Recently, alkali-activated cement (AAC) has been studied to partially replace portland cement (PC) to reduce the environmental impact caused by civil construction and the cement industry. However, with regard to durability, few studies have addressed the behavior of AAC. This study aimed to evaluate the performance of AAC made from blast-furnace slag with contents of 4 and 5% sodium hydroxide as an activator (Na2Oeq of 3.72% and 4.42%, respectively) when subjected to alkali-aggregate reaction (AAR). Length variation tests were carried out on mortar bars immersed in NaOH solution (1 N of NaOH, T = 80°C [176°F]) and on concrete bars (T = 60°C [140°F], RH = 95%); compressive strengths tests and scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) analyses were also made. Two types of PC were used as a comparison. The results showed good behavior of the AAC in relation to the AAR, with expansions lower than those established by the norm (34% of the limit) and without the finding of losses of mechanical resistance or structural integrity. The alkaline activator content had a small influence on the behavior of the AACs, in which the lowest amount of NaOH (4%) showed fewer expansions (only 15% of the limit established by the norm). Even for the highest activator content (5%), the results were good and comparable to those of PC with pozzolans, which is recommended for the inhibition of AAR.

This work evaluates the technical feasibility of a roller-compacted concrete (RCC) pavement with complete replacement of natural aggregates by electric arc furnace slag (EAFS) or basic oxygen furnace slag (BOFS). The methodology includes, initially, the processing of the slags, and physical, chemical, and environmental characterization of the natural and slag aggregates. Subsequently, concrete mixtures were designed, and the compaction at optimum moisture was performed. Finally, the behavior of specimens under service and their mechanical performance were evaluated. Results show that both EAFS and BOFS enhance the RCC’s compressive strength and modulus of elasticity. The RCC produced with BOFS aggregates presented some expansibility due to its high contents of chemically active finer-than-75-µm materials and higher porosity. The EAFS aggregate was stable in durability analysis. In conclusion, through optimal mixture proportions and using compatible energy compression, it is viable to produce pavements with EAFS steelmaking slag in efficient, economical, and environmentally friendly manners. BOFS also showed promising results but requires further investigation.

Blast-furnace slag (BFS) has been increasingly used in cement production and has shown great influence on the electrical resistivity of concrete. The objective of this paper is to compare the theoretical values of electrical resistivity obtained through a mathematical model with experimental values for concrete with BFS. Reference concrete mixtures with ordinary portland cement were also studied. Results indicate higher electrical resistivity and smaller porosity for concretes with CEM III/A. The electrical resistivity of the CEM III/A concrete does not have a well-defined correlation with the water-binder ratio (w/b) or with the compressive strength, unlike CEM I concretes. The correlation between calculated and experimental resistivity requires a correction factor for the CEM III/A concretes. In this study, the correction factor was obtained empirically by reducing the theoretical tortuosity of concrete by 15%. Therefore, the model should be used in cements with BFS with the application of a correction factor.

Disc. 117-M59/From the May 2020 ACI Materials Journal, p. 111 Corrosion Resistance on Recycled Aggregate Concrete Incorporating Slag. Paper by Anwar Al-Yaqout, Moetaz El-Hawary, Khallad Nouh, and Pattan Bazienth Khan

Wet-mix shotcrete has been used more and more for structural applications in the past few decades. Recently, wet-mix shotcrete was successfully used to construct a mass structural wall with congested reinforcement and minimum dimensions of 1.0 m in a sewage treatment plant. A low-heat shotcrete mixture that included up to 40% slag was proposed for shotcrete application. A preconstruction mockup was shot to established proper work procedures for shotcrete application and qualify the shotcrete mixture and shotcrete nozzlemen. Extraction of cores and cut windows from the mockup confirmed proper consolidation around the congested reinforcement. A thermal control plan was developed, which included laboratory and field testing requirements, thermal analysis modeling with a three-dimensional (3-D) finite element program, and thermal control requirements, including installation of cooling pipes and thermal blankets. Shotcrete proved to be an efficient means for mass concrete structural construction. Thermal control for mass shotcrete construction was studied, and the proposed thermal control plan was proved to function properly. The general guidance for mass shotcrete construction is provided.