The development of new, sustainable, low-CO2 construction materials is essential if the global construction industry is to reduce the environmental footprint of its activities, which is incurred particularly through the production of Portland cement. One type of non-Portland cement that is attracting particular attention is based on alkali-aluminosilicate chemistry, including the class of binders that have become known as geopolymers. These materials offer technical properties comparable to those of Portland cement, but with a much lower CO2 footprint and with the potential for performance advantages over traditional cements in certain niche applications. This review discusses the synthesis of alkali-activated binders from blast furnace slag, calcined clay (metakaolin), and fly ash, including analysis of the chemical reaction mechanisms and binder phase assemblages that control the early-age and hardened properties of these materials, in particular initial setting and long-term durability. Perspectives fo...

Geopolymers and Related Alkali-Activated Materials

This study reports the synthesis and characterization of geopolymer foam concrete (GFC). A Class F fly ash with partial slag substitution was used for GFC synthesis by mechanical mixing of preformed foam. The GFCs exhibited 28 d compressive strengths ranging from 3 to 48 MPa with demolded densities from 720 to 1600 kg/m3 (105 °C oven-dried densities from 585 to 1370 kg/m3), with the different densities achieved through alteration of the foam content. The thermal conductivity of GFCs was in the range 0.15–0.48 W/m K, showing better thermal insulation properties than normal Portland cement foam concrete at the same density and/or at the same strength. The GFC derived from alkali activation of fly ash as a sole precursor showed excellent strength retention after heating to temperatures from 100 to 800 °C, and the post-cooling compressive strength increased by as much as 100% after exposure at 800 °C due to densification and phase transformations. Partial substitution of slag for fly ash increased the strength of GFC at room temperature, but led to notable shrinkage and strength loss at high temperature. Thin GFC panels (20–25 mm) exhibited acoustic absorption coefficients of 0.7–1.0 at 40–150 Hz, and 0.1–0.3 at 800–1600 Hz.

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Mechanical, thermal insulation, thermal resistance and acoustic absorption properties of geopolymer foam concrete

Due to their good performance and environmental friendliness, fly ash-based construction materials have great potential as alternatives to ordinary Portland cement. To realize sustainable development and beneficial use of fly ash in the construction industry, this paper presents a comprehensive review of relevant literature to evaluate the properties and performance of fly ash, with a particular focus on recent advances in characterization, compositional understanding, hydration mechanism, activation approaches, durability and sustainability of fly ash as a construction material. Several key aspects governing the performance of fly ash, including chemical composition, activator type and hydrates evolution in concrete, are highlighted. Finally, the important needs, pertinent to the optimal and broad utilization of fly ash as an integral part of sustainable construction materials, are identified for further research and development, where large-scale application studies, further classification of fly ash, advanced characterization tools and technology transfer to biomass fly ash are recommended.

Characteristics and applications of fly ash as a sustainable construction material: A state-of-the-art review

Environmentally sustainable repair materials with reduced carbon footprint have been in great demand by the construction industry worldwide. Gradual deterioration of concrete containing large quantities of Portland cement is inevitable, and requires repair or replacement. Numerous repair materials including cementitious mortars, polymer-modified cementitious mortars, resinous mortars, etc. have been utilized to rectify the problem. Cement-free geopolymer mortars prepared from waste materials with high content of silicate aluminum and alkaline activator solution are emerging as prominent sustainable repair materials. Geopolymer binders are preferred because they generate 70–80% less carbon dioxide with remarkably lesser greenhouse gas emissions than ordinary Portland cement. These new binders are highly sought-after due to their enhanced durability performance, sustainability, and environmental affability. This paper provides a comprehensive overview of state-of-the-art research on sustainable geopolymers for repairing deteriorated and damaged concrete structures as well as restoring their integrity. Present challenges and future prospects of various geopolymer mortars as repair materials are emphasized.

Geopolymer mortars as sustainable repair material: A comprehensive review

Binding mechanism and properties of alkali-activated fly ash/slag mortars

In relation to extraction of coal seams at significant depths, the issue of protection of safety equipment against pressure exerted by rock becomes very important. In many surveys of the effects of pressure exerted by rock it was demonstrated that the intensity of stress around the mine works increases the greater the depth of the mine works. However, surveys of technological mine works have shown that the level of deformation of the mine bracing varies in various types of rock at identical depths and no precise rule was established between the increase in pressure exerted by rock and the increasing depth of the mine works.

Assessment of Long-Term Strength of Rocks

The paper discusses the use of acoustic emission, stress-memory effect, and X-ray computed microtomography (μST) to detect the onset of destruction of specimens of concrete and basalt which are widely used in construction. It is shown that the most informative parameter is acoustic emission activity based on which the onset of the formation of a main crack can be identified. The geometry of the crack is determined using computed X-ray tomography.

Evaluation of Crack Formation in Concrete and Basalt Specimens under Cyclic Uniaxial Load Using Acoustic Emission and Computed X-Ray Tomography

The article deals with the topic of control of the project documentation, the quality of the project documentation and its influence on the final quality of the realized product. The aim is to create tools for monitoring of defects and their analysis. As part of improving the control of project documentation, I am introducing a system of classification of complained defects. These defects are then focused on expert analysis. Based on its evaluation, I apply the knowledge gained to the project documentation control. My goal is to create a system, that will prevent the recurrent occurrence of identical claimed defects. By eliminating of claimed defects it is possible to achieve considerable financial savings within building companies.

/pdf/to-the-quality-of-project-documentation-5dxefbju45.pdf

To the quality of project documentation

Thermal Infrared Radiation and Laser Ultrasound for Deformation and Water Saturation Effects Testing in Limestone

In this article, the methods of non-destructive testing of bored piles were considered. The purpose of the first method was to determine the length of the pile for subsequent verification with the norm. The second method was designed to control the quality of concrete piles over its entire length and is interwell ultrasonic testing. The obtained data were analyzed and corresponding conclusions were drawn on compliance with the standards.

Quality Assessment of Bored Pile Foundations by a set of Nondestructive Testing Methods

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