We investigate the performance of graphene oxide (GO) in improving mechanical properties of cement composites. A polycarboxylate superplasticizer was used to improve the dispersion of GO flakes in the cement. The mechanical strength of graphene-cement nanocomposites containing 0.1–2 wt% GO and 0.5 wt% superplasticizer was measured and compared with that of cement prepared without GO. We found that the tensile strength of the cement mortar increased with GO content, reaching 1.5%, a 48% increase in tensile strength. Ultra high-resolution field emission scanning electron microscopy (FE-SEM) used to observe the fracture surface of samples containing 1.5 wt% GO indicated that the nano-GO flakes were well dispersed in the matrix, and no aggregates were observed. FE-SEM observation also revealed good bonding between the GO surfaces and the surrounding cement matrix. In addition, XRD diffraction data showed growth of the calcium silicate hydrates (C-S-H) gels in GO cement mortar compared with the normal cement mortar.

One of the environmental issues in most regions of Iran is the large number of bottles made from poly-ethylene terephthalate (PET) deposited in domestic wastes and landfills. Due to the high volume of these bottles, more than 1 million m3 landfill space is needed for disposal every year. The purpose of this experimental study was to investigate the possibility of using PET waste in asphalt concrete mixes as aggregate replacement (Plastiphalt) to reduce the environmental effects of PET disposal. For this purpose the mechanical properties of plastiphalt mixes were compared with control samples. This study focused on the parameters of Marshall stability, flow, Marshall quotient (stability-to-flow ratio) and density. The waste PET used in this study was in the form of granules of about 3 mm diameter which would replace (by volume) a portion of the mineral coarse aggregates of an equal size (2.36-4.75 mm). In all prepared mixes the determined 6.6% optimum bitumen content was used. In this investigation, five different percentages of coarse aggregate replacement were used. The results showed that the aggregate replacement of 20% by volume with PET granules would result in a reduction of 2.8% in bulk compacted mix density. The value of flow in the plastiphalt mix was lower than that of the control samples. The results also showed that when PET was used as partial aggregate replacement, the corresponding Marshall stability and Marshall quotient were almost the same as for the control samples. According to most of specification requirement, these results introduce an asphalt mix that has properties that makes it suitable for practical use and furthermore, the recycling of PET for asphalt concrete roads helps alleviate an environmental problem and saves energy.

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In this research, multi-walled carbon nanotubes were used to delay the propagation and growth of cracks in cement mortar on the nanoscale. To improve the dispersion of multi-walled carbon nanotubes in the cement mix a polycarboxylate superplasticizer was used. The mechanical strength of multi-walled carbon nanotubes-cement nanocomposites mix containing 0.1–2% nanotubes by weight (wt) and 0.5% superplasticizer by (wt) was measured and compared with that of cement prepared without multi-walled carbon nanotubes. It was found that the tensile strength of the specimens increased about 70% up to 0.3%, multi-walled carbon nanotubes. With further increase in multi-walled carbon nanotubes, a decrease in tensile strength was observed. Field-emission scanning electron microscopy used to observe the fracture surface of specimens containing 0.3 wt% nanotubes indicated that the multi-walled carbon nanotubes were well dispersed and there were no agglomerates visible in the matrix. Field-emission scanning electron microscopy observation also revealed good bonding between the multi-walled carbon nanotubes and the surrounding cement matrix. In addition, X-ray diffraction data showed the multi-walled carbon nanotubes accelerated the dissolution and growth of the calcium silicate hydrate hydration products compared with the control cement mortar. Mercury intrusion porosimetry test results showed that chemical species could not penetrate the specimens containing 0.1 wt% and 0.3 wt% multi-walled carbon nanotubes as easy as other specimens. Thermogravimetric analysis results indicated that the cement hydration was enhanced in the presence of the multi-walled carbon nanotubes.