Enhancing the engineering properties and microstructure of room temperature cured alkali activated natural pozzolan based concrete utilizing nanosilica

Abstract

The strength gain of alkali-activated binders (AAB) when cured at room temperature is delayed due to the slow polymerization process. This is the major impediment in the utilization of this green concrete in cast in-situ concrete structures. In order to expand the applications of these binders to various fields of construction, attempts have to be intensified to overcome this obstacle. Incorporation of finer materials with high specific surface area to enhance the reactivity of alkali activated concrete (AAC) is one of the potential approaches to accelerate their strength gain. In this regard, nanomaterials, such as nanosilica (NS), can play a key role. Therefore, to enable curing at room temperature, incorporation of NS as partial replacement of natural pozzolan (NP) in developing AAC is the focus of this research work. AAC mixes were prepared by partially replacing NP with NS up to 7.5% by weight. The compressive strength development was monitored until 180 days of room temperature curing (23 ± 2 °C). Flexural strength and modulus of elasticity of concrete were also measured. Constitutive models relating the engineering properties of the developed AAC were formulated using regression analysis. In addition, SEM and XRD techniques were used to assess the nature of the binder formed during alkali activation. The data developed in the reported study indicated that NP, without incorporating NS, can be used as precursor material for producing AAC that could be potentially used as a construction material. However, AAC mixtures incorporating NS exhibited remarkable enhancement in the mechanical properties and microstructural characteristics. The addition of, 5% and 7.5% NS resulted in superior mechanical properties and a denser microstructure due to the greater transformation of precursor material in to polymeric compounds. The tangible outcomes of this research highlights the importance of nanomaterials in improving the properties of green building materials.