Towards sustainable management of polyacrylamide in soil-water environment: Occurrence, degradation, and risk.

Polyacrylamide (PAM) possesses unique characteristics, including high water solubility, elevated viscosity and effective flocculation capabilities. These properties make it valuable in various sectors like agriculture, wastewater treatment, enhanced oil recovery, and mineral processing industries, contributing to a continually expanding market. Despite its widespread use globally, understanding its environmental fate at the soil-water interface remains limited. This article aims to provide an overview of the occurrence, degradation pathways, toxicity, and risks associated with PAM in the bioenvironment. The findings indicate that various degradation pathways of PAM may occur in the bioenvironment through mechanical, thermal, chemical, photocatalytic degradation, and/or biodegradation. Through a series of degradation processes, PAM initially transforms into oligomers and acrylamide (AM). Subsequently, AM may undergo biodegradation, converting into acrylic acid (AA) and other compounds such as ammonia. Notably, among these degradation intermediates, AM demonstrates high biodegradability, and the bioaccumulations of both AM and AA are not considered significant. Ensuring the sustainable use of PAM necessitates a comprehensive understanding among policymakers, scholars, and industry professionals regarding PAM, encompassing its properties, applications, degradation pathways, toxic effect on humans and the environment, and relevant regulations. Additionally, this study offers insights into future priority research directions, such as establishing of a reliable source-to-destination supply chain system, determining the maximum allowable amount for PAM in farmlands, and conducting long-term trials for the PAM-containing demolition residues.

Investigation of the Mechanical Properties of Quick-Strength Geopolymer Material Considering Preheated-to-Room Temperature Ratio of Sand, Na2SiO3-to-NaOH Ratio, and Fly Ash-to-GGBS Ratio.

Geopolymer concrete is a useful alternative construction material for bridge deck systems, as it is characterized by a low carbon footprint, rapid setting, quick strength development, low cost, freeze-thaw resistance, low shrinkage, and sulphate and corrosion resistance. Heat curing enhances the mechanical properties of geopolymer materials (GPM), but it is not suitable for large structures, as it affects construction activities and increases energy consumption. Therefore, this study investigated the effect of preheated sand at varying temperatures on GPM compressive strength (Cs), the influence of Na2SiO3 (sodium silicate)-to-NaOH (sodium hydroxide-10 molar concentration), and fly ash-to-granulated blast furnace slag (GGBS) ratios on the workability, setting time, and mechanical strength properties of high-performance GPM. The results indicate that a mix design with preheated sand improved the Cs of the GPM compared to sand at room temperature (25 ± 2 °C). This was caused by the heat energy increasing the kinetics of the polymerization reaction under similar curing conditions and with a similar curing period and fly ash-to-GGBS quantity. Additionally, 110 °C was shown to be the optimal preheated sand temperature in terms of enhancing the Cs of the GPM. A Cs of 52.56 MPa was achieved after three hours of hot oven curing at a constant temperature of 50 °C. GGBS in the geopolymer paste increased the mechanical and microstructure properties of the GPM as a result of different formations of crystalline calcium silicate (C-S-H) gel. The synthesis of C-S-H and amorphous gel in the Na2SiO3 (SS) and NaOH (SH) solution increased the Cs of the GPM. We conclude that a Na2SiO3-to-NaOH ratio (SS-to-SH) of 5% was optimal in terms of enhancing the Cs of the GPM for sand preheated at 110 °C. Additionally, as the quantity of ground GGBS in the geopolymer paste increased, the thermal resistance of the GPM was significantly reduced.

Experimental Prognostication of Ultra-High-Performance Lightweight Hybrid Fiber-Reinforced Concrete by Using Sintered Fly Ash Aggregate, Palm Oil Shell Aggregate, and Supplementary Cementitious Materials.

To create cost-effective structures, the modern construction industry has sought to reduce the dead load of buildings. Lightweight concrete is a quick way to reduce dead load. The current study is primarily concerned with identifying modern substitutes for coarse aggregate likely to aid in waste management and offer potential alternatives to the most exploited natural resources. According to ACI C 39-M, this study developed a novel lightweight hybrid fiber-reinforced concrete (LWHFRC) with a density of less than 1825 kg/m3 and compressive strength of 50 to 75 MPa. Ordinary Portland cement (53 Grade) was mixed with fly ash, silica fume, and GGBS. Sintered fly ash aggregate (SFA) and palm oil shell aggregate (POS) were used as coarse aggregates. Hooked steel fibers and polyvinyl alcohol fibers were combined in a hybrid form to improve crack propagation properties at the initial and subsequent stages. The water-to-binder ratio was kept constant at 0.30 to 0.35 with a 1% superplasticizer. Four volume fractions of hybrid fibers (both steel and PVA with Vf = 0%, 1%, 1.5%, and 2%) were added. In addition, XRD, SEM, EDS, and EDS mapping tests were performed to finalize the material's chemical composition and crystalline structure. Furthermore, beams and cylinders were tested to determine the modulus of rupture, which was determined to be between 9.5 and 14 MPa by ACI code C 1609-M, and indirect tensile strength, achieved as 10 to 14 MPa by ACI code C 496-M. The researcher altered the modulus of elasticity (Ec) formula for lightweight concrete and discovered a relationship between fc' and fcb, fc' and fspt, and fcb and fspt. Finally, ANOVA and regression tests were run to check the significance of the experiment. The cost analysis revealed that the cost of LWHFRC increased by approximately 16.46%, while the strength increased by 55.98% compared to regular concrete.