Development of sustainable concrete as an alternative to conventional concrete helps in reducing carbon dioxide footprint associated with the use of cement and disposal of waste materials in landfill. One way to achieve that is the use of fly ash (FA) as an alternative to ordinary Portland cement (OPC) because FA is a pozzolanic material and has a high amount of alumina and silica content. Because of its excellent mechanical properties, several studies have been conducted to investigate the use of alkali-activated FA-based concrete as an alternative to conventional concrete. FA, as an industrial by-product, occupies land, thereby causing environmental pollution and health problems. FA-based concrete has numerous advantages, such as it has early strength gaining, it uses low natural resources, and it can be configurated into different structural elements. This study initially presents a review of the classifications, sources, chemical composition, curing regimes and clean production of FA. Then, physical, fresh, and mechanical properties of FA-based concretes are studied. This review helps in better understanding of the behavior of FA-based concrete as a sustainable and eco-friendly material used in construction and building industries.

Ultra-high performance (UHP) concrete is a special type of fibrous cementitious composite that is characterized by high strength and superior ductility, toughness, and durability. This research aimed to investigate the resistance of ultra-high performance fiber-reinforced concrete (UHPFRC) against repeated impacts. An adjusted repeated drop mass impact test was adopted to evaluate the impact performance of 72 UHPFRC disc specimens. The specimens were divided into six mixtures each of 12 discs. The only difference between the mixtures was the types of fibers used, while all other mixture components were the same. Three types of fibers were used: 6 mm micro-steel, 15 mm micro-steel, and polypropylene. All mixtures included 2.5% volumetric content of fibers, however with different combinations of the three fiber types. The test results showed that the mixtures with the 15 mm micro-steel fiber absorbed a higher number of impact blows until cracking compared to other mixtures. The mixture with pure 2.5% of 15 mm micro-steel fiber exhibited the highest impact resistance, with percentage increases over the other mixtures ranging from 25 to 140%. In addition, the Weibull distribution was used to investigate the cracking impact resistance of UHP at different levels of reliability.

Recycled concrete aggregates (RCA) are used in existing green building composites to promote the environmental preservation of natural coarse aggregates (NCA). Besides, the use of RCA leads to potential solutions to the social and economic problems caused by concrete waste. It is found that insufficient information on the longevity and sustainability of RCA production is a serious issue that requires close attention due to its impact on changing aspects of the sector. However, more attention has been paid to explaining the effect of RCA on concrete durability, as well as the properties of fresh and hardened concrete. Therefore, this study aims to provide a critical review on the RCAs for the production of high-performances concrete structures. It begins by reviewing the source, originality, types, prediction of service life, features and properties of RCA, as well as the effect of RCA on concrete performance. In addition, this literature review summarizes the research findings to produce complete insights into the potential applications of RCA as raw, renewable, and sustainable building materials for producing greener concrete composite towards industrializing ecofriendly buildings today. Further, it has also highlighted the differences in the current state of knowledge between RCAs and NCAs, and offers several future research suggestions. Through this critical and analytical study, it can be said that RCA has the possible use in the production of high-performance structural concrete depending on the source and type of recycled aggregate while the RCA can be used widely and safely to produce traditional green concrete.

Foamed concrete (FC) is a high-quality building material with densities from 300 to 1850 kg/m3, which can have potential use in civil engineering, both as insulation from heat and sound, and for load-bearing structures. However, due to the nature of the cement material and its high porosity, FC is very weak in withstanding tensile loads; therefore, it often cracks in a plastic state, during shrinkage while drying, and also in a solid state. This paper is the first comprehensive review of the use of man-made and natural fibres to produce fibre-reinforced foamed concrete (FRFC). For this purpose, various foaming agents, fibres and other components that can serve as a basis for FRFC are reviewed and discussed in detail. Several factors have been found to affect the mechanical properties of FRFC, namely: fresh and hardened densities, particle size distribution, percentage of pozzolanic material used and volume of chemical foam agent. It was found that the rheological properties of the FRFC mix are influenced by the properties of both fibres and foam; therefore, it is necessary to apply an additional dosage of a foam agent to enhance the adhesion and cohesion between the foam agent and the cementitious filler in comparison with materials without fibres. Various types of fibres allow the reduction of by autogenous shrinkage a factor of 1.2–1.8 and drying shrinkage by a factor of 1.3–1.8. Incorporation of fibres leads to only a slight increase in the compressive strength of foamed concrete; however, it can significantly improve the flexural strength (up to 4 times), tensile strength (up to 3 times) and impact strength (up to 6 times). At the same time, the addition of fibres leads to practically no change in the heat and sound insulation characteristics of foamed concrete and this is basically depended on the type of fibres used such as Nylon and aramid fibres. Thus, FRFC having the presented set of properties has applications in various areas of construction, both in the construction of load-bearing and enclosing structures.

