International Concrete Abstracts Portal

Ultra-high performance concrete (UHPC) has seen growing use in the construction industry because of its high compressive, tensile, and flexural strength. The tensile and flexural strength are in part due to the steel fibers added to the UHPC mix. Yet, fibers can segregate due to poor material rheological properties and construction practices, resulting in less than expected material strength. Due to the importance of these fibers, there is a need to verify the volume and orientation of the steel fibers in the UHPC. In this work, we report on the design and testing of electromagnetic sensor systems that are able to test the integrity of the steel fibers in the UHPC structure. We test our sensor system using UHPC samples containing 1% to 3% fiber content by volume and created a calibration based on the results. Our results show a linear relationship between the inductance change versus the fiber percentage with an R-squared value of 99.7 %, which shows that our approach successfully demonstrated the potential of using our approach for characterizing steel fibers in UHPCs.

The presence of chloride ions is one of the most widespread causes of corrosion initiation in reinforcing steel in concrete. Trace chlorides present in cementitious materials or admixtures typically result in very low fresh chloride contents in normal-strength concrete that do not present a danger of corrosion. UHPC mixture designs, however, use much higher dosages of cementitious materials and admixtures that can result in non-negligible total fresh chloride contents. These high chloride values are likely to occur more frequently in the future as more UHPC mixtures are made with locally available materials and alternative cementitious materials and may result in concrete mixtures failing to meet specifications for fresh chloride content limits that are based on mixture proportions used in normal-strength concrete mixtures. UHPC and normal concrete samples were made without fibers and with increasing levels of internally admixed chlorides for four different levels of strength to determine chloride thresholds for internally added chlorides. The chloride threshold for fresh concrete was measured using a slightly modified version of the accelerated test EN 480-14. The water-soluble and acid-soluble chloride ion content of UHPC mixtures tested were measured according to ASTM C1218 and Florida Method FM 5-516 to determine the bound chlorides and fresh chloride limits for corrosion. The results demonstrate that the UHPC had ~ 25% higher chloride threshold than the control mixture when measured as an absolute content per unit volume of concrete. When the UHPC chloride content is normalized by mass of cementitious material, it was found that the amount needed to initiate corrosion may be lower than fresh chloride limits given in ACI-318 and ACI 222. Therefore, the ACI-318 water-soluble chloride limits as a % by mass of cementitious materials were found to be non-conservative for the two of the UHPC mixtures tested and should be re-examined for UHPC.

This article presents the characterizations of mechanical and durability properties on diverse concrete formulas with a lower carbon footprint. The contribution of mineral additions in the binder is currently limited by the NF EN 206/CN (2022) standard with the concept of the equivalent binder. It is now necessary to change these normative provisions to expand low-carbon concrete solutions and accelerate their development in construction. The objective of this study is to formulate concretes based on ternary binders and to evaluate their use properties compared to traditional concrete defined today in the normative context. Several types of addition have been used to form ternary binders: limestone addition, blast-furnace slag, and flash metakaolin. The results obtained with substitution rates ranging from 40% to 60% of clinker have allowed positioning these different concretes regarding the thresholds defined for the performance-based approach according to FD P 18-480 (2022).

The shortage of high-quality fine aggregate as an essential component of concrete has become an emerging worldwide concern for the construction industry. Concrete typically comprises up to 30% fine aggregate, which largely influences the strength and durability of the final product. Therefore, finding suitable substitutes for natural fine aggregate has become an important aspect of current concrete research.

In this study, we investigated the suitability of using remediated thermal-treated soil and tar-containing asphalt as secondary raw materials in a self-compacting concrete (SCC) mixture. The remediated materials were used as both (1) fine aggregate replacement to replace all the river sand and (2) partial filler/supplementary cementitious material (SCM) replacement. The modified Andreasen and Andersen (A&A) particle packing model was used to determine the optimal replacement level. Based on the optimal mixture design, the impact of the replacement on the fresh and mechanical properties of SCC was evaluated. Additionally, the pozzolanic reactivity of the fine fraction (<125 μm) within the secondary sand was assessed and compared to that of limestone powder. Our findings confirm that using remediated thermal-treated soil and tar-containing asphalt can produce a more circular, sustainable SCC by replacing high-quality natural sand and limestone filler and reducing the environmental impact of conventional SCC. This study contributes to finding viable alternatives to natural fine aggregate and promotes the use of recycled materials in construction.

This work investigates the influence of partial substitution of sand, which is becoming scarce, by the fines-rich limestone tuff sand on the fresh and mechanical performances of self-compacting concrete (SCC). A full three-factor design was applied to demonstrate the individual and combined effects of cement dosage, tuff substitution rate, and superplasticizer dosage on the spread, sieve stability and L-box fill rate, and compressive strength of the different formulated SCC. The SCCs were formulated with Algerian Htattba tuff containing 34% fines, at substitution percentages ranging from 35 to 55%. The limestone tuff sand proved to be well suited for use in the formulation of the SCCs, which are expected to perform well in the fresh state. The use of limestone tuff sand at high substitution rates resulted in a fluid, stable SCC that flowed perfectly through the iron bars of the Lbox without blockage and complied with the recommendations of the French Association of Civil Engineering, AFGC. The main influences observed after analysis of the responses obtained highlighted the predominant effect of the superplasticizer followed by the non-negligible positive effect of the limestone tuff, on the fresh characteristics of the formulated SCC. The first results show that the introduction of limestone tuff up to a substitution rate of 55% gives a consequent workability of 690 mm and a good compressive strength of about 40 MPa. It should be noted that a 55% substitution rate presents an undeniable economic and environmental interest by reducing the quantity of sand considered a "noble material" which is less and less available.