EARLY AGE STRENGTH PREDICTION FOR HIGH VOLUME FLY ASH CONCRETE USING MATURITY MODELING

Abstract

The use of fly ash in concrete has received significant attention over recent years due to environmental concerns regarding its disposal and on the other hand its potential use as a cementitious material, with its ability to provide significant benefits to concrete. While a fly ash content less than 25% of total cementitious content is routinely used in concrete, high-volume fly ash (HVFA) contents are not common used due to perceived lower early-age strengths. The objective of this research was to demonstrate that the beneficial effects of high in-place hydration might be able to compensate the slower rate strength gain of HVFA concrete that is typically observed when tested in standard laboratory conditions, in this effort, the maturity-based technique was used. In addition, different methods (match-cured cylinders and pullout testing) were used to estimate the early-age in-place strength of HVFA concrete to confirm the maturity predicted strengths. The results have shown that the standard and field-cured cylinder strengths underestimate the in-place concrete strength. Higher in-place temperatures due to the mass characteristics of structural elements resulted in increased early age in-place strengths, adequate for construction scheduling, as measured by match-cured cylinders,pullout testing, and the maturity approach.

Furthermore, an extensive investigation on the use of the traditional and alternative maturity principles was examined in order to first identify it's applicability to these types of mixtures and, then identify potential adjustments to the maturity modeling as applicable to HVFA concrete mixtures. Two primary directions were followed, the constant and variable ultimate strength (Su) for multiple curing temperatures.

Another objective of the study was to examine alternative methods of predicting activation energies (AE) for these cementitious systems, as compared to the traditional method identified by the maturity process. Among them, the setting time approach of mortar was considered. Finally, a maturity-based approach was developed for estimating in-place strength of HVFA mixtures to assist the construction industry in implementing the results of this study.