (EAH) characteristics were investigated for rGOCC specimens with 0.1% and 0.5% rGO content. Scanning Electron Microscope (SEM), Energy Dispersive X-ray analysis (EDX), and X-ray Diffraction (XRD) were employed to study the EAH characteristics. SEM/EDX, and XRD analysis were performed after 15 min, 1 h, 3 h and 24 h of hydration. (EAH) study on rGOCC-0.1% showed that at 15 min hydration, numerous precipitates of, possibly, C-S-H formed along the grain boundary (GB) of unhydrated cement grains. This served as visual confirmation of Thomas and Scherer\u27s Boundary Nucleation and Growth (BNG) model that hydration of cement grains was initiated by the short burst of nucleation of C-S-H embryos along GB. EDX on rGOCC-0.1% and rGOCC-0.5% showed that Ca/Si ratio in C-S-H was ~2.0. This finding indicated that C-S-H structure in this study was concurrent with that of impure jennite. XRD analysis also evidently showed that jennite was present, possibly possessing a short range ordered (SRO) structure, referring to local crystalline structure in a very short area. After consulting Chen\u27s work, it would be appropriate to say that C-S-H found in this study resembled more as C-S-H (II), which is disordered jennite. It was also observed that as expected with cement with nanomaterials, with continuing hydration, pore spaces were filled with hydration products such as C-S-H, ettringite, CH, sulfoaluminates etc,. Lastly, Electrical resistivity (ER) testing on 9 sets of rGOCC specimens was conducted. The specimen includes 0.5%, 1%, 5% rGO content, and the control conditioned in both oven dry (OD) and saturated surface dry (SSD). ER increased with the increase of rGO content from 0.5% and 1% compared to that of the control. However, the ER of rGOCC-5% was significantly decreased, showing 93% reduction compared to the control, which can be interpreted as a threshold value for sensing applications to be explored. As expected, large reduction of ER value occurred on the specimens with the SSD condition. This reduction can be attributed to the ionic conduction though the pore solution of the composites. As the rGO content increased, so did the potential nucleation sites for hydration (as can be seen in SEM images), which might block the number of contact points among the rGO, resulting in low conduction and high resistivity. However, as rGO content increased to 5%, the contact areas/points increased to a degree that could trump the nucleation seeding sites, resulting in decreased ER. The ER measured with the rGOCC specimens was comparable to that of cement composites incorporating carbon fibers (CF), and steel fibers, but higher content of rGO are required to have a similar ER range of those fiber cement composites. This might be due to smaller sizes of rGO sheets and lower aspect ratio compared to other nanofibers causing drastic reduction of electron tunneling mechanism compared to other fibers

Evaluation Of Recementation Reactivity Of Recycled Concrete Aggregate Fines

The use of recycled concrete aggregate (RCA) as a drainage material in exfiltration trenches and base and subbase layers is becoming increasingly common. During crushing, stockpiling, transporting, and placing, however, RCA may produce fines that could recement and clog the pavement drainage system. Many previous studies indicated that not only the structural capacity but also drainage of pavement subsurface layers can be greatly affected by the properties and gradation of the aggregate used. This study evaluated the recementation reactivity of RCA fines that could eventually impair drainage performance. RCA fines passing the No. 200 sieve (less than 75 μm) were produced through the simulation of an in-place aggregate abrasion process, and cement paste cylinders were cast with complete replacement of cement with RCA fines. The hydration properties of the paste samples with RCA fines were evaluated by means of heat of hydration, pH variation, and Vicat needle penetration in their early age. Compressive strength tests and petrographic examinations such as scanning electron microscopy, energy dispersive X-ray, and X-ray diffraction were also performed to mechanically and chemically verify the recementation reactivity of the hardened paste with RCA fines. Test results demonstrated that recementation of RCA fines was modest, and therefore the compressive strength of the paste specimens with RCA fines was minimal compared with that of ordinary cement paste specimens. The microstructural and chemical composition analyses also indicated that the recementation reactivity of RCA fines was negligible

