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Acceleration-based sensors are widely used in indicating the severity of damage caused to structural buildings during dynamic events. The force rate of change is of interest when investigating the effect of seismic waves on structural elements, and hence the calculation of the jerk is necessary. For most sensors, the technique used for measuring the jerk (m/s3) is based on differentiating the time–acceleration signal. However, this technique is prone to errors especially in small amplitude and low frequency signals, and is deemed not suitable when online feedback is required. Here, we show that direct measurement of the jerk can be achieved using a metal cantilever and a gyroscope. In addition, we focus on the development of the jerk sensor for seismic vibrations. The adopted methodology optimized the dimensions of an austenitic stainless steel cantilever and enhanced the performance in terms of sensitivity and the jerk measurable range. We found, after several analytical and FE analyses, that an L-35 cantilever model with dimensions 35 × 20 × 0.5 (mm3) and a natural frequency of 139 (Hz) has a remarkable performance for seismic measurements. Our theoretical and experimental results show that the L-35 jerk sensor has a constant sensitivity value of 0.05 ((deg/s)/(G/s)) with ±2% error in the seismic frequency bandwidth of 0.1~40 (Hz) and for amplitudes in between 0.1 and 2 (G). Furthermore, the theoretical and experimental calibration curves show linear trends with a high correlation factor of 0.99 and 0.98, respectively. These findings demonstrate the enhanced sensitivity of the jerk sensor, which surpasses previously reported sensitivities in the literature.

The evaluation of hardened concrete quality became significantly important as a result of the continuous and increasing demand on concrete. Mechanical rebound hammer is a quick non-destructive evaluation method used to test the performance of hardened concrete onsite to assure the quality of newly casted concrete or asses the performance of old concrete elements. However, rebound hammer values have uncertainty problems in detecting concrete stiffness and are less reliable. In addition, the device performance is degraded with time due to the fatigue of the mechanical spring. Consequently, this paper presents a new methodology for developing the current measurement technique of Schmidt hammer by using a jerk sensor. Jerk sensors are used in the field of analytical dynamics which includes sensing of acceleration and rate of change of force. The sensor idea is based on using a gyroscope fixed at the free end of a metal cantilever. A cantilever (L-18) of dimensions 18x5x0.5 [mm] and natural frequency 202 [Hz] was designed and modeled using ANSYS finite element analysis (FEA) software. Modal and harmonic analyses were conducted to determine the sensor sensitivity for input jerk. The sensor was applied by constructing a finite element model (FEM) of the mass-spring system inside Schmidt hammer and attaching the sensor to the hammer mass. The correlation relationship between the sensor response and the stiffness modulus of concrete was examined by conducting a transient analysis simulating the Schmidt hammer test of 6 cubic concrete specimens of different grades 20, 30, 37, 45, 50 and 60 [MPa]. Each concrete grade has a different modulus of elasticity. FEA results showed that the L-18 cantilever model has a constant jerk sensitivity of 0.047 [(deg/s)/(G/s)] in the bandwidth 0.1~60 [Hz] and a maximum sensitivity of 1.0 [(deg/sec)/(G/s)] at impact (resonance). The predicted input jerk and output angular velocity are in phase. In addition, the results proved that the stiffness modulus of concrete can be evaluated more efficiently at the impact instant using the rate of change of impact force rather than the rebound distance.

Cement production causes pollution to the environment and the surrounding society especially at Helwan and Suez cities (Egypt) due to the emission of CO2 gas resulting from fuel combustion in cement factories. The research studies the implementation of supplementary cementitious materials (SCM), namely, kaolin (KA) and ground-granulated blast-furnace slag (GGBS), into concrete as a partial replacement of cement and evaluates their effect on concrete mechanical behavior. The study consists of two parts; part I includes activating KA thermally at 750 °C for 3 h to produce metakaolin (MK) and activating GGBS by alkaline solution of 10 molar-concentrated KOH and K2SiO3 with a ratio of 1:2.5, respectively, then investigating their replacing effect on the compressive strength of cement mortars at 3, 7, and 28 days. In part II, the best replacement percentages in terms of compressive strength are selected, and their effects on concrete mechanical behavior at 56 days are investigated. The results showed that 10% MK replacement significantly improves concrete mechanical behavior at 28 days. Moreover, 30% GGBS replacement can be used in production of concrete of 25~35 MPa.