Analysis of alkali leaching mechanism on as-built cement concrete bridge deck pavement: View from the perspective of mesostructure characteristics

Abstract

The emergence of a new distress mode, known as alkali leaching, has been increasingly reported in the cement concrete bridge deck pavement (CCBDP). The presence of defects in the pavement structure causes the accumulation and movement of alkaline solution. The examination of the internal pore features of deteriorated pavements is advantageous in order to comprehensively reveal the mechanism of alkali leaching on CCBDP. The present research focuses on analyzing the mesostructure of alkali leaching specimens obtained from distressed pavement. This analysis is conducted using X-Ray Computed Tomography (X-ray CT) and digital image processing (DIP) technologies. In order to assess the correlation between pore characteristics and alkali leaching, a parameter known as the critical pressure difference (CPD) is defined and calculated to quantify the leaching ability. The results show that alkali leaching cores (ALC) have a higher number of voids compared to Normal Cores (NC), particularly for voids of larger volume. Inadequate compaction effort induces vertical connectivity of voids in the alkali leaching pavements, thereby impeding the movement of alkaline solution. A sensitive porosity interval around 4.5 ∼ 5.5 % is found, the DGAC with larger porosity will easily occur leaching phenomenon in the certain CPD section. The correlation between the porosity and the CPD is also identified, indicating that the porosity is the main inherent factor in alkali leaching.