Table of contents

The 26^th International Conference on Building Materials, Products and Technologies (ICBMPT 2023) was held on 23th to 25th May 2023. The participants appreciated our choice to organize the conference again in the beautiful town of Telč in the Czech Republic, which is popular with many tourists, because it belongs to the cultural heritage under protection of UNESCO.

Despite the short time since last year's conference, the organizers from the Research Institute for Building Materials collected 12 interesting papers among research workplaces in the Czech Republic and abroad. The conference brings not only interesting presentations, but also it creates a platform for scientific discussions and proposals of new mutual projects.

The main topics of ICBMPT 2023 were: Inorganic binders, Composite materials, Building materials based on secondary raw materials, and Technology and test methods in building industry. Also, several keynote speakers were attracted to contribute to our conference. Besides the conference program, there was a possibility to take part in the specialized workshop Healthy Buildings with many interesting topics, among others façade issues, asbestos treatment, healthy indoor environment and biodeteriogens in building environment. We would like to thank all the participants for their valuable contribution to the conference. We would like to express our gratitude to the reviewers for their time, valuable recommendations and constructive evaluation, in order to guarantee high quality of all the papers. We are looking forward to the next conference!

List of Scientific committee and Editors are available in this pdf.

All papers published in this volume have been reviewed through processes administered by the Editors. Reviews were conducted by expert referees to the professional and scientific standards expected of a proceedings journal published by IOP Publishing.

• Type of peer review: Single Anonymous

• Conference submission management system: Morressier

• Number of submissions received: 14

• Number of submissions sent for review: 13

• Number of submissions accepted: 12

• Acceptance Rate (Submissions Accepted / Submissions Received × 100): 85.7

• Average number of reviews per paper: 2.25

• Total number of reviewers involved: 27

• Contact person for queries:

Name: Martin Nejedlík

Email: nejedlik@vush.cz

Affiliation: Výzkumný ústav stavebních hmot, a. s.

Impedance measurements of building materials have been gaining popularity especially in the last twenty years. No electrical component has only resistance, capacitance or inductance, as there is an interplay of these parameters. This is compounded in the case of building materials, which contain a significant number of different phases that vary in chemical composition, crystalline structure and properties. It is, therefore, necessary to choose a connection and measurement system that provides the most accurate information about the building material. This information is primarily meant to include the complex impedance, its components and the quantities derived from them. The derived quantities are electrical resistance or electrical capacitance. Using these quantities we can point out the composition of the material, its conductivity and identify the percolation threshold or describe its sensory properties in more detail. For measurements, an alternating electric field is crucial, and the range of frequencies depends on the instruments used. For materials characterization, the most used frequency range is 100 Hz to 100 kHz; however, we can measure down to 1 MHz.

The aim of this work was to determine stresses in the wall of a buried empty gas pipeline caused by the weight of backfill as well as by heavy-duty vehicles crossing the pipeline, and, on their basis to assess the applicability of protective sleeves. A buried pipeline with zero internal pressure of transported medium (empty pipeline) differs from an unburied pipeline by the vertical load due to the weight of the backfill which causes an ovalness of the circular cross section of the pipeline. This leads to the rise of through-wall bending stresses with the tensile stress at the outside surface at the 3 and 9 o´clock positions and compressive stress at the inside surface. At the 6 and 12 o´clock positions the stresses are tensile at the inside surface and compressive at the outside surface. The current depth of soil cover above gas pipelines is 0.5 m. For pipes DN500, t ~ 6.5 mm the through-wall bending stress is found to be σ_b ≈ ±10 MPa. In comparison with the yield stress of pipeline material, this stress is negligible. The situation is changed when heavy-duty vehicles cross the pipeline. For example, when a MAN truck with the mass load 3270 kg acting on a single wheel of the front axle crosses this pipeline, the pressure transmitted to the pipe will cause the through-wall bending stress σ_b ≈ ±76 MPa. This stress is superimposed to that of the backfill to give the total value ±86 MPa. When dead loads, imposed by backfill cover, together with live loads, caused by truck-wheel loads, are excessive a crushing of side walls of the pipeline and/or ring buckling of the pipe cross section can happen.

3D print of building materials has increasing popularity in the construction industry all around the world. However, geopolymer material, which stands out for its high temperature resistance and low CO₂ emissions compared to concrete, is very rarely used for 3D printing. This work is focused on a composite material based on a geopolymer binder, which is suitable for 3D printing of building elements. The properties of the developed geopolymer composite and the parameters that influence them are described in detail. One of the most important properties of the geopolymer composite for 3D print is setting time and its influence possibilities. The optimal setting time of the developed geopolymer material was 50 minutes. This composite reached up to 70 MPa at room temperature and 35 MPa after exposure to temperature of 800°C.

The degradation processes in surface layers of cementitious composites can be mitigated either by optimizing of the material or by applying surface protection. In this paper, the effect of lithium silicate (LS) sealer is investigated. Water absorbance is studied on standard cement mortar; frost resistance and porosity are examined on two types of concrete (C30/37 and C50/60). The results indicate that LS impregnation improves the water absorbance only slightly and only in the case of short exposure to water; water absorbance was reduced by 15–25% immediately after applying the LS sealer, but the effect was negligible (2–8%) after 24 hours of immersion in water. Frost resistance was not affected by LS impregnation, but a significant improvement of mechanical parameters (flexural tensile strength and weight loss after 50 freeze-thaw cycles) was observed. The resistivity of the concrete surface was increased by LS impregnation by 36–40%, indicating the improvement of quality of the surface layer, while the porosity was practically unaffected.

