Residual Service Life Estimation and its Importance for Pretensioned Concrete (PTC) Bridges in Coastal Cities

Many pre-tensioned concrete (PTC) bridges are experiencing premature chloride-induced corrosion. Hence, it is crucial to estimate their residual service life and update it with newer data on a periodic basis - to plan for corrosionpreventionorcontrolmeasuresandensuresafetyofexistingbridges.Criticalchloridethreshold(Cl th) is one of the parameters necessary to estimate the corrosion initiation period. However, quantitative estimates on Clth for prestressing (PS) steel are not well-reported in literature. This paper presents experimental data on the Clth of PS steel, the chloride diffusion coefficient (Dcl), and surface chloride concentration (Cs) of concrete samples obtained from a PTC bridge girder in a coastal city in India. For estimation of Clth, 5 specimens were cast with PS steel wires embedded in ordinary Portland cement (OPC) mortar containing 30% of Class F fly ash (similar composition as that of the bridge girder). They were cured for 28 days and then subjected to cyclic wet-dry exposure using simulated concrete pore solution containing 3.5%sodiumchloride.(Linear polarization resistance (LPR) tests were performed at the end of each exposure cycle, corrosion initiation was detected using statistical methods, and Clth was determined). Using the determined Clth and Dcl, and other relevant parameters, the cumulative distribution functions of time to corrosion initiation was developed. It was found that the average time to corrosion initiation was about 40 years, whereas the structure was designed for 120 years. Also, it was estimated that the corrosion products will accumulate within the interstitial space between the 7 wires in a strand and will not flow through the concrete cover and reach the concrete surface (showing rust stains) until about 5% of strand is corroded (about 10 years). This indicates a dire need for regular data collection, updating the residual life estimates, which will help in developing corrosion prevention strategies for PTC structures

Assessment of autonomous and autogenous healing on cementitious grouts promoted by additions of microcapsules and crystalline admixtures

The demand for more sustainable building materials has led to the development of systems with self-repairing properties. The self-healing technology has been shown to be effective in concrete and mortars, however, this technology is not often studied in grouts. Cementitious systems can show an autogenous healing, i.e., an intrinsic ability to repair microcracks by themselves. This type of healing can be improved by the addition of crystalline admixtures. In addition, the crack healing can also be enhanced by adding other materials, e.g., through the incorporation of polymeric microcapsules into the cementitious matrix that will promote a healing effect but, in this case, an autonomous healing. Thus, the main objective of this work is to assess the effect of the addition of microcapsules and crystalline admixture on viscosity and water capillary absorption of cementitious grouts. Cementitious grouts (w/b = 0.46 and w/b = 0.39) were prepared containing microcapsules (3% by weight of binder) and crystalline admixture (3% by weight of binder). Rheological measurements and water sorptivity tests were made. Viscosity measurements were taken at 3, 20 and 60 minutes. Sorptivity tests were performed on cracked specimens in order to quantify the healing efficiency. Cracks were created 7 and 28 days after casting and the water absorption was measured for 7, 14 and 28 days after cracking. The results showed that the viscosity changed considerably depending on the w/b ratio and the healing agent type. Among all grouts, reference grout presented the highest viscosity and grout with microcapsules and crystalline admixture the lowest. The water absorption of the grouts with microcapsules was the lowest regardless of curing age and w/b ratio. Regarding crystalline admixture, at both curing ages the water absorption was quite high

Life Cycle Assessment (LCA) of Microcapsule based self-healing in concrete

Self-healing technologies provide the long-term resilience of concrete structures by enabling self-diagnose and self-repair of damages (aging cracks, cyclic load damages, and corrosion-induced cracks). However, self-healing technologies require special additives and materials in addition to the ones in conventional concrete. Hence, it is often perceived to have higher environmental impacts, and therefore, it is necessary to understand the same. This study is aimed to analyse the life cycle assessment (LCA) of concrete with microcapsules produced by different techniques to investigate the sustainability of these concretes. Two microcapsule techniques, namely complex coacervation and membrane emulsification, were studied at the laboratory scale and then projected to the industrial scale. The analysis shows that the concrete with microcapsules does not adversely impact the emissions in the production stage if supplementary cementitious materials are used. Further, if the beneficial effects of the self-healing technologies are considered in the use phase, the impacts are much lower. Thus, this assessment gives meaningful insights by identifying major impacts in the production of self-healing technologies and helps to improve their design and application in concrete

