Within the study presented in previous paragraph, a new US parameter (TG factor) was developed. Sensitivity of this parameter to the presence of various chemical and mineral admixtures was discussed and possibility of using the development of TG factor in time to estimate initial setting time of cement pastes was presented. Within the second part of the post-doc project No. Z2-4069, the procedure has been modified and updated and consequently extended to the mortars and concretes. It turned out that general evolution of the TG parameter in time is unchanged by the presence of aggregates and the presence of aggregates does not influence the ability of the TG parameter to detect the beginning of the setting period of the material. Moreover, simultaneous measurements of the setting period using classical penetration resistance techniques and the developed US procedure indicate that the development of the TG factor in time unambiguously detects the end of the setting period as well. Again, these phenomena are not influenced by the presence of aggregates in the material's composition. These findings are of great importance and represent an important milestone in the field of US testing of cement based materials at early ages. An original scientific article entitled "A new US procedure to determine setting period of cement pastes, mortars, and concretes" was prepared describing these phenomena, which was submitted to "Cement and Concrete Research" journal in December 2012. Currently, the status of the paper is "under review".
Within the post-doc project No. Z2-4069, an original research article entitled "The use of frequency spectrum of ultrasonic P-waves to monitor the setting process of cement pastes" was published in February 2013. The paper was published in "Cement and Concrete Research" journal, being the world's leading scientific journal dealing with the research on cement based materials. The paper describes a possibility of using frequency spectrum of ultrasonic (US) P-waves to monitor setting process of cement pastes and presents a new US parameter called TG factor. This parameter clearly describes the development of various phenomena that occur during the formation of structure process of cement pastes. On the basis of a continuous monitoring of the development of TG factor in time, different stages during the formation of structure process can be observed and initial setting of cement pastes can be determined clearly and unambiguously, regardless of the presence of different chemical and mineral admixtures. Consequently, using the developed US procedure, one can easily and nondestructively analyze the influence of cement paste composition (cement types, chemical and mineral admixtures, etc.) and ambient conditions (curing temperature) on the hydration process, setting, and formation of structure of cement pastes.
COBISS.SI-ID: 1920103
Within the second part of the post-doc project No. Z2-4069, an original article entitled "Influence of superplasticizers on the evolution of ultrasonic P-wave velocity through cement pastes at early age" was prepared. The paper was submitted to "Cement and Concrete Research" journal in April 2012 and is currently at its final stage of the revision procedure. The paper analyzes the influence of two most frequently used chemical admixtures in cement based materials on the evolution of the velocity of US P-waves in time, namely sulfonate naphthalene-formaldehyde superplasticizers and PCE admixtures. The proposed US method was found to be very sensitive to the presence of these admixtures. The presence of PCE types of admixtures retard the formation of structure process of cement pastes significantly, resulting into slower development of the P-wave velocity in time. Moreover, some interesting phenomena can be observed which are not detectable in the case when some classical experimental methods are used (calorimetry, penetration resistance methods, etc.). The results of this study demonstrate the ability of the presented US method to analyze several well known effects of superplasticizers on the setting and hardening properties of cement based materials if properly considered.