Recycling Of Municipal Solid Waste Incineration (Mswi) Ash As Aggregate Replacement In Concrete

In the U.S., about 250 million tons of municipal solid waste (MSW) is being generated annually, but only 34% of it is recycled or composted. The rest is combusted and / or disposed of in landfills. Combusting MSW is one of promising options to convert waste into energy and also it significantly reduces the volume of waste by nearly 90%. As byproduct, municipal solid waste incineration (MSWI) bottom and fly ashes are produced. Unlike European and Asian countries, the beneficial use of MSWI ash has not received an attention in the U.S. The use of MSWI ashes in civil construction sector can be one of promising options. The objective of this paper is to evaluate the feasibility of MSWI bottom ash (BA) as partial replacement of fine aggregate in concrete. Laboratory experimental studies were conducted to evaluate physical, mechanical, and durability performance of concrete containing the BA. The mechanical performance was investigated by measuring compressive strength at 28 days of age and absorption capacity. Analysis on measured data has shown that the addition of MSWI ash into concrete does not increase strength and durability properties but has comparable results with control samples

Recycling of Municipal Solid Waste Incineration (MSWI) Ash as Aggregate Replacement in Concrete

In the U.S., about 250 million tons of municipal solid waste (MSW) is being generated annually, but only 34% of it is recycled or composted. The rest is combusted and / or disposed of in landfills. Combusting MSW is one of promising options to convert waste into energy and also it significantly reduces the volume of waste by nearly 90%. As byproduct, municipal solid waste incineration (MSWI) bottom and fly ashes are produced. Unlike European and Asian countries, the beneficial use of MSWI ash has not received an attention in the U.S. The use of MSWI ashes in civil construction sector can be one of promising options. The objective of this paper is to evaluate the feasibility of MSWI bottom ash (BA) as partial replacement of fine aggregate in concrete. Laboratory experimental studies were conducted to evaluate physical, mechanical, and durability performance of concrete containing the BA. The mechanical performance was investigated by measuring compressive strength at 28 days of age and absorption capacity. Analysis on measured data has shown that the addition of MSWI ash into concrete does not increase strength and durability properties but has comparable results with control samples

Effect Of Chemical Treatment Of Mswi Bottom Ash For Its Use In Concrete

In this paper, municipal solid waste incineration (MSWI) bottom ash was characterised before and after chemica treatment and the effect of ash addition on the performance of concrete as a partial replacement of fine aggregate was evaluated. The chemical treatment aimed to eliminate the side effect of MSWI ash - the creation of a network of bubbles - which can eventually lead to a significant reduction of the overall performance of concrete Petrographic examinations, energy dispersive X-ray spectroscopy and X-ray diffraction, were carried out to chemically characterise the MSWI bottom ash. The mechanical performance of the ash-combined concrete was evaluated by measuring its compressive strength. Analysis of the measured data demonstrates that the chemica treatment successfully transformed metallic aluminium in the ash into a stable form and hence expansion of the concrete due to hydrogen gas evolution was no longer detected in the concrete containing treated ash Consequently, compared with specimens with untreated ash, concrete specimens with treated bottom ash showed improved performance

Effect of chemical treatment of MSWI bottom ash for its use in concrete

In this paper, municipal solid waste incineration (MSWI) bottom ash was characterised before and after chemica treatment and the effect of ash addition on the performance of concrete as a partial replacement of fine aggregate was evaluated. The chemical treatment aimed to eliminate the side effect of MSWI ash - the creation of a network of bubbles - which can eventually lead to a significant reduction of the overall performance of concrete Petrographic examinations, energy dispersive X-ray spectroscopy and X-ray diffraction, were carried out to chemically characterise the MSWI bottom ash. The mechanical performance of the ash-combined concrete was evaluated by measuring its compressive strength. Analysis of the measured data demonstrates that the chemica treatment successfully transformed metallic aluminium in the ash into a stable form and hence expansion of the concrete due to hydrogen gas evolution was no longer detected in the concrete containing treated ash Consequently, compared with specimens with untreated ash, concrete specimens with treated bottom ash showed improved performance