Sol-gel methods or hydrothermal treatment in combination with low-temperature burning are used for low-temperature syntheses of hydraulically active dicalcium silicate. The paper describes a two-stage preparation process without the use of an autoclave. In the first phase, the precursors of hydraulically active phases are prepared. In the second phase, burning up to 1000 °C takes place to form a C₂S-based binder. Unlike commonly used procedures of the sol-gel method, solid raw materials and water are used. The main raw materials are quicklime and a source of SiO₂ and then various activators. X-ray diffraction analysis and electron microscopy methods were used for the research. The resulting binders are similar to hydraulic lime, they achieve low initial strengths, the long-term strengths are satisfactory. It is suitable for the preparation of mortars and plaster mixtures.

In the construction industry, FRP (fibre-reinfoced-polymer) reinforcement is used mainly because of its high resistance to aggressive environments. The production and design of straight FRP rebars are now very well understood and described. However, when designing concrete elements, it is usually necessary to adapt the reinforcement to the structure shape and to use bent rebars. However, during the production process, unfavourable changes in the fibre distribution across the cross-section may occur at the bent section. It has a significant effect on the short and long-term properties of the rebar. The paper addresses the highly topical issue of the composition, manufacturing and testing of shaped composite rebar. Consequently, the article presents experimentally determined values of mechanical characteristics obtained from the performed tests.

This paper deals with the influence of the length of the moist curing period on the development of the internal structure of a paste based on alkali-activated slag. Waterglass was used as the activator. For the purpose of experiment, the test specimens subjected to the experiment were divided into five sets with different curing regimes combining moist and air curing. The reference set was kept in an environment with relative air humidity ≥ 95% during the entire maturing period. The development of the internal structure of the alkali-activated paste was mainly monitored using the resonance method. The obtained results show that the curing regime applied to the test specimens significantly influences the development of the internal structure of the material. The development of the observed dynamic properties (dynamic moduli and Poisson's ratio) shows the formation of damage to the internal structure of the paste after its exposure to the air. Interestingly, a massive decrease in dynamic modulus of elasticity immediately after exposure to air drying was not prevented, even by intensive moist curing of the paste for 28 days.

The paper focuses on the consistency of fresh steel fibre reinforced concrete in relation to the amount of steel fibre used. Consistency was determined by the slump test and the flow table test. Furthermore, the paper deals with monitoring the compressive strength and volume changes during the maturing process of steel fibre reinforced concrete. Volume changes were monitored using a shrinkage drain. The results of the steel fibre reinforced concrete properties are compared with the values of the reference concrete without fibres and with each other. The result is an evaluation of how the amount of fibre affects the properties of fresh and hardened concrete. The dependence between consistency, compressive strength and shrinkage of steel fibre reinforced concrete is also established.

Setting reducing agents were studied with respect to rheological properties of sprayed mortars based on fast-setting cement binder. The aim was to slightly delay the fast-setting effect caused mainly by tricalcium aluminate presence in order to adjust the workability window resulting in improved pumpability. Main experiments were performed using rotational rheometer and powder X-ray diffractometer. Additionally, 7day, 14day and 28day strength tests were done. The results show that chosen chemicals work as retarders, but not in required extent. Moreover, apart from the usual slower development of the strength due to the presence of retarder, at applied amounts, some of them can even have undesirable side effects such as causing weaker overall structure of the cured specimens.

One of the critical factors affecting the performance of alkali-activated slag (AAS) is the nature and dose of alkali activator. The activator type can play a significant role during the transition from pastes to mortars or concretes. Therefore, three basic sodium activators (water glass, carbonate, and hydroxide) of the same molarity of 4M Na⁺ were used to prepare AAS-based mortars with different volume fractions of siliceous sand. These were compared by means of workability, mechanical strength, and long-term shrinkage under autogenous conditions. The results were compared to those obtained on pastes with similar workability. Increasing the content of the sand tended rather to decrease the mechanical properties, while greatly decreased autogenous shrinkage. Nevertheless, the most remarkable differences for different activators were observed when comparing the mortars with pastes. The transition from pastes to mortars resulted in the highest reduction in both compressive and flexural strength for sodium hydroxide. The flexural strength of the mortars with sodium water glass and sodium carbonate even increased considerably in presence of sand.

The use of super insulating materials in the construction industry, including vacuum insulation, closely corresponds to the ever-increasing requirements for the construction of low-energy and passive buildings. Their indisputable advantage is their excellent thermal insulation properties at low thickness compared to conventional thermal insulation materials. However, there are also many risks associated with the experience and practice of the personnel involved in the application of these materials to structures. The paper focuses on the overall comparison of the possible use of vacuum insulation panels in modern building structures in terms of possible design solutions and achieved properties. The paper presents the results of selected case studies of the optimal use of vacuum insulation panels (VIP) in the construction industry, which are focused on different areas of building structures, specifically on the detail of the transition of the terrace and the adjacent floor, as well as on the solution of the filling of openings - doors. Based on the results of the studies carried out, it can be concluded that, provided that all procedures for maintaining the VIP properties are followed in the implementation of these materials in structures, vacuum insulations represent a more suitable solution for structural details in selected details (less thickness and comparable thermal insulation properties compared to conventional insulations).

The aim of the research works is the development of ultra-high-performance fiber concrete (UHPFRC) for architectual purposes, such as facade panels and their accessories. Research is aimed at achieving high utility properties in the form of high flexural tensile strength, low absorption and very good durability of the developed UHPFRC. The research is also focused on the development of the production technology itself, by pouring and spraying fresh UHPFRC mixtures into molds. The development of cast UHPFRC is also focused on the design and optimization of the production technology, which will enable an automatic production process and reduce costs for the production of flat facade panels. The development of sprayed UHPFRC will make it possible to produce 3D elements with higher utility properties compared to currently produced products from ordinary fiberglass concrete (GFRC).