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Decalcification resistance of various alkaliactivated materials
(IOP Publishing, 2021-09-29) Hrubý, Petr; Bílek, Vlastimil; Topolář, Libor; Kalina, Lukáš; Marko, Michal; Šoukal, František; Dvořák, Richard; Herčík, Tomáš
The resistance of alkali-activated materials (AAMs) to degradation processes, particularly the decalcification, was studied in this paper. The ground granulated blast furnace slag was alkali-activated using various activators with the same activator dosage 6% Na2O by slag weight (sodium hydroxide, sodium waterglass and sodium carbonate) and subjected to testing of decalcification resistance (immersion in 6M NH4NO3) for 84 days. The reference samples were stored in water. The progress of degradation was studied using the phenolphthalein technique, mechanical properties testing (compressive and flexural strength), and dilatometry analysis or weight measurements. The results obtained were compared to the CEM III/A 32.5R. The significant loss of mass along with the deterioration of mechanical properties were observed for all binder types, still some of the AAMs showed better durability than the cementitious one.
Blastfurnace Hybrid Cement with Waste Water Glass Activator: Alkali-Silica Reaction Study
(MDPI, 2020-08-17) Kalina, Lukáš; Bílek, Vlastimil; Bradová, Lada; Topolář, Libor
Hybrid systems represent a new sustainable type of cement combining the properties of ordinary Portland cement and alkali-activated materials. In this study, a hybrid system based on blast furnace slag and Portland clinker was investigated. The economic aspects and appropriate waste management resulted in the usage of technological waste from water glass production (WG-waste) as an alkaline activator. Although the Portland clinker content was very low, the incorporation of this by-product significantly improved the mechanical properties. Nevertheless, the high amount of alkalis in combination with possible reactive aggregates raises concerns about the risk of alkali–silica reaction (ASR). The results obtained from expansion measurement, the uranyl acetate fluorescence method, and microstructure characterization revealed that the undesirable effects of alkali–silica reaction in mortars based on the hydration of hybrid cement are minimal.
Correlating Hydration of Alkali-Activated Slag Modified by Organic Additives to the Evolution of Its Properties
(MDPI, 2023-02-25) Bílek, Vlastimil; Kalina, Lukáš; Dvořák, Richard; Novotný, Radoslav; Švec, Jiří; Másilko, Jiří; Šoukal, František
This study investigates the relationships between the hydration kinetics of waterglass-activated slag and the development of its physical-mechanical properties, as well as its color change. To modify the calorimetric response of alkali-activated slag, hexylene glycol was selected from various alcohols for in-depth experiments. In presence of hexylene glycol, the formation of initial reaction products was restricted to the slag surface, which drastically slowed down the further consumption of dissolved species and slag dissolution and consequently delayed the bulk hydration of the waterglass-activated slag by several days. This allowed to show that the corresponding calorimetric peak is directly related to the rapid evolution of the microstructure and physical-mechanical parameters and to the onset of a blue/green color change recorded as a time-lapse video. Workability loss was correlated with the first half of the second calorimetric peak, while the most rapid increase in strengths and autogenous shrinkage was related to the third calorimetric peak. Ultrasonic pulse velocity increased considerably during both the second and third calorimetric peak. Despite the modified morphology of the initial reaction products, the prolonged induction period, and the slightly reduced degree of hydration induced by hexylene glycol, the overall mechanism of alkaline activation remained unchanged in the long-term perspective. It was hypothesized that the main issue of the use of organic admixtures in alkali-activated systems is the destabilizing effect of these admixtures on soluble silicates introduced into the system with an activator.
Influence of alkali-activated materials placement during curing on their dynamic parameters
(EDP Sciences, 2020-04-16) Plšková, Iveta; Matysík, Michal; Topolář, Libor; Bílek, Vlastimil
The production of Portland cement has a considerable environmental impact. Its replacement with alkali-activated binders can contribute to reducing the environmental burden of building production. The paper presents partial results from our experimental research carried out on test specimens made of alkali-activated slag mortar (activated by sodium carbonate). The specimens of dimensions 40x40x160 mm differed in the manner of placement after 28 days of curing in water. The samples were tested by non-destructive methods at different ages. We observed the effect of sample storage on ultrasonic pulse velocity, dominant frequency shifts and dynamic modulus of elasticity as well as changes of these parameters over time.
The Effect of Specimen Size on Acoustic Emission Parameters and Approximate Position of Defects Obtained during Destructive Testing of Cementitious and Alkali-Activated Degraded Fine-Grained Materials
(MDPI, 2023-05-04) Topolář, Libor; Kocáb, Dalibor; Hrubý, Petr; Jakubka, Luboš; Hoduláková, Michaela; Halamová, Romana
Two sizes of test samples were selected to investigate the effect of size on the level of degradation. The smaller test specimens had dimensions of 40 × 40 × 160 mm, and the larger ones had dimensions of 100 × 100 × 400 mm. Both sizes of test specimens were always made of the same mortar. In one case, Blast Furnace Cement was chosen as the binder. In the other case, it was an alkali-activated material as a possibly more environmentally economical substitute. Both types of material were deposited in three degrading solutions: magnesium sulphate, ammonium nitrate and acetic acid. The reference set was stored in a water bath. After six months in the degradation solutions, a static elastic modulus was determined for the specimens during this test, and the acoustic emission was measured. Acoustic emission parameters were evaluated: the number of hits, the amplitude magnitude and a slope from the amplitude magnitude versus time (this slope should correspond to the Kaiser effect). For most of the parameters studied, the size effect was more evident for the more degraded specimens, i.e., those placed in aggressive solutions. The approximate location of emerging defects was also determined using linear localisation for smaller specimens where the degradation effect was more significant. In more aggressive environments (acetic acid, ammonium nitrate), the higher resistance of materials based on alkaline-activated slag was more evident, even in the case of larger test bodies. The experiments show that the acoustic emission results agree with the results of the static modulus of elasticity.

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