At present, plastic concrete is widely used in anti-seepage engineering, and its strength and hydraulic conductivity are important indexes of plastic concrete cutoff walls. The pondus hydrogenii (pH) and electrical conductivity (EC) have an important effect on the strength and hydraulic conductivity of plastic concrete cutoff walls. However, it is not clear why the pH and EC are related to the strength and permeability of these walls. For this reason, plastic concrete composed of sand, cement, water, and bentonite was taken as the research object to study the influence of different mix ratios and curing ages on the unconfined compressive strength and permeability of plastic concrete. The pH and EC of the corresponding mix ratio and curing age were measured. The effects of the pH and EC on the strength and permeability of plastic concrete were studied, and the internal reason was explored from the product type and hydration reaction degree of plastic concrete. Furthermore, the quantitative relationship between pH and EC and the strength and hydraulic conductivity of plastic concrete was established. With increasing cement content, the strength, pH, and EC of plastic concrete increase continuously, while the hydraulic conductivity decreases. With increasing curing age, the strength increases, the hydraulic conductivity decreases, and both the pH and EC show a trend of first increasing and then decreasing. The pH value and electrical conductivity can reflect the product type and hydration reaction degree of plastic concrete, further affecting its strength and hydraulic conductivity. Under different dosage and curing age conditions, the pH showed three stages, namely, 11.7–12.27, 12.27–2.5, and 12.5–12.75, and there is a good power functional relationship among the EC and strength and hydraulic conductivity at each stage.

Waste foundry sand (WFS) is the by-product of the foundry industry, which is produced about 0.6 tons per 1 ton of foundry industry production. While it cannot be recycled or reused, it will be disposed of in landfills. Today, with increasing attention to environmental issues, the reuse and recycle of materials because of limited resources have been considered. Due to the desirable properties of WFS, many studies have been done on the properties and performance of its use in various industries, especially in concrete technology. The purpose of this paper is to conduct a bibliometric analysis of foundry sand research during the years 1971-2020. Various aspects, such as document types, languages, major journals, key countries, authors, and keywords, have been examined. The collaborations among authors and countries were constructed, visualized, and evaluated through the application of the social network analysis method based on co-authorship relations. Also, keyword cluster analysis has been performed using co-occurrence relations to discover the most prominent issues related to WFS. The results showed that the number of publications (TP) has improved significantly in recent years, especially in 2018-2020. It has increased from 1 in 1971 to 38 in 2020. The engineering subdivision with 33% has had the highest number of papers. Also, India, China, and the USA have the highest number of publications, respectively. Statistical data from the author keyword study showed that in general, papers can be classified into three categories in terms of subject: first, characteristics of WFS and its importance; second, the use of WFS in concrete and the study of mechanical and physical properties as one of its applications; and the third, investigation on environmental effects and damage caused by disposal and landfill of WFS and efforts to find solutions for recycling and reuse. The keywords “Waste Foundry Sand,” “Foundry Sand,” and “Compressive Strength” with a growth rate of 2700%, 1900%, and 1100%, respectively, are important topics in the field of WFS research.

The significant contribution of the carbon dioxide emission from the production of Portland cement which is the main binder used in concrete has called for an imminent need to find environmentally friendly materials as alternatives. The availability of large quantities of agricultural wastes such as coconut shell in most developing countries opens a pathway to explore how these materials can be recycled into concrete as the binder composition. The combustion of most solid agricultural wastes results in the production of ash which can be used to replace Portland cement as a binder in concrete. This paper presents the results from the experimental investigation of the effect of coconut shell ash on the workability, mechanical properties, and embodied carbon of concrete. A total of five mixtures were made with coconut shell ash replacing Portland cement up to 20%. Results from this paper showed that coconut shell ash can be incorporated into concrete mixtures to reduce its embodied carbon. A reduction in embodied carbon of about 15% was achieved when 20% of Portland cement was replaced with coconut shell ash. The incorporation of coconut shell ash into concrete mixtures also resulted in an increase in the mechanical properties up to 10% replacement of Portland cement. The compressive, tensile, and flexural strength of mixtures incorporating 10% coconut shell ash as replacement of Portland cement is 12%, 10%, and 9% higher than that of the control mixture without coconut shell ash.

