Abstract

This study investigates the carbonation behaviour of alkali-activated fly ash-based (AFA) concretes. AFA contains 20.67% of unburned carbon. GBFS and OPC were used as sources of calcium (20%). A mixture of NaOH and Na₂SiO₃ was used as activator. OPC concrete was used as reference material. AFA/GBFS, AFA/OPC and OPC concretes, with and without reinforcing steel, were exposed to accelerated carbonation in a chamber under controlled conditions (25 °C, 65% RH, 1% CO₂). In the non-reinforced concrete, the carbonation depth and compressive strength were evaluated up to 360 days. FTIR and SEM were used as complementary tests. Given that carbonation is one of the causes of corrosion in reinforcing steel, the electrochemical behaviour of steels embedded in alkali-activated concrete was evaluated using half-cell potential test, polarization curves and linear polarization resistance techniques. According to the obtained results, AFA/GBFS and AFA/OPC concretes are more susceptible to carbonation than OPC with compressive strength losses of up to 40%. Regarding the corrosion behaviour of the reinforcing steel, the AFA/GBFS concrete showed very negative potentials and high corrosion densities; however, at the end of the exposure period (20 months), the reinforcing steel showed no signs of deterioration, unlike the steel embedded in the OPC concrete.

摘要

本研究调查了碱活化飞灰基 (AFA) 混凝土的碳化行为。AFA 含有 20.67% 的未燃烧碳。GBFS 和 OPC 被用作钙的来源（20%）。NaOH和Na ₂ SiO ₃的混合物用作活化剂。OPC 混凝土用作参考材料。AFA/GBFS、AFA/OPC 和 OPC 混凝土，有和没有钢筋，在受控条件（25 °C、65% RH、1% CO ₂）。在非钢筋混凝土中，碳化深度和抗压强度评估长达 360 天。FTIR 和 SEM 用作补充测试。鉴于碳化是钢筋腐蚀的原因之一，采用半电池电位测试、极化曲线和线性极化电阻技术评估了嵌入碱活化混凝土中的钢的电化学行为。根据获得的结果，AFA/GBFS 和 AFA/OPC 混凝土比 OPC 更容易碳化，抗压强度损失高达 40%。关于钢筋的腐蚀行为，AFA/GBFS混凝土表现出非常负的电位和高腐蚀密度；然而，在暴露期（20 个月）结束时，钢筋没有出现劣化迹象，