Residual Impact Performance of ECC Subjected to Sub-High Temperatures

Despite the fact that the mechanical properties of Engineered Cementitious Composites (ECC) after high-temperature exposure are well investigated in the literature, the repeated impact response of ECC is not yet explored. Aiming to evaluate the residual impact response of ECC subjected to sub-high temperatures under repeated drop weight blows, the ACI 544-2R repeated impact test was utilized in this study. Disk impact specimens (150 mm diameter and 64 mm thickness) were prepared from the M45 ECC mixture but using polypropylene fibers, while similar 100 mm cube specimens and 100 × 100 × 400 mm prism specimens were used to evaluate the compressive and flexural strengths. The specimens were all cast, cured, heated, cooled, and tested under the same conditions and at the same age. The specimens were subjected to three temperatures of 100, 200 and 300 °C, while a group of specimens was tested without heating as a reference group. The test results showed that heating to 100 and 200 °C did not affect the impact resistance noticeably, where the retained cracking and failure impact numbers and ductility were higher or slightly lower than those of unheated specimens. On the other hand, exposure to 300 °C led to a serious deterioration in the impact resistance and ductility. The retained failure impact numbers after exposure to 100, 200, and 300 °C were 313, 257, and 45, respectively, while that of the reference specimens was 259. The results also revealed that the impact resistance at this range of temperature showed a degree of dependency on the compressive strength behavior with temperature.

Mechanical and Impact Properties of Engineered Cementitious Composites Reinforced with PP Fibers at Elevated Temperatures

The repeated impact performance of engineered cementitious composites (ECCs) is not well explored yet, especially after exposure to severe conditions, such as accidental fires. An experimental study was conducted to evaluate the degradation of strength and repeated impact capacity of ECCs reinforced with Polypropylene fibers after high temperature exposure. Compressive strength and flexural strength were tested using cube and beam specimens, while disk specimens were used to conduct repeated impact tests according to the ACI 544-2R procedure. Reference specimens were tested at room temperature, while three other groups were tested after heating to 200, 400 and 600 °C and naturally cooled to room temperature. The test results indicated that the reference ECC specimens exhibited a much higher failure impact resistance compared to normal concrete specimens, which was associated with a ductile failure showing a central surface fracture zone and fine surface multi-cracking under repeated impacts. This behavior was also recorded for specimens subjected to 200 °C, while the exposure to 400 and 600 °C significantly deteriorated the impact resistance and ductility of ECCs. The recorded failure impact numbers decreased from 259 before heating to 257, 24 and 10 after exposure to 200, 400 and 600 °C, respectively. However, after exposure to all temperature levels, the failure impact records of ECCs kept at least four times higher than their corresponding normal concrete ones.

application based comparison of statistical versus deep learning approaches to reciprocating compressor valve condition monitoring

This paper presents a vibration-based condition monitoring approach for early assessment of valve wear in an industrial reciprocating compressor. Valve seat wear is a common fault mode that is caused by repeated impact and accelerated by chatter. Seeded faults consistent with valve seat wear are installed on the head-side discharge valves of a Dresser-Rand ESH-1 industrial reciprocating compressor. Due to the cyclostationary nature of these units a time-frequency analysis is employed where targeted crank angle positions can isolate externally mounted, non-invasive, vibration measurements. A region-of-interest (ROI) is then extracted from the time-frequency analysis and used to train a suitably sized convolutional neural network (CNN). The proposed deep learning method is then compared against a similarly trained discriminant classifier using the same ROIs where features are extracted using texture and shape image statistics. Both methods achieve > 90% success with the CNN classification strategy nearing a perfect result.

Renovation Effect of Flax FRP-Reinforced Cracked Concrete Slabs under Impact Loadings

The impact behaviour of flax fibre-reinforced polymer (FFRP) renovated coconut fibre-reinforced concrete (CFRC) slabs was investigated through two series of experiments and theoretical analysis. The first experiment was carried out to find out the effectiveness of FFRP retrofitted method for the partly damaged concrete structure and its performance under impact loadings. The renovation process was applied on the pre-cracked rectangular CFRC slabs of 600 mm × 300 mm × 50 mm with FFRP laminates, before the repeated impact tests. Then, the parameters of these slabs, i.e., impact force history, deflection history and damage pattern, were discussed in detail. Another experiment was conducted on the FFRP-CFRC square slabs with a dimension of 600 mm × 600 mm × 50 mm. Based on test results, the effect of different FFRP configurations was discussed to find out the effective reinforcement method. In addition, the two-degree-of-freedom spring-mass model was applied to predict the impact force. Results demonstrate that FFRP composites have a good potential to be utilised as renovated construction materials under dynamic load conditions.

Residual Repeated Impact Strength of Concrete Exposed to Elevated Temperatures

Portland cement concrete is known to have good fire resistance; however, its strength would be degraded after exposure to the temperatures of fire. Repeated low-velocity impacts are a type of probable accidental load in many types of structures. Although there is a rich body of literature on the residual mechanical properties of concrete after high temperature exposure, the residual repeated impact performance of concrete has still not been well explored. For this purpose, an experimental study was conducted in this work to evaluate the effect of high temperatures on the repeated impact strength of normal strength concrete. Seven identical concrete patches with six disc specimens each were cast and tested using the ACI 544-2R repeated impact setup at ambient temperature and after exposure to 100, 200, 300, 400, 500 and 500 °C. Similarly, six cubes and six prisms from each patch were used to evaluate the residual compressive and flexural strengths at the same conditions. Additionally, the scattering of the impact strength results was examined using three methods of the Weibull distribution, and the results are presented in terms of reliability. The test results show that the cracking and failure impact numbers of specimens heated to 100 °C reduced slightly by only 2.4 and 3.5%, respectively, while heating to higher temperatures deteriorated the impact resistance much faster than the compressive and flexural strengths. The percentage reduction in impact resistance at 600 °C was generally higher than 96%. It was also found that the deduction trend of the impact strength with temperature is more related to that of the flexural strength than the compressive strength. The test results also show that, within the limits of the adopted concrete type and conducted tests, the strength reduction after high temperature exposure is related to the percentage weight loss.