The cemented structure has a great impact on the behavior and stability of cemented granular materials (CGMs). Therefore, modeling realistic cemented structure is important to capture the macroscopic performance of CGMs. In this study, X-ray microtomography is leveraged to probe the microstructure of 3D CGMs formed by cement grouting. The effect of flowability of self-compacting cement (SCC) on the microstructure of CGMs is investigated. To describe the anisotropy of the intergranular cementation, the cementation tensor is established. The results show that the distribution of cross-sectional area of intergranular bonding follows a log-normal distribution. The SCC flowability has a great influence on the microstructure of CGMs. The average cross-sectional area and average number of all intergranular bonds both increase linearly with the yield stress of SCC. The influence of cementing ratio on the anisotropy degree of various ce-mented structures is also illustrated, providing a viable means to understand the reinforcement effect of cementation.
This paper aims to verify a space-averaged electric filed simulation, where the whole surfaces of reinforcing bars are blended into the 3D finite volume for identifying the electric potential to drive the macro-cell corrosion of structural concrete. Experimental verification is conducted with transparent pseudo-concrete, which has chemical pore-solutions similar to those of concrete, and with which the location of anodic poles accompanying brownish rusts and the cathodic ones surrounded by hydrogen bubbles may be visually identified. The proposed electro-chemical analysis platform to be integrated with ion transport and equilibrium is adopted for full consistency with dispersed reinforcing bars. Global macro-cell corrosions of tunnel mockup and reinforcement layers induced by electric current leakage are verified quantitatively with dispersed multi-ion concentration as well as corrosion profile.
Change in the mechanism of post corrosion bond behavior was investigated in a previous experimental study by analyzing the deformations in concrete using digital image correlation (DIC). Using their DIC data, this study focuses on the local strain non-uniformity in reinforcing bar during the uniaxial tensile test due to the effect of rib height reduction and corrosion layer. The results show that, the local strain below the rib tip is higher than that below the flat part between ribs, due to compressive stress resulting from mechanical interaction at the rib tip. Furthermore, the non-uniformity in local strain is less pronounced in highly corroded reinforcing bar because less compressive stress is transferred due to gentler rib slope. In highly corroded reinforcing bar, the appearance of non-uniformity in local strain is delayed since the accumulated corrosion product on the reinforcing bar surface delays the mechanical interaction and stress transfer between the concrete and the reinforcing bar.
Although numerous studies have proven the effectiveness of self-healing technologies in concrete, its practical application is limited to only few trials. One of the reasons lies in the lack of self-healing in-situ non-destructive evaluation methods as opposed to invasive and extensive laboratory testing. In this study, a novel Terahertz (THz) wave imaging technique is proposed as a simple, non-destructive, and non-contact measurement methodology to quantitatively evaluate the self-healing effectiveness of cementitious materials. Experiments were conducted in fiber-reinforced cementitious composites (FRCC), which confirmed self-healing performance based on a combination of stimulated autogenous and autonomous healing by using supplementary cementitious materials (FRCC), and PVA fibers; the self-healing index was also calculated by using novel THz wave measurement and compared with existing evaluation methods. Simultaneously, sorptivity test and microstructural characterization on damaged and healed specimens were conducted as the conventional methods. As a result, the proposed THz imaging successfully quantified the self-healing performance on cementitious samples. Also, a correlation between the recovery rate (cracked/healed) measured by sorptivity test and THz wave imaging was defined.
Cyclic loading tests are conducted for four cases with upper-limit stress ratios of 35%, 50%, 65%, and 80% in order to investigate the crack resistance under compressive stress of concrete made using granulated blast-furnace slag sand (BFS), obtained from three steelworks in Japan. Mountain sand is used as a natural aggregate for comparison and the energy for crack nucleation and propagation is derived for each type of concrete. It is found that BFS concrete generally has a lower crack propagation energy and a higher strain recovery rate than concrete made using natural aggregate. Within the scope of the study, BFS concrete is deemed to possess adequate resistance with respect to concrete crack propagation, regardless of the type of BFS used. This paper is an English translation of the authors’ previous work [Hashimoto, R. and Onoue, K., (2022). “Crack resistance of concrete using granulated blast-furnace slag sand under compressive stress.” Proceedings of the Japan Concrete Institute, 44, 338-393. (in Japanese)].