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By means of reducing the ratio of water to cement (w/c), incorporating a proper amount of fly ash and superplasticizer, and processing the surface of recycled aggregate (RA), this paper aims at improving the interfacial transition zone (ITZ) submicro-structure of the regenerated concrete (RC). The experimental results of mercury intrusion pressure (MIP) show that RA pretreated by PVA polymer solution and lyophobic active agent can jam its surface pore and hole, thus the porosity of RA is decreased. When reducing w/c ratio, incorporating 20% of fly ash (FA) and 2.5% of superplasticizer (to cement) in the RC, the width of ITZ is effectively narrowed, the structure of ITZ is combined much more compact and the compressive strength of RC is enhanced. Under the same conditions, using RA pretreated by 1% PVA polymer solution, the fluidity of fresh RC can be enhanced and the compressive strength of hardened RC can also be enhanced lightly. Whereas using RA pretreated by lyophobic active agent, the fluidity of fresh RC can be enhanced, but it impairs the adhesion of fresh cement paste and the surface of old concrete, and hinders the strength development of RC. In the ITZ structure of ordinary concrete (prepared with natural coarse and fine aggregate) there are much Ca(OH)2, in plank-and sheet-like, distributing with priority tropism, whereas in the RC structure, Ca(OH)2 with a coarse size is not found in ITZ; the main reason is that the surface of coarse aggregate does not have a layer of water film.

Copper gangue (CG), containing a large amount of water with grain sizes of 0.037 to 0.10mm, is an inactive industrial waste generated from copper refineries. When it is dried and used as a cement admixture, the influence of the presence of finely dispersed metallic particles in CG on the microstructure and compressive strength of cement paste has been studied. The results show that the higher the replacement of CG is, the lower the compressive strength of cement mortar is. However, the long-term strength of the specimens with 10% CG, especially after being cured for 3 months, approached to that of the plain mortar. Its mechanism was studied by an electron probe X-ray microanalyzer (EPXMA). The results indicate that a small quantity of Fe(OH)3·nH2O slowly formed from Fe2O3 in the presence of Ca(OH)2, free CaO and MgO of the clinker also slowly hydrated and formed Ca(OH)2 and Mg(OH)2 respectively, so the hardened cement paste became more compact.

Publisher Summary This chapter investigates the influence of copper gangue (CG) used as a cement admixture on cement mortar strength and the influence of CG used as a raw material on cement clinker mineral morphology. When the CG was used as a cement admixture, the early strengths of the cement decreased with the increase of CG, however the long-term strengths of the cement, especially after 3 months, clearly increased. CG substitution percentage by weight of cement should be controlled below 20%, as the compressive strengths at 1 year incorporating more than 20% CG decreased lightly. CG used as a raw material, due to the Cu, Zn, Ti, Mn, and Ag microelements can decrease clinker burning temperature and liquid viscosity, with advantage to clinker burning. A blended admixture with low content of CaF2-CaSO4 • 2H2O could take a partial mineralization effect and further benefits the clinker burning.