Elastic properties of fly ash-stabilized mixes
Stabilized mixes are used in the construction of bearing layers in asphalt and concrete pavement structures. Two nondestructive methods: resonant frequency method and ultrasonic pulse velocity method, were used for estimation of elastic properties of fly ash–stabilized mixes. Stabilized mixes were designed containing sand from the river Drava and binder composed of different share of cement and fly ash. The aim of the research was to analyze the relationship between the dynamic modulus of elasticity determined by different nondestructive methods. Data showed that average value of elasticity modulus obtained by the ultrasound velocity method is lower than the values of elasticity modulus obtained by resonant frequency method. For further analysis and enhanced discussion of elastic properties of fly ash stabilized mixes, see Dimter et al. [1].
Application of the Ultrasonic Method in Evaluation of Properties of Stabilized Mixes
Application of nondestructive methods in assessing the properties of materials and mixes is very popular because of their simplicity and noninvasive nature. The ultrasonic method is, as one of nondestructive methods, used for more than 60 years in determining the properties of concrete mixes. However, only recently it has been applied application in studies of the stabilization mixes intended for road construction. The ultrasonic method is based on measurement of the travel time of longitudinal ultrasonic waves through the sample. In this paper, the investigation of stabilized mixes containing sand from river Drava stabilized with cement and fly ash are presented. The aim of the research was to determine the impact of changes in the composition of mixes and in the regime of care on the density, compressive strength and ultrasonic velocity. An additional goal was to analyze the relationship between the investigated properties of mixes and the ultrasonic velocity. The compressive strength of the stabilized mixture is determined by the destructive method according to Croatian Standards HRN.U.B1.030 Unconfined Compressive Strength as the average stress in a sample during uniaxial compression testing at the ultimate force. Testing of density and compressive strength of mixes and determination of the ultrasonic speed has been performed after 7, 28 and 90 days of curing at four different temperatures: 5 °C, 15 °C, 25 °C and 35 °C. The obtained results indicated the direct influence of fly ash quantity on the observed properties. Increase in the amount of fly ash caused a decrease in the mixture compressive strength, its density and ultrasonic velocity. A significant influence of treatment temperature on the compressive strength, density and ultrasonic velocity was also observed. Finally, correlation between density and ultrasonic velocity, as well as compressive strength and ultrasonic velocity was established. Exponential relationship between the compressive strength of stabilized mixes and ultrasonic velocity proved to be very strong, and similar to those obtained in previous studies by other researchers. Test results showed that the ultrasonic method can be useful in assessing properties of stabilized mixes.
RELATIONSHIP BETWEEN ULTRASONIC VELOCITY AND COMPRESSIVE STRENGTH FOR HIGH-VOLUME MINERAL-ADMIXTURED CONCRETE
Abstract Ultrasound is used to evaluate the compressive strength of concrete with mineral admixtures. In addition, the relationship between ultrasound velocity and compressive strength of concrete are evaluated. High-volume fly ash (FA), blast furnace slag (BFS) and FA+BFS are used as the mineral admixtures in replacement of Portland cement (PC). Compressive strength and ultrasonic pulse velocity (UPV) were determined at the 3-, 7-, 28- and 120-day curing period. Both compressive strength and UPV were very low for all the levels of mineral admixtures at an early age of curing, especially for samples containing FA. However, with the increase of curing period, both compressive strength and UPV of all the samples increased. The relationship between UPV and compressive strength was exponential for FA, BFS and FA+BFS. However, constants were different for each mineral admixture and each level replacement of PC.