Investigation of peculiarities in the hardening process of portland cements with active additives out of waste

Abstract

This study deals with the impact of waste fluid cracking catalyst (FCC) and cupola dust (CD) on hardening process of various Portland cements (CEM I 42.5 R (PCR), CEM I 42.5 N (PCN), CEM II/A-S 42.5 N (PCSN)). The plain cement pastes and waste modified pastes (with cements replacement for 10 % of additives), also pastes with the well-known pozzolana additive, microsilica (MS), were investigated. The studies of development of hardening structure by ultrasound wave velocity (UWV) measurement method, of change of mineral composition and physical-mechanical properties were carried out. Impact of additives is subject to both the own properties (chemical, mineral composition and fineness) of additive and of cement. FCC accelerates noticeably the development of initial structure of finer cement (PCR) only. Beyond 24 h development of structure in all FCC modified pastes is going somewhat slower, nevertheless, after 28 days their structure is already more compact than that of plain pastes. The strength properties are changing accordingly. The development of initial structure of CD modified PCR, and especially PCSN, pastes is going faster, PCN - almost does not change. Beyond 24 h compacting of structure of all CD modified pastes was slower. For the early strength of cements, the impact of CD was negligible, after 28 and 90 days the strength of CD modified PCR and PCN pastes was lower than that of plain pastes. In the case of PCSN, the slag is activated by alkali and the strength increased. CD additive, like MS and FCC, decreases the OH- concentration in the liquid phase of hydrating cement suspensions at the initial period (till 3 h), however further in the course of 28 days it was growing and became higher than that of plain cement suspensions.

Tokį poveikį tikriausiai nulėmė CD esančios šarminių elementų priemaišos (K+ ir Na+ katijonai). Šios priemaišos portlandcemenčių ankstyvąjį stiprį paprastai didina, o tolesnį jo augimą lėtina. PCSN struktūros stiprumas padidėja tikriausiai dėl šarminių priemaišų aktyvinamojo poveikio šlakams. OH– jonų koncentracijos cemento suspensijose tyrimai parodė, kad pradžioje (iki 3 h) CD, panašiai kaip MS ir FCC, sumažina OH– koncentraciją, tačiau toliau 28 paras ji didėja ir tampa gerokai didesnė nei kontrolinėse suspensijose.