Analysis of the Technical Feasibility of Sustainable Concrete Production Using Waste Foundry Sand as a Fine Aggregate.

Waste foundation sand (WFS) is one of the most abundant residues in the foundation industry. Currently, its annual production is estimated to be three million tons. This material has properties that make it an attractive candidate for implantation as an alternative constituent to a natural fine aggregate in concrete applications. This application can promote greater sustainability, as it would establish a noble destination for the waste generated in large quantities by the metallurgical industry in addition to reducing the exploitation of a natural resource widely used by the civil construction industry. Given this, the present study observed the test of three different proportions of replacement, 25, 50, and 100% by mass, of natural sand by WFS in concrete. To assess the feasibility of these replacements, several tests were carried out covering mechanical properties and aspects related to the durability of concrete. The results indicated a significant improvement in the mechanical performance, with a resistance gain of 25% in relation to the reference concrete. As for the modulus of elasticity, there was no significant variation. As for aspects related to durability, both the absorption test and the alkali aggregate reaction test did not show statistically significant disparity, which attests to the technical feasibility of using nonconcrete WFS.

Evaluation of Internal and Superficial Self-Healing of Cracks in Concrete with Crystalline Admixtures.

Reinforced concrete structures are prone to cracking. The development of cementitious matrices with the capacity for self-healing soon after these cracks appear represents savings with inspections and repairs of the structures. Self-healing can be stimulated with the use of crystalline admixtures. Such materials easily react with water and increase the density of C-S-H (hydrated-calcium-silicate), forming insoluble deposits blocking existing pores and cracks. In this research, self-healing in concrete cracks was evaluated using three different crystalline admixtures, submitted to two and six wetting-drying cycles. The efficiency of self-healing was evaluated by optical microscopy and using the chloride diffusion test, which allowed calculating the predicted useful life of the concretes. The results highlight two important findings: (i) in optical microscopy, crystalline admixtures were not efficient in promoting self-healing on the surface of cracks in any of the studied concretes; (ii) the passage of chlorides by diffusion was lower for concretes with crystalline admixtures compared to the reference, showing better internal healing of these materials and, consequently, greater prediction of the concrete's useful life.