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International Concrete Abstracts Portal

Showing 1-5 of 1115 Abstracts search results

Document: 

SP-349_35

Date: 

April 22, 2021

Author(s):

Alexandre Rodrigue, Josée Duchesne, Benoit Fournier and Benoit Bissonnette

Publication:

Symposium Papers

Volume:

349

Abstract:

Alkali-activated slag/fly ash concretes activated with combined sodium silicate and sodium hydroxide show good mechanical and durability properties in general. When tested in terms of resistance to freezing and thawing cycling in watersaturated conditions, the concretes tested in this study show final values of relative dynamic modulus averaging 100% after 300 cycles. However, all tested concretes showed poor performance towards freezing and thawing in presence of de-icing salts with only one tested mixture showing a final average scaling value below 0.5 kg/m². Early-age microcracking is observed on all tested concretes and is correlated to high values of autogenous shrinkage in equivalent paste mixtures. Increasing the fly ash content reduces both the observed autogenous shrinkage and early-age cracking. Low drying shrinkage values ranging from 470 to 530 μm/m after 448 days of measurements at 50% RH and 23°C are noted. The use of fly ash in these alkali-activated concretes reduces the expansion levels of concrete specimens incorporating alkali-silica reactive aggregates. With increasing fly ash contents (20, 30 and 40% replacement), decreasing expansions are observed for any given reactive aggregate. In general, the durability properties measured in this study were improved by partially substituting slag with fly ash as binder material.


Document: 

SP-349_46

Date: 

April 22, 2021

Author(s):

Shizhe Zhang, Qingge Feng, Dongbo Wang, and Guang Ye

Publication:

Symposium Papers

Volume:

349

Abstract:

Strain-hardening geopolymer composite (SHGC) based on industrial wastes and by-products has emerged as a feasible alternative to strain-hardening cementitious composite (SHCC). Lately, a novel slag/fly ash-based SHGC with promising strain-hardening tensile performance and multiple cracking behavior has been successfully developed. However, its environmental impact with regards to its global warming potential and energy consumption remain to be evaluated.

This paper presents an evaluation and comparative study of the environmental impact factors of a newly developed slag/fly ash-based SHGC and three different types of conventional SHCC materials. The CO2 equivalent global warming potential (GWP) and the embodied energy (EE) were calculated under a life cycle assessment scheme based on the product stage. SHGC has significant advantages in terms of the global warming potential (GWP) while maintaining comparable or lower embodied energy (EE) when compared with greener version of SHCC materials and typical SHCC material (ECC M45), respectively. It could be concluded that the newly developed slag/fly ash-based SHGC demonstrates a very promising LCA record while possessing excellent technical performance. Consequently, SHGC could serve as a promising alternative for SHCC materials with considerably lower environmental impact.


Document: 

SP-349_45

Date: 

April 22, 2021

Author(s):

Bakhta Boukhatem, Ablam Zidol and Arezki Tagnit-Hamou

Publication:

Symposium Papers

Volume:

349

Abstract:

This study presents an accurate corrosion prediction through an intelligent approach based on deep learning. The deep learning is used to predict the time-to-corrosion induced cover cracking in reinforced concrete elements exposed to chlorides ions. The key parameters taken into consideration include thickness, quality and condition of the concrete cover. The prediction performance of the deep learning model is compared against traditional machine learning approaches using neural network and genetic algorithms. Results show that the proposed approach provides better prediction with higher generalization ability. The efficiency of the method is validated by an accelerated corrosion test conducted on 91 and 182-day moist cured reinforced fly ash concrete samples with different water-to-binder ratios. The results are in agreement with the model predictions. They also show that using the proposed model for numerical investigations is very promising, particularly in extracting the effect of fly ash on reducing the extent of corrosion. Such an intelligent prediction will serve as an important input in order to assist in service life prediction of corroding reinforced concrete structures as well as repair evaluation.


Document: 

SP-347_03

Date: 

March 1, 2021

Author(s):

Radoslav Sovják, Sebastjan Kravanja, and Jan Zatloukal

Publication:

Symposium Papers

Volume:

347

Abstract:

Steel fibres in cementitious composites play a crucial role in making structures less susceptible to the damage caused by projectile impacts. A synergistic effect is achieved when steel fibres and an otherwise brittle cementitious matrix are blended together to produce a high-performance fibre-reinforced cementitious composite with enhanced ductility and strength. These composites also display strain hardening in tension, which leads to enhanced energy absorption and dissipation capacity. In this study, in-service 7.62 × 39 mm [0.28 × 1.54 in.] cartridges were used as projectiles. The muzzle velocity and weight of the projectiles were 710 m/s [2329 ft/s] and 8.04 grams [0.284 oz], respectively. Projectiles were shot with a stationary semi-automatic rifle into specimens made of high-performance fibre-reinforced cementitious composites with various fibre volume contents. Fibres used in this study were straight with a smooth surface. The aspect ratio of the fibre was 108:1 and corresponding dimensions were 14×0.13 mm [0.55×0.005 in.]. The tensile strength of the fibres was 2,800 MPa [406 ksi] and the modulus of elasticity was 210 GPa [30,458 ksi]. Owing to their exceptional mechanical properties, the fibres played a key role in controlling the response of the specimens when impacted by projectiles. The highest fibre volume content used in this study was 2% by volume; the cube compressive strength of the resulting mixture was 144 MPa [20.9 ksi]. Specimens were examined for the possible presence of spalling, scabbing, cracking, or full perforation. Depth of penetration, crater area, and crater volume were also tested. Results showed that steel fibres, due to the aforementioned synergistic effect with a cementitious matrix, notably protected specimens from erosion and significantly reduced cratering damage.


Document: 

SP-345_06

Date: 

February 1, 2021

Author(s):

Marco Carlo Rampini, Giulio Zani, Matteo Colombo and Marco di Prisco

Publication:

Symposium Papers

Volume:

345

Abstract:

Fabric-reinforced cementitious matrix (FRCM) composites are promising structural materials representing the extension of textile reinforced concrete (TRC) technology to repairing applications. Recent experiences have proven the ability of FRCMs to increase the mechanical performances of existing elements, ensuring economic and environmental sustainability. Since FRCM composites are generally employed in the form of thin externally bonded layers, one of the main advantages is the ability to improve the overall energy absorption capacity, weakly impacting the structural dead weights and the structural stiffness and, as a direct consequence, the inertial force distributions activated by seismic events. In the framework of new regulatory initiatives, the paper aims at proposing simplified numerical approaches for the structural design of retrofitting interventions on existing reinforced concrete structures. To this purpose, the research is addressed at two main levels: i) the material level is investigated on the uniaxial tensile response of FRCM composites, modeled by means of well-established numerical approaches; and ii) the macro-scale level is evaluated and modeled on a double edge wedge splitting (DEWS) specimen, consisting of an under-reinforced concrete substrate retrofitted with two outer FRCM composites. This novel experimental technique, originally introduced to investigate the fracture behavior of fiber-reinforced concrete, allows transferring substrate tensile stresses to the retrofitting layers by means of the sole chemo-mechanical adhesion, allowing to investigate the FRCM delamination and cracking phenomena occurring in the notched ligament zone. It is believed that the analysis of the experimental results, assisted by simplified and advanced non-linear numerical approaches, may represent an effective starting point for the derivation of robust design-oriented models.


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