Influence of the early-age length change of alkali-activated slag mortars on the corrosion of embedded steel

AbstractAlkali-activated slag (AAS) materials are one of the most promising alternatives to ordinary Portland cement (PC), as the AAS curing process does not require thermal activation, unlike the activation of other wastes. In addition, AAS exhibit lower porosity than PC, but experience shrinkage problems that can negatively affect their in-service implementation and durability. Shrinkage can directly impact the mechanical properties of AAS as well as the corrosion protection of steel reinforced structures in environments with chlorides, and be a factor affecting durability. The length change during the curing of these mortars can generate high stresses that are released through the formation of microcracks or cracks in their structure. Cracks can act as preferential diffusion paths for aggressive chloride ions and favor the corrosion of the reinforcement. The aim of the present work is to study the reduction in shrinkage that can be achieved for AAS using five different activators: NaOH 4 M, waterglass (WG) with two different SiO2/Na2O molar ratios (MR) and Na2CO3 solution without and with 10% MgO additions. The results reveal that AAS activated with Na2CO3 shows very reduced microcracking. The addition of expansive MgO completely eliminates microcracking but makes the mortar more porous. In the latter case, the pits become much smaller and potentially less dangerous than the ones appearing in the other studied mortars.HighlightsAlkali-activated slag mortars manufactured in five different ways (Na2O fixed ratio) are tested.Shrinkage behavior of mortars is related to the corrosion of the embedded steel.Cyclic immersions in NaCl favour chloride diffusion and precipitation in reinforced mortars.Pit morphologies are related to Cl- transport through cracks, microcracks or/and porosity.WG (0.8 SiO2/Na2O MR) or Na2CO3 are promising options to activate slag for carbon steel-reinforced mortars.Keywords: Alkali-activated slagshrinkagecrackingdurabilitycorrosionchlorides Disclosure statementNo potential conflict of interest was reported by the author(s).Additional informationFundingThe authors have been able to carry out the present research thanks to financial support from the Ministerio de Ciencia, Innovación y Universidades of Spain (RTI2018-096428-B-I00 and PID2021-125810OB-C22) and the Madrid Regional Government (Comunidad de Madrid) under the Multiannual UC3M Agreement in the line of “Fostering Young Doctors’ Research” (HORATSO-CS-UC3M) within the context of the V PRICIT (Regional Programme of Research and Technological Innovation).Notes on contributorsSegundo ShagñaySegundo Shagñay: Post-doctoral researcher in Materials Science and Engineering at University Carlos III of Madrid. His work is focused on the study of durability of new ecological materials as alternatives to ordinary Portland cement.Asunción BautistaAsunción Bautista: She is Full Professor at the Materials Science and Engineering Department of University Carlos III of Madrid. Her area of expertise is corrosion and durability of metallic materials. She has carried out aqueous corrosion and oxidation studies, mainly focused on electrochemical characterization of carbon steels and stainless steels for construction applications.Francisco VelascoFrancisco Velasco: He is Full Professor at the Materials Science and Engineering Department of University Carlos III of Madrid. His area of expertise includes ribbed stainless steels and carbon steels for concrete, delving into the influence of processing and microstructure on corrosion mechanisms. At present, he is also working on functionalized organic coatings to improve corrosion and wear properties.Irene Ramón-ÁlvarezIrene Ramón-Álvarez: She is a PhD candidate in Materials Science and Engineering at University Carlos III of Madrid. Her work is focused on producing eco-efficient cementitious materials that avoid the use of Portland cement, since its manufacture entails a large amount of associated emissions. These eco-efficient materials are for implementation in solar thermal power plants as a thermal solid storage medium.Manuel Torres-CarrascoManuel Torres-Carrasco: He is Assistant Professor at the Materials Science and Engineering Department of University Carlos III of Madrid. His research focuses on the preparation of new cementitious materials through alkali activation of different natural products. Moreover, his experience entails the study of Portland cement systems (pastes, mortars, and concretes).