Václav Nežerka

Czech Technical University in Prague | ČVUT · Faculty of Civil Engineering (FSV)

Hyperspectral imaging (HSI) is widely applied in various industries, enabling detailed analysis of material properties or composition through their spectral signatures. However, for classification of construction and demolition waste (CDW) materials, HSI is impractical since real-time sorting requires rapid data acquisition and lightweight classifi...

We explore the automatized transition of point cloud data into a Building Information Model (BIM), an essential task for reconstructions, demolition plans, or auditing. In this study, we use point cloud data generated by 3D laser scanning. The research elaborates on the process of segregating and segmenting floor slabs from point clouds and the dev...

In this study, we explored the potential of microbiologically induced calcite precipitation (MICP) for enhancing the microstructural integrity of waste concrete fines (WCF). Traditionally, ureolytic bacteria, such as Sporosarcina pasteurii, have been widely used in MICP due to their ability to produce calcium carbonate via urea hydrolysis, but this...

Conventional shrinkage and creep experiments do not effectively distinguish between the individual deformation mechanisms. To overcome this problem, a comprehensive experimental study comprising a set of simply supported plain concrete beams with varying dimensions and sealing configurations has been initiated. The five-year data formed the foundat...

This paper presents the development of a 3D digital model of end-of-service-life buildings to facilitate a step change in preparation of pre-demolition protocols that can eliminate problems of inadequate documentation and extensive time spent in preparing pre-demolition audits. The 3D digital model consists of the following four main components: (i...

Asphalt concrete's (AC) durability and maintenance demands are strongly influenced by its fatigue life. Traditional methods for determining this characteristic are both resource-intensive and time-consuming. This study employs artificial neural networks (ANNs) to predict AC fatigue life, focusing on the impact of strain level, binder content, and a...

Amidst environmental challenges, this study utilizes the innovative method of microbially-induced calcite precipitation (MICP) to explore its application in recycling waste concrete fines (WCF). Specifically, we scrutinize the role of porosity in the mechanical behavior of MICP-cemented WCF conglomerates. Through a series of indentation tests, the...

This study investigates the potential of microbially-induced calcite precipitation (MICP) in converting waste concrete fines (WCF), an underutilized byproduct generated during the crushing of old concrete, into construction material. WCF samples treated with Sporosarcina pasteurii DSM 33 for periods ranging from 14 to 90 days exhibited up to an 11%...

The construction industry generates a significant amount of waste, posing challenges for efficient waste management and resource recovery. This paper presents a preliminary study on the use of lightweight computer vision (CV) algorithms for the automatic recognition of construction and demolition waste (CDW) materials. Utilizing image datasets acqu...

This paper presents a novel experimental method developed to determine the increase in concrete strength and the evolution of both axial and lateral deformation under confined compression. In contrast to expensive and time-consuming triaxial experiments, the present method requires only a uniaxial testing machine with displacement control. In the p...

Improper sorting of construction and demolition waste (CDW) leads to significant environmental and economic implications, including inefficient resource use and missed recycling opportunities. To address this, we developed a machine-learning-assisted procedure for recognizing CDW fragments using an RGB camera. Our approach uniquely leverages select...

Abrupt collapse events that result in casualties due to failure of load-bearing structures have been reported in recent years. Continuous remote monitoring of these structures, assessing the behavior under operational load, could provide a reliable prevention, as the developing damage manifests itself through a loss of stiffness, and therefore exce...

Introducing the principles of circular economy into the concrete industry would significantly contribute to the sustainability of this sector. Even though recycling ranks below waste elimination, the generation of concrete waste is inevitable, and modern recycling strategies cannot efficiently tackle waste concrete fines (WCF) that represent an eno...

A novel experimental method has been developed to determine the increase in concrete strength and the evolution of both axial and lateral deformation under confined compression. In contrast to expensive and time-consuming triaxial experiments, the present method requires only a uniaxial testing machine with displacement control.

A significant body of research has been carried out to find suitable waste materials or industrial by-products that could replace portland cement and reduce the environmental footprint of the concrete industry. Many studies focus on technical aspects, lacking an assessment of environmental impacts associated with using these alternative materials,...

Different strains of bacteria capable of calcite precipitation can be incorporated into fresh concrete or cement mortars to efficiently promote self-healing of microcracks after hardening. To date, all bacterial strains investigated have required protection against the highly alkaline environments and high pressures in cementitious matrices. The co...

