High-efficiency stabilization of dredged sediment using nano-modified and chemical-activated binary cement

Utilization of nano-silica is an effective method to improve the early properties of blended cement containing high-volume slag. In current work, the hydration of blended cement with high-volume slag (40 wt%, 60 wt% and 80 wt%) and nano-silica has been investigated by testing setting time, heat of hydration, compressive strength, hydration products and pore structure. The results illustrate that nano-silica can improve the hydration of slag and cement (including tricalcium silicate (C3S) hydration and transition from ettringite to monosulfate) before 3 d. The increased slag content affects the promotion of nano-silica on cement hydration. Besides, nano-silica inhibits the hydration of cement after 3 d. Furthermore, nano-silica can improve the content of chemically bound water and reduce Ca(OH)2 content. Combined use of appropriate content slag and nano-silica can better optimize the pore structure of hardened pastes, including pore size and cumulative porosity. Ultimately, nano-silica enhances the compressive strength of hardened paste, but the improvement effect of nano-silica gradually weakens with the increase of slag content and the extension of curing time. This paper can provide a theoretical basis for nano-silica modified cement with high-volume slag, and help to improve the early performance of cement with high-volume slag. 

Hydration of blended cement with high-volume slag and nano-silica

This study investigates the compressive and tensile strength properties of cement-stabilized dredged sludge (CDS) improved by straw fiber (SF) and nano-SiO2 (NS). The influence factors, in...

Strength Properties of Cement-Stabilized Dredged Sludge Incorporating Nano-SiO 2 and Straw Fiber

High-volume ground granulated blast furnace slag (GGBS) is often used in cementitious materials to produce environmentally friendly building materials. However, high-volume GGBS (HVS) can lead to numerous problems including low strength and loose structure of concrete at the early age. To overcome these drawbacks, nanosilica (NS) is used to compensate the early strength insufficiency of high-volume granulated blast furnace slag (HVS) cementitious material by improving the pore structure. Currently, it is still a challenge to perform accurate testing of the pore structure. Although mercury intrusion porosimetry is widely used to test the pore structure of cementitious materials, there is still some controversy. In this study, the 1H NMR tests are used to measure the pore structure of NS and HVS blended materials and compared with standard MIP tests to comprehensive evaluate the effect of NS on the pore structure of HVS cementitious materials. Results indicate that NS can significantly improve the early strength of HVS cementitious materials and the greater the volume of GGBS, the greater the degree of enhancement exhibited by NS. The compressive strength increases of 23.5% and 30.2% were presented by 3-day S6N2 and S8N2 samples while flexural strength increases of 25.3% and 68.7% was resulted. NS significantly reduces the amount of harmful pores and increases the amount of harmless pores (smaller than 100 nm) in the HVS cementitious materials, it was also found that NS had no significant effect on the reduction of the total pore volume. Results showed that the strength of samples with high porosity was not necessarily low, the pore distribution and pore composition have a greater effect on the strength than the total porosity. The pore volume (>3 nm) obtained from the MIP test was larger than the pore volume measured by 1H NMR for early age samples. The difference in the porosity and pore size distribution obtained from the MIP and 1H NMR test was large at early age. The effect of NS on the pore structure of HVS system was investigated in more detail by 1H NMR and MIP techniques to provide a further theoretical basis for the application of NS in HVS cementitious materials. 

Synergistic effect of nanosilica and high-volume granulated blast furnace slag on pore structure and mechanical properties of cementitious materials

This investigation studies the effects of hot water and hot air curing on the strength development, transport properties, and freeze-thaw resistance of mortars incorporating low-heat blast furnace slag cement and nanosilica (NS). Mortar samples were prepared and stored in ambient conditions for 24 h. After demolding, mortar samples were subjected to two different hot curing methods: Hot water and hot air curing (40 °C and 60 °C) for 24 h. For comparison purposes, mortar reference mixes were prepared and cured in water and air at ambient conditions. Strength development (from 1 to 180 days), capillary water porosity, water sorptivity, and freeze-thaw resistance were tested after 180 days of curing. The experimental results showed that both curing regimes accelerate the strength development of mortars, especially in the first seven days of hydration. The highest early strengths were reported for mortars subjected to a temperature of 60 °C, followed by those cured at 40 °C. The hot water curing regime was found to be more suitable, as a result of more stable strength development. Similar findings were observed in regard to durability-related properties. It is worth noting that thermal curing can more efficiently increase strength in the presence of nanosilica, suggesting that NS is more effective in enhancing strength under thermal curing.

/pdf/the-effects-of-temperature-curing-on-the-strength-bcgjk0kauk.pdf

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

The slow property gains of cement-based materials blended with industrial by-products such as fly ash (FA) and ground granulated blast-furnace slag (GGBS), especially at a high dosage, have been ascribed to be the main obstacle of increasing the sustainability of cement concrete industry. In this work, the effects of 1 mass% nanosilica on the properties of heat-cured cement-based materials blended with FA and GGBS were investigated. Three different percentages of FA or GGBS (15, 30 or 40 mass%) and four different curing temperatures (20, 60, 70 and 80 °C) were studied. The mechanical properties, hydration heat, mineralogy phase, calcium hydroxide content, and morphology were measured and analyzed after 1, 3, 7, and 28 days. The increase in 1-day compressive strength of 37.75% and 38.65% could be seen for samples blended with 30 mass% FA and 30 mass% GGBS and cured at 70 °C, respectively. More calcium hydroxide was consumed due to the acceleration effect of nanosilica on the pozzolanic reactivity of added FA and GGBS. More hydrates and a denser microstructure were observed in samples mixed with nanosilica compared with samples without nanosilica. This work showed the feasibility of using a small dosage of nanosilica to improve the properties of heat curing blended cement-based materials while improving greenability.

Effects of nanosilica on the hydration and hardening properties of blended cement-based materials under heat curing

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Effects of nanosilica on the hydration and hardening properties of blended cement-based materials under heat curing