M. I. VALI^, J. STEPI[NIK: A STUDY OF HYDRATION OF CEMENT... A STUDY OF HYDRATION OF CEMENT PASTES BY REFLECTION OF ULTRASONIC SHEAR WAVES. PART I: APPARATUS, EXPERIMENTAL METHOD AND APPLICATION EXAMPLES

Prejem rokopisa- received: 1998-12-06; sprejem za objavo- accepted for publication: 1998-12-14 In this work an apparatus employing a novel nondestructive method based on the reflection of ultrasonic shear waves is described. Application possibilities for studies of the early hydration process of pastes in selected hydraulic, mostly cementitious materials are presented. The results obtained demonstrate, that the acoustic shear wave method presented is quite sensitive to different parameters (composition, water/cement ratio, fineness, grain size distribution, addition of additives) which influenc e the hydration process of these materials. Applications to curing process following, in time domain, of non-cement compounds are possible. On the basis of an evaluation of these and other ongoing experimental studies a compact ’hardness and cure meter ’ for industrial testing and for research will be constructed. Key words: ultrasound, hydration, cement, shear waves, reflection, elasticity, viscosity V prispevku sta opisani nova naprava in metoda za neporu{no sledenje hidratacije hidravli~nih materialov. Naprava je osnovana na merjenju odboja ultrazvo~nih stri‘nih valov. Prikazani rezultati meritev hidratacije, zlasti cementnih past, ka‘ejo, da je opisana metoda zelo ob~utljiva na razli~ne parametre (sestava, razmerje voda/cement, fino~a, porazdelitev velikosti zrn, uporabljeni aditivi), ki vplivajo na proces hidratacije teh gradiv. Metoda je uporabna tudi za ~asovno sledenje procesa strjevanja drugih ne-cementnih materialov. Na osnovi evaluacije prikazanih rezultatov in meritev, ki potekajo, bo zgrajen kompaktni ’merilec hidratacije in strjevanja ’ za uporabo pri laboratorijski ali procesni kontroli v proizvodnji ter pri raziskavah. Klju~ne besede: ultrazvok, hidratacija, cement, stri‘ni valovi, odboj, elasti~nost, viskoznos