Monitoring Setting Charateristics of Silica Fume Concrete Using Non-Destructive Techniques

Abstract

At early ages of concrete structures, strength monitoring is important to determine the optimum time for loading the structure. Concrete setting and hardening process are also very critical stages during construction of structures since it gives an early indication of the strength of concrete at later stages without waiting for longer durations of 3, 7 and 28 days. This purpose can be achieved by using non-destructive test methods for early age concrete properties. With increase in the use of SCMs in concrete, due to increase in number of high rise buildings there is great demand for high strength concrete, high performance concrete and ultra – high strength concrete because of better durability towards the environmental conditions it becomes a necessity to validate these methods for the detection of changes in setting and hardening patterns. In this research concrete containing different replacements of cement by silica fume have been studied at early ages using NDT of Ultrasonic Pulse Velocity (UPV), Ultrasonic Guided Wave (UGW) and Acoustic Emission (AE) Techniques and then validated using compressive strength and SEM/EDS analysis. Both the techniques are different in their nature of application, i.e., Ultrasonic Guided Wave is active in nature and Acoustic Emission Technique is passive in nature. Ultrasonic Guided Wave depends on the transmitted signal whereas the Acoustic Emission Techniques depends on the stress changes occurring inside the system. The comparison in the setting process of control concrete and concrete containing silica fume is made in the thesis by the use of various NDT techniques. M20 grade of concrete was prepared with w/c ratio of 0.45 and varying replacement levels of silica fume with cement by 3%, 6%, 10% and 12% are made, two NDT techniques of UGW and AE are used to monitor setting of different concrete. Both NDT techniques not only pick up initial setting and hardening of concrete but also that of modified concrete effectively. Clear jump in AE parameters and fall in UGW signals indicate faster setting of SF modified concrete which is further well validated by destructive testing and SEM/EDS analysis.