Konstantinos Sotiriadis

Institute of Theoretical and Applied Mechanics of the CAS | ITAM · Department of Materials Research

Full characterization of fired-clay bricks is crucial for the improvement of process variables in manufacturing and, in case of old bricks, for restoration/replacement purposes. To this aim, five bricks produced in a plant in Czech Republic in the past have been investigated with a combination of analytical techniques in order to derive information...

The paper discusses the influence of flame retardant compositions obtained in the system of silicic acid sol (SiO 2 sol) – flame retardants on the fire retardant properties of thin dense cotton fabrics and low density voluminous tapestry fabrics. The need to develop the optimal composition of a fire-retardant composition for a specific fabric, or t...

The effect of sulfates on chloride ingress and microstructure in Portland-limestone cement – metakaolin paste was studied. Crystalline and amorphous phases were investigated with X-ray powder diffraction and solid-state nuclear magnetic resonance spectroscopy. Free chlorides were determined with ion chromatography. The influence of metakaolin on th...

Magnesium phosphate cements (MPCs) find application as alternative inorganic binders in construction, for crack repair and recycling of hazardous wastes. For the most common formulation, setting occurs through the reaction in water between magnesium oxide and potassium dihydrogen phosphate. The products include MgKPO 4 ·6H 2 O (MKP) and an amorphou...

The use of carboxylic acids in mix design alters the hydration process of cement, the resulting pore structure of the obtained cement paste, and, consequently, the mechanical properties of concrete. All these changes are directly related to the structure of the calcium silicate hydrate phase. In the present study, the effect of acetic acid and oxal...

Synthesized cement systems made with variable C3A/C4AF ratios, containing C3S, gypsum and, optionally, calcite, were stored long-term at humid conditions at 5 or 20 °C, without any protection against atmospheric carbonation. Analytical techniques able to assess both the crystalline and amorphous phases were used. Experimental results were compared...

The scaling of strength across hierarchically structured composite materials is accented by the presence of defects with distinct morphology and origin appearing within the microstructure. In hardened Portland cement pastes, these defects manifest as capillary pores, microcracks, and air voids. The transition of material strength from the nano-to-m...

The hydration kinetics of Portland-limestone cement pastes with organic additives in the form of acetic acid and sodium acetate were studied by using solid-state 13С, 27Al and 29Si NMR spectroscopy. The evolution of the relative content of various phases was monitored over the period of one month: amorphous and crystalline calcite (in 13C spectra),...

In this work, the amorphous part of samples extracted from damaged concrete structural elements of a heritage church of Inousses cluster of islands (Greece) was studied. The samples were obtained from both the interior (dome) and the exterior (two walls and one column) of the church. The techniques employed include simultaneous thermal analysis and...

The changes in structural integrity and microstructure of Portland-limestone cement pastes were investigated in the course of magnesium sulfate attack at low temperature. A deterioration front, consisting of three distinct layers (brucite, gypsum, leached cement matrix), swelled in time due to the expansive nature of the deterioration products, gen...

Portland-limestone cement materials are susceptible to sulfate attack at low temperature and high humidity, because such conditions facilitate the formation of thaumasite, detriment to the structural integrity of calcium silicate hydrates (C─S─H). In this work, the effect of the cation associated with sulfates, concentration of sulfate solution, an...

Recent experimental investigations on the nanoscale of hardened cement paste revealed that the tensile strengths of the microstructural phases present amount to several hundreds of MPa. Confrontation with macroscopic tensile strength testing, by e.g. Brazilian splitting, shows a decrease over two orders of magnitude. A computational model based on...

The self-healing effect of several combinations of different additives (dicarboxylic acids, sodium carbonate, expansive additive, silica fume, fibers) incorporated in artificially cracked concrete specimens, was investigated. Their effectiveness was assessed through stereomicroscopic observations and durability tests. The structure and chemistry of...

