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.

This study aimed to evaluate the effect of isolated silica fume (SF) and SF combined with three contents of crystalizing admixture (CA) in the self-healing of engineered cementitious composites (ECCs) with different polymeric fibers. Self-healing was evaluated in coupon specimens subjected to bending to produce cracking. Healing products were evaluated in the cracks within 84 days. Exposure conditions for self-healing were water-saturated (SAT) and wet-dry cycles (WD). The results showed that the composites with isolated SF presented a continuous layer of healing product covering widths of up to 100 μm. The final widths for these composites were 40 μm for different conditions. In composites with CA, the volume of product generated (gel) was considerably greater, causing it to leak out of the microcracks existing in the ECC, impairing healing. Thus, the results showed that the use of SF+CA reduced the ECC healing potential. Healing from the crystallizing admixture was spot-wise only, decreasing its healing potential. The performance of the crystallizing additive was impaired under wetting and drying conditions. Leaching was observed both under SAT and WD exposure conditions. More leaching was observed from WD, while SAT formed a more uniform product layer.

The durability of reinforced concrete is often compromised by chloride penetration, leading to corrosion of reinforcing steel and reduced structural strength. To improve the sustainability and longevity of concrete structures, it is crucial to model and predict chloride permeability (CP) accurately, thereby minimizing the time and resources required for extensive experimental testing. This paper presents a proof-of-concept study applying Artificial Neural Networks (ANN) to predict CP in concrete structures. The model was trained on a small but carefully controlled experimental dataset of 10 concrete mixtures, considering four key parameters: water-to-cementing materials ratio, silica fume content, cementing materials content, and air content. Despite the limited dataset size, which constrains generalizability and statistical robustness, the ANN captured nonlinear relationships among the input parameters and CP. The comparison between experimental and simulated CP values showed reasonable agreement, with errors ranging between –242 and 420 Coulombs. These results establish the trustworthiness and reliability of the proposed model, providing a valuable tool for predicting CP and informing the design of durable and sustainable concrete structures.

Reinforcing seawater sea-sand concrete (SSC) with basalt fiber reinforced polymer (BFRP) bars can adequately resolve chloride corrosion issues. However, the multiple-element ions in seawater and sea sand can increase the concrete alkalinity and accelerate the degradation of BFRP bars. This study aims to enhance the durability performance of BFRP-SSC beams by regulating concrete alkalinity. A low-alkalinity SSC (L-SSC) is designed by incorporating a high-volume content of fly ash and silica fume. A total of 16 BFRP-SSC beams were designed based on the current standards and prepared using normal SSC (N-SSC) and L-SSC. The beam flexural performances before and after long-term exposure are characterized through the four-point bending test. The test results indicate that exposure in the simulated marine environment can reduce the load-bearing capacity and change the failure mode of BFRP beams with N-SSC. After exposure at 55°C for 4 months, the load-bearing capacity of the BFRP-SSC beams was reduced by 70.0%. Moreover, a slight enhancement of load-bearing capacity and ductility of the BFRP-L-SSC beams was observed due to the enhanced interface performance with further concrete curing. Furthermore, the long-term performance of the sand-coated BFRP bars is better than that of the BFRP bars with deep thread. The load-bearing capacity of the BFRP-L-SSC beams increased by approximately 20% after 4 months of accelerated aging due to concrete strength growth, and the BFRP-L-SSC beams maintained the concrete crushing failure mode after exposure. Finally, a loadbearing capacity calculation model for the BFRP-SSC beams is proposed based on the experimental investigation, and its prediction accuracy is higher than that of the current standards. This study can serve as a valuable reference for applying BFRP-SSC structures in the marine environment.

This study evaluates the potential to use shrinkage-reducing admixture (SRA) and pre-saturated lightweight sand (LWS) to shorten the external moist-curing requirement of ultra-high-performance concrete (UHPC), which is critical in some applications where continuous moist-curing is challenging. Key characteristics of UHPC prepared with and without SRA and LWS and under 3 days, 7 days, and continuous moist curing were investigated. Results indicate that the combined incorporation of 1% SRA and 17% LWS can shorten the required moist-curing duration because such a mixture under 3 days of moist curing exhibited low total shrinkage of 360 με and compressive strength of 135 MPa (19,580 psi) at 56 days, and flexural strength of 18 MPa (2610 psi) at 28 days. This mixture subjected to 3 days of moist curing had a similar hydration degree and 25% lower capillary porosity in paste compared to the Reference UHPC prepared without any SRA and LWS and under continuous moist curing. The incorporation of 17% LWS promoted cement hydration and silica fume pozzolanic reaction to a degree similar to extending the moist-curing duration from 3 to 28 days and offsetting the impact of SRA on reducing cement hydration. The lower capillary porosity in the paste compensated for the porosity induced by porous LWS to secure an acceptable level of total porosity of UHPC.