In English | ISSUE 4/2022
LOIKKA-Project 2
Abstract
Ioanna Orfanoudaki made her master’s thesis on the topic: Effects of accelerators on early strength development of low-carbon concretes. In the scope of the thesis work, the concrete with Ground Granulated Blast Furnace Slag (GGBFS) was studied. The main objective of the reported research was to improve the early strength development of concrete with different content of slag by adding accelerators available at the market.
Three accelerators and five types of cement with varying content of slag were used. The tests were performed with mortars and concrete specimens. The mortar samples were placed into insulated boxes and their temperature development was measured for 2 days to estimate the effect of accelerators and their dosage on the hydration heat. The measured temperature was analysed as a rate of temperature rise as a function of maturity.
Then concrete samples with the defined dosage of accelerators were cast to measure development of the compressive strength and temperature at the early age of hydration. The evolution of temperature was measured for 5 days using the same insulated boxes as for the mortar. Then the total heat development of concrete samples was analyzed. The compressive strength tests were done at 16, 24, 39 and 48 hours for the early-strength and at 7 and 28 days for the long-term strength development.
The outcomes showed that one of the accelerators significantly improved the compressive strength of concretes with high content of slag within first 2 days but decreased the strength at 7 and 28 days. The observed drop of compressive strength at the later ages can still be within the acceptable design limits, as concretes with slag acquire higher strength at 28 days compared to concretes made with CEM I or CEM II cement types.