This paper presents the results of fire test of an I-beam protected by a combined magnesite plate-magnesite mixture heat-insulating material. It was shown that a composite with an average thickness of 37 mm maintained an average temperature of 380 °C on the metal surface after 150 minutes of fire exposure, not exceeding the critical value of 500 °C...

Magnesium phosphate cements are chemically-bonded ceramics exhibiting high strength and good adhesive properties. In-situ investigation of the reaction of Mg-K phosphate cements, indicated that microstructural evolution is controlled by a cement densification process entailing amorphous-to-crystalline transformation during hardening. Owing to the r...

Foam glass production process redounds to large quantities of waste that, if not recycled, are stockpiled in the environment. In this work, increasing amounts of waste foam glass were used to produce metakaolin-based alkali-activated composites. Phase composition and morphology were investigated by means of X-ray powder di�raction, Fourier-transfor...

Portland-limestone cement paste specimens were stored in magnesium sulfate solution at 5°C for 6 months; the occurring microstructural changes have been monitored on a monthly basis. Extent of deterioration was quantitatively assessed with different techniques. The X-ray micro-computed tomography was employed to describe non-invasively the pore str...

In the present work, the self-healing process in concrete was evaluated using analytical techniques. For this purpose, two concrete mixes of different composition (one used as control) were prepared with a water-to-binder ratio of 0.45. The self-healing process was triggered by the introduction in the concrete mix of a commercial expansive admixtur...

Multiple techniques were applied to the investigation of the phase composition of the deteriorated surface of Portland-limestone cement concrete specimens exposed for 10 years to conditions promoting thaumasite sulfate attack. The results were interpreted in terms of the limestone content of cement and the incorporation of supplementary cementitiou...

Three‐dimensional quantitative image analysis from synchrotron X‐ray microcomputed tomography indicated a coarsening of the microstructure of magnesium potassium phosphate cements driven by crystallization of K‐struvite from the first amorphous product. Porosity and pore surface area increased because of the progressive build‐up of a network of elo...

The behavior of a composite material, consisting of metakaolin-based alkaline aluminosilicate binder, granules of the same initial composition used as a swelling agent, and calcium carbonate, was studied during firing in the temperature range 25°C–1,000°C. A combination of techniques was used to investigate its microstructure, composition, and prop...

Magnesium potassium phosphate ceramics are chemically bonded ceramics employed as biomaterials, in nuclear waste encapsulation and for concrete repair. The microstructure dictates material performance and depends on the raw mix composition. Synchrotron X-ray computed microtomography was employed to describe the 3D microstructure and its time evolut...

In this work, a simulation of thaumasite sulfate attack on portland cement mixtures was performed, using synthesized cement phases. Three model systems containing C3S, C3A, and alkali sulfate (CaSO4, Na2SO4, and K2SO4, respectively) and a fourth one consisting of ettringite and C−S−H, were designed, and several mixtures were prepared. CaðOHÞ2 and C...

In the present work, the setting reaction of magnesium sodium phosphate cement was followed in time with in-situ attenuated total reflectance Fourier-transform infrared spectroscopy and solid state nuclear magnetic resonance spectroscopy, in order to gain insights into the products and phase transformations. The results indicated that, during the p...

Fired-clay bricks are frequently object of conservative actions aimed at the preservation of cultural heritage. Information on firing conditions is relevant for the production of custom made replacement bricks, since, as a widely accepted principle, they should be close match to the pre-existing ones. In this work, the mineralogical and microstruct...

Portland–limestone cement concretes were stored in two chloride–sulfate solutions, corresponding to exposure classes XS2, XA2 and XA3 specified by the standard BS EN 206:2013, at 5 ± 1°C. Their performance was evaluated in terms of the limestone content (15% or 35% w/w) of the cements used and the partial replacement of limestone cement with natura...