Despite limited knowledge on the proliferation of bacteria incorporated in concretes as a self-healing agent, there are efforts to standardize such a technology. Proper mathematical models could potentially assist the design of self-healing composites and enable to harness bacterially-induced calcite precipitation (BICP) more efficiently. Here, we...

In this research study, selected fillers originating as stone dust or as back fillers have been used as potential substitutes to normally used limestone filler. They have been analyzed by XRF spectroscopy, density or quality of fine particles. These parameters might influence the effect of used fillers on asphalt mortar properties and mix performan...

The lifetime cost and environmental footprint of asphalt pavements hugely depend on their durability. It is widely accepted that water action plays a crucial role in the deterioration of hot mix asphalt concretes. Researchers seek solutions for promoting adhesion between bituminous binders and aggregate to avoid debonding (stripping) due to the pre...

Mixing, paving, and compaction of hot asphalt mixtures results in the formation of a three-phase system in which aggregates are represented in different fractions including subsieve particles (<0.063 mm), referred to as filler material. Larger particles interlock and form a skeleton, while the bituminous binder bonds individual grains together. Two...

Commonly available digital image correlation (DIC) tools are designed to evaluate displacement/deformation fields using well-optimized correlation functions and computational procedures. However, real-time monitoring at high sampling rates or tracking motion at predefined locations from large sequence images can be hardly accomplished due to extrem...

Poor adhesion of synthetic macro fibers to a cementitious matrix limits their reinforcing capacity when used in fiber-reinforced cementitious composites (FRCCs). As a remedy to this problem, high concentrations of fibers must be incorporated into such mixtures, which makes their dispersion in fresh mixtures difficult to achieve. Several strategies...

Several researchers have considered waste marble sludge (WMS) as an admixture to cementitious composites. However, the scientific community is divided into two groups—one advocating WMS as a suitable microfiller, while the other claiming that WMS inhibits hydration of clinker minerals. Here, the role played by WMS during Portland cement (PC) hydrat...

Recent studies on utilization of recycled concrete have demonstrated that usually discarded finest fractions can be incorporated into cementitious composites without scarifying their structural performance. It has been shown that these fines can increase the resistance of a cementitious matrix to tensile stresses and reduce shrinkage, and that thes...

The mechanical properties of a cementitious composite are strongly affected by interfacial transition zone (ITZ) between the matrix and the aggregates, mainly by its strength and thickness. A micromechanical model based on Mori-Tanaka scheme coupled with an estimation of deviatoric stress in ITZ was developed for evaluation of the effect of selecte...

The costs of construction waste handling, a scarcity of landfill sites, and requirements for sustainable construction have placed recycling of concrete-the most abundant construction material in the world-under scrutiny. Unlike recycling of aggregates, utilization of sub-sieve fractions from recycled concrete has not yet been adopted in the constru...

Asphalt mixtures often fail due to poor interaction between mineral aggregate and bituminous binder. Therefore, many efforts are being made on adhesion improvement between the two materials. In this work, paving grade bitumen 50/70 was doped with two types of adhesion promoters. Asphalt mixtures composed of crushed aggregate Brant coated by binder...

Fiber reinforced concrete mechanical properties are limited due to low adhesion between polymer fibers and cement matrix. To ensure a strong interaction between the two materials, polypropylene fibers (d = 0.305mm) were modified by an oxygen plasma treatment. The interface interaction was moreover activated using finely ground concrete recyclate, w...

The interfacial transition zone (ITZ) has a major detrimental impact on the structural performance of concrete. This negative impact can be modulated by introducing mineral admixtures to a concrete mix, which fill the excessive voids within ITZ and react with portlandite to form more compact products. The approach described here, consisting of char...

Adhesion between bitumen and aggregates has a major impact on the performance of asphalt mixes. In order to avoid stripping and consequent premature failure of a pavement, methods to assess the adhesion have been developed and standardized. These methods, such as the frequently applied rolling bottle test defined in EN 1269-11, are based on visual...

Construction and demolition waste recycling for production of new concrete is usually limited to the use of coarse aggregates, and efficient utilization of fine subsieve fractions remains an unresolved issue. In the presented research, Portland cement pastes containing 50% finely ground recycled concrete, blended with lime, fly ash, or blast furnac...

