The morphology of entrained air voids in hardened cement paste generated with different anionic surfactants

Effect of water-repellent admixtures on the behaviour of aerial lime-based mortars

“…For each additive, two different dosages were proved: 0.06% and 0.5% of the total dried mortar's weight. The first dosage was selected because it is one of the most common dosages used in the literature for this kind of admixture [20,22,27]. The second one was chosen because it involves a very different amount of additive, which is supposed to change the material more dramatically, and it has been previously used in published research [21,30].…”

“…As a consequence, they may be adsorbed and concentrate at the air-paste interface, usually in the air bubble surface. This fact causes reinforcement of the air bubbles and avoids coalescence [22][23][24]. Atahan and co-workers reported that when they mixed SO solutions with cement or Ca(OH) 2 , precipitants of calcium oleate were formed (just like soap).…”

“…The foam index test purposed by Corr [25] and modified by Atahan [22] was used as an effective method to predict the compatibility between lime and SO and CS, respectively. Furthermore, during the execution of this test, the behaviour of each one of the additives in contact with water was also observed.…”

“…This fact considerably reduced the availability of oleate for air-entraining action. Nevertheless, precipitant adsorption on the bubbles' surfaces stabilized them, even though hardened cement pastes treated with SO showed fewer air voids than pastes treated with synthetic detergents like sodium dodecyl sulfate or sodium dodecyl-benzene sulfonate [22].…”

“…A group of very interesting chemical compounds commercialized as water repellents for cement mortars is the fatty acid salts (such as sodium oleate, SO, and calcium stearate, CS). These molecules -anionic surfactants -have also been reported in the scientific literature on cement mortars like AEAs [22][23][24][25], and they can also be found as additives which improve the processability of gypsum plaster composition [26], acting as lubricants. SO and CS are characterized by a long non-polar hydrocarbon chain and a polar group at one end, thus having a bipolar nature.…”