The fire performance of a geocement-based binder was investigated with a combination of analytical techniques, in terms of changes in composition and microstructure. Geocement, formulated as Na2O∙Al2O3∙6SiO2∙20H2O, was prepared using metakaolin, sodium water-glass, rotten stone and sodium hydroxide. The mixture was homogenized by passing through a...

An ordinary portland cement and two portland limestone cements [15 and 35% weight-to-weight ratio (w/w) limestone content] were used for concrete and reinforced mortar specimens preparation. The specimens were exposed to two corrosive solutions (chloride sulfate and chloride) at 5°C. Total (acid-soluble) and free (water-soluble) chloride contents,...

Three dumped raw materials, a tuff and two bentonites, obtained from two mining sites at the North Bohemian basin in the Czech Republic, have been studied in order to evaluate them as pozzolanic admixtures in lime mortars for employment in restoration of cultural heritage objects. After thermal activation (800 °C; 5 h), their pozzolanic properties...

Objective: To characterize the microstructure of two zinc phosphate cement formulations in order to investigate the role of liquid/solid ratio and composition of powder component, on the developed porosity and, consequently, on compressive strength. Methods: X-ray powder diffraction with the Rietveld method was used to study the phase compositio...

Micro-Raman spectroscopy has been used to follow the carbonation reaction up to 16 weeks in lime paste produced with a traditional technology and cured under controlled conditions. The transformation of calcium hydroxide into calcium carbonate was visualized using Raman Imaging. Calcite was the only crystalline CaCO3 polymorph detected under the co...

The reactivity of the MgO powder employed in the formulation of Mg-K phosphate ceramics can be modulated through the calcination temperature of MgCO3 source material, which has a direct impact on production costs. Upon annealing, MgO undergoes sintering, and in order to optimize the design of products for applications, it is of primary importance t...

Mechanical properties and performance of fired-clay bricks are strictly related to their microstructure and mineralogical composition. The need for meeting the requirements of a nondestructive or low impact approach aimed at the conservation of cultural heritage objects, is prompting for the search of new analytical methods for their characterisati...

The aim of the present paper was to study the effect of incorporating rubber aggregates and acrylic or EVA polymers on the properties of cement mortar exposed to acid (HCl, H2SO4, HNO3) and elevated temperature conditions. Compressive and bending strength tests, water absorption test, mass measurements, and visual inspection were performed. Impact-...

In this paper, the application of a heat-reflecting geocement coating, containing perlite, to reduce timber combustibility was studied. An optimized coating composition was prepared, which consisted of a geocement (Na2O·Al2O3·6SiO2·21.5H2O) and expanded perlite (9.5%). The main firing properties of this coating were invastigated. In terms of flamma...

The application of Impact-echo acoustic method to evaluate the degradation and the composition of mortar composites modified with rubber aggregates and EVA polymer binder degraded at high temperatures was studied. Specimens were prepared by using a type CEM I Portland cement and siliceous sand, as well as by substituting 25% of sand with shredded a...

This paper gives the information about the dielectric testing of the cement-based composites prepared from a mix of cement mortar and quartz sand, with shredded automobile tires as an admixture, which were intentionally degraded by high-temperature treatment (in the temperature range from 0 °C to 400 °C). The monitoring of structural changes in th...

The use of impact-echo acoustic method to test cement-based mortar composites modified with rubber aggregates and EVA polymer binder and degraded at high temperatures was studied. The specimens were prepared by using a type CEM I Portland cement and siliceous sand, as well as by substituting 25% of sand with shredded automobile tires and by adding...

The present paper deals with the application of impedance spectroscopy method to test cement-based composites after their exposure to high temperatures. A type CEM I Portland cement, siliceous sand and shredded automobile tires were used to prepare mortar specimens. The specimens differentiated in whether or not a 10 % w/w acrylic polymer binder (p...

The paper deals with testing of CO2 diffusivity through poly(vinyl butyral) (PVB) layers and their efficiency to serve as barriers against cement mortar carbonation. Two different types of PVB were tested; PVB sheet made from original extruded PVB polymer and PVB sheet made from PVB dispersion obtained from recycled windshields. The first part of t...

