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Cement pastes reinforced with various concentrations of functionalised and unfunctionalised carbon nanotubes (CNTs) with different aspect ratios were studied in terms of their dispersion and reinforcement efficiency. Mechanical strength was correlated with geometrical characteristics of CNTs, as well as the microstructure of reinforced pastes. Optimal CNTs of 0·05–0·1 wt% were found effective in increasing the flexural and compressive strength of reinforced pastes up to 36% and 27%, respectively. Efficiently dispersed CNTs were effective in bridging microcracks up to around 1 μm width. The CNTs did not significantly affect the phase composition of cement pastes but accelerated the hydration process. Based on a proposed equation, strength improvement was correlated with CNT aspect ratio and volume concentration. This equation establishes guidelines for maximised strength development based on geometrical and compositional parameters; it can be used for more rational design of CNT-reinforced cement materials, covering different compositions, as well as types and amounts of CNTs.

This paper presents a literature review concerning the characteristics of MgO (magnesium oxide or magnesia) and its application in cementitious materials. It starts with the characterization of MgO in terms of production processes, calcination temperatures, reactivity, and physical properties. Relationships between different MgO characteristics are established. Then, the influence of MgO incorporation on the properties of cementitious materials is investigated. The mechanical strength and durability behaviour of cement pastes, mortars and concrete mixes made with MgO are discussed. The studied properties of MgO–cement mixes include compressive strength, flexural strength, tensile strength, modulus of elasticity, water absorption, porosity, carbonation, chloride ion penetration, shrinkage, expansion, and hydration degree. In addition, microscopic analyses of MgO-cement mixes are also assessed. Summarizing the results of different studies, it is concluded that MgO incorporation in cementitious materials generally decreases the mechanical strength and shrinkage, and increases the porosity, expansion, carbonation and chloride ion migration. However, it should be emphasized that the properties of the specific MgO used (mainly the calcination temperature, the reactivity and the surface area) have a significant influence on the characteristics of the cementitious materials produced.

For the efficient and durable design of concrete, the role of fiber-reinforcements with mineral admixtures needs to be properly investigated considering various factors such as contents of fibers and potential supplementary cementitious material. Interactive effects of fibers and mineral admixtures are also needed to be appropriately studied. In this paper, properties of concrete were investigated with individual and combined incorporation of steel fiber (SF) and micro-silica (MS). SF was used at six different levels i.e., low fiber volume (0.05% and 0.1%), medium fiber volume (0.25% and 0.5%) and high fiber volume (1% and 2%). Each volume fraction of SF was investigated with 0%, 5% and 10% MS as by volume of binder. All concrete mixtures were assessed based on the results of important mechanical and permeability tests. The results revealed that varying fiber dosage showed mixed effects on the compressive (compressive strength and elastic modulus) and permeability (water absorption and chloride ion penetration) properties of concrete. Generally, low to medium volume fractions of fibers were useful in advancing the compressive strength and elastic modulus of concrete, whereas high fiber fractions showed detrimental effects on compressive strength and permeability resistance. The addition of MS with SF is not only beneficial to boost the strength properties, but it also improves the interaction between fibers and binder matrix. MS minimizes the negative effects of high fiber doses on the properties of concrete.