PSI - Issue 77

João Custódio et al. / Procedia Structural Integrity 77 (2026) 447–456 João Custódio, et al. / Structural Integrity Procedia 00 (2026) 000–000

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RILEM, the International Union of Laboratories and Experts in Construction Materials, Systems and Structures, has also issued recommendations on the prevention of ASR in new structures, namely AAR-0 (RILEM, 2003; 2016c; Rønning et al. , 2021), AAR-7.1 (RILEM, 2016a), and AAR-7.3 (RILEM, 2016b). To date, RILEM has not issued any recommendations regarding the prevention and mitigation of delayed ettringite formation in concrete structures. In the USA, ASTM C1778 (ASTM, 2023) provides a process for identifying potentially reactive aggregates through standardised testing procedures and selecting mitigation options to minimise the risk of ASR expansion. In this standard, ASR mitigation methods are selected using prescriptive or performance-based alternatives. Additionally, due to the fact that the potential for deleterious ASR depends on the concrete mixture and in-service exposure, this normative document also provides guidance on the type of structures and exposure environments. AASHTO R80 (AASHTO, 2017) also follows a methodology similar to that of ASTM 1778 (ASTM, 2023), for determining the reactivity of aggregates and selecting appropriate measures for preventing ASR deleterious expansion in new concrete construction. On the other hand, ACI PRC-221.1 (ACI, 2008) and ACI PRC-201.2 (ACI, 2023) propose means to avoid the deleterious effects of ASR, testing methods for potential expansion of aggregates and cement-aggregate combinations, measures to prevent deleterious ASR, and recommendations for evaluating and repairing existing structures. Regarding DEF, ACI PRC-201.2 (ACI, 2023) provides recommendations on how to minimise the risk of the development of deleterious DEF. It recommends restricting the maximum internal temperature of concrete not to exceed 70 °C at any time, and states that if temperatures in the range of 70 °C to 85 °C are unavoidable, then the mitigation measures should be adopted (as per presented in Table 6.2.2.2 of ACI PRC-201.2). They consist roughly of using any ASTM C150/C150M portland cement in combination with the specific proportions of pozzolan or slag cement, or of using an ASTM C595/C595M or ASTM C1157/C1157M blended hydraulic cement with pozzolan or slag cement specific content. In Canada, CSA A23.1/CAS A23.2 (CSA, 2024) also adopts the same methodology defined in ASTM 1778 (ASTM, 2023) and AASHTO R80 (AASHTO, 2017), for assessing the reactivity of concrete aggregates and choosing suitable measures for preventing deleterious expansion in new concrete construction. In addition, in Annex T, CSA A23.1/CAS A23.2 (CSA, 2024) states that the maximum temperature of mass concrete after placement is commonly specified not to exceed 70 °C, that lower maximum concrete temperature limits may be prescribed depending on the level of risk, and that not all concrete mixtures have the same risk for DEF when these are exposed to high temperatures during the curing period. 4.1. Prevention of ASR and DEF in new structures in Portugal The assessment of need and the adoption of preventive measures are critical to avoid the occurrence of ASR and DEF in new structures. In the Portuguese context, LNEC specification E 461 (LNEC, 2021) establishes the methodology for preventing expansive chemical reactions. Depending on the level of risk associated with ASR occurrence in the structure and the category of service environment to which the structure would be exposed, a precaution level is determined, ranging from no need for special precautions against ASR. Then, the ASR preventive measures are selected according to the precaution level. Similarly, a DEF precaution level is determined according to the level of risk associated with DEF occurrence in the structure and the category of service environment to which the structure would be exposed. Afterwards, the DEF preventive measures are established in accordance with the precaution level. The following ASR preventive measures are recommended: restricting pore solution alkalinity; ensuring the use of a non-reactive aggregate or aggregate combination; reducing moisture ingress to maintain the concrete in a sufficiently dry state to prevent deleterious expansion of the gel; modifying the properties of the ASR gel so that it becomes non expansive. Correspondingly, the subsequent DEF preventive measures are proposed: controlling the maximum temperature attained in the concrete; limiting concrete alkali content and limiting binder aluminate and sulphate contents; reducing moisture ingress to maintain the concrete in a sufficiently dry state to prevent deleterious expansion; limiting the calcium hydroxide content; ensuring the use of a non-deleteriously reactive concrete mixture. The restriction of the alkalinity of the pore solution may be achieved by limiting the reactive alkali content of the concrete or by using appropriate binders.