The effects of seawater and nanosilica on the performance of blended cements and composites

Abstract

This study investigates the effects of seawater and nanosilica (3% by weight of cement), on the fresh and hardened properties of cement pastes and mortars produced with two types of low heat cements: Portland pozzolana cement (CEM II) and blast furnace cement (CEM III). The heat of hydration, initial and final setting times, rheological properties, strength development, sorptivity and water accessible porosity of the cement pastes and mortars were determined. The data reveal that cement type has a significant effect on the reaction rate of cement with seawater and nanosilica (NS). Specimens produced with slag-blended cement exhibited a higher cement reaction rate and the composite produced exhibited better mechanical performance, as a result of the additional reaction of alumina rich phases in slag, with seawater. Replacement of freshwater with seawater contributes mostly to a significant improvement of early strength. However, in the case of slag-blended cement, 28 day strength also improved. The incorporation of NS results in additional acceleration of hydration processes, as well as to a decrease in cement setting time. In contrast, the addition of NS results in a noticeable increment in the yield-stress of pastes, with this effect being pronounced when NS is mixed along with seawater. Moreover, the use of seawater and NS has a beneficial effect on microstructure refinement, thus improving the transport properties of cement mortars. Overall, the study has showed that both seawater and NS can be successfully used to accelerate the hydration process of low heat blended cements and to improve the mechanical and transport properties of cement-based composites.Publisher's Note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

The performance of ultra-lightweight foamed concrete incorporating nanosilica

“…The role of nanoparticles as foam stabilizers has been reported on by Sun et al [27]. Moreover, the seeding effect of NS leads to the earlier formation of the C-S-H phase [44], resulting in a substantial effect on thixotropic properties and the early strength development of concrete [45]. Figure 6 presents the results of the fresh density tests of the foamed concrete.…”

Influence of Nanoparticles from Waste Materials on Mechanical Properties, Durability and Microstructure of UHPC

“…It works as a very fine filler that fills the pores and densifies the microstructure. However, it can chemically react with CH in the pozzolanic reaction to produce additional C-S-H, which improves the strength [ 37 , 38 ]. At 28 days, the increase in compressive strength is still obvious; however, at a later age (91 days), the increase in compressive strength was reduced.…”

The Effects of Temperature Curing on the Strength Development, Transport Properties, and Freeze-Thaw Resistance of Blast Furnace Slag Cement Mortars Modified with Nanosilica

“…Reference mixtures (without nanosilica) were designated as series C, while mixtures containing nanosilica were designated as series N. Nanosilica suspension was mixed with water, prior to mixing with dry components. Based on our previous studies [ 40 , 41 , 45 ], 3% of nanosilica (by mass of cement) is the most effective dosage and it was therefore incorporated in the mortars. After mixing, the mortar samples were molded in 40 × 40 × 160 mm 3 prisms for water accessible porosity and water sorptivity tests, while 40 × 40 × 40 mm 3 cubical specimens were produced for compressive strength and freeze-thaw resistance tests.…”

“…The beneficial effects of nanosilica on the properties of cementitious composites, in fresh and hardened states, can be attributed to three synergistic NS effects: Nucleating, filling, and high pozzolanic activity [ 37 , 38 , 39 ]. The effects of NS on the cement hydration process of Ordinary Portland Cement (OPC) and on binary cementitious systems under ambient [ 40 , 41 ] and elevated temperatures [ 42 , 43 ] have been confirmed by calorimetric studies.…”