Effect of high volume fly ash and metakaolin with and without hydrated lime on the properties of self-compacting concrete

Abstract

Properties of self-compacting concrete with high contents of mineral additions have been studied worldwide, but the analysis of their hydration and compressive strength evolution with inclusion of hydrated lime is still incipient. This study evaluated the compressive strength and hydration development of self-compacting concrete with reduced cement content (SCC-LC). To do this, Portland cement (PC), metakaolin (MK), fly ash (FA) and hydrated lime (HL) were used in binary, ternary and quaternary cementitious mixtures. Nine SCC mixtures were produced: one mixture with just cement with 500 kg/m³ (reference), four with binder content of 500 kg/m³ (200 and 150 kg/m3 of cement), and four with binder content of 400 kg/m³ (160 and 120 kg/m3 of cement). Cement replacement with FA and MK, with or without addition of HL was tested in both SCC-LC: binder 500 kg/m³ (B500) and binder 400 kg/m (B400). Normal Vibrated Concrete (NVC) with cement content of 300 kg/m³ was produced just to compare its compressive strength with SCC low cement content (B500 and B400). The replacement promoted a cement reduction equivalent to 60%–70% compared to the reference composition (C500). SCC were evaluated using the slump flow test, T500, V-test, L-box and J-ring tests. The evaluation of the growth of the compressive strength was carried out at 3, 7, 14, 21, 28 and 90 days. Hydration evaluation was performed by X-ray diffraction at 28 days. The obtained results proved the possibility of producing SCC-LC with cement content between 120 and 200 kg/m3 due to the excellent ability of FA and MK to maintain cohesion. Compressive strength measured at 28 days of SCC-LC ranged between 25 and 40 MPa, with a cement use efficiency of 3.2–5.0 kg.m-3 MPa-1. SEM and X-ray diffraction showed that the main hydrated products formed were the gismondine and C–S–H, and that the Portlandite was totally consumed in hydration at 28 days, except for a mixture of SCC with FA and HL.