Assessment of Rational Design of Self-Compacting Concrete Incorporating Fly Ash and Limestone Powder in Terms of Long-Term Durability.

Self-compaction concrete (SCC) is ranked among the main technological innovations of the last decades. Hence, it introduces a suitable possibility for further utilization of supplementary cementitious materials (SCM) in terms of sustainable development. The aim of the work is the assessment of a new approach to binder design, which takes into consideration the activity of the used mineral additive. The proposed approach, which allows a systematic design of a binding system with varied properties of the used mineral additive, was studied on ternary blends consisting of Portland cement (PC), limestone powder and fly ash (FA). The verification was conducted on SCC mixtures in terms of their workability, mechanical properties and the most attention was paid to long-term durability. The long-term durability was assessed on the basis of shrinkage measurement, freeze-thaw resistance and permeability tests including initial surface absorption, chloride migration, water penetration and an accelerated carbonation test, which was compared with the evolution of carbonation front in normal conditions. The durability of studied mixtures was evaluated by using durability loss index, which allow general assessment on the basis of multiple parameters. The carbonation resistance had a dominant importance on the final durability performance of studied mixtures. The experimental program revealed that the proposed design method is reliable only in terms of properties in fresh state and mechanical performance, which were similar with control mixture. Despite suitable results of freeze-thaw resistance and shrinkage, an increasing amount of fly ash in terms of the new design concept led to a fundamental increase of permeability and thus to decay of long-term durability. Acceptable properties were achieved for the lowest dosage of fly ash.

Estimation of Hydration Degree of Blended Cements with the Help of k-Values.

The growing utilization of various mineral additives in the building industry has caused concern worldwide to reduce the emissions of carbon dioxide from Portland cement (OPC) production. The present paper is focused on the determination of the degree of hydration of blended binding systems based on Portland cement. Blast furnace slag, fly ash, and ceramic powder are used in the study; they are applied by 12.5 wt.% up to 50% of OPC replacement. The evolution of the hydration process is monitored using thermogravimetry in selected time intervals to determine the degree of hydration; its ultimate value is obtained from numerical estimation using the Michaelis-Menten equation. However, due to the application of active mineral additives, the correction in terms of equivalent binder is conducted. Corrected values of the degree of hydration exhibit good fit with compressive strength.