Self-Waterproofing Performance of Repair Mortars With Inorganic Healing Agents

In Europe, about 55% of concrete bridges are about 50 years old and require non-structural rapid repair strategies to reinstate the aesthetic and durability performances. Existing strategies focus primarily on superficial restoration that continues to demonstrate premature deterioration due to inevitable micro-crack formations that further propagate to macro-cracks leading to the ingress of moisture along with harmful ions. In this study, the benefits of self-healing technology to control moisture ingress at the microscale were investigated. For this, tailored microcapsule with inorganic healing agent, specifically, commercially available water-repellent agent (SIKAGARD 705L) was added to mortar with two types of commonly used binders namely CEMI 52.5N and CEMI 52.5R. The compatibility assessment in terms of capsule integration, fresh and hardened properties was done. The baseline healing efficiency of the mortars without any healing additions was obtained to understand the autogenous healing capacity of the reference mortars. Subsequently, the reference mortar mixes were compared with mixes containing varying fractions of microcapsules (3, 5, and 10%) for autonomous healing efficiency with capillary absorption as the main durability function. The healing efficiency was further investigated for two different crack mouth widths (350 μm); representative of non-structural residual crack widths. In mortars with microcapsules, a maximum reduction of sorptivity coefficients up to 82% and 78% with CEMI 52.5N and CEMI 52.5R mortars, respectively, for specimens cracked after 7 days of curing was observed. Subsequently, a synergetic effect of autogenous healing action and autonomous water-repellent action for durability recovery was identified and proved useful for repair mortar applications. The healing agent investigated, capsule content, and healing environment considered in the current study lay a foundation for further optimisation to improve the performance and to suit different applications

Large-Scale Laboratory Trials of Self-Healing Technologies

Prolonging the life of the reinforced concrete structure is the most promising solution to reduce the carbon emissions from concrete. To achieve that, the structure should be protected from crack formation, which acts as an easy pathway for deleterious agents. Self-healing technologies are intended to provide long-term resilience against cracking due to various deterioration processes. Technologies that performed well in small, laboratory-scale studies are taken to the next level to assess their performance on a larger scale and monitored using various NDT equipment. A 1m long beam with a cross-section (140×120 mm) was cast with two rebars – one with a cover depth of 50 mm from the top and another with a cover depth of 20 mm from the bottom. The mix design consists of CEM IIIA (50 OPC: 50 Slag) cement and 30% lightweight aggregate as a replacement for coarse aggregate. At 28 days of curing, the concrete beams are subjected to accelerated corrosion (by applying a voltage to the bottom rebar) to induce internal cracking. Once internal cracking is induced, the beams are subjected to another 28 days under water for healing. The performance of the beams is monitored via ultrasonic pulse velocity and half-cell potential before and after voltage application. This paper shows the preliminary results and the self-healing efficiency and corrosion resistance of these beams are continuously being monitored under severe chloride conditions to predict the long-term performance

Assessing road repair materials via digital image correlation

This study investigates the performance of road repair materials using digital image correlation (DIC). Cementitious mortar prisms were produced for slant shear testing and repaired using a commercial belitic calcium sulfoaluminate (BSCA) mortar or polyurethane-based repair material. The repaired prisms were subjected to a slant shear test under repeated loading and unloading, and DIC was utilised to measure and compare the strain developed across the repaired prisms. The DIC-generated strain maps show clear differences in the strain between the two repair materials: the prisms repaired with the BCSA mortar showed less pronounced strain under loading across the prisms until the final loading, whereas the prisms repaired with the polyurethane-based materials exhibited a pronounced but consistent positive and negative strain. These differences in the strain across the samples are attributed to the difference in the elastic modulus of the two repair materials. This work highlights the potential of using DIC to assess the performance of road repair materials for their development in the laboratory and contributes to the longer-term objective of digitising road networks towards safer and longer-lasting roads

Vision-based multi-perspective road pre-damage detection

Road condition evaluation is essential for selecting maintenance strategies to prevent road failures. However, current road evaluation methods are subjective, manually performed and time-consuming, while road maintenance is mostly reactive with associated risks, such as possible network disruptions. Presented herein is a vision-based methodology for road inspection and evaluation. For this purpose, we couple digital image correlation (DIC) with perspective warping to measure material displacement or strain that can be an early warning of pavement failure. Our results show that perspective warped images were able to be successfully used in DIC analysis and obtain strain values within 19% of the images taken at a direct angle to the sample. Perspective warping enables us to bypass the limitation of fixed DIC applications and allows for the collection of images from mobile cameras such as everyday cars in motion. This provides new opportunities for the effective prediction of road damage formation and consequently predictive maintenance