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To explore the reaction mechanism of sludge, slag, lime, and fly ash in high temperature environments, the unconfined compressive strength (UCS) test was hereby implemented to study the effect on curing age, curing temperature, slag content and fly ash content about the strength of sludge. Scanning electron microscopy (SEM) was used to observe the microscopic composition of the substance, and X-ray diffraction (XRD) was used to analyze the mineral composition at the micro level to further disclose its reinforcement mechanism. The experimental results demonstrate the difference in the strength measured by different dosage of curing agent, and results indicate that the strength of high temperature curing sample was obviously higher than that of low temperature curing sample. When the curing temperature rises, the pozzolanic reaction and hydration reaction between materials are accelerated, and a certain amount of gel products are produced, playing a precipitation and bonding role between particles. The 28 days and 90 days strengths of the sludge samples with 20% fly ash and 80% slag dosing at 40°C were 1139 KPa and 1194 KPa, which were 1.4 and 1.1 times of that of pure cement solidified sludge. At 60°C, the strength of 14 days, 28 days and 90 days were 802 KPa, 1298 KPa and 1363 KPa, which were 1.1, 1.5 and 1.3 times of that of pure cement solidified sludge. Under the influence of an alkaline environment, the silicon-aluminum grid structure was interconnected into a denser network structure, and the compressive strength of lime-activated fly ash-slag was thus continuously enhanced. Affected by the high temperature, lime-activated fly ash-slag solidified sludge could significantly improve the middle and late strength of the sample. The research showed that the new solidification material can replace partly the concrete curing agent, thereby alleviating the carbon emission and environmental pollution problems arising from cement solidified sludge. [ABSTRACT FROM AUTHOR]

Chemical solidification based on cement is one of the most widely used methods to treat marine dredged silt (DS) with very poor engineering properties. This study investigated the strength and microstructure of cement-solidified salt-rich dredged silt (CSDS) modified by nanoparticles. The unconfined compressive strength (UCS) test showed that the UCS of CSDS containing 9% NaCl was obviously lower than that without NaCl. Furthermore, the detrimental effect of chloride salt on the UCS increased with its content significantly. The nano-SiO2 (NS) used as cement additives can significantly improve the UCS of CSDS and adding 8% NS can reduce cement usage by at least 40%. Compared with NS, the nano-MgO (NM) mainly improved the early UCS of CSDS within 7 days. The needle-like Friedel's salt (the reaction product of chloridion with cement) and lamellar brucite (expansive mineral) were clearly detected by the X-ray diffraction test. The calcium silicate hydrate and magnesium silicate hydrate mainly contributed to construct the skeleton, which was confirmed by the scanning electron microscopy images. The NS and NM with high reactivity can be used as effective cement additives to overcome the negative effect of chloride salt, so as to increase the strength of CSDS. [ABSTRACT FROM AUTHOR]