An open-source tool for a real-time measurement of relative displacements based on image registration is presented. The use of upsampled matrix-multiplication discrete Fourier transform and measurement limited to predefined points of interest by virtual extensometers allows high sampling frequencies with a subpixel accuracy. This solution was desig...

Pavement structures often fail due to insufficient interphase interaction between bituminous binder and mineral aggregate. A thin bituminous film covering aggregate particles is often replaced by water, resulting in bitumen-water-aggregate system, which is firmly linked to adhesion failure between these materials. This paper describes how to avoid...

A concept of a planar modular mechanical metamaterial inspired by the principle of local adaptivity is proposed. The metamaterial consists of identical pieces similar to jigsaw puzzle tiles. Their rotation within assembly provides a substantial flexibility in terms of structural behavior, whereas mechanical interlocks enable reassembly. The tile de...

A comprehensive study consisting of a microstructure investigation, nanoindentation, and mi-cromechanical modeling was performed to identify phases and assess their impact on macro-scopic properties of cement pastes containing waste marble powder. The proposed model, built on the Mori-Tanaka scheme, was used to estimate the effective Young's modulu...

A concept of a planar modular mechanical metamaterial inspired by the nature's principle of local adaptivity is proposed. The metamaterial consists of identical pieces similar to jigsaw puzzle tiles. Their rotation within assembly provides a substantial flexibility in terms of structural behavior and mechanical interlocks enable reassembly. The til...

We present a cheap solution for assessment of contact angles on sessile drops or menisci formed around partially submerged fibers. The proposed system consists of a simple optical set combined with an open-source software CAMTIA. The fully automatic assessment of contact angles is based on image binarization, identification of regions of interest,...

Cost of experimental testing of materials and structures subjected to mechanical loading often constitutes a significant portion of a project budget. Therefore a collection of data in a maximum possible amount is desirable. Extensometers and strain-gauges attached to the specimen surface often fail and cannot provide full-field information about th...

A stochastic hierarchical model of a glued laminated timber beam loaded in bending is formulated in this paper. Being attributed to the limited number of observed data the model captures both the inherent variability of the elastic properties of individual timber boards making up the laminated beam and the uncertainty of the parameters controlling...

The purpose of this paper is to propose a continuum micromechanics model for the simulation of uniaxial compressive and tensile tests on lime-based mortars, in order to predict their stiffness, compressive and tensile strengths, and tensile fracture energy. In tension, we adopt an incremental strain-controlled form of the Mori-Tanaka scheme with a...

Preliminary outcomes on a novel modular additive manufacturing technology are presentedin this contribution. The capabilities of the proposed system to synthesize materials with conventionalor meta properties are explored. Two limiting and a single mixed compositions are tested in com-pression in order to reveal both, global and local behaviours of...

The purpose of this study is to demonstrate the influence of plasma treatment on the surface properties of PET fibers used as micro reinforcement in cementitious composites. The stress transfer across cracks that untreated fibers are able to accomplish can be enhanced via plasma treatment. The increase in surface roughness and the activation of pol...

This article discusses the potential impact of artificial drying to individual cells respectively cell wall, which pass through during the drying process to a rapid loss of water. Parameter of micromechanical properties was used to determine the effect of drying. New method, called "modulus mapping" was used to determine the mechanical properties o...

Architectural conservation and repair are becoming increasingly important issues in many countries due to numerous prior improper interventions, including the use of inappropriate repair materials over time. As a result, the composition of repair masonry mortars is now being more frequently addressed in mortar research. Just recently, for example,...

Values of the dynamic Young’s modulus were monitored on cement-based samples containing recycled concrete. In particular, the study was focused on investigation of the relationship between the elastic stiffness and amount of recycled microfiller to replace Portland cement. The amount of the microfiller was ranging between 30 and 70 % per weight of...

The waste production from construction sites become very serious problem. Recycling is the best option for disposal of such waste, and the proper sorting and knowledge of the recycled concrete history allows its further use in the construction. The current studies are mostly focused on utilization of recycled concrete in the form of aggregate. The...

The testing results obtained during investigation of 3D mat are presented in the article. The spatial mat is designed to provide a cheap, efficient and durable soil stabilization on slopes. The testing was focused on development of suitable methods to be used when assessing foil properties on-site. The tested samples were extracted from mats that w...

Digital image correlation (DIC) became indispensable when monitoring and analyzing a development of displacement or strain fields. The method is capable of capturing strain localization, it is not limited to a relative measurement of discrete points as conventional methods and appears to be more accurate than measurements by means of extensometers...

