Reactivity and mechanical performance of geopolymer binders from metakaolin/meta-halloysite blends

Kaolin and halloysite are aluminosilicate materials widely available in Cameroon. The present study aims at investigating the fresh and hardened properties of consolidated metakaolin- meta-halloysite blends geopolymer binders cured at room temperature (23 +/- 3 degrees C). To produce the geopolymers, metakaolin was used as the main solid precursor and was replaced by meta-halloysite up to 50 wt%. The raw materials and synthesized products were characterized using BET, FX, XRD, FTIR, SEM/EDS, leachability, setting time, mechanical properties, water absorption, porosity and bulk density. The results revealed that both initial and final settings decreased with the rise of the meta-halloysite content. Such behaviour is related to the higher reactivity of meta-halloysite which led to a higher geopolymerization rate resulting in shorter setting and hardening times of the MK-based binder. Incorporating meta-halloysite increased the rate of release of aluminosilicate oligomers in the alkaline solution favourable for the development of a dense and strong matrix explaining the high mechanical performances. The compressive strength and bulk density increased from 30.3 to 65.2 MPa and 1.75 to 2.12 g.cm(-3), respectively. The highest performance was attained on sample GP50, which contained 50 wt% metakaolin and meta-halloysite (65.2 MPa) and also had a decreased porosity (13.02%) and water absorption (6.72%).