Portland Cement-Based Grouts Enhanced with Basalt Fibers for Post-Tensioned Concrete Duct Filling.

In post-tensioned systems, grouts act as a last line of defense to prevent the penetration of harmful compounds such as chlorides, moisture and other substances that cause corrosion in the prestressing steel. For this reason, improving grouts results in the enhancement of the overall durability of the structure. In this study, the physical properties of grouts with basalt microfiber additions in the amounts of 0.03, 0.07 and 0.10% with respect to the mix volume were evaluated. The fresh properties included flowability and unit mass. Specimens were fabricated to evaluate drying shrinkage, compressive strength, air permeability and rapid permeability to chloride ions. The incorporation of basalt microfibers showed a beneficial effect on the physical properties of the grout by increasing the drying shrinkage resistance and decreasing the permeability compared to the reference mix and two commercial dry prepackaged grouts. The optimal grout mix was the one with a percentage of basalt microfibers of 0.10%, which decreased drying shrinkage by 15.98% at 14 days compared to the reference mix, and permeability to chloride ions decreased by 10.82% compared to the control mix.

Development of a Portland Cement-Based Material with Agave salmiana Leaves Bioaggregate.

Depending on the morphology of the natural fibers, they can be used as reinforcement to improve flexural strength in cement-based composites or as aggregates to improve thermal conductivity properties. In this last aspect, hemp, coconut, flax, sunflower, and corn fibers have been used extensively, and further study is expected into different bioaggregates that allow diversifying of the raw materials. The objective of the research was to develop plant-based concretes with a matrix based on Portland cement and an aggregate of Agave salmiana (AS) leaves, obtained from the residues of the tequila industry that have no current purpose, as a total replacement for the calcareous aggregates commonly used in the manufacturing of mortars and whose extraction is associated with high levels of pollution, to improve their thermal properties and reduce the energy demand for air conditioning in homes. Characterization tests were carried out on the raw materials and the vegetal aggregate was processed to improve its compatibility with the cement paste through four different treatments: (a) freezing (T/C), (b) hornification (T/H), (c) sodium hydroxide (T/NaOH), and (d) solid paraffin (T/P). The effect of the treatments on the physical properties of the resulting composite was evaluated by studying the vegetal concrete under thermal conductivity, bulk density, and compressive strength tests with a volumetric ratio between the vegetal aggregate and the cement paste of 0.36 and a water/cement ratio of 0.35. The hornification treatment showed a 15.2% decrease in the water absorption capacity of the aggregate, resulting in a composite with a thermal conductivity of 0.49 W/mK and a compressive strength of 8.66 MPa, which allows its utilization as a construction material to produce prefabricated blocks.

Effect of the Notch-to-Depth Ratio on the Post-Cracking Behavior of Steel-Fiber-Reinforced Concrete.

Concrete barely possesses tensile strength, and it is susceptible to cracking, which leads to a reduction of its service life. Consequently, it is significant to find a complementary material that helps alleviate these drawbacks. The aim of this research was to determine analytically and experimentally the effect of the addition of the steel fibers on the performance of the post-cracking stage on fiber-reinforced concrete, by studying four notch-to-depth ratios of 0, 0.08, 0.16, and 0.33. This was evaluated through 72 bending tests, using plain concrete (control) and fiber-reinforced concrete with volume fibers of 0.25% and 0.50%. Results showed that the specimens with a notch-to-depth ratio up to 0.33 are capable of attaining a hardening behavior. The study concludes that the increase in the dosage leads to an improvement in the residual performance, even though an increase in the notch-to-depth ratio has also occurred.

Corrosion Behavior of Steel-Reinforced Green Concrete Containing Recycled Coarse Aggregate Additions in Sulfate Media.

Novel green concrete (GC) admixtures containing 50% and 100% recycled coarse aggregate (RCA) were manufactured according to the ACI 211.1 standard. The GC samples were reinforced with AISI 1080 carbon steel and AISI 304 stainless steel. Concrete samples were exposed to 3.5 wt.% Na2SO4 and control (DI-water) solutions. Electrochemical testing was assessed by corrosion potential (Ecorr) according to the ASTM C-876-15 standard and a linear polarization resistance (LPR) technique following ASTM G59-14. The compressive strength of the fully substituted GC decreased 51.5% compared to the control sample. Improved corrosion behavior was found for the specimens reinforced with AISI 304 SS; the corrosion current density (icorr) values of the fully substituted GC were found to be 0.01894 µA/cm2 after Day 364, a value associated with negligible corrosion. The 50% RCA specimen shows good corrosion behavior as well as a reduction in environmental impact. Although having lower mechanical properties, a less dense concrete matrix and high permeability, RCA green concrete presents an improved corrosion behavior thus being a promising approach to the higher pollutant conventional aggregates.

Corrosion Behavior of AISI 304 Stainless Steel Reinforcements in SCBA-SF Ternary Ecological Concrete Exposed to MgSO4.

In this study, ternary ecological concrete (TEC) mixtures were produced with partial substitution of the ordinary Portland cement (OPC) by 10%, 20%, and 30% of sugar cane bagasse ash (SCBA) and silica fume (SF); a control mixture (100% OPC) was prepared according to ACI 211.1 standard. The studied TEC specimens were reinforced with AISI 304 stainless steel and AISI 1018 carbon steel rebars. TEC reinforced specimens were immersed in two different electrolytes, a control (DI-water) and 3.5 wt.% MgSO4 solution, for 180 days. The electrochemical corrosion was monitored by corrosion potential (Ecorr) according to ASTM C-876-15 standard, and the linear polarization resistance (LPR) technique using ASTM G59 standard. The Ecorr and current density icorr results show that AISI 304 stainless steel rebars have a high corrosion resistance, with icorr values below 0.1 µA/cm2, which is interpreted as a level of negligible corrosion. The best corrosion performance was found for the TEC mixture made with a 20% addition of blend of sugar cane bagasse ash-silica fume (SCBA-SF) to the OPC.