International Concrete Abstracts Portal

This research aims to prepare porous ceramsite with low thermal conductivity. The porous ceramsite was also used as fine aggregate to substitute the river sand in pumice concrete. Its impact on improving the thermal insulation performance of pumice concrete was thoroughly investigated. The experimental method included high-temperature calcination, transient planar heat source analysis, as well as the use of X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), and Mercury-Intrusion Porosimetry (MIP) techniques. The investigation revealed that the best calcination parameters were a preheating temperature of 400°C, a preheating duration of 25 minutes, a calcination temperature of 125°C, and a calcination duration of 25 minutes. Under these conditions, the crushing index of the porous ceramsite was determined to be 29.1%, with a thermal conductivity of 0.138 W/(m·K). It is worth noting that an increase in calcination temperature promotes the hole content in ceramsite, leading to a 52.19% increase in macropore volume and a corresponding decrease in thermal conductivity. Furthermore, as the replacement rate of ceramic aggregate increases, the thermal conductivity of pumice concrete gradually decreases, with values ranging from 18% to 34.8%. This reduction occurs because the replacement elevates the volume of coarse capillary pores and non-capillary pores in pumice concrete, increasing by 13.9 to 91.3% and 63.1 to 128.5%, respectively. Additionally, a prediction model for the thermal conductivity of pumice concrete has been established using the Mori-Tanaka homogenization method. The model's verification accuracy falls within an error range of 5%, demonstrating its effectiveness in accurately predicting the thermal conductivity of pumice concrete.

This study employed a mixed microbial culture (MB) comprising Bacillus subtilis (BS), Bacillus polymyxa (PM), and nitrate-reducing bacteria (NRB) in equal proportions. The mixed microbial culture was used to enhance recycled brick aggregate (RBA) through the microbial-induced carbonate precipitation (MICP) method, investigating the effects of this enhancement on both the aggregate and recycled mortar properties. Results indicate that the mineralization activity of the mixed culture significantly exceeded that of individual strains, achieving an 84.64% mineralization rate after 14 days. MICP-enhanced RBA demonstrated markedly improved performance. The compressive strength of the reinforced recycled mortar increased by 32.62% at 3 days and 22.6% at 28 days, with the 28-day compressive strength approaching that of cement mortar using natural aggregates. The interfacial transition zone properties were significantly improved, with its width reduced from 30-wenzhong35 μm to 20-25 μm. This study provides experimental evidence for recycled brick aggregate reinforcement technology while offering technical support for the resource utilization of recycled brick aggregates.

Several approaches are currently used to proportion recycled aggregate concrete (RAC), each having limitations. An effective and universal way to proportion RAC is not only an important tool for developing high-quality concrete but also a critical milestone for promoting the wider use of recycled concrete aggregate (RCA) in concrete. A mixture design method based on particle packing and excess paste theory is proposed in this study. Given the focus on pavement concrete, the modified Box Test was used to quantify RAC workability. RAC mixtures with five different RCAs of varying quality, developed using the proposed method, showed excellent workability (Box Test Rating E1-S1), whereas mixtures developed with conventional mixture design methods failed to achieve adequate workability. Mechanical properties of optimized RACs were either comparable or improved. The adverse effect of RCA on concrete resistivity and shrinkage appeared negligible and was mitigated by the mixture design approach developed in this study. Compared with conventional Direct Weight Replacement (DWR)/Direct Volume Replacement (DVR) mixtures, the proposed design achieved a reduction of surface voids by more than 80%, up to 25% higher compressive strength, and 20% lower shrinkage at 28 days, while maintaining comparable resistivity.

As recycled concrete reaches the end of its service life, a new generation of coarse recycled aggregate (CRA) is created. Although the variables influencing the physical properties of CRA are well understood, the performance of multi-recycled coarse aggregate (MRCA) remains insufficiently explored, being essential to study how the modified properties could affect the performance of recycled concrete. This research involved five recycling cycles to evaluate the properties of MRCA and its impact on the mechanical and durability performance of concrete made with 75% MRCA. The findings indicate that water absorption, porosity, and abrasion of MRCA increase with each recycling cycle. Although the mechanical behaviour of the concretes appears to be unaffected by the number of recycling cycles, the elastic modulus is negatively impacted when MRCA is used. Furthermore, while some permeability properties are significantly influenced by each recycling cycle, both water penetration depth and resistance to sulfate attack remain largely unchanged.

The growing generation of construction and demolition waste necessitates the development of effective recycling strategies to address environmental concerns. This study investigated the replacement of natural fine aggregate (NFA) with recycled fine aggregate (RFA) at 0, 50, and 100% using two treatment methods: (i) sodium silicate (SS)–silica fume (SF) pre-soaking treatment (SS-T) and (ii) organic treatment (OA-T) with bio-additives derived from Persea macranta, Haritaki, and Ciccus glauca roxb. A quantitative comparison of the aggregate and mortar quality was conducted for each method. The combined application of SST and OT demonstrated an 85% improvement in workability and a 68% reduction in water absorption for RFA. Mortar experiments revealed up to 76% improvement in compressive and flexural strengths compared with untreated RFA mortar. Microstructural analyses (SEM, EDS, XRD, and FT-IR) confirmed the enhanced bond strength and mineral composition. This study highlights the potential of SST and OT to produce durable, high-performance RFA mortars using locally available, economical bio-additives.