Performance of Concrete with Mechanochemically Activated Rice Husk Ash-Based Organomineral Modifiers

This study evaluates a wet-activated multicomponent organomineral modifier for sustainable concrete. The modifier was produced by co-grinding Portland cement and rice husk ash (RHA) in the presence of Sika® ViscoCrete®-20HE and was subsequently combined with polypropylene fibers. Three modified mixtures were tested after 28 days of curing and compared with a control concrete. The modified concretes achieved compressive strengths of 42.2–45.0 MPa, compared with 36.8 MPa for the control. Among the tested formulations, Mix 2, containing 6 wt.% RHA, 4 wt.% polypropylene fibers, and 1.3 wt.% superplasticizer, showed the most favorable overall performance. Its compressive and flexural strengths reached 45.0 and 5.8 MPa, corresponding to observed differences of 22.3% and 26.1%, respectively, relative to the control formulation. Because the complete mixture compositions and w/c ratios differed, these comparisons do not isolate the contribution of any individual constituent. Fracture toughness increased from 1.15 to 2.16 MPa·m1/2, water absorption decreased from 6.8% to 5.1%, and freeze–thaw resistance increased from 138 to 242 cycles. Qualitative SEM and XRD observations showed morphological and phase-related differences between selected control and modified specimens; however, these observations did not establish the causes of the measured performance differences. In addition, because no compositionally identical non-activated RHA reference or direct reactivity test was included, the independent effect of wet activation on RHA reactivity could not be established. The investigated integrated modifier therefore shows potential for improving concrete performance while enabling the beneficial use of RHA.