Abstract: Since asbestos has been classified as a hazardous chemical, it is desirable to propose a practical and safe procedure for the disposal of asbestos-cement products, or even better to re-use them. In this work, the temperature conditions of degradation of samples of various types of asbestos and products containing asbestos were examined. Samples were burnt at different temperatures and monitored by XRD, DTA, light and electron microscopy. By evaluation of changes at different burning temperatures, the previous findings on the decomposition of asbestos minerals have been confirmed. It has been found that the burning of asbestos cement materials alone or with the addition of limestone at the temperature above 1100 °C leads to the decomposition of hazardous asbestos and, with or without the addition of a setting regulator, hydraulic binder is formed with technological parameters suitable for the building industry.
Abstract: Early strength of the blended Portland cements containing granulated blast furnace slag and natural pozzolanas (zeolite tuff, etc.) can be enhanced by the alkali-sulfate activation. High early strength of the blended Portland cements as a result of alkali-sulfate activation can be attributed to acceleration of pozzolanic reaction at the early stages and formation of more quantities of ettringite at the early stages of structure formation. The results of the study showed that with high amounts of sodium sulfate in the alkali-sulfate activator, contents of gypsum dihydrate as a setting regulator of the blended Portland cements could be reduced. The effect of sodium sulfate activator on properties of the blended Portland cements was studied and the results are discussed.
Abstract: Alkali-activated slag is known as a building material for more than sixty years and is considered an alternative to Portland cement based binders. Compared to Portland cement it exhibits some superior properties such as higher resistance against chemical attack and exposure to elevated temperatures. Aluminosilicate binders are generally electrical insulators; however, electrical properties of building materials gain the importance in the new field of applications such as self-sensing or self-heating materials. This paper brings a comparison of the electrical properties, especially resistance and capacitance, between Portland cement and alkali-activated slag mortars. The measurements revealed that alkali-activated slag shows enhanced conducting properties due to the presence of mobile hydrated sodium ions and metallic iron microparticles.
Abstract: There are many research devoted to the influence of carbon nanotubes (CNT) on the structure and properties of cement systems. In the course of this research, the combined influence of of multi-walled carbon nanotubes (MWCNT) and polycarboxylate (PCE) plasticizer on the products of hydration and the properties of hardened cement paste was investigated. The strength characteristics of nanomodified hardened cement paste and the hydration products were determined by the usage of modern methods of physico-mechanical and physico-chemical analyses. Based on the physico-chemical investigations, it was concluded the necessity of additional experiments, associated primary with questions of uniform distribution of the nanostructures and their chemical interactions with another components of admixture and cement system.
Abstract: The influence of concentration of cement particles φc on rheological behavior (flow behavior, dynamic yield stress, plastic viscosity) and thixotropy of the Portland cement CEM I 42.5 R paste was investigated in this research. Also, thixotropy was evaluated by index of reversible structure of Portland cement paste. Concentration of cement particles φc ranged from 0.434 to 0.518. Investigation was carried out using rotational rheometer Rheotest RN4.1 with coaxial cylinders. The tests revealed that as φc decreases from 0.518 to 0.434, rheological behavior of Portland cement paste is improved: yield stress decreases from 12.7 Pa to 7.1 Pa as well as plastic viscosity – from 4.3 Pa·s to 0.88 Pa·s. The exponential correlation between φc and index of reversible structure of Portland cement paste was found. As φc decreases from 0.518 to 0.434, index of reversible structure of Portland cement paste, which describes a thixotropy, decreases from 5291 Pa·min to 977 Pa·min.
Abstract: This paper deals with the possibilities of experimental determination of the dynamic and static modulus of elasticity of fine-grained cement composites in the early stage of setting and hardening - up to 72 hours. Several cement pastes and cement mortars were produced for the purpose of this experiment. The measurement of the modulus of elasticity on the manufactured cement-based composites was carried out in the first 24 hours, each time only by the ultrasonic pulse velocity test using the innovative Vikasonic instrument. In the following 48 hours, the resonance method and the static load test were employed. The results of the pilot measurement and particularly the assessment of the possibilities of determination of the moduli of elasticity are presented in this paper.
Abstract: The article contains a short literature review of the effects that carbon nanosystems may have on the properties of building composite materials. Highlighted are the main problems hindering nanosystems from wide industrial implementation, such as coagulation tendency of a dispersed phase, and the need for preliminary processing of nano-elements when producing suspensions with a homogeneous particle distribution. Attempts have been made to explain the mechanism leading to an increase in the main technical characteristics of materials based on mineral binders and modified by multilayer carbon nanotubes. With certain model simplifications, a calculation was made, allowing to estimate the amount of material that nanoscale products involve in the composite formation process, and showing a direct relationship between the increase in the technical characteristics of the final product and the homogeneity of the multilayered carbon nanotubes distribution in modifying suspensions.
Abstract: Currently the replacement of primary raw materials in cement production is relevant topic. One of the potentially usable materials can be recycled glass. But its disadvantage is tendency to agglomeration. This experiment describes the effects of the milling agents on the milling process of the glass powder. At first step seven different milling agents were compared among others and next the dependence between pozzolanic activity and specific surface are were monitored for two of them. The utilization of milling agents increased glass specific surface area significantly. Nevertheless, pozzolanic activity of the glass can be reduced when using milling agents because they may also act to a certain extent repellently to the reaction solution.
Abstract: The paper focuses on examining the properties of mortars in which secondary crystallization (crystalline additive) was used. Laboratory tests have found that the effect of secondary crystallization is influenced by conditions in which specimens have been stored during the first 28 days. The investigation focused on the physical-mechanical properties and microstructure of mortar specimens containing a crystalline additive and polypropylene fibres stored at different levels of humidity for 28 days. The influence of crystalline additive on strength was studied as well and the results show that crystalline additives improves the 28-day strength of the mortars.