Setting Behavior And Shrinkage of High Performance Pavement Concrete

The work presented in this thesis focuses on setting the behavior and shrinkage properties of high-performance pavement concrete and the effect factors, such as supplementary cementitious materials (SCMs), chemical admixtures, and temperature. The thesis consists of two papers: (1) the relation between setting behavior and the maturity of pavement concrete materials and (2) a simple statistical model to predict the shrinkage behavior of high-performance concrete containing supplementary cementitious materials. Setting behaviour and maturity of six different concrete mixtures under three different curing temperatures (18.3, 23.9, and 29.4oC, corresponding to 65, 75 and 85oF) were investigated. The mixtures were made with two different retarders (ASTM Types B and D) and with 0 or 20% Class C fly ash replacement for Type I cement. The initial and final set times of these mixtures were measured by the penetration resistance method according to ASTM C 403. The temperature rise of the mixtures was monitored using a thermal couple, and the concrete maturity was then computed based on the time- temperature factor (TTF). A new approach is introduced for predicting concrete set time (penetration resistance) based on the concrete maturity (time-temperature factor). The results indicate that concrete penetration resistance well correlates with maturity measurements. This relationship enables engineers to assess setting behaviour of field concrete on site autogenous shrinkage and free drying shrinkage of nine different high performance concrete mixtures used for bridge decks and bridge overlays constructions were measured, and the total shrinkage (defined as autogenous shrinkage plus free drying shrinkage) was studied. The mixtures were systemically designed for evaluating effects of class C fly ash and ground granulated blast-furance slag replacement on shrinkage proporties. A simplified exponential model ɛauto/drying(t)=a+b*e(c*t) was introduced for describing and predicting shrinkage in high-performance concrete when different types and amounts of supplementary cementitious materials were used. This model fits for both autogenous and free drying shrinkage and is validated and proved by comparing measured value with predicted shrinkage value of an independent group of mixtures. The results indicate that compare to GGBF slag, fly ash performs much better to reduce the total shrinkage. Additionally, free drying shrinkage increases linearly with autogenous shrinkage between 0 and 14 days. The results of the present study indicate that the concrete maturity method successfully describes the concrete setting behavior; and the exponential model successfully predicts the shrinkage behavior of high-performance concrete with SCMs. Additionally, the results indicate Class C fly ash replacement can reduce the total shrinkage and extend the setting time of high-performance concrete. The addition of Class C fly ash should be considered if extending concrete setting time and reducing the risk of shrinkage cracking are needed.