Influence of curing temperature on freeze-thaw resistance of limestone powder hydraulic concrete

Limestone powder (LS) is a new environmentally-friendly concrete admixture, and its application in concrete engineering is worth exploring. The curing of LS hydraulic concrete under extreme temperatures will significantly affect the interior microstructure of concrete, which has a significant impact on the resistance to freeze-thaw cycles. This study aims to investigate the influence of LS replacement quantity (10 %, 30 % and 50 %) and curing temperatures (5 ℃, 20 ℃ and 50 ℃) on the freeze-thaw resistance of hydraulic concrete. The freeze-thaw resistance was reflected by the mass loss rate, relative dynamic modulus of elasticity (RDM) and ultrasonic inspection. The hydration products, microstructure and pore composition of LS hydraulic concrete were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) to dissect the underlying mechanisms behind the freeze-thaw resistance. The relationship between the pore composition and the mass loss rate and RDM was established to connect the microcosmic properties with the macroscopic properties. Findings from this study provide a guidance for the application of LS in concrete engineering under harsh environments

Improvement of Distance Measurement Based on Dispersive Interferometry Using Femtosecond Optical Frequency Comb

Since the dispersive interferometry (DPI) based on optical frequency combs (OFCs) was proposed, it has been widely used in absolute distance measurements with long-distance and high precision. However, it has a serious problem for the traditional DPI based on the mode-locked OFC. The error of measurements caused by using the fast Fourier transform (FFT) algorithm to process signals cannot be overcome, which is due to the non-uniform sampling intervals in the frequency domain of spectrometers. Therefore, in this paper, we propose a new mathematical model with a simple form of OFC to simulate and analyze various properties of the OFC and the principle of DPI. Moreover, we carry out an experimental verification, in which we adopt the Lomb–Scargle algorithm to improve the accuracy of measurements of DPI. The results show that the Lomb–Scargle algorithm can effectively reduce the error caused by the resolution, and the error of absolute distance measurement is less than 12 μm in the distance of 70 m based on the mode-locked OFC