In the recent past, partial replacement of cement by rice husk ash (RHA) in concrete is a prime focus of global researchers for sustainable development in energy and environmental aspects. The present investigation aims at testing the water absorption capacity of the different types and sizes of the RHA-incorporated cement concrete. A design of experiments (DOE) was conducted using the Taguchi method to develop an L₂₇ matrix to assess the individual effects of each variable. From the experimental study, decreasing the RHA size and increasing the RHA loading, higher bulk density, and surface area led to decreasing the water absorption capacity of the RHA-blended cement concrete during curing. Furthermore, 20 wt% replacement of cement by RHA in concrete furnishes the 3-fold decrease of water absorption capacity compared to normal concrete (without RHA). An empirical model was developed to predict the water absorption capacity of the RHA-incorporated cement concrete. The model indicates that RHA loading, silica content, and specific surface area are the key factors influencing the water absorption capacity of the concrete. And the model appears to be able to predict the water absorption capacity of concrete quite accurately with > 95% confidence level.

The production of cement contributes to 10% of global carbon dioxide (CO₂) pollution and 74 to 81% towards the total CO₂ pollution by concrete. In addition to that, its low strength-to-weight ratio, high density and thermal conductivity are among the few limitations of heavy weight concrete. Therefore, this study was carried out to provide a solution to these limitations by developing innovative eco-friendly lightweight foamed concrete (LFC) of 1800 kg/m³ density incorporating 20–25% palm oil fuel ash (POFA) and 5–15% eggshell powder (ESP) by weight of total binder as supplementary cementitious material (SCM). The influence of combined utilization of POFA and ESP on the fresh state properties of eco-friendly LFC was determined using the J-ring test. To determine the mechanical properties, a total of 48 cubes and 24 cylinders were prepared for compressive strength, splitting tensile strength and modulus of elasticity each. A total of 24 panels were prepared to determine the thermal properties in terms of surface temperature and thermal conductivity. Furthermore, to assess the environmental impact and eco-friendliness of the developed LFC, the embodied carbon and eco-strength efficiency was calculated. It was determined that the utilization of POFA and ESP reduced the workability slightly but enhanced the mechanical properties of LFC (17.05 to 22.60 MPa compressive strength and 1.43 to 2.61 MPa tensile strength), thus satisfies the ACI213R requirements for structural lightweight concrete and that it can be used for structural applications. Additionally, the thermal conductivity reduced ranging from 0.55 to 0.63 W/mK compared to 0.82 W/mK achieved by control sample. Furthermore, the developed LFC showed a 16.96 to 33.55% reduction in embodied carbon and exhibited higher eco-strength efficiency between 47.82 and 76.97%. Overall, the combined utilization of POFA and ESP as SCMs not only enhanced the thermo-mechanical performance, makes the sustainable LFC as structural lightweight concrete, but also has reduced the environmental impacts caused by the disposal of POFA and ESP in landfills as well as reducing the total CO₂ emissions during the production of eco-friendly LFC.

CO₂ uptake due to carbonation is an important issue for sustainability in the concrete industry. This study presents an analysis model of CO₂ uptake of slag-blended concrete considering the service stage and the recycling stage. First, a slag-blended cement hydration model is used to evaluate the content of carbonatable substances, porosity, and diffusivity. Regarding the service stage, a one-dimensional carbonation model is proposed to evaluate carbonation depth. For the recycling stage, an unreacted core model is proposed to evaluate the carbonation fraction of crushed, spherical concrete. Second, CO₂ uptake in the service stage and recycling stage is determined based on the carbonated fraction, shape of the concrete element, concrete component, and exposure conditions. The total CO₂ uptake ratio is determined based on the content of CO₂ uptake and CO₂ emissions. Third, the analysis results show that for concrete with a water-to-binder ratio of 0.3, as the slag replacement ratio increases from 0 to 50%, the total CO₂ uptake ratio increases from 21.43 to 28.87%. For concrete with 50% slag as the binder, as the water-to-binder ratio increases from 0.30 to 0.35, the total CO₂ uptake ratio increases from 28.87 to 30.59%. The sizes and types of the structural elements and the diameter of the crushed concrete can impact the rate of CO₂ uptake, but do not modify the total CO₂ uptake ratio.

