Abstract: Alkali-activated slags represent an alternative to ordinary Portland cement due to reducing the environmental impact of the building industry. In spite of the numerous advantages of alkali activated slag mortars, alkali-activated aluminosilicates have big disadvantage – high value of shrinkage followed by formation of microcracks. This effect is caused by both autogenous and drying shrinkage and it finally results in volume contraction, microcracking and deterioration of the mechanical fracture properties. Therefore, using various types of polymer admixtures can overcome these problems. The aim of this paper is to present the effect of shrinkage-reducing admixture Peramin® SRA 40, polymer polyethylene glycol 1000 and polypropylene glycol on shrinkage and mechanical fracture characteristics of alkali-activated slag mortars. These admixtures were used in amount 0–2.0% weight of slag. The results showed that with increasing content of admixtures compressive and flexural strength decreased. Fracture tests with acoustic emission activity during this testing were carried out. Addition of 2% Peramin® SRA decreased shrinkage by 55%, but with 1% of Peramin® SRA the shrinkage was reduced only by 10%. Specimen with 1% of Peramin® is the most durable material, but more brittle compared to specimens with 1 and 2% of polypropylene glycol.
Abstract: Nowadays, alkali-activated cements (AACs) are the most promising alternatives to ordinary portland cement (OPC). Such cements characterized by better strength and corrosion resistance that determine improved durability of materials based on them. However, the shrinkage of AAC systems is noticeably higher compared with OPC. The purpose of this work was to study the shrinkage behavior of alkali-activated slag cement (AASC) pastes. To improve early age performance of AASCs – OPC and Ca(OH)2, as mineral additives, were added to the designed cement mixtures. The properties, like, flexural and compressive strength of cement mortars, chemical shrinkage, autogenous shrinkage and drying shrinkage of cement pastes were studied. The results showed that the chemical shrinkage, autogenous shrinkage and drying shrinkage at 28 days were between 0.064 – 0.074 ml/g, 4.5 – 7.9 mm/m and 3.3 – 4.9 mm/m, respectively. The relationship between the nature of alkaline components, the type of mineral additives and the shrinkage behavior of cements were discussed.
Abstract: Alkali-activated slag is studied using transmission electron microscopy (TEM), scanning electron microscopy (SEM), and x-ray microanalysis. Attention is focused on delineating the phases induced by the alkali activation, as these phases are important in determining the mechanical properties of the material. The starting material, slag, is found to be a heterogeneous material with at least two phases. Upon alkali activation the material becomes more heterogeneous, now exhibiting at least four phases with significant different chemical composition. Furthermore, the alkali activation is found to modify the phase rich in Ca in the unactivated slag more than the other. Alkali activation of the slag produced mostly an amorphous material with some crystalline phases such as hydrotalcite and calcite, also some nanocrystalline structures were detected by TEM.
Abstract: The alkali-activated slag is an alternative building material to ordinary Portland cement based materials. This type of material is effective in reducing CO2 emissions and energy consumption. Addition of graphite powder increases its electric conductivity, hence, introducing new functionality to building materials such as self-sensing and self-heating properties. In this study, the effect of graphite filler on the crack initiation of alkali-activated slag composite is investigated. The graphite powder was added in the amount of 5, 10 and 15% with respect to the slag mass. Beam specimens with an initial stress concentrator were tested in three-point bending at the age of 28 days. The load versus crack mouth crack opening displacement (F–CMOD) diagrams were recorded during the fracture tests and subsequently evaluated using the Double-K fracture model. This model allows the quantification of two different levels of crack propagation: initiation, which corresponds to the beginning of stable crack growth, and the level of unstable crack propagation. The course of fracture tests was also monitored by acoustic emission (AE) method.
Abstract: Alkali-activated slag materials are known for their high chloride penetration resistance. This makes them potentially applicable as repair systems for damaged steel-reinforced concrete structures, which are exposed to chloride attack. For this purpose, the influence of the activator composition, i.e. the SiO2 and Na2O concentration of the alkaline solution on a) the compressive strength, b) shrinkage and mass change and c) the resistance against chloride penetration of four alkali-activated slag mortars (AASM) were studied. An ordinary Portland cement-based mortar was used as the reference sample. Increasing SiO2 and Na2O concentrations increased the strength, shrinkage and mass loss of the AASMs. The resistance of the mortars against chloride penetration was evaluated using the non-steady-state migration coefficient Dnssm obtained from NT BUILD 492. The results indicate that the Dnssm is related to differences in the pore solution of the AASMs rather than to differences in their microstructure. An upcoming study of the authors is going to evaluate this hypothesis by the accelerated chloride penetration (diffusion) test.
Abstract: Pore solution of hardened alkali-activated fly ash paste was extracted by the steel-die method. The aqueous phase composition of pore solution was analyzed using ICP-OES analysis technique. The results show that the concentrations of Si, Al, Ca, K and OH- decrease with curing time regardless of the curing temperatures (40°C/60°C) and alkaline activators (sodium hydroxide with/without sodium silicate). On the contrary, the concentration of S increases with curing time. A higher temperature curing decreases the solubility of Si, Al, Ca and K in the alkali-activated fly ash, while it doesn’t show much influence on the solubility of S. The plot of the concentration of Al versus the concentration of Si displays a quasi-linear logarithmic relationship. This relationship implies congruent removal of Si and Al from the frameworks of fly ash.
Abstract: Metakaolinite was introduced to alkali activated slag mortars and pastes. Properties of fresh and hardened mortars as well as phase composition and microstructure of hardened pastes were investigated. Introduction of metakaolinite both as addition as well as substitution of slag results in severe decrease in strength of the mortars. SEM observations revealed, that metakaolinite presence results in much less compacted microstructure comparing to reference slag paste. The reason for that are differences in phase composition as determined with XRD. C-S-H phase formation is retained in the presence of metakaolinite and thus degree of hydration of slag is decreased comparing to reference, slag paste.
Abstract: Alkali-activated materials based on fly ash are widely developed and also produced on the present. Some of fly ashes are not suitable for production of alkali-activated materials because of their inconvenient chemical composition. Alumina-silicates are the most important components that are needed to accomplish the successful reaction. The proper content of amorphous phase of alumina-silicates and its proportion as well should be provided for the final composition of alkali-activated materials. The influence of pure aluminum oxide powder as well as raw milled natural perlite on mechanical properties and durability of alkali-activated mortars was investigated. These minerals were used as partial replacement of fly ash coming from black coal combustion. In addition, the mortars were prepared by using different alkali activators.
Abstract: The paper describes alkali-activation of the brick body with potassium water glass having the silicate modulus of 1.0. The 28-days compressive strengths, elasticity modulus, effective fracture toughness, effective toughness, and specific fracture energy of the specimens stored at 20, 40 and 60 °C are evaluated. The storage temperature of specimens and the content of the alkaline solution have a significant influence on all mechanical fracture properties of the studied materials.
Abstract: Influence of copper mine tailings on properties of soda activated ground granulated blast furnace slag mortars and pastes was investigated. Calcination of copper mine tailings was found to be a method of increasing their pozzolanic activity. Material calcined at 750°C possessed highest pozzolanic activity. So obtained material can be used as a partial substitution of ground granulated slag in soda activated blends. Introduction of calcined copper mine tailings decrease strength up to 28 days, but after 56 days strength results are similar or even higher comparing to control samples. Phase composition of hydrated material is not affected significantly by the presence of calcined copper mine tailings.