Microscopic analysis of pigmented concrete with rubber waste applied to the interlocking block

ABSTRACT In this work the microstructure of pigmented concrete with and without rubber residue was analyzed by scanning electron microscope, aiming its application in the manufacture of interlocking block. It was verified that the reference concrete (without rubber) presented dense and compact paste and according to the increase of the rubber content in the concrete, the tendency was observed to increase the porosity and number of voids in the cement paste, appearance of cracks and zone of sharp transition between aggregates and paste, except for the trace containing 5% rubber. These analyzes allowed a better understanding of the mechanical behavior of these concretes. The binder employed was structural white Portland cement. In order to give the interlocking block another architectural and aesthetic advantage, an inorganic type pigment based on iron oxides and blue chrome was used. The rubber residue used as a partial replacement for fine aggregate (natural sand) came from the tire retreading process and was added to the concrete in the following proportions 2.5%, 5.0%, 10%, 20%, 30% while the pigment content was kept constant, being 6% in relation to the cement mass. Regarding the mechanical tests, the results indicated that, for the traces containing 2.5% and 5.0% of rubber residues, the ABNT NBR 9781:2013 standard is attended with respect to the characteristic compressive strength at 28 days (greater than or equal to 35 MPa), which did not happen for the traces with 10%, 20%, 30%. Considering the concrete compositions studied in this research, it can be stated that the use of rubber waste as a partial substitute for sand is an alternative for recycling the product which adds a lot to the environment and avoids the inappropriate disposal of this environmental liability.

摘要 本研究采用扫描电子显微镜（Scanning Electron Microscope）分析了掺加橡胶残渣与未掺加橡胶残渣的着色混凝土的微观结构，旨在将其应用于联锁砌块（interlocking block）的生产。研究证实，基准混凝土（未掺加橡胶）的浆体致密密实；随着混凝土中橡胶掺量的提升，除掺加5%橡胶的配合比试样外，水泥浆体的孔隙率与孔隙数量均呈上升趋势，且会出现裂缝以及骨料与浆体间的突变过渡区。上述分析有助于更深入理解此类混凝土的力学性能。本研究所用胶凝材料为结构级白色硅酸盐水泥。为赋予联锁砌块额外的建筑与美学优势，本研究采用了以氧化铁和蓝铬为基料的无机颜料。本研究中作为细骨料（天然砂）部分替代材料的橡胶残渣来自轮胎翻修工艺，其在混凝土中的掺加比例依次为2.5%、5.0%、10%、20%、30%，同时颜料掺量保持恒定，为水泥质量的6%。关于力学性能测试，结果显示：对于掺加2.5%和5.0%橡胶残渣的配合比试样，其28天特征抗压强度符合ABNT NBR 9781:2013标准的要求（≥35MPa），而掺加10%、20%、30%橡胶残渣的试样则未达到该标准。综合本研究中的混凝土配合比设计，可得出结论：将橡胶废料作为天然砂的部分替代材料用于混凝土中，是一种环保的废料回收利用途径，可避免该类废弃物不当处置带来的环境隐患。