Crystalline admixture (CA) is an effective self-healing agent for mortar. However, the effects of crack parameters (i.e. crack width and cracking age) and the service environment on the self-healing behavior of CA-containing mortar are not well understood. Herein, the self-healing behavior of mortar containing a self-developed CA was assessed by testing strength recovery, impermeability recovery, and crack closure in pre-cracked specimens. Three initial crack widths (0.2, 0.3, and 0.4 mm), five cracking ages (3, 7, 14, 28, and 56 days), and four external exposure conditions (humidity chamber, air exposure, water immersion, and wet-dry cycles) are investigated. Furthermore, the influence of different external conditions on the healing products at the region of crack and the pore structure of hardened paste containing CA are studied. The results show that adding 4.54% CA into mortar allows rapid healing of 300 μm-wide cracks. Although wider cracks (400 μm) are more difficult to heal, the sorptivity coefficients of the mortars with 400 μm-wide cracks after healing decrease. When the cracks are produced at an earlier age, the pre-cracked specimens have higher recovery ratios of strength and impermeability after healing, and the specimens pe-cracked at a later age still have acceptable compressive strengths after healing. The analysis shows that the strengths and impermeabilities of pre-cracked mortars containing CA exposed to the four external conditions are all recovered. The best self-healing performance is observed for the specimens exposed to water immersion and wet-dry cycles conditions. Somewhat less good self-healing was observed in the specimens exposed to humid chamber condition, while the worst self-healing performance was in the specimens exposed to air exposure condition. This study provides a theoretical basis for the application of novel CAs in cement-based materials.

In preterm infants, there is a risk of life-lasting impairments due to hemorrhagic/ischemic lesions. Our time-domain (TD) near-infrared optical tomography (NIROT) system “Pioneer” aims at detecting both disorders with high spatial resolution. Successfully tested on phantoms, “Pioneer” entered the phase of improvements and enhancements. The current probe (A-probe) was adapted for an optoacoustics instrument. A new probe (B-probe) optimized for TD measurements is required. Our aim is to determine the optimal arrangement of light sources in the B-probe to increase the sensitivity and the resolution of Pioneer and to improve the ability of the system to detect both ischemia and hemorrhage. To do this, we simulated TD-NIROT signals in NIRFAST, a MATLAB-based package used to model near-infrared light propagation through tissue. We used 16 × 16 detector array, with ~2.2 mm distance between the detectors. Light sources were arranged around the field of view (FoV). We performed forward simulations of light propagation through a “homogeneous case” (HC) tissue (μ′_s = 5.6 cm⁻¹, μ_a = 0.07 cm⁻¹). Next, we simulated light propagation through “inhomogeneous case” -tissue’ (IC) tissue by adding ischemia (μ_a = μ_a · 2.5 cm⁻¹) or hemorrhage (μ_a = μ_a · 50 cm⁻¹) to HT as a spherical inclusion of 5 mm radius at different depths in the FoV center and identified the source location that provides the higher contrast on the FoV: max_i ∈ I (FoVContrast_SOURCE). It was found that sources located closer to the FoV center generate greater contrast for late photons. This study suggests the light sources in B-probe should be closer to the FoV center. The higher sensitivity is expected to lead to a higher image quality.

The neonatal brain is a vulnerable organ, and lesions due to hemorrhage and/or ischemia occur frequently in preterm neonates. Even though neuroprotective therapies exist, there is no tool available to detect the ischemic lesions. To address this problem, we have recently designed and built the new time-domain near-infrared optical tomography (TD NIROT) system – Pioneer. Here we present the results of a phantom study of the system performance. We used silicone phantoms to mimic risky situations for brain lesions: hemorrhage and hypoxia. Employing Pioneer, we were able to reconstruct accurately both position and optical properties of these inhomogeneities.