An Experimental Study Of Oceanic Polymetallic Nodules And Cobalt-rich Crusts Residue Used As Cement Replacement And Cement Admixture

This is part of the Tenth-Five Project (DY105-2-04-14) Study on Application ofOceanic Polymetallic Nodules and Cobalt-rich Crusts Leaching Residues asFunctional Filling managed by China Ocean Mineral Resources R & Dassociation(COMRA). This paper focuses on experimental investigation on theresidue of ocean polymetallic nodules and cobalt-rich crusts used as cementreplacement and cement admixture. The microstructure and pore size distribution ofconcrete containing residue, hydration product of blended cement were investigatedusing SEM, mercury injection apparatus and XRD. The mechanism of the residueincorporated in concrete and blended cement was explored.The results indicate that using ocean polymetallic nodules to replace portlandcement at 5% by weight can increase the 28-day compressive strength of the concreteby 19.8%;using cobalt-rich crusts residue to replace portland cement at 5% and 10%by weight can increase the 28-day compressive strength of the concrete by 17.5% and11.6% respectively at 28 day. Incorporating certain amount of residue into concretecan improve its pore size distribution, decrease its average pore diameter, increase itsbulk density, also improve the transition zone structure, which results in a strongtransition zone between matrix and aggregate, as a result, enhances the strength andability against permeability of the concrete, etc.Compressive strength of the blended cement containing 10%～20% residue byweight satisfy Chinese Standard of the Portland Cement Grade 32.5. When cobalt-richcrusts residue which is heat activated at a temperature of 800℃ for 1 hour( 20wt.% )is incorporated into blended cement, the 3-day compressive strength and 28-daycompressive strength of the blended cement are increased by 21.0% and 6.6%respectively in comparison to the plain cement. XRD analysis indicates thatRhodochrosite does not react in the early hydration period;more amount of AFt isfounded in the early hydration product of blended cement containing cobalt-richcrusts residue, as it has semi-hydrated gypsum content up to 21%, which reactes withC3A. The semi-hydrated gypsum in cobalt-rich crusts residue turns intocalcined-gypsum (Ⅱ) after heat activation, and because of the low dissolution rate ofcalcined-gypsum, the retarded action of ettringite on clinker hydration is decreased, sothe whole clinker mineral hydration is accelerated, and the cement strength isenhanced. All kinds of the blended cement provide comparatively high durabilityproperties.This paper analyzed technical feasibility, economic and social efficiency ofocean polymetallic nodules and cobalt-rich crusts used as cement replacement andcement admixture. And believe the application of the residue in cement and concreteindustry could save energy and resources, protect environment, which is inaccordance with "Building Resources Efficient and Environment Friendly Society" .