PSI - Issue 77

João Custódio et al. / Procedia Structural Integrity 77 (2026) 447–456

452

6

João Custódio, et al. / Structural Integrity Procedia 00 (2026) 000–000

The control of the reactive silica content may be ensured by selecting a non-reactive aggregate or aggregate combination, which can be confirmed through petrographic analysis, complemented by mortar/concrete tests, such as the mortar-bar test or the concrete prism test. The ASR expansive gels may be modified to non-expansive gels by incorporating lithium salts into the concrete mixture, namely lithium nitrate. The control of the maximum temperature to 65 ºC at early ages, during the hydration process, may be guaranteed through an adequate mix design (by using low heat cements and/or limiting the cement incorporation percentage), as well as proper temperature monitorization and control of concrete during its production, placement and compaction, which may be managed by insulating water supply lines and tanks, shading of materials and concrete-making facilities from direct sunshine, and sprinkling the aggregates with clean uncontaminated water, painting the drums of truck mixers and cement silos white to reduce heat gain. Other measures to minimise concrete temperature include the use of cold water in the mixture, the use of liquid nitrogen or the use of cooling pipes. For the limitation of the alkali content in the concrete and of the binder aluminate and sulphate contents, the maximum concrete temperature during the first hours after production should not surpass 75 ºC and should not exceed 70 ºC for longer than 4 hours. Furthermore, the content of active alkali should be lower than 3.0 kg Na 2 O eq /m 3 of concrete, and a sulphate-resistant cement should be used. The control of moisture ingress in concrete can be achieved through the use of adequate concrete surface protection systems, which should be properly inspected and maintained over time. Moreover, the structure should be designed to avoid water accumulation and ensure rapid drainage. In case of DEF prevention, these measures should be complemented by the maximum concrete temperature control at early ages. The calcium hydroxide content in concrete can be limited by combining portland cement with type II additions, provided that the sulphate content of the cement is less than 3 % and the tricalcium aluminate content is less than 8 %. This preventive measure should be complemented by the maximum concrete temperature control at early ages. If other DEF precautionary measures cannot be met or are not sufficient, the use of a non-deleteriously reactive concrete mixture may be ensured by limiting the test longitudinal deformation of the concrete at 12 months. 5. Mitigation of ASR and DEF in existing structures Once present in a structure, it is not possible to eliminate ASR and DEF. Therefore, the interventions are solely focused on limiting their future development to prolong the structure's useful life as close as possible to the design value. Several measures can be employed to mitigate the future effects of ASR and DEF on the structure, including controlling water content, expansion, and temperature of the concrete; changing the characteristics of ASR gel; repairing, reinforcing, or introducing structural modifications; replacing concrete; demolishing and reconstructing; and implementing structural redundancy. The external water ingress can be minimised through injections, the application of surface protection systems, cladding, lining/membrane application, as well as the repair, modification, or installation of drainage or ventilation systems. The expansion can be limited by confining the concrete (e.g. using concrete, steel, or advanced composite materials; steel and composite elements can be passive or prestressed). The temperature of the concrete can be controlled through the use of specific coatings and panels. The ASR gel’s expansive nature may also be altered to a non-expansive gel by applying a lithium solution onto the affected structure. However, the penetrability of the lithium compounds in concrete is somewhat limited, so this technique is usually applied to thin elements. In structures such as pavements, bridge decks, and median barriers, this may be carried out using truck-mounted spraying systems or handheld pressurised spray bottles. Other application techniques include electrochemical lithium impregnation and vacuum impregnation with lithium. The minimisation of the consequences of future expansion can be achieved through structural modifications, such as cuts in the concrete of dams to release stresses and reverse the deformations caused by expansion, as well as alterations to supports and connections of equipment (generator units and gates in dams, etc.), and the creation of expansion joints. Regarding the repair of the most deteriorated structures, concrete mass regeneration can be carried out through the injection, confinement and reinforcement and/or replacement of parts or volumes considered irrecoverable. The