The presented article deals with the influence of the drying process on the micro-mechanical properties of the composite middle lamella. The purpose of the composite middle lamella is to connecti individual cells. Micromechanical properties were obtained using nanoindentation and directly continuous stiffness measurement technique. Indentation modu...

Gypsum, as well as cementitious materials, attains after hardening relatively high compressive strength, however its tensile (or flexural) strength is low. Therefore, it is often necessary to improve the tensile properties, such as strength and ductility, via suitable modifications or by adding reinforcement. Dispersed reinforcement appears to be q...

Several different types of aggregates were used for production of tested samples, namely: the standard sand of a fraction 0-4 mm, quartz sand of a fraction 0-0.4 mm, finely ground recycled limestone powder of a fraction 0-0.07 mm, finely ground recycled concrete of a fraction 0-0.13 mm (ground by Lavaris Company), and finally crushed bricks of a fr...

This work deals with determination of location of micro fibers positions in fiber-reinforced concrete. The digital images of sectioned cement-paste samples with dimension equal to 40 × 40 mm were used as an information source about the monofilaments positions. Properly acquired digital image of high resolution allows to determinate the number of fi...

The unique properties of nanotextiles based on poly(vinyl-alcohol) (PVA) manufactured using the electrospinning method have been known and exploited for many years. Recently, the enrichment of nanofiber textiles with nanoparticles, such as ions or nanodiamond particles (NDP), has become a popular way to modify the textile mechanical, chemical and p...

Knowledge about the microstructure and the morphology of individual phases within wood tissues is essential for numerous applications in materials engineering and in the construction industry. The purpose of the work presented here is to monitor the distribution of elastic stiffness within the tissues of individual cells using state-of-art equipmen...

Polymers have been used for modifying cement-based composites and other building materials since the 1930s. Recent studies have assumed that even water soluble polymers can be used as an admixture for a modification of this kind. Several ways for modifying mortars, wood-based products and bituminous asphalts with a polymer are known and are current...

This paper deals with using resonance method for determine the development of the mechanical properties of cement paste with different polyvinyl alcohol content. Main properties which were monitored are the dynamic Young’s modulus and dynamic shear modulus. Those properties were measured during 161 days for better understanding of influence of Poly...

Nanofiber textiles became indispensible in medicine and many other industries because of their unique properties. Recently, the pioneering works suggested their use also in a building industry in the form of moisture barriers. For a better chemical stability and resistance to air humidity it is suitable to stabilize the spun textiles. Our study is...

Cell wall of Norway spruce is composed of several layers, which is, due to their small size, difficult to characterize. For this reason, the work uses a combination of methods, atomic force microscopy (AFM) is used to determine the topography of a sample and nanoindentation has been used to locally characterize the surface mechanical properties of...

In order to develop a constitutive material model and to verify its consistency when implemented in a computational code, it is necessary to understand the material and to carry out a comprehensive experimental analysis. This can be a challenging task in the case of composite materials and structures, such as masonry, when using conventional measur...

The paper presents results of long-time investigation of mechanical properties of composite gypsum material using nondestructive technique. The gypsum block was put to the façade of the building for four years. Then it was removed and cut to smaller specimens, which were investigated. The matrix of 6 × 4 specimens of dimensions 40 × 40 × 160 mm wer...

The use of recycled materials is nowadays greatly promoted and these are exploited in many industries, including construction and civil engineering. It is advantageous and efficient to exploit mainly those materials that cannot find their use in any other application. The steel wires from old automobile tires are a perfect example – they can be use...

In order to understand the behavior of lime-based mortars, and to identify the influence of pozzolans, it is important to investigate the microstructure and properties of lime-based pastes without any aggregates. In our work, nine different sets of pastes with additions of metakaolin and brick dust were studied. The chemical composition and microst...

The aim of the presented study was to find a relationship between PVA concentration and properties of cement pastes. The PVA solution was added into fresh mortar in the amount equal to 1.4 and 2.8 % of cement weight. The produced samples were consequently stored in different curing conditions – exposed to air in common laboratory environment or sub...

The presented study addresses the mechanical performance of micro-filler cement-based material produced from recycled concrete sleepers. Such material can be considered both, as a binder and filler at the same time. The main advantage of such material is the energy efficiency of the production process, since there is no demand for increased tempera...