The acid attack on cement mortars modified with rubber aggregates and EVA polymer binder was studied. Mortar specimens were prepared using a type CEM I 42.5 Portland cement and siliceous sand, as well as by substituting 25% of sand with shredded used automobile tires, and by adding EVA polymer binder in two percentages (5% and 10% of cement mass)....

The effect of rubber aggregates and acrylic polymer binder on the durability of modified cement mortars exposed to acid solutions was investigated. Mortar specimens were prepared with a type CEM I cement and siliceous sand, as well as by substituting 25% of sand with shredded automobile tires and by adding acrylic polymer binder in two percentages...

The present paper deals with the use of Impact-echo acoustic method to test cementbased mortar composites degraded at high temperatures. The specimens were prepared by using a type CEM I Portland cement and siliceous sand, as well as by substituting 25% of sand with shredded automobile tires and by adding acrylic polymer binder (20% w/w to cement m...

The chloride diffusion in limestone cement concrete exposed to combined chloride and sulfate solutions at low temperature was studied. For this purpose, a normal Portland cement and two Portland limestone cements (15% and 35% w/w limestone content) were used for concrete preparation. The specimens were immersed in two combined chloride-sulfate solu...

Two different thermal insulating materials based on geocement (formulated as Na2O·Al2O3·6SiO2·20H2O) were produced as possible environmentally friendly materials, to substitute existing thermal insulation of technological equipment. Expanded perlite was added as filler during the mixing process. The two thermal insulating perlite composite material...

A new thermal insulating material was developed on the basis of a geocement, formulated as Na2O·Al2O3·6SiO2·20H2O. Ground limestone and aluminosilicate pellets were used as fillers for its production (composition: geocement – 64.29 wt. [%]; fillers – 35.71 wt. [%]). This material, which is applied having a thickness of 3.0-4.5 mm, swells when it is...

Three different types of geocement thermal insulating materials were produced as possible materials to insulate for an energy storage facility. Expanded perlite and vermiculite were added as fillers during the mixing process. The produced materials were subjected to heat treatment before determining their properties. The materials chosen as the mos...

The long term behaviour of limestone cement concrete, stored in combined chloride and sulfate environment, was studied, taking into consideration the effect of both the limestone content of the cement used and the mineral admixtures addition. Concrete specimens of seven different compositions were prepared. Three of them were made from ordinary Por...

In this work the effect of mineral admixtures on the thaumasite form of sulfate attack in limestone cement concrete is studied. Additionally, the effect of the type of sand (calcareous or siliceous) and the storage temperature is investigated. Limestone cement, containing 15% limestone, was used. Concrete specimens were prepared by replacing a part...

Two factors which affect concrete’s durability were investigated, including the effect of the mineral admixtures used, as well as the effect of chlorides on concrete’s deterioration due to the thaumasite form of sulfate attack. Concrete specimens were prepared with Portland limestone cement as well as by replacing a certain amount of limestone ceme...

Concrete durability was investigated, taking under consideration the limestone content of the cement used, as well as the effect of chlorides on concrete’s deterioration due to the thaumasite form of sulfate attack. A normal Portland cement and two Portland limestone cements (15% and 35% w/w limestone content) were used for concrete preparation. Th...

In this paper the effect of chlorides on the thaumasite form of sulfate attack in limestone cement concrete is studied. Concrete specimens made from ordinary Portland cement and two Portland limestone cements (limestone content 15% and 35% respectively) were prepared. After 28 days of curing the specimens were immersed in six solutions of various s...

The thaumasite form of sulphate attack (TSA) concerns cements and concretes containing limestone and is attributed to the formation of thaumasite (CaSiO3·CaCO3·CaSO4·15H2O). During the last 10 years, the TSA has been found in field structures and buildings in many countries worldwide. In the present work the behavior of Portland limestone cements w...