International Concrete Abstracts Portal

ASTM C31 describes the procedure for making concrete specimens in the field. Its origin can be traced to 1920, proposing rodding or stroking each 100 mm thick layer 25-30 times. Concrete technology has evolved tremendously over the last century, but specimens are still prepared following this 100-year-old methodology. This paper investigates the density and compressive strength of concrete cylinders for different consolidation procedures. Mix design variations include paste volume, w/c, aggregate grain size distribution, fly ash, and plasticizer. An increase in compressive strength of approximately 5 MPa can be obtained if 100 × 200 mm cylinders are rodded in 4 layers, 25 rods each, if the slump is not over 100 mm. For all other mixtures, the current rodding procedure of 2 layers, 25 rods each, is recommended. For mixtures with higher slump, 2 layers with less rodding per layer deliver similar strength values, but the variability is high.

Engineered cementitious composite (ECC), a prominent innovation in the realm of concrete materials in recent years, contains a substantial amount of cement in its composition, thereby resulting in a significant environmental impact. To enhance the environmental sustainability of ECC, it is plausible to substitute a large portion of cement in the composition with fly ash, a by-product of coal-fired power plants. Recent years have seen increased research in ECC containing high-volume fly ash (HVFA) binder and its wider application in construction practices. In this particular context, it becomes imperative to review the role of HVFA binder in ECC. This review first examines the effects of incorporating HVFA binder in ECC on the fiber dispersion and fiber-matrix interface behavior. Additionally, mechanical properties, including compressive strength, tensile behavior, and cracking behavior under loading, as well as durability performances of HVFA-based ECC under various exposure conditions, are explored. Last, this review summarizes the research needs pertaining to HVFA-based ECC, proving valuable guidance for future endeavors in this field.

This research establishes a systematic methodology for selectinga migratory corrosion inhibitor (M-CoI) as a repair strategy forreinforced concrete (RC) structures exposed to aggressive environments. Conducted in two phases, Phase 1 involves corrosion testing in pore solutions to evaluate inhibitor efficacy, while Phase 2 examines the percolation ability of M-CoIs in different concrete systems and performance of M-CoI in RC with corroded reinforcing bars. The findings reveal that the efficiency of the compounds as repair measures is significantly lower than their preventive performance, primarily due to the presence of corrosion products onthe steel surface. Additionally, the effectiveness of the M-CoIs isinfluenced by their concentration and form at the reinforcing barlevel; specifically, 4-Aminobenzoic acid (ABA) achieved maximumconcentration in its purest form, whereas Salicylaldehyde (SA) and2-Aminopyridine (AP) reached the reinforcing bar in lower concentrations. Importantly, the study highlights that compounds effective in pore solution may not perform well in concrete, underscoring the necessity of considering the intended application—preventive or repair—when selecting inhibitors. Thus, a comprehensive approach involving both pore solution testing and migration ability assessments is essential for optimal corrosion protection in reinforced concrete.

The production of carbonated aggregates from Class F fly ash(FA) is challenging due to its low calcium content, typically lessthan 10%. This study investigates the production of carbonatedalkali-activated aggregates using FA and calcium carbide sludge(CCS). Sodium hydroxide was used as an activator, and the effectsof autoclave treatment on the properties of these aggregates wereexamined. The optimal mixture, comprising 70% FA and 30%CCS, achieved a single aggregate strength of >5 MPa in autoclavecarbonated (AC) aggregates, comparable to the strength obtainedafter 14 days of water curing without-autoclave carbonated(WAC) aggregates. Both AC and WAC aggregates exhibited a bulkdensity of 790 to 805 kg/m3, and the CO2 uptake was 12.5% and13.3% in AC and WAC aggregates, respectively. Field-emissionscanning electron microscopy (FE-SEM) and Fourier-transforminfrared spectroscopy (FTIR) analysis indicated the formation ofcalcium-aluminum-silicate-hydrate (C-A-S-H) gel in non-carbonatedaggregates, while calcite and vaterite, along with sodiumaluminum-silicate-hydrate (N-A-S-H) gel, formed in carbonatedaggregates. Concrete incorporating AC and WAC aggregatesexhibited compressive strength of 39 and 38 MPa, with concretedensity of 2065 kg/m3 and 2085 kg/m3, respectively. Furthermore,AC and WAC aggregate concrete showed a reduction in CO2emissions of 18% and 31%, respectively, compared to autoclavenon-carbonated (ANC) aggregate concrete. These findings highlightthe potential of producing carbonated alkali-activated aggregatesfrom FA and CCS as sustainable materials for constructionapplications.