Alena Sicakova

Influence of High Dosage of Specific C&DW Micro-Fillers on the Fluidity of Concrete

Waste valorisation in production of building materials can be improved by their modification using some treatment technologies. Subsequently, products prepared using these optimized raw materials can show better or even new properties. Utilisation of construction and demolition waste (C&DW) for production of building materials is discussed for a longer time world-wide, whether in the form of coarse aggregates or in the fine-grain form as a micro-filler or as a binder. Both of these forms show specific problems have to be solved for increasing the quantities consumed. Fine-grain form can be obtained by techniques like crushing, grinding and sorting as well as by their combinations.This article is aimed on the utilization of specific portion of fine-grain C&DW (ceramics, glass and concrete) for production of concrete mixes of higher fluidity. C&DW were modified by specific process (defined method of crushing followed by sorting of particles under 250 μm). This material was expected as a micro-filler - substitution of natural aggregate (NA) in 0/4 fraction to the extent possible, that the rules allow. Using relevant calculations, 40% dosage was found as complying with standard limit for the maximum content (600 kg.m-3) of particles of less than 250 μm in whole mixture including the relative share of cement and NA. In accordance with these limiting factors, standard recipes were designed. Amount of water, as well as dosage of plasticizer was adjusted during mixing in order to keep the water/cement ratio (max. 0.6) and flow class F5 – F6.Resulting water consumption and dosage of plasticizer are discussed in the terms of influence of tested C&DW on the consistency and bleeding of concrete. Generally positive effect of fine-grain form of brick, glass and concrete was found compared to the reference concrete not containing those additive fine particles.

The Effect of Mixing Technique and Prolonged Mixing Time on Strength Characteristics of Concrete

The experiment aims to test the triple mixing (3M) technique to produce the concrete with recycled concrete aggregate (RCA). Then, the impact prolonged mixing, representing the influence of delivery and discharge time in praxis, is analysed by the change in strength properties. Both the 28-day compressive strength and tensile splitting strength are evaluated in two aspects: the prolonged mixing time (0, 45 and 90 min after initial mixing), and the mixing method (normal and triple). Prolonged mixing time brought both the positive and negative changes in strength characteristics however the worst difference between initial mixing (0′) and 90′ minutes of mixing was only 8.4% for compressive strength and 8.5% for tensile splitting strength.

Testing the Supplementary Cementitious Material Based on GGBFS and Zeolite for Prediction of the Activity Index

The article deals with cement supplementary materials based on ground granulated blast furnace slag and zeolite. Purpose of the experiment was to observe dependences (if they exist) between selected parameters (modulus of basicity, modulus of hydraulicity and initial setting time) and activity indexes, for easier and quicker way to determine or predict the activity index. Testing showed that moderate dependences between those parameters and activity indexes were observed. Results showed that prediction of activity indexes based on chemical composition is feasible.

Basic Physical – Mechanical Properties of Geopolymers Depending on the Content of Ground Fly Ash and Fines of Sludge

Abstract The binding potential of fly ash (FA) as a typical basic component of building mixtures can be improved in mechanical way, which unfolds new possibilities of its utilization. This paper presents the possibilities of preparing the geopolymer mixtures based on ground (dm = 31.0 μm) FA, used in varying percentages to the original (unground; dm = 74.1 μm) one. As a modification, fine-grain sludge from the process of washing the crushed aggregates was used as filler in order to obtain mortar-type material. The basic physical-mechanical properties of mixtures are presented and discussed in the paper, focusing on time dependence. The following standard tests were executed after 2, 7, 28, and 120 days: density, total water absorption, flexural strength, and compressive strength. Ground FA provided for positive effect in all tested parameters, while incorporation of fine portion of sludge into the geopolymer mixture does not offer a significant technical profit. On the other hand, it does not cause the decline in the properties, so the environmental effect (reduction of environmental burden) can be applied through its incorporation into the geopolymer mixtures.

Long-Term Properties of Cement-Based Composites Incorporating Natural Zeolite as a Feature of Progressive Building Material

This study is aimed at the utilization of natural zeolite as a prospective type of Supplementary Cementitious Material in connection with the innovations of construction solutions through the materials. The influence of zeolite on several properties of cement-based composites is studied. Basic characteristics of input powdery materials as well as the technological parameters of zeolite tested on mortar containing 50% of cement replacement are presented. The technical parameters of concrete containing 8, 13, and 25% of cement replacement by zeolite are presented as well. The paper is valuable due to the three-year testing period. The density of the hardened concrete was found to be decreasing with increasing zeolite content. While no significant differences in compressive strength were found after 28 days, differences between individual samples were clear after the long-term period. The presence of zeolite influenced the compressive strength positively in the case of the 8% and 13% replacement, while the higher proportion of natural zeolite (25%) caused lower compressive strength after 28 days but was similar to the reference concrete after three years. A major increase in strength was detected for all samples in the long-term period. It confirms the long-term potential of zeolite for strength improvement.

Verification of specific grinding parameters and strength activity index of glass and clay brick

The aim of this paper is to verify activity index (pozzolanic reactivity) of finegrained waste glass and clay brick. First part of this work consists from milling process with variation in milling parameters (time, grinding ratio) and determination (analysis) of the grain size distribution. Subsequently strength activity index is assessed for samples of particles size 50-60 μm. According to EN 450-1 method, tested samples does not reached an appropriate limit values as 25% substitute of cement. This result does not disqualify this type of construction and demolition waste as active additive in building materials but it is necessary improving their input parameters.

Analysis of Building Stone of the Medieval Historical Building

The reconstruction of the historical buildings needs the replacement of the original and damaged materials using possible compatible materials that closely replicates the original ones in its appearance, chemical, physical and mineralogical properties, strength and durability. Thus, a complex approach based on advanced analytical methods is needed to identifying of the suitable materials. The paper is aimed at the study of the chemical and mineralogical properties of the historical stones of the medieval castle in the East Slovakia in order to replacement the original materials by the new ones with similar composition. The carbonates and silicates were confirmed as the main components of the stones by X ray fluorescence (XRF) and Fourier transformation infrared (FTIR) methods. The mineralogical analysis confirmed the presence of the calcite as the dominated carbonate minerals as well as the presence of the quartz and muscovite representing the silicate forms.