The filler effect: The influence of filler content and type on the hydration rate of tricalcium silicate

The partial replacement of ordinary portland cement (OPC) by fine mineral fillers accelerates the rate of hydration reactions. This acceleration, known as the filler effect, has been attributed to enhanced heterogeneous nucleation of C‐S‐H on the extra surface provided by fillers. This study isolates the cause of the filler effect by examining how the composition and replacement levels of two filler agents influence the hydration of tricalcium silicate (T1‐Ca₃SiO₅; C₃S), a polymorph of the major phase in ordinary portland cement (OPC). For a unit increase in surface area of the filler, C₃S reaction rates increase far less than expected. This is because the agglomeration of fine filler particles can render up to 65% of their surface area unavailable for C‐S‐H nucleation. By analysis of mixtures with equal surface areas, it is hypothesized that limestone is a superior filler as compared to quartz due to the sorption of its aqueous CO₃^2? ions by the C‐S‐H—which in turn releases OH^? species to increase the driving force for C‐S‐H growth. This hypothesis is supported by kinetic data of C₃S hydration occurring in the presence of CO₃^2? and SO₄^2? ions provisioned by readily soluble salts. Contrary to prior investigations, these results suggest that differences in heterogeneous nucleation of the C‐S‐H on filler particle surfaces, caused due to differences in their interfacial properties, have little if any effect on C₃S hydration kinetics.     

Effective recovery of pure aluminum from waste composite laminates by sub- and super-critical water

An innovative and environment-friendly sub- and super-critical water processes have been proposed for successful recovery of aluminum from composite laminated wastes. The effects of reaction temperature (190-400 °C) and residence time (10 and 30 min) were mainly investigated to recover aluminum in an intact form from two commercially available packaging materials, which were made by dry and extrusion lamination methods (samples A and B), respectively. After the reaction, carbon and oxygen contents in the solid-phase were measured by CHNS/O analyzer and the aqueous-phase was subjected for TOC, ICP and ethylene glycol analyses. The results suggested that, the dry laminated ‘sample A’ exhibited a gradual decrease in carbon and oxygen level with increase in reaction temperatures indicating separation of polymers from aluminum. At 10 min, temperature ranges from 340 to 400 °C and at 30 min, from 310 to 340 °C were optimum for the aluminum recovery, showing the lowest percentage of carbon and oxygen in the solid-phase. The aluminum was oxidized above the optimum temperatures. On the other hand, the extrusion laminated ‘sample B’ showed resistance to separation of polymers and the carbon and oxygen level decreased drastically only near the critical point of water. At 30 min, 370-400 °C led to an efficient recovery of aluminum. The results revealed that, temperature, reaction time and the lamination method were the key parameters that determined the recovery of aluminum. This study provides a framework for the effective material cycling of huge wastes of laminated composites using sub- and super-critical water technology.