How can graphene oxide improve the properties of cement?
In a recent study published in the journal MaterialsChinese researchers have studied the improvement of concrete properties through the addition of graphene oxide (GO).
Study: Effective use of graphene oxide in layered cement mortar. Image Credit: Daniel Ramirez-Gonzalez/Shutterstock.com
Concrete and nanomaterials
Concrete is the most widely used construction material due to its high compressive strength and low cost. The main limitation of concrete is that it is a brittle material with low tensile strength and low corrosion resistance. In addition, during the manufacture of Portland cement, a significant amount of CO2 is released. For this reason, researchers around the world are trying to improve the durability and mechanical properties of concrete.
Geometry of laminated cement mortar specimens. Image Credit: Liu, S et al., Materials
The advancement of nanomaterials has provided valuable opportunities to improve the properties of concrete in recent years. Several studies have demonstrated that nanomaterials like nano-silica, carbon nanotubes and GO improve the strength, toughness and durability of cement composites.
The present study analyzed the properties of cement mortar samples in layers with a graded distribution of GO.
The materials used by the researchers were ordinary Portland cement (OPC), standard sand and graphene. Cement and sand were used to prepare the concrete, and graphene was used to prepare the GO suspension. The method used was wet-on-wet lamination fabrication, in which a layer of fresh cement mortar containing GO was poured over a layer of previously poured cement mortar.
The researchers prepared two varieties of cement mortar samples: the first was an ordinary cement mortar without GO solution, and the second was a cement mortar incorporated with GO. The water-cement and sand-cement mass ratios for the two samples were 2.0 and 0.4, respectively. Additionally, to ensure that the samples had comparable workability, the amount of superplasticizer was adjusted and a mini-slump test was used to determine workability.
The mortar mix was poured into molds and mixed on a vibrating table to ensure high compaction during sample development. The molds were surrounded by polyethylene sheets and, in addition, the samples were molded and treated in a saturated lime water bath before testing to prevent water evaporation. Successive layers of fresh cement mortar and cement mortar with GO were poured to prepare the cement mortar beams in layers with the graduated distribution of GO.
Four cut locations of each sample. Image Credit: Liu, S et al., Materials
Scanning electron microscope (SEM) images of the plain cement mortar sample showed a loose and porous microstructure. SEM images of the GO-added cement mortar sample revealed a denser structure. The improvement in the mechanical properties of mortar cement incorporated with GO results from changes in the microstructure of the cement.
The bending strength results revealed that the strength increased to a maximum and then decreased as the delay time increased. Moreover, the resistance did not depend on the thickness of the cement layer. The highest flexural strength was found with a GO layer thickness of 12 mm and a delay time of 50 minutes. The maximum bending strength depended on the delay time for samples with different GO layer thicknesses.
Studying the images of layered cement mortar beams after flexural failure revealed a significant difference in crack development between layered and smooth cement mortar GO beams. In ordinary cement mortar, the beam crack was completely vertical and had a relatively flat fracture surface.
On the laminated cement mortar beam containing GO, inclined and tortuous cracks were observed. Also, compared to the control sample, the properties of layered cement mortar beams did not change when GO was added only in the tensile region of the samples. However, the interface developed between the layers of the samples significantly influenced the mechanical properties. Moreover, the interface adhesion was also affected by the delay time and the amount of GO in the samples.
Rapid chloride migration (RCM) tests revealed that a small amount of GO could significantly reduce chloride influx, and when the amount of GO was increased, the RCM effect also increased. The reason for the increase was that the presence of GO nanosheets increased the tortuosity of the cement matrix, which immobilized the migration of water and chloride ions by chemical bonding.
Development of specimen cracks: (a) L8T50, (b) L12T50, (vs) L16T50, (D) M, and (and) L12T300. Fractured surfaces of samples: (a’) L8T50, (b’) L12T50, (vs’) L16T50. Image Credit: Liu, S et al., Materials
The researchers developed functionally graded cement mortar beams using successive layers of mortar cement and embedded mortar cement GO. The effects of the thickness of each layer of cement mortar incorporated into the GO and the delay time on the mechanical and durability properties were studied.
The study demonstrated that the GO nanomaterial could be used in parts of cementitious composites to improve mechanical properties. This method provides a new approach to efficiently use nanomaterials in cementitious materials. Future research should investigate ways to improve interfacial adhesion between GO-incorporated cement mortar layers and GO-free cement mortar layers.
Liu, S.; Lu, F.; Chen, Y.; Dong, B.; Du, H.; Li, X. Effective use of graphene oxide in layered cement mortar. Materials 2022, 15, 2181. https://www.mdpi.com/1996-1944/15/6/2181