Non-destructive evaluation of concrete with high contents of mixed waste from wind-turbine blades

Abstract

The mixed waste from wind-turbine blades, named Raw-Crushed Wind-Turbine Blade (RCWTB), contains fibers of Glass Fiber-Reinforced Polymer (GFRP) and particles of polymers and balsa wood. The performance of concrete incorporating RCWTB is altered by GFRP-fibers stitching the cementitious matrix and the low strength and stiffness of such particles acting as aggregates. This paper explores the suitability of Non-Destructive Testing (NDT) in assessing the mechanical behavior of such concrete. Regarding the variations of NDT properties, Ultrasonic Pulse Velocity (UPV) and rebound index decreased on average 0.03 km/s and 0.71 units per 1% RCWTB, respectively. Polymers and balsa wood reduced its density and surface hardness. In contrast, thermal conductivity was increased by 0.08 W/(m·K) per 1% RCWTB, although the heat insulation of GFRP and balsa wood kept values constant up to 4% RCWTB. In regression terms, flexural strength, tensile splitting strength and Poisson's coefficient could not be significantly predicted with any NDT property, either isolated or combined, due to their dependence on GFRP-fiber stitching effect. Compressive strength was successfully estimated using simple regression with any NDT property, although the highest accuracy was provided by multiple regression combining UPV and rebound index. Finally, only UPV showed a random residual distribution when developing predictive models for the modulus of elasticity. Thus, non-linear multiple-regression models for compression-related mechanical properties could be developed through conventional NDT measurements. These models had R2 coefficients above 90%, mean deviations between experimental and predicted values of 2% and safety factors of around 1.1 for the minimum expected value.