International Concrete Abstracts Portal

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.

The production of Ordinary Portland Cement (OPC) is a major contributor to carbon emissions. One immediate and viable solution is the use of optimized concrete mixtures that employ a decreased quantity of cement and increased dosage of high-range water-reducing (HRWR) admixtures. This study investigates five different concrete mixtures with varying w/c (0.37 to 0.42) and reduced cement contents. The mixtures with “low cement + high dosage HRWR admixture” content had over 30% increase in mechanical strength and presented 40% lower water absorption, and 68 to 97% higher formation factor, indicating enhanced durability. The optimized concrete mixtures with reduced cement and lower w/c have a service life increase of up to 117% and a life-cycle cost reduction of 29%. The application of “low cement + high dosage HRWR admixture” mixtures can improve the sustainability of concrete mixtures by reducing cement and water contents and increasing the service life of concrete in severe environments.

Portland Limestone Cement (PLC) has gained widespread use as the most accessible and sustainable blended cement in the market. However, in many African countries, including Ghana, the use of clay pozzolana in the concrete industry has primarily relied on Ordinary Portland Cement (OPC). In this study, PLC Type II/B-L was partially replaced with clay pozzolana at levels ranging from 10% to 50% by weight. The investigation included compressive strength testing, non-destructive evaluations using electrical surface resistivity, pulse velocity, and chloride penetration tests, targeting a characteristic strength of 30 MPa. Additionally, an environmental impact assessment based on the carbon footprint of both control and clay pozzolana concretes was conducted. The mix design followed the EN 206 standard. A total of 72 cubic moulds were produced for the strength test. The results showed that clay pozzolana concretes with between 10 and 20% replacement achieved strength values of 35 and 33 MPa, respectively, higher than the target of 30 MPa (4351.13 psi) strength at 28 days. However, mixtures with 30% to 50% replacement required extended curing periods of 60 to 90 days to reach the desired strength. At extended curing, 10-50% clay pozzolana replacement attained strength between 32 and 41 MPa. Non-destructive test results showed no direct correlation with compressive strength, confirming that different factors govern strength, resistivity, and pulse velocity. The environmental impact assessment revealed a 14 to 51% reduction in CSi and a 19 to 36% increase in CRi with 10 to 50% clay pozzolana (for CSi) and 10 to 40% (for CRi). The thermodynamic modelling also revealed that pozzolana contents below 30% primarily promoted pozzolanic reactions, enhancing performance compared to the control mix. Based on these results, 20–30% clay pozzolana replacement is recommended to ensure reliable performance, while higher levels (>30%) require further durability evaluation for long-term use.

Corrosion in reinforcing steel bars is a critical factor influencing the durability and structural performance of reinforced concrete structures. This paper investigates the effects of corrosion on the mechanical properties of thermo-mechanically treated steel bars. The study parameters included bar diameter, corrosion technique, and varying corrosion levels (CLs). The impressed current technique was used to accelerate corrosion. Load-displacement data from uniaxial tensile tests were analyzed to determine stress-strain relationships of corroded bars. The results showed that the mechanical properties of the bars were unaffected by diameter or corrosion technique. However, a consistent reduction in both nominal yield strength and ultimate strength was observed with increasing CLs, while the elastic modulus remained unchanged. The strength factors for yield strength and ultimate strengths of the corroded bars varied in the range of 0.0013 to 0.015 and 0.0032 to 0.012, respectively, which were higher than reported in the literature. The fracture strain of the bars decreased at higher CLs. Predictive models were developed to estimate the residual mechanical properties, which are crucial for defining the constitutive relations needed to determine analytical stress-strain behavior. Analytical methods for determining these constitutive relations were also proposed, showing a good correlation with the experimental stress-strain curves.

This paper presents findings from an experimental study focused on the performance of concrete composed entirely of 100% slag aggregate, enhanced with polypropylene (PP) fibers, subjected to severe freeze-thaw cycling between -60°C and +60°C. The research employed varying fiber lengths of 19.01, 38.1, and 57.15 mm and dosages of 3, 6, and 9 kg/m³. Findings indicate that the incorporation of fibers contributes to the overall resilience of the slag aggregate concrete under freeze-thaw conditions. To evaluate freeze-thaw resistance, the coefficient of thermal expansion (CTE) was determined using the Ohio CTE method and AASHTO TP60-00. Additionally, dynamic modulus, mass loss, and flexural strength were assessed. X-ray fluorescence (XRF) analysis was performed on slag aggregates to characterize their chemical composition. Findings indicate that the incorporation of fibers, particularly at a dosage of 9 kg/m³ and a length of 57.15 mm, enhances the resilience of the slag aggregate concrete under 300 freeze-thaw conditions as specified in ASTM C666/C666M-15, leading to improved flexural strength and reduced mass loss (less than 7%). However, some fiber-reinforced concrete samples experienced up to a 26.776% decrease in flexural strength after freeze-thaw cycles. Additionally, 38.1 mm fibers at varying dosages effectively mitigated the adverse effects of freeze-thaw cycles on the concrete's thermal expansion. In contrast, concrete without fibers lost over 40% of its mass. This contribution is particularly significant given the scarcity of data on the performance of concrete entirely made up of slag aggregate and mixed with PP fibers of different lengths in extreme weather environments.