Avaliação das incertezas nas informações sobre as resistências à tração na flexão e compressão de argamassas cimentícias com lodo de ETA

Abstract

Research on the incorporation of water treatment plant sludge (WTS) into cementitious mortars plays an important role in environmental sustainability by enabling the reuse of solid waste and reducing improper disposal. This study investigated the incorporation of WTS, in both dried (uncalcined) and calcined forms, into Portland cement mortars, with emphasis on the measurement of flexural and compressive strengths, as well as on the evaluation of the uncertainties associated with these measurements. The sludge characterization included thermogravimetric analysis (TGA), X-ray diffraction (XRD), and the Modified Chapelle test. The XRD results indicated a high amorphous fraction in both dried and calcined samples, while the TGA defined 515 °C as the ideal calcination temperature. The consistency index showed that adding 10 % WTS significantly reduced workability (by about 40 %), whereas the mixture with 5 % WTS and superplasticizer maintained a consistency similar to that of the standard mortar. Regarding mechanical performance, the addition of 10 % dried WTS reduced flexural strength by approximately 64 % (2.7 MPa → 7.4 MPa control) and compressive strength by 42 % (14.4 MPa → 24.7 MPa control). The mixture with 10 % calcined WTS showed only a 4 % reduction, and the mixture with 5 % calcined WTS reached 30.9 MPa, about 25 % higher than the control, possibly due to the pozzolanic activity confirmed by the Pozzolanic Activity Index (PAI) and Modified Chapelle tests. The relative standard uncertainties for flexural and compressive strengths were below 5 %, consistent with laboratory measurement conditions. The analysis of the Kessel coefficients indicated that the applied load at the center of the specimens and the maximum failure load were the main contributors to the flexural and compressive strengths, respectively. The comparison of strength results, considering the expanded uncertainty, allowed the assessment of conformity with technical standards and the feasibility of using the mixtures in different applications. The study reinforces the importance of the metrological evaluation of uncertainties in mechanical tests, ensuring greater reliability and traceability of the experimental results of mortars incorporating WTS.