Concrete is certainly prone to internal deteriorations or defects during the construction and operating periods. Compared with other nondestructive techniques, infrared thermography can easily detect the subsurface delamination in a very short period of time, but accurately identifying its size and depth in concrete is a very challenging task. In this study, experimental testing was carried out on a concrete specimen having internal delaminations of various sizes and at varying depths. Delaminations at 1 and 2 cm deep showed a good temperature contrast after only 5-minute heating, but delaminations at 3 cm practically identified the value of the temperature contrast from heating of 15 minutes. In addition, the size of the delamination at 3 cm deep could be estimated with a difference of 10% to 28% for 20 minutes of heating. The depth of the delamination was linearly correlated with the increase in its size.

An irreversible thermochromic material based on manganese violet (MnNH₄P₂O₇) is synthesized. The crystal phase, chemical composition, and morphology of the synthesized material are analyzed using X-ray diffraction, scanning electron microscopy coupled with energy-dispersive X-ray spectrometry, and Fourier-transform infrared spectroscopy. The absorption spectra of the synthesized material are obtained using a UV-Vis spectrometer, and the thermochromism exhibited by the powdered samples at high temperatures is also investigated. The as-synthesized manganese violet pigment consists of pure α-MnNH₄P₂O₇ phase. In addition, the synthesized pigment largely consists of hexagonal crystals with a diameter of hundreds of nanometers. On heating, the pigment simultaneously loses H₂O and NH₃ in two successive steps at approximately 330–434.4 °C and 434.4–527 °C, which correspond to the formation of an intermediate phase and of Mn₂P₄O₁₂, respectively. An overall mass loss of 14.22% is observed, which is consistent with the expected 13.79%. An irreversible color change from violet to white is observed after exposure of the synthesized manganese violet pigment at 400 °C for 30 min. This is attributed to the oxidation of ammonia to hydroxylamine, which then decomposes to nitrogen and water, or alternatively to the direct oxidation of ammonia to nitrogen. Furthermore, we demonstrate the potential application of synthesized manganese violet in the production of irreversible thermochromic paint by mixing with potassium silicate solution as a binder and deionized water as a solvent at a specific ratio. The thermochromic paint is then applied in fabrication of irreversible thermochromic sensors by coating it onto a steel plate surface. Finally, we show that manganese violet-based irreversible thermochromic sensors are able to detect temperatures around 400 °C by changing color from violet to white/milky.

This paper presents the results of a study aimed at investigating the effects of restrained shrinkage on the in-plane deflection behavior of reinforced beams cast with self-compacting concrete. The load-deflection data from the tests on two sets of heavily-reinforced concrete beams were analyzed. The first set of beams was made with self-compacting concrete while conventionally vibrated concrete with shrinkage reducing admixture was used in the second set. It was found out that the first set underwent shrinkage cracking at early ages and this cracking caused the member responses of the beams to be closer to the fully-cracked response at the initial stages of loading. The second set of beams was found to have initial responses approximate to the uncracked response and the maximum shrinkage restraint stresses were calculated to be in the order of 20–40% of the modulus of rupture of concrete. The maximum shrinkage-induced restraint stress expressions of the AS 3600-2001, AS 3600-2009, EC2, and CSA A23.3-04 codes were found to underestimate the restraint stresses developed in the first set, yet the estimates from code solutions were in closer agreement with the experimental values in the second set.

The concrete breakout shear strength of stirrup-reinforced cast-in-place anchors during earthquakes was experimentally evaluated. Uncracked and cracked concrete specimens were manufactured using M36 anchors reinforced with D10 stirrups (spacing, 100 mm; edge distance, 180 mm). Shaking table tests were performed to assess the dynamic strength of the reinforced anchors using the Northridge seismic wave. The experimental results showed that the dynamic shear resistance was slightly higher than the static shear resistance due to the strain rate effect of the material. In addition, Etag 001, which is based on the resistance of concrete, and ACI 318, which accounts for the resistance of concrete or steel reinforcement to evaluate the strength of the reinforced anchors, yielded conservative values for the static and dynamic shear strengths of the stirrup-reinforced anchors. An appropriate method that can account for both concrete and stirrup resistance to evaluate the design shear strength of stirrup-reinforced anchors under earthquakes is proposed.