Assessment of measures to mitigate concrete shrinkage

Abstract

Concrete can have high tendency to shrink over time and this can cause its cracking and thus jeopardize its durability and increase significantly maintenance, repair or rehabilitation costs. In this context, this study intends to evaluate measures to mitigate concrete shrinkage through the incorporation of different percentages of fly ash (FA), shrinkage reducing admixtures (SRA) or superabsorbent polymers (SAP). For this, one has developed an experimental campaign on mortar specimens that consisted in the manufacture and subsequent shrinkage measurement of free specimens and sealed ones made with the different selected mix-designs. Shrinkage was recorded along time up to 304 days of age and not only the total shrinkage was evaluated so as the autogeneous and drying shrinkage also. For the case of FA addition, one has studied different percentages of cement replacement by weight: 20, 40 and 60 %. The SRA type and content was selected based on previous study which permits to obtain the best shrinkage performance. As for the mortar containing SAP one has adopted a dosage currently used. As a complement to the shrinkage measurements, one has evaluated also the mass loss of the samples and the compressive strength of the compositions over time. All specimens were placed in a controlled environment with an average temperature of 23.5 ºC and 89.0 % of moisture content. Based on the obtained results one can conclude that: the inclusion of FA considerably decreased the total shrinkage and also reduced, in an even more significantly way, the autogeneous shrinkage. These effects were more pronounced as the FA dosage had increased. However, it hasn’t had a great effect reducing drying shrinkage; the addition of SRA was responsible for an important reduction of all the types of shrinkage measured, being more efficient on the drying shrinkage; the inclusion of SAP was beneficial in the mitigation of all types of shrinkage, being more effective in autogeneous shrinkage. The composition with 60 % of FA was the most efficient in the decreasing of autogeneous shrinkage and the one with SRA was the most effective in the reduction of drying shrinkage.