Silica fume (SF) is a mineral additive that is widely used in the construction industry when producing sustainable concrete. The integration of SF in concrete as a partial replacement for cement has several evident benefits, including reduced CO2 emissions, cost-effective concrete, increased durability, and mechanical qualities. As environmental issues continue to grow, the development of predictive machine learning models is critical. Thus, this study aims to create modelling tools for estimating the compressive and cracking tensile strengths of silica fume concrete. Multilayer perceptron neural networks (MLPNN), adaptive neural fuzzy detection systems (ANFIS), and genetic programming are all used (GEP). From accessible literature data, a broad and accurate database of 283 compressive strengths and 149 split tensile strengths was created. The six most significant input parameters were cement, fine aggregate, coarse aggregate, water, superplasticizer, and silica fume. Different statistical measures were used to evaluate models, including mean absolute error, root mean square error, root mean squared log error and the coefficient of determination. Both machine learning models, MLPNN and ANFIS, produced acceptable results with high prediction accuracy. Statistical analysis revealed that the ANFIS model outperformed the MLPNN model in terms of compressive and tensile strength prediction. The GEP models outperformed all other models. The predicted values for compressive strength and splitting tensile strength for GEP models were consistent with experimental values, with an R2 value of 0.97 for compressive strength and 0.93 for splitting tensile strength. Furthermore, sensitivity tests revealed that cement and water are the determining parameters in the growth of compressive strength but have the least effect on splitting tensile strength. Cross-validation was used to avoid overfitting and to confirm the output of the generalized modelling technique. GEP develops an empirical expression for each outcome to forecast future databases’ features to promote the usage of green concrete.

The novelty of this paper lies in the identification of the scientific patterns of the influence of thermal power plant waste (TPPW) on the hydration mechanism and the structure of the gypsum-cement binder (GCB). The classification of raw materials for the production of GCB has been developed taking into account the genesis, which contributes to the prediction of the properties of composites. The features of the hydration phase formation and hardening of GCB have been studied taking into account the chemical, structural and morphological features of fly ash and slag. In addition, the microstructural, morphological, and thermal properties of the cured binders at a 28 day cure were determined. For the first time, scientific data on the properties of gypsum-cement fiber-reinforced composite using TPPW and microfiber have been obtained. The results show that the synergistic effect of gypsum-cement binder, TPPW, and polyamide or basalt microfiber improves the physicomechanical properties of a 28 day cured binder: compressive strength of 20 MPa, flexural strength of 8.9 MPa, and softening coefficient 0.87.

Concrete is the most common building material; therefore, when designing structures, it is obligatory to consider all structural parameters and design characteristics such as acoustic properties. In particular, this is to ensure comfortable living conditions for people in residential premises, including acoustic comfort. Different types of concrete behave differently as a sound conductor; especially dense mixtures are superior sound reflectors, and light ones are sound absorbers. It is found that the level of sound reflection in modified concrete is highly dependent on the type of aggregates, size and distribution of pores, and changes in concrete mix design constituents. The sound absorption of acoustic insulation concrete (AIC) can be improved by forming open pores in concrete matrices by either using a porous aggregate or foam agent. To this end, this article reviews the noise and sound transmission in buildings, types of acoustic insulating materials, and the AIC properties. This literature study also provides a critical review on the type of concretes, the acoustic insulation of buildings and their components, the assessment of sound insulation of structures, as well as synopsizes the research development trends to generate comprehensive insights into the potential applications of AIC as applicable material to mitigate noise pollution for increase productivity, health, and well-being.

The self-compacting concrete (SCC) was invented to overcome the compaction problems in deep sections, owing to its perfect workability characteristics. Steel fibers when used with SCC would affect the required fluidity characteristics but improve its impact resistance. In this research, an experimental work was conducted to evaluate the impact response of micro-steel fiber-reinforced SCC, under flexural impact. A 5.47 kg free-falling mass was dropped repeatedly from 100 mm height on the top center of 270 mm-length beam specimens. Eight mixtures with two design grades of 30 and 50 MPa were prepared to distinguish the normal and high-strength SCCs. The distinguishing variable for each design grade was the fiber content, where four volumetric contents of 0%, 0.5%, 0.75%, and 1.0% were used. The test results showed that the impact resistance and ductility were significantly improved due to the incorporation of micro-steel fibers. The percentage improvements were noticeably higher at failure stage than at cracking stage. For the 30 MPa mixtures, the maximum percentage improvements at cracking and failure stages were 543% and 836%, respectively. Weibull’s linear correlations with R2 values of 0.84 to 0.97 were obtained at the failure stage, which meant that the impact failure number followed the Wiebull distribution.