Self-compacted concrete (SCC) is a special type of concrete; it is a liquid mixture appropriate for structural elements with excessive reinforcement without vibration. SCC is commonly produced by increasing the paste volume and cement content. As cement production is one of the huge factors in releasing CO₂ gas into the atmosphere, by-product materials such as fly ash are utilized as a cement replacement in concrete. In addition to the positive environmental impact, fly ash can maintain an excellent fresh and mechanical property. Incorporating fly ash into self-compacted concrete is widely applied in practice. However, its application is frequently limited by a lack of knowledge about the mixed material gained from laboratory tests. The most significant mechanical property for all concrete types is compressive strength (CS); also, the slump flow diameter (SL) in the fresh state is a crucial property for SCC. Hence, developing an accurate and reliable model for predicting the CS and SL is very important for saving time and energy, as well as lowering the cost. This research study proposed a projection of both the CS and SL of SCC modified with fly ash by three different model approaches: Nonlinear regression (NLR), Multi-Linear regression (MLR), and Artificial Neural Networks (ANN). In this regard, two different datasets were collected and analyzed for developing models: 308 data samples were used for predicting the CS, and 86 data samples for the SL. Each database included the same five independent parameters. The ranges for CS prediction were: cement (134.7–583 kg/m³), water-to-binder ratio (0.27–0.9), fly ash (0–525 kg/m³), sand (478–1180 kg/m³), coarse aggregate (578–1125 kg/m³), and superplasticizer (0–1.4%). The dependent parameter (CS) ranged from 9.7 to 81.3 MPa. On the other hand, the data ranges for the SL prediction included independent parameters such as cement (83–733 kg/m³), water-to-binder ratio (0.26–0.58), fly ash (0–468 kg/m³), sand (624–1038 kg/m³), coarse aggregate (590–966 kg/m³), and superplasticizer (0.087–21.84%). Also, the dependent parameter (SL) ranged from 615 to 800 m. Various statistical assessment tools, such as the coefficient of determination (R²), Root Mean Squared Error (RMSE), Mean Absolute Error (MAE), Objective value (OBJ), and Scatter Index (SI), were used to evaluate the performance of the developed models. The results showed that the ANN model best predicted the CS and SL of SCC mixtures modified with fly ash. Furthermore, the sensitivity analysis demonstrated that the cement content is the most effective factor in predicting the CS and SL of SCC mixtures.

Concrete is one of the most reliable, durable, and desired construction materials. It became the second most used material after water in the world. Many studies and investigations reported that the amount of CO2 released into the atmosphere is nearly 1 ton in the production of 1 ton of cement, which contributes to 5-7 % of total CO2 emissions worldwide. Geopolymer concrete (GPC) is a new development in the world of concrete, which does not need to use cement. The most used materials in geopolymer are by-products such as fly ash, ground granulated blast furnace slag, silica fume, etc. Industrial waste materials are a great problem for human health, environment, and scarcity of land, therefore, reusing them in GPC manufacturing can be seen as a great advantage. Fortunately, most of the recent research concludes that most by-products exhibit similar or better durability, mechanical and physical properties when compared to ordinary concrete. Therefore, GPC became a good sustainable engineering material with many advantages over conventional concrete, such as high early strength, excellent resistance to chemical attacks and steel reinforcement corrosion, elimination of water curing, low cost, etc. This paper reviews the process of geopolymer concrete, constituents, types, properties, durability, and particular applications.

Concrete is one of the most popular and used construction materials. It is strong, durable, and relatively inexpensive, but it has a higher tendency to form cracks. The cracks provide a low service life for the concrete and high maintenance costs. The penetration of aggressive ions through cracks results in corrosion of steel reinforcement, carbonation, sulphate attack, alkali-aggregate reaction, etc. However, prevention of cracks formation is impossible, however, they can be controlled or repaired by various methods. Self-healing concrete is well known as a suitable remedial method to improve concrete's long-term durability. It is a new, rapid, and environmentally friendly approach. In this technology, when concrete is exposed to water, the healing agent material produces calcium carbonate (CaCO3), which fills in the cracks and decreases permeability while enhancing concrete durability. The materials that are used as the healing agents are mostly bacteria, polymers, and chemical compounds. Bacteria are the most preferred material in concrete for healing. Therefore, bio concrete or bacterial concrete is another name for self-healing concrete. This article provides a comprehensive overview of self-healing concrete including, the system, process, mechanical properties, and durability of healed concrete.