International Concrete Abstracts Portal

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.

As global demand for concrete has been forecasted to continue rising, one of the approaches toward more sustainable construction is the adoption of mixture designs that replace conventional ones. The current study contains a comparison between concrete mixtures that constitute only ordinary portland cement (OPC) and mixtures incorporating 25% OPC with a 75% replacement by supplementary cementitious materials (SCMs). The major experimental hypothesis focuses on investigating whether it is effective to use thermal treatment under moderately elevated temperatures to enhance physical and mechanical properties of concrete. Comparisons were performed using mechanical tests such as compressive strength, tensile strength, and flexural strength, and through several nondestructive physical experiments, as well as microstructural investigation using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). In conclusion, the experimental results showed a mostly positive influence, observing significant enhancements after thermal treatment. However, treated concrete mixtures that constitute only OPC seem to excel in overall performance compared to those incorporating SCMs.

The amount of recycled concrete powder (RCP) experiences an exponential increase due to the construction and demolition activities associated with buildings and infrastructure. To enhance the reactivity and utilization of RCP, this study investigated the effect of thermal (calcination), inorganic (calcium hydroxide, CH), organic (diethanolisopropanolamine, DEIPA), and synergistic activation on the strength development of recycled concrete powder-cement (RCP-C) pastes. The microstructure of hardened pastes was characterized by X-ray diffraction (XRD), Fourier transform-infrared spectroscopy (FT-IR), thermogravimetric (TG) analysis, and scanning electron microscope (SEM). The results indicated that the optimal compressive and flexural strength were achieved when pastes were activated by calcination at 700°C for 30 minutes, followed by inorganic and organic activation using CH and DEIPA as activators successively. The compressive (flexural) strength at 1, 3, and 28 days increased by 42% (26.9%), 27.0% (18.6%), and 25.5% (16.3%), respectively, compared to the control group. The microstructure analysis revealed that the enhancement mechanism can be attributed to a thermal-inorganic-organic synergistic activation.

To use alternative cements such as belitic calcium sulfoaluminate (BCSA) cement for structural concrete, perhaps the most important consideration is ensuring that the rectangular stress block parameters used in flexural strength design are still applicable. This paper describes a complex experimental study consisting of flexural- compression specimens loaded to replicate the compression side of the stress distribution in a reinforced concrete beam. From these coupled flexural-compression tests, the shape of the stress distribution in a BCSA cement concrete specimen can be derived and used to develop equivalent rectangular stress distribution parameters. BCSA cement concrete and portland cement concrete (PCC) unreinforced flexural-compression specimens with various water-cement ratios (w/c) were fabricated and tested at varying ages. The results from the BCSA cement concrete flexural-compression specimens were compared with PCC tests, extensive historical PCC data, and design code values. The current Code equations approximating the rectangular stress block were found to be equivalent or conservative for BCSA cement concrete flexural members within the strength range of 54 to 85 MPa (7.8 to 12.4 ksi); this should give designers confidence in using this cement for structural concrete.

This study investigated the flexural behavior and seismic connection performance of precast lightweight aggregate concrete shear walls (PLCWs) using the relative emulation evaluation procedure specified in the Architectural Institute of Japan (AIJ). Six PLCW specimens connected through a bolting technique were prepared and tested under constant axial and cyclic lateral loads. In addition, three companion shear walls connected through the most commonly used spliced sleeve technique for precast concrete members were prepared to confirm the effectiveness of the bolting technique for the seismic connection performance. The main parameters were the concrete type (all-lightweight aggregate (ALWAC), sand-lightweight aggregate (SLWAC), and normal-weight concrete (NWC), the compressive strength of the concrete, and the connection technique. The test results showed that none of the specimens connected through the conventional spliced sleeve technique reached the allowable design drift ratio specified by the AIJ, indicating that the spliced sleeve is an unfavorable technique for obtaining a seismic connection performance of PLCWs equivalent to that of cast-in-place reinforced concrete shear walls. However, the specimens made of ALWAC or NWC and connected through the bolting technique not only reached the allowable design drift ratio specified by the AIJ but also satisfied the requirements of the seismic connection performance (lateral loads and allowable error at yield displacement) within the allowable design drift ratio. Consequently, the displacement ductility ratio of the specimens connected through the bolting technique was 1.52 times higher than that of the specimens connected through the conventional spliced sleeve technique, respectively. This difference was more prominent in the specimens made of ALWAC than in those made of SLWAC or NWC. Thus, the use of the bolting technique as a wall-to-base connection in shear walls can effectively achieve a seismic connection performance equivalent to that of cast-in-place shear walls while maintaining the medium ductility grades.