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This paper presents the investigations of selected properties of concrete containing two fractions of fly ash microspheres (FAMs) with grain size up to 200 µm and up to 500 µm. Concrete mixtures with ordinary Portland cement and three substitution rates of cement by FAMs, 1.3%, 2.0%, and 2.6%, were investigated. For all concrete mixes, the constant water–binder ratio (w/b) equal to 0.50 was used. The research program included the determination of chemical composition, particle size distribution, and pozzolanic activity of FAMs. The analysis showed that the microspheres consist of three main elements: silicon, aluminum, and iron, whose oxides constitute about 89% of the material. The total content of air pores, measured in concrete at 28 days, ranges from 1.3 to 3.1% for the grain sizes below 200 µm and from 1.4% to 3.9% for the grain sizes up to 500 µm. The FAMs with a particle diameter < 200 µm have a relatively high level of activity pozzolanic at 28 days. The SEM analysis proved that the use of microspheres reduces gaps and increases the CSH phase. The compression test showed that the addition of fly ash microspheres with grain size below 200 µm increases long-term concrete strength. [ABSTRACT FROM AUTHOR]

The hydration process of cementitious materials involves a thermally activated reaction that depends on the composition of the mixture and the curing temperature. The main parameter affecting the temperature variation of cast-in-place concrete is the apparent activation energy, which can be used for the efficient prediction of the temperature evolution and maturity index of hardening concrete. This paper discusses two methods to determine the activation energy of mortar specimens, whose mixture proportions are based on standards. The first approach is based on isothermal calorimetry measurements, and the second involves compression tests of mortar samples stored under four different temperature conditions. Mortar mixtures with ordinary portland cement and two rates of cement substitution with siliceous fly ash (10% and 20%) are investigated. The values of the activation energy obtained using the two approaches are compared. Finally, the effectiveness of different tests in determining the activation energy, and thus, maturity index is highlighted. [ABSTRACT FROM AUTHOR]

• Detailed characteristics of post-flotation waste from copper ore. • The use of waste to partially replace three types of Portland cement: CEM I, CEM II/B-V and CEM III/A. • The effective method to utilize the post floatation waste in in cement building material. • New direction of post-mining precipitation management. The current way of managing the copper ore flotation waste is by placing it in waste neutralization facilities. However, flotation waste has great potential in application in cement composites. The article presents the detailed characteristics of post-flotation waste (PFW) and three types of cements: CEM I, CEM II/B-V, and CEM III/A, 42.5 MPa class. The post-flotation waste added for 20% of the cement mass increase the water demand to obtain the standard consistency. The highest pozzolanic activity was noted for mortars made of Ordinary Portland Cement and cured at 20 °C. The lower curing temperature, i.e. 10 °C, delays the hydration reaction, extends setting time, and reduces compressive strength. The conducted tests showed that the specimens produced from CEM I and PFW have the highest compressive strength (after 28 and 90 days), which means that PFW does not react with silica fly ash (from CEM II/B-V) and granulated blast furnace slag (from CEM III/A). The reaction of the waste with the components of the Portland clinker is preferred. The performed studies proved that the utilization of copper post-flotation waste allows for the development of sustainable and durable composite made of CEM I and indicated the possibilities of further testing of waste, in the direction of its use as a mineral additive for concrete. [ABSTRACT FROM AUTHOR]