Little is known about external sulfate attacks (ESA) when dealing with new concrete mixtures such as low-CO2 binders. Resistance to external sulfate attacks is therefore a key challenge for the development of new mixtures and for structural durability. However, tools dedicated to accurately quantify and predict the phenomena are missing and more research is needed on this topic to better understand and capture the degradation occurring in the field. In particular, the existing ESA test procedures are not always appropriate. A more inclusive assessment of surface damage, including both expansive (scaling) and softening or disintegration types of destruction, is required. After the review of the ESA mechanisms and the report on field aspects and observed cases, this chapter presents a review and analysis of the current standards applied in various countries (e.g., ASTM, CSA, SIA, etc.) and of some other existing lab test methods (in accelerated conditions). The various parameters influencing the test results are in particular reviewed. Then, a focus on recent developments and promising research is introduced. The methods reviewed in this chapter are applied to estimate if the tested cement can be regarded as a sulfate-resisting (SR) cement or are dedicated to the assessment (in the lab) of the resistance of concrete exposed to ESA. The main features of each test method are described in this chapter, such as:type of mixtures used (cement paste, mortar, or concrete),type of binders used,limitations on cement types if any,sample dimensions,preconditioning procedure,test conditions: type of (sulfate) solution, sulfate concentration, temperature, pH constant or not, wetting-drying cycles, etc.parameters measured: expansion, visual changes, mass loss, loss of tensile strength, loss of compressive strength, dynamic modulus of elasticity, etc.In the review and critical analysis of the available test methods, the following important aspects have been considered:test methods on both mortar and concrete (and cement paste) specimens,relevant parameters for evaluation (and ranking),with regard to existing test methods:analysis of agreements/disagreements,investigation of the improvements needed,with regard to new test methods:impact of acceleration of the processes,innovative methods of acceleration of the processes.In addition, recommendations for a new testing methodology are proposed, as a basis for future European standardization on this topic along with dedicated RRTs (e.g., within the framework of CEN/TC51-TC104/WG12/TG1 “Sulfate resistance to external sulfate attack”). Moreover, the questions still open, perspectives and further steps needed, as well as the possible adaptation of tests/models to low-CO2 binders, are briefly discussed at the end of the chapter. type of mixtures used (cement paste, mortar, or concrete), type of binders used, limitations on cement types if any, sample dimensions, preconditioning procedure, test conditions: type of (sulfate)
