Development of Next-Generation Construction Materials with Graphene Additives

Abstract

The developments of ordinary Portland cement (OPC) composites and alkali-activated binder composites have attracted significant attention in the past decade. Different technologies have been proposed to address current drawbacks of these construction materials (e.g. low tensile strength, flexural strength, and brittleness), reduce the amount of cement consumption or replace OPC products for minimizing the environmental impact of construction materials. Among many additives explored to address these problems, graphene-based materials have emerged in the last few years as one of the most promising additives with many exciting results. However, it is still lacking the depth of understanding the influence of key parameters of graphene materials, such as dosages and sizes, on mechanical and durability properties of the composites, and enhancing mechanism of pristine graphene (PRG) in the cement matrix. Moreover, no study has been reported on the influence of graphene oxide (GO) additives on mechanical and durability properties of fly ash (FA)/ ground granulated blast furnace slag (GGBS) alkali-activated binder (AAB) composites prepared with natural sand (NS) or lead smelter slag (LSS) sand cured at ambient temperature. This thesis consists of a series of studies with the focus on addressing current research gaps and making a contribution to the development of next-generation construction materials using graphene additives. The first experimental study on the effect of the dosage of an ultra-large size (56μm) of PRG industrially manufactured by an electrochemical process on compressive and tensile strengths of cement-based mortars reveals that the addition of PRG to mortars improves their mechanical properties, with characteristic concentration dependence. The mortar with 0.07% PRG is identified as the optimal concentration, which provides 34.3% and 26.9% improvement in compressive and tensile strength at 28 days, respectively. However, with the further increases in PRG contents, the enhancement of mechanical properties of mortars is limited due to the impact of the van der Waals force on the sedimentation of PRG suspension. The second study focuses on the size effect of PRG on mechanical strengths of cement-based mortars by considering a variety of PRG sizes, such as 5μm, 43μm, 56μm, and 73μm at the optimal dosage of 0.07% PRG. The study reveals that the mechanical strengths of mortars at 7 and 28 days significantly depend on the sizes of PRG. The mixes with size 56μm and 73μm show a significant influence on both the compressive and tensile strengths of mortars. In contrast, the mix containing size 43μm exhibits a significant increase in tensile strengths only. There are no significant effects on either compressive or tensile strengths for the mix with size 5μm. The third study presents the proposed reinforcing mechanism and optimized dosage of PRG for enhancing mechanical properties of cement-based mortars. The results confirmed that the strengths of the mortars depend on PRG dosages. The size of PRG has a significant effect on the enhancement rate of the mechanical strengths of the mortars, whereas it does not have a significant influence on the optimized PRG dosage for the mechanical strengths of the cement-based mortars. The dosage at 0.07% PRG is identified as the optimized concentration of PRG for enhancing mechanical strengths. The reinforcing mechanism of PRG in the cement matrix highly depends on the surface area of PRG sheets. The fourth and fifth studies show the effect of the dosages, sizes, and densities of PRG as well as design mixes on mechanical and durability properties of cement-based mortars cured at short-term and long-term periods. The study reveals that the addition of PRG to mortars can enhance compressive, flexural, and tensile strengths of mortars at different curing ages. The 0.07% PRG is identified as the optimum dosage for enhancing the mechanical strengths of the mortars. Incorporating a small amount of PRG additives into the mortar can improve its durability, such as water absorptions, voids, sulphate expansion, and water penetration depths. The results of the mix containing PRG size 73μm show the best improvement in the mechanical and durability properties of the mortars, followed by that of size 20μm and then size 40μm. The last experimental study on the influence of GO additive on mechanical and durability properties of AAB mortars containing NS and LSS sand cured at ambient temperature reveals that the increase of GGBS% in AAB results in a significant increase in compressive and tensile strengths, and a decrease in flowability, water absorption and dry shrinkage of the mortars. The results also show that the mortars with 0.05% and 0.1% GO additives provide better mechanical and durability properties compared to the control mixes. The results generated from this thesis show great potential for using PRG and GO as additives in OPC and AAB composites to develop next-generation construction materials. They not only address the current drawbacks of OPC and AAB composites but also reduce the environmental impact of using OPC and NS.