In this work, a simulation of thaumasite sulfate attack on portland cement mixtures was performed, using synthesized cement phases. Three model systems containing ${\mathrm{C}}_3\mathrm{S}$ , ${\mathrm{C}}_3\mathrm{A}$ , and alkali sulfate (${\mathrm{CaSO}}_4$ , ${\mathrm{Na}}_2{\mathrm{SO}}_4$ , and ${\mathrm{K}}_2{\mathrm{SO}}_4$ , respectively) and a fourth one consisting of ettringite and C−S−H, were designed, and several mixtures were prepared. $\mathrm{Ca}(\mathrm{OH}{)}_2$ and ${\mathrm{CaCO}}_3$ were optionally added. Specimens stored at 5°C and 20°C in an atmosphere saturated in water vapor for 75 months were investigated with X-ray diffraction analysis and scanning electron microscopy. Thaumasite formed in all samples without ${\mathrm{C}}_3\mathrm{A}$ at 5°C, and at 20°C when sulfates were derived from ${\mathrm{CaSO}}_4$ . Solid solution of thaumasite and ettringite was detected in samples incorporating ${\mathrm{C}}_3\mathrm{A}$ and ${\mathrm{CaSO}}_4$ or ${\mathrm{Na}}_2{\mathrm{SO}}_4$ at 5°C. This was also observed at 20°C when ${\mathrm{CaSO}}_4$ was the source of sulfates, whereas ettringite formed in the case of ${\mathrm{Na}}_2{\mathrm{SO}}_4$ . The absence of thaumasite and ettringite in specimens containing ${\mathrm{C}}_3\mathrm{A}$ and ${\mathrm{K}}_2{\mathrm{SO}}_4$ was attributed to the alkali carbonation process. In the fourth system, decomposition of ettringite occurred in the specimens exempt of ${\mathrm{Ca}(\mathrm{OH})}_2$ . The work is supposed to contribute to understanding the primary causes of concrete damage when the concrete is subjected to long-term sulfate attack.

A significant reduction in the CO₂ emission associated with cement production is obtained by partially replacing Portland cement with supplementary cementing materials (SCM’s): e.g., siliceous fly ash or granulated blast furnace slag. In the near future, the limited availability of these materials will do more attractive to use ashes from combustion in fluidized bed boilers, which currently are mainly deposited in various landfills. Paper identifies the effect of Fluidized Bed Combustion (FBC) fly ash from both hard and brown coal combustion on the durability of mortars exposed to sodium and magnesium sulfate solution at different curing temperature: 20 and 5 °C. The evaluation was based on the results of long-term linear changes of mortar samples made with Portland cement and different amounts of FBC fly ash addition stored in a corrosive environment, as well as the evaluation of the type of formed corrosion products using XRD and microstructural studies (SEM/EDS). It has been shown that amount of FBC fly ashes used in binders significantly determines sulfate resistance of prepared cements as well as its chemical composition. By using fluidized ashes, the sulfate resistance of cement binders can be achieved with their content even of 15%.

This paper presents the results of an extensive experimental study on the effect of the addition of two types of fly ash produced during fluidized bed combustion of bituminous coal and lignite, which differ substantially in their chemical and mineral compositions, on the compressive strength of concrete. Concretes with water/binder ratios of 0.65, 0.55 and 0.45 made with CEM I 42.5 R Portland cement and gravel aggregate were tested. The analyzed amounts of fly ash added to the binder were 0, 15% and 30% by weight. Based on the results of compressive strength testing after 28 and 90 days of curing, the relationships with the water/binder ratio and fly ash content in the binder were determined. The fly ashes used were highly active and capable of pozzolanic reaction. The relationships established allow the compressive strength of concretes based on composite cement-fly ash binder to be predicted with sufficient accuracy. The results presented in this study are an important contribution to the knowledge of concretes with combined binders. They have the exploratory value of establishing the dependence of compressive strength at 28 and 90 days on binder composition and water-binder ratio. In addition, they could be used almost directly in practical applications.

This paper presents the results of research on the properties of CEM II/A-F cements containing fine fraction of material from concrete rubble processing plant, as one of the main constituents of cement. The material obtained from concrete recycling plant was ground to produce a constituent that, according to EN 197-6, can be classified as constituent F. A portion of this material was further thermally processed by calcination at three different temperatures: 400 °C, 600 °C and 700 °C. The tests demonstrated a positive influence of thermal treatment on the properties of the binders, despite the relatively low content of hardened cement paste in the recycled material. A particularly beneficial effect, relative to the reference cement containing siliceous fly ash, when constituent F calcined at 600 °C was found.

The article presents the results of research on cements containing calcined illite clay with relatively low clay minerals (20-23 wt.%) and a high limestone content used as a substitute for Portland cement (CEM I 42.5R) in an amount of 10% to 30% by weight of the binder. The results were compared with OPC and cements containing 30 wt.% siliceous fly ash or granulated blast furnace slag, or mixtures of these components with calcined illite clay in weight ratios of 1:2 or 2:1. The results showed a relatively high reactivity of the carbonate component with the calcined clay minerals. This caused a shorter induction time than cements containing a comparable amount of siliceous fly ash or granulated blast furnace slag and higher strength characteristics in the first days of hydration. The high reactivity in the tested system results in higher strengths up to day 7 compared to slag-containing cements and up to day 28 compared to siliceous fly ash. DTA/TG analysis showed the consumption of Ca(OH)2, calcium carbonate, and the formation of carboaluminates with increased calcined clay content.