Modificatin of ITZ structure and properties of regenerated concrete

Abstract

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.