Monitoring early age behavior of mortar by ultrasound technique for environmental issues: Effects of sand grading and salinity of mixing water

Abstract

This paper aims to study the effects of different sand grading and salinity of mixing water on setting and hardening of cement mortar. For this purpose, a newly developed measurement method based on ultrasound pulse echo technique was used. Using this method, the attenuation coefficient and the modulus of reflection coefficient are measured to characterize the early age behavior of tested mortars. Ultrasound P-waves were generated using a 1 MHz central frequency immersion transducer and mortar samples were prepared with Portland composite cement CPJ 45. Mortar samples were classified into two series: first series considered mortar mixes prepared using fresh water and different sand grading form 56μm to 400μm. These laboratory tests (series 1) aimed to obtain the optimum grain size of respective mortar mixes in terms of optimum workability and rheology. Continually, the optimum grain size (from series 1) is used in the second series of experiments (series 2) mortar mixes prepared using artificial sea water with different concentrations of sea salt, i.e., 0 g/l, 10 g/l, 20 g/l, 37 g/l and 50 g/l. The results show that the increase of sand size grading in mortar allows faster setting and hardening and earlier occurrence of aluminate hydrates phase transition AFt – AFm, precipitates the solid percolation and achieves denser microstructure. Also, the stepwise increase of Sea Salt dosage in mixing water from 0 g/l to 37 g/l resulted in a later achieve of final set and later occurrence of AFt – AFm transition.