International Concrete Abstracts Portal

Firstly, the proposed static test was carried out on eight fly ash foamed concrete walls with different axial compression ratios μ and steel ratios ρ. Secondly, the quantitative analysis method of wall damage was proposed based on the crack development theory, and the real damage index was proposed. Then, through theoretical analysis and curve fitting, two kinds of seismic damage models— energy method and Park-Ang-W—were proposed, and the damage values were calculated to compare with the real damage values. Finally, the Park-Ang-W model was used to analyze the parameter expansion of 16 Abaqus wall models with different axial compression ratios μ and steel ratios ρ. The results show that the damage evaluation index based on crack development theory can effectively reflect the damage of fly ash foamed concrete walls. The accuracy of the energy method model is not high at the low number of cycles, and the error is less than 20% at the high number of cycles. The Park-Ang-W model has an error of approximately 10% at a high number of cycles, which better reflects the true damage of the specimen. The axial compression ratio μ has little effect on the wall damage, with a maximum effect range of 6.7%. Increasing the reinforcement ratio can effectively reduce the wall damage, with a maximum effect range of 12.6%. The results of the study provide a theoretical basis for the future application of fly ash foamed concrete in construction projects.

The use of construction waste to prepare recycled micro powder can improve the use of construction waste resources and effectively reduce carbon emissions. In this paper, researchers used waste concrete processing micro powder to prepare foam concrete (FC) and quantitatively characterized the performance and pore structure of FC by scanning electron microscopy (SEM), pore and fissure image recognition and analysis system (PCAS), and mechanical property testing methods with different mixing ratios of micro powder. The results showed that the effect of single mixing of micro powder or fly ash is better than the composite mixing test, and the optimal proportion of compressive strength of single mixing of micro powder is higher than that of single mixing of fly ash. The optimum mixing ratio is 6:4 between cement and micro powder, and the best effect is achieved when the micro powder mixing amount is 40%. Single or double mixing can fill the pores between the foam and strengthen the performance of the substrate. The tests of single-mixed or compound-mixed micro powder showed that the fractal dimension decreased with the increase of porosity; when the fractal dimension of the specimen increased, the average shape factor became smaller, the compressive strength decreased, and the water absorption rate increased.

The atmospheric purification capacity of concrete has not beenadequately investigated. This study examines the feasibility ofusing sustainable foam-concrete granules as a porous materialfor reducing air pollutants in concrete. To enable the removal of nitrogen oxide (NOx) and sulfur oxide (SOx) using titanium dioxide (TiO2) nanoparticles, foam concrete was crushed into granules with porosity exceeding 30%. Ordinary portland cement (OPC), fly ash (FA), and slag cement were used as source cementitious materials. OPC was replaced with 0 to 40% FA and 0 or 40% slag cement by weight. Test results indicate that 30% FA and unit cementitious materials content exceeding 500 kg/m3 (31.2 lb/ft3) are optimal for replacing cement and foam-concrete granules, respectively. Considering the particle-size distribution and specific surface area, 6 to 13 mm (0.24 to 0.51 in.) and 6 to 9 mm (0.24 to 0.35 in.), were selected as optimal granule sizes. The coating procedures yielded improved SOx and NOx removal, with the removal rates reaching 83.8 and 45% using granules of 6 to 9 mm (0.24 to 0.35 in.), respectively. Consequently, the foam-concrete granules coated with TiO2 nanoparticles are promising in developing porous concrete with the reduction capability of air pollutants.

Ultra-high-performance concrete (UHPC) is a new class of cementitious material with unique characteristics, including self-consolidation, and excellent mechanical and durability properties. To achieve the desired properties, a very dense internal structure and a very low water-binder ratio (w/b) are necessary. Due to the very different mixture design compared to conventional concrete, it is critical to incorporate different types of chemical admixtures to achieve appropriate fresh concrete behavior of UHPC. To ensure the successful placement of UHPC, it is important to have a good understanding of the workability and rheological characteristics of UHPC with different types and dosages of chemical admixtures. This paper presents a detailed study of the impact of high-range water reducer, workability-retaining admixture, and anti-foaming admixture on the workability and rheological characteristics over different mixture elapsed times. Besides the flowability, both Bingham and modified Bingham models were used to obtain key rheological parameters, including yield stress, viscosity, and thixotropy. Furthermore, the authors developed stability indexes to assess the fiber stability of UHPC in both fresh and hardened states. Based on the experimental results, the paper presented suggested criteria to ensure appropriate flowability and fiber stability for UHPC placement.

This paper investigates the application of nanotechnology in three-dimensional (3D) concrete printing (3DCP), in particular for enhancing thixotropic material behavior, improving buildability or the vertical building rate, and the amelioration of typical 3DCP anisotropic mechanical properties. Two 3D-printable cementitious materials are investigated in this study: 1) high-performance concrete (HPC) with respective nano-silica (nS) and silicon carbide (SiC) nanoparticle additions; and 2) lightweight foamed concrete (LWFC) with nS addition. The results indicate a significant increase in thixotropic material behavior for the HPC at low nanoparticle dosages. The inclusion of SiC nanoparticles improved the HPC’s buildability performance by 45%. The incorporation of 3% nS to the LWFC increased the static yield shear stress by up to five times, which is validated by the improved buildability performance. Hardened state mechanical properties improved for both cementitious materials and nanoparticle additions. Especially noteworthy is nanoparticles’ favorable influence on the interlayer bond strength.