One of the most significant parameters in concrete design is compressive strength. Time and money could be saved if the compressive strength of concrete is accurately measured. In this study, two machine learning models, namely, boosted decision tree regression (BDTR) and support vector machine (SVM), were developed to predict concrete compressive strength (CCS) using a complete dataset through the previous scientific studies. Eight concrete mixture parameters were used as the input dataset. Four statistical indices, namely the coefficient of determination (R²) and root mean square error (RMSE), mean absolute error (MAE), and RMSE-Standard Deviation Ratio (RSR), were used to illustrate the efficiency of the proposed models. The results show that the BDTR model outperformed SVM model with the overall result of R²=0.86 and RMSE=6.19 and MAE=4.91 and RSR=0.37, respectively. The results of this study suggest that the compressive strength of high-performance concrete (HPC) can be accurately calculated using the proposed BDTR model.

Nano-titania (n-TiO₂), due to its unique photocatalytic and hydrophobic properties, can be used to prepare self-cleaning cement-based smart building materials. The n-TiO₂ degrades organic and inorganic pollutants through its photocatalytic action and convert them into non-toxic byproducts, i.e., improves the air quality. In this review, aspects such as methodologies of n-TiO₂ synthesis, approaches for n-TiO₂ loading on cementitious materials, photocatalytic properties, self-cleaning mechanism, and application of n-TiO₂ in cement-based materials have been overviewed. Further, the n-TiO₂ can be used either as coatings or admixtures in pavement blocks, mortars/concrete at zebra crossings, road dividers and linings, and high rise buildings. Moreover, the implications and economic aspects of n-TiO₂ usage in cement-based materials revealed that n-TiO₂ increases the material cost by ~ 27%, (101 to 128.1$) in comparison to conventional building materials. Furthermore, the low-cost carbonized materials such as biochars have been suggested to be used as support of n-TiO₂ to lower the cost and improve the remediation efficiency of photocatalytic concrete.

This study investigated the influence of coal bottom ash (CBA) on the concrete properties and evaluate the effects of combined exposure of sulphate and chloride conditions on the concrete containing CBA. During concrete mixing, cement was replaced with CBA by 10% of cement weight. Initially, concrete samples were kept in normal water for 28 days. Next, the specimens were moved to a combined solution of 5% sodium sulphate (Na₂SO₄) and 5% sodium chloride (NaCl) solution for a further 28 to 180 days. The experimental findings demonstrated that the concrete containing 10% CBA (M2) gives 12% higher compressive strength than the water cured normal concrete (M1). However, when it was exposed to a solution of 5% Na₂SO₄ and 5% NaCl, gives 0.2% greater compressive strength with reference to M1. The presence of 10% CBA decreases the chloride penetration and drying shrinkage around 33.6% and 29.2% respectively at 180 days. Hence, this study declared 10% CBA as optimum that can be used for future research.

The utilization of construction and demolition waste materials for the radionuclide immobilization by sorption processes was investigated. Given that the liquid radioactive waste usually has a complex composition and that effects of competition may significantly influence the efficiency of the treatment, the Simplex Centroid experimental design was used to explore ions sorption from multi-component solutions. For the purpose of this study, the common components of construction and demolition waste, such as pathway concrete and different bricks samples, were used along with the multi-component Sr²⁺, Co²⁺, and Ni²⁺ ions solutions. The equations for the prediction of metal ions sorption capacities were derived. The coefficients that correspond to the linear and interaction terms were obtained using a special cubic model. Likewise, by analysis of variance, statistically significant terms of the obtained polynomial were defined. The investigation has shown that the most effective sorption was onto the pathway concrete for all three cations, while the highest sorption capacity was found for Co²⁺ ions. Also, it has been determined that concerning Sr²⁺ ion removal there was a competition with coexisting Co²⁺ and Ni²⁺ ions, reducing its sorption capacity, while sorption of Co²⁺ and Ni²⁺ occurred more independently on other cations in multi-component solutions. Based on the obtained results, the applied experimental design can be efficiently used for the description of competitive sorption process and could be a powerful tool for the prediction of cation immobilization in liquid radioactive waste treatment.